// OpenZeppelin Contracts v4.4.1 (utils/math/SafeMath.sol)

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 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;
        }
    }
}

// File: @openzeppelin/contracts/utils/Counters.sol


// OpenZeppelin Contracts v4.4.1 (utils/Counters.sol)

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/security/ReentrancyGuard.sol


// OpenZeppelin Contracts v4.4.1 (security/ReentrancyGuard.sol)

pragma solidity ^0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `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/interfaces/IERC20.sol


// OpenZeppelin Contracts v4.4.1 (interfaces/IERC20.sol)

pragma solidity ^0.8.0;


// File: @openzeppelin/contracts/utils/Strings.sol


// OpenZeppelin Contracts v4.4.1 (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @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);
    }
}

// File: @openzeppelin/contracts/utils/Context.sol


// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol


// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)

pragma solidity ^0.8.0;


/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract 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);
    }
}

// File: @openzeppelin/contracts/utils/Address.sol


// OpenZeppelin Contracts v4.4.1 (utils/Address.sol)

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/token/ERC721/IERC721Receiver.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC721/IERC721Receiver.sol)

pragma solidity ^0.8.0;

/**
 * @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 `IERC721.onERC721Received.selector`.
     */
    function onERC721Received(
        address operator,
        address from,
        uint256 tokenId,
        bytes calldata data
    ) external returns (bytes4);
}

// File: @openzeppelin/contracts/utils/introspection/IERC165.sol


// OpenZeppelin Contracts v4.4.1 (utils/introspection/IERC165.sol)

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/interfaces/IERC165.sol


// OpenZeppelin Contracts v4.4.1 (interfaces/IERC165.sol)

pragma solidity ^0.8.0;


// File: @openzeppelin/contracts/interfaces/IERC2981.sol


// OpenZeppelin Contracts v4.4.1 (interfaces/IERC2981.sol)

pragma solidity ^0.8.0;


/**
 * @dev Interface for the NFT Royalty Standard
 */
interface IERC2981 is IERC165 {
    /**
     * @dev Called with the sale price to determine how much royalty is owed and to whom.
     * @param tokenId - the NFT asset queried for royalty information
     * @param salePrice - the sale price of the NFT asset specified by `tokenId`
     * @return receiver - address of who should be sent the royalty payment
     * @return royaltyAmount - the royalty payment amount for `salePrice`
     */
    function royaltyInfo(uint256 tokenId, uint256 salePrice)
        external
        view
        returns (address receiver, uint256 royaltyAmount);
}

// File: @openzeppelin/contracts/utils/introspection/ERC165.sol


// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;


/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
 * for the additional interface id that will be supported. For example:
 *
 * ```solidity
 * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
 *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
 * }
 * ```
 *
 * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
 */
abstract contract ERC165 is IERC165 {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC721/IERC721.sol)

pragma solidity ^0.8.0;


/**
 * @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/token/ERC721/extensions/IERC721Enumerable.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC721/extensions/IERC721Enumerable.sol)

pragma solidity ^0.8.0;


/**
 * @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 tokenId);

    /**
     * @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);
}

// File: @openzeppelin/contracts/token/ERC721/extensions/IERC721Metadata.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC721/extensions/IERC721Metadata.sol)

pragma solidity ^0.8.0;


/**
 * @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);
}

pragma solidity ^0.8.0;

error ApprovalCallerNotOwnerNorApproved();
error ApprovalQueryForNonexistentToken();
error ApproveToCaller();
error ApprovalToCurrentOwner();
error BalanceQueryForZeroAddress();
error MintedQueryForZeroAddress();
error BurnedQueryForZeroAddress();
error AuxQueryForZeroAddress();
error MintToZeroAddress();
error MintZeroQuantity();
error OwnerIndexOutOfBounds();
error OwnerQueryForNonexistentToken();
error TokenIndexOutOfBounds();
error TransferCallerNotOwnerNorApproved();
error TransferFromIncorrectOwner();
error TransferToNonERC721ReceiverImplementer();
error TransferToZeroAddress();
error URIQueryForNonexistentToken();

