// File: contracts/CrashTrading.sol





// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

// Sources flattened with hardhat v2.3.0 https://hardhat.org

// File @openzeppelin/contracts/utils/introspection/IERC165.sol@v4.1.0

/**
 * @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/token/ERC721/IERC721.sol@v4.1.0

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/IERC721Receiver.sol@v4.1.0

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/token/ERC721/extensions/IERC721Metadata.sol@v4.1.0

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/Address.sol@v4.1.0

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;
 // solhint-disable-next-line no-inline-assembly
 assembly {
 size := extcodesize(account)
 }
 return size > 0;
 }

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

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

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

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

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

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

 // solhint-disable-next-line avoid-low-level-calls
 (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');

 // solhint-disable-next-line avoid-low-level-calls
 (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');

 // solhint-disable-next-line avoid-low-level-calls
 (bool success, bytes memory returndata) = target.delegatecall(data);
 return _verifyCallResult(success, returndata, errorMessage);
 }

 function _verifyCallResult(
 bool success,
 bytes memory returndata,
 string memory errorMessage
 ) private 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

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

// File @openzeppelin/contracts/utils/Context.sol@v4.1.0

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) {
 this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
 return msg.data;
 }
}

// File @openzeppelin/contracts/utils/Strings.sol@v4.1.0

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
 bytes16 private constant alphabet = '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] = alphabet[value & 0xf];
 value >>= 4;
 }
 require(value == 0, 'Strings: hex length insufficient');
 return string(buffer);
 }
}

// File @openzeppelin/contracts/utils/introspection/ERC165.sol@v4.1.0

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/ERC721.sol@v4.1.0

pragma solidity ^0.8.0;

/**
 * @dev Implementation of https://eips.ethereum.org/EIPS/eip-721[ERC721] Non-Fungible Token Standard, including
 * the Metadata extension, but not including the Enumerable extension, which is available separately as
 * {ERC721Enumerable}.
 */
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
 using Address for address;
 using Strings for uint256;

 // Token name
 string private _name;

 // Token symbol
 string private _symbol;

 // Mapping from token ID to owner address
 mapping(uint256 => address) private _owners;

 // Mapping owner address to token count
 mapping(address => uint256) private _balances;

 // 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;

 /**
 * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
 */
 constructor(string memory name_, string memory symbol_) {
 _name = name_;
 _symbol = symbol_;
 }

 /**
 * @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 virtual override returns (uint256) {
 require(owner != address(0), 'ERC721: balance query for the zero address');
 return _balances[owner];
 }

 /**
 * @dev See {IERC721-ownerOf}.
 */
 function ownerOf(uint256 tokenId) public view virtual override returns (address) {
 address owner = _owners[tokenId];
 require(owner != address(0), 'ERC721: owner query for nonexistent token');
 return owner;
 }

 /**
 * @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) {
 require(_exists(tokenId), 'ERC721Metadata: URI query for nonexistent token');

 string memory baseURI = _baseURI();
 return bytes(baseURI).length > 0 ? string(abi.encodePacked(baseURI, tokenId.toString())) : '';
 }

 /**
 * @dev Base URI for computing {tokenURI}. 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 virtual override {
 address owner = ERC721.ownerOf(tokenId);
 require(to != owner, 'ERC721: approval to current owner');

 require(_msgSender() == owner || isApprovedForAll(owner, _msgSender()), 'ERC721: approve caller is not owner nor approved for all');

 _approve(to, tokenId);
 }

 /**
 * @dev See {IERC721-getApproved}.
 */
 function getApproved(uint256 tokenId) public view virtual override returns (address) {
 require(_exists(tokenId), 'ERC721: approved query for nonexistent token');

 return _tokenApprovals[tokenId];
 }

 /**
 * @dev See {IERC721-setApprovalForAll}.
 */
 function setApprovalForAll(address operator, bool approved) public virtual override {
 require(operator != _msgSender(), 'ERC721: approve to caller');

