ERC-20 (In-Game Currencies)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract GameCurrency is ERC20, Ownable {
    constructor() ERC20("Gold Coins", "GOLD") Ownable(msg.sender) {
        _mint(msg.sender, 1000000 * 10 ** decimals());
    }

    function mint(address to, uint256 amount) external onlyOwner {
        _mint(to, amount);
    }
}

const REWARDS = {
  'first_kill': 100n * 10n ** 18n,
  'level_10': 500n * 10n ** 18n,
  'boss_defeated': 1000n * 10n ** 18n,
};

async function grantAchievement(player: string, achievement: string) {
  const reward = REWARDS[achievement];
  if (reward) await currencyContract.mint(player, reward);
}

async function claimDailyReward(player: string) {
  const lastClaim = await getLastClaimTime(player);
  if (Date.now() - lastClaim < 24 * 60 * 60 * 1000) {
    throw new Error('Already claimed today');
  }
  
  await currencyContract.mint(player, 50n * 10n ** 18n);
  await setLastClaimTime(player, Date.now());
}

async function purchaseItem(player: string, itemId: string, price: bigint) {
  // Transfer from player to treasury
  await currencyContract.transferFrom(player, TREASURY, price);
  
  // Grant the item
  await grantItem(player, itemId);
}

// Frontend: Request approval
async function approveSpending(amount: bigint) {
  const signer = await ethersProvider.getSigner();
  const currency = new ethers.Contract(CURRENCY_ADDRESS, ERC20_ABI, signer);
  await currency.approve(GAME_CONTRACT, amount);
}

// Direct contract call
const balance = await currencyContract.balanceOf(playerAddress);
console.log(`${ethers.formatEther(balance)} GOLD`);

// Via Indexer API
const tokens = await indexer.listTokensByAccountAddress({
  chainName: 'imtbl-zkevm-mainnet',
  accountAddress: playerAddress,
});