Ensure Idempotency for API Write Operations to Prevent Duplicates

const axios = require('axios');
const { v4: uuidv4 } = require('uuid'); // Install with: npm install uuid

const API_PAYMENT_URL = 'https://api.your-payment-gateway.com/charges'; // Example payment endpoint

/**
 * Creates a unique idempotency key for the request.
 * This key should be generated once per logical operation.
 */
function generateIdempotencyKey() {
  // A UUID is a common choice for an idempotency key.
  // For requests involving a specific user/session, you might prefix or suffix it
  // with a user ID or session ID for better server-side lookup, if applicable.
  return uuidv4();
}

/**
 * Makes an API call for a payment, ensuring idempotency.
 * @param {object} paymentDetails - Details for the payment.
 * @param {string} idempotencyKey - A unique key for this specific operation.
 */
async function processPayment(paymentDetails, idempotencyKey) {
  try {
    const response = await axios.post(
      API_PAYMENT_URL,
      paymentDetails,
      {
        headers: {
          'Content-Type': 'application/json',
          'Idempotency-Key': idempotencyKey, // Crucial header for idempotency
          'Authorization': 'Bearer YOUR_AUTH_TOKEN', // Replace with actual auth
        },
        // Optional: you might want a timeout for requests that take too long
        timeout: 10000, // 10 seconds
      }
    );
    console.log('Payment processed successfully:', response.data);
    return response.data;
  } catch (error) {
    if (error.response) {
      console.error('Error processing payment (status:', error.response.status, 'data:', error.response.data);
      // Servers might return specific status codes (e.g., 409 Conflict)
      // to indicate an idempotent request was received and already processed.
      if (error.response.status === 409) { // Example conflict status
        console.warn('Payment with this idempotency key was likely already processed.');
      }
    } else {
      console.error('Network or other error processing payment:', error.message);
    }
    throw new Error('Payment processing failed.');
  }
}

// Example usage:
(async () => {
  const paymentDetails = {
    amount: 5000, // in cents
    currency: 'usd',
    customer_id: 'cust_12345',
    payment_method_id: 'pm_card_visa',
    description: 'Purchase of premium subscription',
  };

  const currentIdempotencyKey = generateIdempotencyKey();
  console.log('Generated Idempotency Key:', currentIdempotencyKey);

  try {
    // First attempt to process payment
    await processPayment(paymentDetails, currentIdempotencyKey);
    console.log('First payment attempt completed.');

    // Simulate a network issue or retry:
    // If the first request timed out or failed *after* the server received it,
    // retrying with the *same* idempotency key ensures the payment isn't duplicated.
    console.log('
Simulating a retry with the same idempotency key...');
    await processPayment(paymentDetails, currentIdempotencyKey);
    console.log('Second payment attempt (retry) completed. Server should handle it idempotently.');

  } catch (error) {
    console.error('Overall process failed:', error.message);
  }
})();