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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../utils/Context.sol";

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _setOwner(_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 {
        _setOwner(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");
        _setOwner(newOwner);
    }

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: @openzeppelin/contracts/security/ReentrancyGuard.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

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

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

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

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

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

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

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

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/Address.sol";

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

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

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

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

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

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

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

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

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../../utils/introspection/IERC165.sol";

/**
 * @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;
}

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



// 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
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        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");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

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

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

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

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

        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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;
    }
}

// File: @openzeppelin/contracts/utils/introspection/IERC165.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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);
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

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

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

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

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. 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;
        }
    }
}

// File: contracts/HaktAuctionHouse.sol



pragma solidity ^0.8.0;
pragma experimental ABIEncoderV2;
//SPDX-License-Identifier: MIT

/*
    )              )           (                )   
 ( /(   (       ( /(   *   )   )\ )    (     ( /(   
 )\())  )\      )\())` )  /(  (()/(    )\    )\())  
((_)\((((_)(  |((_)\  ( )(_))  /(_))((((_)( ((_)\   
 _((_))\ _ )\ |_ ((_)(_(_())  (_))_  )\ _ )\  ((_)  
| || |(_)_\(_)| |/ / |_   _|   |   \ (_)_\(_)/ _ \  
| __ | / _ \    ' <    | |     | |) | / _ \ | (_) | 
|_||_|/_/ \_\  _|\_\   |_|     |___/ /_/ \_\ \___/ 
                                                  
*/

/* 
A big thanks to Zora for sharing their auction contracts with the world! 
It has provided us with much inspiration and guidance.
*/

import "@openzeppelin/contracts/utils/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/utils/Counters.sol";
import "./IAuctionHouse.sol";

interface IWETH {
    function deposit() external payable;
    function withdraw(uint wad) external;

    function transfer(address to, uint256 value) external returns (bool);
}
/**
 * @title An auction house for the HaktDAO project
 */
contract HaktAuctionHouse is IAuctionHouse, ReentrancyGuard, Ownable {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;
    using Counters for Counters.Counter;

    // The minimum amount of time left in an auction after a new bid is created
    uint256 public timeBuffer;

    // The minimum percentage difference between the last bid amount and the current bid.
    uint8 public minBidIncrementPercentage;

    // / The address of the WETH contract, so that any ETH transferred can be handled as an ERC-20
    address public wethAddress;

    // A mapping of all of the auctions currently running.
    mapping(uint256 => IAuctionHouse.Auction) public auctions;

    bytes4 constant interfaceId = 0x80ac58cd; // 721 interface id

    Counters.Counter private _auctionIdTracker;

    // DAO Address
    address public daoAddress;

    /**
     * @notice Require that the specified auction exists
     */
    modifier auctionExists(uint256 auctionId) {
        require(_exists(auctionId), "Auction doesn't exist");
        _;
    }

    /*
     * Constructor
     */
    constructor(address _weth, address _dao) {
        wethAddress = _weth;
        timeBuffer = 15 * 60; // extend 15 minutes after every bid made in last 15 minutes
        minBidIncrementPercentage = 5; // 5%
        daoAddress = _dao;
    }

    /**
     * @notice Set a new Time Buffer.
     * @dev Only allow the Owner to change it.
     */
    function setTimeBuffer(uint256 _timeBuffer) public onlyOwner {
        timeBuffer = _timeBuffer;
    }

    /**
     * @notice Set a new min bid increment percentage.
     * @dev Only allow the Owner to change it.
     */
    function setMinBidIncrementPercentage(uint8 _minBidIncrementPercentage) public onlyOwner {
        minBidIncrementPercentage = _minBidIncrementPercentage;
    }

    /**
     * @notice Set a new DAO address.
     * @dev Only allow the DAO address to change the DAO address in this contract.
     */
    function setDAOAddress(address _dao) public {
        require(daoAddress == msg.sender, "Can only be called by the DAO Address");
        daoAddress = _dao;
    }

