const CACHE_NAME = 'grabengasse-v1.0';
const STATIC_ASSETS = [
  '/',
  '/index.html',
  '/manifest.webmanifest',
  '/icon-192.png',
  '/icon-512.png',
  '/apple-touch-icon.png',
  '/favicon.png'
];

// Install: Cache essential shell assets
self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then((cache) => {
      return cache.addAll(STATIC_ASSETS);
    }).then(() => self.skipWaiting())
  );
});

// Activate: Clean up previous cache versions
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: Network-first for API data, Stale-while-revalidate for static assets
self.addEventListener('fetch', (event) => {
  const { request } = event;
  const url = new URL(request.url);

  // API calls: Network first with no fallback caching of stale live metrics
  if (url.pathname.startsWith('/api/')) {
    event.respondWith(
      fetch(request).catch(() => {
        return new Response(JSON.stringify({ error: 'Offline / Telemetry Link Offline' }), {
          status: 503,
          headers: { 'Content-Type': 'application/json' }
        });
      })
    );
    return;
  }

  // Navigation requests: Network first, fallback to cached /index.html (SPA routing)
  if (request.mode === 'navigate') {
    event.respondWith(
      fetch(request).catch(() => {
        return caches.match('/index.html');
      })
    );
    return;
  }

  // Static assets (CSS, JS, Fonts, Images): Cache-first with network fallback & cache update
  event.respondWith(
    caches.match(request).then((cachedResponse) => {
      if (cachedResponse) {
        // Fetch in background to update cache
        fetch(request).then((networkResponse) => {
          if (networkResponse && networkResponse.status === 200) {
            caches.open(CACHE_NAME).then((cache) => cache.put(request, networkResponse));
          }
        }).catch(() => {});
        return cachedResponse;
      }

      return fetch(request).then((networkResponse) => {
        if (!networkResponse || networkResponse.status !== 200 || networkResponse.type !== 'basic') {
          return networkResponse;
        }
        const responseToCache = networkResponse.clone();
        caches.open(CACHE_NAME).then((cache) => {
          cache.put(request, responseToCache);
        });
        return networkResponse;
      });
    })
  );
});