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

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

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

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

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

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

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

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

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

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

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

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

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

        return c;
    }

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

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

        return c;
    }

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

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

        return c;
    }

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

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

        return c;
    }

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

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

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

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.2;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies in 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");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

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

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

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

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

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;




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

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

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

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

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

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

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

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

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

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.0.0, only sets of type `address` (`AddressSet`) and `uint256`
 * (`UintSet`) are supported.
 */
library EnumerableSet {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;

        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) { // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            bytes32 lastvalue = set._values[lastIndex];

            // Move the last value to the index where the value to delete is
            set._values[toDeleteIndex] = lastvalue;
            // Update the index for the moved value
            set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint256(_at(set._inner, index)));
    }


    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}

// File: @openzeppelin/contracts/introspection/IERC1820Registry.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @dev Interface of the global ERC1820 Registry, as defined in the
 * https://eips.ethereum.org/EIPS/eip-1820[EIP]. Accounts may register
 * implementers for interfaces in this registry, as well as query support.
 *
 * Implementers may be shared by multiple accounts, and can also implement more
 * than a single interface for each account. Contracts can implement interfaces
 * for themselves, but externally-owned accounts (EOA) must delegate this to a
 * contract.
 *
 * {IERC165} interfaces can also be queried via the registry.
 *
 * For an in-depth explanation and source code analysis, see the EIP text.
 */
interface IERC1820Registry {
    /**
     * @dev Sets `newManager` as the manager for `account`. A manager of an
     * account is able to set interface implementers for it.
     *
     * By default, each account is its own manager. Passing a value of `0x0` in
     * `newManager` will reset the manager to this initial state.
     *
     * Emits a {ManagerChanged} event.
     *
     * Requirements:
     *
     * - the caller must be the current manager for `account`.
     */
    function setManager(address account, address newManager) external;

    /**
     * @dev Returns the manager for `account`.
     *
     * See {setManager}.
     */
    function getManager(address account) external view returns (address);

    /**
     * @dev Sets the `implementer` contract as ``account``'s implementer for
     * `interfaceHash`.
     *
     * `account` being the zero address is an alias for the caller's address.
     * The zero address can also be used in `implementer` to remove an old one.
     *
     * See {interfaceHash} to learn how these are created.
     *
     * Emits an {InterfaceImplementerSet} event.
     *
     * Requirements:
     *
     * - the caller must be the current manager for `account`.
     * - `interfaceHash` must not be an {IERC165} interface id (i.e. it must not
     * end in 28 zeroes).
     * - `implementer` must implement {IERC1820Implementer} and return true when
     * queried for support, unless `implementer` is the caller. See
     * {IERC1820Implementer-canImplementInterfaceForAddress}.
     */
    function setInterfaceImplementer(address account, bytes32 interfaceHash, address implementer) external;

    /**
     * @dev Returns the implementer of `interfaceHash` for `account`. If no such
     * implementer is registered, returns the zero address.
     *
     * If `interfaceHash` is an {IERC165} interface id (i.e. it ends with 28
     * zeroes), `account` will be queried for support of it.
     *
     * `account` being the zero address is an alias for the caller's address.
     */
    function getInterfaceImplementer(address account, bytes32 interfaceHash) external view returns (address);

    /**
     * @dev Returns the interface hash for an `interfaceName`, as defined in the
     * corresponding
     * https://eips.ethereum.org/EIPS/eip-1820#interface-name[section of the EIP].
     */
    function interfaceHash(string calldata interfaceName) external pure returns (bytes32);

    /**
     *  @notice Updates the cache with whether the contract implements an ERC165 interface or not.
     *  @param account Address of the contract for which to update the cache.
     *  @param interfaceId ERC165 interface for which to update the cache.
     */
    function updateERC165Cache(address account, bytes4 interfaceId) external;

    /**
     *  @notice Checks whether a contract implements an ERC165 interface or not.
     *  If the result is not cached a direct lookup on the contract address is performed.
     *  If the result is not cached or the cached value is out-of-date, the cache MUST be updated manually by calling
     *  {updateERC165Cache} with the contract address.
     *  @param account Address of the contract to check.
     *  @param interfaceId ERC165 interface to check.
     *  @return True if `account` implements `interfaceId`, false otherwise.
     */
    function implementsERC165Interface(address account, bytes4 interfaceId) external view returns (bool);

    /**
     *  @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
     *  @param account Address of the contract to check.
     *  @param interfaceId ERC165 interface to check.
     *  @return True if `account` implements `interfaceId`, false otherwise.
     */
    function implementsERC165InterfaceNoCache(address account, bytes4 interfaceId) external view returns (bool);

    event InterfaceImplementerSet(address indexed account, bytes32 indexed interfaceHash, address indexed implementer);

    event ManagerChanged(address indexed account, address indexed newManager);
}

// File: @openzeppelin/contracts/token/ERC777/IERC777Recipient.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC777TokensRecipient standard as defined in the EIP.
 *
 * Accounts can be notified of {IERC777} tokens being sent to them by having a
 * contract implement this interface (contract holders can be their own
 * implementer) and registering it on the
 * https://eips.ethereum.org/EIPS/eip-1820[ERC1820 global registry].
 *
 * See {IERC1820Registry} and {ERC1820Implementer}.
 */
interface IERC777Recipient {
    /**
     * @dev Called by an {IERC777} token contract whenever tokens are being
     * moved or created into a registered account (`to`). The type of operation
     * is conveyed by `from` being the zero address or not.
     *
     * This call occurs _after_ the token contract's state is updated, so
     * {IERC777-balanceOf}, etc., can be used to query the post-operation state.
     *
     * This function may revert to prevent the operation from being executed.
     */
    function tokensReceived(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData
    ) external;
}

// File: contracts/IWETH.sol

pragma solidity ^0.6.0;

interface IWETH {
  function deposit() external payable;
  function transfer(address to, uint value) external returns (bool);
  function withdraw(uint) external;
  function balanceOf(address who) external view returns (uint256);
  function approve(address spender, uint256 amount) external returns (bool);
  function allowance(address owner, address spender) external returns (uint256);
}

// File: contracts/AbstractOwnable.sol

pragma solidity ^0.6.0;

abstract contract AbstractOwnable {

  modifier onlyOwner() {
    require(_owner() == msg.sender, "caller is not the owner");
    _;
  }

  function _owner() internal virtual returns(address);

}

// File: contracts/Withdrawable.sol

pragma solidity >=0.4.24;




abstract contract Withdrawable is AbstractOwnable {
  using SafeERC20 for IERC20;
  address constant ETHER = address(0);

  event LogWithdrawToken(
    address indexed _from,
    address indexed _token,
    uint amount
  );

  /**
   * @dev Withdraw asset.
   * @param asset Asset to be withdrawn.
   */
  function adminWithdraw(address asset) public onlyOwner {
    uint tokenBalance = adminWithdrawAllowed(asset);
    require(tokenBalance > 0, "admin witdraw not allowed");
    _withdraw(asset, tokenBalance);
  }

  function _withdraw(address _tokenAddress, uint _amount) internal {
    if (_tokenAddress == ETHER) {
      msg.sender.transfer(_amount);
    } else {
      IERC20(_tokenAddress).safeTransfer(msg.sender, _amount);
    }
    emit LogWithdrawToken(msg.sender, _tokenAddress, _amount);
  }

  // can be overridden to disallow withdraw for some token
  function adminWithdrawAllowed(address asset) internal virtual view returns(uint allowedAmount) {
    allowedAmount = asset == ETHER
      ? address(this).balance
      : IERC20(asset).balanceOf(address(this));
  }
}

// File: contracts/PERC20OnEosVault.sol

pragma solidity ^0.6.0;








contract PERC20OnEosVault is Withdrawable, IERC777Recipient {
    using SafeERC20 for IERC20;
    using EnumerableSet for EnumerableSet.AddressSet;

    IERC1820Registry private _erc1820 = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
    bytes32 constant private TOKENS_RECIPIENT_INTERFACE_HASH = keccak256("ERC777TokensRecipient");

    EnumerableSet.AddressSet private supportedTokens;
    address public PNETWORK;
    IWETH public weth;

    event PegIn(address _tokenAddress, address _tokenSender, uint256 _tokenAmount, string _destinationAddress);

    constructor(
        address _weth,
        address [] memory _tokensToSupport
    ) public {
        PNETWORK = msg.sender;
        for (uint256 i = 0; i < _tokensToSupport.length; i++) {
            supportedTokens.add(_tokensToSupport[i]);
        }
        weth = IWETH(_weth);
        _erc1820.setInterfaceImplementer(address(this), TOKENS_RECIPIENT_INTERFACE_HASH, address(this));
    }

    modifier onlyPNetwork() {
        require(msg.sender == PNETWORK, "Caller must be PNETWORK address!");
        _;
    }

    receive() external payable {
        require(msg.sender == address(weth));
    }

    function setWeth(address _weth) external onlyPNetwork {
        weth = IWETH(_weth);
    }

    function setPNetwork(address _pnetwork) external onlyPNetwork {
        PNETWORK = _pnetwork;
    }

    function IS_TOKEN_SUPPORTED(address _token) external view returns(bool) {
        return supportedTokens.contains(_token);
    }

    function _owner() internal override returns(address) {
        return PNETWORK;
    }

    function adminWithdrawAllowed(address asset) internal override view returns(uint) {
        return supportedTokens.contains(asset) ? 0 : super.adminWithdrawAllowed(asset);
    }

    function addSupportedToken(
        address _tokenAddress
    )
        external
        onlyPNetwork
        returns (bool SUCCESS)
    {
        supportedTokens.add(_tokenAddress);
        return true;
    }

    function removeSupportedToken(
        address _tokenAddress
    )
        external
        onlyPNetwork
        returns (bool SUCCESS)
    {
        return supportedTokens.remove(_tokenAddress);
    }

    function pegIn(
        uint256 _tokenAmount,
        address _tokenAddress,
        string calldata _destinationAddress
    )
        external
        returns (bool)
    {
        require(supportedTokens.contains(_tokenAddress), "Token at supplied address is NOT supported!");
        require(_tokenAmount > 0, "Token amount must be greater than zero!");
        IERC20(_tokenAddress).safeTransferFrom(msg.sender, address(this), _tokenAmount);
        emit PegIn(_tokenAddress, msg.sender, _tokenAmount, _destinationAddress);
        return true;
    }

