// File: BITRING.sol



/**
 *Submitted for verification at Etherscan.io on 2023-2-09
*/

pragma solidity ^0.8.13;

interface IOperatorFilterRegistry {
    function isOperatorAllowed(address registrant, address operator) external view returns (bool);
    function register(address registrant) external;
    function registerAndSubscribe(address registrant, address subscription) external;
    function registerAndCopyEntries(address registrant, address registrantToCopy) external;
    function updateOperator(address registrant, address operator, bool filtered) external;
    function updateOperators(address registrant, address[] calldata operators, bool filtered) external;
    function updateCodeHash(address registrant, bytes32 codehash, bool filtered) external;
    function updateCodeHashes(address registrant, bytes32[] calldata codeHashes, bool filtered) external;
    function subscribe(address registrant, address registrantToSubscribe) external;
    function unsubscribe(address registrant, bool copyExistingEntries) external;
    function subscriptionOf(address addr) external returns (address registrant);
    function subscribers(address registrant) external returns (address[] memory);
    function subscriberAt(address registrant, uint256 index) external returns (address);
    function copyEntriesOf(address registrant, address registrantToCopy) external;
    function isOperatorFiltered(address registrant, address operator) external returns (bool);
    function isCodeHashOfFiltered(address registrant, address operatorWithCode) external returns (bool);
    function isCodeHashFiltered(address registrant, bytes32 codeHash) external returns (bool);
    function filteredOperators(address addr) external returns (address[] memory);
    function filteredCodeHashes(address addr) external returns (bytes32[] memory);
    function filteredOperatorAt(address registrant, uint256 index) external returns (address);
    function filteredCodeHashAt(address registrant, uint256 index) external returns (bytes32);
    function isRegistered(address addr) external returns (bool);
    function codeHashOf(address addr) external returns (bytes32);
}

// File: OperatorFilterer.sol


pragma solidity ^0.8.13;


abstract contract OperatorFilterer {
    error OperatorNotAllowed(address operator);

    IOperatorFilterRegistry constant operatorFilterRegistry =
        IOperatorFilterRegistry(0x000000000000AAeB6D7670E522A718067333cd4E);

    constructor(address subscriptionOrRegistrantToCopy, bool subscribe) {
        // If an inheriting token contract is deployed to a network without the registry deployed, the modifier
        // will not revert, but the contract will need to be registered with the registry once it is deployed in
        // order for the modifier to filter addresses.
        if (address(operatorFilterRegistry).code.length > 0) {
            if (subscribe) {
                operatorFilterRegistry.registerAndSubscribe(address(this), subscriptionOrRegistrantToCopy);
            } else {
                if (subscriptionOrRegistrantToCopy != address(0)) {
                    operatorFilterRegistry.registerAndCopyEntries(address(this), subscriptionOrRegistrantToCopy);
                } else {
                    operatorFilterRegistry.register(address(this));
                }
            }
        }
    }

    modifier onlyAllowedOperator(address from) virtual {
        // Check registry code length to facilitate testing in environments without a deployed registry.
        if (address(operatorFilterRegistry).code.length > 0) {
            // Allow spending tokens from addresses with balance
            // Note that this still allows listings and marketplaces with escrow to transfer tokens if transferred
            // from an EOA.
            if (from == msg.sender) {
                _;
                return;
            }
            if (
                !(
                    operatorFilterRegistry.isOperatorAllowed(address(this), msg.sender)
                        && operatorFilterRegistry.isOperatorAllowed(address(this), from)
                )
            ) {
                revert OperatorNotAllowed(msg.sender);
            }
        }
        _;
    }
}

// File: DefaultOperatorFilterer.sol


pragma solidity ^0.8.13;


abstract contract DefaultOperatorFilterer is OperatorFilterer {
    address constant DEFAULT_SUBSCRIPTION = address(0x3cc6CddA760b79bAfa08dF41ECFA224f810dCeB6);

    constructor() OperatorFilterer(DEFAULT_SUBSCRIPTION, true) {}
}

// File: undead-ape-yacht-club.sol



// File: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/cryptography/MerkleProof.sol


// OpenZeppelin Contracts (last updated v4.5.0) (utils/cryptography/MerkleProof.sol)

pragma solidity ^0.8.0;

