404. 轉移 - ERC721 (ep.26)

1. 轉移NFT安全版本 function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;

1. 呼叫者msg.sender試圖將持有者from名下, 編號為tokenId的NFT給第三方位址to
2. 須要觸發Transfer事件
3. 特殊檢查
4. 若呼叫者沒有以下身份, 則撤回整筆交易

• 呼叫者為持有者
• 呼叫者被持有者授權管理全部的NFT(透過isApprovedForAll檢查)
• 互叫者被持有者授權管理該NFT(透過isApprovedForAll檢查)

2. 轉移tokenId的NFT給第三方地址 function transferFrom(address from, address to, uint256 tokenId);

轉移時要做以下事情：

1. 移除tokenId的被授權者, 轉移後原先的授權關係會取消

delete _tokenApproval[tokenId]

2. 對owner的balance -1
3. 對receiver的balance +1
4. 設定receiver為tokenId的新擁有者
5. 觸發轉移事件

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.23;

interface IERC721 {
    // Event
    event Transfer(address indexed from, address indexed to, uint256 tokenId);
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
    
    //Query
    function balanceOf(address account) external view returns(uint256 balance);
    function ownerOf(uint256 tokenId) external view returns (address owner);

    //Transfer
    // function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
    // function safeTransferFrom(address from, address to, uint256 tokenId) external;
    function transferFrom(address from, address to, uint256 tokenId) external;

    // Approve
    function approve(address to, uint256 tokenId) external;
    function setApprovalforAll(address operator, bool _approved) external;
    function getApproved(uint256 tokenId) external view returns (address operator);
    function isApprovedForAll(address owner, address operator) external view returns(bool);
}

contract ERC721 is IERC721 {
    mapping(address => uint256) _balances;
    mapping(uint256 => address) _owners;
    mapping(uint256 => address) _tokenApprovals;
    mapping(address => mapping(address => bool)) _operatorApprovals; 

    function balanceOf(address owner) public view returns(uint256){
        require(owner != address(0), "ERROR: address 0 cannot be owner");
        return _balances[owner];
    }

    function ownerOf(uint256 tokenId) public view returns (address){
        address owner = _owners[tokenId];
        require(owner != address(0), "ERROR: tokenId is not valid Id");
        return owner;
    }

    function approve(address to, uint256 tokenId) public {
        address owner = _owners[tokenId];
        require(owner != to,"ERROR: owner == to");
        require(owner == msg.sender || isApprovedForAll(owner, msg.sender), "Error: Caller is not token owner / approved for all");
        _tokenApprovals[tokenId] = to;
        emit Approval(owner, to, tokenId);
    }

    function getApproved(uint256 tokenId) public view returns (address){
        address owner = _owners[tokenId];
        require(owner != address(0), "ERROR: Token is not minted or is burn");
        return _tokenApprovals[tokenId];
    }

    function setApprovalforAll(address operator, bool _approved) public {
        require(msg.sender != operator, "ERROR: owner == operator");
        _operatorApprovals[msg.sender][operator] = _approved;
        emit ApprovalForAll(msg.sender, operator, _approved); 
    }
    function isApprovedForAll(address owner, address operator) public view returns(bool){
        return _operatorApprovals[owner][operator];
    }

    function transferFrom(address from, address to, uint256 tokenId) public {
        address owner = _owners[tokenId];
        require(owner == from, "ERROR: Owner is not the from address");
        require(msg.sender == owner || isApprovedForAll(owner, msg.sender) || getApproved(tokenId) == msg.sender, "ERROR: Caller doesn't have permission to transfer");
        delete _tokenApprovals[tokenId];
        _balances[from] -= 1;
        _balances[to] += 1;
        _owners[tokenId] = to;
        emit Transfer(from, to, tokenId);
    }
}