    /**
     * @dev Implementation of IERC777Recipient.
     */
    function tokensReceived(
        address /*operator*/,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata /*operatorData*/
    ) external override {
        address _tokenAddress = msg.sender;
        require(supportedTokens.contains(_tokenAddress), "caller is not a supported ERC777 token!");
        require(to == address(this), "Token receiver is not this contract");
        if (userData.length > 0) {
            require(amount > 0, "Token amount must be greater than zero!");
            (bytes32 tag, string memory _destinationAddress) = abi.decode(userData, (bytes32, string));
            require(tag == keccak256("ERC777-pegIn"), "Invalid tag for automatic pegIn on ERC777 send");
            emit PegIn(_tokenAddress, from, amount, _destinationAddress);
        }
    }

    function pegInEth(string calldata _destinationAddress)
        external
        payable
        returns (bool)
    {
        require(supportedTokens.contains(address(weth)), "WETH is NOT supported!");
        require(msg.value > 0, "Ethers amount must be greater than zero!");
        weth.deposit.value(msg.value)();
        emit PegIn(address(weth), msg.sender, msg.value, _destinationAddress);
        return true;
    }

    function pegOut(
        address payable _tokenRecipient,
        address _tokenAddress,
        uint256 _tokenAmount
    )
        external
        onlyPNetwork
        returns (bool)
    {
        if (_tokenAddress == address(weth)) {
            weth.withdraw(_tokenAmount);
            _tokenRecipient.transfer(_tokenAmount);
        } else {
            IERC20(_tokenAddress).safeTransfer(_tokenRecipient, _tokenAmount);
        }
        return true;
    }

    function migrate(
        address payable _to
    )
        external
        onlyPNetwork
    {
        for (uint256 i = 0; i < supportedTokens.length(); i++) {
            address tokenAddress = supportedTokens.at(i);
            _migrateSingle(_to, tokenAddress);
        }
    }

    function destroy()
        external
        onlyPNetwork
    {
        for (uint256 i = 0; i < supportedTokens.length(); i++) {
            address tokenAddress = supportedTokens.at(i);
            require(IERC20(tokenAddress).balanceOf(address(this)) == 0, "Balance of supported tokens must be 0");
        }
        selfdestruct(msg.sender);
    }

    function migrateSingle(
        address payable _to,
        address _tokenAddress
    )
        external
        onlyPNetwork
    {
        _migrateSingle(_to, _tokenAddress);
    }

    function _migrateSingle(
        address payable _to,
        address _tokenAddress
    )
        private
    {
        if (supportedTokens.contains(_tokenAddress)) {
            uint balance = IERC20(_tokenAddress).balanceOf(address(this));
            IERC20(_tokenAddress).safeTransfer(_to, balance);
            supportedTokens.remove(_tokenAddress);
        }
    }
}

// File: @openzeppelin/contracts/GSN/Context.sol

pragma solidity ^0.6.0;

/*
 * @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.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }

    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;
    }
}

// File: @openzeppelin/contracts/token/ERC777/IERC777.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC777Token standard as defined in the EIP.
 *
 * This contract uses the
 * https://eips.ethereum.org/EIPS/eip-1820[ERC1820 registry standard] to let
 * token holders and recipients react to token movements by using setting implementers
 * for the associated interfaces in said registry. See {IERC1820Registry} and
 * {ERC1820Implementer}.
 */
interface IERC777 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the smallest part of the token that is not divisible. This
     * means all token operations (creation, movement and destruction) must have
     * amounts that are a multiple of this number.
     *
     * For most token contracts, this value will equal 1.
     */
    function granularity() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

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

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * If send or receive hooks are registered for the caller and `recipient`,
     * the corresponding functions will be called with `data` and empty
     * `operatorData`. See {IERC777Sender} and {IERC777Recipient}.
     *
     * Emits a {Sent} event.
     *
     * Requirements
     *
     * - the caller must have at least `amount` tokens.
     * - `recipient` cannot be the zero address.
     * - if `recipient` is a contract, it must implement the {IERC777Recipient}
     * interface.
     */
    function send(address recipient, uint256 amount, bytes calldata data) external;

    /**
     * @dev Destroys `amount` tokens from the caller's account, reducing the
     * total supply.
     *
     * If a send hook is registered for the caller, the corresponding function
     * will be called with `data` and empty `operatorData`. See {IERC777Sender}.
     *
     * Emits a {Burned} event.
     *
     * Requirements
     *
     * - the caller must have at least `amount` tokens.
     */
    function burn(uint256 amount, bytes calldata data) external;

    /**
     * @dev Returns true if an account is an operator of `tokenHolder`.
     * Operators can send and burn tokens on behalf of their owners. All
     * accounts are their own operator.
     *
     * See {operatorSend} and {operatorBurn}.
     */
    function isOperatorFor(address operator, address tokenHolder) external view returns (bool);

    /**
     * @dev Make an account an operator of the caller.
     *
     * See {isOperatorFor}.
     *
     * Emits an {AuthorizedOperator} event.
     *
     * Requirements
     *
     * - `operator` cannot be calling address.
     */
    function authorizeOperator(address operator) external;

    /**
     * @dev Revoke an account's operator status for the caller.
     *
     * See {isOperatorFor} and {defaultOperators}.
     *
     * Emits a {RevokedOperator} event.
     *
     * Requirements
     *
     * - `operator` cannot be calling address.
     */
    function revokeOperator(address operator) external;

    /**
     * @dev Returns the list of default operators. These accounts are operators
     * for all token holders, even if {authorizeOperator} was never called on
     * them.
     *
     * This list is immutable, but individual holders may revoke these via
     * {revokeOperator}, in which case {isOperatorFor} will return false.
     */
    function defaultOperators() external view returns (address[] memory);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient`. The caller must
     * be an operator of `sender`.
     *
     * If send or receive hooks are registered for `sender` and `recipient`,
     * the corresponding functions will be called with `data` and
     * `operatorData`. See {IERC777Sender} and {IERC777Recipient}.
     *
     * Emits a {Sent} event.
     *
     * Requirements
     *
     * - `sender` cannot be the zero address.
     * - `sender` must have at least `amount` tokens.
     * - the caller must be an operator for `sender`.
     * - `recipient` cannot be the zero address.
     * - if `recipient` is a contract, it must implement the {IERC777Recipient}
     * interface.
     */
    function operatorSend(
        address sender,
        address recipient,
        uint256 amount,
        bytes calldata data,
        bytes calldata operatorData
    ) external;

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the total supply.
     * The caller must be an operator of `account`.
     *
     * If a send hook is registered for `account`, the corresponding function
     * will be called with `data` and `operatorData`. See {IERC777Sender}.
     *
     * Emits a {Burned} event.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     * - the caller must be an operator for `account`.
     */
    function operatorBurn(
        address account,
        uint256 amount,
        bytes calldata data,
        bytes calldata operatorData
    ) external;

    event Sent(
        address indexed operator,
        address indexed from,
        address indexed to,
        uint256 amount,
        bytes data,
        bytes operatorData
    );

    event Minted(address indexed operator, address indexed to, uint256 amount, bytes data, bytes operatorData);

    event Burned(address indexed operator, address indexed from, uint256 amount, bytes data, bytes operatorData);

    event AuthorizedOperator(address indexed operator, address indexed tokenHolder);

    event RevokedOperator(address indexed operator, address indexed tokenHolder);
}

// File: @openzeppelin/contracts/token/ERC777/IERC777Recipient.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC777TokensRecipient standard as defined in the EIP.
 *
 * Accounts can be notified of {IERC777} tokens being sent to them by having a
 * contract implement this interface (contract holders can be their own
 * implementer) and registering it on the
 * https://eips.ethereum.org/EIPS/eip-1820[ERC1820 global registry].
 *
 * See {IERC1820Registry} and {ERC1820Implementer}.
 */
interface IERC777Recipient {
    /**
     * @dev Called by an {IERC777} token contract whenever tokens are being
     * moved or created into a registered account (`to`). The type of operation
     * is conveyed by `from` being the zero address or not.
     *
     * This call occurs _after_ the token contract's state is updated, so
     * {IERC777-balanceOf}, etc., can be used to query the post-operation state.
     *
     * This function may revert to prevent the operation from being executed.
     */
    function tokensReceived(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData
    ) external;
}

// File: @openzeppelin/contracts/token/ERC777/IERC777Sender.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC777TokensSender standard as defined in the EIP.
 *
 * {IERC777} Token holders can be notified of operations performed on their
 * tokens by having a contract implement this interface (contract holders can be
 *  their own implementer) and registering it on the
 * https://eips.ethereum.org/EIPS/eip-1820[ERC1820 global registry].
 *
 * See {IERC1820Registry} and {ERC1820Implementer}.
 */
interface IERC777Sender {
    /**
     * @dev Called by an {IERC777} token contract whenever a registered holder's
     * (`from`) tokens are about to be moved or destroyed. The type of operation
     * is conveyed by `to` being the zero address or not.
     *
     * This call occurs _before_ the token contract's state is updated, so
     * {IERC777-balanceOf}, etc., can be used to query the pre-operation state.
     *
     * This function may revert to prevent the operation from being executed.
     */
    function tokensToSend(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData
    ) external;
}

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

pragma solidity ^0.6.0;

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

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

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

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

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

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

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

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

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

pragma solidity ^0.6.0;