 _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 {
 //solhint-disable-next-line max-line-length
 require(_isApprovedOrOwner(_msgSender(), tokenId), 'ERC721: transfer caller is not owner nor approved');

 _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 {
 require(_isApprovedOrOwner(_msgSender(), tokenId), 'ERC721: transfer caller is not owner nor approved');
 _safeTransfer(from, to, tokenId, _data);
 }

 /**
 * @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.
 *
 * `_data` is additional data, it has no specified format and it is sent in call to `to`.
 *
 * This internal function is equivalent to {safeTransferFrom}, and can be used to e.g.
 * implement alternative mechanisms to perform token transfer, such as signature-based.
 *
 * Requirements:
 *
 * - `from` cannot be the zero address.
 * - `to` cannot be the zero address.
 * - `tokenId` token must exist and be owned by `from`.
 * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
 *
 * Emits a {Transfer} event.
 */
 function _safeTransfer(
 address from,
 address to,
 uint256 tokenId,
 bytes memory _data
 ) internal virtual {
 _transfer(from, to, tokenId);
 require(_checkOnERC721Received(from, to, tokenId, _data), 'ERC721: transfer to non ERC721Receiver implementer');
 }

 /**
 * @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`),
 * and stop existing when they are burned (`_burn`).
 */
 function _exists(uint256 tokenId) internal view virtual returns (bool) {
 return _owners[tokenId] != address(0);
 }

 /**
 * @dev Returns whether `spender` is allowed to manage `tokenId`.
 *
 * Requirements:
 *
 * - `tokenId` must exist.
 */
 function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
 require(_exists(tokenId), 'ERC721: operator query for nonexistent token');
 address owner = ERC721.ownerOf(tokenId);
 return (spender == owner || getApproved(tokenId) == spender || isApprovedForAll(owner, spender));
 }

 /**
 * @dev Safely mints `tokenId` and transfers it to `to`.
 *
 * Requirements:
 *
 * - `tokenId` must not exist.
 * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
 *
 * Emits a {Transfer} event.
 */
 function _safeMint(address to, uint256 tokenId) internal virtual {
 _safeMint(to, tokenId, '');
 }

 /**
 * @dev Same as {xref-ERC721-_safeMint-address-uint256-}[`_safeMint`], with an additional `data` parameter which is
 * forwarded in {IERC721Receiver-onERC721Received} to contract recipients.
 */
 function _safeMint(
 address to,
 uint256 tokenId,
 bytes memory _data
 ) internal virtual {
 _mint(to, tokenId);
 require(_checkOnERC721Received(address(0), to, tokenId, _data), 'ERC721: transfer to non ERC721Receiver implementer');
 }

 /**
 * @dev Mints `tokenId` and transfers it to `to`.
 *
 * WARNING: Usage of this method is discouraged, use {_safeMint} whenever possible
 *
 * Requirements:
 *
 * - `tokenId` must not exist.
 * - `to` cannot be the zero address.
 *
 * Emits a {Transfer} event.
 */
 function _mint(address to, uint256 tokenId) internal virtual {
 require(to != address(0), 'ERC721: mint to the zero address');
 require(!_exists(tokenId), 'ERC721: token already minted');

 _beforeTokenTransfer(address(0), to, tokenId);

 _balances[to] += 1;
 _owners[tokenId] = to;

 emit Transfer(address(0), to, tokenId);
 }

 /**
 * @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 {
 address owner = ERC721.ownerOf(tokenId);

 _beforeTokenTransfer(owner, address(0), tokenId);

 // Clear approvals
 _approve(address(0), tokenId);

 _balances[owner] -= 1;
 delete _owners[tokenId];

 emit Transfer(owner, address(0), tokenId);
 }

 /**
 * @dev Transfers `tokenId` from `from` to `to`.
 * As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
 *
 * 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
 ) internal virtual {
 require(ERC721.ownerOf(tokenId) == from, 'ERC721: transfer of token that is not own');
 require(to != address(0), 'ERC721: transfer to the zero address');

