// Contract: YoungPunks
// Target function: function _checkContractOnERC721Received(
 as `_currentIndex` does not decrement,
	// and it is initialized to `_startTokenId()`.
	unchecked {
		return _currentIndex - _startTokenId();
	}
}

/**
 * @dev Returns the total number of tokens burned.
 */
function _totalBurned() internal view virtual returns (uint256) {
	return _burnCounter;
}

// =============================================================
//                    ADDRESS DATA OPERATIONS
// =============================================================

/**
 * @dev Returns the number of tokens in `owner`'s account.
 */
function balanceOf(address owner) public view virtual override returns (uint256) {
	if (owner == address(0)) revert BalanceQueryForZeroAddress();
	return _packedAddressData[owner] & _BITMASK_ADDRESS_DATA_ENTRY;
}

/**
 * Returns the number of tokens minted by `owner`.
 */
function _numberMinted(address owner) internal view returns (uint256) {
	return (_packedAddressData[owner] >> _BITPOS_NUMBER_MINTED) & _BITMASK_ADDRESS_DATA_ENTRY;
}

/**
 * Returns the number of tokens burned by or on behalf of `owner`.
 */
function _numberBurned(address owner) internal view returns (uint256) {
	return (_packedAddressData[owner] >> _BITPOS_NUMBER_BURNED) & _BITMASK_ADDRESS_DATA_ENTRY;
}

/**
 * Returns the auxiliary data for `owner`. (e.g. number of whitelist mint slots used).
 */
function _getAux(address owner) internal view returns (uint64) {
	return uint64(_packedAddressData[owner] >> _BITPOS_AUX);
}

/**
 * Sets the auxiliary data for `owner`. (e.g. number of whitelist mint slots used).
 * If there are multiple variables, please pack them into a uint64.
 */
function _setAux(address owner, uint64 aux) internal virtual {
	uint256 packed = _packedAddressData[owner];
	uint256 auxCasted;
	// Cast `aux` with assembly to avoid redundant masking.
	assembly {
		auxCasted := aux
	}
	packed = (packed & _BITMASK_AUX_COMPLEMENT) | (auxCasted << _BITPOS_AUX);
	_packedAddressData[owner] = packed;
}

// =============================================================
//                            IERC165
// =============================================================

/**
 * @dev Returns true if this contract implements the interface defined by
 * `interfaceId`. See the corresponding
 * [EIP section](https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified)
 * to learn more about how these ids are created.
 *
 * This function call must use less than 30000 gas.
 */
function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
	// The interface IDs are constants representing the first 4 bytes
	// of the XOR of all function selectors in the interface.
	// See: [ERC165](https://eips.ethereum.org/EIPS/eip-165)
	// (e.g. `bytes4(i.functionA.selector ^ i.functionB.selector ^ ...)`)
	return
		interfaceId == 0x01ffc9a7 || // ERC165 interface ID for ERC165.
		interfaceId == 0x80ac58cd || // ERC165 interface ID for ERC721.
		interfaceId == 0x5b5e139f; // ERC165 interface ID for ERC721Metadata.
}

// =============================================================
//                        IERC721Metadata
// =============================================================

/**
 * @dev Returns the token collection name.
 */
 
function name() public view virtual override returns (string memory) {
	return '';
}


function symbol() public view virtual override returns (string memory) {
	return '';
}



/**
 * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
 */
function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
	if (!_exists(tokenId)) revert URIQueryForNonexistentToken();

	string memory baseURI = _baseURI();
	return bytes(baseURI).length != 0 ? string(abi.encodePacked('ipfs://', baseURI, '/', _toString(tokenId), '.json')) : '';
}

/**
 * @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, it can be overridden in child contracts.
 */
function _baseURI() internal view virtual returns (string memory) {
	return '';
}

// =============================================================
//                     OWNERSHIPS OPERATIONS
// =============================================================

/**
 * @dev Returns the owner of the `tokenId` token.
 *
 * Requirements:
 *
 * - `tokenId` must exist.
 */
function ownerOf(uint256 tokenId) public view virtual override returns (address) {
	return address(uint160(_packedOwnershipOf(tokenId)));
}

/**
 * @dev Gas spent here starts off proportional to the maximum mint batch size.
 * It gradually moves to O(1) as tokens get transferred around over time.
 */
function _ownershipOf(uint256 tokenId) internal view virtual returns (TokenOwnership memory) {
	return _unpackedOwnership(_packedOwnershipOf(tokenId));
}

/**
 * @dev Returns the unpacked `TokenOwnership` struct at `index`.
 */
function _ownershipAt(uint256 index) internal view virtual returns (TokenOwnership memory) {
	return _unpackedOwnership(_packedOwnerships[index]);
}

/**
 * @dev Initializes the ownership slot minted at `index` for efficiency purposes.
 */
function _initializeOwnershipAt(uint256 index) internal virtual {
	if (_packedOwnerships[index] == 0) {
		_packedOwnerships[index] = _packedOwnershipOf(index);
	}
}

