// Sources flattened with hardhat v2.1.2 https://hardhat.org

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


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);
}


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


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;
    }
}


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


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);
            }
        }
    }
}


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


pragma solidity >=0.6.0 <0.8.0;



/**
 * @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 @openzeppelin/contracts-upgradeable/utils/AddressUpgradeable.sol


pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library AddressUpgradeable {
    /**
     * @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);
    }

    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);
            }
        }
    }
}


// File @openzeppelin/contracts-upgradeable/proxy/Initializable.sol


// solhint-disable-next-line compiler-version
pragma solidity >=0.4.24 <0.8.0;

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract contract Initializable {

    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private _initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;

    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || _isConstructor() || !_initialized, "Initializable: contract is already initialized");

        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }

        _;

        if (isTopLevelCall) {
            _initializing = false;
        }
    }

    /// @dev Returns true if and only if the function is running in the constructor
    function _isConstructor() private view returns (bool) {
        return !AddressUpgradeable.isContract(address(this));
    }
}


// File @openzeppelin/contracts-upgradeable/utils/ContextUpgradeable.sol


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 ContextUpgradeable is Initializable {
    function __Context_init() internal initializer {
        __Context_init_unchained();
    }

    function __Context_init_unchained() internal initializer {
    }
    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;
    }
    uint256[50] private __gap;
}


// File @openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol


pragma solidity >=0.6.0 <0.8.0;


/**
 * @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 OwnableUpgradeable is Initializable, ContextUpgradeable {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    function __Ownable_init() internal initializer {
        __Context_init_unchained();
        __Ownable_init_unchained();
    }

    function __Ownable_init_unchained() internal initializer {
        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;
    }
    uint256[49] private __gap;
}


// File @openzeppelin/contracts-upgradeable/utils/ReentrancyGuardUpgradeable.sol


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 ReentrancyGuardUpgradeable is Initializable {
    // 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;

    function __ReentrancyGuard_init() internal initializer {
        __ReentrancyGuard_init_unchained();
    }

    function __ReentrancyGuard_init_unchained() internal initializer {
        _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;
    }
    uint256[49] private __gap;
}


// File contracts/TokensFarm.sol

pragma solidity 0.6.12;





contract TokensFarm is OwnableUpgradeable, ReentrancyGuardUpgradeable {

    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    // Enums
    enum EarlyWithdrawPenalty {
        NO_PENALTY,
        BURN_REWARDS,
        REDISTRIBUTE_REWARDS
    }

    // Info of each user.
    struct StakeInfo {
        // How many tokens the user has provided.
        uint256 amount;
        // Reward debt.
        uint256 rewardDebt;
        // Time when user deposited.
        uint256 depositTime;
        // Time when user withdraw
        uint256 withdrawTime;
        // Address of user
        address addressOfUser;
    }

    // Address of ERC20 token contract.
    IERC20 public tokenStaked;
    // Last time number that ERC20s distribution occurs.
    uint256 public lastRewardTime;
    // Accumulated ERC20s per share, times 1e18.
    uint256 public accERC20PerShare;
    // Total tokens deposited in the farm.
    uint256 public totalDeposits;
    // If contractor allows early withdraw on stakes
    bool public isEarlyWithdrawAllowed;
    // Minimal period of time to stake
    uint256 public minTimeToStake;
    // Address of the ERC20 Token contract.
    IERC20 public erc20;
    // The total amount of ERC20 that's paid out as reward.
    uint256 public paidOut;
    // ERC20 tokens rewarded per second.
    uint256 public rewardPerSecond;
    // Total rewards added to farm
    uint256 public totalRewards;
    // Info of each user that stakes ERC20 tokens.
    mapping(address => StakeInfo[]) public stakeInfo;
    // The time when farming starts.
    uint256 public startTime;
    // The time when farming ends.
    uint256 public endTime;
    // Early withdraw penalty
    EarlyWithdrawPenalty public penalty;
    // Stake fee percent
    uint256 public stakeFeePercent;
    // Reward fee percent
    uint256 public rewardFeePercent;
    // Fee collector address
    address payable public feeCollector;
    // Flat fee amount
    uint256 public flatFeeAmount;
    // Fee option
    bool public isFlatFeeAllowed;
    // Total tokens burned
    uint256 public totalTokensBurned;
    // Total fee collected
    uint256 public totalFeeCollectedETH;
    // Total fee collected in tokens
    uint256 public totalFeeCollectedTokens;
    // Address of farm instance
    address public farmImplementation;
    // NumberOfUsers participating in farm
    uint256 public noOfUsers;
    // Addresses of all users that are currently participating
    address[] public participants;
    // Mapping of every users spot in array
    mapping(address => uint256) public id;

    // Events
    event Deposit(
        address indexed user,
        uint256 indexed stakeId,
        uint256 indexed amount
    );
    event Withdraw(
        address indexed user,
        uint256 indexed stakeId,
        uint256 indexed amount
    );
    event EmergencyWithdraw(
        address indexed user,
        uint256 indexed stakeId,
        uint256 indexed amount
    );
    event EarlyWithdrawPenaltySet(EarlyWithdrawPenalty indexed penalty);
    event MinTimeToStakeSet(uint256 indexed minTimeToStake);
    event IsEarlyWithdrawAllowedSet(bool indexed allowed);
    event StakeFeePercentSet(uint256 indexed stakeFeePercent);
    event RewardFeePercentSet(uint256 indexed rewardFeePercent);
    event FlatFeeAmountSet(uint256 indexed flatFeeAmount);
    event IsFlatFeeAllowedSet(bool indexed allowed);
    event FeeCollectorSet(address payable indexed feeCollector);

    // Modifiers
    modifier validateStakeByStakeId(address _user, uint256 stakeId) {
        require(stakeId < stakeInfo[_user].length, "Stake does not exist");
        _;
    }

    /**
     * @notice function sets initial state of contract
     *
     * @param _erc20 - address of reward token
     * @param _rewardPerSecond - number of reward per second
     * @param _startTime - beginning of farm
     * @param _minTimeToStake - how much time needs to pass before staking
     * @param _isEarlyWithdrawAllowed - is early withdraw allowed or not
     * @param _penalty - ENUM(what type of penalty)
     * @param _tokenStaked - address of token which is staked
     * @param _stakeFeePercent - fee percent for staking
     * @param _rewardFeePercent - fee percent for reward distribution
     * @param _flatFeeAmount - flat fee amount
     * @param _isFlatFeeAllowed - is flat fee  allowed or not
     */
    function initialize(
        address _erc20,
        uint256 _rewardPerSecond,
        uint256 _startTime,
        uint256 _minTimeToStake,
        bool _isEarlyWithdrawAllowed,
        uint256 _penalty,
        address _tokenStaked,
        uint256 _stakeFeePercent,
        uint256 _rewardFeePercent,
        uint256 _flatFeeAmount,
        address payable _feeCollector,
        bool _isFlatFeeAllowed,
        address _farmImplementation
    )
        external
        initializer
    {
        // Upgrading ownership
        __Ownable_init();
        __ReentrancyGuard_init();

        // Requires for correct initialization
        require(_erc20 != address(0x0), "Wrong token address.");
        require(_rewardPerSecond > 0, "Rewards per second must be > 0.");
        require(
            _startTime >= block.timestamp,
            "Start time can not be in the past."
        );
        require(_stakeFeePercent < 100, "Stake fee must be < 100.");
        require(_rewardFeePercent < 100, "Reward fee must be < 100.");
        require(
            _feeCollector != address(0x0),
            "Wrong fee collector address."
        );

        // Initialization of contract
        erc20 = IERC20(_erc20);
        rewardPerSecond = _rewardPerSecond;
        startTime = _startTime;
        endTime = _startTime;
        minTimeToStake = _minTimeToStake;
        isEarlyWithdrawAllowed = _isEarlyWithdrawAllowed;
        stakeFeePercent = _stakeFeePercent;
        rewardFeePercent = _rewardFeePercent;
        flatFeeAmount = _flatFeeAmount;
        feeCollector = _feeCollector;
        isFlatFeeAllowed = _isFlatFeeAllowed;
        farmImplementation = _farmImplementation;

        _setEarlyWithdrawPenalty(_penalty);
        _addPool(IERC20(_tokenStaked));
    }

    // All Internal functions

    /**
     * @notice function is adding a new ERC20 token to the pool
     *
     * @param _tokenStaked - address of token staked
     */
    function _addPool(
        IERC20 _tokenStaked
    )
        internal
    {
        require(
            address(_tokenStaked) != address(0x0),
            "Must input valid address."
        );
        require(
            address(tokenStaked) == address(0x0),
            "Pool can be set only once."
        );

        uint256 _lastRewardTime = block.timestamp > startTime
        ? block.timestamp
        : startTime;

        tokenStaked = _tokenStaked;
        lastRewardTime = _lastRewardTime;
        accERC20PerShare = 0;
        totalDeposits = 0;
    }

    /**
     * @notice function is setting early withdrawal penalty, if applicable
     *
     * @param _penalty - number of penalty
     */
    function _setEarlyWithdrawPenalty(
        uint256 _penalty
    )
        internal
    {
        penalty = EarlyWithdrawPenalty(_penalty);
        emit EarlyWithdrawPenaltySet(penalty);
    }

    /**
     * @notice function is adding participant from farm
     *
     * @param user - address of user
     *
     * @return boolean - if adding is successful or not
     */
    function _addParticipant(
        address user
    )
        internal
        returns(bool)
    {
        if(stakeInfo[user].length > 0){
            return false;
        }

        id[user] = noOfUsers;
        noOfUsers++;
        participants.push(user);

        return true;
    }

    /**
     * @notice function is removing participant from farm
     *
     * @param user - address of user
     * @param amount - how many is user withdrawing
     *
     * @return boolean - if removal is successful or not
     */
    function _removeParticipant(
        address user,
        uint256 amount
    )
        internal
        returns(bool)
    {
        uint256 totalAmount;

        if(noOfUsers == 1){
            totalAmount = 0;
            for(uint256 i = 0; i < stakeInfo[user].length; i++){
                totalAmount += stakeInfo[user][i].amount;
            }

            if(amount == totalAmount){
                delete id[user];
                participants.pop();
                noOfUsers--;

                return true;
            }
        }
        else{
            totalAmount = 0;
            for(uint256 i = 0; i < stakeInfo[user].length; i++){
                totalAmount += stakeInfo[user][i].amount;
            }

            if(amount == totalAmount){
                uint256 deletedUserId = id[user];
                address lastUserInParticipantsArray = participants[participants.length - 1];
                participants[deletedUserId] = lastUserInParticipantsArray;
                id[lastUserInParticipantsArray] = deletedUserId;

                delete id[user];
                participants.pop();
                noOfUsers--;

                return true;
            }
        }

        return false;
    }

    // All setter's functions

    /**
     * @notice function is setting new minimum time to stake value
     *
     * @param _minTimeToStake - min time to stake
     */
    function setMinTimeToStake(
        uint256 _minTimeToStake
    )
        external
        onlyOwner
    {
        minTimeToStake = _minTimeToStake;
        emit MinTimeToStakeSet(minTimeToStake);
    }