 _beforeTokenTransfer(from, to, tokenId);

 // Clear approvals from the previous owner
 _approve(address(0), tokenId);

 _balances[from] -= 1;
 _balances[to] += 1;
 _owners[tokenId] = to;

 emit Transfer(from, to, tokenId);
 }

 /**
 * @dev Approve `to` to operate on `tokenId`
 *
 * Emits a {Approval} event.
 */
 function _approve(address to, uint256 tokenId) internal virtual {
 _tokenApprovals[tokenId] = to;
 emit Approval(ERC721.ownerOf(tokenId), to, tokenId);
 }

 /**
 * @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target address.
 * The call is not executed if the target address is not a 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 _checkOnERC721Received(
 address from,
 address to,
 uint256 tokenId,
 bytes memory _data
 ) private returns (bool) {
 if (to.isContract()) {
 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('ERC721: transfer to non ERC721Receiver implementer');
 } else {
 // solhint-disable-next-line no-inline-assembly
 assembly {
 revert(add(32, reason), mload(reason))
 }
 }
 }
 } else {
 return true;
 }
 }

 /**
 * @dev Hook that is called before any token transfer. This includes minting
 * and burning.
 *
 * Calling conditions:
 *
 * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
 * transferred to `to`.
 * - When `from` is zero, `tokenId` will be minted for `to`.
 * - When `to` is zero, ``from``'s `tokenId` will be burned.
 * - `from` cannot be the zero address.
 * - `to` cannot be the zero address.
 *
 * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
 */
 function _beforeTokenTransfer(
 address from,
 address to,
 uint256 tokenId
 ) internal virtual {}
}

// File @openzeppelin/contracts/token/ERC721/extensions/IERC721Enumerable.sol@v4.1.0

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/ERC721Enumerable.sol@v4.1.0

pragma solidity ^0.8.0;

/**
 * @dev This implements an optional extension of {ERC721} defined in the EIP that adds
 * enumerability of all the token ids in the contract as well as all token ids owned by each
 * account.
 */
abstract contract ERC721Enumerable is ERC721, IERC721Enumerable {
 // Mapping from owner to list of owned token IDs
 mapping(address => mapping(uint256 => uint256)) private _ownedTokens;

 // Mapping from token ID to index of the owner tokens list
 mapping(uint256 => uint256) private _ownedTokensIndex;

 // Array with all token ids, used for enumeration
 uint256[] private _allTokens;

 // Mapping from token id to position in the allTokens array
 mapping(uint256 => uint256) private _allTokensIndex;

 /**
 * @dev See {IERC165-supportsInterface}.
 */
 function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC721) returns (bool) {
 return interfaceId == type(IERC721Enumerable).interfaceId || super.supportsInterface(interfaceId);
 }

 /**
 * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
 */
 function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
 require(index < ERC721.balanceOf(owner), 'ERC721Enumerable: owner index out of bounds');
 return _ownedTokens[owner][index];
 }

 /**
 * @dev See {IERC721Enumerable-totalSupply}.
 */
 function totalSupply() public view virtual override returns (uint256) {
 return _allTokens.length;
 }

 /**
 * @dev See {IERC721Enumerable-tokenByIndex}.
 */
 function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
 require(index < ERC721Enumerable.totalSupply(), 'ERC721Enumerable: global index out of bounds');
 return _allTokens[index];
 }

