How to fix messaging/device-message-rate-exceeded: Single device receiving too many messages in Firebase

// Example logging for FCM sends
console.log('Sending to device:', deviceToken, 'at:', new Date().toISOString());

// Example: Batch messages and send every 30 seconds
const messageQueue = new Map();

function queueMessage(deviceToken, message) {
  if (!messageQueue.has(deviceToken)) {
    messageQueue.set(deviceToken, []);
  }
  messageQueue.get(deviceToken).push(message);
}

// Send batched messages periodically
setInterval(async () => {
  for (const [deviceToken, messages] of messageQueue.entries()) {
    if (messages.length > 0) {
      // Send only the most recent message or combine them
      const latestMessage = messages[messages.length - 1];
      await admin.messaging().send(latestMessage);
      messageQueue.set(deviceToken, []);
    }
  }
}, 30000); // Every 30 seconds

const message = {
  token: deviceToken,
  data: {
    messageCount: '3'
  },
  android: {
    collapseKey: 'new_messages' // Same collapse key for all message count updates
  },
  apns: {
    headers: {
      'apns-collapse-id': 'new_messages'
    }
  }
};

async function sendWithRetry(message, maxRetries = 3) {
  let retryCount = 0;
  let delay = 1000; // Start with 1 second

  while (retryCount < maxRetries) {
    try {
      await admin.messaging().send(message);
      return; // Success
    } catch (error) {
      if (error.code === 'messaging/device-message-rate-exceeded') {
        retryCount++;
        console.log(`Rate limited, waiting ${delay}ms before retry ${retryCount}`);
        await new Promise(resolve => setTimeout(resolve, delay));
        delay *= 2; // Exponential backoff: 1s, 2s, 4s, etc.
      } else {
        throw error; // Other errors should not be retried
      }
    }
  }
  throw new Error('Max retries exceeded');
}

// Subscribe devices to topics
await admin.messaging().subscribeToTopic([deviceToken1, deviceToken2], 'news_updates');

// Send to topic (counts as one message for rate limiting purposes)
const message = {
  topic: 'news_updates',
  notification: {
    title: 'News Update',
    body: 'Check out our latest news!'
  }
};
await admin.messaging().send(message);

// Track rate limit errors
const stats = {
  rateLimitErrors: 0,
  successfulSends: 0
};

try {
  await admin.messaging().send(message);
  stats.successfulSends++;
} catch (error) {
  if (error.code === 'messaging/device-message-rate-exceeded') {
    stats.rateLimitErrors++;
    console.warn('Rate limit hit for device:', message.token);
  }
  throw error;
}

// Log stats periodically
console.log('FCM Stats:', stats);