// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }
    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }
    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }
    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a >= b ? a : b;
    }
    /**
     * @dev Returns the smallest of two numbers.
     */
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }
    /**
     * @dev Returns the average of two numbers. The result is rounded towards
     * zero.
     */
    function average(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b) / 2 can overflow, so we distribute
        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }
    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }
    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) return (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }
    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }
    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }
    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }
    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) return 0;
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }
    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }
    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }
    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }
    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }
    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);
    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);
    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);
    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);
    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);
    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);
    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
import "./IERC20.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";
/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;
    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }
    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }
    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }
    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }
    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }
    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.
        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.2 <0.8.0;
/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.
        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }
    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");
        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }
    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }
    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly
                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.
    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;
    uint256 private _status;
    constructor () internal {
        _status = _NOT_ENTERED;
    }
    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");
        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;
        _;
        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}
// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity ^0.7.0;
pragma experimental ABIEncoderV2;
import "@openzeppelin-solc-0.7/contracts/utils/ReentrancyGuard.sol";
import "@openzeppelin-solc-0.7/contracts/math/Math.sol";
import "@openzeppelin-solc-0.7/contracts/math/SafeMath.sol";
import "@openzeppelin-solc-0.7/contracts/token/ERC20/SafeERC20.sol";
import "@openzeppelin-solc-0.7/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin-solc-0.7/contracts/access/Ownable.sol";
import "./interfaces/IFeeDistributor.sol";
import "./interfaces/IVotingEscrow.sol";
// solhint-disable not-rely-on-time
/**
 * @title Fee Distributor
 * @author Balancer Labs. Original version https://github.com/balancer/balancer-v2-monorepo/blob/master/pkg/liquidity-mining/contracts/fee-distribution/FeeDistributor.sol
 * @notice Distributes any tokens transferred to the contract (e.g. Protocol fees) among veSTG
 * holders proportionally based on a snapshot of the week at which the tokens are sent to the FeeDistributor contract.
 * @dev Supports distributing arbitrarily many different tokens. In order to start distributing a new token to veSTG holders call `depositToken`.
 */
contract FeeDistributor is IFeeDistributor, Ownable, ReentrancyGuard {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;
    // gas optimization
    uint256 private constant WEEK_MINUS_SECOND = 1 weeks - 1;
    IVotingEscrow private immutable _votingEscrow;
    uint256 private immutable _startTime;
    // Global State
    uint256 private _timeCursor;
    mapping(uint256 => uint256) private _veSupplyCache;
    // Token State
    // `startTime` and `timeCursor` are both timestamps so comfortably fit in a uint64.
    // `cachedBalance` will comfortably fit the total supply of any meaningful token.
    // Should more than 2^128 tokens be sent to this contract then checkpointing this token will fail until enough
    // tokens have been claimed to bring the total balance back below 2^128.
    struct TokenState {
        uint64 startTime;
        uint64 timeCursor;
        uint128 cachedBalance;
    }
    mapping(IERC20 => TokenState) private _tokenState;
    mapping(IERC20 => mapping(uint256 => uint256)) private _tokensPerWeek;
    mapping(IERC20 => bool) private _tokenClaimingEnabled;
    // User State
    // `startTime` and `timeCursor` are timestamps so will comfortably fit in a uint64.
    // For `lastEpochCheckpointed` to overflow would need over 2^128 transactions to the VotingEscrow contract.
    struct UserState {
        uint64 startTime;
        uint64 timeCursor;
        uint128 lastEpochCheckpointed;
    }
    mapping(address => UserState) internal _userState;
    mapping(address => mapping(uint256 => uint256)) private _userBalanceAtTimestamp;
    mapping(address => mapping(IERC20 => uint256)) private _userTokenTimeCursor;
    mapping(address => bool) private _onlyVeHolderClaimingEnabled;
    /**
     * @dev Reverts if only the VotingEscrow holder can claim their rewards and the given address is a third-party caller.
     * @param user - The address to validate as the only allowed caller.
     */
    modifier userAllowedToClaim(address user) {
        if (_onlyVeHolderClaimingEnabled[user]) {
            require(msg.sender == user, "Claiming is not allowed");
        }
        _;
    }
    /**
     * @dev Reverts if the given token cannot be claimed.
     * @param token - The token to check.
     */
    modifier tokenCanBeClaimed(IERC20 token) {
        _checkIfClaimingEnabled(token);
        _;
    }
    /**
     * @dev Reverts if the given tokens cannot be claimed.
     * @param tokens - The tokens to check.
     */
    modifier tokensCanBeClaimed(IERC20[] calldata tokens) {
        uint256 tokensLength = tokens.length;
        for (uint256 i = 0; i < tokensLength; ++i) {
            _checkIfClaimingEnabled(tokens[i]);
        }
        _;
    }
    constructor(IVotingEscrow votingEscrow, uint256 startTime) {
        _votingEscrow = votingEscrow;
        startTime = _roundDownTimestamp(startTime);
        uint256 currentWeek = _roundDownTimestamp(block.timestamp);
        require(startTime >= currentWeek, "Cannot start before current week");
        IVotingEscrow.Point memory pt = votingEscrow.point_history(0);
        require(startTime > pt.ts, "Cannot start before VotingEscrow first epoch");
        _startTime = startTime;
        _timeCursor = startTime;
    }
    /**
     * @notice Returns the VotingEscrow (veSTG) token contract
     */
    function getVotingEscrow() external view override returns (IVotingEscrow) {
        return _votingEscrow;
    }
    /**
     * @notice Returns the time when fee distribution starts.
     */
    function getStartTime() external view override returns (uint256) {
        return _startTime;
    }
    /**
     * @notice Returns the global time cursor representing the most earliest uncheckpointed week.
     */
    function getTimeCursor() external view override returns (uint256) {
        return _timeCursor;
    }
    /**
     * @notice Returns the user-level start time representing the first week they're eligible to claim tokens.
     * @param user - The address of the user to query.
     */
    function getUserStartTime(address user) external view override returns (uint256) {
        return _userState[user].startTime;
    }
    /**
     * @notice Returns the user-level time cursor representing the most earliest uncheckpointed week.
     * @param user - The address of the user to query.
     */
    function getUserTimeCursor(address user) external view override returns (uint256) {
        return _userState[user].timeCursor;
    }
    /**
     * @notice Returns the user-level last checkpointed epoch.
     * @param user - The address of the user to query.
     */
    function getUserLastEpochCheckpointed(address user) external view override returns (uint256) {
        return _userState[user].lastEpochCheckpointed;
    }
    /**
     * @notice True if the given token can be claimed, false otherwise.
     * @param token - The ERC20 token address to query.
     */
    function canTokenBeClaimed(IERC20 token) external view override returns (bool) {
        return _tokenClaimingEnabled[token];
    }
    /**
     * @notice Returns the token-level start time representing the timestamp users could start claiming this token
     * @param token - The ERC20 token address to query.
     */
    function getTokenStartTime(IERC20 token) external view override returns (uint256) {
        return _tokenState[token].startTime;
    }
    /**
     * @notice Returns the token-level time cursor storing the timestamp at up to which tokens have been distributed.
     * @param token - The ERC20 token address to query.
     */
    function getTokenTimeCursor(IERC20 token) external view override returns (uint256) {
        return _tokenState[token].timeCursor;
    }
    /**
     * @notice Returns the token-level cached balance.
     * @param token - The ERC20 token address to query.
     */
    function getTokenCachedBalance(IERC20 token) external view override returns (uint256) {
        return _tokenState[token].cachedBalance;
    }
    /**
     * @notice Returns the user-level time cursor storing the timestamp of the latest token distribution claimed.
     * @param user - The address of the user to query.
     * @param token - The ERC20 token address to query.
     */
    function getUserTokenTimeCursor(address user, IERC20 token) external view override returns (uint256) {
        return _getUserTokenTimeCursor(user, token);
    }
    /**
     * @notice Returns the user's cached balance of veSTG as of the provided timestamp.
     * @dev Only timestamps which fall on Thursdays 00:00:00 UTC will return correct values.
     * This function requires `user` to have been checkpointed past `timestamp` so that their balance is cached.
     * @param user - The address of the user of which to read the cached balance of.
     * @param timestamp - The timestamp at which to read the `user`'s cached balance at.
     */
    function getUserBalanceAtTimestamp(address user, uint256 timestamp) external view override returns (uint256) {
        return _userBalanceAtTimestamp[user][timestamp];
    }
    /**
     * @notice Returns the cached total supply of veSTG as of the provided timestamp.
     * @dev Only timestamps which fall on Thursdays 00:00:00 UTC will return correct values.
     * This function requires the contract to have been checkpointed past `timestamp` so that the supply is cached.
     * @param timestamp - The timestamp at which to read the cached total supply at.
     */
    function getTotalSupplyAtTimestamp(uint256 timestamp) external view override returns (uint256) {
        return _veSupplyCache[timestamp];
    }
    /**
     * @notice Returns the FeeDistributor's cached balance of `token`.
     */
    function getTokenLastBalance(IERC20 token) external view override returns (uint256) {
        return _tokenState[token].cachedBalance;
    }
    /**
     * @notice Returns the amount of `token` which the FeeDistributor received in the week beginning at `timestamp`.
     * @param token - The ERC20 token address to query.
     * @param timestamp - The timestamp corresponding to the beginning of the week of interest.
     */
    function getTokensDistributedInWeek(IERC20 token, uint256 timestamp) external view override returns (uint256) {
        return _tokensPerWeek[token][timestamp];
    }
    // Preventing third-party claiming
    /**
     * @notice Enables / disables rewards claiming only by the VotingEscrow holder for the message sender.
     * @param enabled - True if only the VotingEscrow holder can claim their rewards, false otherwise.
     */
    function enableOnlyVeHolderClaiming(bool enabled) external override {
        _onlyVeHolderClaimingEnabled[msg.sender] = enabled;
        emit OnlyVeHolderClaimingEnabled(msg.sender, enabled);
    }
    /**
     * @notice Returns true if only the VotingEscrow holder can claim their rewards, false otherwise.
     */
    function onlyVeHolderClaimingEnabled(address user) external view override returns (bool) {
        return _onlyVeHolderClaimingEnabled[user];
    }
    // Depositing
    /**
     * @notice Deposits tokens to be distributed in the current week.
     * @dev Sending tokens directly to the FeeDistributor instead of using `depositToken` may result in tokens being
     * retroactively distributed to past weeks, or for the distribution to carry over to future weeks.
     *
     * If for some reason `depositToken` cannot be called, in order to ensure that all tokens are correctly distributed
     * manually call `checkpointToken` before and after the token transfer.
     * @param token - The ERC20 token address to distribute.
     * @param amount - The amount of tokens to deposit.
     */
    function depositToken(IERC20 token, uint256 amount) external override nonReentrant tokenCanBeClaimed(token) {
        _checkpointToken(token, false);
        token.safeTransferFrom(msg.sender, address(this), amount);
        _checkpointToken(token, true);
    }
    /**
     * @notice Deposits tokens to be distributed in the current week.
     * @dev A version of `depositToken` which supports depositing multiple `tokens` at once.
     * See `depositToken` for more details.
     * @param tokens - An array of ERC20 token addresses to distribute.
     * @param amounts - An array of token amounts to deposit.
     */
    function depositTokens(IERC20[] calldata tokens, uint256[] calldata amounts) external override nonReentrant {
        require(tokens.length == amounts.length, "Input length mismatch");
        uint256 length = tokens.length;
        for (uint256 i = 0; i < length; ++i) {
            _checkIfClaimingEnabled(tokens[i]);
            _checkpointToken(tokens[i], false);
            tokens[i].safeTransferFrom(msg.sender, address(this), amounts[i]);
            _checkpointToken(tokens[i], true);
        }
    }
    // Checkpointing
    /**
     * @notice Caches the total supply of veSTG at the beginning of each week.
     * This function will be called automatically before claiming tokens to ensure the contract is properly updated.
     */
    function checkpoint() external override nonReentrant {
        _checkpointTotalSupply();
    }
    /**
     * @notice Caches the user's balance of veSTG at the beginning of each week.
     * This function will be called automatically before claiming tokens to ensure the contract is properly updated.
     * @param user - The address of the user to be checkpointed.
     */
    function checkpointUser(address user) external override nonReentrant {
        _checkpointUserBalance(user);
    }
    /**
     * @notice Assigns any newly-received tokens held by the FeeDistributor to weekly distributions.
     * @dev Any `token` balance held by the FeeDistributor above that which is returned by `getTokenLastBalance`
     * will be distributed evenly across the time period since `token` was last checkpointed.
     *
     * This function will be called automatically before claiming tokens to ensure the contract is properly updated.
     * @param token - The ERC20 token address to be checkpointed.
     */
    function checkpointToken(IERC20 token) external override nonReentrant tokenCanBeClaimed(token) {
        _checkpointToken(token, true);
    }
    /**
     * @notice Assigns any newly-received tokens held by the FeeDistributor to weekly distributions.