 /**
 * @dev Hook that is called before any token transfer. This includes minting
 * and burning.
 *
 * Calling conditions:
 *
 * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
 * transferred to `to`.
 * - When `from` is zero, `tokenId` will be minted for `to`.
 * - When `to` is zero, ``from``'s `tokenId` will be burned.
 * - `from` cannot be the zero address.
 * - `to` cannot be the zero address.
 *
 * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
 */
 function _beforeTokenTransfer(
 address from,
 address to,
 uint256 tokenId
 ) internal virtual override {
 super._beforeTokenTransfer(from, to, tokenId);

 if (from == address(0)) {
 _addTokenToAllTokensEnumeration(tokenId);
 } else if (from != to) {
 _removeTokenFromOwnerEnumeration(from, tokenId);
 }
 if (to == address(0)) {
 _removeTokenFromAllTokensEnumeration(tokenId);
 } else if (to != from) {
 _addTokenToOwnerEnumeration(to, tokenId);
 }
 }

 /**
 * @dev Private function to add a token to this extension's ownership-tracking data structures.
 * @param to address representing the new owner of the given token ID
 * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
 */
 function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
 uint256 length = ERC721.balanceOf(to);
 _ownedTokens[to][length] = tokenId;
 _ownedTokensIndex[tokenId] = length;
 }

 /**
 * @dev Private function to add a token to this extension's token tracking data structures.
 * @param tokenId uint256 ID of the token to be added to the tokens list
 */
 function _addTokenToAllTokensEnumeration(uint256 tokenId) private {
 _allTokensIndex[tokenId] = _allTokens.length;
 _allTokens.push(tokenId);
 }

 /**
 * @dev Private function to remove a token from this extension's ownership-tracking data structures. Note that
 * while the token is not assigned a new owner, the `_ownedTokensIndex` mapping is _not_ updated: this allows for
 * gas optimizations e.g. when performing a transfer operation (avoiding double writes).
 * This has O(1) time complexity, but alters the order of the _ownedTokens array.
 * @param from address representing the previous owner of the given token ID
 * @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
 */
 function _removeTokenFromOwnerEnumeration(address from, uint256 tokenId) private {
 // To prevent a gap in from's tokens array, we store the last token in the index of the token to delete, and
 // then delete the last slot (swap and pop).

 uint256 lastTokenIndex = ERC721.balanceOf(from) - 1;
 uint256 tokenIndex = _ownedTokensIndex[tokenId];

 // When the token to delete is the last token, the swap operation is unnecessary
 if (tokenIndex != lastTokenIndex) {
 uint256 lastTokenId = _ownedTokens[from][lastTokenIndex];

 _ownedTokens[from][tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
 _ownedTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index
 }

 // This also deletes the contents at the last position of the array
 delete _ownedTokensIndex[tokenId];
 delete _ownedTokens[from][lastTokenIndex];
 }

 /**
 * @dev Private function to remove a token from this extension's token tracking data structures.
 * This has O(1) time complexity, but alters the order of the _allTokens array.
 * @param tokenId uint256 ID of the token to be removed from the tokens list
 */
 function _removeTokenFromAllTokensEnumeration(uint256 tokenId) private {
 // To prevent a gap in the tokens array, we store the last token in the index of the token to delete, and
 // then delete the last slot (swap and pop).

 uint256 lastTokenIndex = _allTokens.length - 1;
 uint256 tokenIndex = _allTokensIndex[tokenId];

 // When the token to delete is the last token, the swap operation is unnecessary. However, since this occurs so
 // rarely (when the last minted token is burnt) that we still do the swap here to avoid the gas cost of adding
 // an 'if' statement (like in _removeTokenFromOwnerEnumeration)
 uint256 lastTokenId = _allTokens[lastTokenIndex];

 _allTokens[tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
 _allTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index

 // This also deletes the contents at the last position of the array
 delete _allTokensIndex[tokenId];
 _allTokens.pop();
 }
}

// File @openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol@v4.1.0

pragma solidity ^0.8.0;

/**
 * @dev ERC721 token with storage based token URI management.
 */
abstract contract ERC721URIStorage is ERC721 {
 using Strings for uint256;

 // Optional mapping for token URIs
 mapping(uint256 => string) private _tokenURIs;