/**
 * @dev Implementation of https://eips.ethereum.org/EIPS/eip-721[ERC721] Non-Fungible Token Standard, including
 * the Metadata extension. Built to optimize for lower gas during batch mints.
 *
 * Assumes serials are sequentially minted starting at _startTokenId() (defaults to 0, e.g. 0, 1, 2, 3..).
 *
 * Assumes that an owner cannot have more than 2**64 - 1 (max value of uint64) of supply.
 *
 * Assumes that the maximum token id cannot exceed 2**256 - 1 (max value of uint256).
 */
contract ERC721A is Context, ERC165, IERC721, IERC721Metadata {
	using Address for address;
	using Strings for uint256;

	// Compiler will pack this into a single 256bit word.
	struct TokenOwnership {
		// The address of the owner.
		address addr;
		// Keeps track of the start time of ownership with minimal overhead for tokenomics.
		uint64 startTimestamp;
		// Whether the token has been burned.
		bool burned;
	}

	// Compiler will pack this into a single 256bit word.
	struct AddressData {
		// Realistically, 2**64-1 is more than enough.
		uint64 balance;
		// Keeps track of mint count with minimal overhead for tokenomics.
		uint64 numberMinted;
		// Keeps track of burn count with minimal overhead for tokenomics.
		uint64 numberBurned;
		// For miscellaneous variable(s) pertaining to the address
		// (e.g. number of whitelist mint slots used).
		// If there are multiple variables, please pack them into a uint64.
		uint64 aux;
	}

	// The tokenId of the next token to be minted.
	uint256 internal _currentIndex;

	// The number of tokens burned.
	uint256 internal _burnCounter;

	// Token name
	string private _name;

	// Token symbol
	string private _symbol;

	// Mapping from token ID to ownership details
	// An empty struct value does not necessarily mean the token is unowned. See ownershipOf implementation for details.
	mapping(uint256 => TokenOwnership) internal _ownerships;

	// Mapping owner address to address data
	mapping(address => AddressData) private _addressData;

	// Mapping from token ID to approved address
	mapping(uint256 => address) private _tokenApprovals;

	// Mapping from owner to operator approvals
	mapping(address => mapping(address => bool)) private _operatorApprovals;

	constructor(string memory name_, string memory symbol_) {
		_name = name_;
		_symbol = symbol_;
		_currentIndex = _startTokenId();
	}

	/**
	 * To change the starting tokenId, please override this function.
	 */
	function _startTokenId() internal view virtual returns (uint256) {
		return 0;
	}

	/**
	 * @dev See {IERC721Enumerable-totalSupply}.
	 * @dev Burned tokens are calculated here, use _totalMinted() if you want to count just minted tokens.
	 */
	function totalSupply() public view returns (uint256) {
		// Counter underflow is impossible as _burnCounter cannot be incremented
		// more than _currentIndex - _startTokenId() times
		unchecked {
			return _currentIndex - _burnCounter - _startTokenId();
		}
	}

	/**
	 * Returns the total amount of tokens minted in the contract.
	 */
	function _totalMinted() internal view returns (uint256) {
		// Counter underflow is impossible as _currentIndex does not decrement,
		// and it is initialized to _startTokenId()
		unchecked {
			return _currentIndex - _startTokenId();
		}
	}

	/**
	 * @dev See {IERC165-supportsInterface}.
	 */
	function supportsInterface(bytes4 interfaceId)
		public
		view
		virtual
		override(ERC165, IERC165)
		returns (bool)
	{
		return
			interfaceId == type(IERC721).interfaceId ||
			interfaceId == type(IERC721Metadata).interfaceId ||
			super.supportsInterface(interfaceId);
	}

	/**
	 * @dev See {IERC721-balanceOf}.
	 */
	function balanceOf(address owner) public view override returns (uint256) {
		if (owner == address(0)) revert BalanceQueryForZeroAddress();
		return uint256(_addressData[owner].balance);
	}

	/**
	 * Returns the number of tokens minted by `owner`.
	 */
	function _numberMinted(address owner) internal view returns (uint256) {
		if (owner == address(0)) revert MintedQueryForZeroAddress();
		return uint256(_addressData[owner].numberMinted);
	}

	/**
	 * Returns the number of tokens burned by or on behalf of `owner`.
	 */
	function _numberBurned(address owner) internal view returns (uint256) {
		if (owner == address(0)) revert BurnedQueryForZeroAddress();
		return uint256(_addressData[owner].numberBurned);
	}