     * @dev A version of `checkpointToken` which supports checkpointing multiple tokens.
     * See `checkpointToken` for more details.
     * @param tokens - An array of ERC20 token addresses to be checkpointed.
     */
    function checkpointTokens(IERC20[] calldata tokens) external override nonReentrant {
        uint256 tokensLength = tokens.length;
        for (uint256 i = 0; i < tokensLength; ++i) {
            _checkIfClaimingEnabled(tokens[i]);
            _checkpointToken(tokens[i], true);
        }
    }
    // Claiming
    /**
     * @notice Claims all pending distributions of the provided token for a user.
     * @dev It's not necessary to explicitly checkpoint before calling this function, it will ensure the FeeDistributor
     * is up to date before calculating the amount of tokens to be claimed.
     * @param user - The user on behalf of which to claim.
     * @param token - The ERC20 token address to be claimed.
     * @return The amount of `token` sent to `user` as a result of claiming.
     */
    function claimToken(address user, IERC20 token) external override nonReentrant userAllowedToClaim(user) tokenCanBeClaimed(token) returns (uint256) {
        _checkpointTotalSupply();
        _checkpointUserBalance(user);
        _checkpointToken(token, false);
        return _claimToken(user, token);
    }
    /**
     * @notice Claims a number of tokens on behalf of a user.
     * @dev A version of `claimToken` which supports claiming multiple `tokens` on behalf of `user`.
     * See `claimToken` for more details.
     * @param user - The user on behalf of which to claim.
     * @param tokens - An array of ERC20 token addresses to be claimed.
     * @return An array of the amounts of each token in `tokens` sent to `user` as a result of claiming.
     */
    function claimTokens(address user, IERC20[] calldata tokens) external override nonReentrant userAllowedToClaim(user) tokensCanBeClaimed(tokens) returns (uint256[] memory) {
        _checkpointTotalSupply();
        _checkpointUserBalance(user);
        uint256 tokensLength = tokens.length;
        uint256[] memory amounts = new uint256[](tokensLength);
        for (uint256 i = 0; i < tokensLength; ++i) {
            _checkpointToken(tokens[i], false);
            amounts[i] = _claimToken(user, tokens[i]);
        }
        return amounts;
    }
    // Governance
    /**
     * @notice Withdraws the specified `amount` of the `token` from the contract to the `recipient`. Can be called only by Stargate DAO.
     * @param token - The token to withdraw.
     * @param amount - The amount to withdraw.
     * @param recipient - The address to transfer the tokens to.
     */
    function withdrawToken(IERC20 token, uint256 amount, address recipient) external override onlyOwner {
        token.safeTransfer(recipient, amount);
        emit TokenWithdrawn(token, amount, recipient);
    }
    /**
     * @notice Enables or disables claiming of the given token. Can be called only by Stargate DAO.
     * @param token - The token to enable or disable claiming.
     * @param enable - True if the token can be claimed, false otherwise.
     */
    function enableTokenClaiming(IERC20 token, bool enable) external override onlyOwner {
        _tokenClaimingEnabled[token] = enable;
        emit TokenClaimingEnabled(token, enable);
    }
    // Internal functions
    /**
     * @dev It is required that both the global, token and user state have been properly checkpointed
     * before calling this function.
     */
    function _claimToken(address user, IERC20 token) internal returns (uint256) {
        TokenState storage tokenState = _tokenState[token];
        uint256 nextUserTokenWeekToClaim = _getUserTokenTimeCursor(user, token);
        // The first week which cannot be correctly claimed is the earliest of:
        // - A) The global or user time cursor (whichever is earliest), rounded up to the end of the week.
        // - B) The token time cursor, rounded down to the beginning of the week.
        //
        // This prevents the two failure modes:
        // - A) A user may claim a week for which we have not processed their balance, resulting in tokens being locked.
        // - B) A user may claim a week which then receives more tokens to be distributed. However the user has
        //      already claimed for that week so their share of these new tokens are lost.
        uint256 firstUnclaimableWeek = Math.min(_roundUpTimestamp(Math.min(_timeCursor, _userState[user].timeCursor)), _roundDownTimestamp(tokenState.timeCursor));
        mapping(uint256 => uint256) storage tokensPerWeek = _tokensPerWeek[token];
        mapping(uint256 => uint256) storage userBalanceAtTimestamp = _userBalanceAtTimestamp[user];
        uint256 amount;
        for (uint256 i = 0; i < 20; ++i) {
            // We clearly cannot claim for `firstUnclaimableWeek` and so we break here.
            if (nextUserTokenWeekToClaim >= firstUnclaimableWeek) break;
            amount += (tokensPerWeek[nextUserTokenWeekToClaim] * userBalanceAtTimestamp[nextUserTokenWeekToClaim]) / _veSupplyCache[nextUserTokenWeekToClaim];
            nextUserTokenWeekToClaim += 1 weeks;
        }
        // Update the stored user-token time cursor to prevent this user claiming this week again.
        _userTokenTimeCursor[user][token] = nextUserTokenWeekToClaim;
        if (amount > 0) {
            // For a token to be claimable it must have been added to the cached balance so this is safe.
            tokenState.cachedBalance = uint128(tokenState.cachedBalance - amount);
            token.safeTransfer(user, amount);
            emit TokensClaimed(user, token, amount, nextUserTokenWeekToClaim);
        }
        return amount;
    }
    /**
     * @dev Calculate the amount of `token` to be distributed to `_votingEscrow` holders since the last checkpoint.
     */
    function _checkpointToken(IERC20 token, bool force) internal {
        TokenState storage tokenState = _tokenState[token];
        uint256 lastTokenTime = tokenState.timeCursor;
        uint256 timeSinceLastCheckpoint;
        if (lastTokenTime == 0) {
            // Prevent someone from assigning tokens to an inaccessible week.
            require(block.timestamp > _startTime, "Fee distribution has not started yet");
            // If it's the first time we're checkpointing this token then start distributing from now.
            // Also mark at which timestamp users should start attempts to claim this token from.
            lastTokenTime = block.timestamp;
            tokenState.startTime = uint64(_roundDownTimestamp(block.timestamp));
        } else {
            timeSinceLastCheckpoint = block.timestamp - lastTokenTime;
            if (!force) {
                // Checkpointing N times within a single week is completely equivalent to checkpointing once at the end.
                // We then want to get as close as possible to a single checkpoint every Wed 23:59 UTC to save gas.
                // We then skip checkpointing if we're in the same week as the previous checkpoint.
                bool alreadyCheckpointedThisWeek = _roundDownTimestamp(block.timestamp) == _roundDownTimestamp(lastTokenTime);
                // However we want to ensure that all of this week's fees are assigned to the current week without
                // overspilling into the next week. To mitigate this, we checkpoint if we're near the end of the week.
                bool nearingEndOfWeek = _roundUpTimestamp(block.timestamp) - block.timestamp < 1 days;
                // This ensures that we checkpoint once at the beginning of the week and again for each user interaction
                // towards the end of the week to give an accurate final reading of the balance.
                if (alreadyCheckpointedThisWeek && !nearingEndOfWeek) {
                    return;
                }
            }
        }
        tokenState.timeCursor = uint64(block.timestamp);
        uint256 tokenBalance = token.balanceOf(address(this));
        uint256 newTokensToDistribute = tokenBalance.sub(tokenState.cachedBalance);
        if (newTokensToDistribute == 0) return;
        require(tokenBalance <= type(uint128).max, "Maximum token balance exceeded");
        tokenState.cachedBalance = uint128(tokenBalance);
        uint256 firstIncompleteWeek = _roundDownTimestamp(lastTokenTime);
        uint256 nextWeek = 0;
        // Distribute `newTokensToDistribute` evenly across the time period from `lastTokenTime` to now.
        // These tokens are assigned to weeks proportionally to how much of this period falls into each week.
        mapping(uint256 => uint256) storage tokensPerWeek = _tokensPerWeek[token];
        for (uint256 i = 0; i < 20; ++i) {
            // This is safe as we're incrementing a timestamp.
            nextWeek = firstIncompleteWeek + 1 weeks;
            if (block.timestamp < nextWeek) {
                // `firstIncompleteWeek` is now the beginning of the current week, i.e. this is the final iteration.
                if (timeSinceLastCheckpoint == 0 && block.timestamp == lastTokenTime) {
                    tokensPerWeek[firstIncompleteWeek] += newTokensToDistribute;
                } else {
                    // block.timestamp >= lastTokenTime by definition.
                    tokensPerWeek[firstIncompleteWeek] += (newTokensToDistribute * (block.timestamp - lastTokenTime)) / timeSinceLastCheckpoint;
                }
                // As we've caught up to the present then we should now break.
                break;
            } else {
                // We've gone a full week or more without checkpointing so need to distribute tokens to previous weeks.
                if (timeSinceLastCheckpoint == 0 && nextWeek == lastTokenTime) {
                    // It shouldn't be possible to enter this block
                    tokensPerWeek[firstIncompleteWeek] += newTokensToDistribute;
                } else {
                    // nextWeek > lastTokenTime by definition.
                    tokensPerWeek[firstIncompleteWeek] += (newTokensToDistribute * (nextWeek - lastTokenTime)) / timeSinceLastCheckpoint;
                }
            }
            // We've now "checkpointed" up to the beginning of next week so must update timestamps appropriately.
            lastTokenTime = nextWeek;
            firstIncompleteWeek = nextWeek;
        }
        emit TokenCheckpointed(token, newTokensToDistribute, lastTokenTime);
    }
    /**
     * @dev Cache the `user`'s balance of `_votingEscrow` at the beginning of each new week
     */
    function _checkpointUserBalance(address user) internal {
        uint256 maxUserEpoch = _votingEscrow.user_point_epoch(user);
        // If user has no epochs then they have never locked STG.
        // They clearly will not then receive fees.
        require(maxUserEpoch > 0, "veSTG balance is zero");
        UserState storage userState = _userState[user];
        // `nextWeekToCheckpoint` represents the timestamp of the beginning of the first week
        // which we haven't checkpointed the user's VotingEscrow balance yet.
        uint256 nextWeekToCheckpoint = userState.timeCursor;
        uint256 userEpoch;
        if (nextWeekToCheckpoint == 0) {
            // First checkpoint for user so need to do the initial binary search
            userEpoch = _findTimestampUserEpoch(user, _startTime, 0, maxUserEpoch);
        } else {
            if (nextWeekToCheckpoint >= block.timestamp) {
                // User has checkpointed the current week already so perform early return.
                // This prevents a user from processing epochs created later in this week, however this is not an issue
                // as if a significant number of these builds up then the user will skip past them with a binary search.
                return;
            }
            // Otherwise use the value saved from last time
            userEpoch = userState.lastEpochCheckpointed;
            // This optimizes a scenario common for power users, which have frequent `VotingEscrow` interactions in
            // the same week. We assume that any such user is also claiming fees every week, and so we only perform
            // a binary search here rather than integrating it into the main search algorithm, effectively skipping
            // most of the week's irrelevant checkpoints.
            // The slight tradeoff is that users who have multiple infrequent `VotingEscrow` interactions and also don't
            // claim frequently will also perform the binary search, despite it not leading to gas savings.
            if (maxUserEpoch - userEpoch > 20) {
                userEpoch = _findTimestampUserEpoch(user, nextWeekToCheckpoint, userEpoch, maxUserEpoch);
            }
        }
        // Epoch 0 is always empty so bump onto the next one so that we start on a valid epoch.
        if (userEpoch == 0) {
            userEpoch = 1;
        }
        IVotingEscrow.Point memory nextUserPoint = _votingEscrow.user_point_history(user, userEpoch);
        // If this is the first checkpoint for the user, calculate the first week they're eligible for.
        // i.e. the timestamp of the first Thursday after they locked.
        // If this is earlier then the first distribution then fast forward to then.
        if (nextWeekToCheckpoint == 0) {
            // Disallow checkpointing before `startTime`.
            require(block.timestamp > _startTime, "Fee distribution has not started yet");
            nextWeekToCheckpoint = Math.max(_startTime, _roundUpTimestamp(nextUserPoint.ts));
            userState.startTime = uint64(nextWeekToCheckpoint);
        }
        // It's safe to increment `userEpoch` and `nextWeekToCheckpoint` in this loop as epochs and timestamps
        // are always much smaller than 2^256 and are being incremented by small values.
        IVotingEscrow.Point memory currentUserPoint;
        for (uint256 i = 0; i < 50; ++i) {
            if (nextWeekToCheckpoint >= nextUserPoint.ts && userEpoch <= maxUserEpoch) {
                // The week being considered is contained in a user epoch after that described by `currentUserPoint`.
                // We then shift `nextUserPoint` into `currentUserPoint` and query the Point for the next user epoch.
                // We do this in order to step though epochs until we find the first epoch starting after
                // `nextWeekToCheckpoint`, making the previous epoch the one that contains `nextWeekToCheckpoint`.
                userEpoch += 1;
                currentUserPoint = nextUserPoint;
                if (userEpoch > maxUserEpoch) {
                    nextUserPoint = IVotingEscrow.Point(0, 0, 0, 0);
                } else {
                    nextUserPoint = _votingEscrow.user_point_history(user, userEpoch);
                }
            } else {
                // The week being considered lies inside the user epoch described by `oldUserPoint`
                // we can then use it to calculate the user's balance at the beginning of the week.
                if (nextWeekToCheckpoint >= block.timestamp) {
                    // Break if we're trying to cache the user's balance at a timestamp in the future.
                    // We only perform this check here to ensure that we can still process checkpoints created
                    // in the current week.
                    break;
                }
                int128 dt = int128(nextWeekToCheckpoint - currentUserPoint.ts);
                uint256 userBalance = currentUserPoint.bias > currentUserPoint.slope * dt ? uint256(currentUserPoint.bias - currentUserPoint.slope * dt) : 0;
                // User's lock has expired and they haven't relocked yet.
                if (userBalance == 0 && userEpoch > maxUserEpoch) {
                    nextWeekToCheckpoint = _roundUpTimestamp(block.timestamp);
                    break;
                }
                // User had a nonzero lock and so is eligible to collect fees.
                _userBalanceAtTimestamp[user][nextWeekToCheckpoint] = userBalance;
                nextWeekToCheckpoint += 1 weeks;
            }
        }
        // We subtract off 1 from the userEpoch to step back once so that on the next attempt to checkpoint
        // the current `currentUserPoint` will be loaded as `nextUserPoint`. This ensures that we can't skip over the
        // user epoch containing `nextWeekToCheckpoint`.
        // userEpoch > 0 so this is safe.
        userState.lastEpochCheckpointed = uint64(userEpoch - 1);
