[ERC7160] NFTに複数のメタデータを紐づける仕組みを理解しよう！

/// @title EIP-721 Multi-Metdata Extension
/// @dev The ERC-165 identifier for this interface is 0x06e1bc5b.
interface IERC7160 {

  /// @dev This event emits when a token uri is pinned and is
  ///  useful for indexing purposes.
  event TokenUriPinned(uint256 indexed tokenId, uint256 indexed index);

  /// @dev This event emits when a token uri is unpinned and is
  ///  useful for indexing purposes.
  event TokenUriUnpinned(uint256 indexed tokenId);

  /// @notice Get all token uris associated with a particular token
  /// @dev If a token uri is pinned, the index returned SHOULD be the index in the string array
  /// @dev This call MUST revert if the token does not exist
  /// @param tokenId The identifier for the nft
  /// @return index An unisgned integer that specifies which uri is pinned for a token (or the default uri if unpinned)
  /// @return uris A string array of all uris associated with a token
  /// @return pinned A boolean showing if the token has pinned metadata or not
  function tokenURIs(uint256 tokenId) external view returns (uint256 index, string[] memory uris, bool pinned);

  /// @notice Pin a specific token uri for a particular token
  /// @dev This call MUST revert if the token does not exist
  /// @dev This call MUST emit a `TokenUriPinned` event
  /// @dev This call MAY emit a `MetadataUpdate` event from ERC-4096
  /// @param tokenId The identifier of the nft
  /// @param index The index in the string array returned from the `tokenURIs` function that should be pinned for the token
  function pinTokenURI(uint256 tokenId, uint256 index) external;

  /// @notice Unpin metadata for a particular token
  /// @dev This call MUST revert if the token does not exist
  /// @dev This call MUST emit a `TokenUriUnpinned` event
  /// @dev This call MAY emit a `MetadataUpdate` event from ERC-4096
  /// @dev It is up to the developer to define what this function does and is intentionally left open-ended
  /// @param tokenId The identifier of the nft
  function unpinTokenURI(uint256 tokenId) external;

  /// @notice Check on-chain if a token id has a pinned uri or not
  /// @dev This call MUST revert if the token does not exist
  /// @dev Useful for on-chain mechanics that don't require the tokenURIs themselves
  /// @param tokenId The identifier of the nft
  /// @return pinned A bool specifying if a token has metadata pinned or not
  function hasPinnedTokenURI(uint256 tokenId) external view returns (bool pinned);
}

event TokenUriPinned(uint256 indexed tokenId, uint256 indexed index);

event TokenUriUnpinned(uint256 indexed tokenId);

function tokenURIs(uint256 tokenId) external view returns (uint256 index, string[] memory uris, bool pinned);

function pinTokenURI(uint256 tokenId, uint256 index) external;

function unpinTokenURI(uint256 tokenId) external;

function hasPinnedTokenURI(uint256 tokenId) external view returns (bool pinned);

// SPDX-License-Identifier: CC0-1.0

pragma solidity ^0.8.19;

import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
import {IERC4906} from "@openzeppelin/contracts/interfaces/IERC4906.sol";
import {IERC7160} from "./IERC7160.sol";

contract MultiMetadata is ERC721, Ownable, IERC7160, IERC4906 {
  mapping(uint256 => string[]) private _tokenURIs;
  mapping(uint256 => uint256) private _pinnedURIIndices;
  mapping(uint256 => bool) private _hasPinnedTokenURI;

  constructor(string memory _name, string memory _symbol) ERC721(_name, _symbol) Ownable() {
    _mint(msg.sender, 1);
  }

  // @notice Returns the pinned URI index or the last token URI index (length - 1).
  function _getTokenURIIndex(uint256 tokenId) internal view returns (uint256) {
    return _hasPinnedTokenURI[tokenId] ? _pinnedURIIndices[tokenId] : _tokenURIs[tokenId].length - 1;
  }

  // @notice Implementation of ERC721.tokenURI for backwards compatibility.
  // @inheritdoc ERC721.tokenURI
  function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
    _requireMinted(tokenId);

    uint256 index = _getTokenURIIndex(tokenId);
    string[] memory uris = _tokenURIs[tokenId];
    string memory uri = uris[index];

    // Revert if no URI is found for the token.
    require(bytes(uri).length > 0, "ERC721: not URI found");
    return uri;
  }

  /// @inheritdoc IERC721MultiMetadata.tokenURIs
  function tokenURIs(uint256 tokenId) external view returns (uint256 index, string[] memory uris, bool pinned) {
    _requireMinted(tokenId);
    return (_getTokenURIIndex(tokenId), _tokenURIs[tokenId], _hasPinnedTokenURI[tokenId]);
  }

  /// @inheritdoc IERC721MultiMetadata.pinTokenURI
  function pinTokenURI(uint256 tokenId, uint256 index) external {
    require(msg.sender == ownerOf(tokenId), "Unauthorized");
    _pinnedURIIndices[tokenId] = index;
    _hasPinnedTokenURI[tokenId] = true;
    emit TokenUriPinned(tokenId, index);
  }

  /// @inheritdoc IERC721MultiMetadata.unpinTokenURI
  function unpinTokenURI(uint256 tokenId) external {
    require(msg.sender == ownerOf(tokenId), "Unauthorized");
    _pinnedURIIndices[tokenId] = 0;
    _hasPinnedTokenURI[tokenId] = false;
    emit TokenUriUnpinned(tokenId);
  }

  /// @inheritdoc IERC721MultiMetadata.hasPinnedTokenURI
  function hasPinnedTokenURI(uint256 tokenId) external view returns (bool pinned) {
    return _hasPinnedTokenURI[tokenId];
  }

  /// @notice Sets a specific metadata URI for a token at the given index.
  function setUri(uint256 tokenId, uint256 index, string calldata uri) external onlyOwner {
    if (_tokenURIs[tokenId].length > index) {
      _tokenURIs[tokenId][index] = uri;
    } else {
      _tokenURIs[tokenId].push(uri);
    }

    emit MetadataUpdate(tokenId);
  }

  // Overrides supportsInterface to include IERC721MultiMetadata interface support.
  function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC721) returns (bool) {
    return (
      interfaceId == type(IERC7160).interfaceId ||
      super.supportsInterface(interfaceId)
    );
  }
}