/**
 * Returns the packed ownership data of `tokenId`.
 */
function _packedOwnershipOf(uint256 tokenId) private view returns (uint256) {
	uint256 curr = tokenId;

	unchecked {
		if (_startTokenId() <= curr)
			if (curr < _currentIndex) {
				uint256 packed = _packedOwnerships[curr];
				// If not burned.
				if (packed & _BITMASK_BURNED == 0) {
					// Invariant:
					// There will always be an initialized ownership slot
					// (i.e. `ownership.addr != address(0) && ownership.burned == false`)
					// before an unintialized ownership slot
					// (i.e. `ownership.addr == address(0) && ownership.burned == false`)
					// Hence, `curr` will not underflow.
					//
					// We can directly compare the packed value.
					// If the address is zero, packed will be zero.
					while (packed == 0) {
						packed = _packedOwnerships[--curr];
					}
					return packed;
				}
			}
	}
	revert OwnerQueryForNonexistentToken();
}

/**
 * @dev Returns the unpacked `TokenOwnership` struct from `packed`.
 */
function _unpackedOwnership(uint256 packed) private pure returns (TokenOwnership memory ownership) {
	ownership.addr = address(uint160(packed));
	ownership.startTimestamp = uint64(packed >> _BITPOS_START_TIMESTAMP);
	ownership.burned = packed & _BITMASK_BURNED != 0;
	ownership.extraData = uint24(packed >> _BITPOS_EXTRA_DATA);
}

/**
 * @dev Packs ownership data into a single uint256.
 */
function _packOwnershipData(address owner, uint256 flags) private view returns (uint256 result) {
	assembly {
		// Mask `owner` to the lower 160 bits, in case the upper bits somehow aren't clean.
		owner := and(owner, _BITMASK_ADDRESS)
		// `owner | (block.timestamp << _BITPOS_START_TIMESTAMP) | flags`.
		result := or(owner, or(shl(_BITPOS_START_TIMESTAMP, timestamp()), flags))
	}
}

/**
 * @dev Returns the `nextInitialized` flag set if `quantity` equals 1.
 */
function _nextInitializedFlag(uint256 quantity) private pure returns (uint256 result) {
	// For branchless setting of the `nextInitialized` flag.
	assembly {
		// `(quantity == 1) << _BITPOS_NEXT_INITIALIZED`.
		result := shl(_BITPOS_NEXT_INITIALIZED, eq(quantity, 1))
	}
}

// =============================================================
//                      APPROVAL OPERATIONS
// =============================================================

/**
 * @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) public payable virtual override {
	address owner = ownerOf(tokenId);

	if (_msgSenderERC721A() != owner)
		if (!isApprovedForAll(owner, _msgSenderERC721A())) {
			revert ApprovalCallerNotOwnerNorApproved();
		}

	_tokenApprovals[tokenId].value = to;
	emit Approval(owner, to, tokenId);
}

/**
 * @dev Returns the account approved for `tokenId` token.
 *
 * Requirements:
 *
 * - `tokenId` must exist.
 */
function getApproved(uint256 tokenId) public view virtual override returns (address) {
	if (!_exists(tokenId)) revert ApprovalQueryForNonexistentToken();

	return _tokenApprovals[tokenId].value;
}

/**
 * @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) public virtual override {
	_operatorApprovals[_msgSenderERC721A()][operator] = approved;
	emit ApprovalForAll(_msgSenderERC721A(), operator, approved);
}

/**
 * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
 *
 * See {setApprovalForAll}.
 */
function isApprovedForAll(address owner, address operator) public view virtual override returns (bool) {
	return _operatorApprovals[owner][operator];
}

/**
 * @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. See {_mint}.
 */
function _exists(uint256 tokenId) internal view virtual returns (bool) {
	return
		_startTokenId() <= tokenId &&
		tokenId < _currentIndex && // If within bounds,
		_packedOwnerships[tokenId] & _BITMASK_BURNED == 0; // and not burned.
}

/**
 * @dev Returns whether `msgSender` is equal to `approvedAddress` or `owner`.
 */
function _isSenderApprovedOrOwner(
	address approvedAddress,
	address owner,
	address msgSender
) private pure returns (bool result) {
	assembly {
		// Mask `owner` to the lower 160 bits, in case the upper bits somehow aren't clean.
		owner := and(owner, _BITMASK_ADDRESS)
		// Mask `msgSender` to the lower 160 bits, in case the upper bits somehow aren't clean.
		msgSender := and(msgSender, _BITMASK_ADDRESS)
		// `msgSender == owner || msgSender == approvedAddress`.
		result := or(eq(msgSender, owner), eq(msgSender, approvedAddress))
	}
}