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

        return c;
    }

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

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

        return c;
    }

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

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

        return c;
    }

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

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

        return c;
    }

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

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

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

pragma solidity ^0.6.2;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

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

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

// File: @openzeppelin/contracts/introspection/IERC1820Registry.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the global ERC1820 Registry, as defined in the
 * https://eips.ethereum.org/EIPS/eip-1820[EIP]. Accounts may register
 * implementers for interfaces in this registry, as well as query support.
 *
 * Implementers may be shared by multiple accounts, and can also implement more
 * than a single interface for each account. Contracts can implement interfaces
 * for themselves, but externally-owned accounts (EOA) must delegate this to a
 * contract.
 *
 * {IERC165} interfaces can also be queried via the registry.
 *
 * For an in-depth explanation and source code analysis, see the EIP text.
 */
interface IERC1820Registry {
    /**
     * @dev Sets `newManager` as the manager for `account`. A manager of an
     * account is able to set interface implementers for it.
     *
     * By default, each account is its own manager. Passing a value of `0x0` in
     * `newManager` will reset the manager to this initial state.
     *
     * Emits a {ManagerChanged} event.
     *
     * Requirements:
     *
     * - the caller must be the current manager for `account`.
     */
    function setManager(address account, address newManager) external;

    /**
     * @dev Returns the manager for `account`.
     *
     * See {setManager}.
     */
    function getManager(address account) external view returns (address);

    /**
     * @dev Sets the `implementer` contract as ``account``'s implementer for
     * `interfaceHash`.
     *
     * `account` being the zero address is an alias for the caller's address.
     * The zero address can also be used in `implementer` to remove an old one.
     *
     * See {interfaceHash} to learn how these are created.
     *
     * Emits an {InterfaceImplementerSet} event.
     *
     * Requirements:
     *
     * - the caller must be the current manager for `account`.
     * - `interfaceHash` must not be an {IERC165} interface id (i.e. it must not
     * end in 28 zeroes).
     * - `implementer` must implement {IERC1820Implementer} and return true when
     * queried for support, unless `implementer` is the caller. See
     * {IERC1820Implementer-canImplementInterfaceForAddress}.
     */
    function setInterfaceImplementer(address account, bytes32 interfaceHash, address implementer) external;

    /**
     * @dev Returns the implementer of `interfaceHash` for `account`. If no such
     * implementer is registered, returns the zero address.
     *
     * If `interfaceHash` is an {IERC165} interface id (i.e. it ends with 28
     * zeroes), `account` will be queried for support of it.
     *
     * `account` being the zero address is an alias for the caller's address.
     */
    function getInterfaceImplementer(address account, bytes32 interfaceHash) external view returns (address);

    /**
     * @dev Returns the interface hash for an `interfaceName`, as defined in the
     * corresponding
     * https://eips.ethereum.org/EIPS/eip-1820#interface-name[section of the EIP].
     */
    function interfaceHash(string calldata interfaceName) external pure returns (bytes32);

    /**
     *  @notice Updates the cache with whether the contract implements an ERC165 interface or not.
     *  @param account Address of the contract for which to update the cache.
     *  @param interfaceId ERC165 interface for which to update the cache.
     */
    function updateERC165Cache(address account, bytes4 interfaceId) external;

    /**
     *  @notice Checks whether a contract implements an ERC165 interface or not.
     *  If the result is not cached a direct lookup on the contract address is performed.
     *  If the result is not cached or the cached value is out-of-date, the cache MUST be updated manually by calling
     *  {updateERC165Cache} with the contract address.
     *  @param account Address of the contract to check.
     *  @param interfaceId ERC165 interface to check.
     *  @return True if `account` implements `interfaceId`, false otherwise.
     */
    function implementsERC165Interface(address account, bytes4 interfaceId) external view returns (bool);

    /**
     *  @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
     *  @param account Address of the contract to check.
     *  @param interfaceId ERC165 interface to check.
     *  @return True if `account` implements `interfaceId`, false otherwise.
     */
    function implementsERC165InterfaceNoCache(address account, bytes4 interfaceId) external view returns (bool);

    event InterfaceImplementerSet(address indexed account, bytes32 indexed interfaceHash, address indexed implementer);

    event ManagerChanged(address indexed account, address indexed newManager);
}

// File: @openzeppelin/contracts/token/ERC777/ERC777.sol

pragma solidity ^0.6.0;









/**
 * @dev Implementation of the {IERC777} 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}.
 *
 * Support for ERC20 is included in this contract, as specified by the EIP: both
 * the ERC777 and ERC20 interfaces can be safely used when interacting with it.
 * Both {IERC777-Sent} and {IERC20-Transfer} events are emitted on token
 * movements.
 *
 * Additionally, the {IERC777-granularity} value is hard-coded to `1`, meaning that there
 * are no special restrictions in the amount of tokens that created, moved, or
 * destroyed. This makes integration with ERC20 applications seamless.
 */
contract ERC777 is Context, IERC777, IERC20 {
    using SafeMath for uint256;
    using Address for address;

    IERC1820Registry constant internal _ERC1820_REGISTRY = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);

    mapping(address => uint256) private _balances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    // We inline the result of the following hashes because Solidity doesn't resolve them at compile time.
    // See https://github.com/ethereum/solidity/issues/4024.

    // keccak256("ERC777TokensSender")
    bytes32 constant private _TOKENS_SENDER_INTERFACE_HASH =
        0x29ddb589b1fb5fc7cf394961c1adf5f8c6454761adf795e67fe149f658abe895;

    // keccak256("ERC777TokensRecipient")
    bytes32 constant private _TOKENS_RECIPIENT_INTERFACE_HASH =
        0xb281fc8c12954d22544db45de3159a39272895b169a852b314f9cc762e44c53b;

    // This isn't ever read from - it's only used to respond to the defaultOperators query.
    address[] private _defaultOperatorsArray;

    // Immutable, but accounts may revoke them (tracked in __revokedDefaultOperators).
    mapping(address => bool) private _defaultOperators;

    // For each account, a mapping of its operators and revoked default operators.
    mapping(address => mapping(address => bool)) private _operators;
    mapping(address => mapping(address => bool)) private _revokedDefaultOperators;

    // ERC20-allowances
    mapping (address => mapping (address => uint256)) private _allowances;

    /**
     * @dev `defaultOperators` may be an empty array.
     */
    constructor(
        string memory name,
        string memory symbol,
        address[] memory defaultOperators
    ) public {
        _name = name;
        _symbol = symbol;

        _defaultOperatorsArray = defaultOperators;
        for (uint256 i = 0; i < _defaultOperatorsArray.length; i++) {
            _defaultOperators[_defaultOperatorsArray[i]] = true;
        }

        // register interfaces
        _ERC1820_REGISTRY.setInterfaceImplementer(address(this), keccak256("ERC777Token"), address(this));
        _ERC1820_REGISTRY.setInterfaceImplementer(address(this), keccak256("ERC20Token"), address(this));
    }

    /**
     * @dev See {IERC777-name}.
     */
    function name() public view override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IERC777-symbol}.
     */
    function symbol() public view override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev See {ERC20-decimals}.
     *
     * Always returns 18, as per the
     * [ERC777 EIP](https://eips.ethereum.org/EIPS/eip-777#backward-compatibility).
     */
    function decimals() public pure returns (uint8) {
        return 18;
    }

    /**
     * @dev See {IERC777-granularity}.
     *
     * This implementation always returns `1`.
     */
    function granularity() public view override returns (uint256) {
        return 1;
    }

    /**
     * @dev See {IERC777-totalSupply}.
     */
    function totalSupply() public view override(IERC20, IERC777) returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev Returns the amount of tokens owned by an account (`tokenHolder`).
     */
    function balanceOf(address tokenHolder) public view override(IERC20, IERC777) returns (uint256) {
        return _balances[tokenHolder];
    }

    /**
     * @dev See {IERC777-send}.
     *
     * Also emits a {IERC20-Transfer} event for ERC20 compatibility.
     */
    function send(address recipient, uint256 amount, bytes memory data) public override  {
        _send(_msgSender(), recipient, amount, data, "", true);
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Unlike `send`, `recipient` is _not_ required to implement the {IERC777Recipient}
     * interface if it is a contract.
     *
     * Also emits a {Sent} event.
     */
    function transfer(address recipient, uint256 amount) public override returns (bool) {
        require(recipient != address(0), "ERC777: transfer to the zero address");

        address from = _msgSender();

        _callTokensToSend(from, from, recipient, amount, "", "");

        _move(from, from, recipient, amount, "", "");

        _callTokensReceived(from, from, recipient, amount, "", "", false);

        return true;
    }

    /**
     * @dev See {IERC777-burn}.
     *
     * Also emits a {IERC20-Transfer} event for ERC20 compatibility.
     */
    function burn(uint256 amount, bytes memory data) public override  {
        _burn(_msgSender(), amount, data, "");
    }

    /**
     * @dev See {IERC777-isOperatorFor}.
     */
    function isOperatorFor(
        address operator,
        address tokenHolder
    ) public view override returns (bool) {
        return operator == tokenHolder ||
            (_defaultOperators[operator] && !_revokedDefaultOperators[tokenHolder][operator]) ||
            _operators[tokenHolder][operator];
    }

    /**
     * @dev See {IERC777-authorizeOperator}.
     */
    function authorizeOperator(address operator) public override  {
        require(_msgSender() != operator, "ERC777: authorizing self as operator");

        if (_defaultOperators[operator]) {
            delete _revokedDefaultOperators[_msgSender()][operator];
        } else {
            _operators[_msgSender()][operator] = true;
        }

        emit AuthorizedOperator(operator, _msgSender());
    }

    /**
     * @dev See {IERC777-revokeOperator}.
     */
    function revokeOperator(address operator) public override  {
        require(operator != _msgSender(), "ERC777: revoking self as operator");

        if (_defaultOperators[operator]) {
            _revokedDefaultOperators[_msgSender()][operator] = true;
        } else {
            delete _operators[_msgSender()][operator];
        }

        emit RevokedOperator(operator, _msgSender());
    }

    /**
     * @dev See {IERC777-defaultOperators}.
     */
    function defaultOperators() public view override returns (address[] memory) {
        return _defaultOperatorsArray;
    }