/**
 * @dev These functions deal with verification of Merkle Trees proofs.
 *
 * The proofs can be generated using the JavaScript library
 * https://github.com/miguelmota/merkletreejs[merkletreejs].
 * Note: the hashing algorithm should be keccak256 and pair sorting should be enabled.
 *
 * See `test/utils/cryptography/MerkleProof.test.js` for some examples.
 *
 * WARNING: You should avoid using leaf values that are 64 bytes long prior to
 * hashing, or use a hash function other than keccak256 for hashing leaves.
 * This is because the concatenation of a sorted pair of internal nodes in
 * the merkle tree could be reinterpreted as a leaf value.
 */
library MerkleProof {
    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     */
    function verify(
        bytes32[] memory proof,
        bytes32 root,
        bytes32 leaf
    ) internal pure returns (bool) {
        return processProof(proof, leaf) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merkle tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leafs & pre-images are assumed to be sorted.
     *
     * _Available since v4.4._
     */
    function processProof(bytes32[] memory proof, bytes32 leaf) internal pure returns (bytes32) {
        bytes32 computedHash = leaf;
        for (uint256 i = 0; i < proof.length; i++) {
            bytes32 proofElement = proof[i];
            if (computedHash <= proofElement) {
                // Hash(current computed hash + current element of the proof)
                computedHash = _efficientHash(computedHash, proofElement);
            } else {
                // Hash(current element of the proof + current computed hash)
                computedHash = _efficientHash(proofElement, computedHash);
            }
        }
        return computedHash;
    }

    function _efficientHash(bytes32 a, bytes32 b) private pure returns (bytes32 value) {
        assembly {
            mstore(0x00, a)
            mstore(0x20, b)
            value := keccak256(0x00, 0x40)
        }
    }
}

// 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/Address.sol


// OpenZeppelin Contracts (last updated v4.5.0) (utils/Address.sol)

pragma solidity ^0.8.1;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 0;
    }

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

// 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/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/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);
}

// 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: contracts/erc721a.sol



// Creator: Chiru Labs



pragma solidity ^0.8.4;










error ApprovalCallerNotOwnerNorApproved();

error ApprovalQueryForNonexistentToken();

error ApproveToCaller();

error ApprovalToCurrentOwner();

error BalanceQueryForZeroAddress();

error MintToZeroAddress();

error MintZeroQuantity();

error OwnerQueryForNonexistentToken();

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 1;

    }



    /**

     * @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) {

        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) {

        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) {

        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 {

        _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 virtual 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);



        if (prevOwnership.addr != from) revert TransferFromIncorrectOwner();



        bool isApprovedOrOwner = (_msgSender() == from ||

            isApprovedForAll(from, _msgSender()) ||

            getApproved(tokenId) == _msgSender());



        if (!isApprovedOrOwner) revert TransferCallerNotOwnerNorApproved();

        if (to == address(0)) revert TransferToZeroAddress();



        _beforeTokenTransfers(from, to, tokenId, 1);



        // Clear approvals from the previous owner

        _approve(address(0), tokenId, from);



        // 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;



            TokenOwnership storage currSlot = _ownerships[tokenId];

            currSlot.addr = to;

            currSlot.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;

            TokenOwnership storage nextSlot = _ownerships[nextTokenId];

            if (nextSlot.addr == address(0)) {

                // This will suffice for checking _exists(nextTokenId),

                // as a burned slot cannot contain the zero address.

                if (nextTokenId != _currentIndex) {

                    nextSlot.addr = from;

                    nextSlot.startTimestamp = prevOwnership.startTimestamp;

                }

            }

        }



        emit Transfer(from, to, tokenId);

        _afterTokenTransfers(from, to, tokenId, 1);

    }



    /**

     * @dev This is equivalent to _burn(tokenId, false)

     */

    function _burn(uint256 tokenId) internal virtual {

        _burn(tokenId, false);

    }



    /**

     * @dev Destroys `tokenId`.

     * The approval is cleared when the token is burned.

     *

     * Requirements:

     *

     * - `tokenId` must exist.

     *

     * Emits a {Transfer} event.

     */

    function _burn(uint256 tokenId, bool approvalCheck) internal virtual {

        TokenOwnership memory prevOwnership = _ownershipOf(tokenId);



        address from = prevOwnership.addr;



        if (approvalCheck) {

            bool isApprovedOrOwner = (_msgSender() == from ||

                isApprovedForAll(from, _msgSender()) ||

                getApproved(tokenId) == _msgSender());



            if (!isApprovedOrOwner) revert TransferCallerNotOwnerNorApproved();

        }



        _beforeTokenTransfers(from, address(0), tokenId, 1);



        // Clear approvals from the previous owner

        _approve(address(0), tokenId, from);



        // 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 storage addressData = _addressData[from];

            addressData.balance -= 1;

            addressData.numberBurned += 1;



            // Keep track of who burned the token, and the timestamp of burning.

            TokenOwnership storage currSlot = _ownerships[tokenId];

            currSlot.addr = from;

            currSlot.startTimestamp = uint64(block.timestamp);

            currSlot.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;

            TokenOwnership storage nextSlot = _ownerships[nextTokenId];

            if (nextSlot.addr == address(0)) {

                // This will suffice for checking _exists(nextTokenId),

                // as a burned slot cannot contain the zero address.

                if (nextTokenId != _currentIndex) {

                    nextSlot.addr = from;

                    nextSlot.startTimestamp = prevOwnership.startTimestamp;

                }

            }

        }



        emit Transfer(from, address(0), tokenId);

        _afterTokenTransfers(from, 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 {}

}

// 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 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/blob/master/contracts/token/ERC721/extensions/ERC721Burnable.sol