    /**
     * @notice function is setting new state of early withdraw
     *
     * @param _isEarlyWithdrawAllowed - is early withdraw allowed or not
     */
    function setIsEarlyWithdrawAllowed(
        bool _isEarlyWithdrawAllowed
    )
        external
        onlyOwner
    {
        isEarlyWithdrawAllowed = _isEarlyWithdrawAllowed;
        emit IsEarlyWithdrawAllowedSet(isEarlyWithdrawAllowed);
    }

    /**
     * @notice function is setting new stake fee percent value
     *
     * @param _stakeFeePercent - stake fee percent
     */
    function setStakeFeePercent(
        uint256 _stakeFeePercent
    )
        external
        onlyOwner
    {
        stakeFeePercent = _stakeFeePercent;
        emit StakeFeePercentSet(stakeFeePercent);
    }

    /**
     * @notice function is setting new reward fee percent value
     *
     * @param _rewardFeePercent - reward fee percent
     */
    function setRewardFeePercent(
        uint256 _rewardFeePercent
    )
        external
        onlyOwner
    {
        rewardFeePercent = _rewardFeePercent;
        emit RewardFeePercentSet(rewardFeePercent);

    }

    /**
     * @notice function is setting new flat fee amount
     *
     * @param _flatFeeAmount - flat fee amount
     */
    function setFlatFeeAmount(
        uint256 _flatFeeAmount
    )
        external
        onlyOwner
    {
        flatFeeAmount = _flatFeeAmount;
        emit FlatFeeAmountSet(flatFeeAmount);
    }

    /**
     * @notice function is setting flat fee allowed
     *
     * @param _isFlatFeeAllowed - is flat fee allowed or not
     */
    function setIsFlatFeeAllowed(
        bool _isFlatFeeAllowed
    )
        external
        onlyOwner
    {
        isFlatFeeAllowed = _isFlatFeeAllowed;
        emit IsFlatFeeAllowedSet(isFlatFeeAllowed);
    }

    /**
     * @notice function is setting feeCollector on new address
     *
     * @param _feeCollector - address of newFeeCollector
     */
    function setFeeCollector(
        address payable _feeCollector
    )
        external
        onlyOwner
    {
        feeCollector = _feeCollector;
        emit FeeCollectorSet(feeCollector);
    }

    // All view functions

    /**
     * @notice function is getting number to see deposited ERC20 token for a user.
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return deposited ERC20 token for a user
     */
    function deposited(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory  stake = stakeInfo[_user][stakeId];
        return stake.amount;
    }

    /**
     * @notice function is getting number to see pending ERC20s for a user.
     *
     * @dev pending reward = (user.amount * pool.accERC20PerShare) - user.rewardDebt
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return pending ERC20s for a user.
     */
    function pending(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory stake = stakeInfo[_user][stakeId];

        if (stake.amount == 0) {
            return 0;
        }

        uint256 _accERC20PerShare = accERC20PerShare;
        uint256 tokenSupply = totalDeposits;

        if (block.timestamp > lastRewardTime && tokenSupply != 0) {
            uint256 lastTime = block.timestamp < endTime
            ? block.timestamp
            : endTime;
            uint256 timeToCompare = lastRewardTime < endTime
            ? lastRewardTime
            : endTime;
            uint256 nrOfSeconds = lastTime.sub(timeToCompare);
            uint256 erc20Reward = nrOfSeconds.mul(rewardPerSecond);
            _accERC20PerShare = _accERC20PerShare.add(
                erc20Reward.mul(1e18).div(tokenSupply)
            );
        }

        return
        stake.amount.mul(_accERC20PerShare).div(1e18).sub(stake.rewardDebt);
    }

    /**
     * @notice function is getting number to see deposit timestamp for a user.
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return time when user deposited specific stake
     */
    function depositTimestamp(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory stake = stakeInfo[_user][stakeId];
        return stake.depositTime;
    }

    /**
     * @notice function is getting number to see withdraw timestamp for a user.
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return time when user withdraw specific stake
     */
    function withdrawTimestamp(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory stake = stakeInfo[_user][stakeId];
        return stake.withdrawTime;
    }

    /**
     * @notice function is getting number for total rewards the farm has yet to pay out.
     *
     * @return how many total reward the farm has yet to pay out.
     */
    function totalPending()
        external
        view
        returns (uint256)
    {
        if (block.timestamp <= startTime) {
            return 0;
        }

        uint256 lastTime = block.timestamp < endTime
        ? block.timestamp
        : endTime;
        return rewardPerSecond.mul(lastTime - startTime).sub(paidOut);
    }

    /**
     * @notice function is getting number of stakes user has
     *
     * @param user - address of user
     *
     * @return how many times has user staked tokens
     */
    function getNumberOfUserStakes(
        address user
    )
        external
        view
        returns (uint256)
    {
        return stakeInfo[user].length;
    }

    /**
     * @notice function is getting user pending amounts, stakes and deposit time
     *
     * @param user - address of user
     *
     * @return array of deposits,pendingAmounts and depositTime
     */
    function getUserStakesAndPendingAmounts(
        address user
    )
        external
        view
        returns (
            uint256[] memory,
            uint256[] memory,
            uint256[] memory
        )
    {
        uint256 numberOfStakes = stakeInfo[user].length;

        uint256[] memory deposits = new uint256[](numberOfStakes);
        uint256[] memory pendingAmounts = new uint256[](numberOfStakes);
        uint256[] memory depositTime = new uint256[](numberOfStakes);

        for (uint256 i = 0; i < numberOfStakes; i++) {
            deposits[i] = deposited(user, i);
            pendingAmounts[i] = pending(user, i);
            depositTime[i] = depositTimestamp(user, i);
        }

        return (deposits, pendingAmounts, depositTime);
    }

    /**
     * @notice function is getting total rewards locked/unlocked
     *
     * @return totalRewardsUnlocked
     * @return totalRewardsLocked
     */
    function getTotalRewardsLockedUnlocked()
        external
        view
        returns (uint256, uint256)
    {
        uint256 totalRewardsLocked;
        uint256 totalRewardsUnlocked;

        if (block.timestamp <= startTime) {
            totalRewardsUnlocked = 0;
            totalRewardsLocked = totalRewards;
        } else {
            uint256 lastTime = block.timestamp < endTime
            ? block.timestamp
            : endTime;
            totalRewardsUnlocked = rewardPerSecond.mul(lastTime - startTime);
            totalRewardsLocked = totalRewards - totalRewardsUnlocked;
        }

        return (totalRewardsUnlocked, totalRewardsLocked);
    }

    // Money managing functions

    /**
     * @notice function is funding the farm, increase the end time
     *
     * @param _amount - how many tokens is funded
     */
    function fund(
        uint256 _amount
    )
        external
    {
        uint256 balanceBefore = erc20.balanceOf(address(this));
        erc20.safeTransferFrom(address(msg.sender), address(this), _amount);
        uint256 balanceAfter = erc20.balanceOf(address(this));

        uint256 fundAmount;
        if(balanceAfter.sub(balanceBefore) <= _amount){
            fundAmount = balanceAfter.sub(balanceBefore);
        }
        else{
            fundAmount = _amount;
        }

        _fundInternal(fundAmount);
    }

    /**
     * @notice function is internally funding the farm by adding farmed rewards by user to the end
     *
     * @param _amount - how many tokens is funded
     */
    function _fundInternal(
        uint256 _amount
    )
        internal
    {
        require(
            block.timestamp < endTime,
            "fund: too late, the farm is closed"
        );
        require(_amount > 0, "Amount must be greater than 0.");
        // Compute new end time
        endTime += _amount.div(rewardPerSecond);
        // Increase farm total rewards
        totalRewards = totalRewards.add(_amount);
    }

    /**
     * @notice function is updating reward variables of the given pool to be up-to-date.
     */
    function updatePool()
        public
    {
        uint256 lastTime = block.timestamp < endTime
        ? block.timestamp
        : endTime;

        if (lastTime <= lastRewardTime) {
            return;
        }

        uint256 tokenSupply = totalDeposits;

        if (tokenSupply == 0) {
            lastRewardTime = lastTime;
            return;
        }

        uint256 nrOfSeconds = lastTime.sub(lastRewardTime);
        uint256 erc20Reward = nrOfSeconds.mul(rewardPerSecond);

        accERC20PerShare = accERC20PerShare.add(
            erc20Reward.mul(1e18).div(tokenSupply)
        );
        lastRewardTime = block.timestamp;
    }

    /**
     * @notice function is depositing ERC20 tokens to Farm for ERC20 allocation.
     *
     * @param _amount - how many tokens user is depositing
     */
    function deposit(
        uint256 _amount
    )
        external
        nonReentrant
        payable
    {
        require(
            block.timestamp < endTime,
            "Deposit: too late, the farm is closed"
        );

        StakeInfo memory stake;
        uint256 stakedAmount;

        // Update pool
        updatePool();

        uint256 beforeBalance = tokenStaked.balanceOf(address(this));
        tokenStaked.safeTransferFrom(
            address(msg.sender),
            address(this),
            _amount
        );
        uint256 afterBalance = tokenStaked.balanceOf(address(this));

        if(afterBalance.sub(beforeBalance) <= _amount){
            stakedAmount = afterBalance.sub(beforeBalance);
        }
        else{
            stakedAmount = _amount;
        }

        if (isFlatFeeAllowed) {
            // Collect flat fee
            require(
                msg.value >= flatFeeAmount,
                "Payable amount is less than fee amount."
            );

            totalFeeCollectedETH = totalFeeCollectedETH.add(msg.value);
        } else if (stakeFeePercent > 0) {
            // Handle this case only if flat fee is not allowed, and stakeFeePercent > 0
            // Compute the fee
            uint256 feeAmount = stakedAmount.mul(stakeFeePercent).div(100);
            // Compute stake amount
            stakedAmount = stakedAmount.sub(feeAmount);
            totalFeeCollectedTokens = totalFeeCollectedTokens.add(feeAmount);
        }

        // Increase total deposits
        totalDeposits = totalDeposits.add(stakedAmount);
        // Update user accounting
        stake.amount = stakedAmount;
        stake.rewardDebt = stake.amount.mul(accERC20PerShare).div(1e18);
        stake.depositTime = block.timestamp;
        stake.addressOfUser = address(msg.sender);
        stake.withdrawTime = 0;