    /**
     * @dev See {IERC777-operatorSend}.
     *
     * Emits {Sent} and {IERC20-Transfer} events.
     */
    function operatorSend(
        address sender,
        address recipient,
        uint256 amount,
        bytes memory data,
        bytes memory operatorData
    )
    public override
    {
        require(isOperatorFor(_msgSender(), sender), "ERC777: caller is not an operator for holder");
        _send(sender, recipient, amount, data, operatorData, true);
    }

    /**
     * @dev See {IERC777-operatorBurn}.
     *
     * Emits {Burned} and {IERC20-Transfer} events.
     */
    function operatorBurn(address account, uint256 amount, bytes memory data, bytes memory operatorData) public override {
        require(isOperatorFor(_msgSender(), account), "ERC777: caller is not an operator for holder");
        _burn(account, amount, data, operatorData);
    }

    /**
     * @dev See {IERC20-allowance}.
     *
     * Note that operator and allowance concepts are orthogonal: operators may
     * not have allowance, and accounts with allowance may not be operators
     * themselves.
     */
    function allowance(address holder, address spender) public view override returns (uint256) {
        return _allowances[holder][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Note that accounts cannot have allowance issued by their operators.
     */
    function approve(address spender, uint256 value) public override returns (bool) {
        address holder = _msgSender();
        _approve(holder, spender, value);
        return true;
    }

   /**
    * @dev See {IERC20-transferFrom}.
    *
    * Note that operator and allowance concepts are orthogonal: operators cannot
    * call `transferFrom` (unless they have allowance), and accounts with
    * allowance cannot call `operatorSend` (unless they are operators).
    *
    * Emits {Sent}, {IERC20-Transfer} and {IERC20-Approval} events.
    */
    function transferFrom(address holder, address recipient, uint256 amount) public override returns (bool) {
        require(recipient != address(0), "ERC777: transfer to the zero address");
        require(holder != address(0), "ERC777: transfer from the zero address");

        address spender = _msgSender();

        _callTokensToSend(spender, holder, recipient, amount, "", "");

        _move(spender, holder, recipient, amount, "", "");
        _approve(holder, spender, _allowances[holder][spender].sub(amount, "ERC777: transfer amount exceeds allowance"));

        _callTokensReceived(spender, holder, recipient, amount, "", "", false);

        return true;
    }

    /**
     * @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * If a send hook is registered for `account`, the corresponding function
     * will be called with `operator`, `data` and `operatorData`.
     *
     * See {IERC777Sender} and {IERC777Recipient}.
     *
     * Emits {Minted} and {IERC20-Transfer} events.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - if `account` is a contract, it must implement the {IERC777Recipient}
     * interface.
     */
    function _mint(
        address account,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData
    )
    internal virtual
    {
        require(account != address(0), "ERC777: mint to the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, address(0), account, amount);

        // Update state variables
        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);

        _callTokensReceived(operator, address(0), account, amount, userData, operatorData, true);

        emit Minted(operator, account, amount, userData, operatorData);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Send tokens
     * @param from address token holder address
     * @param to address recipient address
     * @param amount uint256 amount of tokens to transfer
     * @param userData bytes extra information provided by the token holder (if any)
     * @param operatorData bytes extra information provided by the operator (if any)
     * @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
     */
    function _send(
        address from,
        address to,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData,
        bool requireReceptionAck
    )
        internal
    {
        require(from != address(0), "ERC777: send from the zero address");
        require(to != address(0), "ERC777: send to the zero address");

        address operator = _msgSender();

        _callTokensToSend(operator, from, to, amount, userData, operatorData);

        _move(operator, from, to, amount, userData, operatorData);

        _callTokensReceived(operator, from, to, amount, userData, operatorData, requireReceptionAck);
    }

    /**
     * @dev Burn tokens
     * @param from address token holder address
     * @param amount uint256 amount of tokens to burn
     * @param data bytes extra information provided by the token holder
     * @param operatorData bytes extra information provided by the operator (if any)
     */
    function _burn(
        address from,
        uint256 amount,
        bytes memory data,
        bytes memory operatorData
    )
        internal virtual
    {
        require(from != address(0), "ERC777: burn from the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, from, address(0), amount);

        _callTokensToSend(operator, from, address(0), amount, data, operatorData);

        // Update state variables
        _balances[from] = _balances[from].sub(amount, "ERC777: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);

        emit Burned(operator, from, amount, data, operatorData);
        emit Transfer(from, address(0), amount);
    }

    function _move(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData
    )
        private
    {
        _beforeTokenTransfer(operator, from, to, amount);

        _balances[from] = _balances[from].sub(amount, "ERC777: transfer amount exceeds balance");
        _balances[to] = _balances[to].add(amount);

        emit Sent(operator, from, to, amount, userData, operatorData);
        emit Transfer(from, to, amount);
    }

    /**
     * @dev See {ERC20-_approve}.
     *
     * Note that accounts cannot have allowance issued by their operators.
     */
    function _approve(address holder, address spender, uint256 value) internal {
        require(holder != address(0), "ERC777: approve from the zero address");
        require(spender != address(0), "ERC777: approve to the zero address");

        _allowances[holder][spender] = value;
        emit Approval(holder, spender, value);
    }

    /**
     * @dev Call from.tokensToSend() if the interface is registered
     * @param operator address operator requesting the transfer
     * @param from address token holder address
     * @param to address recipient address
     * @param amount uint256 amount of tokens to transfer
     * @param userData bytes extra information provided by the token holder (if any)
     * @param operatorData bytes extra information provided by the operator (if any)
     */
    function _callTokensToSend(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData
    )
        private
    {
        address implementer = _ERC1820_REGISTRY.getInterfaceImplementer(from, _TOKENS_SENDER_INTERFACE_HASH);
        if (implementer != address(0)) {
            IERC777Sender(implementer).tokensToSend(operator, from, to, amount, userData, operatorData);
        }
    }

    /**
     * @dev Call to.tokensReceived() if the interface is registered. Reverts if the recipient is a contract but
     * tokensReceived() was not registered for the recipient
     * @param operator address operator requesting the transfer
     * @param from address token holder address
     * @param to address recipient address
     * @param amount uint256 amount of tokens to transfer
     * @param userData bytes extra information provided by the token holder (if any)
     * @param operatorData bytes extra information provided by the operator (if any)
     * @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
     */
    function _callTokensReceived(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData,
        bool requireReceptionAck
    )
        private
    {
        address implementer = _ERC1820_REGISTRY.getInterfaceImplementer(to, _TOKENS_RECIPIENT_INTERFACE_HASH);
        if (implementer != address(0)) {
            IERC777Recipient(implementer).tokensReceived(operator, from, to, amount, userData, operatorData);
        } else if (requireReceptionAck) {
            require(!to.isContract(), "ERC777: token recipient contract has no implementer for ERC777TokensRecipient");
        }
    }

    /**
     * @dev Hook that is called before any token transfer. This includes
     * calls to {send}, {transfer}, {operatorSend}, minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, ``from``'s `tokenId` will be
     * transferred to `to`.
     * - when `from` is zero, `tokenId` will be minted for `to`.
     * - when `to` is zero, ``from``'s `tokenId` 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 operator, address from, address to, uint256 tokenId) internal virtual { }
}

// File: @openzeppelin/contracts/access/Ownable.sol

pragma solidity ^0.6.0;

/**
 * @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.
 */
contract Ownable is Context {
    address private _owner;

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view 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;
    }
}

// File: @openzeppelin/contracts/GSN/IRelayRecipient.sol

pragma solidity ^0.6.0;

/**
 * @dev Base interface for a contract that will be called via the GSN from {IRelayHub}.
 *
 * TIP: You don't need to write an implementation yourself! Inherit from {GSNRecipient} instead.
 */
interface IRelayRecipient {
    /**
     * @dev Returns the address of the {IRelayHub} instance this recipient interacts with.
     */
    function getHubAddr() external view returns (address);

    /**
     * @dev Called by {IRelayHub} to validate if this recipient accepts being charged for a relayed call. Note that the
     * recipient will be charged regardless of the execution result of the relayed call (i.e. if it reverts or not).
     *
     * The relay request was originated by `from` and will be served by `relay`. `encodedFunction` is the relayed call
     * calldata, so its first four bytes are the function selector. The relayed call will be forwarded `gasLimit` gas,
     * and the transaction executed with a gas price of at least `gasPrice`. ``relay``'s fee is `transactionFee`, and the
     * recipient will be charged at most `maxPossibleCharge` (in wei). `nonce` is the sender's (`from`) nonce for
     * replay attack protection in {IRelayHub}, and `approvalData` is a optional parameter that can be used to hold a signature
     * over all or some of the previous values.
     *
     * Returns a tuple, where the first value is used to indicate approval (0) or rejection (custom non-zero error code,
     * values 1 to 10 are reserved) and the second one is data to be passed to the other {IRelayRecipient} functions.
     *
     * {acceptRelayedCall} is called with 50k gas: if it runs out during execution, the request will be considered
     * rejected. A regular revert will also trigger a rejection.
     */
    function acceptRelayedCall(
        address relay,
        address from,
        bytes calldata encodedFunction,
        uint256 transactionFee,
        uint256 gasPrice,
        uint256 gasLimit,
        uint256 nonce,
        bytes calldata approvalData,
        uint256 maxPossibleCharge
    )
        external
        view
        returns (uint256, bytes memory);

    /**
     * @dev Called by {IRelayHub} on approved relay call requests, before the relayed call is executed. This allows to e.g.
     * pre-charge the sender of the transaction.
     *
     * `context` is the second value returned in the tuple by {acceptRelayedCall}.
     *
     * Returns a value to be passed to {postRelayedCall}.
     *
     * {preRelayedCall} is called with 100k gas: if it runs out during exection or otherwise reverts, the relayed call
     * will not be executed, but the recipient will still be charged for the transaction's cost.
     */
    function preRelayedCall(bytes calldata context) external returns (bytes32);

