Comprehensive comparison for Payment Processing technology in Software Development applications

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

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

// Initialize Adyen client
const config = new Config();
config.apiKey = process.env.ADYEN_API_KEY;
config.merchantAccount = process.env.ADYEN_MERCHANT_ACCOUNT;
const client = new Client({ config });
const checkout = new CheckoutAPI(client);

// Create payment session endpoint
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 fields' });
    }

    const paymentRequest = {
      amount: {
        currency: currency,
        value: amount // Amount in minor units (e.g., 1000 = $10.00)
      },
      reference: reference,
      merchantAccount: config.merchantAccount,
      returnUrl: returnUrl || `${process.env.BASE_URL}/payment/result`,
      countryCode: countryCode || 'US',
      shopperLocale: 'en-US',
      channel: 'Web',
      // Enable stored payment methods for returning customers
      storePaymentMethod: true,
      recurringProcessingModel: 'CardOnFile'
    };

    const response = await checkout.sessions(paymentRequest);
    
    res.json({
      sessionId: response.id,
      sessionData: response.sessionData
    });
  } catch (error) {
    console.error('Payment session creation failed:', error);
    res.status(500).json({ 
      error: 'Failed to create payment session',
      message: error.message 
    });
  }
});

// Handle payment webhook notifications
app.post('/api/webhooks/adyen', async (req, res) => {
  try {
    const notificationRequest = req.body;
    const notificationItems = notificationRequest.notificationItems;

    // Validate HMAC signature for security
    const hmacKey = process.env.ADYEN_HMAC_KEY;
    
    for (const item of notificationItems) {
      const notification = item.NotificationRequestItem;
      
      // Verify HMAC signature
      const expectedSign = calculateHmac(notification, hmacKey);
      if (notification.additionalData?.hmacSignature !== expectedSign) {
        console.error('Invalid HMAC signature');
        return res.status(401).json({ error: 'Invalid signature' });
      }

      // Process notification based on event code
      const { eventCode, success, pspReference, merchantReference } = notification;
      
      if (eventCode === 'AUTHORISATION') {
        if (success === 'true') {
          // Payment authorized - update order status
          await updateOrderStatus(merchantReference, 'AUTHORIZED', pspReference);
          console.log(`Payment authorized: ${pspReference}`);
        } else {
          // Payment failed
          await updateOrderStatus(merchantReference, 'FAILED', pspReference);
          console.log(`Payment failed: ${pspReference}`);
        }
      } else if (eventCode === 'CAPTURE') {
        // Payment captured - fulfill order
        await updateOrderStatus(merchantReference, 'CAPTURED', pspReference);
        console.log(`Payment captured: ${pspReference}`);
      } else if (eventCode === 'REFUND') {
        // Refund processed
        await updateOrderStatus(merchantReference, 'REFUNDED', pspReference);
        console.log(`Refund processed: ${pspReference}`);
      }
    }

    // Always return [accepted] to acknowledge receipt
    res.status(200).send('[accepted]');
  } catch (error) {
    console.error('Webhook processing error:', error);
    res.status(500).json({ error: 'Webhook processing failed' });
  }
});

// Calculate HMAC signature for webhook validation
function calculateHmac(notification, hmacKey) {
  const signedString = [
    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(signedString);
  return hmac.digest('base64');
}

// Mock function to update order status in database
async function updateOrderStatus(orderReference, status, pspReference) {
  // Implementation would update your database
  console.log(`Updating order ${orderReference} to ${status} (PSP: ${pspReference})`);
  return Promise.resolve();
}

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