        _addParticipant(address(msg.sender));

        // Compute stake id
        uint256 stakeId = stakeInfo[msg.sender].length;
        // Push new stake to array of stakes for user
        stakeInfo[msg.sender].push(stake);
        // Emit deposit event
        emit Deposit(msg.sender, stakeId, stakedAmount);
    }

    // All withdraw functions

    /**
     * @notice function is withdrawing with caring about rewards
     *
     * @param _amount - how many tokens wants to be withdrawn
     * @param stakeId - Id of user stake
     */
    function withdraw(
        uint256 _amount,
        uint256 stakeId
    )
        external
        nonReentrant
        payable
        validateStakeByStakeId(msg.sender, stakeId)
    {
        bool minimalTimeStakeRespected;
        StakeInfo storage stake = stakeInfo[msg.sender][stakeId];

        require(
            stake.amount >= _amount,
            "withdraw: can't withdraw more than deposit"
        );

        updatePool();
        minimalTimeStakeRespected =
        stake.depositTime.add(minTimeToStake) <= block.timestamp;
        // if early withdraw is not allowed, user can't withdraw funds before
        if (!isEarlyWithdrawAllowed) {
            // Check if user has respected minimal time to stake, require it.
            require(
                minimalTimeStakeRespected,
                "User can not withdraw funds yet."
            );
        }

        // Compute pending rewards amount of user rewards
        uint256 pendingAmount = stake
        .amount
        .mul(accERC20PerShare)
        .div(1e18)
        .sub(stake.rewardDebt);

        // Penalties in case user didn't stake enough time
        if (pendingAmount > 0) {
            if (
                penalty == EarlyWithdrawPenalty.BURN_REWARDS &&
                !minimalTimeStakeRespected
            ) {
                // Burn to address (1)
                totalTokensBurned = totalTokensBurned.add(pendingAmount);
                _erc20Transfer(address(1), pendingAmount);
            } else if (
                penalty == EarlyWithdrawPenalty.REDISTRIBUTE_REWARDS &&
                !minimalTimeStakeRespected
            ) {
                if (block.timestamp >= endTime) {
                    // Burn rewards because farm can not be funded anymore since it ended
                    _erc20Transfer(address(1), pendingAmount);
                    totalTokensBurned = totalTokensBurned.add(pendingAmount);
                } else {
                    // Re-fund the farm
                    _fundInternal(pendingAmount);
                }
            } else {
                // In case either there's no penalty
                _erc20Transfer(msg.sender, pendingAmount);
            }
        }

        _removeParticipant(address(msg.sender), _amount);

        stake.withdrawTime = block.timestamp;
        stake.amount = stake.amount.sub(_amount);
        stake.rewardDebt = stake.amount.mul(accERC20PerShare).div(1e18);

        tokenStaked.safeTransfer(address(msg.sender), _amount);
        totalDeposits = totalDeposits.sub(_amount);

        // Emit Withdraw event
        emit Withdraw(msg.sender, stakeId, _amount);
    }

    /**
     * @notice function is withdrawing without caring about rewards. EMERGENCY ONLY.
     *
     * @param stakeId - Id of user stake
     */
    function emergencyWithdraw(
        uint256 stakeId
    )
        external
        nonReentrant
        validateStakeByStakeId(msg.sender, stakeId)
    {
        StakeInfo storage stake = stakeInfo[msg.sender][stakeId];

        // if early withdraw is not allowed, user can't withdraw funds before
        if (!isEarlyWithdrawAllowed) {
            bool minimalTimeStakeRespected = stake.depositTime.add(
                minTimeToStake
            ) <= block.timestamp;
            // Check if user has respected minimal time to stake, require it.
            require(
                minimalTimeStakeRespected,
                "User can not withdraw funds yet."
            );
        }

        tokenStaked.safeTransfer(address(msg.sender), stake.amount);
        totalDeposits = totalDeposits.sub(stake.amount);

        _removeParticipant(address(msg.sender), stake.amount);
        stake.withdrawTime = block.timestamp;

        emit EmergencyWithdraw(msg.sender, stakeId, stake.amount);

        stake.amount = 0;
        stake.rewardDebt = 0;
    }

    /**
     * @notice function is withdrawing fee collected in ERC value
     */
    function withdrawCollectedFeesERC()
        external
        onlyOwner
    {
        erc20.transfer(feeCollector, totalFeeCollectedTokens);
        totalFeeCollectedTokens = 0;
    }

    /**
     * @notice function is withdrawing fee collected in ETH value
     */
    function withdrawCollectedFeesETH()
        external
        onlyOwner
    {
        (bool sent, ) = payable(feeCollector).call{value: totalFeeCollectedETH}("");
        require(sent, "Failed to end flat fee");
        totalFeeCollectedETH = 0;
    }

    /**
     * @notice function is withdrawing tokens if stuck
     *
     * @param _erc20 - address of token address
     * @param _amount - number of how many tokens
     * @param _beneficiary - address of user that collects tokens deposited by mistake
     */
    function withdrawTokensIfStuck(
        address _erc20,
        uint256 _amount,
        address _beneficiary
    )
        external
        onlyOwner
    {
        IERC20 token = IERC20(_erc20);
        require(tokenStaked != token, "User tokens can not be pulled");
        require(
            _beneficiary != address(0x0),
            "_beneficiary can not be 0x0 address"
        );

        token.safeTransfer(_beneficiary, _amount);
    }

    /**
     * @notice function is transferring ERC20,
     * and update the required ERC20 to payout all rewards
     *
     * @param _to - transfer on this address
     * @param _amount - number of how many tokens
     */
    function _erc20Transfer(
        address _to,
        uint256 _amount
    )
        internal
    {
        if (isFlatFeeAllowed) {
            // Collect flat fee
            require(
                msg.value >= flatFeeAmount,
                "Payable amount is less than fee amount."
            );
            // Increase amount of fees collected
            totalFeeCollectedETH = totalFeeCollectedETH.add(msg.value);
            // send reward
            erc20.transfer(_to, _amount);
            paidOut += _amount;
        } else if (stakeFeePercent > 0) {
            // Collect reward fee
            uint256 feeAmount = _amount.mul(rewardFeePercent).div(100);
            uint256 rewardAmount = _amount.sub(feeAmount);

            // Increase amount of fees collected
            totalFeeCollectedTokens = totalFeeCollectedTokens.add(feeAmount);

            // send reward
            erc20.transfer(_to, rewardAmount);
            paidOut += _amount;
        } else {
            erc20.transfer(_to, _amount);
            paidOut += _amount;
        }
    }
}