    /**
     * @dev Called by {IRelayHub} on approved relay call requests, after the relayed call is executed. This allows to e.g.
     * charge the user for the relayed call costs, return any overcharges from {preRelayedCall}, or perform
     * contract-specific bookkeeping.
     *
     * `context` is the second value returned in the tuple by {acceptRelayedCall}. `success` is the execution status of
     * the relayed call. `actualCharge` is an estimate of how much the recipient will be charged for the transaction,
     * not including any gas used by {postRelayedCall} itself. `preRetVal` is {preRelayedCall}'s return value.
     *
     *
     * {postRelayedCall} is called with 100k gas: if it runs out during execution or otherwise reverts, the relayed call
     * and the call to {preRelayedCall} will be reverted retroactively, but the recipient will still be charged for the
     * transaction's cost.
     */
    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external;
}

// File: @openzeppelin/contracts/GSN/IRelayHub.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface for `RelayHub`, the core contract of the GSN. Users should not need to interact with this contract
 * directly.
 *
 * See the https://github.com/OpenZeppelin/openzeppelin-gsn-helpers[OpenZeppelin GSN helpers] for more information on
 * how to deploy an instance of `RelayHub` on your local test network.
 */
interface IRelayHub {
    // Relay management

    /**
     * @dev Adds stake to a relay and sets its `unstakeDelay`. If the relay does not exist, it is created, and the caller
     * of this function becomes its owner. If the relay already exists, only the owner can call this function. A relay
     * cannot be its own owner.
     *
     * All Ether in this function call will be added to the relay's stake.
     * Its unstake delay will be assigned to `unstakeDelay`, but the new value must be greater or equal to the current one.
     *
     * Emits a {Staked} event.
     */
    function stake(address relayaddr, uint256 unstakeDelay) external payable;

    /**
     * @dev Emitted when a relay's stake or unstakeDelay are increased
     */
    event Staked(address indexed relay, uint256 stake, uint256 unstakeDelay);

    /**
     * @dev Registers the caller as a relay.
     * The relay must be staked for, and not be a contract (i.e. this function must be called directly from an EOA).
     *
     * This function can be called multiple times, emitting new {RelayAdded} events. Note that the received
     * `transactionFee` is not enforced by {relayCall}.
     *
     * Emits a {RelayAdded} event.
     */
    function registerRelay(uint256 transactionFee, string calldata url) external;

    /**
     * @dev Emitted when a relay is registered or re-registerd. Looking at these events (and filtering out
     * {RelayRemoved} events) lets a client discover the list of available relays.
     */
    event RelayAdded(address indexed relay, address indexed owner, uint256 transactionFee, uint256 stake, uint256 unstakeDelay, string url);

    /**
     * @dev Removes (deregisters) a relay. Unregistered (but staked for) relays can also be removed.
     *
     * Can only be called by the owner of the relay. After the relay's `unstakeDelay` has elapsed, {unstake} will be
     * callable.
     *
     * Emits a {RelayRemoved} event.
     */
    function removeRelayByOwner(address relay) external;

    /**
     * @dev Emitted when a relay is removed (deregistered). `unstakeTime` is the time when unstake will be callable.
     */
    event RelayRemoved(address indexed relay, uint256 unstakeTime);

    /** Deletes the relay from the system, and gives back its stake to the owner.
     *
     * Can only be called by the relay owner, after `unstakeDelay` has elapsed since {removeRelayByOwner} was called.
     *
     * Emits an {Unstaked} event.
     */
    function unstake(address relay) external;

    /**
     * @dev Emitted when a relay is unstaked for, including the returned stake.
     */
    event Unstaked(address indexed relay, uint256 stake);

    // States a relay can be in
    enum RelayState {
        Unknown, // The relay is unknown to the system: it has never been staked for
        Staked, // The relay has been staked for, but it is not yet active
        Registered, // The relay has registered itself, and is active (can relay calls)
        Removed    // The relay has been removed by its owner and can no longer relay calls. It must wait for its unstakeDelay to elapse before it can unstake
    }

    /**
     * @dev Returns a relay's status. Note that relays can be deleted when unstaked or penalized, causing this function
     * to return an empty entry.
     */
    function getRelay(address relay) external view returns (uint256 totalStake, uint256 unstakeDelay, uint256 unstakeTime, address payable owner, RelayState state);

    // Balance management

    /**
     * @dev Deposits Ether for a contract, so that it can receive (and pay for) relayed transactions.
     *
     * Unused balance can only be withdrawn by the contract itself, by calling {withdraw}.
     *
     * Emits a {Deposited} event.
     */
    function depositFor(address target) external payable;

    /**
     * @dev Emitted when {depositFor} is called, including the amount and account that was funded.
     */
    event Deposited(address indexed recipient, address indexed from, uint256 amount);

    /**
     * @dev Returns an account's deposits. These can be either a contracts's funds, or a relay owner's revenue.
     */
    function balanceOf(address target) external view returns (uint256);

    /**
     * Withdraws from an account's balance, sending it back to it. Relay owners call this to retrieve their revenue, and
     * contracts can use it to reduce their funding.
     *
     * Emits a {Withdrawn} event.
     */
    function withdraw(uint256 amount, address payable dest) external;

    /**
     * @dev Emitted when an account withdraws funds from `RelayHub`.
     */
    event Withdrawn(address indexed account, address indexed dest, uint256 amount);

    // Relaying

    /**
     * @dev Checks if the `RelayHub` will accept a relayed operation.
     * Multiple things must be true for this to happen:
     *  - all arguments must be signed for by the sender (`from`)
     *  - the sender's nonce must be the current one
     *  - the recipient must accept this transaction (via {acceptRelayedCall})
     *
     * Returns a `PreconditionCheck` value (`OK` when the transaction can be relayed), or a recipient-specific error
     * code if it returns one in {acceptRelayedCall}.
     */
    function canRelay(
        address relay,
        address from,
        address to,
        bytes calldata encodedFunction,
        uint256 transactionFee,
        uint256 gasPrice,
        uint256 gasLimit,
        uint256 nonce,
        bytes calldata signature,
        bytes calldata approvalData
    ) external view returns (uint256 status, bytes memory recipientContext);

    // Preconditions for relaying, checked by canRelay and returned as the corresponding numeric values.
    enum PreconditionCheck {
        OK,                         // All checks passed, the call can be relayed
        WrongSignature,             // The transaction to relay is not signed by requested sender
        WrongNonce,                 // The provided nonce has already been used by the sender
        AcceptRelayedCallReverted,  // The recipient rejected this call via acceptRelayedCall
        InvalidRecipientStatusCode  // The recipient returned an invalid (reserved) status code
    }

    /**
     * @dev Relays a transaction.
     *
     * For this to succeed, multiple conditions must be met:
     *  - {canRelay} must `return PreconditionCheck.OK`
     *  - the sender must be a registered relay
     *  - the transaction's gas price must be larger or equal to the one that was requested by the sender
     *  - the transaction must have enough gas to not run out of gas if all internal transactions (calls to the
     * recipient) use all gas available to them
     *  - the recipient must have enough balance to pay the relay for the worst-case scenario (i.e. when all gas is
     * spent)
     *
     * If all conditions are met, the call will be relayed and the recipient charged. {preRelayedCall}, the encoded
     * function and {postRelayedCall} will be called in that order.
     *
     * Parameters:
     *  - `from`: the client originating the request
     *  - `to`: the target {IRelayRecipient} contract
     *  - `encodedFunction`: the function call to relay, including data
     *  - `transactionFee`: fee (%) the relay takes over actual gas cost
     *  - `gasPrice`: gas price the client is willing to pay
     *  - `gasLimit`: gas to forward when calling the encoded function
     *  - `nonce`: client's nonce
     *  - `signature`: client's signature over all previous params, plus the relay and RelayHub addresses
     *  - `approvalData`: dapp-specific data forwared to {acceptRelayedCall}. This value is *not* verified by the
     * `RelayHub`, but it still can be used for e.g. a signature.
     *
     * Emits a {TransactionRelayed} event.
     */
    function relayCall(
        address from,
        address to,
        bytes calldata encodedFunction,
        uint256 transactionFee,
        uint256 gasPrice,
        uint256 gasLimit,
        uint256 nonce,
        bytes calldata signature,
        bytes calldata approvalData
    ) external;

    /**
     * @dev Emitted when an attempt to relay a call failed.
     *
     * This can happen due to incorrect {relayCall} arguments, or the recipient not accepting the relayed call. The
     * actual relayed call was not executed, and the recipient not charged.
     *
     * The `reason` parameter contains an error code: values 1-10 correspond to `PreconditionCheck` entries, and values
     * over 10 are custom recipient error codes returned from {acceptRelayedCall}.
     */
    event CanRelayFailed(address indexed relay, address indexed from, address indexed to, bytes4 selector, uint256 reason);

    /**
     * @dev Emitted when a transaction is relayed.
     * Useful when monitoring a relay's operation and relayed calls to a contract
     *
     * Note that the actual encoded function might be reverted: this is indicated in the `status` parameter.
     *
     * `charge` is the Ether value deducted from the recipient's balance, paid to the relay's owner.
     */
    event TransactionRelayed(address indexed relay, address indexed from, address indexed to, bytes4 selector, RelayCallStatus status, uint256 charge);

    // Reason error codes for the TransactionRelayed event
    enum RelayCallStatus {
        OK,                      // The transaction was successfully relayed and execution successful - never included in the event
        RelayedCallFailed,       // The transaction was relayed, but the relayed call failed
        PreRelayedFailed,        // The transaction was not relayed due to preRelatedCall reverting
        PostRelayedFailed,       // The transaction was relayed and reverted due to postRelatedCall reverting
        RecipientBalanceChanged  // The transaction was relayed and reverted due to the recipient's balance changing
    }

    /**
     * @dev Returns how much gas should be forwarded to a call to {relayCall}, in order to relay a transaction that will
     * spend up to `relayedCallStipend` gas.
     */
    function requiredGas(uint256 relayedCallStipend) external view returns (uint256);

    /**
     * @dev Returns the maximum recipient charge, given the amount of gas forwarded, gas price and relay fee.
     */
    function maxPossibleCharge(uint256 relayedCallStipend, uint256 gasPrice, uint256 transactionFee) external view returns (uint256);

     // Relay penalization.
     // Any account can penalize relays, removing them from the system immediately, and rewarding the
    // reporter with half of the relay's stake. The other half is burned so that, even if the relay penalizes itself, it
    // still loses half of its stake.

