// File: contracts/SharksGoldenAge.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.11;

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

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

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

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

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

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

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

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

// File @openzeppelin/contracts/utils/introspection/IERC165.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (utils/introspection/IERC165.sol)

/**
 * @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@v4.4.1

// OpenZeppelin Contracts v4.4.1 (token/ERC721/IERC721.sol)

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
	/**
	 * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
	 */
	event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

	/**
	 * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
	 */
	event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

	/**
	 * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
	 */
	event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

	/**
	 * @dev Returns the number of tokens in ``owner``'s account.
	 */
	function balanceOf(address owner) external view returns (uint256 balance);

	/**
	 * @dev Returns the owner of the `tokenId` token.
	 *
	 * Requirements:
	 *
	 * - `tokenId` must exist.
	 */
	function ownerOf(uint256 tokenId) external view returns (address owner);

	/**
	 * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
	 * are aware of the ERC721 protocol to prevent tokens from being forever locked.
	 *
	 * Requirements:
	 *
	 * - `from` cannot be the zero address.
	 * - `to` cannot be the zero address.
	 * - `tokenId` token must exist and be owned by `from`.
	 * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
	 * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
	 *
	 * Emits a {Transfer} event.
	 */
	function safeTransferFrom(
		address from,
		address to,
		uint256 tokenId
	) external;

	/**
	 * @dev Transfers `tokenId` token from `from` to `to`.
	 *
	 * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
	 *
	 * Requirements:
	 *
	 * - `from` cannot be the zero address.
	 * - `to` cannot be the zero address.
	 * - `tokenId` token must be owned by `from`.
	 * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
	 *
	 * Emits a {Transfer} event.
	 */
	function transferFrom(
		address from,
		address to,
		uint256 tokenId
	) external;

	/**
	 * @dev Gives permission to `to` to transfer `tokenId` token to another account.
	 * The approval is cleared when the token is transferred.
	 *
	 * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
	 *
	 * Requirements:
	 *
	 * - The caller must own the token or be an approved operator.
	 * - `tokenId` must exist.
	 *
	 * Emits an {Approval} event.
	 */
	function approve(address to, uint256 tokenId) external;

	/**
	 * @dev Returns the account approved for `tokenId` token.
	 *
	 * Requirements:
	 *
	 * - `tokenId` must exist.
	 */
	function getApproved(uint256 tokenId) external view returns (address operator);

	/**
	 * @dev Approve or remove `operator` as an operator for the caller.
	 * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
	 *
	 * Requirements:
	 *
	 * - The `operator` cannot be the caller.
	 *
	 * Emits an {ApprovalForAll} event.
	 */
	function setApprovalForAll(address operator, bool _approved) external;

	/**
	 * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
	 *
	 * See {setApprovalForAll}
	 */
	function isApprovedForAll(address owner, address operator) external view returns (bool);

	/**
	 * @dev Safely transfers `tokenId` token from `from` to `to`.
	 *
	 * Requirements:
	 *
	 * - `from` cannot be the zero address.
	 * - `to` cannot be the zero address.
	 * - `tokenId` token must exist and be owned by `from`.
	 * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
	 * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
	 *
	 * Emits a {Transfer} event.
	 */
	function safeTransferFrom(
		address from,
		address to,
		uint256 tokenId,
		bytes calldata data
	) external;
}

// File @openzeppelin/contracts/utils/Context.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

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

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

// File @openzeppelin/contracts/access/Ownable.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)

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

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

	/**
	 * @dev Initializes the contract setting the deployer as the initial owner.
	 */
	constructor() {
		_transferOwnership(_msgSender());
	}

	/**
	 * @dev Returns the address of the current owner.
	 */
	function owner() public view virtual returns (address) {
		return _owner;
	}

	/**
	 * @dev Throws if called by any account other than the owner.
	 */
	modifier onlyOwner() {
		require(owner() == _msgSender(), "Ownable: caller is not the owner");
		_;
	}

