2차 과제

// Klaytn IDE uses solidity 0.4.24, 0.5.6 versions.
pragma solidity >=0.4.24 <=0.5.6;
contract NFTSimple {
      
    string public name ="KlayLion";
    string public symbol = "KL";
     
    mapping(uint256 => address) public tokenOwner;
    mapping(uint256 => string) public tokenURIs;


    //소유한 토큰 리스트
    mapping(address => uint256[]) private _ownedTokens; 
    
    // mint(tokenId, uri-글자, owner)
    //transform(from, to , tokenId)
    
    //mint - token 발급 및 토큰에 메세지 작성
    function mintWithTokenURI(address to, uint256 tokenId, string memory tokenURI) public returns(bool){
        // to에게 tokenId를 발급하겠다
        // 적힐 글자는 tokenURI
        tokenOwner[tokenId] = to;
        tokenURIs[tokenId] = tokenURI;

        //add token to list
        _ownedTokens[to].push(tokenId);

        return true;
    }

    // 다른 사용자에게 토큰 전달
    function safeTransforFrom(address from, address to, uint256 tokenId) public {
        require(from == msg.sender , " from != msg.sender");
        require(from == tokenOwner[tokenId], "you are not the Owner of the token");

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

    // 다른 사용자에게 토큰 전달후에 가지고 잇는 토큰 리스트에서 제거
    function _removeTokenFromList(address from,uint256 tokenId) private{
        // 10,15,19,20 --> 19 삭제 원함
        // 10,15,20,19 로 위치 변경
        // 10,15,20 
         
        for(uint256 i=0; i < _ownedTokens[from].length; i++){
            if(tokenId == _ownedTokens[from][i]){
                uint256 temp = _ownedTokens[from][i+1];
                _ownedTokens[from][i] = _ownedTokens[from][i+1];
                _ownedTokens[from][i+1] = temp;
                break;
            }
        }
    }

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

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


     
}

contract NFTMarket{

    function buyNFT(uint256 tokenId, address NFTAddress, address to) public returns (bool){
        NFTSimple(NFTAddress).safeTransforFrom(address(this), to, tokenId);
        return true;
    }
}