    /**
     * @dev Penalize a relay that signed two transactions using the same nonce (making only the first one valid) and
     * different data (gas price, gas limit, etc. may be different).
     *
     * The (unsigned) transaction data and signature for both transactions must be provided.
     */
    function penalizeRepeatedNonce(bytes calldata unsignedTx1, bytes calldata signature1, bytes calldata unsignedTx2, bytes calldata signature2) external;

    /**
     * @dev Penalize a relay that sent a transaction that didn't target ``RelayHub``'s {registerRelay} or {relayCall}.
     */
    function penalizeIllegalTransaction(bytes calldata unsignedTx, bytes calldata signature) external;

    /**
     * @dev Emitted when a relay is penalized.
     */
    event Penalized(address indexed relay, address sender, uint256 amount);

    /**
     * @dev Returns an account's nonce in `RelayHub`.
     */
    function getNonce(address from) external view returns (uint256);
}

// File: @openzeppelin/contracts/GSN/GSNRecipient.sol

pragma solidity ^0.6.0;




/**
 * @dev Base GSN recipient contract: includes the {IRelayRecipient} interface
 * and enables GSN support on all contracts in the inheritance tree.
 *
 * TIP: This contract is abstract. The functions {IRelayRecipient-acceptRelayedCall},
 *  {_preRelayedCall}, and {_postRelayedCall} are not implemented and must be
 * provided by derived contracts. See the
 * xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategies] for more
 * information on how to use the pre-built {GSNRecipientSignature} and
 * {GSNRecipientERC20Fee}, or how to write your own.
 */
abstract contract GSNRecipient is IRelayRecipient, Context {
    // Default RelayHub address, deployed on mainnet and all testnets at the same address
    address private _relayHub = 0xD216153c06E857cD7f72665E0aF1d7D82172F494;

    uint256 constant private _RELAYED_CALL_ACCEPTED = 0;
    uint256 constant private _RELAYED_CALL_REJECTED = 11;

    // How much gas is forwarded to postRelayedCall
    uint256 constant internal _POST_RELAYED_CALL_MAX_GAS = 100000;

    /**
     * @dev Emitted when a contract changes its {IRelayHub} contract to a new one.
     */
    event RelayHubChanged(address indexed oldRelayHub, address indexed newRelayHub);

    /**
     * @dev Returns the address of the {IRelayHub} contract for this recipient.
     */
    function getHubAddr() public view override returns (address) {
        return _relayHub;
    }

    /**
     * @dev Switches to a new {IRelayHub} instance. This method is added for future-proofing: there's no reason to not
     * use the default instance.
     *
     * IMPORTANT: After upgrading, the {GSNRecipient} will no longer be able to receive relayed calls from the old
     * {IRelayHub} instance. Additionally, all funds should be previously withdrawn via {_withdrawDeposits}.
     */
    function _upgradeRelayHub(address newRelayHub) internal virtual {
        address currentRelayHub = _relayHub;
        require(newRelayHub != address(0), "GSNRecipient: new RelayHub is the zero address");
        require(newRelayHub != currentRelayHub, "GSNRecipient: new RelayHub is the current one");

        emit RelayHubChanged(currentRelayHub, newRelayHub);

        _relayHub = newRelayHub;
    }

    /**
     * @dev Returns the version string of the {IRelayHub} for which this recipient implementation was built. If
     * {_upgradeRelayHub} is used, the new {IRelayHub} instance should be compatible with this version.
     */
    // This function is view for future-proofing, it may require reading from
    // storage in the future.
    function relayHubVersion() public view returns (string memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return "1.0.0";
    }

    /**
     * @dev Withdraws the recipient's deposits in `RelayHub`.
     *
     * Derived contracts should expose this in an external interface with proper access control.
     */
    function _withdrawDeposits(uint256 amount, address payable payee) internal virtual {
        IRelayHub(_relayHub).withdraw(amount, payee);
    }

    // Overrides for Context's functions: when called from RelayHub, sender and
    // data require some pre-processing: the actual sender is stored at the end
    // of the call data, which in turns means it needs to be removed from it
    // when handling said data.

    /**
     * @dev Replacement for msg.sender. Returns the actual sender of a transaction: msg.sender for regular transactions,
     * and the end-user for GSN relayed calls (where msg.sender is actually `RelayHub`).
     *
     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.sender`, and use {_msgSender} instead.
     */
    function _msgSender() internal view virtual override returns (address payable) {
        if (msg.sender != _relayHub) {
            return msg.sender;
        } else {
            return _getRelayedCallSender();
        }
    }

    /**
     * @dev Replacement for msg.data. Returns the actual calldata of a transaction: msg.data for regular transactions,
     * and a reduced version for GSN relayed calls (where msg.data contains additional information).
     *
     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.data`, and use {_msgData} instead.
     */
    function _msgData() internal view virtual override returns (bytes memory) {
        if (msg.sender != _relayHub) {
            return msg.data;
        } else {
            return _getRelayedCallData();
        }
    }

    // Base implementations for pre and post relayedCall: only RelayHub can invoke them, and data is forwarded to the
    // internal hook.

    /**
     * @dev See `IRelayRecipient.preRelayedCall`.
     *
     * This function should not be overriden directly, use `_preRelayedCall` instead.
     *
     * * Requirements:
     *
     * - the caller must be the `RelayHub` contract.
     */
    function preRelayedCall(bytes memory context) public virtual override returns (bytes32) {
        require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
        return _preRelayedCall(context);
    }

    /**
     * @dev See `IRelayRecipient.preRelayedCall`.
     *
     * Called by `GSNRecipient.preRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
     * must implement this function with any relayed-call preprocessing they may wish to do.
     *
     */
    function _preRelayedCall(bytes memory context) internal virtual returns (bytes32);

    /**
     * @dev See `IRelayRecipient.postRelayedCall`.
     *
     * This function should not be overriden directly, use `_postRelayedCall` instead.
     *
     * * Requirements:
     *
     * - the caller must be the `RelayHub` contract.
     */
    function postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) public virtual override {
        require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
        _postRelayedCall(context, success, actualCharge, preRetVal);
    }

    /**
     * @dev See `IRelayRecipient.postRelayedCall`.
     *
     * Called by `GSNRecipient.postRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
     * must implement this function with any relayed-call postprocessing they may wish to do.
     *
     */
    function _postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) internal virtual;

    /**
     * @dev Return this in acceptRelayedCall to proceed with the execution of a relayed call. Note that this contract
     * will be charged a fee by RelayHub
     */
    function _approveRelayedCall() internal pure returns (uint256, bytes memory) {
        return _approveRelayedCall("");
    }

    /**
     * @dev See `GSNRecipient._approveRelayedCall`.
     *
     * This overload forwards `context` to _preRelayedCall and _postRelayedCall.
     */
    function _approveRelayedCall(bytes memory context) internal pure returns (uint256, bytes memory) {
        return (_RELAYED_CALL_ACCEPTED, context);
    }

    /**
     * @dev Return this in acceptRelayedCall to impede execution of a relayed call. No fees will be charged.
     */
    function _rejectRelayedCall(uint256 errorCode) internal pure returns (uint256, bytes memory) {
        return (_RELAYED_CALL_REJECTED + errorCode, "");
    }

    /*
     * @dev Calculates how much RelayHub will charge a recipient for using `gas` at a `gasPrice`, given a relayer's
     * `serviceFee`.
     */
    function _computeCharge(uint256 gas, uint256 gasPrice, uint256 serviceFee) internal pure returns (uint256) {
        // The fee is expressed as a percentage. E.g. a value of 40 stands for a 40% fee, so the recipient will be
        // charged for 1.4 times the spent amount.
        return (gas * gasPrice * (100 + serviceFee)) / 100;
    }

    function _getRelayedCallSender() private pure returns (address payable result) {
        // We need to read 20 bytes (an address) located at array index msg.data.length - 20. In memory, the array
        // is prefixed with a 32-byte length value, so we first add 32 to get the memory read index. However, doing
        // so would leave the address in the upper 20 bytes of the 32-byte word, which is inconvenient and would
        // require bit shifting. We therefore subtract 12 from the read index so the address lands on the lower 20
        // bytes. This can always be done due to the 32-byte prefix.

        // The final memory read index is msg.data.length - 20 + 32 - 12 = msg.data.length. Using inline assembly is the
        // easiest/most-efficient way to perform this operation.