/**
 * @dev Returns the storage slot and value for the approved address of `tokenId`.
 */
function _getApprovedSlotAndAddress(uint256 tokenId)
	private
	view
	returns (uint256 approvedAddressSlot, address approvedAddress)
{
	TokenApprovalRef storage tokenApproval = _tokenApprovals[tokenId];
	// The following is equivalent to `approvedAddress = _tokenApprovals[tokenId].value`.
	assembly {
		approvedAddressSlot := tokenApproval.slot
		approvedAddress := sload(approvedAddressSlot)
	}
}

// =============================================================
//                      TRANSFER OPERATIONS
// =============================================================

/**
 * @dev Transfers `tokenId` from `from` to `to`.
 *
 * 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
) public payable virtual override {
	uint256 prevOwnershipPacked = _packedOwnershipOf(tokenId);

	if (address(uint160(prevOwnershipPacked)) != from) revert TransferFromIncorrectOwner();

	(uint256 approvedAddressSlot, address approvedAddress) = _getApprovedSlotAndAddress(tokenId);

	// The nested ifs save around 20+ gas over a compound boolean condition.
	if (!_isSenderApprovedOrOwner(approvedAddress, from, _msgSenderERC721A()))
		if (!isApprovedForAll(from, _msgSenderERC721A())) revert TransferCallerNotOwnerNorApproved();

	if (to == address(0)) revert TransferToZeroAddress();

	_beforeTokenTransfers(from, to, tokenId, 1);

	// Clear approvals from the previous owner.
	assembly {
		if approvedAddress {
			// This is equivalent to `delete _tokenApprovals[tokenId]`.
			sstore(approvedAddressSlot, 0)
		}
	}

	// Underflow of the sender's balance is impossible because we check for
	// ownership above and the recipient's balance can't realistically overflow.
	// Counter overflow is incredibly unrealistic as `tokenId` would have to be 2**256.
	unchecked {
		// We can directly increment and decrement the balances.
		--_packedAddressData[from]; // Updates: `balance -= 1`.
		++_packedAddressData[to]; // Updates: `balance += 1`.

		// Updates:
		// - `address` to the next owner.
		// - `startTimestamp` to the timestamp of transfering.
		// - `burned` to `false`.
		// - `nextInitialized` to `true`.
		_packedOwnerships[tokenId] = _packOwnershipData(
			to,
			_BITMASK_NEXT_INITIALIZED | _nextExtraData(from, to, prevOwnershipPacked)
		);

		// If the next slot may not have been initialized (i.e. `nextInitialized == false`) .
		if (prevOwnershipPacked & _BITMASK_NEXT_INITIALIZED == 0) {
			uint256 nextTokenId = tokenId + 1;
			// If the next slot's address is zero and not burned (i.e. packed value is zero).
			if (_packedOwnerships[nextTokenId] == 0) {
				// If the next slot is within bounds.
				if (nextTokenId != _currentIndex) {
					// Initialize the next slot to maintain correctness for `ownerOf(tokenId + 1)`.
					_packedOwnerships[nextTokenId] = prevOwnershipPacked;
				}
			}
		}
	}

	emit Transfer(from, to, tokenId);
	_afterTokenTransfers(from, to, tokenId, 1);
}

/**
 * @dev Equivalent to `safeTransferFrom(from, to, tokenId, '')`.
 */
function safeTransferFrom(
	address from,
	address to,
	uint256 tokenId
) public payable virtual override {
	safeTransferFrom(from, to, tokenId, '');
}

/**
 * @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 memory _data
) public payable virtual override {
	transferFrom(from, to, tokenId);
	if (to.code.length != 0)
		if (!_checkContractOnERC721Received(from, to, tokenId, _data)) {
			revert TransferToNonERC721ReceiverImplementer();
		}
}

/**
 * @dev Hook that is called before a set of serially-ordered token IDs
 * are about to be transferred. This includes minting.
 * And also called before burning one token.
 *
 * `startTokenId` - the first token ID to be transferred.
 * `quantity` - the amount to be transferred.
 *
 * Calling conditions:
 *
 * - When `from` and `to` are both non-zero, `from`'s `tokenId` will be
 * transferred to `to`.
 * - When `from` is zero, `tokenId` will be minted for `to`.
 * - When `to` is zero, `tokenId` will be burned by `from`.
 * - `from` and `to` are never both zero.
 */
function _beforeTokenTransfers(
	address from,
	address to,
	uint256 startTokenId,
	uint256 quantity
) internal virtual {}

/**
 * @dev Hook that is called after a set of serially-ordered token IDs
 * have been transferred. This includes minting.
 * And also called after one token has been burned.
 *
 * `startTokenId` - the first token ID to be transferred.
 * `quantity` - the amount to be transferred.
 *
 * Calling conditions:
 *
 * - When `from` and `to` are both non-zero, `from`'s `tokenId` has been
 * transferred to `to`.
 * - When `from` is zero, `tokenId` has been minted for `to`.
 * - When `to` is zero, `tokenId` has been burned by `from`.
 * - `from` and `to` are never both zero.
 */
function _afterTokenTransfers(
	address from,
	address to,
	uint256 startTokenId,
	uint256 quantity
) internal virtual {}