balanceOf_contract

pragma solidity >=0.4.24 <=0.5.6;

/*contract name*/
contract NFTSimple {
    string public name = "KlytnLion";
    string public symbol = "KL";    //사용하는 화폐

    mapping (uint256 => address) public tokenOwner;     // 주소를 정수형이랑 매핑
    mapping (uint256 => string) public tokenURIs;      // 글자를 정수형이랑 매핑

    // 소유한 토큰 리스트
    mapping(address => uint256[]) private _ownedTokens;
    // onKIP17Received bytes value
    bytes4 private constant _KIP17_RECEIVED = 0x6745782b;

    //mint(tokenId, uri, owner)
    //transferfrom(from, to, token) => owner가 바뀌는 것 from에서 to로

    function mintWithTokenURI(address to, uint256 tokenId, string memory tokenURI) public returns (bool) {
        //to에게 tokenId(일련번호)를 발행하는 함수
        //적힐 글자는 tokenURI

        tokenOwner[tokenId] = to; //msg.sender 가능
        tokenURIs[tokenId] = tokenURI;

        //ownedTokens에 추가
        _ownedTokens[to].push(tokenId);

        return true;
    }

    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public{
        require(from == msg.sender, "from != msg.sender");
        require(from == tokenOwner[tokenId], "You're not the owner of the token");

        _removeTokenFromList(from, tokenId);
        _ownedTokens[to].push(tokenId);

        tokenOwner[tokenId] = to;

        // 만약에 받는 쪽이 실행할 코드가 있는 스마트 컨트랙트라면 코드를 실행할 것
        require(
            _checkOnKIP17Received(from, to, tokenId, _data), "KIP17: transfer to non KIP17Receiver implementer"
        );
    }

    function _checkOnKIP17Received(address from, address to, uint256 tokenId, bytes memory _data) internal returns (bool){
        bool success;
        bytes memory returndata;

        if (!isContract(to)){
            return true;
        }

        (success, returndata) = to.call(
            abi.encodeWithSelector(
                _KIP17_RECEIVED,
                msg.sender,
                from,
                tokenId,
                _data
            )
        );
        if(
            returndata.length != 0 &&
            abi.decode(returndata, (bytes4)) == _KIP17_RECEIVED
        ) {
            return true;
        }
        return false;
    }

    function isContract(address account) internal view returns (bool){
        uint256 size;
        assembly {size := extcodesize(account)}
        return size > 0;
    }

    function _removeTokenFromList(address from, uint256 tokenId) private {
        uint256 lastTokenIdex = _ownedTokens[from].length - 1;
        for(uint256 i=0; i<_ownedTokens[from].length; i++){
            if(tokenId == _ownedTokens[from][i]){
                _ownedTokens[from][i] = _ownedTokens[from][lastTokenIdex];
                _ownedTokens[from][lastTokenIdex] = tokenId;
                break;
            }
        }

        _ownedTokens[from].length--;
    }

     
    function ownedTokens(address owner) public view returns (uint256[] memory) {
        return _ownedTokens[owner];
    }
    

    function setTokenUri(uint256 id, string memory uri) public{
        tokenURIs[id] = uri;
    }

    function balanceOf(address owner) public view returns (uint256) {
        require(
            owner != address(0),
            "KIP17: balance query for the zero address"
        );

        return _ownedTokens[owner].length;
    }
}