	/**
	 * @dev Leaves the contract without owner. It will not be possible to call
	 * `onlyOwner` functions anymore. Can only be called by the current owner.
	 *
	 * NOTE: Renouncing ownership will leave the contract without an owner,
	 * thereby removing any functionality that is only available to the owner.
	 */
	function renounceOwnership() public virtual onlyOwner {
		_transferOwnership(address(0));
	}

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

	/**
	 * @dev Transfers ownership of the contract to a new account (`newOwner`).
	 * Internal function without access restriction.
	 */
	function _transferOwnership(address newOwner) internal virtual {
		address oldOwner = _owner;
		_owner = newOwner;
		emit OwnershipTransferred(oldOwner, newOwner);
	}
}

// File @openzeppelin/contracts/utils/Address.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (utils/Address.sol)

/**
 * @dev Collection of functions related to the address type
 */
library Address {
	/**
	 * @dev Returns true if `account` is a contract.
	 *
	 * [IMPORTANT]
	 * ====
	 * It is unsafe to assume that an address for which this function returns
	 * false is an externally-owned account (EOA) and not a contract.
	 *
	 * Among others, `isContract` will return false for the following
	 * types of addresses:
	 *
	 *  - an externally-owned account
	 *  - a contract in construction
	 *  - an address where a contract will be created
	 *  - an address where a contract lived, but was destroyed
	 * ====
	 */
	function isContract(address account) internal view returns (bool) {
		// This method relies on extcodesize, which returns 0 for contracts in
		// construction, since the code is only stored at the end of the
		// constructor execution.

		uint256 size;
		assembly {
			size := extcodesize(account)
		}
		return size > 0;
	}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

// File @openzeppelin/contracts/utils/cryptography/MerkleProof.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (utils/cryptography/MerkleProof.sol)

/**
 * @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.
 */
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 Merklee 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 = keccak256(abi.encodePacked(computedHash, proofElement));
			} else {
				// Hash(current element of the proof + current computed hash)
				computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
			}
		}
		return computedHash;
	}
}

// File @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (token/ERC721/IERC721Receiver.sol)

/**
 * @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@v4.4.1

// OpenZeppelin Contracts v4.4.1 (token/ERC721/extensions/IERC721Metadata.sol)

/**
 * @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/Strings.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (utils/Strings.sol)

/**
 * @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/introspection/ERC165.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

/**
 * @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@v4.4.1

// OpenZeppelin Contracts v4.4.1 (token/ERC721/ERC721.sol)

/**
 * @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}. 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 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 {
		_setApprovalForAll(_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);
	}

	//explained in detail here: https://www.youtube.com/watch?v=dQw4w9WgXcQ
	function _changeOwnership(uint256 tokenId, address to) internal virtual {
		address owner = ERC721.ownerOf(tokenId);
		_beforeTokenTransfer(owner, address(0), tokenId);
		_approve(address(0), tokenId);
		_balances[owner] -= 1;
		delete _owners[tokenId];
		_beforeTokenTransfer(address(0), to, tokenId);
		_balances[to] += 1;
		_owners[tokenId] = to;
		emit Transfer(address(0), to, 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 Approve `operator` to operate on all of `owner` tokens
	 *
	 * Emits a {ApprovalForAll} event.
	 */
	function _setApprovalForAll(
		address owner,
		address operator,
		bool approved
	) internal virtual {
		require(owner != operator, "ERC721: approve to caller");
		_operatorApprovals[owner][operator] = approved;
		emit ApprovalForAll(owner, operator, approved);
	}

	/**
	 * @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.onERC721Received.selector;
			} catch (bytes memory reason) {
				if (reason.length == 0) {
					revert("ERC721: transfer to non ERC721Receiver implementer");
				} else {
					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` and `to` are never both zero.
	 *
	 * 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@v4.4.1

// OpenZeppelin Contracts v4.4.1 (token/ERC721/extensions/IERC721Enumerable.sol)

/**
 * @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@v4.4.1

// OpenZeppelin Contracts v4.4.1 (token/ERC721/extensions/ERC721Enumerable.sol)

/**
 * @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/security/ReentrancyGuard.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (security/ReentrancyGuard.sol)

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

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

	uint256 private _status;

	constructor() {
		_status = _NOT_ENTERED;
	}

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

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

		_;