        userState.timeCursor = uint64(nextWeekToCheckpoint);
    }
    /**
     * @dev Cache the totalSupply of VotingEscrow token at the beginning of each new week
     */
    function _checkpointTotalSupply() internal {
        uint256 nextWeekToCheckpoint = _timeCursor;
        uint256 weekStart = _roundDownTimestamp(block.timestamp);
        // We expect `timeCursor == weekStart + 1 weeks` when fully up to date.
        if (nextWeekToCheckpoint > weekStart || weekStart == block.timestamp) {
            // We've already checkpointed up to this week so perform early return
            return;
        }
        _votingEscrow.checkpoint();
        // Step through the each week and cache the total supply at beginning of week on this contract
        for (uint256 i = 0; i < 20; ++i) {
            if (nextWeekToCheckpoint > weekStart) break;
            // NOTE: Replaced Balancer's logic with Solidly/Velodrome implementation due to the differences in the VotingEscrow totalSupply function
            // See https://github.com/velodrome-finance/v1/blob/master/contracts/RewardsDistributor.sol#L143
            uint256 epoch = _findTimestampEpoch(nextWeekToCheckpoint);
            IVotingEscrow.Point memory pt = _votingEscrow.point_history(epoch);
            int128 dt = nextWeekToCheckpoint > pt.ts ? int128(nextWeekToCheckpoint - pt.ts) : 0;
            int128 supply = pt.bias - pt.slope * dt;
            _veSupplyCache[nextWeekToCheckpoint] = supply > 0 ? uint256(supply) : 0;
            // This is safe as we're incrementing a timestamp
            nextWeekToCheckpoint += 1 weeks;
        }
        // Update state to the end of the current week (`weekStart` + 1 weeks)
        _timeCursor = nextWeekToCheckpoint;
    }
    // Helper functions
    /**
     * @dev Wrapper around `_userTokenTimeCursor` which returns the start timestamp for `token`
     * if `user` has not attempted to interact with it previously.
     */
    function _getUserTokenTimeCursor(address user, IERC20 token) internal view returns (uint256) {
        uint256 userTimeCursor = _userTokenTimeCursor[user][token];
        if (userTimeCursor > 0) return userTimeCursor;
        // This is the first time that the user has interacted with this token.
        // We then start from the latest out of either when `user` first locked veSTG or `token` was first checkpointed.
        return Math.max(_userState[user].startTime, _tokenState[token].startTime);
    }
    /**
     * @dev Return the user epoch number for `user` corresponding to the provided `timestamp`
     */
    function _findTimestampUserEpoch(address user, uint256 timestamp, uint256 minUserEpoch, uint256 maxUserEpoch) internal view returns (uint256) {
        uint256 min = minUserEpoch;
        uint256 max = maxUserEpoch;
        // Perform binary search through epochs to find epoch containing `timestamp`
        for (uint256 i = 0; i < 128; ++i) {
            if (min >= max) break;
            // Algorithm assumes that inputs are less than 2^128 so this operation is safe.
            // +2 avoids getting stuck in min == mid < max
            uint256 mid = (min + max + 2) / 2;
            IVotingEscrow.Point memory pt = _votingEscrow.user_point_history(user, mid);
            if (pt.ts <= timestamp) {
                min = mid;
            } else {
                // max > min so this is safe.
                max = mid - 1;
            }
        }
        return min;
    }
    /**
     * @dev Return the global epoch number corresponding to the provided `timestamp`
     */
    function _findTimestampEpoch(uint256 timestamp) internal view returns (uint256) {
        uint256 min = 0;
        uint256 max = _votingEscrow.epoch();
        // Perform binary search through epochs to find epoch containing `timestamp`
        for (uint256 i = 0; i < 128; i++) {
            if (min >= max) break;
            // Algorithm assumes that inputs are less than 2^128 so this operation is safe.
            // +2 avoids getting stuck in min == mid < max
            uint256 mid = (min + max + 2) / 2;
            IVotingEscrow.Point memory pt = _votingEscrow.point_history(mid);
            if (pt.ts <= timestamp) {
                min = mid;
            } else {
                max = mid - 1;
            }
        }
        return min;
    }
    /**
     * @dev Rounds the provided timestamp down to the beginning of the previous week (Thurs 00:00 UTC)
     */
    function _roundDownTimestamp(uint256 timestamp) private pure returns (uint256) {
        // Division by zero or overflows are impossible here.
        return (timestamp / 1 weeks) * 1 weeks;
    }
    /**
     * @dev Rounds the provided timestamp up to the beginning of the next week (Thurs 00:00 UTC)
     */
    function _roundUpTimestamp(uint256 timestamp) private pure returns (uint256) {
        // Overflows are impossible here for all realistic inputs.
        return _roundDownTimestamp(timestamp + WEEK_MINUS_SECOND);
    }
    /**
     * @dev Reverts if the provided token cannot be claimed.
     */
    function _checkIfClaimingEnabled(IERC20 token) private view {
        require(_tokenClaimingEnabled[token], "Token is not allowed");
    }
}
// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity >=0.7.0 <0.9.0;
pragma experimental ABIEncoderV2;
import "@openzeppelin-solc-0.7/contracts/token/ERC20/IERC20.sol";
import "./IVotingEscrow.sol";
/**
 * @title Fee Distributor
 * @notice Distributes any tokens transferred to the contract (e.g. Protocol fees) among veSTG
 * holders proportionally based on a snapshot of the week at which the tokens are sent to the FeeDistributor contract.
 * @dev Supports distributing arbitrarily many different tokens. In order to start distributing a new token to veSTG
 * holders simply transfer the tokens to the `FeeDistributor` contract and then call `checkpointToken`.
 */
interface IFeeDistributor {
    event TokenCheckpointed(IERC20 token, uint256 amount, uint256 lastCheckpointTimestamp);
    event TokensClaimed(address user, IERC20 token, uint256 amount, uint256 userTokenTimeCursor);
    event TokenWithdrawn(IERC20 token, uint256 amount, address recipient);
    event TokenClaimingEnabled(IERC20 token, bool enabled);
    event OnlyVeHolderClaimingEnabled(address user, bool enabled);
    /**
     * @notice Returns the VotingEscrow (veSTG) token contract
     */
    function getVotingEscrow() external view returns (IVotingEscrow);
    /**
     * @notice Returns the time when fee distribution starts.
     */
    function getStartTime() external view returns (uint256);
    /**
     * @notice Returns the global time cursor representing the most earliest uncheckpointed week.
     */
    function getTimeCursor() external view returns (uint256);
    /**
     * @notice Returns the user-level time cursor representing the most earliest uncheckpointed week.
     * @param user - The address of the user to query.
     */
    function getUserTimeCursor(address user) external view returns (uint256);
    /**
     * @notice Returns the user-level start time representing the first week they're eligible to claim tokens.
     * @param user - The address of the user to query.
     */
    function getUserStartTime(address user) external view returns (uint256);
    /**
     * @notice True if the given token can be claimed, false otherwise.
     * @param token - The ERC20 token address to query.
     */
    function canTokenBeClaimed(IERC20 token) external view returns (bool);
    /**
     * @notice Returns the token-level start time representing the timestamp users could start claiming this token
     * @param token - The ERC20 token address to query.
     */
    function getTokenStartTime(IERC20 token) external view returns (uint256);
    /**
     * @notice Returns the token-level time cursor storing the timestamp at up to which tokens have been distributed.
     * @param token - The ERC20 token address to query.
     */
    function getTokenTimeCursor(IERC20 token) external view returns (uint256);
    /**
     * @notice Returns the token-level cached balance.
     * @param token - The ERC20 token address to query.
     */
    function getTokenCachedBalance(IERC20 token) external view returns (uint256);
    /**
     * @notice Returns the user-level last checkpointed epoch.
     * @param user - The address of the user to query.
     */
    function getUserLastEpochCheckpointed(address user) external view returns (uint256);
    /**
     * @notice Returns the user-level time cursor storing the timestamp of the latest token distribution claimed.
     * @param user - The address of the user to query.
     * @param token - The ERC20 token address to query.
     */
    function getUserTokenTimeCursor(address user, IERC20 token) external view returns (uint256);
    /**
     * @notice Returns the user's cached balance of veSTG as of the provided timestamp.
     * @dev Only timestamps which fall on Thursdays 00:00:00 UTC will return correct values.
     * This function requires `user` to have been checkpointed past `timestamp` so that their balance is cached.
     * @param user - The address of the user of which to read the cached balance of.
     * @param timestamp - The timestamp at which to read the `user`'s cached balance at.
     */
    function getUserBalanceAtTimestamp(address user, uint256 timestamp) external view returns (uint256);
    /**
     * @notice Returns the cached total supply of veSTG as of the provided timestamp.
     * @dev Only timestamps which fall on Thursdays 00:00:00 UTC will return correct values.
     * This function requires the contract to have been checkpointed past `timestamp` so that the supply is cached.
     * @param timestamp - The timestamp at which to read the cached total supply at.
     */
    function getTotalSupplyAtTimestamp(uint256 timestamp) external view returns (uint256);
    /**
     * @notice Returns the FeeDistributor's cached balance of `token`.
     */
    function getTokenLastBalance(IERC20 token) external view returns (uint256);
    /**
     * @notice Returns the amount of `token` which the FeeDistributor received in the week beginning at `timestamp`.
     * @param token - The ERC20 token address to query.
     * @param timestamp - The timestamp corresponding to the beginning of the week of interest.
     */
    function getTokensDistributedInWeek(IERC20 token, uint256 timestamp) external view returns (uint256);
    // Preventing third-party claiming
    /**
     * @notice Enables / disables rewards claiming only by the VotingEscrow holder for the message sender.
     * @param enabled - True if only the VotingEscrow holder can claim their rewards, false otherwise.
     */
    function enableOnlyVeHolderClaiming(bool enabled) external;
    /**
     * @notice Returns true if only the VotingEscrow holder can claim their rewards, false otherwise.
     */
    function onlyVeHolderClaimingEnabled(address user) external view returns (bool);
    // Depositing
    /**
     * @notice Deposits tokens to be distributed in the current week.
     * @dev Sending tokens directly to the FeeDistributor instead of using `depositTokens` may result in tokens being
     * retroactively distributed to past weeks, or for the distribution to carry over to future weeks.
     *
     * If for some reason `depositTokens` cannot be called, in order to ensure that all tokens are correctly distributed
     * manually call `checkpointToken` before and after the token transfer.
     * @param token - The ERC20 token address to distribute.
     * @param amount - The amount of tokens to deposit.
     */
    function depositToken(IERC20 token, uint256 amount) external;
    /**
     * @notice Deposits tokens to be distributed in the current week.
     * @dev A version of `depositToken` which supports depositing multiple `tokens` at once.
     * See `depositToken` for more details.
     * @param tokens - An array of ERC20 token addresses to distribute.
     * @param amounts - An array of token amounts to deposit.
     */
    function depositTokens(IERC20[] calldata tokens, uint256[] calldata amounts) external;
    // Checkpointing
    /**
     * @notice Caches the total supply of veSTG at the beginning of each week.
     * This function will be called automatically before claiming tokens to ensure the contract is properly updated.
     */
    function checkpoint() external;
    /**
     * @notice Caches the user's balance of veSTG at the beginning of each week.
     * This function will be called automatically before claiming tokens to ensure the contract is properly updated.
     * @param user - The address of the user to be checkpointed.
     */
    function checkpointUser(address user) external;
    /**
     * @notice Assigns any newly-received tokens held by the FeeDistributor to weekly distributions.
     * @dev Any `token` balance held by the FeeDistributor above that which is returned by `getTokenLastBalance`
     * will be distributed evenly across the time period since `token` was last checkpointed.
     *
     * This function will be called automatically before claiming tokens to ensure the contract is properly updated.
     * @param token - The ERC20 token address to be checkpointed.
     */
    function checkpointToken(IERC20 token) external;
    /**
     * @notice Assigns any newly-received tokens held by the FeeDistributor to weekly distributions.
     * @dev A version of `checkpointToken` which supports checkpointing multiple tokens.
     * See `checkpointToken` for more details.
     * @param tokens - An array of ERC20 token addresses to be checkpointed.
     */
    function checkpointTokens(IERC20[] calldata tokens) external;
    // Claiming
    /**
     * @notice Claims all pending distributions of the provided token for a user.
     * @dev It's not necessary to explicitly checkpoint before calling this function, it will ensure the FeeDistributor
     * is up to date before calculating the amount of tokens to be claimed.
     * @param user - The user on behalf of which to claim.
     * @param token - The ERC20 token address to be claimed.
     * @return The amount of `token` sent to `user` as a result of claiming.
     */
    function claimToken(address user, IERC20 token) external returns (uint256);
    /**
     * @notice Claims a number of tokens on behalf of a user.
     * @dev A version of `claimToken` which supports claiming multiple `tokens` on behalf of `user`.
     * See `claimToken` for more details.
     * @param user - The user on behalf of which to claim.
     * @param tokens - An array of ERC20 token addresses to be claimed.
     * @return An array of the amounts of each token in `tokens` sent to `user` as a result of claiming.
     */
    function claimTokens(address user, IERC20[] calldata tokens) external returns (uint256[] memory);
    // Governance
    /**
     * @notice Withdraws the specified `amount` of the `token` from the contract to the `recipient`. Can be called only by Stargate DAO.
     * @param token - The token to withdraw.
     * @param amount - The amount to withdraw.
     * @param recipient - The address to transfer the tokens to.
     */
    function withdrawToken(IERC20 token, uint256 amount, address recipient) external;
    /**
     * @notice Enables or disables claiming of the given token. Can be called only by Stargate DAO.
     * @param token - The token to enable or disable claiming.
     * @param enable - True if the token can be claimed, false otherwise.
     */
    function enableTokenClaiming(IERC20 token, bool enable) external;
}
// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity >=0.7.0 <0.9.0;
pragma experimental ABIEncoderV2;
// For compatibility, we're keeping the same function names as in the original Curve code, including the mixed-case
// naming convention.
// solhint-disable func-name-mixedcase
interface IVotingEscrow {
    struct Point {
        int128 bias;
        int128 slope; // - dweight / dt
        uint256 ts;
        uint256 blk; // block
    }
    function epoch() external view returns (uint256);
    function balanceOfAtT(address user, uint256 timestamp) external view returns (uint256);
    function totalSupplyAtT(uint256 timestamp) external view returns (uint256);
    function user_point_epoch(address user) external view returns (uint256);
    function point_history(uint256 timestamp) external view returns (Point memory);
    function user_point_history(address user, uint256 timestamp) external view returns (Point memory);
    function checkpoint() external;
    function locked__end(address user) external view returns (uint256);
}