// SPDX-License-Identifier: MIT
// File contracts/proxy/Proxy.sol
pragma solidity ^0.8.0;
/**
 * @dev This abstract contract provides a fallback function that delegates all calls to another contract using the EVM
 * instruction `delegatecall`. We refer to the second contract as the _implementation_ behind the proxy, and it has to
 * be specified by overriding the virtual {_implementation} function.
 *
 * Additionally, delegation to the implementation can be triggered manually through the {_fallback} function, or to a
 * different contract through the {_delegate} function.
 *
 * The success and return data of the delegated call will be returned back to the caller of the proxy.
 */
abstract contract Proxy {
    /**
     * @dev Delegates the current call to `implementation`.
     *
     * This function does not return to its internall call site, it will return directly to the external caller.
     */
    function _delegate(address implementation) internal virtual {
        // solhint-disable-next-line no-inline-assembly
        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 This is a virtual function that should be overriden so it returns the address to which the fallback function
     * and {_fallback} should delegate.
     */
    function _implementation() internal view virtual returns (address);
    /**
     * @dev Delegates the current call to the address returned by `_implementation()`.
     *
     * This function does not return to its internall call site, it will return directly to the external caller.
     */
    function _fallback() internal virtual {
        _beforeFallback();
        _delegate(_implementation());
    }
    /**
     * @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if no other
     * function in the contract matches the call data.
     */
    fallback() external payable {
        _fallback();
    }
    /**
     * @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if call data
     * is empty.
     */
    receive() external payable {
        _fallback();
    }
    /**
     * @dev Hook that is called before falling back to the implementation. Can happen as part of a manual `_fallback`
     * call, or as part of the Solidity `fallback` or `receive` functions.
     *
     * If overriden should call `super._beforeFallback()`.
     */
    function _beforeFallback() internal virtual {}
}
// File contracts/utils/Address.sol
/**
 * @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);
            }
        }
    }
}
// File contracts/proxy/ERC1967/ERC1967Proxy.sol
/**
 * @dev This contract implements an upgradeable proxy. It is upgradeable because calls are delegated to an
 * implementation address that can be changed. This address is stored in storage in the location specified by
 * https://eips.ethereum.org/EIPS/eip-1967[EIP1967], so that it doesn't conflict with the storage layout of the
 * implementation behind the proxy.
 *
 * Upgradeability is only provided internally through {_upgradeTo}. For an externally upgradeable proxy see
 * {TransparentUpgradeableProxy}.
 */
contract ERC1967Proxy is Proxy {
    /**
     * @dev Initializes the upgradeable proxy with an initial implementation specified by `_logic`.
     *
     * If `_data` is nonempty, it's used as data in a delegate call to `_logic`. This will typically be an encoded
     * function call, and allows initializating the storage of the proxy like a Solidity constructor.
     */
    constructor(address _logic, bytes memory _data) payable {
        assert(
            _IMPLEMENTATION_SLOT ==
                bytes32(uint256(keccak256("eip1967.proxy.implementation")) - 1)
        );
        _setImplementation(_logic);
        if (_data.length > 0) {
            Address.functionDelegateCall(_logic, _data);
        }
    }
    /**
     * @dev Emitted when the implementation is upgraded.
     */
    event Upgraded(address indexed implementation);
    /**
     * @dev Storage slot with the address of the current implementation.
     * This is the keccak-256 hash of "eip1967.proxy.implementation" subtracted by 1, and is
     * validated in the constructor.
     */
    bytes32 private constant _IMPLEMENTATION_SLOT =
        0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;
    /**
     * @dev Returns the current implementation address.
     */
    function _implementation()
        internal
        view
        virtual
        override
        returns (address impl)
    {
        bytes32 slot = _IMPLEMENTATION_SLOT;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            impl := sload(slot)
        }
    }
    /**
     * @dev Upgrades the proxy to a new implementation.
     *
     * Emits an {Upgraded} event.
     */
    function _upgradeTo(address newImplementation) internal virtual {
        _setImplementation(newImplementation);
        emit Upgraded(newImplementation);
    }
    /**
     * @dev Stores a new address in the EIP1967 implementation slot.
     */
    function _setImplementation(address newImplementation) private {
        require(
            Address.isContract(newImplementation),
            "ERC1967Proxy: new implementation is not a contract"
        );
        bytes32 slot = _IMPLEMENTATION_SLOT;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(slot, newImplementation)
        }
    }
}
// File contracts/proxy/transparent/TransparentUpgradeableProxy.sol
/**
 * @dev This contract implements a proxy that is upgradeable by an admin.
 *
 * To avoid https://medium.com/nomic-labs-blog/malicious-backdoors-in-ethereum-proxies-62629adf3357[proxy selector
 * clashing], which can potentially be used in an attack, this contract uses the
 * https://blog.openzeppelin.com/the-transparent-proxy-pattern/[transparent proxy pattern]. This pattern implies two
 * things that go hand in hand:
 *
 * 1. If any account other than the admin calls the proxy, the call will be forwarded to the implementation, even if
 * that call matches one of the admin functions exposed by the proxy itself.
 * 2. If the admin calls the proxy, it can access the admin functions, but its calls will never be forwarded to the
 * implementation. If the admin tries to call a function on the implementation it will fail with an error that says
 * "admin cannot fallback to proxy target".
 *
 * These properties mean that the admin account can only be used for admin actions like upgrading the proxy or changing
 * the admin, so it's best if it's a dedicated account that is not used for anything else. This will avoid headaches due
 * to sudden errors when trying to call a function from the proxy implementation.
 *
 * Our recommendation is for the dedicated account to be an instance of the {ProxyAdmin} contract. If set up this way,
 * you should think of the `ProxyAdmin` instance as the real administrative interface of your proxy.
 */
contract TransparentUpgradeableProxy is ERC1967Proxy {
    /**
     * @dev Initializes an upgradeable proxy managed by `_admin`, backed by the implementation at `_logic`, and
     * optionally initialized with `_data` as explained in {UpgradeableProxy-constructor}.
     */
    constructor(
        address _logic,
        address admin_,
        bytes memory _data
    ) payable ERC1967Proxy(_logic, _data) {
        assert(
            _ADMIN_SLOT ==
                bytes32(uint256(keccak256("eip1967.proxy.admin")) - 1)
        );
        _setAdmin(admin_);
    }
    /**
     * @dev Emitted when the admin account has changed.
     */
    event AdminChanged(address previousAdmin, address newAdmin);
    /**
     * @dev Storage slot with the admin of the contract.
     * This is the keccak-256 hash of "eip1967.proxy.admin" subtracted by 1, and is
     * validated in the constructor.
     */
    bytes32 private constant _ADMIN_SLOT =
        0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103;
    /**
     * @dev Modifier used internally that will delegate the call to the implementation unless the sender is the admin.
     */
    modifier ifAdmin() {
        if (msg.sender == _admin()) {
            _;
        } else {
            _fallback();
        }
    }
    /**
     * @dev Returns the current admin.
     *
     * NOTE: Only the admin can call this function. See {ProxyAdmin-getProxyAdmin}.
     *
     * TIP: To get this value clients can read directly from the storage slot shown below (specified by EIP1967) using the
     * https://eth.wiki/json-rpc/API#eth_getstorageat[`eth_getStorageAt`] RPC call.
     * `0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103`
     */
    function admin() external ifAdmin returns (address admin_) {
        admin_ = _admin();
    }
    /**
     * @dev Returns the current implementation.
     *
     * NOTE: Only the admin can call this function. See {ProxyAdmin-getProxyImplementation}.
     *
     * TIP: To get this value clients can read directly from the storage slot shown below (specified by EIP1967) using the
     * https://eth.wiki/json-rpc/API#eth_getstorageat[`eth_getStorageAt`] RPC call.
     * `0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc`
     */
    function implementation()
        external
        ifAdmin
        returns (address implementation_)
    {
        implementation_ = _implementation();
    }
    /**
     * @dev Changes the admin of the proxy.
     *
     * Emits an {AdminChanged} event.
     *
     * NOTE: Only the admin can call this function. See {ProxyAdmin-changeProxyAdmin}.
     */
    function changeAdmin(address newAdmin) external virtual ifAdmin {
        require(
            newAdmin != address(0),
            "TransparentUpgradeableProxy: new admin is the zero address"
        );
        emit AdminChanged(_admin(), newAdmin);
        _setAdmin(newAdmin);
    }
    /**
     * @dev Upgrade the implementation of the proxy.
     *
     * NOTE: Only the admin can call this function. See {ProxyAdmin-upgrade}.
     */
    function upgradeTo(address newImplementation) external virtual ifAdmin {
        _upgradeTo(newImplementation);
    }
    /**
     * @dev Upgrade the implementation of the proxy, and then call a function from the new implementation as specified
     * by `data`, which should be an encoded function call. This is useful to initialize new storage variables in the
     * proxied contract.
     *
     * NOTE: Only the admin can call this function. See {ProxyAdmin-upgradeAndCall}.
     */
    function upgradeToAndCall(address newImplementation, bytes calldata data)
        external
        payable
        virtual
        ifAdmin
    {
        _upgradeTo(newImplementation);
        Address.functionDelegateCall(newImplementation, data);
    }
    /**
     * @dev Returns the current admin.
     */
    function _admin() internal view virtual returns (address adm) {
        bytes32 slot = _ADMIN_SLOT;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            adm := sload(slot)
        }
    }
    /**
     * @dev Stores a new address in the EIP1967 admin slot.
     */
    function _setAdmin(address newAdmin) private {
        bytes32 slot = _ADMIN_SLOT;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(slot, newAdmin)
        }
    }
    /**
     * @dev Makes sure the admin cannot access the fallback function. See {Proxy-_beforeFallback}.
     */
    function _beforeFallback() internal virtual override {
        require(
            msg.sender != _admin(),
            "TransparentUpgradeableProxy: admin cannot fallback to proxy target"
        );
        super._beforeFallback();
    }
}

// File: contracts/interfaces/IUniswapV2Pair.sol

pragma solidity >=0.5.0;

interface IUniswapV2Pair {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external pure returns (string memory);
    function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;

    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint);
    function factory() external view returns (address);
    function token0() external view returns (address);
    function token1() external view returns (address);
    function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
    function price0CumulativeLast() external view returns (uint);
    function price1CumulativeLast() external view returns (uint);
    function kLast() external view returns (uint);

    function mint(address to) external returns (uint liquidity);
    function burn(address to) external returns (uint amount0, uint amount1);
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;
    function skim(address to) external;
    function sync() external;

    function initialize(address, address) external;
}

// File: contracts/interfaces/IUniswapV2ERC20.sol

pragma solidity >=0.5.0;

interface IUniswapV2ERC20 {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external pure returns (string memory);
    function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;
}

// File: contracts/libraries/SafeMath.sol

pragma solidity =0.5.16;

// a library for performing overflow-safe math, courtesy of DappHub (https://github.com/dapphub/ds-math)

library SafeMath {
    function add(uint x, uint y) internal pure returns (uint z) {
        require((z = x + y) >= x, 'ds-math-add-overflow');
    }

    function sub(uint x, uint y) internal pure returns (uint z) {
        require((z = x - y) <= x, 'ds-math-sub-underflow');
    }

    function mul(uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x, 'ds-math-mul-overflow');
    }
}

// File: contracts/UniswapV2ERC20.sol

pragma solidity =0.5.16;



contract UniswapV2ERC20 is IUniswapV2ERC20 {
    using SafeMath for uint;

    string public constant name = 'Uniswap V2';
    string public constant symbol = 'UNI-V2';
    uint8 public constant decimals = 18;
    uint  public totalSupply;
    mapping(address => uint) public balanceOf;
    mapping(address => mapping(address => uint)) public allowance;

    bytes32 public DOMAIN_SEPARATOR;
    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    bytes32 public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
    mapping(address => uint) public nonces;

    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    constructor() public {
        uint chainId;
        assembly {
            chainId := chainid
        }
        DOMAIN_SEPARATOR = keccak256(
            abi.encode(
                keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
                keccak256(bytes(name)),
                keccak256(bytes('1')),
                chainId,
                address(this)
            )
        );
    }

    function _mint(address to, uint value) internal {
        totalSupply = totalSupply.add(value);
        balanceOf[to] = balanceOf[to].add(value);
        emit Transfer(address(0), to, value);
    }

    function _burn(address from, uint value) internal {
        balanceOf[from] = balanceOf[from].sub(value);
        totalSupply = totalSupply.sub(value);
        emit Transfer(from, address(0), value);
    }

    function _approve(address owner, address spender, uint value) private {
        allowance[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    function _transfer(address from, address to, uint value) private {
        balanceOf[from] = balanceOf[from].sub(value);
        balanceOf[to] = balanceOf[to].add(value);
        emit Transfer(from, to, value);
    }

    function approve(address spender, uint value) external returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    function transfer(address to, uint value) external returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    function transferFrom(address from, address to, uint value) external returns (bool) {
        if (allowance[from][msg.sender] != uint(-1)) {
            allowance[from][msg.sender] = allowance[from][msg.sender].sub(value);
        }
        _transfer(from, to, value);
        return true;
    }

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        require(deadline >= block.timestamp, 'UniswapV2: EXPIRED');
        bytes32 digest = keccak256(
            abi.encodePacked(
                '\x19\x01',
                DOMAIN_SEPARATOR,
                keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, nonces[owner]++, deadline))
            )
        );
        address recoveredAddress = ecrecover(digest, v, r, s);
        require(recoveredAddress != address(0) && recoveredAddress == owner, 'UniswapV2: INVALID_SIGNATURE');
        _approve(owner, spender, value);
    }
}

// File: contracts/libraries/Math.sol

pragma solidity =0.5.16;

// a library for performing various math operations

library Math {
    function min(uint x, uint y) internal pure returns (uint z) {
        z = x < y ? x : y;
    }

    // babylonian method (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method)
    function sqrt(uint y) internal pure returns (uint z) {
        if (y > 3) {
            z = y;
            uint x = y / 2 + 1;
            while (x < z) {
                z = x;
                x = (y / x + x) / 2;
            }
        } else if (y != 0) {
            z = 1;
        }
    }
}

// File: contracts/libraries/UQ112x112.sol

pragma solidity =0.5.16;

// a library for handling binary fixed point numbers (https://en.wikipedia.org/wiki/Q_(number_format))

// range: [0, 2**112 - 1]
// resolution: 1 / 2**112

library UQ112x112 {
    uint224 constant Q112 = 2**112;

    // encode a uint112 as a UQ112x112
    function encode(uint112 y) internal pure returns (uint224 z) {
        z = uint224(y) * Q112; // never overflows
    }