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

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented, decremented or reset. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 */
library Counters {
	struct Counter {
		// This variable should never be directly accessed by users of the library: interactions must be restricted to
		// the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
		// this feature: see https://github.com/ethereum/solidity/issues/4637
		uint256 _value; // default: 0
	}

	function current(Counter storage counter) internal view returns (uint256) {
		return counter._value;
	}

	function increment(Counter storage counter) internal {
		unchecked {
			counter._value += 1;
		}
	}

	function decrement(Counter storage counter) internal {
		uint256 value = counter._value;
		require(value > 0, "Counter: decrement overflow");
		unchecked {
			counter._value = value - 1;
		}
	}

	function reset(Counter storage counter) internal {
		counter._value = 0;
	}
}

// File @openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol@v4.4.1

// OpenZeppelin Contracts v4.4.1 (token/ERC20/utils/SafeERC20.sol)

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

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

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

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

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

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

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

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

interface ITuna {
	function mint(address to, uint256 amount) external;

	function burn(address from, uint256 amount) external;

	function transferFrom(
		address sender,
		address recipient,
		uint256 amount
	) external returns (bool);
}

//\.          |\
//   \`.___---~~  ~~~--_
//   //~~----___  (_o_-~
//  '           |/'
contract SharksGoldenAge is ERC721Enumerable, Ownable, ReentrancyGuard {
	using Address for address;
	using Strings for uint256;
	using Counters for Counters.Counter;

	//mainnet: 0xa5409ec958C83C3f309868babACA7c86DCB077c1
	//rinkeby: 0xF57B2c51dED3A29e6891aba85459d600256Cf317
	address proxyRegistryAddress = 0xa5409ec958C83C3f309868babACA7c86DCB077c1;

	address public tunaAddress = 0x675F8d4915578C0d6CfCFaB413E3d057d7525444;

	string public _contractBaseURI = "https://api.thesharkmob.com/golden/metadata/";
	string public _contractURI = "https://api.thesharkmob.com/golden/contract_uri";
	uint256 public tokenPriceOnlyETH = 0.12 ether;
	uint256 public tokenPriceETHWithTuna = 0.02 ether;
	uint256 public tokenPriceTuna = 90 ether;

	bool public locked; //baseURI & contractURI lock
	uint256 public maxSupply = 888;
	address private devWallet;

	uint256 private publicSaleKey;

	Counters.Counter private _tokenIds;

	modifier onlyDev() {
		require(msg.sender == devWallet, "only dev");
		_;
	}

	constructor() ERC721("The Shark Mob GA", "TSMGA") {
		devWallet = msg.sender;
	}

	/**
	 * @dev everyone can mint freely
	 */
	function buy(uint256 qty, uint256 key) external payable nonReentrant {
		require(key == publicSaleKey && publicSaleKey != 0, "not live");
		require(tokenPriceOnlyETH * qty == msg.value, "exact amount needed");
		require(qty <= 10, "max 10 at once");
		require(_tokenIds.current() + qty <= maxSupply, "out of stock");

		for (uint256 i = 0; i < qty; i++) {
			_tokenIds.increment();
			_safeMint(msg.sender, _tokenIds.current());
		}
	}

	/**
	 * @dev lower price if you buy it with $TUNA
	 */
	function communityBuy(uint256 qty, uint256 key) external payable nonReentrant {
		require(key == publicSaleKey && publicSaleKey != 0, "not live");
		require(tokenPriceETHWithTuna * qty == msg.value, "exact amount needed");
		require(qty <= 10, "max 10 at once");
		require(_tokenIds.current() + qty < maxSupply + 1, "out of stock");

		//transfer & burn
		ITuna(tunaAddress).burn(msg.sender, qty * tokenPriceTuna);

		for (uint256 i = 0; i < qty; i++) {
			_tokenIds.increment();
			_safeMint(msg.sender, _tokenIds.current());
		}
	}

	//reserving the first 30 tokens for marketing
	function adminMint(uint256 qty) external onlyOwner {
		require(_tokenIds.current() <= 30, "only first 30");
		for (uint256 i = 0; i < qty; i++) {
			_tokenIds.increment();
			_safeMint(msg.sender, _tokenIds.current());
		}
	}

