abstract contract ERC721 {
    /*///////////////////////////////////////////////////////////////
                            EVENTS
    //////////////////////////////////////////////////////////////*/

    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    event Approval(address indexed owner, address indexed spender, uint256 indexed tokenId);

    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /*///////////////////////////////////////////////////////////////
                            METADATA STORAGE
    //////////////////////////////////////////////////////////////*/
    
    string public name;

    string public symbol;

    /*///////////////////////////////////////////////////////////////
                            ERC-721 STORAGE
    //////////////////////////////////////////////////////////////*/
    
    uint256 public totalSupply;
    
    mapping(address => uint256) public balanceOf;

    mapping(uint256 => address) public ownerOf;

    mapping(uint256 => address) public getApproved;

    mapping(address => mapping(address => bool)) public isApprovedForAll;

    /*///////////////////////////////////////////////////////////////
                            EIP-2612-LIKE STORAGE
    //////////////////////////////////////////////////////////////*/
    
    bytes32 public constant PERMIT_TYPEHASH =
        keccak256("Permit(address spender,uint256 tokenId,uint256 nonce,uint256 deadline)");

    bytes32 public constant PERMIT_ALL_TYPEHASH = 
        keccak256("Permit(address owner,address spender,uint256 nonce,uint256 deadline)");
    
    uint256 internal immutable INITIAL_CHAIN_ID;

    bytes32 internal immutable INITIAL_DOMAIN_SEPARATOR;

    mapping(uint256 => uint256) public nonces;

    mapping(address => uint256) public noncesForAll;
    
    /*///////////////////////////////////////////////////////////////
                            CONSTRUCTOR
    //////////////////////////////////////////////////////////////*/
    
    constructor(string memory _name, string memory _symbol) {
        name = _name;
        symbol = _symbol;
        
        INITIAL_CHAIN_ID = block.chainid;
        INITIAL_DOMAIN_SEPARATOR = computeDomainSeparator();
    }

    /*///////////////////////////////////////////////////////////////
                            ERC-20-LIKE LOGIC
    //////////////////////////////////////////////////////////////*/

    function transfer(address to, uint256 tokenId) public virtual returns (bool success) {
        require(msg.sender == ownerOf[tokenId], "NOT_OWNER");
        
        // Cannot overflow because because ownership is checked
        // against decrement, and sum of all user
        // balances can't exceed the max uint256 value.
        unchecked {
            balanceOf[msg.sender]--; 
        
            balanceOf[to]++;
        }
        
        delete getApproved[tokenId];
        
        ownerOf[tokenId] = to;
        
        emit Transfer(msg.sender, to, tokenId); 
        
        success = true;
    }

    /*///////////////////////////////////////////////////////////////
                            ERC-721 LOGIC
    //////////////////////////////////////////////////////////////*/

    function supportsInterface(bytes4 interfaceId) public pure virtual returns (bool supported) {
        supported = interfaceId == 0x80ac58cd || interfaceId == 0x5b5e139f || interfaceId == 0x01ffc9a7;
    }
    
    function approve(address spender, uint256 tokenId) public virtual {
        address owner = ownerOf[tokenId];
        
        require(msg.sender == owner || isApprovedForAll[owner][msg.sender], "NOT_APPROVED");
        
        getApproved[tokenId] = spender;
        
        emit Approval(owner, spender, tokenId); 
    }
    
    function setApprovalForAll(address operator, bool approved) public virtual {
        isApprovedForAll[msg.sender][operator] = approved;
        
        emit ApprovalForAll(msg.sender, operator, approved);
    }
    
    function transferFrom(
        address from, 
        address to, 
        uint256 tokenId
    ) public virtual {
        require(from == ownerOf[tokenId], 'NOT_OWNER');
        
        require(
            msg.sender == from 
            || msg.sender == getApproved[tokenId]
            || isApprovedForAll[from][msg.sender], 
            'NOT_APPROVED'
        );
        
        // this is safe because ownership is checked
        // against decrement, and sum of all user
        // balances can't exceed 'type(uint256).max'
        unchecked { 
            balanceOf[from]--; 
        
            balanceOf[to]++;
        }
        
        delete getApproved[tokenId];
        
        ownerOf[tokenId] = to;
        
        emit Transfer(from, to, tokenId); 
    }
    
    function safeTransferFrom(
        address from, 
        address to, 
        uint256 tokenId
    ) public virtual {
        safeTransferFrom(from, to, tokenId, "");
    }
    
    function safeTransferFrom(
        address from, 
        address to, 
        uint256 tokenId, 
        bytes memory data
    ) public virtual {
        transferFrom(from, to, tokenId); 
        