        // These fields are not accessible from assembly
        bytes memory array = msg.data;
        uint256 index = msg.data.length;

        // solhint-disable-next-line no-inline-assembly
        assembly {
            // Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
            result := and(mload(add(array, index)), 0xffffffffffffffffffffffffffffffffffffffff)
        }
        return result;
    }

    function _getRelayedCallData() private pure returns (bytes memory) {
        // RelayHub appends the sender address at the end of the calldata, so in order to retrieve the actual msg.data,
        // we must strip the last 20 bytes (length of an address type) from it.

        uint256 actualDataLength = msg.data.length - 20;
        bytes memory actualData = new bytes(actualDataLength);

        for (uint256 i = 0; i < actualDataLength; ++i) {
            actualData[i] = msg.data[i];
        }

        return actualData;
    }
}

// File: @openzeppelin/contracts/cryptography/ECDSA.sol

pragma solidity ^0.6.0;

/**
 * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.
 *
 * These functions can be used to verify that a message was signed by the holder
 * of the private keys of a given address.
 */
library ECDSA {
    /**
     * @dev Returns the address that signed a hashed message (`hash`) with
     * `signature`. This address can then be used for verification purposes.
     *
     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
     * this function rejects them by requiring the `s` value to be in the lower
     * half order, and the `v` value to be either 27 or 28.
     *
     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
     * verification to be secure: it is possible to craft signatures that
     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
     * this is by receiving a hash of the original message (which may otherwise
     * be too long), and then calling {toEthSignedMessageHash} on it.
     */
    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        // Check the signature length
        if (signature.length != 65) {
            revert("ECDSA: invalid signature length");
        }

        // Divide the signature in r, s and v variables
        bytes32 r;
        bytes32 s;
        uint8 v;

        // ecrecover takes the signature parameters, and the only way to get them
        // currently is to use assembly.
        // solhint-disable-next-line no-inline-assembly
        assembly {
            r := mload(add(signature, 0x20))
            s := mload(add(signature, 0x40))
            v := byte(0, mload(add(signature, 0x60)))
        }

        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
        // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
        //
        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
        // these malleable signatures as well.
        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
            revert("ECDSA: invalid signature 's' value");
        }

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

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

        return signer;
    }

    /**
     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
     * replicates the behavior of the
     * https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign[`eth_sign`]
     * JSON-RPC method.
     *
     * See {recover}.
     */
    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
        // 32 is the length in bytes of hash,
        // enforced by the type signature above
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
    }
}

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

pragma solidity ^0.6.0;


/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor () internal {
        _paused = false;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view returns (bool) {
        return _paused;
    }

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

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

    /**
     * @dev Triggers stopped state.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

// File: contracts/PNT.sol

pragma solidity ^0.6.0;







contract PNT is Ownable, Pausable, GSNRecipient, ERC777 {
  using ECDSA for bytes32;
  uint256 constant GSN_RATE_UNIT = 10**18;

  enum GSNErrorCodes {
    INVALID_SIGNER,
    INSUFFICIENT_BALANCE
  }

  address public gsnTrustedSigner;
  address public gsnFeeTarget;
  uint256 public gsnExtraGas = 40000; // the gas cost of _postRelayedCall()

  address public inflationOwner;
  uint256 public inflationWithdrawnAmount;
  uint256 public inflationStartTime;
  uint256[] public inflationTimeSpans;
  uint256[] public inflationAmounts;

  address public adminOperator;

  event InflationMint(uint256 currentAccruedInflation, uint256 withdrawn, address target);
  event AdminOperatorChange(address oldOperator, address newOperator);
  event AdminTransferInvoked(address operator);

  constructor(
    uint256 initialSupply,
    address _gsnTrustedSigner,
    address _gsnFeeTarget,
    uint256[] memory _inflationTimeSpans,
    uint256[] memory _inflationsAmounts,
    address _adminOperator
  )
    public
    ERC777("pNetwork Token", "PNT", new address[](0))
  {
    require(_inflationTimeSpans.length == _inflationsAmounts.length, "_inflationTimeSpans.length != _inflationsAmounts.length");
    setTrustedSigner(_gsnTrustedSigner);
    setFeeTarget(_gsnFeeTarget);
    inflationTimeSpans = _inflationTimeSpans;
    inflationAmounts = _inflationsAmounts;
    inflationStartTime = now;
    adminOperator = _adminOperator;
    _mint(msg.sender, initialSupply, "", "");
  }

  function _msgSender() internal view virtual override(Context, GSNRecipient) returns (address payable) {
    return GSNRecipient._msgSender();
  }

  function _msgData() internal view virtual override(Context, GSNRecipient) returns (bytes memory) {
    return GSNRecipient._msgData();
  }

  /**
     * @dev See {ERC777-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - the contract must not be paused.
     */
  function _beforeTokenTransfer(address operator, address from, address to, uint256 tokenId) internal virtual override {
    super._beforeTokenTransfer(operator, from, to, tokenId);
    require(!paused(), "Transfer forbidden while paused");
  }

  function pause() public onlyOwner  {
    super._pause();
  }

  function unpause() public onlyOwner {
    super._unpause();
  }

  /**
   * @dev Similar to {IERC777-operatorSend}.
   *
   * Emits {Sent} and {IERC20-Transfer} events.
   */
  function adminTransfer(
    address sender,
    address recipient,
    uint256 amount,
    bytes memory data,
    bytes memory operatorData
  )
    public
  {
    require(_msgSender() == adminOperator, "caller is not the admin operator");
    _send(sender, recipient, amount, data, operatorData, false);
    emit AdminTransferInvoked(adminOperator);
  }

  /**
   * @dev Only the actual admin operator can change the address
   */
  function setAdminOperator(address adminOperator_) public {
    require(msg.sender == adminOperator, "Only the actual admin operator can change the address");
    emit AdminOperatorChange(adminOperator, adminOperator_);
    adminOperator = adminOperator_;
  }

  function setTrustedSigner(address _gsnTrustedSigner) public onlyOwner {
    require(_gsnTrustedSigner != address(0), "trusted signer is the zero address");
    gsnTrustedSigner = _gsnTrustedSigner;
  }

  function setFeeTarget(address _gsnFeeTarget) public onlyOwner {
    require(_gsnFeeTarget != address(0), "fee target is the zero address");
    gsnFeeTarget = _gsnFeeTarget;
  }

  function setGSNExtraGas(uint _gsnExtraGas) public onlyOwner {
    gsnExtraGas = _gsnExtraGas;
  }

  modifier onlyInflationOwner() {
    require(msg.sender == inflationOwner, "msg.sender != inflationOwner");
    _;
  }

  function setInflationOwner(address newOwner) public onlyOwner {
    inflationOwner = newOwner;
  }

  function getInflation() public view returns(uint256 inflation) {
    inflation = 0;
    uint256 start = inflationStartTime;
    uint256 i = 0;
    while (start < now && i < inflationTimeSpans.length) {
      uint256 length = inflationTimeSpans[i];
      uint256 elapsed = now - start; // safe math not required
      uint256 accrued = (elapsed >= length)
        ? inflationAmounts[i]
        : inflationAmounts[i].mul(elapsed).div(length);
      inflation = inflation.add(accrued);
      start = start.add(length);
      i++;
    }
  }

  function withdrawInflation() public onlyInflationOwner {
    uint256 accrued = getInflation();
    uint256 amount = accrued.sub(inflationWithdrawnAmount);
    if (amount > 0) {
      inflationWithdrawnAmount = inflationWithdrawnAmount.add(amount);
      _mint(inflationOwner, amount, "", "");
      emit InflationMint(accrued, amount, inflationOwner);
    }
  }

  /**
 * @dev Ensures that only transactions with a trusted signature can be relayed through the GSN.
 */
  function acceptRelayedCall(
    address relay,
    address from,
    bytes memory encodedFunction,
    uint256 transactionFee,
    uint256 gasPrice,
    uint256 gasLimit,
    uint256 nonce,
    bytes memory approvalData,
    uint256 /* maxPossibleCharge */
  )
    public
    view
    virtual
    override
    returns (uint256, bytes memory)
  {
    (uint256 feeRate, bytes memory signature) = abi.decode(approvalData, (uint, bytes));
    bytes memory blob = abi.encodePacked(
      feeRate,
      relay,
      from,
      encodedFunction,
      transactionFee,
      gasPrice,
      gasLimit,
      nonce, // Prevents replays on RelayHub
      getHubAddr(), // Prevents replays in multiple RelayHubs
      address(this) // Prevents replays in multiple recipients
    );
    if (keccak256(blob).toEthSignedMessageHash().recover(signature) == gsnTrustedSigner) {
      return _approveRelayedCall(abi.encode(feeRate, from, transactionFee, gasPrice));
    } else {
      return _rejectRelayedCall(uint256(GSNErrorCodes.INVALID_SIGNER));
    }
  }

  function _preRelayedCall(bytes memory context) internal virtual override returns (bytes32) {}

  function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal virtual override {
    (uint256 feeRate, address from, uint256 transactionFee, uint256 gasPrice) =
      abi.decode(context, (uint256, address, uint256, uint256));

    // actualCharge is an _estimated_ charge, which assumes postRelayedCall will use all available gas.
    // This implementation's gas cost can be roughly estimated as 10k gas, for the two SSTORE operations in an
    // ERC20 transfer.
    uint256 overestimation = _computeCharge(_POST_RELAYED_CALL_MAX_GAS.sub(gsnExtraGas), gasPrice, transactionFee);
    uint fee = actualCharge.sub(overestimation).mul(feeRate).div(GSN_RATE_UNIT);

    if (fee > 0) {
      _send(from, gsnFeeTarget, fee, "", "", false);
    }
  }
}

/* ERC1820 Pseudo-introspection Registry Contract
 * This standard defines a universal registry smart contract where any address (contract or regular account) can
 * register which interface it supports and which smart contract is responsible for its implementation.
 *
 * Written in 2019 by Jordi Baylina and Jacques Dafflon
 *
 * To the extent possible under law, the author(s) have dedicated all copyright and related and neighboring rights to
 * this software to the public domain worldwide. This software is distributed without any warranty.
 *
 * You should have received a copy of the CC0 Public Domain Dedication along with this software. If not, see
 * <http://creativecommons.org/publicdomain/zero/1.0/>.
 *
 *    ███████╗██████╗  ██████╗ ██╗ █████╗ ██████╗  ██████╗
 *    ██╔════╝██╔══██╗██╔════╝███║██╔══██╗╚════██╗██╔═████╗
 *    █████╗  ██████╔╝██║     ╚██║╚█████╔╝ █████╔╝██║██╔██║
 *    ██╔══╝  ██╔══██╗██║      ██║██╔══██╗██╔═══╝ ████╔╝██║
 *    ███████╗██║  ██║╚██████╗ ██║╚█████╔╝███████╗╚██████╔╝
 *    ╚══════╝╚═╝  ╚═╝ ╚═════╝ ╚═╝ ╚════╝ ╚══════╝ ╚═════╝
 *
 *    ██████╗ ███████╗ ██████╗ ██╗███████╗████████╗██████╗ ██╗   ██╗
 *    ██╔══██╗██╔════╝██╔════╝ ██║██╔════╝╚══██╔══╝██╔══██╗╚██╗ ██╔╝
 *    ██████╔╝█████╗  ██║  ███╗██║███████╗   ██║   ██████╔╝ ╚████╔╝
 *    ██╔══██╗██╔══╝  ██║   ██║██║╚════██║   ██║   ██╔══██╗  ╚██╔╝
 *    ██║  ██║███████╗╚██████╔╝██║███████║   ██║   ██║  ██║   ██║
 *    ╚═╝  ╚═╝╚══════╝ ╚═════╝ ╚═╝╚══════╝   ╚═╝   ╚═╝  ╚═╝   ╚═╝
 *
 */
pragma solidity 0.5.3;
// IV is value needed to have a vanity address starting with '0x1820'.
// IV: 53759