    // divide a UQ112x112 by a uint112, returning a UQ112x112
    function uqdiv(uint224 x, uint112 y) internal pure returns (uint224 z) {
        z = x / uint224(y);
    }
}

// File: contracts/interfaces/IERC20.sol

pragma solidity >=0.5.0;

interface IERC20 {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function decimals() external view returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);
}

// File: contracts/interfaces/IUniswapV2Factory.sol

pragma solidity >=0.5.0;

interface IUniswapV2Factory {
    event PairCreated(address indexed token0, address indexed token1, address pair, uint);

    function feeTo() external view returns (address);
    function feeToSetter() external view returns (address);

    function getPair(address tokenA, address tokenB) external view returns (address pair);
    function allPairs(uint) external view returns (address pair);
    function allPairsLength() external view returns (uint);

    function createPair(address tokenA, address tokenB) external returns (address pair);

    function setFeeTo(address) external;
    function setFeeToSetter(address) external;
}

// File: contracts/interfaces/IUniswapV2Callee.sol

pragma solidity >=0.5.0;

interface IUniswapV2Callee {
    function uniswapV2Call(address sender, uint amount0, uint amount1, bytes calldata data) external;
}

// File: contracts/UniswapV2Pair.sol

pragma solidity =0.5.16;








contract UniswapV2Pair is IUniswapV2Pair, UniswapV2ERC20 {
    using SafeMath  for uint;
    using UQ112x112 for uint224;

    uint public constant MINIMUM_LIQUIDITY = 10**3;
    bytes4 private constant SELECTOR = bytes4(keccak256(bytes('transfer(address,uint256)')));

    address public factory;
    address public token0;
    address public token1;

    uint112 private reserve0;           // uses single storage slot, accessible via getReserves
    uint112 private reserve1;           // uses single storage slot, accessible via getReserves
    uint32  private blockTimestampLast; // uses single storage slot, accessible via getReserves

    uint public price0CumulativeLast;
    uint public price1CumulativeLast;
    uint public kLast; // reserve0 * reserve1, as of immediately after the most recent liquidity event

    uint private unlocked = 1;
    modifier lock() {
        require(unlocked == 1, 'UniswapV2: LOCKED');
        unlocked = 0;
        _;
        unlocked = 1;
    }

    function getReserves() public view returns (uint112 _reserve0, uint112 _reserve1, uint32 _blockTimestampLast) {
        _reserve0 = reserve0;
        _reserve1 = reserve1;
        _blockTimestampLast = blockTimestampLast;
    }

    function _safeTransfer(address token, address to, uint value) private {
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(SELECTOR, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'UniswapV2: TRANSFER_FAILED');
    }

    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    constructor() public {
        factory = msg.sender;
    }

    // called once by the factory at time of deployment
    function initialize(address _token0, address _token1) external {
        require(msg.sender == factory, 'UniswapV2: FORBIDDEN'); // sufficient check
        token0 = _token0;
        token1 = _token1;
    }

    // update reserves and, on the first call per block, price accumulators
    function _update(uint balance0, uint balance1, uint112 _reserve0, uint112 _reserve1) private {
        require(balance0 <= uint112(-1) && balance1 <= uint112(-1), 'UniswapV2: OVERFLOW');
        uint32 blockTimestamp = uint32(block.timestamp % 2**32);
        uint32 timeElapsed = blockTimestamp - blockTimestampLast; // overflow is desired
        if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
            // * never overflows, and + overflow is desired
            price0CumulativeLast += uint(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) * timeElapsed;
            price1CumulativeLast += uint(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) * timeElapsed;
        }
        reserve0 = uint112(balance0);
        reserve1 = uint112(balance1);
        blockTimestampLast = blockTimestamp;
        emit Sync(reserve0, reserve1);
    }

    // if fee is on, mint liquidity equivalent to 1/6th of the growth in sqrt(k)
    function _mintFee(uint112 _reserve0, uint112 _reserve1) private returns (bool feeOn) {
        address feeTo = IUniswapV2Factory(factory).feeTo();
        feeOn = feeTo != address(0);
        uint _kLast = kLast; // gas savings
        if (feeOn) {
            if (_kLast != 0) {
                uint rootK = Math.sqrt(uint(_reserve0).mul(_reserve1));
                uint rootKLast = Math.sqrt(_kLast);
                if (rootK > rootKLast) {
                    uint numerator = totalSupply.mul(rootK.sub(rootKLast));
                    uint denominator = rootK.mul(5).add(rootKLast);
                    uint liquidity = numerator / denominator;
                    if (liquidity > 0) _mint(feeTo, liquidity);
                }
            }
        } else if (_kLast != 0) {
            kLast = 0;
        }
    }

    // this low-level function should be called from a contract which performs important safety checks
    function mint(address to) external lock returns (uint liquidity) {
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        uint balance0 = IERC20(token0).balanceOf(address(this));
        uint balance1 = IERC20(token1).balanceOf(address(this));
        uint amount0 = balance0.sub(_reserve0);
        uint amount1 = balance1.sub(_reserve1);

        bool feeOn = _mintFee(_reserve0, _reserve1);
        uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
        if (_totalSupply == 0) {
            liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
           _mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
        } else {
            liquidity = Math.min(amount0.mul(_totalSupply) / _reserve0, amount1.mul(_totalSupply) / _reserve1);
        }
        require(liquidity > 0, 'UniswapV2: INSUFFICIENT_LIQUIDITY_MINTED');
        _mint(to, liquidity);

        _update(balance0, balance1, _reserve0, _reserve1);
        if (feeOn) kLast = uint(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
        emit Mint(msg.sender, amount0, amount1);
    }

    // this low-level function should be called from a contract which performs important safety checks
    function burn(address to) external lock returns (uint amount0, uint amount1) {
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        address _token0 = token0;                                // gas savings
        address _token1 = token1;                                // gas savings
        uint balance0 = IERC20(_token0).balanceOf(address(this));
        uint balance1 = IERC20(_token1).balanceOf(address(this));
        uint liquidity = balanceOf[address(this)];

        bool feeOn = _mintFee(_reserve0, _reserve1);
        uint _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
        amount0 = liquidity.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
        amount1 = liquidity.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
        require(amount0 > 0 && amount1 > 0, 'UniswapV2: INSUFFICIENT_LIQUIDITY_BURNED');
        _burn(address(this), liquidity);
        _safeTransfer(_token0, to, amount0);
        _safeTransfer(_token1, to, amount1);
        balance0 = IERC20(_token0).balanceOf(address(this));
        balance1 = IERC20(_token1).balanceOf(address(this));

        _update(balance0, balance1, _reserve0, _reserve1);
        if (feeOn) kLast = uint(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
        emit Burn(msg.sender, amount0, amount1, to);
    }

    // this low-level function should be called from a contract which performs important safety checks
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external lock {
        require(amount0Out > 0 || amount1Out > 0, 'UniswapV2: INSUFFICIENT_OUTPUT_AMOUNT');
        (uint112 _reserve0, uint112 _reserve1,) = getReserves(); // gas savings
        require(amount0Out < _reserve0 && amount1Out < _reserve1, 'UniswapV2: INSUFFICIENT_LIQUIDITY');

        uint balance0;
        uint balance1;
        { // scope for _token{0,1}, avoids stack too deep errors
        address _token0 = token0;
        address _token1 = token1;
        require(to != _token0 && to != _token1, 'UniswapV2: INVALID_TO');
        if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
        if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
        if (data.length > 0) IUniswapV2Callee(to).uniswapV2Call(msg.sender, amount0Out, amount1Out, data);
        balance0 = IERC20(_token0).balanceOf(address(this));
        balance1 = IERC20(_token1).balanceOf(address(this));
        }
        uint amount0In = balance0 > _reserve0 - amount0Out ? balance0 - (_reserve0 - amount0Out) : 0;
        uint amount1In = balance1 > _reserve1 - amount1Out ? balance1 - (_reserve1 - amount1Out) : 0;
        require(amount0In > 0 || amount1In > 0, 'UniswapV2: INSUFFICIENT_INPUT_AMOUNT');
        { // scope for reserve{0,1}Adjusted, avoids stack too deep errors
        uint balance0Adjusted = balance0.mul(1000).sub(amount0In.mul(3));
        uint balance1Adjusted = balance1.mul(1000).sub(amount1In.mul(3));
        require(balance0Adjusted.mul(balance1Adjusted) >= uint(_reserve0).mul(_reserve1).mul(1000**2), 'UniswapV2: K');
        }

        _update(balance0, balance1, _reserve0, _reserve1);
        emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
    }

    // force balances to match reserves
    function skim(address to) external lock {
        address _token0 = token0; // gas savings
        address _token1 = token1; // gas savings
        _safeTransfer(_token0, to, IERC20(_token0).balanceOf(address(this)).sub(reserve0));
        _safeTransfer(_token1, to, IERC20(_token1).balanceOf(address(this)).sub(reserve1));
    }

    // force reserves to match balances
    function sync() external lock {
        _update(IERC20(token0).balanceOf(address(this)), IERC20(token1).balanceOf(address(this)), reserve0, reserve1);
    }
}

// Sources flattened with hardhat v2.1.2 https://hardhat.org

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


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);
}


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


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;
    }
}


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


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);
            }
        }
    }
}


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


pragma solidity >=0.6.0 <0.8.0;



/**
 * @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 @openzeppelin/contracts-upgradeable/utils/AddressUpgradeable.sol


pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library AddressUpgradeable {
    /**
     * @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);
    }

    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);
            }
        }
    }
}


// File @openzeppelin/contracts-upgradeable/proxy/Initializable.sol


// solhint-disable-next-line compiler-version
pragma solidity >=0.4.24 <0.8.0;

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract contract Initializable {

    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private _initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;

    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || _isConstructor() || !_initialized, "Initializable: contract is already initialized");

        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }

        _;

        if (isTopLevelCall) {
            _initializing = false;
        }
    }

    /// @dev Returns true if and only if the function is running in the constructor
    function _isConstructor() private view returns (bool) {
        return !AddressUpgradeable.isContract(address(this));
    }
}


// File @openzeppelin/contracts-upgradeable/utils/ContextUpgradeable.sol


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 ContextUpgradeable is Initializable {
    function __Context_init() internal initializer {
        __Context_init_unchained();
    }

    function __Context_init_unchained() internal initializer {
    }
    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;
    }
    uint256[50] private __gap;
}


// File @openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol


pragma solidity >=0.6.0 <0.8.0;


/**
 * @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 OwnableUpgradeable is Initializable, ContextUpgradeable {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    function __Ownable_init() internal initializer {
        __Context_init_unchained();
        __Ownable_init_unchained();
    }

    function __Ownable_init_unchained() internal initializer {
        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;
    }
    uint256[49] private __gap;
}


