// This global constant __APP_CACHE_VERSION__ will be replaced by Vite
// during the build process due to the `define` config in vite.config.js.
const CACHE_VERSION = typeof __APP_CACHE_VERSION__ !== 'undefined' 
    ? __APP_CACHE_VERSION__ 
    : 'nexus-timer-cache-fallback-dev-vManual'; // Fallback for dev or if define fails

const APP_SHELL_URLS = [
  // Note: '/' (index.html) is handled by NetworkFirst strategy, no need to precache explicitly here.
  '/manifest.json', // Will be served from public, copied to dist root
  '/favicon.ico',   // Will be served from public, copied to dist root
  // Icons from public/icons, will be copied to dist/icons
  '/icons/icon-192x192.png',
  '/icons/icon-512x512.png',
  '/icons/maskable-icon-192x192.png',
  '/icons/maskable-icon-512x512.png',
  '/icons/shortcut-setup-96x96.png',
  '/icons/shortcut-info-96x96.png',
  // Any other critical static assets from the public folder that should be part of the app shell
];

self.addEventListener('install', event => {
  console.log(`[SW ${CACHE_VERSION}] Install`);
  event.waitUntil(
    caches.open(CACHE_VERSION)
      .then(cache => {
        console.log(`[SW ${CACHE_VERSION}] Caching app shell essentials`);
        return cache.addAll(APP_SHELL_URLS);
      })
      .then(() => {
        console.log(`[SW ${CACHE_VERSION}] Skip waiting on install.`);
        return self.skipWaiting();
      })
  );
});

self.addEventListener('activate', event => {
  console.log(`[SW ${CACHE_VERSION}] Activate`);
  event.waitUntil(
    caches.keys().then(cacheNames => {
      return Promise.all(
        cacheNames.map(cacheName => {
          if (cacheName !== CACHE_VERSION) {
            console.log(`[SW ${CACHE_VERSION}] Deleting old cache: ${cacheName}`);
            return caches.delete(cacheName);
          }
        })
      );
    }).then(() => {
      console.log(`[SW ${CACHE_VERSION}] Clients claimed.`);
      return self.clients.claim();
    })
  );
});

self.addEventListener('fetch', event => {
  const { request } = event;
  const url = new URL(request.url);

  if (request.method !== 'GET' || !url.protocol.startsWith('http')) {
    // console.log(`[SW ${CACHE_VERSION}] Ignoring non-GET or non-http(s) request: ${request.url}`);
    return;
  }

  // Strategy 1: Network First for HTML (navigations or direct / request)
  if (request.mode === 'navigate' || (request.destination === 'document' || url.pathname === '/')) {
    // console.log(`[SW ${CACHE_VERSION}] NetworkFirst for: ${request.url}`);
    event.respondWith(
      fetch(request)
        .then(response => {
          if (response.ok) {
             const responseClone = response.clone();
             caches.open(CACHE_VERSION).then(cache => cache.put(request, responseClone));
          }
          return response;
        })
        .catch(async () => {
          // console.warn(`[SW ${CACHE_VERSION}] Network fetch failed for ${request.url}, trying cache.`);
          const cachedResponse = await caches.match(request);
          if (cachedResponse) return cachedResponse;
          // Fallback to root /index.html from cache if specific page not found offline
          const rootCache = await caches.match('/'); 
          if (rootCache) return rootCache;
          // console.error(`[SW ${CACHE_VERSION}] Network and cache miss for navigation: ${request.url}`);
          return new Response('Network error: You are offline and this page is not cached.', { 
            status: 404, 
            statusText: 'Not Found',
            headers: { 'Content-Type': 'text/html' } // Important for SPA offline fallback
          });
        })
    );
    return;
  }

  // Strategy 2: Stale-While-Revalidate for assets (CSS, JS, images, fonts)
  if (request.destination === 'style' ||
      request.destination === 'script' ||
      request.destination === 'worker' ||
      request.destination === 'image' ||
      request.destination === 'font') {
    // console.log(`[SW ${CACHE_VERSION}] StaleWhileRevalidate for: ${request.url}`);
    event.respondWith(
      caches.open(CACHE_VERSION).then(cache => {
        return cache.match(request).then(cachedResponse => {
          const fetchPromise = fetch(request).then(networkResponse => {
            if (networkResponse.ok) {
              const responseToCache = networkResponse.clone();
              cache.put(request, responseToCache);
            } else {
              // console.warn(`[SW ${CACHE_VERSION}] StaleWhileRevalidate: Network fetch for ${request.url} failed with status ${networkResponse.status}`);
            }
            return networkResponse;
          }).catch(err => {
            // console.warn(`[SW ${CACHE_VERSION}] StaleWhileRevalidate: Network fetch error for ${request.url}:`, err);
            // If fetch fails, and we already served from cache, that's okay.
            // If cache also missed (i.e., cachedResponse was null), then this error will propagate.
            throw err; 
          });
          return cachedResponse || fetchPromise;
        }).catch(err => {
            // This catch block handles errors from cache.match() or if fetchPromise was returned and rejected
            // console.error(`[SW ${CACHE_VERSION}] StaleWhileRevalidate: Error for ${request.url}. Trying network fallback.`, err);
            return fetch(request); // Final fallback to network if cache interactions fail
        });
      })
    );
    return;
  }

  // Strategy 3: Cache First for other types of requests (e.g., manifest.json if not in APP_SHELL_URLS)
  // console.log(`[SW ${CACHE_VERSION}] CacheFirst for: ${request.url}`);
  event.respondWith(
    caches.match(request)
      .then(response => {
        return response || fetch(request).then(networkResponse => {
            if(networkResponse.ok) {
                const responseClone = networkResponse.clone();
                caches.open(CACHE_VERSION).then(cache => cache.put(request, responseClone));
            }
            return networkResponse;
        });
      })
  );
});

self.addEventListener('message', event => {
  if (event.data && event.data.action === 'skipWaiting') {
    console.log(`[SW ${CACHE_VERSION}] Received skipWaiting message, activating new SW.`);
    self.skipWaiting();
  }
});