FCM (Push)

// 1) Setup — server side
// npm install firebase-admin
import { initializeApp, applicationDefault } from 'firebase-admin/app';
import { getMessaging } from 'firebase-admin/messaging';

initializeApp({ credential: applicationDefault() });
const messaging = getMessaging();

// 2) Client gets FCM token (Web example)
import { initializeApp } from 'firebase/app';
import { getMessaging, getToken, onMessage } from 'firebase/messaging';

const app = initializeApp({ /* config */ });
const messaging = getMessaging(app);

// Request permission + token
async function registerForPush() {
    const permission = await Notification.requestPermission();
    if (permission !== 'granted') return null;

    const token = await getToken(messaging, {
        vapidKey: 'BNkR...',
        serviceWorkerRegistration: await navigator.serviceWorker.register('/firebase-messaging-sw.js'),
    });
    // Send token to your backend
    await fetch('/api/devices', { method: 'POST', body: JSON.stringify({ token }) });
    return token;
}

// firebase-messaging-sw.js (service worker for background messages)
importScripts('https://www.gstatic.com/firebasejs/10.7.0/firebase-app-compat.js');
importScripts('https://www.gstatic.com/firebasejs/10.7.0/firebase-messaging-compat.js');
firebase.initializeApp({ /* same config */ });
const sw_messaging = firebase.messaging();
sw_messaging.onBackgroundMessage((payload) => {
    self.registration.showNotification(payload.notification.title, {
        body: payload.notification.body,
        icon: '/icon-192.png',
        data: payload.data,
    });
});

// 3) Foreground messages — handled in main thread
onMessage(messaging, (payload) => {
    console.log('foreground push', payload);
    // Show in-app banner or react to the data
});

// 4) Send to a single token (server)
await messaging.send({
    token: 'fcm-token-here',
    notification: { title: 'Hello', body: 'World' },
    data: { route: '/dashboard', userId: '42' },     // strings only
    android: {
        notification: { channelId: 'default', priority: 'high', sound: 'default' },
    },
    apns: {
        payload: { aps: { sound: 'default', badge: 1, 'mutable-content': 1 } },
    },
    webpush: {
        notification: { icon: '/icon-192.png' },
        fcmOptions: { link: 'https://app.example.com/dashboard' },
    },
});

// 5) Batch send — up to 500 messages
const messages = tokens.map((token) => ({
    token,
    notification: { title: 'Sale!', body: '24h discount inside' },
}));
const response = await messaging.sendEach(messages);
console.log(`${response.successCount} sent, ${response.failureCount} failed`);

response.responses.forEach((r, i) => {
    if (!r.success && r.error?.code === 'messaging/registration-token-not-registered') {
        // Token invalid — remove from your DB
        deleteToken(tokens[i]);
    }
});

// 6) Topic broadcasts — millions of devices
await messaging.subscribeToTopic(['token1', 'token2'], 'news');
await messaging.send({
    topic: 'news',
    notification: { title: 'Breaking', body: 'Big news' },
});
await messaging.unsubscribeFromTopic(['token1'], 'news');

// Or send to a CONDITION (combine topics):
await messaging.send({
    condition: "'news' in topics && 'finance' in topics",
    notification: { title: 'Markets update' },
});

// 7) Per-platform overrides
await messaging.send({
    token: 'fcm-token',
    notification: { title: 'Generic', body: 'Default' },
    android: {
        priority: 'high',
        notification: {
            title: 'Android title',   // overrides generic
            color:  '#ff5722',
            sound:  'default',
            visibility: 'public',
            channelId: 'high_priority',
        },
    },
    apns: {
        headers: { 'apns-priority': '10' },
        payload: {
            aps: {
                alert: { title: 'iOS title', body: 'iOS body' },
                'thread-id': 'group-1',
                'mutable-content': 1,
                'content-available': 1,
            },
        },
    },
});

// 8) Data-only messages — silent push for background sync
await messaging.send({
    token: 'fcm-token',
    data: { type: 'sync', orderId: '42' },
    android: { priority: 'high' },
    apns: { payload: { aps: { 'content-available': 1 } } },
});

// • Android: app's FCM listener fires; can update local DB
// • iOS: app gets background time (limited by system)

// 9) Notification channels (Android 8+)
// Define in app at install/runtime:
await LocalNotifications.createChannel({
    id: 'high_priority',
    name: 'Important alerts',
    importance: 5,
    visibility: 1,
});

// 10) Token lifecycle
// • Tokens rotate; client onTokenRefresh / getToken on each login + 30 days
// • Save (userId, token, platform, lastSeen) to your DB
// • Delete tokens flagged as 'unregistered' on send errors
// • On logout: delete the token + revoke server-side

// 11) Scheduled / delayed sends
// FCM doesn't schedule natively. Schedule on your backend:
import { CronJob } from 'cron';
new CronJob('0 9 * * 1', () => sendNewsletter(), null, true);

// Or use Cloud Functions scheduled triggers.

// 12) Click handlers + deep links
// Include 'data.route' + 'data.target' + 'webpush.fcmOptions.link' so the app can navigate.

// 13) Cost + limits
// • FCM is FREE for typical use
// • Topic msgs: 1 message rate per second per topic
// • Multicast: 500 tokens per send call
// • Daily quotas vary; check Firebase console

// 14) iOS specific — APNs certificate
// Firebase Console → Project Settings → Cloud Messaging → upload .p8 APNs auth key
// Or .p12 certificate (legacy)
// Without this, iOS pushes fail silently.

// 15) Testing
// Firebase Console → Cloud Messaging → 'New campaign'
// Or curl HTTP v1:
curl -X POST 'https://fcm.googleapis.com/v1/projects/$PROJECT/messages:send' \\
    -H 'Authorization: Bearer $ACCESS_TOKEN' \\
    -H 'Content-Type: application/json' \\
    -d '{ "message": { "token": "...", "notification": { "title": "Hi" } } }'

// 16) Common bugs
// • iOS doesn't show notifications → APNs key missing in Firebase Console
// • Tokens save but pushes don't arrive → check Service Worker scope; HTTPS required
// • 'Requested entity was not found' → token expired; remove from DB
// • OPPO/Xiaomi background killing app → vendor power management; show user guidance
// • Data-only messages on iOS without 'content-available' → not delivered
// • Web Push only on HTTPS (or localhost) — fails silently elsewhere
// • Channel id mismatch → Android shows but in 'Other' channel; create explicit channel
// • Browser closed but Service Worker not registered → background push doesn't fire
// • Topic broadcasts limited to 1/sec — implement queueing for bursts
// • Foreground messages NOT shown as system notification — show manually via Notifications API

import { getMessaging, getToken, onMessage } from 'firebase/messaging';
const msg = getMessaging(app);
const token = await getToken(msg, { vapidKey: '…' });
onMessage(msg, payload => console.log('msg', payload));