pragma solidity ^0.4.24;

// File: zos-lib/contracts/upgradeability/Proxy.sol

/**
 * @title Proxy
 * @dev Implements delegation of calls to other contracts, with proper
 * forwarding of return values and bubbling of failures.
 * It defines a fallback function that delegates all calls to the address
 * returned by the abstract _implementation() internal function.
 */
contract Proxy {
  /**
   * @dev Fallback function.
   * Implemented entirely in `_fallback`.
   */
  function () payable external {
    _fallback();
  }

  /**
   * @return The Address of the implementation.
   */
  function _implementation() internal view returns (address);

  /**
   * @dev Delegates execution to an implementation contract.
   * This is a low level function that doesn't return to its internal call site.
   * It will return to the external caller whatever the implementation returns.
   * @param implementation Address to delegate.
   */
  function _delegate(address implementation) internal {
    assembly {
      // Copy msg.data. We take full control of memory in this inline assembly
      // block because it will not return to Solidity code. We overwrite the
      // Solidity scratch pad at memory position 0.
      calldatacopy(0, 0, calldatasize)

      // Call the implementation.
      // out and outsize are 0 because we don't know the size yet.
      let result := delegatecall(gas, implementation, 0, calldatasize, 0, 0)

      // Copy the returned data.
      returndatacopy(0, 0, returndatasize)

      switch result
      // delegatecall returns 0 on error.
      case 0 { revert(0, returndatasize) }
      default { return(0, returndatasize) }
    }
  }

  /**
   * @dev Function that is run as the first thing in the fallback function.
   * Can be redefined in derived contracts to add functionality.
   * Redefinitions must call super._willFallback().
   */
  function _willFallback() internal {
  }

  /**
   * @dev fallback implementation.
   * Extracted to enable manual triggering.
   */
  function _fallback() internal {
    _willFallback();
    _delegate(_implementation());
  }
}

// File: openzeppelin-solidity/contracts/AddressUtils.sol

/**
 * Utility library of inline functions on addresses
 */
library AddressUtils {

  /**
   * Returns whether the target address is a contract
   * @dev This function will return false if invoked during the constructor of a contract,
   * as the code is not actually created until after the constructor finishes.
   * @param addr address to check
   * @return whether the target address is a contract
   */
  function isContract(address addr) internal view returns (bool) {
    uint256 size;
    // XXX Currently there is no better way to check if there is a contract in an address
    // than to check the size of the code at that address.
    // See https://ethereum.stackexchange.com/a/14016/36603
    // for more details about how this works.
    // TODO Check this again before the Serenity release, because all addresses will be
    // contracts then.
    // solium-disable-next-line security/no-inline-assembly
    assembly { size := extcodesize(addr) }
    return size > 0;
  }

}

// File: zos-lib/contracts/upgradeability/UpgradeabilityProxy.sol

/**
 * @title UpgradeabilityProxy
 * @dev This contract implements a proxy that allows to change the
 * implementation address to which it will delegate.
 * Such a change is called an implementation upgrade.
 */
contract UpgradeabilityProxy is Proxy {
  /**
   * @dev Emitted when the implementation is upgraded.
   * @param implementation Address of the new implementation.
   */
  event Upgraded(address implementation);

  /**
   * @dev Storage slot with the address of the current implementation.
   * This is the keccak-256 hash of "org.zeppelinos.proxy.implementation", and is
   * validated in the constructor.
   */
  bytes32 private constant IMPLEMENTATION_SLOT = 0x7050c9e0f4ca769c69bd3a8ef740bc37934f8e2c036e5a723fd8ee048ed3f8c3;

  /**
   * @dev Contract constructor.
   * @param _implementation Address of the initial implementation.
   */
  constructor(address _implementation) public {
    assert(IMPLEMENTATION_SLOT == keccak256("org.zeppelinos.proxy.implementation"));

    _setImplementation(_implementation);
  }

  /**
   * @dev Returns the current implementation.
   * @return Address of the current implementation
   */
  function _implementation() internal view returns (address impl) {
    bytes32 slot = IMPLEMENTATION_SLOT;
    assembly {
      impl := sload(slot)
    }
  }

  /**
   * @dev Upgrades the proxy to a new implementation.
   * @param newImplementation Address of the new implementation.
   */
  function _upgradeTo(address newImplementation) internal {
    _setImplementation(newImplementation);
    emit Upgraded(newImplementation);
  }

  /**
   * @dev Sets the implementation address of the proxy.
   * @param newImplementation Address of the new implementation.
   */
  function _setImplementation(address newImplementation) private {
    require(AddressUtils.isContract(newImplementation), "Cannot set a proxy implementation to a non-contract address");

    bytes32 slot = IMPLEMENTATION_SLOT;

    assembly {
      sstore(slot, newImplementation)
    }
  }
}

// File: zos-lib/contracts/upgradeability/AdminUpgradeabilityProxy.sol

/**
 * @title AdminUpgradeabilityProxy
 * @dev This contract combines an upgradeability proxy with an authorization
 * mechanism for administrative tasks.
 * All external functions in this contract must be guarded by the
 * `ifAdmin` modifier. See ethereum/solidity#3864 for a Solidity
 * feature proposal that would enable this to be done automatically.
 */
contract AdminUpgradeabilityProxy is UpgradeabilityProxy {
  /**
   * @dev Emitted when the administration has been transferred.
   * @param previousAdmin Address of the previous admin.
   * @param newAdmin Address of the new admin.
   */
  event AdminChanged(address previousAdmin, address newAdmin);

  /**
   * @dev Storage slot with the admin of the contract.
   * This is the keccak-256 hash of "org.zeppelinos.proxy.admin", and is
   * validated in the constructor.
   */
  bytes32 private constant ADMIN_SLOT = 0x10d6a54a4754c8869d6886b5f5d7fbfa5b4522237ea5c60d11bc4e7a1ff9390b;

  /**
   * @dev Modifier to check whether the `msg.sender` is the admin.
   * If it is, it will run the function. Otherwise, it will delegate the call
   * to the implementation.
   */
  modifier ifAdmin() {
    if (msg.sender == _admin()) {
      _;
    } else {
      _fallback();
    }
  }

  /**
   * Contract constructor.
   * It sets the `msg.sender` as the proxy administrator.
   * @param _implementation address of the initial implementation.
   */
  constructor(address _implementation) UpgradeabilityProxy(_implementation) public {
    assert(ADMIN_SLOT == keccak256("org.zeppelinos.proxy.admin"));

    _setAdmin(msg.sender);
  }

  /**
   * @return The address of the proxy admin.
   */
  function admin() external view ifAdmin returns (address) {
    return _admin();
  }

  /**
   * @return The address of the implementation.
   */
  function implementation() external view ifAdmin returns (address) {
    return _implementation();
  }

  /**
   * @dev Changes the admin of the proxy.
   * Only the current admin can call this function.
   * @param newAdmin Address to transfer proxy administration to.
   */
  function changeAdmin(address newAdmin) external ifAdmin {
    require(newAdmin != address(0), "Cannot change the admin of a proxy to the zero address");
    emit AdminChanged(_admin(), newAdmin);
    _setAdmin(newAdmin);
  }

  /**
   * @dev Upgrade the backing implementation of the proxy.
   * Only the admin can call this function.
   * @param newImplementation Address of the new implementation.
   */
  function upgradeTo(address newImplementation) external ifAdmin {
    _upgradeTo(newImplementation);
  }

  /**
   * @dev Upgrade the backing implementation of the proxy and call a function
   * on the new implementation.
   * This is useful to initialize the proxied contract.
   * @param newImplementation Address of the new implementation.
   * @param data Data to send as msg.data in the low level call.
   * It should include the signature and the parameters of the function to be
   * called, as described in
   * https://solidity.readthedocs.io/en/develop/abi-spec.html#function-selector-and-argument-encoding.
   */
  function upgradeToAndCall(address newImplementation, bytes data) payable external ifAdmin {
    _upgradeTo(newImplementation);
    require(address(this).call.value(msg.value)(data));
  }

  /**
   * @return The admin slot.
   */
  function _admin() internal view returns (address adm) {
    bytes32 slot = ADMIN_SLOT;
    assembly {
      adm := sload(slot)
    }
  }

  /**
   * @dev Sets the address of the proxy admin.
   * @param newAdmin Address of the new proxy admin.
   */
  function _setAdmin(address newAdmin) internal {
    bytes32 slot = ADMIN_SLOT;

    assembly {
      sstore(slot, newAdmin)
    }
  }

  /**
   * @dev Only fall back when the sender is not the admin.
   */
  function _willFallback() internal {
    require(msg.sender != _admin(), "Cannot call fallback function from the proxy admin");
    super._willFallback();
  }
}

// File: contracts/FiatTokenProxy.sol

/**
* Copyright CENTRE SECZ 2018
*
* Permission is hereby granted, free of charge, to any person obtaining a copy 
* of this software and associated documentation files (the "Software"), to deal 
* in the Software without restriction, including without limitation the rights 
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
* copies of the Software, and to permit persons to whom the Software is furnished to 
* do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all 
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN 
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

pragma solidity ^0.4.24;