// File @openzeppelin/contracts-upgradeable/utils/ReentrancyGuardUpgradeable.sol


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 ReentrancyGuardUpgradeable is Initializable {
    // 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;

    function __ReentrancyGuard_init() internal initializer {
        __ReentrancyGuard_init_unchained();
    }

    function __ReentrancyGuard_init_unchained() internal initializer {
        _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;
    }
    uint256[49] private __gap;
}


// File contracts/TokensFarm.sol

pragma solidity 0.6.12;





contract TokensFarm is OwnableUpgradeable, ReentrancyGuardUpgradeable {

    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    // Enums
    enum EarlyWithdrawPenalty {
        NO_PENALTY,
        BURN_REWARDS,
        REDISTRIBUTE_REWARDS
    }

    // Info of each user.
    struct StakeInfo {
        // How many tokens the user has provided.
        uint256 amount;
        // Reward debt.
        uint256 rewardDebt;
        // Time when user deposited.
        uint256 depositTime;
        // Time when user withdraw
        uint256 withdrawTime;
        // Address of user
        address addressOfUser;
    }

    // Address of ERC20 token contract.
    IERC20 public tokenStaked;
    // Last time number that ERC20s distribution occurs.
    uint256 public lastRewardTime;
    // Accumulated ERC20s per share, times 1e18.
    uint256 public accERC20PerShare;
    // Total tokens deposited in the farm.
    uint256 public totalDeposits;
    // If contractor allows early withdraw on stakes
    bool public isEarlyWithdrawAllowed;
    // Minimal period of time to stake
    uint256 public minTimeToStake;
    // Address of the ERC20 Token contract.
    IERC20 public erc20;
    // The total amount of ERC20 that's paid out as reward.
    uint256 public paidOut;
    // ERC20 tokens rewarded per second.
    uint256 public rewardPerSecond;
    // Total rewards added to farm
    uint256 public totalRewards;
    // Info of each user that stakes ERC20 tokens.
    mapping(address => StakeInfo[]) public stakeInfo;
    // The time when farming starts.
    uint256 public startTime;
    // The time when farming ends.
    uint256 public endTime;
    // Early withdraw penalty
    EarlyWithdrawPenalty public penalty;
    // Stake fee percent
    uint256 public stakeFeePercent;
    // Reward fee percent
    uint256 public rewardFeePercent;
    // Fee collector address
    address payable public feeCollector;
    // Flat fee amount
    uint256 public flatFeeAmount;
    // Fee option
    bool public isFlatFeeAllowed;
    // Total tokens burned
    uint256 public totalTokensBurned;
    // Total fee collected
    uint256 public totalFeeCollectedETH;
    // Total fee collected in tokens
    uint256 public totalFeeCollectedTokens;
    // Address of farm instance
    address public farmImplementation;
    // NumberOfUsers participating in farm
    uint256 public noOfUsers;
    // Addresses of all users that are currently participating
    address[] public participants;
    // Mapping of every users spot in array
    mapping(address => uint256) public id;

    // Events
    event Deposit(
        address indexed user,
        uint256 indexed stakeId,
        uint256 indexed amount
    );
    event Withdraw(
        address indexed user,
        uint256 indexed stakeId,
        uint256 indexed amount
    );
    event EmergencyWithdraw(
        address indexed user,
        uint256 indexed stakeId,
        uint256 indexed amount
    );
    event EarlyWithdrawPenaltySet(EarlyWithdrawPenalty indexed penalty);
    event MinTimeToStakeSet(uint256 indexed minTimeToStake);
    event IsEarlyWithdrawAllowedSet(bool indexed allowed);
    event StakeFeePercentSet(uint256 indexed stakeFeePercent);
    event RewardFeePercentSet(uint256 indexed rewardFeePercent);
    event FlatFeeAmountSet(uint256 indexed flatFeeAmount);
    event IsFlatFeeAllowedSet(bool indexed allowed);
    event FeeCollectorSet(address payable indexed feeCollector);

    // Modifiers
    modifier validateStakeByStakeId(address _user, uint256 stakeId) {
        require(stakeId < stakeInfo[_user].length, "Stake does not exist");
        _;
    }

    /**
     * @notice function sets initial state of contract
     *
     * @param _erc20 - address of reward token
     * @param _rewardPerSecond - number of reward per second
     * @param _startTime - beginning of farm
     * @param _minTimeToStake - how much time needs to pass before staking
     * @param _isEarlyWithdrawAllowed - is early withdraw allowed or not
     * @param _penalty - ENUM(what type of penalty)
     * @param _tokenStaked - address of token which is staked
     * @param _stakeFeePercent - fee percent for staking
     * @param _rewardFeePercent - fee percent for reward distribution
     * @param _flatFeeAmount - flat fee amount
     * @param _isFlatFeeAllowed - is flat fee  allowed or not
     */
    function initialize(
        address _erc20,
        uint256 _rewardPerSecond,
        uint256 _startTime,
        uint256 _minTimeToStake,
        bool _isEarlyWithdrawAllowed,
        uint256 _penalty,
        address _tokenStaked,
        uint256 _stakeFeePercent,
        uint256 _rewardFeePercent,
        uint256 _flatFeeAmount,
        address payable _feeCollector,
        bool _isFlatFeeAllowed,
        address _farmImplementation
    )
        external
        initializer
    {
        // Upgrading ownership
        __Ownable_init();
        __ReentrancyGuard_init();

        // Requires for correct initialization
        require(_erc20 != address(0x0), "Wrong token address.");
        require(_rewardPerSecond > 0, "Rewards per second must be > 0.");
        require(
            _startTime >= block.timestamp,
            "Start time can not be in the past."
        );
        require(_stakeFeePercent < 100, "Stake fee must be < 100.");
        require(_rewardFeePercent < 100, "Reward fee must be < 100.");
        require(
            _feeCollector != address(0x0),
            "Wrong fee collector address."
        );

        // Initialization of contract
        erc20 = IERC20(_erc20);
        rewardPerSecond = _rewardPerSecond;
        startTime = _startTime;
        endTime = _startTime;
        minTimeToStake = _minTimeToStake;
        isEarlyWithdrawAllowed = _isEarlyWithdrawAllowed;
        stakeFeePercent = _stakeFeePercent;
        rewardFeePercent = _rewardFeePercent;
        flatFeeAmount = _flatFeeAmount;
        feeCollector = _feeCollector;
        isFlatFeeAllowed = _isFlatFeeAllowed;
        farmImplementation = _farmImplementation;

        _setEarlyWithdrawPenalty(_penalty);
        _addPool(IERC20(_tokenStaked));
    }

    // All Internal functions

    /**
     * @notice function is adding a new ERC20 token to the pool
     *
     * @param _tokenStaked - address of token staked
     */
    function _addPool(
        IERC20 _tokenStaked
    )
        internal
    {
        require(
            address(_tokenStaked) != address(0x0),
            "Must input valid address."
        );
        require(
            address(tokenStaked) == address(0x0),
            "Pool can be set only once."
        );

        uint256 _lastRewardTime = block.timestamp > startTime
        ? block.timestamp
        : startTime;

        tokenStaked = _tokenStaked;
        lastRewardTime = _lastRewardTime;
        accERC20PerShare = 0;
        totalDeposits = 0;
    }

    /**
     * @notice function is setting early withdrawal penalty, if applicable
     *
     * @param _penalty - number of penalty
     */
    function _setEarlyWithdrawPenalty(
        uint256 _penalty
    )
        internal
    {
        penalty = EarlyWithdrawPenalty(_penalty);
        emit EarlyWithdrawPenaltySet(penalty);
    }

    /**
     * @notice function is adding participant from farm
     *
     * @param user - address of user
     *
     * @return boolean - if adding is successful or not
     */
    function _addParticipant(
        address user
    )
        internal
        returns(bool)
    {
        if(stakeInfo[user].length > 0){
            return false;
        }

        id[user] = noOfUsers;
        noOfUsers++;
        participants.push(user);

        return true;
    }

    /**
     * @notice function is removing participant from farm
     *
     * @param user - address of user
     * @param amount - how many is user withdrawing
     *
     * @return boolean - if removal is successful or not
     */
    function _removeParticipant(
        address user,
        uint256 amount
    )
        internal
        returns(bool)
    {
        uint256 totalAmount;

        if(noOfUsers == 1){
            totalAmount = 0;
            for(uint256 i = 0; i < stakeInfo[user].length; i++){
                totalAmount += stakeInfo[user][i].amount;
            }

            if(amount == totalAmount){
                delete id[user];
                participants.pop();
                noOfUsers--;

                return true;
            }
        }
        else{
            totalAmount = 0;
            for(uint256 i = 0; i < stakeInfo[user].length; i++){
                totalAmount += stakeInfo[user][i].amount;
            }

            if(amount == totalAmount){
                uint256 deletedUserId = id[user];
                address lastUserInParticipantsArray = participants[participants.length - 1];
                participants[deletedUserId] = lastUserInParticipantsArray;
                id[lastUserInParticipantsArray] = deletedUserId;

                delete id[user];
                participants.pop();
                noOfUsers--;

                return true;
            }
        }

        return false;
    }

    // All setter's functions

    /**
     * @notice function is setting new minimum time to stake value
     *
     * @param _minTimeToStake - min time to stake
     */
    function setMinTimeToStake(
        uint256 _minTimeToStake
    )
        external
        onlyOwner
    {
        minTimeToStake = _minTimeToStake;
        emit MinTimeToStakeSet(minTimeToStake);
    }

    /**
     * @notice function is setting new state of early withdraw
     *
     * @param _isEarlyWithdrawAllowed - is early withdraw allowed or not
     */
    function setIsEarlyWithdrawAllowed(
        bool _isEarlyWithdrawAllowed
    )
        external
        onlyOwner
    {
        isEarlyWithdrawAllowed = _isEarlyWithdrawAllowed;
        emit IsEarlyWithdrawAllowedSet(isEarlyWithdrawAllowed);
    }

    /**
     * @notice function is setting new stake fee percent value
     *
     * @param _stakeFeePercent - stake fee percent
     */
    function setStakeFeePercent(
        uint256 _stakeFeePercent
    )
        external
        onlyOwner
    {
        stakeFeePercent = _stakeFeePercent;
        emit StakeFeePercentSet(stakeFeePercent);
    }

    /**
     * @notice function is setting new reward fee percent value
     *
     * @param _rewardFeePercent - reward fee percent
     */
    function setRewardFeePercent(
        uint256 _rewardFeePercent
    )
        external
        onlyOwner
    {
        rewardFeePercent = _rewardFeePercent;
        emit RewardFeePercentSet(rewardFeePercent);

