Stablecoin Card Settlement

// settlement/iso8583-handler.ts
import { parseISO8583, buildResponse } from '@/lib/iso8583';
import { settleInUSDC } from '@/lib/usdc-settlement';

export async function handleAuthorizationRequest(message: Buffer) {
  const parsed = parseISO8583(message);

  // Extract key fields from bitmap
  const { pan, amount, currency, mcc, terminalId } = parsed;

  // Route to issuer for approval
  const authResponse = await routeToIssuer({
    cardNumber: maskPAN(pan),
    amount: parseAmount(amount),
    merchantCategory: mcc
  });

  if (authResponse.approved) {
    // Queue for USDC settlement (replaces T+2 wire)
    await queueSettlement({
      type: 'ISSUER_OBLIGATION',
      amount: authResponse.settleAmount,
      chain: 'base',
      token: 'USDC'
    });
  }

  // Build ISO 8583 0110 response
  return buildResponse('0110', {
    responseCode: authResponse.approved ? '00' : '05',
    authCode: authResponse.authCode
  });
}

// settlement/usdc-engine.ts
import { createPublicClient, createWalletClient, http } from 'viem';
import { base } from 'viem/chains';
import { USDC_ABI, USDC_ADDRESS } from '@/lib/contracts';

export async function settleInUSDC(params: SettlementParams) {
  const { from, to, amount, reference } = params;

  // Create settlement transaction on Base
  const txHash = await walletClient.writeContract({
    address: USDC_ADDRESS,
    abi: USDC_ABI,
    functionName: 'transfer',
    args: [to, parseUnits(amount.toString(), 6)]
  });

  // Wait for confirmation (~2 seconds on Base)
  const receipt = await publicClient.waitForTransactionReceipt({
    hash: txHash,
    confirmations: 1
  });

  // Emit settlement event for reconciliation
  await emitSettlementEvent({
    txHash,
    reference,
    settledAt: new Date(),
    blockNumber: receipt.blockNumber,
    // Compare: Traditional would be T+2 (48+ hours)
    settlementTime: 'INSTANT'
  });

  return { txHash, status: 'SETTLED' };
}