Modeler Webhook & Idempotensi Kriptografi

import crypto from 'crypto';

// 1. Verifikasi Signature HMAC-SHA256 & Timestamp Replay Attack
export function verifyWebhookSignature(payload: string, signatureHeader: string, secret: string) {
  // Signature format: t=1729340000,v1=abcdef0123456789...
  const parts = Object.fromEntries(signatureHeader.split(',').map(kv => kv.split('=')));
  const timestamp = parts['t'];
  const expectedSignature = parts['v1'];

  // Cegah Replay Attack: Toleransi waktu maksimal 5 menit (300 detik)
  const currentTimestamp = Math.floor(Date.now() / 1000);
  if (Math.abs(currentTimestamp - parseInt(timestamp, 10)) > 300) {
    throw new Error('Replay attack detected: timestamp out of tolerance window');
  }

  // Hitung HMAC SHA-256 dari timestamp.payload
  const signedPayload = `${timestamp}.${payload}`;
  const computedSignature = crypto
    .createHmac('sha256', secret)
    .update(signedPayload)
    .digest('hex');

  // Gunakan timingSafeEqual untuk mencegah timing attack
  const isMatch = crypto.timingSafeEqual(
    Buffer.from(computedSignature, 'utf8'),
    Buffer.from(expectedSignature, 'utf8')
  );

  if (!isMatch) {
    throw new Error('Invalid cryptographic webhook signature');
  }

  return true;
}

// 2. Pola Idempotensi Kunci Transaksi dengan Redis Atomic Lock
export async function processIdempotentWebhook(redisClient: any, idempotencyKey: string, handler: () => Promise<void>) {
  // SET key value NX EX 86400 (Atomic lock 24 jam)
  const acquired = await redisClient.set(`webhook:idempotency:${idempotencyKey}`, 'PROCESSING', 'NX', 'EX', 86400);
  
  if (!acquired) {
    // Event ini sudah pernah diproses atau sedang diproses: kembalikan 200 OK seketika
    return { status: 'DUPLICATE_IGNORED' };
  }

  try {
    await handler();
    await redisClient.set(`webhook:idempotency:${idempotencyKey}`, 'COMPLETED', 'XX', 'EX', 86400);
    return { status: 'SUCCESS' };
  } catch (err) {
    // Hapus lock jika gagal agar dapat dicoba ulang
    await redisClient.del(`webhook:idempotency:${idempotencyKey}`);
    throw err;
  }
}