/**
 * @title FiatTokenProxy
 * @dev This contract proxies FiatToken calls and enables FiatToken upgrades
*/ 
contract FiatTokenProxy is AdminUpgradeabilityProxy {
    constructor(address _implementation) public AdminUpgradeabilityProxy(_implementation) {
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;
/**
@title Voting Escrow
@author Curve Finance
@license MIT
@notice Votes have a weight depending on time, so that users are
        committed to the future of (whatever they are voting for)
@dev Vote weight decays linearly over time. Lock time cannot be
     more than `MAXTIME` (3 years).
# Voting escrow to have time-weighted votes
# Votes have a weight depending on time, so that users are committed
# to the future of (whatever they are voting for).
# The weight in this implementation is linear, and lock cannot be more than maxtime:
# w ^
# 1 +        /
#   |      /
#   |    /
#   |  /
#   |/
# 0 +--------+------> time
#       maxtime (3 years?)
*/
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/interfaces/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
struct Point {
    int128 bias;
    int128 slope; // # -dweight / dt
    uint ts;
    uint blk; // block
}
/* We cannot really do block numbers per se b/c slope is per time, not per block
 * and per block could be fairly bad b/c Ethereum changes blocktimes.
 * What we can do is to extrapolate ***At functions */
struct LockedBalance {
    int128 amount;
    uint end;
}
contract VotingEscrow is Ownable, ReentrancyGuard {
    using SafeERC20 for IERC20;
    enum DepositType {
        DEPOSIT_FOR_TYPE,
        CREATE_LOCK_TYPE,
        INCREASE_LOCK_AMOUNT,
        INCREASE_UNLOCK_TIME
    }
    event Deposit(address indexed provider, uint value, uint indexed locktime, DepositType deposit_type, uint ts);
    event Withdraw(address indexed provider, uint value, uint ts);
    event Supply(uint prevSupply, uint supply);
    uint internal constant WEEK = 1 weeks;
    uint public constant MAXTIME = 3 * 365 * 86400;
    int128 internal constant iMAXTIME = 3 * 365 * 86400;
    uint internal constant MULTIPLIER = 1 ether;
    uint public immutable MINTIME;
    address public immutable token;
    uint public supply;
    bool public unlocked;
    mapping(address => LockedBalance) public locked;
    uint public epoch;
    mapping(uint => Point) public point_history; // epoch -> unsigned point
    mapping(address => Point[1000000000]) public user_point_history; // user -> Point[user_epoch]
    mapping(address => uint) public user_point_epoch;
    mapping(uint => int128) public slope_changes; // time -> signed slope change
    // Aragon's view methods for compatibility
    address public controller;
    bool public transfersEnabled;
    string public constant name = "veSTG";
    string public constant symbol = "veSTG";
    string public constant version = "1.0.0";
    uint8 public constant decimals = 18;
    // Whitelisted (smart contract) wallets which are allowed to deposit
    // The goal is to prevent tokenizing the escrow
    mapping(address => bool) public contracts_whitelist;
    /// @notice Contract constructor
    /// @param token_addr `ERC20CRV` token address
    constructor(address token_addr, uint min_time) {
        token = token_addr;
        point_history[0].blk = block.number;
        point_history[0].ts = block.timestamp;
        controller = msg.sender;
        transfersEnabled = true;
        MINTIME = min_time;
    }
    modifier onlyUserOrWhitelist() {
        if (msg.sender != tx.origin) {
            require(contracts_whitelist[msg.sender], "Smart contract not allowed");
        }
        _;
    }
    modifier notUnlocked() {
        require(!unlocked, "unlocked globally");
        _;
    }
    /// @notice Add address to whitelist smart contract depositors `addr`
    /// @param addr Address to be whitelisted
    function add_to_whitelist(address addr) external onlyOwner {
        contracts_whitelist[addr] = true;
    }
    /// @notice Remove a smart contract address from whitelist
    /// @param addr Address to be removed from whitelist
    function remove_from_whitelist(address addr) external onlyOwner {
        contracts_whitelist[addr] = false;
    }
    /// @notice Unlock all locked balances
    function unlock() external onlyOwner {
        unlocked = true;
    }
    /// @notice Get the most recently recorded rate of voting power decrease for `_addr`
    /// @param addr Address of the user wallet
    /// @return Value of the slope
    function get_last_user_slope(address addr) external view returns (int128) {
        uint uepoch = user_point_epoch[addr];
        return user_point_history[addr][uepoch].slope;
    }
    /// @notice Get the timestamp for checkpoint `_idx` for `_addr`
    /// @param _addr User wallet address
    /// @param _idx User epoch number
    /// @return Epoch time of the checkpoint
    function user_point_history__ts(address _addr, uint _idx) external view returns (uint) {
        return user_point_history[_addr][_idx].ts;
    }
    /// @notice Get timestamp when `_addr`'s lock finishes
    /// @param _addr User wallet address
    /// @return Epoch time of the lock end
    function locked__end(address _addr) external view returns (uint) {
        return locked[_addr].end;
    }
    /// @notice Record global and per-user data to checkpoint
    /// @param _addr User's wallet address. No user checkpoint if 0x0
    /// @param old_locked Pevious locked amount / end lock time for the user
    /// @param new_locked New locked amount / end lock time for the user
    function _checkpoint(address _addr, LockedBalance memory old_locked, LockedBalance memory new_locked) internal {
        Point memory u_old;
        Point memory u_new;
        int128 old_dslope = 0;
        int128 new_dslope = 0;
        uint _epoch = epoch;
        if (_addr != address(0x0)) {
            // Calculate slopes and biases
            // Kept at zero when they have to
            if (old_locked.end > block.timestamp && old_locked.amount > 0) {
                u_old.slope = old_locked.amount / iMAXTIME;
                u_old.bias = u_old.slope * int128(int(old_locked.end - block.timestamp));
            }
            if (new_locked.end > block.timestamp && new_locked.amount > 0) {
                u_new.slope = new_locked.amount / iMAXTIME;
                u_new.bias = u_new.slope * int128(int(new_locked.end - block.timestamp));
            }
            // Read values of scheduled changes in the slope
            // old_locked.end can be in the past and in the future
            // new_locked.end can ONLY by in the FUTURE unless everything expired: than zeros
            old_dslope = slope_changes[old_locked.end];
            if (new_locked.end != 0) {
                if (new_locked.end == old_locked.end) {
                    new_dslope = old_dslope;
                } else {
                    new_dslope = slope_changes[new_locked.end];
                }
            }
        }
        Point memory last_point = Point({bias: 0, slope: 0, ts: block.timestamp, blk: block.number});
        if (_epoch > 0) {
            last_point = point_history[_epoch];
        }
        uint last_checkpoint = last_point.ts;
        // initial_last_point is used for extrapolation to calculate block number
        // (approximately, for *At methods) and save them
        // as we cannot figure that out exactly from inside the contract
        uint initial_last_point_ts = last_point.ts;
        uint initial_last_point_blk = last_point.blk;
        uint block_slope = 0; // dblock/dt
        if (block.timestamp > last_point.ts) {
            block_slope = (MULTIPLIER * (block.number - last_point.blk)) / (block.timestamp - last_point.ts);
        }
        // If last point is already recorded in this block, slope=0
        // But that's ok b/c we know the block in such case
        // Go over weeks to fill history and calculate what the current point is
        uint t_i = (last_checkpoint / WEEK) * WEEK;
        for (uint i = 0; i < 255; ++i) {
            // Hopefully it won't happen that this won't get used in 5 years!
            // If it does, users will be able to withdraw but vote weight will be broken
            t_i += WEEK;
            int128 d_slope = 0;
            if (t_i > block.timestamp) {
                t_i = block.timestamp;
            } else {
                d_slope = slope_changes[t_i];
            }
            last_point.bias -= last_point.slope * int128(int(t_i - last_checkpoint));
            last_point.slope += d_slope;
            if (last_point.bias < 0) {
                // This can happen
                last_point.bias = 0;
            }
            if (last_point.slope < 0) {
                // This cannot happen - just in case
                last_point.slope = 0;
            }
            last_checkpoint = t_i;
            last_point.ts = t_i;
            last_point.blk = initial_last_point_blk + (block_slope * (t_i - initial_last_point_ts)) / MULTIPLIER;
            _epoch += 1;
            if (t_i == block.timestamp) {
                last_point.blk = block.number;
                break;
            } else {
                point_history[_epoch] = last_point;
            }
        }
        epoch = _epoch;
        // Now point_history is filled until t=now
        if (_addr != address(0x0)) {
            // If last point was in this block, the slope change has been applied already
            // But in such case we have 0 slope(s)
            last_point.slope += (u_new.slope - u_old.slope);
            last_point.bias += (u_new.bias - u_old.bias);
            if (last_point.slope < 0) {
                last_point.slope = 0;
            }
            if (last_point.bias < 0) {
                last_point.bias = 0;
            }
        }
        // Record the changed point into history
        point_history[_epoch] = last_point;
        if (_addr != address(0x0)) {
            // Schedule the slope changes (slope is going down)
            // We subtract new_user_slope from [new_locked.end]
            // and add old_user_slope to [old_locked.end]
            if (old_locked.end > block.timestamp) {
                // old_dslope was <something> - u_old.slope, so we cancel that
                old_dslope += u_old.slope;
                if (new_locked.end == old_locked.end) {
                    old_dslope -= u_new.slope; // It was a new deposit, not extension
                }
                slope_changes[old_locked.end] = old_dslope;
            }
            if (new_locked.end > block.timestamp) {
                if (new_locked.end > old_locked.end) {
                    new_dslope -= u_new.slope; // old slope disappeared at this point
                    slope_changes[new_locked.end] = new_dslope;
                }
                // else: we recorded it already in old_dslope
            }
            // Now handle user history
            address addr = _addr;
            uint user_epoch = user_point_epoch[addr] + 1;
            user_point_epoch[addr] = user_epoch;
            u_new.ts = block.timestamp;
            u_new.blk = block.number;
            user_point_history[addr][user_epoch] = u_new;
        }
    }
    /// @notice Deposit and lock tokens for a user
    /// @param _addr User's wallet address
    /// @param _value Amount to deposit
    /// @param unlock_time New time when to unlock the tokens, or 0 if unchanged
    /// @param locked_balance Previous locked amount / timestamp
    /// @param deposit_type The type of deposit
    function _deposit_for(address _addr, uint _value, uint unlock_time, LockedBalance memory locked_balance, DepositType deposit_type) internal {
        LockedBalance memory _locked = locked_balance;
        uint supply_before = supply;
        supply = supply_before + _value;
        LockedBalance memory old_locked;
        (old_locked.amount, old_locked.end) = (_locked.amount, _locked.end);
        // Adding to existing lock, or if a lock is expired - creating a new one
        _locked.amount += int128(int(_value));
        if (unlock_time != 0) {
            _locked.end = unlock_time;
        }
        locked[_addr] = _locked;
        // Possibilities:
        // Both old_locked.end could be current or expired (>/< block.timestamp)
        // value == 0 (extend lock) or value > 0 (add to lock or extend lock)
        // _locked.end > block.timestamp (always)
        _checkpoint(_addr, old_locked, _locked);
        if (_value != 0) {
            IERC20(token).safeTransferFrom(_addr, address(this), _value);
        }
        emit Deposit(_addr, _value, _locked.end, deposit_type, block.timestamp);
        emit Supply(supply_before, supply_before + _value);
    }
    /// @notice Record global data to checkpoint
    function checkpoint() external notUnlocked {
        _checkpoint(address(0x0), LockedBalance(0, 0), LockedBalance(0, 0));
    }
    /// @notice Deposit `_value` tokens for `_addr` and add to the lock
    /// @dev Anyone (even a smart contract) can deposit for someone else, but
    ///      cannot extend their locktime and deposit for a brand new user
    /// @param _addr User's wallet address
    /// @param _value Amount to add to user's lock
    function deposit_for(address _addr, uint _value) external nonReentrant notUnlocked {
        LockedBalance memory _locked = locked[_addr];
        require(_value > 0); // dev: need non-zero value
        require(_locked.amount > 0, "No existing lock found");
        require(_locked.end > block.timestamp, "Cannot add to expired lock. Withdraw");
        _deposit_for(_addr, _value, 0, _locked, DepositType.DEPOSIT_FOR_TYPE);
    }
    /// @notice Deposit `_value` tokens for `msg.sender` and lock until `_unlock_time`
    /// @param _value Amount to deposit
    /// @param _unlock_time Epoch time when tokens unlock, rounded down to whole weeks
    function _create_lock(uint _value, uint _unlock_time) internal {
        require(_value > 0); // dev: need non-zero value
        LockedBalance memory _locked = locked[msg.sender];
        require(_locked.amount == 0, "Withdraw old tokens first");
        uint unlock_time = (_unlock_time / WEEK) * WEEK; // Locktime is rounded down to weeks
        require(unlock_time >= block.timestamp + MINTIME, "Voting lock must be at least MINTIME");
        require(unlock_time <= block.timestamp + MAXTIME, "Voting lock can be 3 years max");
        _deposit_for(msg.sender, _value, unlock_time, _locked, DepositType.CREATE_LOCK_TYPE);
    }
    /// @notice External function for _create_lock
    /// @param _value Amount to deposit
    /// @param _unlock_time Epoch time when tokens unlock, rounded down to whole weeks
    function create_lock(uint _value, uint _unlock_time) external nonReentrant onlyUserOrWhitelist notUnlocked {
        _create_lock(_value, _unlock_time);
    }
    /// @notice Deposit `_value` additional tokens for `msg.sender` without modifying the unlock time
    /// @param _value Amount of tokens to deposit and add to the lock
    function increase_amount(uint _value) external nonReentrant onlyUserOrWhitelist notUnlocked {
        _increase_amount(_value);
    }
    function _increase_amount(uint _value) internal {
        LockedBalance memory _locked = locked[msg.sender];
        require(_value > 0); // dev: need non-zero value
        require(_locked.amount > 0, "No existing lock found");
        require(_locked.end > block.timestamp, "Cannot add to expired lock. Withdraw");
        _deposit_for(msg.sender, _value, 0, _locked, DepositType.INCREASE_LOCK_AMOUNT);
    }
    /// @notice Extend the unlock time for `msg.sender` to `_unlock_time`
    /// @param _unlock_time New epoch time for unlocking
    function increase_unlock_time(uint _unlock_time) external nonReentrant onlyUserOrWhitelist notUnlocked {
        _increase_unlock_time(_unlock_time);
    }
    function _increase_unlock_time(uint _unlock_time) internal {
        LockedBalance memory _locked = locked[msg.sender];
        uint unlock_time = (_unlock_time / WEEK) * WEEK; // Locktime is rounded down to weeks
        require(_locked.end > block.timestamp, "Lock expired");
        require(_locked.amount > 0, "Nothing is locked");
        require(unlock_time > _locked.end, "Can only increase lock duration");
        require(unlock_time <= block.timestamp + MAXTIME, "Voting lock can be 3 years max");
        _deposit_for(msg.sender, 0, unlock_time, _locked, DepositType.INCREASE_UNLOCK_TIME);
    }
    /// @notice Extend the unlock time and/or for `msg.sender` to `_unlock_time`
    /// @param _unlock_time New epoch time for unlocking
    function increase_amount_and_time(uint _value, uint _unlock_time) external nonReentrant onlyUserOrWhitelist notUnlocked {
        require(_value > 0 || _unlock_time > 0, "Value and Unlock cannot both be 0");
        if (_value > 0 && _unlock_time > 0) {
            _increase_amount(_value);
            _increase_unlock_time(_unlock_time);
        } else if (_value > 0 && _unlock_time == 0) {
            _increase_amount(_value);
        } else {
            _increase_unlock_time(_unlock_time);
        }
    }
    /// @notice Withdraw all tokens for `msg.sender`
    /// @dev Only possible if the lock has expired
    function _withdraw() internal {
        LockedBalance memory _locked = locked[msg.sender];
        uint value = uint(int(_locked.amount));
        if (!unlocked) {
            require(block.timestamp >= _locked.end, "The lock didn't expire");
        }
        locked[msg.sender] = LockedBalance(0, 0);
        uint supply_before = supply;
        supply = supply_before - value;
        // old_locked can have either expired <= timestamp or zero end
        // _locked has only 0 end
        // Both can have >= 0 amount
        _checkpoint(msg.sender, _locked, LockedBalance(0, 0));
        IERC20(token).safeTransfer(msg.sender, value);
        emit Withdraw(msg.sender, value, block.timestamp);
        emit Supply(supply_before, supply_before - value);
    }
    function withdraw() external nonReentrant {
        _withdraw();
    }
    /// @notice Deposit `_value` tokens for `msg.sender` and lock until `_unlock_time`
    /// @param _value Amount to deposit
    /// @param _unlock_time Epoch time when tokens unlock, rounded down to whole weeks
    function withdraw_and_create_lock(uint _value, uint _unlock_time) external nonReentrant onlyUserOrWhitelist notUnlocked {
        _withdraw();
        _create_lock(_value, _unlock_time);
    }
    // The following ERC20/minime-compatible methods are not real balanceOf and supply!
    // They measure the weights for the purpose of voting, so they don't represent
    // real coins.
    /// @notice Binary search to estimate timestamp for block number
    /// @param _block Block to find
    /// @param max_epoch Don't go beyond this epoch
    /// @return Approximate timestamp for block
    function _find_block_epoch(uint _block, uint max_epoch) internal view returns (uint) {
        // Binary search
        uint _min = 0;
        uint _max = max_epoch;
        for (uint i = 0; i < 128; ++i) {
            // Will be always enough for 128-bit numbers
            if (_min >= _max) {
                break;
            }
            uint _mid = (_min + _max + 1) / 2;
            if (point_history[_mid].blk <= _block) {
                _min = _mid;
            } else {
                _max = _mid - 1;
            }
        }
        return _min;
    }
    /// @notice Get the current voting power for `msg.sender`
    /// @dev Adheres to the ERC20 `balanceOf` interface for Aragon compatibility
    /// @param addr User wallet address
    /// @param _t Epoch time to return voting power at
    /// @return User voting power
    function _balanceOf(address addr, uint _t) internal view returns (uint) {
        uint _epoch = user_point_epoch[addr];
        if (_epoch == 0) {
            return 0;
        } else {
            Point memory last_point = user_point_history[addr][_epoch];
            last_point.bias -= last_point.slope * int128(int(_t) - int(last_point.ts));
            if (last_point.bias < 0) {
                last_point.bias = 0;
            }
            return uint(int(last_point.bias));
        }
    }
    function balanceOfAtT(address addr, uint _t) external view returns (uint) {
        return _balanceOf(addr, _t);
    }
    function balanceOf(address addr) external view returns (uint) {
        return _balanceOf(addr, block.timestamp);
    }
    /// @notice Measure voting power of `addr` at block height `_block`
    /// @dev Adheres to MiniMe `balanceOfAt` interface: https://github.com/Giveth/minime
    /// @param addr User's wallet address
    /// @param _block Block to calculate the voting power at
    /// @return Voting power
    function balanceOfAt(address addr, uint _block) external view returns (uint) {
        // Copying and pasting totalSupply code because Vyper cannot pass by
        // reference yet
        require(_block <= block.number);
        // Binary search
        uint _min = 0;
        uint _max = user_point_epoch[addr];
        for (uint i = 0; i < 128; ++i) {
            // Will be always enough for 128-bit numbers
            if (_min >= _max) {
                break;
            }
            uint _mid = (_min + _max + 1) / 2;
            if (user_point_history[addr][_mid].blk <= _block) {
                _min = _mid;
            } else {
                _max = _mid - 1;
            }
        }
        Point memory upoint = user_point_history[addr][_min];
        uint max_epoch = epoch;
        uint _epoch = _find_block_epoch(_block, max_epoch);
        Point memory point_0 = point_history[_epoch];
        uint d_block = 0;
        uint d_t = 0;
        if (_epoch < max_epoch) {
            Point memory point_1 = point_history[_epoch + 1];
            d_block = point_1.blk - point_0.blk;
            d_t = point_1.ts - point_0.ts;
        } else {
            d_block = block.number - point_0.blk;
            d_t = block.timestamp - point_0.ts;
        }
        uint block_time = point_0.ts;
        if (d_block != 0) {
            block_time += (d_t * (_block - point_0.blk)) / d_block;
        }
        upoint.bias -= upoint.slope * int128(int(block_time - upoint.ts));
        if (upoint.bias >= 0) {
            return uint(uint128(upoint.bias));
        } else {
            return 0;
        }
    }
    /// @notice Calculate total voting power at some point in the past
    /// @param point The point (bias/slope) to start search from
    /// @param t Time to calculate the total voting power at
    /// @return Total voting power at that time
    function _supply_at(Point memory point, uint t) internal view returns (uint) {
        Point memory last_point = point;
        uint t_i = (last_point.ts / WEEK) * WEEK;
        for (uint i = 0; i < 255; ++i) {
            t_i += WEEK;
            int128 d_slope = 0;
            if (t_i > t) {
                t_i = t;
            } else {
                d_slope = slope_changes[t_i];
            }
            last_point.bias -= last_point.slope * int128(int(t_i - last_point.ts));
            if (t_i == t) {
                break;
            }
            last_point.slope += d_slope;
            last_point.ts = t_i;
        }
        if (last_point.bias < 0) {
            last_point.bias = 0;
        }
        return uint(uint128(last_point.bias));
    }
    /// @notice Calculate total voting power
    /// @dev Adheres to the ERC20 `totalSupply` interface for Aragon compatibility
    /// @return Total voting power
    function _totalSupply(uint t) internal view returns (uint) {
        uint _epoch = epoch;
        Point memory last_point = point_history[_epoch];
        return _supply_at(last_point, t);
    }
    function totalSupplyAtT(uint t) external view returns (uint) {
        return _totalSupply(t);
    }
    function totalSupply() external view returns (uint) {
        return _totalSupply(block.timestamp);
    }
    /// @notice Calculate total voting power at some point in the past
    /// @param _block Block to calculate the total voting power at
    /// @return Total voting power at `_block`
    function totalSupplyAt(uint _block) external view returns (uint) {
        require(_block <= block.number);
        uint _epoch = epoch;
        uint target_epoch = _find_block_epoch(_block, _epoch);
        Point memory point = point_history[target_epoch];
        uint dt = 0;
        if (target_epoch < _epoch) {
            Point memory point_next = point_history[target_epoch + 1];
            if (point.blk != point_next.blk) {
                dt = ((_block - point.blk) * (point_next.ts - point.ts)) / (point_next.blk - point.blk);
            }
        } else {
            if (point.blk != block.number) {
                dt = ((_block - point.blk) * (block.timestamp - point.ts)) / (block.number - point.blk);
            }
        }
        // Now dt contains info on how far are we beyond point
        return _supply_at(point, point.ts + dt);
    }
    // Dummy methods for compatibility with Aragon
    function changeController(address _newController) external {
        require(msg.sender == controller);
        controller = _newController;
    }
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)
pragma solidity ^0.8.0;
import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }
    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }
    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }
    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }
    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (security/ReentrancyGuard.sol)
pragma solidity ^0.8.0;
/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.
    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;
    uint256 private _status;
    constructor() {
        _status = _NOT_ENTERED;
    }
    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");
        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;
        _;
        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (interfaces/IERC20.sol)
pragma solidity ^0.8.0;
import "../token/ERC20/IERC20.sol";
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/utils/SafeERC20.sol)
pragma solidity ^0.8.0;
import "../IERC20.sol";
import "../../../utils/Address.sol";
/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using Address for address;
    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }
    function safeTransferFrom(
        IERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }
    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }
    function safeIncreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender) + value;
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }
    function safeDecreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        unchecked {
            uint256 oldAllowance = token.allowance(address(this), spender);
            require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
            uint256 newAllowance = oldAllowance - value;
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
        }
    }
    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.
        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) {
            // Return data is optional
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)
pragma solidity ^0.8.0;
/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/IERC20.sol)
pragma solidity ^0.8.0;
/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);
    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);
    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);
    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);
    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);
    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool);
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);
    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (utils/Address.sol)
pragma solidity ^0.8.1;
/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.
        return account.code.length > 0;
    }
    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");
        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain `call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCall(target, data, "Address: low-level call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }
    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(success, returndata, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");
        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }
    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount)
        external
        returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender)
        external
        view
        returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

