sw.js

// Service Worker for Vocab Cards PWA
const CACHE_NAME = 'vocab-cards-v4';
const ASSETS = [
  '/',
  '/index.html',
  '/styles.css',
  '/app.js',
  '/manifest.json',
  '/icons/icon-192.svg',
  '/icons/icon-512.svg'
];

// Install - cache assets
self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then((cache) => cache.addAll(ASSETS))
      .then(() => self.skipWaiting())
  );
});

// Activate - clean old caches
self.addEventListener('activate', (event) => {
  event.waitUntil(
    caches.keys()
      .then((keys) => {
        return Promise.all(
          keys.filter((key) => key !== CACHE_NAME)
              .map((key) => caches.delete(key))
        );
      })
      .then(() => self.clients.claim())
  );
});

// Fetch - serve from cache, fallback to network
self.addEventListener('fetch', (event) => {
  event.respondWith(
    caches.match(event.request)
      .then((response) => {
        if (response) {
          return response;
        }
        return fetch(event.request)
          .then((fetchResponse) => {
            // Don't cache non-GET or external requests
            if (event.request.method !== 'GET' ||
                !event.request.url.startsWith(self.location.origin)) {
              return fetchResponse;
            }
            // Cache the new resource
            const responseClone = fetchResponse.clone();
            caches.open(CACHE_NAME)
              .then((cache) => cache.put(event.request, responseClone));
            return fetchResponse;
          });
      })
      .catch(() => {
        // Offline fallback for navigation requests
        if (event.request.mode === 'navigate') {
          return caches.match('/index.html');
        }
      })
  );
});