	/**
	 * Returns the auxillary data for `owner`. (e.g. number of whitelist mint slots used).
	 */
	function _getAux(address owner) internal view returns (uint64) {
		if (owner == address(0)) revert AuxQueryForZeroAddress();
		return _addressData[owner].aux;
	}

	/**
	 * Sets the auxillary data for `owner`. (e.g. number of whitelist mint slots used).
	 * If there are multiple variables, please pack them into a uint64.
	 */
	function _setAux(address owner, uint64 aux) internal {
		if (owner == address(0)) revert AuxQueryForZeroAddress();
		_addressData[owner].aux = aux;
	}

	/**
	 * Gas spent here starts off proportional to the maximum mint batch size.
	 * It gradually moves to O(1) as tokens get transferred around in the collection over time.
	 */
	function ownershipOf(uint256 tokenId) internal view returns (TokenOwnership memory) {
		uint256 curr = tokenId;

		unchecked {
			if (_startTokenId() <= curr && curr < _currentIndex) {
				TokenOwnership memory ownership = _ownerships[curr];
				if (!ownership.burned) {
					if (ownership.addr != address(0)) {
						return ownership;
					}
					// Invariant:
					// There will always be an ownership that has an address and is not burned
					// before an ownership that does not have an address and is not burned.
					// Hence, curr will not underflow.
					while (true) {
						curr--;
						ownership = _ownerships[curr];
						if (ownership.addr != address(0)) {
							return ownership;
						}
					}
				}
			}
		}
		revert OwnerQueryForNonexistentToken();
	}

	/**
	 * @dev See {IERC721-ownerOf}.
	 */
	function ownerOf(uint256 tokenId) public view override returns (address) {
		return ownershipOf(tokenId).addr;
	}

	/**
	 * @dev See {IERC721Metadata-name}.
	 */
	function name() public view virtual override returns (string memory) {
		return _name;
	}

	/**
	 * @dev See {IERC721Metadata-symbol}.
	 */
	function symbol() public view virtual override returns (string memory) {
		return _symbol;
	}

	/**
	 * @dev See {IERC721Metadata-tokenURI}.
	 */
	function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
		if (!_exists(tokenId)) revert URIQueryForNonexistentToken();

		string memory baseURI = _baseURI();
		return bytes(baseURI).length != 0 ? string(abi.encodePacked(baseURI, tokenId.toString())) : "";
	}

	/**
	 * @dev Base URI for computing {tokenURI}. If set, the resulting URI for each
	 * token will be the concatenation of the `baseURI` and the `tokenId`. Empty
	 * by default, can be overriden in child contracts.
	 */
	function _baseURI() internal view virtual returns (string memory) {
		return "";
	}

	/**
	 * @dev See {IERC721-approve}.
	 */
	function approve(address to, uint256 tokenId) public override {
		address owner = ERC721A.ownerOf(tokenId);
		if (to == owner) revert ApprovalToCurrentOwner();

		if (_msgSender() != owner && !isApprovedForAll(owner, _msgSender())) {
			revert ApprovalCallerNotOwnerNorApproved();
		}

		_approve(to, tokenId, owner);
	}

	/**
	 * @dev See {IERC721-getApproved}.
	 */
	function getApproved(uint256 tokenId) public view override returns (address) {
		if (!_exists(tokenId)) revert ApprovalQueryForNonexistentToken();

		return _tokenApprovals[tokenId];
	}

	/**
	 * @dev See {IERC721-setApprovalForAll}.
	 */
	function setApprovalForAll(address operator, bool approved) public override {
		if (operator == _msgSender()) revert ApproveToCaller();

		_operatorApprovals[_msgSender()][operator] = approved;
		emit ApprovalForAll(_msgSender(), operator, approved);
	}

	/**
	 * @dev See {IERC721-isApprovedForAll}.
	 */
	function isApprovedForAll(address owner, address operator)
		public
		view
		virtual
		override
		returns (bool)
	{
		return _operatorApprovals[owner][operator];
	}

	/**
	 * @dev See {IERC721-transferFrom}.
	 */
	function transferFrom(
		address from,
		address to,
		uint256 tokenId
	) public virtual override {
		_transfer(from, to, tokenId);
	}

	/**
	 * @dev See {IERC721-safeTransferFrom}.
	 */
	function safeTransferFrom(
		address from,
		address to,
		uint256 tokenId
	) public virtual override {
		safeTransferFrom(from, to, tokenId, "");
	}

