// SPDX-License-Identifier: CC0-1.0 pragma solidity ^0.8.0; import "@openzeppelin/contracts/token/ERC721/ERC721.sol"; import "./IERC5008.sol"; contract ERC5008 is ERC721, IERC5008 { mapping(uint256 => uint256) private _tokenNonce; constructor(string memory name_, string memory symbol_)ERC721(name_, symbol_){ } /// @notice Get the nonce of an NFT /// Throws if `tokenId` is not a valid NFT /// @param tokenId The NFT to get the nonce for /// @return The nonce of this NFT function nonce(uint256 tokenId) public virtual override view returns(uint256) { require(_exists(tokenId), "Error: query for nonexistent token"); return _tokenNonce[tokenId]; } function _beforeTokenTransfer( address from, address to, uint256 tokenId ) internal virtual override{ super._beforeTokenTransfer(from, to, tokenId); _tokenNonce[tokenId]++; } /// @dev See {IERC165-supportsInterface}. function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) { return interfaceId == type(IERC5008).interfaceId || super.supportsInterface(interfaceId); } }