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

// Initialize AppDynamics agent
const appd = appdynamics.profile({
  controllerHostname: process.env.APPD_CONTROLLER_HOST,
  controllerPort: process.env.APPD_CONTROLLER_PORT || 443,
  controllerSslEnabled: true,
  accountName: process.env.APPD_ACCOUNT_NAME,
  accountAccessKey: process.env.APPD_ACCESS_KEY,
  applicationName: 'PaymentProcessingService',
  tierName: 'API-Tier',
  nodeName: process.env.HOSTNAME || 'payment-node-1'
});

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

// Custom business transaction decorator
function trackBusinessTransaction(btName) {
  return function(req, res, next) {
    req.btHandle = appdynamics.startTransaction(btName, {
      entryPointType: 'HTTP',
      identifyingProperties: {
        userId: req.body.userId || 'anonymous',
        paymentMethod: req.body.paymentMethod
      }
    });
    next();
  };
}

// Payment processing endpoint with AppDynamics instrumentation
app.post('/api/v1/payments/process', 
  trackBusinessTransaction('ProcessPayment'),
  async (req, res) => {
    const exitCallHandle = null;
    
    try {
      const { userId, amount, currency, paymentMethod, orderId } = req.body;
      
      // Input validation with custom metrics
      if (!userId || !amount || !currency || !paymentMethod) {
        appdynamics.addSnapshotData('ValidationError', 'Missing required fields');
        appdynamics.reportMetric('Payment.Validation.Failures', 1);
        return res.status(400).json({ error: 'Missing required fields' });
      }
      
      // Track payment amount as custom metric
      appdynamics.reportMetric(`Payment.Amount.${currency}`, amount);
      appdynamics.reportMetric('Payment.Requests.Total', 1);
      
      // Exit call to payment gateway with correlation
      const exitCallHandle = appdynamics.startExitCall({
        exitType: 'HTTP',
        label: 'PaymentGatewayAPI',
        backendName: 'StripePaymentGateway',
        identifyingProperties: {
          URL: 'https://api.stripe.com/v1/charges'
        }
      });
      
      const correlationHeader = appdynamics.getCorrelationHeader(exitCallHandle);
      
      // Call external payment gateway
      const paymentResponse = await axios.post(
        'https://api.stripe.com/v1/charges',
        {
          amount: amount * 100,
          currency: currency,
          source: paymentMethod,
          metadata: { orderId, userId }
        },
        {
          headers: {
            'Authorization': `Bearer ${process.env.STRIPE_SECRET_KEY}`,
            'singularityheader': correlationHeader
          },
          timeout: 5000
        }
      );
      
      appdynamics.endExitCall(exitCallHandle);
      
      // Track successful payment
      if (paymentResponse.data.status === 'succeeded') {
        appdynamics.reportMetric('Payment.Success.Count', 1);
        appdynamics.addSnapshotData('PaymentStatus', 'SUCCESS');
        appdynamics.addSnapshotData('TransactionId', paymentResponse.data.id);
        
        res.json({
          success: true,
          transactionId: paymentResponse.data.id,
          status: 'completed'
        });
      } else {
        throw new Error('Payment processing failed');
      }
      
    } catch (error) {
      // Error handling with AppDynamics tracking
      if (exitCallHandle) {
        appdynamics.endExitCall(exitCallHandle, error);
      }
      
      appdynamics.reportMetric('Payment.Failure.Count', 1);
      appdynamics.addSnapshotData('ErrorMessage', error.message);
      appdynamics.addSnapshotData('ErrorStack', error.stack);
      
      // Mark business transaction as error
      if (req.btHandle) {
        appdynamics.markBusinessTransactionAsError(req.btHandle, error.message);
      }
      
      console.error('Payment processing error:', error);
      
      res.status(500).json({
        success: false,
        error: 'Payment processing failed',
        message: error.message
      });
    } finally {
      // End business transaction
      if (req.btHandle) {
        appdynamics.endTransaction(req.btHandle);
      }
    }
  }
);

// Health check endpoint
app.get('/health', (req, res) => {
  res.json({ status: 'healthy', service: 'payment-processing' });
});

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