	/**
	 * @dev See {IERC721-safeTransferFrom}.
	 */
	function safeTransferFrom(
		address from,
		address to,
		uint256 tokenId,
		bytes memory _data
	) public virtual override {
		_transfer(from, to, tokenId);
		if (to.isContract() && !_checkContractOnERC721Received(from, to, tokenId, _data)) {
			revert TransferToNonERC721ReceiverImplementer();
		}
	}

	/**
	 * @dev Returns whether `tokenId` exists.
	 *
	 * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
	 *
	 * Tokens start existing when they are minted (`_mint`),
	 */
	function _exists(uint256 tokenId) internal view returns (bool) {
		return _startTokenId() <= tokenId && tokenId < _currentIndex && !_ownerships[tokenId].burned;
	}

	function _safeMint(address to, uint256 quantity) internal {
		_safeMint(to, quantity, "");
	}

	/**
	 * @dev Safely mints `quantity` tokens and transfers them to `to`.
	 *
	 * Requirements:
	 *
	 * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called for each safe transfer.
	 * - `quantity` must be greater than 0.
	 *
	 * Emits a {Transfer} event.
	 */
	function _safeMint(
		address to,
		uint256 quantity,
		bytes memory _data
	) internal {
		_mint(to, quantity, _data, true);
	}

	/**
	 * @dev Mints `quantity` tokens and transfers them to `to`.
	 *
	 * Requirements:
	 *
	 * - `to` cannot be the zero address.
	 * - `quantity` must be greater than 0.
	 *
	 * Emits a {Transfer} event.
	 */
	function _mint(
		address to,
		uint256 quantity,
		bytes memory _data,
		bool safe
	) internal {
		uint256 startTokenId = _currentIndex;
		if (to == address(0)) revert MintToZeroAddress();
		if (quantity == 0) revert MintZeroQuantity();

		_beforeTokenTransfers(address(0), to, startTokenId, quantity);

		// Overflows are incredibly unrealistic.
		// balance or numberMinted overflow if current value of either + quantity > 1.8e19 (2**64) - 1
		// updatedIndex overflows if _currentIndex + quantity > 1.2e77 (2**256) - 1
		unchecked {
			_addressData[to].balance += uint64(quantity);
			_addressData[to].numberMinted += uint64(quantity);

			_ownerships[startTokenId].addr = to;
			_ownerships[startTokenId].startTimestamp = uint64(block.timestamp);

			uint256 updatedIndex = startTokenId;
			uint256 end = updatedIndex + quantity;

			if (safe && to.isContract()) {
				do {
					emit Transfer(address(0), to, updatedIndex);
					if (!_checkContractOnERC721Received(address(0), to, updatedIndex++, _data)) {
						revert TransferToNonERC721ReceiverImplementer();
					}
				} while (updatedIndex != end);
				// Reentrancy protection
				if (_currentIndex != startTokenId) revert();
			} else {
				do {
					emit Transfer(address(0), to, updatedIndex++);
				} while (updatedIndex != end);
			}
			_currentIndex = updatedIndex;
		}
		_afterTokenTransfers(address(0), to, startTokenId, quantity);
	}

	/**
	 * @dev Transfers `tokenId` from `from` to `to`.
	 *
	 * Requirements:
	 *
	 * - `to` cannot be the zero address.
	 * - `tokenId` token must be owned by `from`.
	 *
	 * Emits a {Transfer} event.
	 */
	function _transfer(
		address from,
		address to,
		uint256 tokenId
	) private {
		TokenOwnership memory prevOwnership = ownershipOf(tokenId);

		bool isApprovedOrOwner = (_msgSender() == prevOwnership.addr ||
			isApprovedForAll(prevOwnership.addr, _msgSender()) ||
			getApproved(tokenId) == _msgSender());

		if (!isApprovedOrOwner) revert TransferCallerNotOwnerNorApproved();
		if (prevOwnership.addr != from) revert TransferFromIncorrectOwner();
		if (to == address(0)) revert TransferToZeroAddress();

		_beforeTokenTransfers(from, to, tokenId, 1);

		// Clear approvals from the previous owner
		_approve(address(0), tokenId, prevOwnership.addr);

		// Underflow of the sender's balance is impossible because we check for
		// ownership above and the recipient's balance can't realistically overflow.
		// Counter overflow is incredibly unrealistic as tokenId would have to be 2**256.
		unchecked {
			_addressData[from].balance -= 1;
			_addressData[to].balance += 1;