    /**
     * @notice Create an auction.
     * @dev Store the auction details in the auctions mapping and emit an AuctionCreated event.
     */
    function createAuction(
        uint256 tokenId,
        address tokenContract,
        uint256 duration,
        uint256 reservePrice,
        address auctionCurrency
    ) public override nonReentrant onlyOwner returns (uint256) {
        require(
            IERC165(tokenContract).supportsInterface(interfaceId),
            "tokenContract does not support ERC721 interface"
        );
        address tokenOwner = IERC721(tokenContract).ownerOf(tokenId);
        require(address(this) == IERC721(tokenContract).getApproved(tokenId), "Caller must be approved or owner for token id");
        uint256 auctionId = _auctionIdTracker.current();

        auctions[auctionId] = Auction({
            tokenId: tokenId,
            tokenContract: tokenContract,
            amount: 0,
            duration: duration,
            firstBidTime: 0,
            reservePrice: reservePrice,
            tokenOwner: tokenOwner,
            bidder: payable(address(0)),
            auctionCurrency: auctionCurrency
        });

        IERC721(tokenContract).transferFrom(tokenOwner, address(this), tokenId);

        _auctionIdTracker.increment();

        emit AuctionCreated(auctionId, tokenId, tokenContract, duration, reservePrice, tokenOwner, auctionCurrency);

        return auctionId;
    }

     /**
     * @notice Create a bid on a token, with a given amount.
     * @dev If provided a valid bid, transfers the provided amount to this contract.
     * If the auction is run in native ETH, the ETH is wrapped so it can be identically to other
     * auction currencies in this contract.
     */
    function createBid(uint256 auctionId, uint256 amount)
    external
    override
    payable
    auctionExists(auctionId)
    nonReentrant
    {
        address payable lastBidder = auctions[auctionId].bidder;
        require(
            auctions[auctionId].firstBidTime == 0 ||
            block.timestamp <
            auctions[auctionId].firstBidTime.add(auctions[auctionId].duration),
            "Auction expired"
        );
        require(
            amount >= auctions[auctionId].reservePrice,
                "Must send at least reservePrice"
        );
        require(
            amount >= auctions[auctionId].amount.add(
                auctions[auctionId].amount.mul(minBidIncrementPercentage).div(100)
            ),
            "Must send more than last bid by minBidIncrementPercentage amount"
        );

        // If this is the first valid bid, we should set the starting time now.
        // If it's not, then we should refund the last bidder
        if(auctions[auctionId].firstBidTime == 0) {
            auctions[auctionId].firstBidTime = block.timestamp;
        } else if(lastBidder != address(0)) {
            _handleOutgoingBid(lastBidder, auctions[auctionId].amount, auctions[auctionId].auctionCurrency);
        }

        _handleIncomingBid(amount, auctions[auctionId].auctionCurrency);

        auctions[auctionId].amount = amount;
        auctions[auctionId].bidder = payable(msg.sender);


        bool extended = false;
        // at this point we know that the timestamp is less than start + duration (since the auction would be over, otherwise)
        // we want to know by how much the timestamp is less than start + duration
        // if the difference is less than the timeBuffer, increase the duration by the timeBuffer
        if (
            auctions[auctionId].firstBidTime.add(auctions[auctionId].duration).sub(
                block.timestamp
            ) < timeBuffer
        ) {
            // Playing code golf for gas optimization:
            // uint256 expectedEnd = auctions[auctionId].firstBidTime.add(auctions[auctionId].duration);
            // uint256 timeRemaining = expectedEnd.sub(block.timestamp);
            // uint256 timeToAdd = timeBuffer.sub(timeRemaining);
            // uint256 newDuration = auctions[auctionId].duration.add(timeToAdd);
            uint256 oldDuration = auctions[auctionId].duration;
            auctions[auctionId].duration =
                oldDuration.add(timeBuffer.sub(auctions[auctionId].firstBidTime.add(oldDuration).sub(block.timestamp)));
            extended = true;
        }

        emit AuctionBid(
            auctionId,
            auctions[auctionId].tokenId,
            auctions[auctionId].tokenContract,
            msg.sender,
            amount,
            lastBidder == address(0), // firstBid boolean
            extended
        );

        if (extended) {
            emit AuctionDurationExtended(
                auctionId,
                auctions[auctionId].tokenId,
                auctions[auctionId].tokenContract,
                auctions[auctionId].duration
            );
        }
    }