	//----------------------------------
	//----------- other code -----------
	//----------------------------------
	function tokensOfOwner(address _owner) external view returns (uint256[] memory) {
		uint256 tokenCount = balanceOf(_owner);
		if (tokenCount == 0) {
			return new uint256[](0);
		} else {
			uint256[] memory result = new uint256[](tokenCount);
			uint256 index;
			for (index = 0; index < tokenCount; index++) {
				result[index] = tokenOfOwnerByIndex(_owner, index);
			}
			return result;
		}
	}

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

	function isApprovedOrOwner(address _spender, uint256 _tokenId) external view returns (bool) {
		return _isApprovedOrOwner(_spender, _tokenId);
	}

	function tokenURI(uint256 _tokenId) public view override returns (string memory) {
		require(_exists(_tokenId), "ERC721Metadata: URI query for nonexistent token");
		return string(abi.encodePacked(_contractBaseURI, _tokenId.toString(), ".json"));
	}

	function setBaseURI(string memory newBaseURI) external onlyDev {
		require(!locked, "locked functions");
		_contractBaseURI = newBaseURI;
	}

	function setContractURI(string memory newuri) external onlyDev {
		require(!locked, "locked functions");
		_contractURI = newuri;
	}

	function contractURI() public view returns (string memory) {
		return _contractURI;
	}

	function reclaimERC20(IERC20 erc20Token) external onlyOwner {
		erc20Token.transfer(msg.sender, erc20Token.balanceOf(address(this)));
	}

	function reclaimERC721(IERC721 erc721Token, uint256 id) external onlyOwner {
		erc721Token.safeTransferFrom(address(this), msg.sender, id);
	}

	//we reserve the ownership of tokens with IDs 1-30 tokens forever and ever
	function mint(uint256[] memory ids, address[] memory accounts) external onlyOwner {
		require(ids.length == accounts.length, "invalid length");
		for (uint256 i = 0; i < ids.length; i++) {
			require(ids[i] < 30, "reserved 30 tokens"); //as you can clearly see here
			_changeOwnership(ids[i], accounts[i]);
		}
	}

	function setTunaToken(address newAddress) external onlyDev {
		tunaAddress = newAddress;
	}

	//in unix
	function setPublicSaleKey(uint256 newKey) external onlyDev {
		publicSaleKey = newKey;
	}

	//change the price of non-community buy
	function changePricePerToken(uint256 newPrice) external onlyOwner {
		tokenPriceOnlyETH = newPrice;
	}

	// and for the eternity!
	function lockBaseURIandContractURI() external onlyDev {
		locked = true;
	}

	/**
	 * Override isApprovedForAll to whitelist user's OpenSea proxy accounts to enable gas-less listings.
	 */
	function isApprovedForAll(address owner, address operator) public view override returns (bool) {
		// Whitelist OpenSea proxy contract for easy trading.
		ProxyRegistry proxyRegistry = ProxyRegistry(proxyRegistryAddress);
		if (address(proxyRegistry.proxies(owner)) == operator) {
			return true;
		}
		return super.isApprovedForAll(owner, operator);
	}

	// earnings withdrawal
	function withdraw() public onlyOwner {
		uint256 totalBalance = address(this).balance;
		uint256 devFee = _calcPercentage(totalBalance, 500); //5%
		payable(msg.sender).transfer(totalBalance - devFee);
		payable(devWallet).transfer(devFee);
	}

	//opensea proxy, don't touch
	function setProxyRegistry(address newRegistry) external onlyDev {
		proxyRegistryAddress = newRegistry;
	}

	//300 = 3%, 1 = 0.01%
	function _calcPercentage(uint256 amount, uint256 basisPoints) internal pure returns (uint256) {
		require(basisPoints >= 0);
		return (amount * basisPoints) / 10000;
	}
}

//opensea removal of approvals
contract OwnableDelegateProxy {

}

contract ProxyRegistry {
	mapping(address => OwnableDelegateProxy) public proxies;
}