PSP #1 Adapter -- PassimPay

import crypto from 'crypto'

/**
 * Sign a PassimPay API request.
 * Contract: HMAC-SHA256( platformId + ";" + jsonBody + ";" + secret, secret )
 *
 * IMPORTANT: JSON.stringify escapes forward slashes as "\/" in some environments.
 * PassimPay expects escaped slashes. Use the replaceAll below to be safe.
 */
export function signRequest(
  platformId: number,
  body: Record<string, unknown>,
  secret: string,
): string {
  const jsonBody = JSON.stringify(body).replaceAll('/', '\/')
  const contract = `${platformId};${jsonBody};${secret}`
  return crypto
    .createHmac('sha256', secret)
    .update(contract)
    .digest('hex')
}

/**
 * Verify an incoming PassimPay webhook.
 * Same contract -- compare computed signature with x-signature header.
 */
export function verifyWebhook(
  platformId: number,
  rawBody: string,       // raw unparsed request body string
  secret: string,
  receivedSignature: string,
): boolean {
  const contract = `${platformId};${rawBody};${secret}`
  const expected = crypto
    .createHmac('sha256', secret)
    .update(contract)
    .digest('hex')
  return crypto.timingSafeEqual(
    Buffer.from(expected, 'hex'),
    Buffer.from(receivedSignature, 'hex'),
  )
}

import express from 'express'
import { verifyWebhook } from './passimpay-signature'

const router = express.Router()

// IMPORTANT: use express.raw() -- NOT express.json() -- for this route.
// You need the raw body bytes for signature verification.
router.post(
  '/webhooks/passimpay',
  express.raw({ type: 'application/json' }),
  async (req, res) => {
    const rawBody = req.body.toString('utf-8')
    const signature = req.headers['x-signature'] as string

    // Step 1 -- verify signature
    const valid = verifyWebhook(
      Number(process.env.PASSIMPAY_PLATFORM_ID),
      rawBody,
      process.env.PASSIMPAY_API_SECRET!,
      signature,
    )
    if (!valid) {
      return res.status(400).json({ error: 'INVALID_SIGNATURE' })
    }

    // Step 2 -- parse body
    const payload = JSON.parse(rawBody)

    // Step 3 -- idempotency check (orderId or transactionId)
    const idempotencyKey = payload.orderId ?? payload.transactionId
    const alreadyProcessed = await db.webhookEvents.exists(idempotencyKey)
    if (alreadyProcessed) {
      return res.status(200).json({ ok: true }) // return 200 to stop PSP retries
    }

    // Step 4 -- enqueue for orchestrator (do NOT process inline)
    await queue.push({ type: 'passimpay_webhook', payload, rawBody })

    // Step 5 -- respond 200 immediately
    // PassimPay retries up to 2 times if 200 is not returned promptly.
    return res.status(200).json({ ok: true })
  },
)