403. 授權 - ERC721 (ep.25)

1. 授權特定NFT給第三方管理 function approve(address to, uint256 tokenId) external;

1. 呼叫者msg.sender授權編號為tokenId的NFT從持有者from轉移給接收者to
2. 須要觸發Approval事件
3. 特殊判斷：

• to跟owner不能相同, 避免發生授權給持有者自己的情況
• 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)

2. 查詢特定NFT授權給誰 function getApproved(uint256 tokenId) returns (address );

1. 給定一個Token ID(uint256), 回傳該NFT的被授權者 address
2. 特殊檢查 - tokenId 必須是已經被鑄造且未被銷毀的NFT

3. 授權 / 撤銷全部的NFT管理權給第三方位址 function setApprovalforAll(address operator, bool _approved) external;

1. 呼叫者msg.sender​授權或撤銷(以 _approved為準
2. NFT管理第三方位址operator
3. 須要觸發ApprovalForall事件
4. 特殊判斷: operator與owner不能相同, 避免發生授權給持有者自己的情況。

4. 查詢授權/撤銷全部管理權限的情況 function isApprovedForAll(address owner, address operator) external view returns(bool);

1. 給定持有者位址owner與欲查詢之第三方位址operator, 回傳是否授權

// 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];
    }

}