 /**
 * @dev See {IERC721Metadata-tokenURI}.
 */
 function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
 require(_exists(tokenId), 'ERC721URIStorage: URI query for nonexistent token');

 string memory _tokenURI = _tokenURIs[tokenId];
 string memory base = _baseURI();

 // If there is no base URI, return the token URI.
 if (bytes(base).length == 0) {
 return _tokenURI;
 }
 // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
 if (bytes(_tokenURI).length > 0) {
 return string(abi.encodePacked(base, _tokenURI));
 }

 return super.tokenURI(tokenId);
 }

 /**
 * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
 *
 * Requirements:
 *
 * - `tokenId` must exist.
 */
 function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
 require(_exists(tokenId), 'ERC721URIStorage: URI set of nonexistent token');
 _tokenURIs[tokenId] = _tokenURI;
 }

 /**
 * @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 override {
 super._burn(tokenId);

 if (bytes(_tokenURIs[tokenId]).length != 0) {
 delete _tokenURIs[tokenId];
 }
 }
}

// File @openzeppelin/contracts/security/Pausable.sol@v4.1.0

pragma solidity ^0.8.0;

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

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

 bool private _paused;

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

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

 /**
 * @dev Modifier to make a function callable only when the contract is not paused.
 *
 * Requirements:
 *
 * - The contract must not be paused.
 */
 modifier whenNotPaused() {
 require(!paused(), 'Pausable: paused');
 _;
 }

 /**
 * @dev Modifier to make a function callable only when the contract is paused.
 *
 * Requirements:
 *
 * - The contract must be paused.
 */
 modifier whenPaused() {
 require(paused(), 'Pausable: not paused');
 _;
 }

 /**
 * @dev Triggers stopped state.
 *
 * Requirements:
 *
 * - The contract must not be paused.
 */
 function _pause() internal virtual whenNotPaused {
 _paused = true;
 emit Paused(_msgSender());
 }

 /**
 * @dev Returns to normal state.
 *
 * Requirements:
 *
 * - The contract must be paused.
 */
 function _unpause() internal virtual whenPaused {
 _paused = false;
 emit Unpaused(_msgSender());
 }
}

// File @openzeppelin/contracts/access/Ownable.sol@v4.1.0

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() {
 address msgSender = _msgSender();
 _owner = msgSender;
 emit OwnershipTransferred(address(0), 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 {
 emit OwnershipTransferred(_owner, address(0));
 _owner = address(0);
 }

 /**
 * @dev Transfers ownership of the contract to a new account (`newOwner`).
 * Can only be called by the current owner.
 */
 function transferOwnership(address newOwner) public virtual onlyOwner {
 require(newOwner != address(0), 'Ownable: new owner is the zero address');
 emit OwnershipTransferred(_owner, newOwner);
 _owner = newOwner;
 }
}

// File @openzeppelin/contracts/token/ERC721/extensions/ERC721Burnable.sol@v4.1.0

pragma solidity ^0.8.0;

/**
 * @title ERC721 Burnable Token
 * @dev ERC721 Token that can be irreversibly burned (destroyed).
 */
abstract contract ERC721Burnable is Context, ERC721 {
 /**
 * @dev Burns `tokenId`. See {ERC721-_burn}.
 *
 * Requirements:
 *
 * - The caller must own `tokenId` or be an approved operator.
 */
 function burn(uint256 tokenId) public virtual {
 //solhint-disable-next-line max-line-length
 require(_isApprovedOrOwner(_msgSender(), tokenId), 'ERC721Burnable: caller is not owner nor approved');
 _burn(tokenId);
 }
}

// File @openzeppelin/contracts/utils/Counters.sol@v4.1.0

pragma solidity ^0.8.0;

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented or decremented by one. 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;
 }
 }
}

pragma solidity ^0.8.0;

contract CrashTrading is ERC721, ERC721Enumerable, ERC721URIStorage, Pausable, Ownable, ERC721Burnable {
 using Counters for Counters.Counter;

