Multi-Gateway Webhook & Double-Entry Reconcile

// Idempotent Multi-Gateway Webhook Controller & Outbox Pattern di NestJS
@Controller('billing/webhooks')
@UseGuards(HmacSignatureGuard)
export class BillingWebhookController {
  constructor(
    private readonly redlockService: RedlockService,
    @InjectDataSource() private readonly dataSource: DataSource,
  ) {}

  @Post(':gateway')
  async handleGatewayWebhook(
    @Param('gateway') gateway: string,
    @Body() payload: PaymentWebhookDto,
    @Res() res: Response,
  ) {
    const lockKey = `lock:webhook:${payload.invoiceId}`;

    // 1. Acquire Distributed Mutex via Redis Redlock (TTL 2000ms)
    let lock: Lock;
    try {
      lock = await this.redlockService.acquire([lockKey], 2000);
    } catch {
      // Gracefully absorb duplicate retry callbacks
      return res.status(HttpStatus.ACCEPTED).json({ status: 'duplicate_event_absorbed' });
    }

    try {
      // 2. Transaksi Atomik: Settle Invoice + Double-Entry Ledger + Transactional Outbox
      await this.dataSource.transaction('READ COMMITTED', async (manager) => {
        const invoice = await manager.createQueryBuilder(Invoice, 'inv')
          .setLock('pessimistic_write')
          .where('inv.id = :id', { id: payload.invoiceId })
          .getOne();

        if (invoice?.status === 'SETTLED') return;

        await manager.update(Invoice, payload.invoiceId, {
          status: 'SETTLED',
          settledAt: new Date(),
        });

        await manager.insert(LedgerEntry, {
          invoiceId: payload.invoiceId,
          debitAccount: `GATEWAY_CLEARING_${gateway.toUpperCase()}`,
          creditAccount: 'AR_CUSTOMER',
          amount: payload.amount,
        });

        await manager.insert(OutboxEvent, {
          topic: 'billing.invoice.settled',
          payload: JSON.stringify(payload),
          status: 'PENDING',
        });
      });

      return res.status(HttpStatus.OK).json({ status: 'settled' });
    } finally {
      await lock.release().catch(() => null);
    }
  }
}