// SPDX-License-Identifier: MIT
// Creator: Chiru Labs

pragma solidity ^0.8.4;

/**
 * @title ERC721A Burnable Token
 * @dev ERC721A Token that can be irreversibly burned (destroyed).
 */
abstract contract ERC721ABurnable is ERC721A {
    /**
     * @dev Burns `tokenId`. See {ERC721A-_burn}.
     *
     * Requirements:
     *
     * - The caller must own `tokenId` or be an approved operator.
     */
    function burn(uint256 tokenId) public virtual {
        _burn(tokenId, true);
    }
}

// File: contracts/contract.sol


pragma solidity ^0.8.4;


contract BITRING is Ownable, ERC721A, DefaultOperatorFilterer, ERC721ABurnable  {

    using Strings for uint256;

    string private baseTokenURI;

    uint256 public presaleCost = 0.05 ether;
    uint256 public publicSaleCost = 0.1 ether;

    uint64 public maxSupply = 1000;

    bool public presaleActive = false;
    bool public publicSaleActive = false;

    constructor() ERC721A("BITRING", "BITRING"){}

    modifier mintCompliance(uint256 _mintAmount) {
        require(_mintAmount > 0 , "Invalid mint amount!");
        require(totalMinted() + _mintAmount <= maxSupply, "Max supply exceeded!");
        _;
    }

    ///Mints NFTs for whitelist members during the presale
    function presaleMint(uint64 _mintAmount) public payable mintCompliance(_mintAmount) {
        require(presaleActive, "Presale is not Active");
        _safeMint(msg.sender, _mintAmount);
    }

    ///Allows any address to mint when the public sale is open
    function publicMint(uint64 _mintAmount) public payable mintCompliance(_mintAmount) {
        require(publicSaleActive, "Public is not Active");
        require(tx.origin == msg.sender);
        require(msg.value == publicSaleCost * _mintAmount, "Insufficient funds!");
        _safeMint(msg.sender, _mintAmount);
    }

    ///Allows owner of the collection to airdrop a token to any address
    function ownerMint(uint256 _mintAmount, address _receiver) public mintCompliance(_mintAmount) onlyOwner {
        _safeMint(_receiver, _mintAmount);
    }

    //@return token ids owned by an address in the collection
    function walletOfOwner(address _owner)
        external
        view
        returns (uint256[] memory)
    {
        uint256 ownerTokenCount = balanceOf(_owner);
        uint256[] memory ownedTokenIds = new uint256[](ownerTokenCount);
        uint256 currentTokenId = 1;
        uint256 ownedTokenIndex = 0;

        while (ownedTokenIndex < ownerTokenCount && currentTokenId <= maxSupply) {
            if(exists(currentTokenId) == true) {
                address currentTokenOwner = ownerOf(currentTokenId);

                if (currentTokenOwner == _owner) {
                    ownedTokenIds[ownedTokenIndex] = currentTokenId;
                    ownedTokenIndex++;
                }
            }
            currentTokenId++;
        }

        return ownedTokenIds;
    }

    function setPubCost(uint256 _newCost) public onlyOwner {
        publicSaleCost = _newCost;
    }

    function transferFrom(address from, address to, uint256 tokenId) public override onlyAllowedOperator(from) {
        super.transferFrom(from, to, tokenId);
    }

    function safeTransferFrom(address from, address to, uint256 tokenId) public override onlyAllowedOperator(from) {
        super.safeTransferFrom(from, to, tokenId);
    }

    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory data)
        public
        override
        onlyAllowedOperator(from)
    {
        super.safeTransferFrom(from, to, tokenId, data);
    }

    //@return full url for passed in token id 
    function tokenURI(uint256 _tokenId)

        public
        view
        virtual
        override
        returns (string memory)

    {

        require(
        _exists(_tokenId),
        "ERC721Metadata: URI query for nonexistent token"
        );

        string memory currentBaseURI = _baseURI();

        return bytes(currentBaseURI).length > 0

            ? string(abi.encodePacked(currentBaseURI, _tokenId.toString(), ".json"))

            : "";
    }

    //@return all NFT's minted including burned tokens
    function totalMinted() public view returns (uint256) {
        return _totalMinted();
    }

    function exists(uint256 _tokenId) public view returns (bool) {
        return _exists(_tokenId);
    }

    //@return url for the nft metadata
    function _baseURI() internal view virtual override returns (string memory) {
        return baseTokenURI;
    }

    function setBaseURI(string calldata _URI) external onlyOwner {
        baseTokenURI = _URI;
    }
    
    function setPresaleActive(bool _state) public onlyOwner {
        presaleActive = _state;
    }

    function setPublicActive(bool _state) public onlyOwner {
        publicSaleActive = _state;
    }

    function withdraw() public onlyOwner {
        (bool os, ) = payable(owner()).call{value: address(this).balance}("");
        require(os);
    }

    /// Fallbacks 
    receive() external payable { }
    fallback() external payable { }
}