[ERC7634] NFTのTransfer回数を制限する仕組みを理解しよう！

pragma solidity ^0.8.4;

/// @title IERC7634 Interface for Limited Transferable NFT
/// @dev Interface for ERC7634 Limited Transferable NFT extension for ERC721
/// @author Saber Yu

interface IERC7634 {

    /**
     * @dev Emitted when transfer count is set or updated
     */
    event TransferCount(uint256 indexed tokenId, address owner, uint256 counts);

    /**
     * @dev Returns the current transfer count for a tokenId
     */
    function transferCountOf(uint256 tokenId) external view returns (uint256);

    /**
     * @dev Sets the transfer limit for a tokenId. Can only be called by the token owner or an approved address.
     * @param tokenId The ID of the token for which to set the limit
     * @param limit The maximum number of transfers allowed for the token
     */
    function setTransferLimit(uint256 tokenId, uint256 limit) external;

    /**
     * @dev Returns the transfer limit for a tokenId
     */
    function transferLimitOf(uint256 tokenId) external view returns (uint256);
}

pragma solidity ^0.8.4;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "./IERC7634.sol";

/// @title Limited Transferable NFT Extension for ERC721
/// @dev Implementation of the Limited Transferable NFT extension for ERC721
/// @author Saber Yu

contract ERC7634 is ERC721, IERC7634 {

    // Mapping from tokenId to the transfer count
    mapping(uint256 => uint256) private _transferCounts;

    // Mapping from tokenId to its maximum transfer limit
    mapping(uint256 => uint256) private _transferLimits;

    /**
     * @dev See {IERC7634-transferCountOf}.
     */
    function transferCountOf(uint256 tokenId) public view override returns (uint256) {
        require(_exists(tokenId), "ERC7634: Nonexistent token");
        return _transferCounts[tokenId];
    }

    /**
     * @dev See {IERC7634-setTransferLimit}.
     */
    function setTransferLimit(uint256 tokenId, uint256 limit) public override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC7634: caller is not owner nor approved");
        _transferLimits[tokenId] = limit;
    }

    /**
     * @dev See {IERC7634-transferLimitOf}.
     */
    function transferLimitOf(uint256 tokenId) public view override returns (uint256) {
        require(_exists(tokenId), "ERC7634: Nonexistent token");
        return _transferLimits[tokenId];
    }

    /**
     * @dev Internal function to increment transfer count.
     */
    function _incrementTransferCount(uint256 tokenId) internal {
        _transferCounts[tokenId] += 1;
        emit TransferCount(tokenId, ownerOf(tokenId), _transferCounts[tokenId]);
    }

    /**
     * @dev Override {_beforeTokenTransfer} to enforce transfer limit.
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 tokenId
    ) internal override {
        require(_transferCounts[tokenId] < _transferLimits[tokenId], "ERC7634: Transfer limit reached");
        super._beforeTokenTransfer(from, to, tokenId);
    }

    /**
     * @dev Override {_afterTokenTransfer} to handle post-transfer logic.
     */
    function _afterTokenTransfer(
        address from,
        address to,
        uint256 tokenId,
        uint256 quantity
    ) internal virtual override {
        _incrementTransferCount(tokenId);

        if (_transferCounts[tokenId] == _transferLimits[tokenId]) {
            // Optional post-transfer operations once the limit is reached
            // Uncomment the following based on the desired behavior such as the `burn` opearation
            // ---------------------------------------
            // _burn(tokenId); // Burn the token
            // ---------------------------------------
        }

        super._afterTokenTransfer(from, to, tokenId, quantity);
    }


    /**
     * @dev Override {supportsInterface} to declare support for IERC7634.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC721) returns (bool) {
        return interfaceId == type(IERC7634).interfaceId || super.supportsInterface(interfaceId);
    }
}