Comprehensive comparison for Payment Processing technology in Software Development applications

const express = require('express');
const crypto = require('crypto');
const axios = require('axios');

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

// PayU Configuration
const PAYU_CONFIG = {
  merchantKey: process.env.PAYU_MERCHANT_KEY,
  merchantSalt: process.env.PAYU_MERCHANT_SALT,
  apiUrl: process.env.PAYU_ENV === 'production' 
    ? 'https://secure.payu.in/_payment' 
    : 'https://test.payu.in/_payment'
};

// Generate hash for PayU transaction
function generateHash(data) {
  const hashString = `${PAYU_CONFIG.merchantKey}|${data.txnid}|${data.amount}|${data.productinfo}|${data.firstname}|${data.email}|||||||||||${PAYU_CONFIG.merchantSalt}`;
  return crypto.createHash('sha512').update(hashString).digest('hex');
}

// Verify hash for callback
function verifyHash(data) {
  const hashString = `${PAYU_CONFIG.merchantSalt}|${data.status}|||||||||||${data.email}|${data.firstname}|${data.productinfo}|${data.amount}|${data.txnid}|${PAYU_CONFIG.merchantKey}`;
  const generatedHash = crypto.createHash('sha512').update(hashString).digest('hex');
  return generatedHash === data.hash;
}

// Initiate payment endpoint
app.post('/api/payments/initiate', async (req, res) => {
  try {
    const { amount, productInfo, customerName, customerEmail, customerPhone, orderId } = req.body;
    
    // Validate required fields
    if (!amount || !productInfo || !customerName || !customerEmail || !orderId) {
      return res.status(400).json({ error: 'Missing required fields' });
    }
    
    // Generate unique transaction ID
    const txnid = `TXN${Date.now()}${Math.random().toString(36).substr(2, 9)}`;
    
    const paymentData = {
      key: PAYU_CONFIG.merchantKey,
      txnid: txnid,
      amount: parseFloat(amount).toFixed(2),
      productinfo: productInfo,
      firstname: customerName,
      email: customerEmail,
      phone: customerPhone || '',
      surl: `${process.env.BASE_URL}/api/payments/success`,
      furl: `${process.env.BASE_URL}/api/payments/failure`,
      udf1: orderId,
      udf2: '',
      udf3: '',
      udf4: '',
      udf5: ''
    };
    
    // Generate hash
    paymentData.hash = generateHash(paymentData);
    
    // Store transaction in database (pseudo-code)
    // await db.transactions.create({ txnid, orderId, amount, status: 'pending' });
    
    res.json({
      success: true,
      paymentUrl: PAYU_CONFIG.apiUrl,
      paymentData: paymentData
    });
    
  } catch (error) {
    console.error('Payment initiation error:', error);
    res.status(500).json({ error: 'Failed to initiate payment' });
  }
});

// Payment success callback
app.post('/api/payments/success', async (req, res) => {
  try {
    const paymentResponse = req.body;
    
    // Verify hash to ensure data integrity
    if (!verifyHash(paymentResponse)) {
      console.error('Hash verification failed');
      return res.status(400).send('Invalid payment response');
    }
    
    // Update transaction status in database
    // await db.transactions.update({ txnid: paymentResponse.txnid }, { 
    //   status: 'success',
    //   payuId: paymentResponse.mihpayid,
    //   paymentMode: paymentResponse.mode
    // });
    
    // Process order fulfillment
    // await processOrder(paymentResponse.udf1);
    
    res.redirect(`${process.env.FRONTEND_URL}/payment/success?txnid=${paymentResponse.txnid}`);
    
  } catch (error) {
    console.error('Payment success handler error:', error);
    res.status(500).send('Error processing payment');
  }
});

// Payment failure callback
app.post('/api/payments/failure', async (req, res) => {
  try {
    const paymentResponse = req.body;
    
    // Update transaction status
    // await db.transactions.update({ txnid: paymentResponse.txnid }, { 
    //   status: 'failed',
    //   errorMessage: paymentResponse.error_Message
    // });
    
    res.redirect(`${process.env.FRONTEND_URL}/payment/failure?txnid=${paymentResponse.txnid}`);
    
  } catch (error) {
    console.error('Payment failure handler error:', error);
    res.status(500).send('Error processing payment failure');
  }
});

// Verify payment status endpoint
app.get('/api/payments/verify/:txnid', async (req, res) => {
  try {
    const { txnid } = req.params;
    const command = 'verify_payment';
    const hashString = `${PAYU_CONFIG.merchantKey}|${command}|${txnid}|${PAYU_CONFIG.merchantSalt}`;
    const hash = crypto.createHash('sha512').update(hashString).digest('hex');
    
    const response = await axios.post('https://info.payu.in/merchant/postservice.php?form=2', 
      `key=${PAYU_CONFIG.merchantKey}&command=${command}&var1=${txnid}&hash=${hash}`,
      { headers: { 'Content-Type': 'application/x-www-form-urlencoded' } }
    );
    
    res.json({ success: true, data: response.data });
    
  } catch (error) {
    console.error('Payment verification error:', error);
    res.status(500).json({ error: 'Failed to verify payment' });
  }
});

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