Comprehensive comparison for Payment Processing technology in Software Development applications

const express = require('express');
const { Client, CheckoutAPI } = require('@adyen/api-library');
const crypto = require('crypto');

const app = express();
app.use(express.json());

// Initialize Adyen client with credentials
const client = new Client({
  apiKey: process.env.ADYEN_API_KEY,
  environment: process.env.ADYEN_ENVIRONMENT || 'TEST'
});
const checkout = new CheckoutAPI(client);

// Endpoint to create a payment session
app.post('/api/payments/sessions', async (req, res) => {
  try {
    const { amount, currency, reference, returnUrl, countryCode } = req.body;

    // Validate required fields
    if (!amount || !currency || !reference) {
      return res.status(400).json({ error: 'Missing required payment fields' });
    }

    const sessionRequest = {
      amount: {
        currency: currency,
        value: amount // Amount in minor units (e.g., cents)
      },
      reference: reference,
      merchantAccount: process.env.ADYEN_MERCHANT_ACCOUNT,
      returnUrl: returnUrl || `${process.env.BASE_URL}/payment/result`,
      countryCode: countryCode || 'US',
      shopperLocale: 'en-US',
      channel: 'Web',
      lineItems: req.body.lineItems || []
    };

    const session = await checkout.sessions(sessionRequest);

    res.json({
      sessionId: session.id,
      sessionData: session.sessionData
    });
  } catch (error) {
    console.error('Payment session creation failed:', error);
    res.status(500).json({ error: 'Failed to create payment session' });
  }
});

// Webhook endpoint to handle payment notifications
app.post('/api/webhooks/adyen', async (req, res) => {
  try {
    const notificationRequest = req.body;
    const hmacKey = process.env.ADYEN_HMAC_KEY;

    // Verify webhook authenticity using HMAC signature
    const notificationRequestItems = notificationRequest.notificationItems;

    if (!notificationRequestItems || notificationRequestItems.length === 0) {
      return res.status(400).send('[accepted]');
    }

    for (const item of notificationRequestItems) {
      const notification = item.NotificationRequestItem;

      // Verify HMAC signature
      const expectedSign = calculateHMAC(notification, hmacKey);
      if (expectedSign !== notification.additionalData['hmacSignature']) {
        console.error('Invalid HMAC signature');
        return res.status(401).send('[rejected]');
      }

      // Process the notification based on event code
      await processNotification(notification);
    }

    // Always return [accepted] for valid webhooks
    res.status(200).send('[accepted]');
  } catch (error) {
    console.error('Webhook processing error:', error);
    res.status(500).send('[rejected]');
  }
});

// Calculate HMAC signature for webhook verification
function calculateHMAC(notification, hmacKey) {
  const data = [
    notification.pspReference,
    notification.originalReference,
    notification.merchantAccountCode,
    notification.merchantReference,
    notification.amount.value,
    notification.amount.currency,
    notification.eventCode,
    notification.success
  ].join(':');

  const hmac = crypto.createHmac('sha256', Buffer.from(hmacKey, 'hex'));
  hmac.update(data);
  return hmac.digest('base64');
}

// Process different notification types
async function processNotification(notification) {
  const { eventCode, success, merchantReference, pspReference } = notification;

  console.log(`Processing ${eventCode} for ${merchantReference}`);

  if (eventCode === 'AUTHORISATION' && success === 'true') {
    // Update order status to paid
    await updateOrderStatus(merchantReference, 'PAID', pspReference);
  } else if (eventCode === 'CANCELLATION') {
    await updateOrderStatus(merchantReference, 'CANCELLED', pspReference);
  } else if (eventCode === 'REFUND') {
    await updateOrderStatus(merchantReference, 'REFUNDED', pspReference);
  }
}

// Mock function to update order status in database
async function updateOrderStatus(orderId, status, paymentReference) {
  // Implementation would update your database
  console.log(`Order ${orderId} updated to ${status} with reference ${paymentReference}`);
}

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Payment service running on port ${PORT}`);
});