// File: contracts/v1/AbstractFiatTokenV1.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

abstract contract AbstractFiatTokenV1 is IERC20 {
    function _approve(
        address owner,
        address spender,
        uint256 value
    ) internal virtual;

    function _transfer(
        address from,
        address to,
        uint256 value
    ) internal virtual;
}

// File: contracts/v1/Ownable.sol

/**
 * Copyright (c) 2018 zOS Global Limited.
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
pragma solidity 0.6.12;

/**
 * @notice The Ownable contract has an owner address, and provides basic
 * authorization control functions
 * @dev Forked from https://github.com/OpenZeppelin/openzeppelin-labs/blob/3887ab77b8adafba4a26ace002f3a684c1a3388b/upgradeability_ownership/contracts/ownership/Ownable.sol
 * Modifications:
 * 1. Consolidate OwnableStorage into this contract (7/13/18)
 * 2. Reformat, conform to Solidity 0.6 syntax, and add error messages (5/13/20)
 * 3. Make public functions external (5/27/20)
 */
contract Ownable {
    // Owner of the contract
    address private _owner;

    /**
     * @dev Event to show ownership has been transferred
     * @param previousOwner representing the address of the previous owner
     * @param newOwner representing the address of the new owner
     */
    event OwnershipTransferred(address previousOwner, address newOwner);

    /**
     * @dev The constructor sets the original owner of the contract to the sender account.
     */
    constructor() public {
        setOwner(msg.sender);
    }

    /**
     * @dev Tells the address of the owner
     * @return the address of the owner
     */
    function owner() external view returns (address) {
        return _owner;
    }

    /**
     * @dev Sets a new owner address
     */
    function setOwner(address newOwner) internal {
        _owner = newOwner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(msg.sender == _owner, "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Allows the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function transferOwnership(address newOwner) external onlyOwner {
        require(
            newOwner != address(0),
            "Ownable: new owner is the zero address"
        );
        emit OwnershipTransferred(_owner, newOwner);
        setOwner(newOwner);
    }
}

// File: contracts/v1/Pausable.sol

/**
 * Copyright (c) 2016 Smart Contract Solutions, Inc.
 * Copyright (c) 2018-2020 CENTRE SECZ0
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @notice Base contract which allows children to implement an emergency stop
 * mechanism
 * @dev Forked from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/feb665136c0dae9912e08397c1a21c4af3651ef3/contracts/lifecycle/Pausable.sol
 * Modifications:
 * 1. Added pauser role, switched pause/unpause to be onlyPauser (6/14/2018)
 * 2. Removed whenNotPause/whenPaused from pause/unpause (6/14/2018)
 * 3. Removed whenPaused (6/14/2018)
 * 4. Switches ownable library to use ZeppelinOS (7/12/18)
 * 5. Remove constructor (7/13/18)
 * 6. Reformat, conform to Solidity 0.6 syntax and add error messages (5/13/20)
 * 7. Make public functions external (5/27/20)
 */
contract Pausable is Ownable {
    event Pause();
    event Unpause();
    event PauserChanged(address indexed newAddress);

    address public pauser;
    bool public paused = false;

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     */
    modifier whenNotPaused() {
        require(!paused, "Pausable: paused");
        _;
    }

    /**
     * @dev throws if called by any account other than the pauser
     */
    modifier onlyPauser() {
        require(msg.sender == pauser, "Pausable: caller is not the pauser");
        _;
    }

    /**
     * @dev called by the owner to pause, triggers stopped state
     */
    function pause() external onlyPauser {
        paused = true;
        emit Pause();
    }

    /**
     * @dev called by the owner to unpause, returns to normal state
     */
    function unpause() external onlyPauser {
        paused = false;
        emit Unpause();
    }

    /**
     * @dev update the pauser role
     */
    function updatePauser(address _newPauser) external onlyOwner {
        require(
            _newPauser != address(0),
            "Pausable: new pauser is the zero address"
        );
        pauser = _newPauser;
        emit PauserChanged(pauser);
    }
}

// File: contracts/v1/Blacklistable.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title Blacklistable Token
 * @dev Allows accounts to be blacklisted by a "blacklister" role
 */
contract Blacklistable is Ownable {
    address public blacklister;
    mapping(address => bool) internal blacklisted;

    event Blacklisted(address indexed _account);
    event UnBlacklisted(address indexed _account);
    event BlacklisterChanged(address indexed newBlacklister);

    /**
     * @dev Throws if called by any account other than the blacklister
     */
    modifier onlyBlacklister() {
        require(
            msg.sender == blacklister,
            "Blacklistable: caller is not the blacklister"
        );
        _;
    }

    /**
     * @dev Throws if argument account is blacklisted
     * @param _account The address to check
     */
    modifier notBlacklisted(address _account) {
        require(
            !blacklisted[_account],
            "Blacklistable: account is blacklisted"
        );
        _;
    }

    /**
     * @dev Checks if account is blacklisted
     * @param _account The address to check
     */
    function isBlacklisted(address _account) external view returns (bool) {
        return blacklisted[_account];
    }

    /**
     * @dev Adds account to blacklist
     * @param _account The address to blacklist
     */
    function blacklist(address _account) external onlyBlacklister {
        blacklisted[_account] = true;
        emit Blacklisted(_account);
    }

    /**
     * @dev Removes account from blacklist
     * @param _account The address to remove from the blacklist
     */
    function unBlacklist(address _account) external onlyBlacklister {
        blacklisted[_account] = false;
        emit UnBlacklisted(_account);
    }

    function updateBlacklister(address _newBlacklister) external onlyOwner {
        require(
            _newBlacklister != address(0),
            "Blacklistable: new blacklister is the zero address"
        );
        blacklister = _newBlacklister;
        emit BlacklisterChanged(blacklister);
    }
}

// File: contracts/v1/FiatTokenV1.sol

/**
 *
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title FiatToken
 * @dev ERC20 Token backed by fiat reserves
 */
contract FiatTokenV1 is AbstractFiatTokenV1, Ownable, Pausable, Blacklistable {
    using SafeMath for uint256;

    string public name;
    string public symbol;
    uint8 public decimals;
    string public currency;
    address public masterMinter;
    bool internal initialized;

    mapping(address => uint256) internal balances;
    mapping(address => mapping(address => uint256)) internal allowed;
    uint256 internal totalSupply_ = 0;
    mapping(address => bool) internal minters;
    mapping(address => uint256) internal minterAllowed;

    event Mint(address indexed minter, address indexed to, uint256 amount);
    event Burn(address indexed burner, uint256 amount);
    event MinterConfigured(address indexed minter, uint256 minterAllowedAmount);
    event MinterRemoved(address indexed oldMinter);
    event MasterMinterChanged(address indexed newMasterMinter);

    function initialize(
        string memory tokenName,
        string memory tokenSymbol,
        string memory tokenCurrency,
        uint8 tokenDecimals,
        address newMasterMinter,
        address newPauser,
        address newBlacklister,
        address newOwner
    ) public {
        require(!initialized, "FiatToken: contract is already initialized");
        require(
            newMasterMinter != address(0),
            "FiatToken: new masterMinter is the zero address"
        );
        require(
            newPauser != address(0),
            "FiatToken: new pauser is the zero address"
        );
        require(
            newBlacklister != address(0),
            "FiatToken: new blacklister is the zero address"
        );
        require(
            newOwner != address(0),
            "FiatToken: new owner is the zero address"
        );

        name = tokenName;
        symbol = tokenSymbol;
        currency = tokenCurrency;
        decimals = tokenDecimals;
        masterMinter = newMasterMinter;
        pauser = newPauser;
        blacklister = newBlacklister;
        setOwner(newOwner);
        initialized = true;
    }

