static/service-worker.js

/**
 * BattleWords Service Worker
 * Enables PWA functionality: offline caching, install prompt, etc.
 *
 * Security Note: This file contains no secrets or sensitive data.
 * It only caches public assets for offline access.
 */

const CACHE_NAME = 'battlewords-v0.2.29';
const RUNTIME_CACHE = 'battlewords-runtime';

// Assets to cache on install (minimal for faster install)
const PRECACHE_URLS = [
  '/',
  '/app/static/manifest.json',
  '/app/static/icon-192.png',
  '/app/static/icon-512.png'
];

// Install event - cache essential files
self.addEventListener('install', event => {
  console.log('[ServiceWorker] Installing...');
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then(cache => {
        console.log('[ServiceWorker] Precaching app shell');
        return cache.addAll(PRECACHE_URLS);
      })
      .then(() => self.skipWaiting()) // Activate immediately
  );
});

// Activate event - clean up old caches
self.addEventListener('activate', event => {
  console.log('[ServiceWorker] Activating...');
  event.waitUntil(
    caches.keys().then(cacheNames => {
      return Promise.all(
        cacheNames.map(cacheName => {
          if (cacheName !== CACHE_NAME && cacheName !== RUNTIME_CACHE) {
            console.log('[ServiceWorker] Deleting old cache:', cacheName);
            return caches.delete(cacheName);
          }
        })
      );
    }).then(() => self.clients.claim()) // Take control immediately
  );
});

// Fetch event - network first, fall back to cache
self.addEventListener('fetch', event => {
  // Skip non-GET requests
  if (event.request.method !== 'GET') {
    return;
  }

  // Skip chrome-extension and other non-http requests
  if (!event.request.url.startsWith('http')) {
    return;
  }

  event.respondWith(
    caches.open(RUNTIME_CACHE).then(cache => {
      return fetch(event.request)
        .then(response => {
          // Cache successful responses for future offline access
          if (response.status === 200) {
            cache.put(event.request, response.clone());
          }
          return response;
        })
        .catch(() => {
          // Network failed, try cache
          return caches.match(event.request).then(cachedResponse => {
            if (cachedResponse) {
              console.log('[ServiceWorker] Serving from cache:', event.request.url);
              return cachedResponse;
            }

            // No cache available, return offline page or error
            return new Response('Offline - Please check your connection', {
              status: 503,
              statusText: 'Service Unavailable',
              headers: new Headers({
                'Content-Type': 'text/plain'
              })
            });
          });
        });
    })
  );
});

// Message event - handle commands from the app
self.addEventListener('message', event => {
  if (event.data.action === 'skipWaiting') {
    self.skipWaiting();
  }
});