    /**
     * @notice End an auction, finalizing the bid if applicable and paying out the respective parties.
     * @dev If for some reason the auction cannot be finalized (invalid token recipient, for example),
     * The auction is reset and the NFT is transferred back to the auction creator.
     */
    function endAuction(uint256 auctionId) external override auctionExists(auctionId) nonReentrant {

        require(
            uint256(auctions[auctionId].firstBidTime) != 0,
            "Auction hasn't begun"
        );
        require(
            block.timestamp >=
            auctions[auctionId].firstBidTime.add(auctions[auctionId].duration),
            "Auction hasn't completed"
        );

        require(
            msg.sender == owner() || msg.sender == auctions[auctionId].bidder,
            "Can only be called by Owner or winner"
        );

        address currency = auctions[auctionId].auctionCurrency == address(0) ? wethAddress : auctions[auctionId].auctionCurrency;

        uint256 tokenOwnerProfit = auctions[auctionId].amount;

        // Otherwise, transfer the token to the winner and pay out the participants below
        try IERC721(auctions[auctionId].tokenContract).safeTransferFrom(address(this), auctions[auctionId].bidder, auctions[auctionId].tokenId) {} catch {
            _handleOutgoingBid(auctions[auctionId].bidder, auctions[auctionId].amount, auctions[auctionId].auctionCurrency);
            _cancelAuction(auctionId);
            return;
        }

        // DAO address receives the Profit
        _handleOutgoingBid(daoAddress, tokenOwnerProfit, auctions[auctionId].auctionCurrency);

        emit AuctionEnded(
            auctionId,
            auctions[auctionId].tokenId,
            auctions[auctionId].tokenContract,
            auctions[auctionId].tokenOwner,
            auctions[auctionId].bidder,
            daoAddress,
            tokenOwnerProfit,
            currency
        );
    }

    /**
     * @notice Cancel an auction.
     * @dev Transfers the NFT back to the auction creator and emits an AuctionCanceled event
     */
    function cancelAuction(uint256 auctionId) external override nonReentrant auctionExists(auctionId) onlyOwner {
        require(
            uint256(auctions[auctionId].firstBidTime) == 0,
            "Can't cancel an auction once it's begun"
        );
        _cancelAuction(auctionId);
    }

    function getCurrentAuctionId() public view returns(Counters.Counter memory) {
        return _auctionIdTracker;
    }

    /**
     * @dev Given an amount and a currency, transfer the currency to this contract.
     * If the currency is ETH (0x0), attempt to wrap the amount as WETH
     */
    function _handleIncomingBid(uint256 amount, address currency) internal {
        // If this is an ETH bid, ensure they sent enough and convert it to WETH under the hood
        if(currency == address(0)) {
            require(msg.value == amount, "Sent ETH Value does not match specified bid amount");
            IWETH(wethAddress).deposit{value: amount}();
        } else {
            // We must check the balance that was actually transferred to the auction,
            // as some tokens impose a transfer fee and would not actually transfer the
            // full amount to the market, resulting in potentally locked funds
            IERC20 token = IERC20(currency);
            uint256 beforeBalance = token.balanceOf(address(this));
            token.safeTransferFrom(msg.sender, address(this), amount);
            uint256 afterBalance = token.balanceOf(address(this));
            require(beforeBalance.add(amount) == afterBalance, "Token transfer call did not transfer expected amount");
        }
    }

    function _handleOutgoingBid(address to, uint256 amount, address currency) internal {
        // If the auction is in ETH, unwrap it from its underlying WETH and try to send it to the recipient.
        if(currency == address(0)) {
            IWETH(wethAddress).withdraw(amount);