        if (to.code.length > 0) {
            // selector = "onERC721Received(address,address,uint256,bytes)".
            (, bytes memory returned) = to.staticcall(abi.encodeWithSelector(0x150b7a02,
                msg.sender, from, tokenId, data));
                
            bytes4 selector = abi.decode(returned, (bytes4));
            
            require(selector == 0x150b7a02, 'NOT_ERC721_RECEIVER');
        }
    }

    /*///////////////////////////////////////////////////////////////
                            EIP-2612-LIKE LOGIC
    //////////////////////////////////////////////////////////////*/
    
    function permit(
        address spender,
        uint256 tokenId,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual {
        require(block.timestamp <= deadline, "PERMIT_DEADLINE_EXPIRED");
        
        address owner = ownerOf[tokenId];
        
        // Unchecked because the only math done is incrementing
        // the owner's nonce which cannot realistically overflow.
        unchecked {
            bytes32 digest = keccak256(
                abi.encodePacked(
                    "\x19\x01",
                    DOMAIN_SEPARATOR(),
                    keccak256(abi.encode(PERMIT_TYPEHASH, spender, tokenId, nonces[tokenId]++, deadline))
                )
            );

            address recoveredAddress = ecrecover(digest, v, r, s);

            require(recoveredAddress != address(0), "INVALID_PERMIT_SIGNATURE");

            require(recoveredAddress == owner || isApprovedForAll[owner][recoveredAddress], "INVALID_SIGNER");
        }
        
        getApproved[tokenId] = spender;

        emit Approval(owner, spender, tokenId);
    }
    
    function permitAll(
        address owner,
        address operator,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual {
        require(block.timestamp <= deadline, "PERMIT_DEADLINE_EXPIRED");
        
        // Unchecked because the only math done is incrementing
        // the owner's nonce which cannot realistically overflow.
        unchecked {
            bytes32 digest = keccak256(
                abi.encodePacked(
                    "\x19\x01",
                    DOMAIN_SEPARATOR(),
                    keccak256(abi.encode(PERMIT_ALL_TYPEHASH, owner, operator, noncesForAll[owner]++, deadline))
                )
            );

            address recoveredAddress = ecrecover(digest, v, r, s);
            
            require(
                (recoveredAddress != address(0) && recoveredAddress == owner) || isApprovedForAll[owner][recoveredAddress],
                'INVALID_PERMIT_SIGNATURE'
            );
        }
        
        isApprovedForAll[owner][operator] = true;

        emit ApprovalForAll(owner, operator, true);
    }

    function DOMAIN_SEPARATOR() public view virtual returns (bytes32 domainSeparator) {
        domainSeparator = block.chainid == INITIAL_CHAIN_ID ? INITIAL_DOMAIN_SEPARATOR : computeDomainSeparator();
    }

    function computeDomainSeparator() internal view virtual returns (bytes32 domainSeparator) {
        domainSeparator = keccak256(
            abi.encode(
                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
                keccak256(bytes(name)),
                keccak256(bytes("1")),
                block.chainid,
                address(this)
            )
        );
    }

    /*///////////////////////////////////////////////////////////////
                            MINT/BURN LOGIC
    //////////////////////////////////////////////////////////////*/
    
    function _mint(
        address to, 
        uint256 tokenId
    ) internal virtual { 
        require(ownerOf[tokenId] == address(0), "ALREADY_MINTED");
  
        // Cannot realistically overflow from incrementing total supply beyond
        // the max uint256 value, and because the sum of all user balances 
        // can't exceed the max uint256 value.
        unchecked {
            totalSupply++;
            
            balanceOf[to]++;
        }
        
        ownerOf[tokenId] = to;
        
        emit Transfer(address(0), to, tokenId); 
    }
    
    function _burn(uint256 tokenId) internal virtual { 
        address owner = ownerOf[tokenId];
        
        require(ownerOf[tokenId] != address(0), "NOT_MINTED");
        
        // Cannot underflow because a user's balance
        // will never be larger than the total supply.
        unchecked {
            totalSupply--;
        
            balanceOf[owner]--;
        }
        
        delete ownerOf[tokenId];
        
        emit Transfer(owner, address(0), tokenId); 
    }
}
/// @notice Modern and gas efficient ERC-721 + ERC-20/EIP-2612-like implementation,
/// including the MetaData, and partially, Enumerable extensions.
/// @author from an unmerged solmate PR from z0r0z & distractedm1nd
function supportsInterface(bytes4 interfaceId) public pure virtual returns (bool supported) {
        supported = interfaceId == 0x80ac58cd || interfaceId == 0x5b5e139f || interfaceId == 0x01ffc9a7;
    }
/*///////////////////////////////////////////////////////////////
 ERC-721 LOGIC
 //////////////////////////////////////////////////////////////*/