			_ownerships[tokenId].addr = to;
			_ownerships[tokenId].startTimestamp = uint64(block.timestamp);

			// If the ownership slot of tokenId+1 is not explicitly set, that means the transfer initiator owns it.
			// Set the slot of tokenId+1 explicitly in storage to maintain correctness for ownerOf(tokenId+1) calls.
			uint256 nextTokenId = tokenId + 1;
			if (_ownerships[nextTokenId].addr == address(0)) {
				// This will suffice for checking _exists(nextTokenId),
				// as a burned slot cannot contain the zero address.
				if (nextTokenId < _currentIndex) {
					_ownerships[nextTokenId].addr = prevOwnership.addr;
					_ownerships[nextTokenId].startTimestamp = prevOwnership.startTimestamp;
				}
			}
		}

		emit Transfer(from, to, tokenId);
		_afterTokenTransfers(from, to, tokenId, 1);
	}

	/**
	 * @dev Destroys `tokenId`.
	 * The approval is cleared when the token is burned.
	 *
	 * Requirements:
	 *
	 * - `tokenId` must exist.
	 *
	 * Emits a {Transfer} event.
	 */
	function _burn(uint256 tokenId) internal virtual {
		TokenOwnership memory prevOwnership = ownershipOf(tokenId);

		_beforeTokenTransfers(prevOwnership.addr, address(0), tokenId, 1);

		// Clear approvals from the previous owner
		_approve(address(0), tokenId, prevOwnership.addr);

		// Underflow of the sender's balance is impossible because we check for
		// ownership above and the recipient's balance can't realistically overflow.
		// Counter overflow is incredibly unrealistic as tokenId would have to be 2**256.
		unchecked {
			_addressData[prevOwnership.addr].balance -= 1;
			_addressData[prevOwnership.addr].numberBurned += 1;

			// Keep track of who burned the token, and the timestamp of burning.
			_ownerships[tokenId].addr = prevOwnership.addr;
			_ownerships[tokenId].startTimestamp = uint64(block.timestamp);
			_ownerships[tokenId].burned = true;

			// If the ownership slot of tokenId+1 is not explicitly set, that means the burn initiator owns it.
			// Set the slot of tokenId+1 explicitly in storage to maintain correctness for ownerOf(tokenId+1) calls.
			uint256 nextTokenId = tokenId + 1;
			if (_ownerships[nextTokenId].addr == address(0)) {
				// This will suffice for checking _exists(nextTokenId),
				// as a burned slot cannot contain the zero address.
				if (nextTokenId < _currentIndex) {
					_ownerships[nextTokenId].addr = prevOwnership.addr;
					_ownerships[nextTokenId].startTimestamp = prevOwnership.startTimestamp;
				}
			}
		}

		emit Transfer(prevOwnership.addr, address(0), tokenId);
		_afterTokenTransfers(prevOwnership.addr, address(0), tokenId, 1);

		// Overflow not possible, as _burnCounter cannot be exceed _currentIndex times.
		unchecked {
			_burnCounter++;
		}
	}

	/**
	 * @dev Approve `to` to operate on `tokenId`
	 *
	 * Emits a {Approval} event.
	 */
	function _approve(
		address to,
		uint256 tokenId,
		address owner
	) private {
		_tokenApprovals[tokenId] = to;
		emit Approval(owner, to, tokenId);
	}

	/**
	 * @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target contract.
	 *
	 * @param from address representing the previous owner of the given token ID
	 * @param to target address that will receive the tokens
	 * @param tokenId uint256 ID of the token to be transferred
	 * @param _data bytes optional data to send along with the call
	 * @return bool whether the call correctly returned the expected magic value
	 */
	function _checkContractOnERC721Received(
		address from,
		address to,
		uint256 tokenId,
		bytes memory _data
	) private returns (bool) {
		try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data) returns (
			bytes4 retval
		) {
			return retval == IERC721Receiver(to).onERC721Received.selector;
		} catch (bytes memory reason) {
			if (reason.length == 0) {
				revert TransferToNonERC721ReceiverImplementer();
			} else {
				assembly {
					revert(add(32, reason), mload(reason))
				}
			}
		}
	}