    /**
     * @dev Throws if called by any account other than a minter
     */
    modifier onlyMinters() {
        require(minters[msg.sender], "FiatToken: caller is not a minter");
        _;
    }

    /**
     * @dev Function to mint tokens
     * @param _to The address that will receive the minted tokens.
     * @param _amount The amount of tokens to mint. Must be less than or equal
     * to the minterAllowance of the caller.
     * @return A boolean that indicates if the operation was successful.
     */
    function mint(address _to, uint256 _amount)
        external
        whenNotPaused
        onlyMinters
        notBlacklisted(msg.sender)
        notBlacklisted(_to)
        returns (bool)
    {
        require(_to != address(0), "FiatToken: mint to the zero address");
        require(_amount > 0, "FiatToken: mint amount not greater than 0");

        uint256 mintingAllowedAmount = minterAllowed[msg.sender];
        require(
            _amount <= mintingAllowedAmount,
            "FiatToken: mint amount exceeds minterAllowance"
        );

        totalSupply_ = totalSupply_.add(_amount);
        balances[_to] = balances[_to].add(_amount);
        minterAllowed[msg.sender] = mintingAllowedAmount.sub(_amount);
        emit Mint(msg.sender, _to, _amount);
        emit Transfer(address(0), _to, _amount);
        return true;
    }

    /**
     * @dev Throws if called by any account other than the masterMinter
     */
    modifier onlyMasterMinter() {
        require(
            msg.sender == masterMinter,
            "FiatToken: caller is not the masterMinter"
        );
        _;
    }

    /**
     * @dev Get minter allowance for an account
     * @param minter The address of the minter
     */
    function minterAllowance(address minter) external view returns (uint256) {
        return minterAllowed[minter];
    }

    /**
     * @dev Checks if account is a minter
     * @param account The address to check
     */
    function isMinter(address account) external view returns (bool) {
        return minters[account];
    }

    /**
     * @notice Amount of remaining tokens spender is allowed to transfer on
     * behalf of the token owner
     * @param owner     Token owner's address
     * @param spender   Spender's address
     * @return Allowance amount
     */
    function allowance(address owner, address spender)
        external
        override
        view
        returns (uint256)
    {
        return allowed[owner][spender];
    }

    /**
     * @dev Get totalSupply of token
     */
    function totalSupply() external override view returns (uint256) {
        return totalSupply_;
    }

    /**
     * @dev Get token balance of an account
     * @param account address The account
     */
    function balanceOf(address account)
        external
        override
        view
        returns (uint256)
    {
        return balances[account];
    }

    /**
     * @notice Set spender's allowance over the caller's tokens to be a given
     * value.
     * @param spender   Spender's address
     * @param value     Allowance amount
     * @return True if successful
     */
    function approve(address spender, uint256 value)
        external
        override
        whenNotPaused
        notBlacklisted(msg.sender)
        notBlacklisted(spender)
        returns (bool)
    {
        _approve(msg.sender, spender, value);
        return true;
    }

    /**
     * @dev Internal function to set allowance
     * @param owner     Token owner's address
     * @param spender   Spender's address
     * @param value     Allowance amount
     */
    function _approve(
        address owner,
        address spender,
        uint256 value
    ) internal override {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        allowed[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /**
     * @notice Transfer tokens by spending allowance
     * @param from  Payer's address
     * @param to    Payee's address
     * @param value Transfer amount
     * @return True if successful
     */
    function transferFrom(
        address from,
        address to,
        uint256 value
    )
        external
        override
        whenNotPaused
        notBlacklisted(msg.sender)
        notBlacklisted(from)
        notBlacklisted(to)
        returns (bool)
    {
        require(
            value <= allowed[from][msg.sender],
            "ERC20: transfer amount exceeds allowance"
        );
        _transfer(from, to, value);
        allowed[from][msg.sender] = allowed[from][msg.sender].sub(value);
        return true;
    }

    /**
     * @notice Transfer tokens from the caller
     * @param to    Payee's address
     * @param value Transfer amount
     * @return True if successful
     */
    function transfer(address to, uint256 value)
        external
        override
        whenNotPaused
        notBlacklisted(msg.sender)
        notBlacklisted(to)
        returns (bool)
    {
        _transfer(msg.sender, to, value);
        return true;
    }

    /**
     * @notice Internal function to process transfers
     * @param from  Payer's address
     * @param to    Payee's address
     * @param value Transfer amount
     */
    function _transfer(
        address from,
        address to,
        uint256 value
    ) internal override {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");
        require(
            value <= balances[from],
            "ERC20: transfer amount exceeds balance"
        );

        balances[from] = balances[from].sub(value);
        balances[to] = balances[to].add(value);
        emit Transfer(from, to, value);
    }

    /**
     * @dev Function to add/update a new minter
     * @param minter The address of the minter
     * @param minterAllowedAmount The minting amount allowed for the minter
     * @return True if the operation was successful.
     */
    function configureMinter(address minter, uint256 minterAllowedAmount)
        external
        whenNotPaused
        onlyMasterMinter
        returns (bool)
    {
        minters[minter] = true;
        minterAllowed[minter] = minterAllowedAmount;
        emit MinterConfigured(minter, minterAllowedAmount);
        return true;
    }

    /**
     * @dev Function to remove a minter
     * @param minter The address of the minter to remove
     * @return True if the operation was successful.
     */
    function removeMinter(address minter)
        external
        onlyMasterMinter
        returns (bool)
    {
        minters[minter] = false;
        minterAllowed[minter] = 0;
        emit MinterRemoved(minter);
        return true;
    }

    /**
     * @dev allows a minter to burn some of its own tokens
     * Validates that caller is a minter and that sender is not blacklisted
     * amount is less than or equal to the minter's account balance
     * @param _amount uint256 the amount of tokens to be burned
     */
    function burn(uint256 _amount)
        external
        whenNotPaused
        onlyMinters
        notBlacklisted(msg.sender)
    {
        uint256 balance = balances[msg.sender];
        require(_amount > 0, "FiatToken: burn amount not greater than 0");
        require(balance >= _amount, "FiatToken: burn amount exceeds balance");

        totalSupply_ = totalSupply_.sub(_amount);
        balances[msg.sender] = balance.sub(_amount);
        emit Burn(msg.sender, _amount);
        emit Transfer(msg.sender, address(0), _amount);
    }

    function updateMasterMinter(address _newMasterMinter) external onlyOwner {
        require(
            _newMasterMinter != address(0),
            "FiatToken: new masterMinter is the zero address"
        );
        masterMinter = _newMasterMinter;
        emit MasterMinterChanged(masterMinter);
    }
}

// File: @openzeppelin/contracts/utils/Address.sol

pragma solidity ^0.6.2;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;

            bytes32 accountHash
         = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            codehash := extcodehash(account)
        }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(
            address(this).balance >= amount,
            "Address: insufficient balance"
        );

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(
            success,
            "Address: unable to send value, recipient may have reverted"
        );
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data)
        internal
        returns (bytes memory)
    {
        return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return
            functionCallWithValue(
                target,
                data,
                value,
                "Address: low-level call with value failed"
            );
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(
            address(this).balance >= value,
            "Address: insufficient balance for call"
        );
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(
        address target,
        bytes memory data,
        uint256 weiValue,
        string memory errorMessage
    ) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{
            value: weiValue
        }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/SafeERC20.sol

pragma solidity ^0.6.0;

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(
            token,
            abi.encodeWithSelector(token.transfer.selector, to, value)
        );
    }

    function safeTransferFrom(
        IERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(
            token,
            abi.encodeWithSelector(token.transferFrom.selector, from, to, value)
        );
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(
            token,
            abi.encodeWithSelector(token.approve.selector, spender, value)
        );
    }

    function safeIncreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(
            value
        );
        _callOptionalReturn(
            token,
            abi.encodeWithSelector(
                token.approve.selector,
                spender,
                newAllowance
            )
        );
    }

    function safeDecreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(
            value,
            "SafeERC20: decreased allowance below zero"
        );
        _callOptionalReturn(
            token,
            abi.encodeWithSelector(
                token.approve.selector,
                spender,
                newAllowance
            )
        );
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(
            data,
            "SafeERC20: low-level call failed"
        );
        if (returndata.length > 0) {
            // Return data is optional
            // solhint-disable-next-line max-line-length
            require(
                abi.decode(returndata, (bool)),
                "SafeERC20: ERC20 operation did not succeed"
            );
        }
    }
}

// File: contracts/v1.1/Rescuable.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

contract Rescuable is Ownable {
    using SafeERC20 for IERC20;

    address private _rescuer;

    event RescuerChanged(address indexed newRescuer);

    /**
     * @notice Returns current rescuer
     * @return Rescuer's address
     */
    function rescuer() external view returns (address) {
        return _rescuer;
    }

    /**
     * @notice Revert if called by any account other than the rescuer.
     */
    modifier onlyRescuer() {
        require(msg.sender == _rescuer, "Rescuable: caller is not the rescuer");
        _;
    }

    /**
     * @notice Rescue ERC20 tokens locked up in this contract.
     * @param tokenContract ERC20 token contract address
     * @param to        Recipient address
     * @param amount    Amount to withdraw
     */
    function rescueERC20(
        IERC20 tokenContract,
        address to,
        uint256 amount
    ) external onlyRescuer {
        tokenContract.safeTransfer(to, amount);
    }

    /**
     * @notice Assign the rescuer role to a given address.
     * @param newRescuer New rescuer's address
     */
    function updateRescuer(address newRescuer) external onlyOwner {
        require(
            newRescuer != address(0),
            "Rescuable: new rescuer is the zero address"
        );
        _rescuer = newRescuer;
        emit RescuerChanged(newRescuer);
    }
}

// File: contracts/v1.1/FiatTokenV1_1.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title FiatTokenV1_1
 * @dev ERC20 Token backed by fiat reserves
 */
contract FiatTokenV1_1 is FiatTokenV1, Rescuable {

}

// File: contracts/v2/AbstractFiatTokenV2.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

abstract contract AbstractFiatTokenV2 is AbstractFiatTokenV1 {
    function _increaseAllowance(
        address owner,
        address spender,
        uint256 increment
    ) internal virtual;

    function _decreaseAllowance(
        address owner,
        address spender,
        uint256 decrement
    ) internal virtual;
}

// File: contracts/util/ECRecover.sol

/**
 * Copyright (c) 2016-2019 zOS Global Limited
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title ECRecover
 * @notice A library that provides a safe ECDSA recovery function
 */
library ECRecover {
    /**
     * @notice Recover signer's address from a signed message
     * @dev Adapted from: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/65e4ffde586ec89af3b7e9140bdc9235d1254853/contracts/cryptography/ECDSA.sol
     * Modifications: Accept v, r, and s as separate arguments
     * @param digest    Keccak-256 hash digest of the signed message
     * @param v         v of the signature
     * @param r         r of the signature
     * @param s         s of the signature
     * @return Signer address
     */
    function recover(
        bytes32 digest,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address) {
        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
        // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
        //
        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
        // these malleable signatures as well.
        if (
            uint256(s) >
            0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0
        ) {
            revert("ECRecover: invalid signature 's' value");
        }

        if (v != 27 && v != 28) {
            revert("ECRecover: invalid signature 'v' value");
        }

        // If the signature is valid (and not malleable), return the signer address
        address signer = ecrecover(digest, v, r, s);
        require(signer != address(0), "ECRecover: invalid signature");

        return signer;
    }
}

// File: contracts/util/EIP712.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title EIP712
 * @notice A library that provides EIP712 helper functions
 */
library EIP712 {
    /**
     * @notice Make EIP712 domain separator
     * @param name      Contract name
     * @param version   Contract version
     * @return Domain separator
     */
    function makeDomainSeparator(string memory name, string memory version)
        internal
        view
        returns (bytes32)
    {
        uint256 chainId;
        assembly {
            chainId := chainid()
        }
        return
            keccak256(
                abi.encode(
                    // keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)")
                    0x8b73c3c69bb8fe3d512ecc4cf759cc79239f7b179b0ffacaa9a75d522b39400f,
                    keccak256(bytes(name)),
                    keccak256(bytes(version)),
                    chainId,
                    address(this)
                )
            );
    }

    /**
     * @notice Recover signer's address from a EIP712 signature
     * @param domainSeparator   Domain separator
     * @param v                 v of the signature
     * @param r                 r of the signature
     * @param s                 s of the signature
     * @param typeHashAndData   Type hash concatenated with data
     * @return Signer's address
     */
    function recover(
        bytes32 domainSeparator,
        uint8 v,
        bytes32 r,
        bytes32 s,
        bytes memory typeHashAndData
    ) internal pure returns (address) {
        bytes32 digest = keccak256(
            abi.encodePacked(
                "\x19\x01",
                domainSeparator,
                keccak256(typeHashAndData)
            )
        );
        return ECRecover.recover(digest, v, r, s);
    }
}

// File: contracts/v2/EIP712Domain.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title EIP712 Domain
 */
contract EIP712Domain {
    /**
     * @dev EIP712 Domain Separator
     */
    bytes32 public DOMAIN_SEPARATOR;
}