    }

    /**
     * @notice function is setting new flat fee amount
     *
     * @param _flatFeeAmount - flat fee amount
     */
    function setFlatFeeAmount(
        uint256 _flatFeeAmount
    )
        external
        onlyOwner
    {
        flatFeeAmount = _flatFeeAmount;
        emit FlatFeeAmountSet(flatFeeAmount);
    }

    /**
     * @notice function is setting flat fee allowed
     *
     * @param _isFlatFeeAllowed - is flat fee allowed or not
     */
    function setIsFlatFeeAllowed(
        bool _isFlatFeeAllowed
    )
        external
        onlyOwner
    {
        isFlatFeeAllowed = _isFlatFeeAllowed;
        emit IsFlatFeeAllowedSet(isFlatFeeAllowed);
    }

    /**
     * @notice function is setting feeCollector on new address
     *
     * @param _feeCollector - address of newFeeCollector
     */
    function setFeeCollector(
        address payable _feeCollector
    )
        external
        onlyOwner
    {
        feeCollector = _feeCollector;
        emit FeeCollectorSet(feeCollector);
    }

    // All view functions

    /**
     * @notice function is getting number to see deposited ERC20 token for a user.
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return deposited ERC20 token for a user
     */
    function deposited(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory  stake = stakeInfo[_user][stakeId];
        return stake.amount;
    }

    /**
     * @notice function is getting number to see pending ERC20s for a user.
     *
     * @dev pending reward = (user.amount * pool.accERC20PerShare) - user.rewardDebt
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return pending ERC20s for a user.
     */
    function pending(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory stake = stakeInfo[_user][stakeId];

        if (stake.amount == 0) {
            return 0;
        }

        uint256 _accERC20PerShare = accERC20PerShare;
        uint256 tokenSupply = totalDeposits;

        if (block.timestamp > lastRewardTime && tokenSupply != 0) {
            uint256 lastTime = block.timestamp < endTime
            ? block.timestamp
            : endTime;
            uint256 timeToCompare = lastRewardTime < endTime
            ? lastRewardTime
            : endTime;
            uint256 nrOfSeconds = lastTime.sub(timeToCompare);
            uint256 erc20Reward = nrOfSeconds.mul(rewardPerSecond);
            _accERC20PerShare = _accERC20PerShare.add(
                erc20Reward.mul(1e18).div(tokenSupply)
            );
        }

        return
        stake.amount.mul(_accERC20PerShare).div(1e18).sub(stake.rewardDebt);
    }

    /**
     * @notice function is getting number to see deposit timestamp for a user.
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return time when user deposited specific stake
     */
    function depositTimestamp(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory stake = stakeInfo[_user][stakeId];
        return stake.depositTime;
    }

    /**
     * @notice function is getting number to see withdraw timestamp for a user.
     *
     * @param _user - address of user
     * @param stakeId - id of user stake
     *
     * @return time when user withdraw specific stake
     */
    function withdrawTimestamp(
        address _user,
        uint256 stakeId
    )
        public
        view
        validateStakeByStakeId(_user, stakeId)
        returns (uint256)
    {
        StakeInfo memory stake = stakeInfo[_user][stakeId];
        return stake.withdrawTime;
    }

    /**
     * @notice function is getting number for total rewards the farm has yet to pay out.
     *
     * @return how many total reward the farm has yet to pay out.
     */
    function totalPending()
        external
        view
        returns (uint256)
    {
        if (block.timestamp <= startTime) {
            return 0;
        }

        uint256 lastTime = block.timestamp < endTime
        ? block.timestamp
        : endTime;
        return rewardPerSecond.mul(lastTime - startTime).sub(paidOut);
    }

    /**
     * @notice function is getting number of stakes user has
     *
     * @param user - address of user
     *
     * @return how many times has user staked tokens
     */
    function getNumberOfUserStakes(
        address user
    )
        external
        view
        returns (uint256)
    {
        return stakeInfo[user].length;
    }

    /**
     * @notice function is getting user pending amounts, stakes and deposit time
     *
     * @param user - address of user
     *
     * @return array of deposits,pendingAmounts and depositTime
     */
    function getUserStakesAndPendingAmounts(
        address user
    )
        external
        view
        returns (
            uint256[] memory,
            uint256[] memory,
            uint256[] memory
        )
    {
        uint256 numberOfStakes = stakeInfo[user].length;

        uint256[] memory deposits = new uint256[](numberOfStakes);
        uint256[] memory pendingAmounts = new uint256[](numberOfStakes);
        uint256[] memory depositTime = new uint256[](numberOfStakes);

        for (uint256 i = 0; i < numberOfStakes; i++) {
            deposits[i] = deposited(user, i);
            pendingAmounts[i] = pending(user, i);
            depositTime[i] = depositTimestamp(user, i);
        }

        return (deposits, pendingAmounts, depositTime);
    }

    /**
     * @notice function is getting total rewards locked/unlocked
     *
     * @return totalRewardsUnlocked
     * @return totalRewardsLocked
     */
    function getTotalRewardsLockedUnlocked()
        external
        view
        returns (uint256, uint256)
    {
        uint256 totalRewardsLocked;
        uint256 totalRewardsUnlocked;

        if (block.timestamp <= startTime) {
            totalRewardsUnlocked = 0;
            totalRewardsLocked = totalRewards;
        } else {
            uint256 lastTime = block.timestamp < endTime
            ? block.timestamp
            : endTime;
            totalRewardsUnlocked = rewardPerSecond.mul(lastTime - startTime);
            totalRewardsLocked = totalRewards - totalRewardsUnlocked;
        }

        return (totalRewardsUnlocked, totalRewardsLocked);
    }

    // Money managing functions

    /**
     * @notice function is funding the farm, increase the end time
     *
     * @param _amount - how many tokens is funded
     */
    function fund(
        uint256 _amount
    )
        external
    {
        uint256 balanceBefore = erc20.balanceOf(address(this));
        erc20.safeTransferFrom(address(msg.sender), address(this), _amount);
        uint256 balanceAfter = erc20.balanceOf(address(this));

        uint256 fundAmount;
        if(balanceAfter.sub(balanceBefore) <= _amount){
            fundAmount = balanceAfter.sub(balanceBefore);
        }
        else{
            fundAmount = _amount;
        }

        _fundInternal(fundAmount);
    }

    /**
     * @notice function is internally funding the farm by adding farmed rewards by user to the end
     *
     * @param _amount - how many tokens is funded
     */
    function _fundInternal(
        uint256 _amount
    )
        internal
    {
        require(
            block.timestamp < endTime,
            "fund: too late, the farm is closed"
        );
        require(_amount > 0, "Amount must be greater than 0.");
        // Compute new end time
        endTime += _amount.div(rewardPerSecond);
        // Increase farm total rewards
        totalRewards = totalRewards.add(_amount);
    }

    /**
     * @notice function is updating reward variables of the given pool to be up-to-date.
     */
    function updatePool()
        public
    {
        uint256 lastTime = block.timestamp < endTime
        ? block.timestamp
        : endTime;

        if (lastTime <= lastRewardTime) {
            return;
        }

        uint256 tokenSupply = totalDeposits;

        if (tokenSupply == 0) {
            lastRewardTime = lastTime;
            return;
        }

        uint256 nrOfSeconds = lastTime.sub(lastRewardTime);
        uint256 erc20Reward = nrOfSeconds.mul(rewardPerSecond);

        accERC20PerShare = accERC20PerShare.add(
            erc20Reward.mul(1e18).div(tokenSupply)
        );
        lastRewardTime = block.timestamp;
    }

    /**
     * @notice function is depositing ERC20 tokens to Farm for ERC20 allocation.
     *
     * @param _amount - how many tokens user is depositing
     */
    function deposit(
        uint256 _amount
    )
        external
        nonReentrant
        payable
    {
        require(
            block.timestamp < endTime,
            "Deposit: too late, the farm is closed"
        );

        StakeInfo memory stake;
        uint256 stakedAmount;

        // Update pool
        updatePool();

        uint256 beforeBalance = tokenStaked.balanceOf(address(this));
        tokenStaked.safeTransferFrom(
            address(msg.sender),
            address(this),
            _amount
        );
        uint256 afterBalance = tokenStaked.balanceOf(address(this));

        if(afterBalance.sub(beforeBalance) <= _amount){
            stakedAmount = afterBalance.sub(beforeBalance);
        }
        else{
            stakedAmount = _amount;
        }

        if (isFlatFeeAllowed) {
            // Collect flat fee
            require(
                msg.value >= flatFeeAmount,
                "Payable amount is less than fee amount."
            );

            totalFeeCollectedETH = totalFeeCollectedETH.add(msg.value);
        } else if (stakeFeePercent > 0) {
            // Handle this case only if flat fee is not allowed, and stakeFeePercent > 0
            // Compute the fee
            uint256 feeAmount = stakedAmount.mul(stakeFeePercent).div(100);
            // Compute stake amount
            stakedAmount = stakedAmount.sub(feeAmount);
            totalFeeCollectedTokens = totalFeeCollectedTokens.add(feeAmount);
        }

        // Increase total deposits
        totalDeposits = totalDeposits.add(stakedAmount);
        // Update user accounting
        stake.amount = stakedAmount;
        stake.rewardDebt = stake.amount.mul(accERC20PerShare).div(1e18);
        stake.depositTime = block.timestamp;
        stake.addressOfUser = address(msg.sender);
        stake.withdrawTime = 0;

        _addParticipant(address(msg.sender));

        // Compute stake id
        uint256 stakeId = stakeInfo[msg.sender].length;
        // Push new stake to array of stakes for user
        stakeInfo[msg.sender].push(stake);
        // Emit deposit event
        emit Deposit(msg.sender, stakeId, stakedAmount);
    }

    // All withdraw functions

    /**
     * @notice function is withdrawing with caring about rewards
     *
     * @param _amount - how many tokens wants to be withdrawn
     * @param stakeId - Id of user stake
     */
    function withdraw(
        uint256 _amount,
        uint256 stakeId
    )
        external
        nonReentrant
        payable
        validateStakeByStakeId(msg.sender, stakeId)
    {
        bool minimalTimeStakeRespected;
        StakeInfo storage stake = stakeInfo[msg.sender][stakeId];

        require(
            stake.amount >= _amount,
            "withdraw: can't withdraw more than deposit"
        );

        updatePool();
        minimalTimeStakeRespected =
        stake.depositTime.add(minTimeToStake) <= block.timestamp;
        // if early withdraw is not allowed, user can't withdraw funds before
        if (!isEarlyWithdrawAllowed) {
            // Check if user has respected minimal time to stake, require it.
            require(
                minimalTimeStakeRespected,
                "User can not withdraw funds yet."
            );
        }