 Counters.Counter private _tokenIdCounter;
 uint256 public maxSupply = 300;
 uint256 public price = 500000000000000000;
 uint256 public reservedToOwner = 11;
 uint256 public whitelistPhaseOneStopAt = 100;
 uint256 public whitelistPhaseTwoStopAt = 200;

 bool public presaleOpen = false;
 bool public reservedTokensToOwnerMinted = false;
 string public baseURI;

 address withdrawWallet = 0x2B6c8d60b8A67223bF473CbF7189Dde381926154;

 mapping(address => uint256) public Whitelist;

 receive() external payable {}

 constructor() ERC721('Crash Trading', 'CT') {
 _tokenIdCounter.increment();
 setBaseURI("https://moonshotgarageproject.mypinata.cloud/ipfs/QmS2ipqc7qNBoxe7AwVxcmvyFm3MxvaCj6sbArD4Goq8my/");
 mintReservedTokensToOwner();
 }

 function mintReservedTokensToOwner() public onlyOwner {
 if(!reservedTokensToOwnerMinted){
 for (uint256 i = 1; i <= reservedToOwner; i++) internalMint(withdrawWallet);
 reservedTokensToOwnerMinted = true;
 }
 }

 function whitelistAddress(address[] memory who, uint256 amount) public onlyOwner {
 for (uint256 i = 0; i < who.length; i++) Whitelist[who[i]] = amount;
 }

 function withdraw() public onlyOwner {
 uint256 balance = address(this).balance;
 payable(withdrawWallet).transfer(balance);
 }

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

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

 function currentToken() public view returns (uint256) {
 return _tokenIdCounter.current();
 }

 function togglePresale() public onlyOwner {
 presaleOpen = !presaleOpen;
 }

 function setBaseURI(string memory newBaseURI) public onlyOwner {
 baseURI = newBaseURI;
 }

 function setPrice(uint256 newPrice) public onlyOwner {
 price = newPrice;
 }

 function _baseURI() internal view override returns (string memory) {
 return baseURI;
 }

 function internalMint(address to) internal {
 require(totalSupply() < maxSupply, 'supply depleted');
 _safeMint(to, _tokenIdCounter.current());
 _tokenIdCounter.increment();
 }

 function checkPresaleTogglePoints() internal {
 bool shouldStopMinting = currentToken() == whitelistPhaseOneStopAt || currentToken() == whitelistPhaseTwoStopAt;

 if(shouldStopMinting){
 presaleOpen = false;
 }
 }

 function mint(uint256 amount) public payable {
 require(msg.value >= price * amount, 'not enough was paid');
 require(presaleOpen == true, 'presale is not open');
 uint256 who = Whitelist[msg.sender];
 require(who > 0, 'this address is not whitelisted for the presale');
 require(amount <= who, 'this address is not allowed to mint that many during the presale');
 for (uint256 i = 0; i < amount; i++) internalMint(msg.sender);
 Whitelist[msg.sender] = who - amount;
 checkPresaleTogglePoints();
 }

 function _beforeTokenTransfer(
 address from,
 address to,
 uint256 tokenId
 ) internal override(ERC721, ERC721Enumerable) whenNotPaused {
 super._beforeTokenTransfer(from, to, tokenId);
 }

 // The following functions are overrides required by Solidity.

 function _burn(uint256 tokenId) internal override(ERC721, ERC721URIStorage) {
 super._burn(tokenId);
 }

 function tokenURI(uint256 tokenId) public view override(ERC721, ERC721URIStorage) returns (string memory) {
 return super.tokenURI(tokenId);
 }

 function supportsInterface(bytes4 interfaceId) public view override(ERC721, ERC721Enumerable) returns (bool) {
 return super.supportsInterface(interfaceId);
 }
}