ERC-721 NFT Implementation — Kudos build — collectibles step

Objective Add ERC-721 badges to the Kudos app for contributors who hold Kudos tokens.

Flow Gate minting on holding Kudos, emit Transfer/Approval events, and expose a stable baseURI so marketplaces can render badges.

What to write

1. Scaffold
   ERC721URIStorage + AccessControl + counter.
   Copy

   contract KudosBadge is ERC721URIStorage, AccessControl {
       bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
       IERC20 public immutable kudos;
       uint256 private _nextId = 1;
       string private _base;

   Sets roles, links to Kudos ERC-20, and tracks token IDs.

2. Constructor
   Wire token address, base URI, and roles.
   Copy

       constructor(address kudosToken, string memory base) ERC721("Kudos Badge", "KBDG") {
           kudos = IERC20(kudosToken);
           _base = base;
           _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
           _grantRole(MINTER_ROLE, msg.sender);
       }

   Anchors metadata and roles; sets the ERC-721 name/symbol.

3. Gate minting
   Require Kudos balance and set tokenURI.
   Copy

       function safeMint(address to, string calldata uri) external onlyRole(MINTER_ROLE) {
           require(kudos.balanceOf(to) > 0, "needs kudos");
           uint256 id = _nextId++;
           _safeMint(to, id);
           _setTokenURI(id, uri);
       }

   Ties badges to contributors; emits standard events.

4. Base URI
   Expose baseURI for consistent metadata.
   Copy

       function _baseURI() internal view override returns (string memory) { return _base; }

   Keeps metadata stable and indexer-friendly.

Why Gating on Kudos ties badges to real contribution, stable URIs make marketplaces happy, and role-gated minting avoids rogue supply.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import {ERC721URIStorage, ERC721} from "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import {AccessControl} from "@openzeppelin/contracts/access/AccessControl.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract KudosBadge is ERC721URIStorage, AccessControl {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
    IERC20 public immutable kudos;
    uint256 private _nextId = 1;
    string private _base;

    constructor(address kudosToken, string memory base) ERC721("Kudos Badge", "KBDG") {
        kudos = IERC20(kudosToken);
        _base = base;
        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
        _grantRole(MINTER_ROLE, msg.sender);
    }

    function safeMint(address to, string calldata uri) external onlyRole(MINTER_ROLE) {
        require(kudos.balanceOf(to) > 0, "needs kudos");
        uint256 id = _nextId++;
        _safeMint(to, id);
        _setTokenURI(id, uri);
    }

    function _baseURI() internal view override returns (string memory) { return _base; }

    function supportsInterface(bytes4 id) public view override(ERC721URIStorage, AccessControl) returns (bool) {
        return super.supportsInterface(id);
    }
}

Next Plug in oracles and randomness to enrich badge traits.