        // Compute pending rewards amount of user rewards
        uint256 pendingAmount = stake
        .amount
        .mul(accERC20PerShare)
        .div(1e18)
        .sub(stake.rewardDebt);

        // Penalties in case user didn't stake enough time
        if (pendingAmount > 0) {
            if (
                penalty == EarlyWithdrawPenalty.BURN_REWARDS &&
                !minimalTimeStakeRespected
            ) {
                // Burn to address (1)
                totalTokensBurned = totalTokensBurned.add(pendingAmount);
                _erc20Transfer(address(1), pendingAmount);
            } else if (
                penalty == EarlyWithdrawPenalty.REDISTRIBUTE_REWARDS &&
                !minimalTimeStakeRespected
            ) {
                if (block.timestamp >= endTime) {
                    // Burn rewards because farm can not be funded anymore since it ended
                    _erc20Transfer(address(1), pendingAmount);
                    totalTokensBurned = totalTokensBurned.add(pendingAmount);
                } else {
                    // Re-fund the farm
                    _fundInternal(pendingAmount);
                }
            } else {
                // In case either there's no penalty
                _erc20Transfer(msg.sender, pendingAmount);
            }
        }

        _removeParticipant(address(msg.sender), _amount);

        stake.withdrawTime = block.timestamp;
        stake.amount = stake.amount.sub(_amount);
        stake.rewardDebt = stake.amount.mul(accERC20PerShare).div(1e18);

        tokenStaked.safeTransfer(address(msg.sender), _amount);
        totalDeposits = totalDeposits.sub(_amount);

        // Emit Withdraw event
        emit Withdraw(msg.sender, stakeId, _amount);
    }

    /**
     * @notice function is withdrawing without caring about rewards. EMERGENCY ONLY.
     *
     * @param stakeId - Id of user stake
     */
    function emergencyWithdraw(
        uint256 stakeId
    )
        external
        nonReentrant
        validateStakeByStakeId(msg.sender, stakeId)
    {
        StakeInfo storage stake = stakeInfo[msg.sender][stakeId];

        // if early withdraw is not allowed, user can't withdraw funds before
        if (!isEarlyWithdrawAllowed) {
            bool minimalTimeStakeRespected = stake.depositTime.add(
                minTimeToStake
            ) <= block.timestamp;
            // Check if user has respected minimal time to stake, require it.
            require(
                minimalTimeStakeRespected,
                "User can not withdraw funds yet."
            );
        }

        tokenStaked.safeTransfer(address(msg.sender), stake.amount);
        totalDeposits = totalDeposits.sub(stake.amount);

        _removeParticipant(address(msg.sender), stake.amount);
        stake.withdrawTime = block.timestamp;

        emit EmergencyWithdraw(msg.sender, stakeId, stake.amount);

        stake.amount = 0;
        stake.rewardDebt = 0;
    }

    /**
     * @notice function is withdrawing fee collected in ERC value
     */
    function withdrawCollectedFeesERC()
        external
        onlyOwner
    {
        erc20.transfer(feeCollector, totalFeeCollectedTokens);
        totalFeeCollectedTokens = 0;
    }

    /**
     * @notice function is withdrawing fee collected in ETH value
     */
    function withdrawCollectedFeesETH()
        external
        onlyOwner
    {
        (bool sent, ) = payable(feeCollector).call{value: totalFeeCollectedETH}("");
        require(sent, "Failed to end flat fee");
        totalFeeCollectedETH = 0;
    }

    /**
     * @notice function is withdrawing tokens if stuck
     *
     * @param _erc20 - address of token address
     * @param _amount - number of how many tokens
     * @param _beneficiary - address of user that collects tokens deposited by mistake
     */
    function withdrawTokensIfStuck(
        address _erc20,
        uint256 _amount,
        address _beneficiary
    )
        external
        onlyOwner
    {
        IERC20 token = IERC20(_erc20);
        require(tokenStaked != token, "User tokens can not be pulled");
        require(
            _beneficiary != address(0x0),
            "_beneficiary can not be 0x0 address"
        );

        token.safeTransfer(_beneficiary, _amount);
    }

    /**
     * @notice function is transferring ERC20,
     * and update the required ERC20 to payout all rewards
     *
     * @param _to - transfer on this address
     * @param _amount - number of how many tokens
     */
    function _erc20Transfer(
        address _to,
        uint256 _amount
    )
        internal
    {
        if (isFlatFeeAllowed) {
            // Collect flat fee
            require(
                msg.value >= flatFeeAmount,
                "Payable amount is less than fee amount."
            );
            // Increase amount of fees collected
            totalFeeCollectedETH = totalFeeCollectedETH.add(msg.value);
            // send reward
            erc20.transfer(_to, _amount);
            paidOut += _amount;
        } else if (stakeFeePercent > 0) {
            // Collect reward fee
            uint256 feeAmount = _amount.mul(rewardFeePercent).div(100);
            uint256 rewardAmount = _amount.sub(feeAmount);

            // Increase amount of fees collected
            totalFeeCollectedTokens = totalFeeCollectedTokens.add(feeAmount);

            // send reward
            erc20.transfer(_to, rewardAmount);
            paidOut += _amount;
        } else {
            erc20.transfer(_to, _amount);
            paidOut += _amount;
        }
    }
}

// SPDX-License-Identifier: MIT
// solhint-disable-next-line compiler-version
pragma solidity ^0.8.0;
import "./Initializable.sol";
import "./v2/CappedEPIK.sol";
import "./v2/MintableEPIK.sol";
import "./v2/Ownable.sol";
/**
 * @title EPIK LOGIC TOKEN
 * @dev This contract is a mock to test initializable functionality
 */
contract EPIKERC20 is Initializable, ERC20Capped, ERC20Mintable, Ownable {
  function initialize(string memory name_, string memory symbol_, uint8 decimals_, uint256 cap_, address owner_) public initializer {
    _name = name_;
    _symbol = symbol_;
    _decimals = decimals_;
    _cap = cap_;
    _owner = owner_;
  }
  /**
    * @dev Function to mint tokens.
    *
    * NOTE: restricting access to owner only. See {ERC20Mintable-mint}.
    *
    * @param account The address that will receive the minted tokens
    * @param amount The amount of tokens to mint
    */
  function _mint(address account, uint256 amount) internal override onlyOwner {
      super._mint(account, amount);
  }
  /**
    * @dev Function to stop minting new tokens.
    *
    * NOTE: restricting access to owner only. See {ERC20Mintable-finishMinting}.
    */
  function _finishMinting() internal override onlyOwner {
      super._finishMinting();
  }
  /**
    * @dev See {ERC20-_beforeTokenTransfer}. See {ERC20Capped-_beforeTokenTransfer}.
    */
  function _beforeTokenTransfer(address from, address to, uint256 amount) internal override(ERC20, ERC20Capped) {
      super._beforeTokenTransfer(from, to, amount);
  }
}
// SPDX-License-Identifier: MIT
// solhint-disable-next-line compiler-version
pragma solidity ^0.8.0;
/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract contract Initializable {
    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private _initialized;
    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;
    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || !_initialized, "Initializable: contract is already initialized");
        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }
        _;
        if (isTopLevelCall) {
            _initializing = false;
        }
    }
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./ERC20.sol";
/**
 * @dev Extension of {ERC20} that adds a cap to the supply of tokens.
 */
abstract contract ERC20Capped is ERC20 {
    using SafeMath for uint256;
    uint256 internal _cap;
    /**
     * @dev Returns the cap on the token's total supply.
     */
    function cap() public view returns (uint256) {
        return _cap;
    }
    /**
     * @dev See {ERC20-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - minted tokens must not cause the total supply to go over the cap.
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override {
        super._beforeTokenTransfer(from, to, amount);
        if (from == address(0)) { // When minting tokens
            require(totalSupply().add(amount) <= _cap, "ERC20Capped: cap exceeded");
        }
    }
}// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./ERC20.sol";
/**
 * @title ERC20Mintable
 * @dev Implementation of the ERC20Mintable. Extension of {ERC20} that adds a minting behaviour.
 */
abstract contract ERC20Mintable is ERC20 {
    // indicates if minting is finished
    bool internal _mintingFinished = false;
    /**
     * @dev Emitted during finish minting
     */
    event MintFinished();
    /**
     * @dev Tokens can be minted only before minting finished.
     */
    modifier canMint() {
        require(!_mintingFinished, "ERC20Mintable: minting is finished");
        _;
    }
    /**
     * @return if minting is finished or not.
     */
    function mintingFinished() public view returns (bool) {
        return _mintingFinished;
    }
    /**
     * @dev Function to mint tokens.
     *
     * WARNING: it allows everyone to mint new tokens. Access controls MUST be defined in derived contracts.
     *
     * @param account The address that will receive the minted tokens
     * @param amount The amount of tokens to mint
     */
    function mint(address account, uint256 amount) public canMint {
        _mint(account, amount);
    }
    /**
     * @dev Function to stop minting new tokens.
     *
     * WARNING: it allows everyone to finish minting. Access controls MUST be defined in derived contracts.
     */
    function finishMinting() public canMint {
        _finishMinting();
    }
    /**
     * @dev Function to stop minting new tokens.
     */
    function _finishMinting() internal virtual {
        _mintingFinished = true;
        emit MintFinished();
    }
}// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/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 internal _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    /**
     * @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 ^0.8.0;
import "@openzeppelin/contracts/utils/Context.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/utils/math/SafeMath.sol";
/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;
    mapping (address => uint256) private _balances;
    mapping (address => mapping (address => uint256)) private _allowances;
    uint256 private _totalSupply;
    string internal _name;
    string internal _symbol;
    uint8 internal _decimals;
    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }
    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }
    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }
    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }
    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }
    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }
    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }
    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }
    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }
    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }
    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }
    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        _beforeTokenTransfer(sender, recipient, amount);
        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }
    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");
        _beforeTokenTransfer(address(0), account, amount);
        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }
    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");
        _beforeTokenTransfer(account, address(0), amount);
        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }
    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}// SPDX-License-Identifier: MIT
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) {
        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 ^0.8.0;
/**
 * @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 ^0.8.0;
// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.
/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
 * now has built in overflow checking.
 */
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) {
        unchecked {
            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) {
        unchecked {
            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) {
        unchecked {
            // 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) {
        unchecked {
            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) {
        unchecked {
            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) {
        return a + b;
    }
    /**
     * @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 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) {
        return a * b;
    }
    /**
     * @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.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        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) {
        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) {
        unchecked {
            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.
     *
     * 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).
     *
     * 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) {
        unchecked {
            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) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}