Generate Idempotency Keys for Safe API Retries

function generateUUID() {
  // Standard compliant UUID v4 generator
  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    const r = Math.random() * 16 | 0,
          v = c === 'x' ? r : (r & 0x3 | 0x8);
    return v.toString(16);
  });
}

async function makeIdempotentRequest(url, options = {}, idempotencyKey = null) {
  const finalIdempotencyKey = idempotencyKey || generateUUID();

  const headers = {
    'Content-Type': 'application/json',
    'Idempotency-Key': finalIdempotencyKey, // Custom header for idempotency
    ...options.headers,
  };

  try {
    const response = await fetch(url, { ...options, headers });
    if (!response.ok) {
      throw new Error(`API error: ${response.status} ${response.statusText}`);
    }
    return await response.json();
  } catch (error) {
    console.error('Idempotent request failed:', error);
    throw error;
  }
}

// Example Usage:
// When submitting an order, generate an idempotency key once and reuse it if retrying.
// const orderData = { amount: 100, currency: 'USD', items: [...] };
// const myOrderIdempotencyKey = generateUUID(); // Generate once per logical transaction

// // First attempt
// makeIdempotentRequest('/api/orders', {
//   method: 'POST',
//   body: JSON.stringify(orderData)
// }, myOrderIdempotencyKey)
// .then(data => console.log('Order placed successfully (first attempt):', data))
// .catch(error => {
//   console.error('First attempt failed, retrying...', error);
//   // If network error, client can safely retry with the SAME key
//   makeIdempotentRequest('/api/orders', {
//     method: 'POST',
//     body: JSON.stringify(orderData)
//   }, myOrderIdempotencyKey)
//   .then(retryData => console.log('Order placed successfully (retry attempt):', retryData))
//   .catch(retryError => console.error('Retry attempt also failed:', retryError));
// });

// Or for a non-retry scenario, it can generate automatically:
// makeIdempotentRequest('/api/notifications', {
//   method: 'POST',
//   body: JSON.stringify({ message: 'User signed up!' })
// })
// .then(data => console.log('Notification sent:', data))
// .catch(error => console.error('Notification failed:', error));