	/**
	 * @dev Hook that is called before a set of serially-ordered token ids are about to be transferred. This includes minting.
	 * And also called before burning one token.
	 *
	 * startTokenId - the first token id to be transferred
	 * quantity - the amount to be transferred
	 *
	 * Calling conditions:
	 *
	 * - When `from` and `to` are both non-zero, `from`'s `tokenId` will be
	 * transferred to `to`.
	 * - When `from` is zero, `tokenId` will be minted for `to`.
	 * - When `to` is zero, `tokenId` will be burned by `from`.
	 * - `from` and `to` are never both zero.
	 */
	function _beforeTokenTransfers(
		address from,
		address to,
		uint256 startTokenId,
		uint256 quantity
	) internal virtual {}

	/**
	 * @dev Hook that is called after a set of serially-ordered token ids have been transferred. This includes
	 * minting.
	 * And also called after one token has been burned.
	 *
	 * startTokenId - the first token id to be transferred
	 * quantity - the amount to be transferred
	 *
	 * Calling conditions:
	 *
	 * - When `from` and `to` are both non-zero, `from`'s `tokenId` has been
	 * transferred to `to`.
	 * - When `from` is zero, `tokenId` has been minted for `to`.
	 * - When `to` is zero, `tokenId` has been burned by `from`.
	 * - `from` and `to` are never both zero.
	 */
	function _afterTokenTransfers(
		address from,
		address to,
		uint256 startTokenId,
		uint256 quantity
	) internal virtual {}
}


//SPDX-License-Identifier: MIT
//Contract based on [https://docs.openzeppelin.com/contracts/3.x/erc721](https://docs.openzeppelin.com/contracts/3.x/erc721)

pragma solidity ^0.8.0;



contract MergePortals is ERC721A, IERC2981, Ownable, ReentrancyGuard {
    using Counters for Counters.Counter;
    using Strings for uint256;

    Counters.Counter private tokenCounter;

    string private baseURI = "ipfs://bafybeicbu7pv2neolznvpwf7rxttn4kusdhcjk5z6uz4nfjanqmmrossrq";
    address private openSeaProxyRegistryAddress = 0xa5409ec958C83C3f309868babACA7c86DCB077c1;
    bool private isOpenSeaProxyActive = true;

    uint256 public MAX_FREE_MINTS = 1;
    uint256 public constant MAX_MINTS_PER_TX = 10;
    uint256 public maxSupply = 1000;

    uint256 public constant PUBLIC_SALE_PRICE = 0.002 ether;
    uint256 public NUM_FREE_MINTS = 500;
    bool public isPublicSaleActive = true;




    // ============ ACCESS CONTROL/SANITY MODIFIERS ============

    modifier publicSaleActive() {
        require(isPublicSaleActive, "Public sale is not open");
        _;
    }

    modifier maxMintsPerTX(uint256 numberOfTokens) {
        require(
            numberOfTokens <= MAX_MINTS_PER_TX,
            "Max mints per transaction exceeded"
        );
        _;
    }

    modifier canMintNFTs(uint256 numberOfTokens) {
        require(
            totalSupply() + numberOfTokens <=
                maxSupply,
            "Not enough mints remaining to mint"
        );
        _;
    }

    modifier freeMintsAvailable() {
        require(
            totalSupply() <=
                NUM_FREE_MINTS,
            "Not enough free mints remain"
        );
        _;
    }


    modifier isCorrectPayment(uint256 price, uint256 numberOfTokens) {
        if(totalSupply()>NUM_FREE_MINTS){
        require(
            (price * numberOfTokens) == msg.value,
            "Incorrect ETH value sent"
        );
        }
        _;
    }


    constructor(
    ) ERC721A("Merge Portals", "PORTAL") {
    }

    // ============ PUBLIC FUNCTIONS FOR MINTING ============

    function mint(uint256 numberOfTokens)
        external
        payable
        nonReentrant
        isCorrectPayment(PUBLIC_SALE_PRICE, numberOfTokens)
        publicSaleActive
        canMintNFTs(numberOfTokens)
        maxMintsPerTX(numberOfTokens)
    {

        uint payForCount = numberOfTokens;
        uint mintedSoFar = _numberMinted(msg.sender);
        
