Programmable Wallets — Create 10,000 User Wallets Without Key Management

You: Set up programmable wallets for our app. We need:
- Auto-create a wallet when users sign up
- Support USDC on Ethereum and Polygon
- Users can send/receive USDC
- We control gas (users don't pay tx fees)

// === wallet-service.js ===
import { CircleSDK } from '@circle-fin/circle-sdk';

const circle = new CircleSDK({
  apiKey: process.env.CIRCLE_API_KEY,
  entitySecret: process.env.CIRCLE_ENTITY_SECRET
});

// Create wallet set (one per environment)
async function initWalletSet() {
  const response = await circle.wallets.createWalletSet({
    name: 'production-users'
  });
  return response.data.walletSet;
}

// Create wallet for new user (called during signup)
async function createUserWallet(userId) {
  const response = await circle.wallets.createWallet({
    walletSetId: WALLET_SET_ID,
    blockchains: ['ETH', 'MATIC'],  // Ethereum + Polygon
    count: 1,
    metadata: [{ name: 'userId', value: userId }]
  });

  const wallet = response.data.wallets[0];

  // Store wallet ID (NOT keys — Circle manages those)
  await db.users.update(userId, {
    circleWalletId: wallet.id,
    ethAddress: wallet.address
  });

  return wallet;
}

// Send USDC (user-initiated, you sign with Circle)
async function sendUSDC({ fromUserId, toAddress, amount, chain }) {
  const user = await db.users.findById(fromUserId);

  const response = await circle.transactions.createTransfer({
    walletId: user.circleWalletId,
    tokenId: USDC_TOKEN_IDS[chain],
    destinationAddress: toAddress,
    amounts: [amount.toString()],
    fee: {
      type: 'level',
      config: { feeLevel: 'MEDIUM' }
    }
  });

  return response.data;
}

// Check balance
async function getBalance(userId) {
  const user = await db.users.findById(userId);
  const response = await circle.wallets.getWalletBalance(
    user.circleWalletId
  );
  return response.data.tokenBalances;
}

skills:
  - circle-wallets
  - stablecoin-payments