            // If the ETH transfer fails (sigh), rewrap the ETH and try send it as WETH.
            if(!_safeTransferETH(to, amount)) {
                IWETH(wethAddress).deposit{value: amount}();
                IERC20(wethAddress).safeTransfer(to, amount);
            }
        } else {
            IERC20(currency).safeTransfer(to, amount);
        }
    }

    function _safeTransferETH(address to, uint256 value) internal returns (bool) {
        (bool success, ) = to.call{value: value}(new bytes(0));
        return success;
    }

    function _cancelAuction(uint256 auctionId) internal {
        address tokenOwner = auctions[auctionId].tokenOwner;
        IERC721(auctions[auctionId].tokenContract).safeTransferFrom(address(this), tokenOwner, auctions[auctionId].tokenId);

        emit AuctionCanceled(auctionId, auctions[auctionId].tokenId, auctions[auctionId].tokenContract, tokenOwner);
        delete auctions[auctionId];
    }

    function _exists(uint256 auctionId) internal view returns(bool) {
        return auctions[auctionId].tokenOwner != address(0);
    } 

    // TODO: consider reverting if the message sender is not WETH
    receive() external payable {}
    fallback() external payable {}
}
// File: contracts/IAuctionHouse.sol



pragma solidity ^0.8.0;
pragma experimental ABIEncoderV2;
//SPDX-License-Identifier: MIT

/**
 * @title Interface for Auction Houses
 */
interface IAuctionHouse {
    struct Auction {
        // ID for the ERC721 token
        uint256 tokenId;
        // Address for the ERC721 contract
        address tokenContract;
        // The current highest bid amount
        uint256 amount;
        // The length of time to run the auction for, after the first bid was made
        uint256 duration;
        // The time of the first bid
        uint256 firstBidTime;
        // The minimum price of the first bid
        uint256 reservePrice;
        // The address that should receive the funds once the NFT is sold.
        address tokenOwner;
        // The address of the current highest bid
        address payable bidder;
        // The address of the ERC-20 currency to run the auction with.
        // If set to 0x0, the auction will be run in ETH
        address auctionCurrency;
    }

    event AuctionCreated(
        uint256 indexed auctionId,
        uint256 indexed tokenId,
        address indexed tokenContract,
        uint256 duration,
        uint256 reservePrice,
        address tokenOwner,
        address auctionCurrency
    );

    event AuctionApprovalUpdated(
        uint256 indexed auctionId,
        uint256 indexed tokenId,
        address indexed tokenContract,
        bool approved
    );

    event AuctionReservePriceUpdated(
        uint256 indexed auctionId,
        uint256 indexed tokenId,
        address indexed tokenContract,
        uint256 reservePrice
    );

    event AuctionBid(
        uint256 indexed auctionId,
        uint256 indexed tokenId,
        address indexed tokenContract,
        address sender,
        uint256 value,
        bool firstBid,
        bool extended
    );

    event AuctionDurationExtended(
        uint256 indexed auctionId,
        uint256 indexed tokenId,
        address indexed tokenContract,
        uint256 duration
    );

    event AuctionEnded(
        uint256 indexed auctionId,
        uint256 indexed tokenId,
        address indexed tokenContract,
        address tokenOwner,
        address winner,
        address daoAddress,
        uint256 amount,
        address auctionCurrency
    );

    event AuctionCanceled(
        uint256 indexed auctionId,
        uint256 indexed tokenId,
        address indexed tokenContract,
        address tokenOwner
    );

    function createAuction(
        uint256 tokenId,
        address tokenContract,
        uint256 duration,
        uint256 reservePrice,
        address auctionCurrency
    ) external returns (uint256);

    function createBid(uint256 auctionId, uint256 amount) external payable;

    function endAuction(uint256 auctionId) external;

    function cancelAuction(uint256 auctionId) external;
}