        //1 Free Mints Default
        uint maxFree = MAX_FREE_MINTS;

        if(mintedSoFar < maxFree) {
            uint remainingFreeMints = maxFree - mintedSoFar;
            if(numberOfTokens > remainingFreeMints) {
                payForCount = numberOfTokens - remainingFreeMints;
            }
            else {
                payForCount = 0;
            }
        }

		require(
			msg.value >= payForCount * PUBLIC_SALE_PRICE,
			'Ether value sent is not sufficient'
		);

        _safeMint(msg.sender, numberOfTokens);
    }


    //A simple free mint function to avoid confusion
    //The normal mint function with a cost of 0 would work too

    // ============ PUBLIC READ-ONLY FUNCTIONS ============

    function getBaseURI() external view returns (string memory) {
        return baseURI;
    }

    // ============ OWNER-ONLY ADMIN FUNCTIONS ============

    function setBaseURI(string memory _baseURI) external onlyOwner {
        baseURI = _baseURI;
    }

    // function to disable gasless listings for security in case
    // opensea ever shuts down or is compromised
    function setIsOpenSeaProxyActive(bool _isOpenSeaProxyActive)
        external
        onlyOwner
    {
        isOpenSeaProxyActive = _isOpenSeaProxyActive;
    }

    function setIsPublicSaleActive(bool _isPublicSaleActive)
        external
        onlyOwner
    {
        isPublicSaleActive = _isPublicSaleActive;
    }


    function setNumFreeMints(uint256 _numfreemints)
        external
        onlyOwner
    {
        NUM_FREE_MINTS = _numfreemints;
    }

    function setLowerMaxSupply(uint256 _newMax)
        external
        onlyOwner
    {
        maxSupply = _newMax;
    }

    function withdraw() public onlyOwner {
        uint256 balance = address(this).balance;
        payable(msg.sender).transfer(balance);
    }

    function withdrawTokens(IERC20 token) public onlyOwner {
        uint256 balance = token.balanceOf(address(this));
        token.transfer(msg.sender, balance);
    }

    function airdrop(address to, uint count) external onlyOwner {
		require(
			totalSupply() + count <= maxSupply,
			'Exceeds max supply'
		);
		_safeMint(to, count);
	}

    function burn(uint256[] calldata nums) external onlyOwner {
        for (uint i=0; i < nums.length; i++) {
            _burn(nums[i]);
        }
	}



    // ============ SUPPORTING FUNCTIONS ============

    function nextTokenId() private returns (uint256) {
        tokenCounter.increment();
        return tokenCounter.current();
    }

    // ============ FUNCTION OVERRIDES ============

    function supportsInterface(bytes4 interfaceId)
        public
        view
        virtual
        override(ERC721A, IERC165)
        returns (bool)
    {
        return
            interfaceId == type(IERC2981).interfaceId ||
            super.supportsInterface(interfaceId);
    }

    /**
     * @dev Override isApprovedForAll to allowlist user's OpenSea proxy accounts to enable gas-less listings.
     */
    function isApprovedForAll(address owner, address operator)
        public
        view
        override
        returns (bool)
    {
        // Get a reference to OpenSea's proxy registry contract by instantiating
        // the contract using the already existing address.
        ProxyRegistry proxyRegistry = ProxyRegistry(
            openSeaProxyRegistryAddress
        );
        if (
            isOpenSeaProxyActive &&
            address(proxyRegistry.proxies(owner)) == operator
        ) {
            return true;
        }

        return super.isApprovedForAll(owner, operator);
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId)
        public
        view
        virtual
        override
        returns (string memory)
    {
        require(_exists(tokenId), "Nonexistent token");

        return
            string(abi.encodePacked(baseURI, "/", (tokenId+1).toString(), ".json"));
            //string(abi.encodePacked(baseURI, "/", (tokenId+1).toString(), ""));
    }

    /**
     * @dev See {IERC165-royaltyInfo}.
     */
    function royaltyInfo(uint256 tokenId, uint256 salePrice)
        external
        view
        override
        returns (address receiver, uint256 royaltyAmount)
    {
        require(_exists(tokenId), "Nonexistent token");

        return (address(this), SafeMath.div(SafeMath.mul(salePrice, 5), 100));
    }
}

// These contract definitions are used to create a reference to the OpenSea
// ProxyRegistry contract by using the registry's address (see isApprovedForAll).
contract OwnableDelegateProxy {

}

contract ProxyRegistry {
    mapping(address => OwnableDelegateProxy) public proxies;
}