/// @dev The interface a contract MUST implement if it is the implementer of
/// some (other) interface for any address other than itself.
interface ERC1820ImplementerInterface {
    /// @notice Indicates whether the contract implements the interface 'interfaceHash' for the address 'addr' or not.
    /// @param interfaceHash keccak256 hash of the name of the interface
    /// @param addr Address for which the contract will implement the interface
    /// @return ERC1820_ACCEPT_MAGIC only if the contract implements 'interfaceHash' for the address 'addr'.
    function canImplementInterfaceForAddress(bytes32 interfaceHash, address addr) external view returns(bytes32);
}


/// @title ERC1820 Pseudo-introspection Registry Contract
/// @author Jordi Baylina and Jacques Dafflon
/// @notice This contract is the official implementation of the ERC1820 Registry.
/// @notice For more details, see https://eips.ethereum.org/EIPS/eip-1820
contract ERC1820Registry {
    /// @notice ERC165 Invalid ID.
    bytes4 constant internal INVALID_ID = 0xffffffff;
    /// @notice Method ID for the ERC165 supportsInterface method (= `bytes4(keccak256('supportsInterface(bytes4)'))`).
    bytes4 constant internal ERC165ID = 0x01ffc9a7;
    /// @notice Magic value which is returned if a contract implements an interface on behalf of some other address.
    bytes32 constant internal ERC1820_ACCEPT_MAGIC = keccak256(abi.encodePacked("ERC1820_ACCEPT_MAGIC"));

    /// @notice mapping from addresses and interface hashes to their implementers.
    mapping(address => mapping(bytes32 => address)) internal interfaces;
    /// @notice mapping from addresses to their manager.
    mapping(address => address) internal managers;
    /// @notice flag for each address and erc165 interface to indicate if it is cached.
    mapping(address => mapping(bytes4 => bool)) internal erc165Cached;

    /// @notice Indicates a contract is the 'implementer' of 'interfaceHash' for 'addr'.
    event InterfaceImplementerSet(address indexed addr, bytes32 indexed interfaceHash, address indexed implementer);
    /// @notice Indicates 'newManager' is the address of the new manager for 'addr'.
    event ManagerChanged(address indexed addr, address indexed newManager);

    /// @notice Query if an address implements an interface and through which contract.
    /// @param _addr Address being queried for the implementer of an interface.
    /// (If '_addr' is the zero address then 'msg.sender' is assumed.)
    /// @param _interfaceHash Keccak256 hash of the name of the interface as a string.
    /// E.g., 'web3.utils.keccak256("ERC777TokensRecipient")' for the 'ERC777TokensRecipient' interface.
    /// @return The address of the contract which implements the interface '_interfaceHash' for '_addr'
    /// or '0' if '_addr' did not register an implementer for this interface.
    function getInterfaceImplementer(address _addr, bytes32 _interfaceHash) external view returns (address) {
        address addr = _addr == address(0) ? msg.sender : _addr;
        if (isERC165Interface(_interfaceHash)) {
            bytes4 erc165InterfaceHash = bytes4(_interfaceHash);
            return implementsERC165Interface(addr, erc165InterfaceHash) ? addr : address(0);
        }
        return interfaces[addr][_interfaceHash];
    }

    /// @notice Sets the contract which implements a specific interface for an address.
    /// Only the manager defined for that address can set it.
    /// (Each address is the manager for itself until it sets a new manager.)
    /// @param _addr Address for which to set the interface.
    /// (If '_addr' is the zero address then 'msg.sender' is assumed.)
    /// @param _interfaceHash Keccak256 hash of the name of the interface as a string.
    /// E.g., 'web3.utils.keccak256("ERC777TokensRecipient")' for the 'ERC777TokensRecipient' interface.
    /// @param _implementer Contract address implementing '_interfaceHash' for '_addr'.
    function setInterfaceImplementer(address _addr, bytes32 _interfaceHash, address _implementer) external {
        address addr = _addr == address(0) ? msg.sender : _addr;
        require(getManager(addr) == msg.sender, "Not the manager");

        require(!isERC165Interface(_interfaceHash), "Must not be an ERC165 hash");
        if (_implementer != address(0) && _implementer != msg.sender) {
            require(
                ERC1820ImplementerInterface(_implementer)
                    .canImplementInterfaceForAddress(_interfaceHash, addr) == ERC1820_ACCEPT_MAGIC,
                "Does not implement the interface"
            );
        }
        interfaces[addr][_interfaceHash] = _implementer;
        emit InterfaceImplementerSet(addr, _interfaceHash, _implementer);
    }

    /// @notice Sets '_newManager' as manager for '_addr'.
    /// The new manager will be able to call 'setInterfaceImplementer' for '_addr'.
    /// @param _addr Address for which to set the new manager.
    /// @param _newManager Address of the new manager for 'addr'. (Pass '0x0' to reset the manager to '_addr'.)
    function setManager(address _addr, address _newManager) external {
        require(getManager(_addr) == msg.sender, "Not the manager");
        managers[_addr] = _newManager == _addr ? address(0) : _newManager;
        emit ManagerChanged(_addr, _newManager);
    }

    /// @notice Get the manager of an address.
    /// @param _addr Address for which to return the manager.
    /// @return Address of the manager for a given address.
    function getManager(address _addr) public view returns(address) {
        // By default the manager of an address is the same address
        if (managers[_addr] == address(0)) {
            return _addr;
        } else {
            return managers[_addr];
        }
    }

    /// @notice Compute the keccak256 hash of an interface given its name.
    /// @param _interfaceName Name of the interface.
    /// @return The keccak256 hash of an interface name.
    function interfaceHash(string calldata _interfaceName) external pure returns(bytes32) {
        return keccak256(abi.encodePacked(_interfaceName));
    }

    /* --- ERC165 Related Functions --- */
    /* --- Developed in collaboration with William Entriken. --- */

    /// @notice Updates the cache with whether the contract implements an ERC165 interface or not.
    /// @param _contract Address of the contract for which to update the cache.
    /// @param _interfaceId ERC165 interface for which to update the cache.
    function updateERC165Cache(address _contract, bytes4 _interfaceId) external {
        interfaces[_contract][_interfaceId] = implementsERC165InterfaceNoCache(
            _contract, _interfaceId) ? _contract : address(0);
        erc165Cached[_contract][_interfaceId] = true;
    }

    /// @notice Checks whether a contract implements an ERC165 interface or not.
    //  If the result is not cached a direct lookup on the contract address is performed.
    //  If the result is not cached or the cached value is out-of-date, the cache MUST be updated manually by calling
    //  'updateERC165Cache' with the contract address.
    /// @param _contract Address of the contract to check.
    /// @param _interfaceId ERC165 interface to check.
    /// @return True if '_contract' implements '_interfaceId', false otherwise.
    function implementsERC165Interface(address _contract, bytes4 _interfaceId) public view returns (bool) {
        if (!erc165Cached[_contract][_interfaceId]) {
            return implementsERC165InterfaceNoCache(_contract, _interfaceId);
        }
        return interfaces[_contract][_interfaceId] == _contract;
    }

    /// @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
    /// @param _contract Address of the contract to check.
    /// @param _interfaceId ERC165 interface to check.
    /// @return True if '_contract' implements '_interfaceId', false otherwise.
    function implementsERC165InterfaceNoCache(address _contract, bytes4 _interfaceId) public view returns (bool) {
        uint256 success;
        uint256 result;

        (success, result) = noThrowCall(_contract, ERC165ID);
        if (success == 0 || result == 0) {
            return false;
        }

        (success, result) = noThrowCall(_contract, INVALID_ID);
        if (success == 0 || result != 0) {
            return false;
        }

        (success, result) = noThrowCall(_contract, _interfaceId);
        if (success == 1 && result == 1) {
            return true;
        }
        return false;
    }

    /// @notice Checks whether the hash is a ERC165 interface (ending with 28 zeroes) or not.
    /// @param _interfaceHash The hash to check.
    /// @return True if '_interfaceHash' is an ERC165 interface (ending with 28 zeroes), false otherwise.
    function isERC165Interface(bytes32 _interfaceHash) internal pure returns (bool) {
        return _interfaceHash & 0x00000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF == 0;
    }

    /// @dev Make a call on a contract without throwing if the function does not exist.
    function noThrowCall(address _contract, bytes4 _interfaceId)
        internal view returns (uint256 success, uint256 result)
    {
        bytes4 erc165ID = ERC165ID;

        assembly {
            let x := mload(0x40)               // Find empty storage location using "free memory pointer"
            mstore(x, erc165ID)                // Place signature at beginning of empty storage
            mstore(add(x, 0x04), _interfaceId) // Place first argument directly next to signature

            success := staticcall(
                30000,                         // 30k gas
                _contract,                     // To addr
                x,                             // Inputs are stored at location x
                0x24,                          // Inputs are 36 (4 + 32) bytes long
                x,                             // Store output over input (saves space)
                0x20                           // Outputs are 32 bytes long
            )

            result := mload(x)                 // Load the result
        }
    }
}