// File: contracts/v2/EIP3009.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title EIP-3009
 * @notice Provide internal implementation for gas-abstracted transfers
 * @dev Contracts that inherit from this must wrap these with publicly
 * accessible functions, optionally adding modifiers where necessary
 */
abstract contract EIP3009 is AbstractFiatTokenV2, EIP712Domain {
    // keccak256("TransferWithAuthorization(address from,address to,uint256 value,uint256 validAfter,uint256 validBefore,bytes32 nonce)")
    bytes32
        public constant TRANSFER_WITH_AUTHORIZATION_TYPEHASH = 0x7c7c6cdb67a18743f49ec6fa9b35f50d52ed05cbed4cc592e13b44501c1a2267;

    // keccak256("ReceiveWithAuthorization(address from,address to,uint256 value,uint256 validAfter,uint256 validBefore,bytes32 nonce)")
    bytes32
        public constant RECEIVE_WITH_AUTHORIZATION_TYPEHASH = 0xd099cc98ef71107a616c4f0f941f04c322d8e254fe26b3c6668db87aae413de8;

    // keccak256("CancelAuthorization(address authorizer,bytes32 nonce)")
    bytes32
        public constant CANCEL_AUTHORIZATION_TYPEHASH = 0x158b0a9edf7a828aad02f63cd515c68ef2f50ba807396f6d12842833a1597429;

    /**
     * @dev authorizer address => nonce => bool (true if nonce is used)
     */
    mapping(address => mapping(bytes32 => bool)) private _authorizationStates;

    event AuthorizationUsed(address indexed authorizer, bytes32 indexed nonce);
    event AuthorizationCanceled(
        address indexed authorizer,
        bytes32 indexed nonce
    );

    /**
     * @notice Returns the state of an authorization
     * @dev Nonces are randomly generated 32-byte data unique to the
     * authorizer's address
     * @param authorizer    Authorizer's address
     * @param nonce         Nonce of the authorization
     * @return True if the nonce is used
     */
    function authorizationState(address authorizer, bytes32 nonce)
        external
        view
        returns (bool)
    {
        return _authorizationStates[authorizer][nonce];
    }

    /**
     * @notice Execute a transfer with a signed authorization
     * @param from          Payer's address (Authorizer)
     * @param to            Payee's address
     * @param value         Amount to be transferred
     * @param validAfter    The time after which this is valid (unix time)
     * @param validBefore   The time before which this is valid (unix time)
     * @param nonce         Unique nonce
     * @param v             v of the signature
     * @param r             r of the signature
     * @param s             s of the signature
     */
    function _transferWithAuthorization(
        address from,
        address to,
        uint256 value,
        uint256 validAfter,
        uint256 validBefore,
        bytes32 nonce,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        _requireValidAuthorization(from, nonce, validAfter, validBefore);

        bytes memory data = abi.encode(
            TRANSFER_WITH_AUTHORIZATION_TYPEHASH,
            from,
            to,
            value,
            validAfter,
            validBefore,
            nonce
        );
        require(
            EIP712.recover(DOMAIN_SEPARATOR, v, r, s, data) == from,
            "FiatTokenV2: invalid signature"
        );

        _markAuthorizationAsUsed(from, nonce);
        _transfer(from, to, value);
    }

    /**
     * @notice Receive a transfer with a signed authorization from the payer
     * @dev This has an additional check to ensure that the payee's address
     * matches the caller of this function to prevent front-running attacks.
     * @param from          Payer's address (Authorizer)
     * @param to            Payee's address
     * @param value         Amount to be transferred
     * @param validAfter    The time after which this is valid (unix time)
     * @param validBefore   The time before which this is valid (unix time)
     * @param nonce         Unique nonce
     * @param v             v of the signature
     * @param r             r of the signature
     * @param s             s of the signature
     */
    function _receiveWithAuthorization(
        address from,
        address to,
        uint256 value,
        uint256 validAfter,
        uint256 validBefore,
        bytes32 nonce,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        require(to == msg.sender, "FiatTokenV2: caller must be the payee");
        _requireValidAuthorization(from, nonce, validAfter, validBefore);

        bytes memory data = abi.encode(
            RECEIVE_WITH_AUTHORIZATION_TYPEHASH,
            from,
            to,
            value,
            validAfter,
            validBefore,
            nonce
        );
        require(
            EIP712.recover(DOMAIN_SEPARATOR, v, r, s, data) == from,
            "FiatTokenV2: invalid signature"
        );

        _markAuthorizationAsUsed(from, nonce);
        _transfer(from, to, value);
    }

    /**
     * @notice Attempt to cancel an authorization
     * @param authorizer    Authorizer's address
     * @param nonce         Nonce of the authorization
     * @param v             v of the signature
     * @param r             r of the signature
     * @param s             s of the signature
     */
    function _cancelAuthorization(
        address authorizer,
        bytes32 nonce,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        _requireUnusedAuthorization(authorizer, nonce);

        bytes memory data = abi.encode(
            CANCEL_AUTHORIZATION_TYPEHASH,
            authorizer,
            nonce
        );
        require(
            EIP712.recover(DOMAIN_SEPARATOR, v, r, s, data) == authorizer,
            "FiatTokenV2: invalid signature"
        );

        _authorizationStates[authorizer][nonce] = true;
        emit AuthorizationCanceled(authorizer, nonce);
    }

    /**
     * @notice Check that an authorization is unused
     * @param authorizer    Authorizer's address
     * @param nonce         Nonce of the authorization
     */
    function _requireUnusedAuthorization(address authorizer, bytes32 nonce)
        private
        view
    {
        require(
            !_authorizationStates[authorizer][nonce],
            "FiatTokenV2: authorization is used or canceled"
        );
    }

    /**
     * @notice Check that authorization is valid
     * @param authorizer    Authorizer's address
     * @param nonce         Nonce of the authorization
     * @param validAfter    The time after which this is valid (unix time)
     * @param validBefore   The time before which this is valid (unix time)
     */
    function _requireValidAuthorization(
        address authorizer,
        bytes32 nonce,
        uint256 validAfter,
        uint256 validBefore
    ) private view {
        require(
            now > validAfter,
            "FiatTokenV2: authorization is not yet valid"
        );
        require(now < validBefore, "FiatTokenV2: authorization is expired");
        _requireUnusedAuthorization(authorizer, nonce);
    }

    /**
     * @notice Mark an authorization as used
     * @param authorizer    Authorizer's address
     * @param nonce         Nonce of the authorization
     */
    function _markAuthorizationAsUsed(address authorizer, bytes32 nonce)
        private
    {
        _authorizationStates[authorizer][nonce] = true;
        emit AuthorizationUsed(authorizer, nonce);
    }
}

// File: contracts/v2/EIP2612.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title EIP-2612
 * @notice Provide internal implementation for gas-abstracted approvals
 */
abstract contract EIP2612 is AbstractFiatTokenV2, EIP712Domain {
    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)")
    bytes32
        public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;

    mapping(address => uint256) private _permitNonces;

    /**
     * @notice Nonces for permit
     * @param owner Token owner's address (Authorizer)
     * @return Next nonce
     */
    function nonces(address owner) external view returns (uint256) {
        return _permitNonces[owner];
    }

    /**
     * @notice Verify a signed approval permit and execute if valid
     * @param owner     Token owner's address (Authorizer)
     * @param spender   Spender's address
     * @param value     Amount of allowance
     * @param deadline  The time at which this expires (unix time)
     * @param v         v of the signature
     * @param r         r of the signature
     * @param s         s of the signature
     */
    function _permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        require(deadline >= now, "FiatTokenV2: permit is expired");

        bytes memory data = abi.encode(
            PERMIT_TYPEHASH,
            owner,
            spender,
            value,
            _permitNonces[owner]++,
            deadline
        );
        require(
            EIP712.recover(DOMAIN_SEPARATOR, v, r, s, data) == owner,
            "EIP2612: invalid signature"
        );

        _approve(owner, spender, value);
    }
}

// File: contracts/v2/FiatTokenV2.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

/**
 * @title FiatToken V2
 * @notice ERC20 Token backed by fiat reserves, version 2
 */
contract FiatTokenV2 is FiatTokenV1_1, EIP3009, EIP2612 {
    uint8 internal _initializedVersion;

    /**
     * @notice Initialize v2
     * @param newName   New token name
     */
    function initializeV2(string calldata newName) external {
        // solhint-disable-next-line reason-string
        require(initialized && _initializedVersion == 0);
        name = newName;
        DOMAIN_SEPARATOR = EIP712.makeDomainSeparator(newName, "2");
        _initializedVersion = 1;
    }

    /**
     * @notice Increase the allowance by a given increment
     * @param spender   Spender's address
     * @param increment Amount of increase in allowance
     * @return True if successful
     */
    function increaseAllowance(address spender, uint256 increment)
        external
        whenNotPaused
        notBlacklisted(msg.sender)
        notBlacklisted(spender)
        returns (bool)
    {
        _increaseAllowance(msg.sender, spender, increment);
        return true;
    }

    /**
     * @notice Decrease the allowance by a given decrement
     * @param spender   Spender's address
     * @param decrement Amount of decrease in allowance
     * @return True if successful
     */
    function decreaseAllowance(address spender, uint256 decrement)
        external
        whenNotPaused
        notBlacklisted(msg.sender)
        notBlacklisted(spender)
        returns (bool)
    {
        _decreaseAllowance(msg.sender, spender, decrement);
        return true;
    }

    /**
     * @notice Execute a transfer with a signed authorization
     * @param from          Payer's address (Authorizer)
     * @param to            Payee's address
     * @param value         Amount to be transferred
     * @param validAfter    The time after which this is valid (unix time)
     * @param validBefore   The time before which this is valid (unix time)
     * @param nonce         Unique nonce
     * @param v             v of the signature
     * @param r             r of the signature
     * @param s             s of the signature
     */
    function transferWithAuthorization(
        address from,
        address to,
        uint256 value,
        uint256 validAfter,
        uint256 validBefore,
        bytes32 nonce,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external whenNotPaused notBlacklisted(from) notBlacklisted(to) {
        _transferWithAuthorization(
            from,
            to,
            value,
            validAfter,
            validBefore,
            nonce,
            v,
            r,
            s
        );
    }

    /**
     * @notice Receive a transfer with a signed authorization from the payer
     * @dev This has an additional check to ensure that the payee's address
     * matches the caller of this function to prevent front-running attacks.
     * @param from          Payer's address (Authorizer)
     * @param to            Payee's address
     * @param value         Amount to be transferred
     * @param validAfter    The time after which this is valid (unix time)
     * @param validBefore   The time before which this is valid (unix time)
     * @param nonce         Unique nonce
     * @param v             v of the signature
     * @param r             r of the signature
     * @param s             s of the signature
     */
    function receiveWithAuthorization(
        address from,
        address to,
        uint256 value,
        uint256 validAfter,
        uint256 validBefore,
        bytes32 nonce,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external whenNotPaused notBlacklisted(from) notBlacklisted(to) {
        _receiveWithAuthorization(
            from,
            to,
            value,
            validAfter,
            validBefore,
            nonce,
            v,
            r,
            s
        );
    }

    /**
     * @notice Attempt to cancel an authorization
     * @dev Works only if the authorization is not yet used.
     * @param authorizer    Authorizer's address
     * @param nonce         Nonce of the authorization
     * @param v             v of the signature
     * @param r             r of the signature
     * @param s             s of the signature
     */
    function cancelAuthorization(
        address authorizer,
        bytes32 nonce,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external whenNotPaused {
        _cancelAuthorization(authorizer, nonce, v, r, s);
    }

    /**
     * @notice Update allowance with a signed permit
     * @param owner       Token owner's address (Authorizer)
     * @param spender     Spender's address
     * @param value       Amount of allowance
     * @param deadline    Expiration time, seconds since the epoch
     * @param v           v of the signature
     * @param r           r of the signature
     * @param s           s of the signature
     */
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external whenNotPaused notBlacklisted(owner) notBlacklisted(spender) {
        _permit(owner, spender, value, deadline, v, r, s);
    }

    /**
     * @notice Internal function to increase the allowance by a given increment
     * @param owner     Token owner's address
     * @param spender   Spender's address
     * @param increment Amount of increase
     */
    function _increaseAllowance(
        address owner,
        address spender,
        uint256 increment
    ) internal override {
        _approve(owner, spender, allowed[owner][spender].add(increment));
    }

    /**
     * @notice Internal function to decrease the allowance by a given decrement
     * @param owner     Token owner's address
     * @param spender   Spender's address
     * @param decrement Amount of decrease
     */
    function _decreaseAllowance(
        address owner,
        address spender,
        uint256 decrement
    ) internal override {
        _approve(
            owner,
            spender,
            allowed[owner][spender].sub(
                decrement,
                "ERC20: decreased allowance below zero"
            )
        );
    }
}

// File: contracts/v2/FiatTokenV2_1.sol

/**
 * Copyright (c) 2018-2020 CENTRE SECZ
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

pragma solidity 0.6.12;

// solhint-disable func-name-mixedcase

/**
 * @title FiatToken V2.1
 * @notice ERC20 Token backed by fiat reserves, version 2.1
 */
contract FiatTokenV2_1 is FiatTokenV2 {
    /**
     * @notice Initialize v2.1
     * @param lostAndFound  The address to which the locked funds are sent
     */
    function initializeV2_1(address lostAndFound) external {
        // solhint-disable-next-line reason-string
        require(_initializedVersion == 1);

        uint256 lockedAmount = balances[address(this)];
        if (lockedAmount > 0) {
            _transfer(address(this), lostAndFound, lockedAmount);
        }
        blacklisted[address(this)] = true;

        _initializedVersion = 2;
    }

    /**
     * @notice Version string for the EIP712 domain separator
     * @return Version string
     */
    function version() external view returns (string memory) {
        return "2";
    }
}