// service-worker.js
// Cache-Strategie: Cache First (offline works, then network)

const CACHE_NAME = 'roll-calculator-v1';
const ASSETS_TO_CACHE = [
  './',
  './roll_calculator_v8.html',
  './article-data.json',
  './service-worker.js'
];

// Install Event: Cache alle kritischen Assets
self.addEventListener('install', event => {
  console.log('[ServiceWorker] Installing...');
  event.waitUntil(
    caches.open(CACHE_NAME).then(cache => {
      console.log('[ServiceWorker] Caching assets:', ASSETS_TO_CACHE);
      return cache.addAll(ASSETS_TO_CACHE);
    }).catch(err => {
      console.error('[ServiceWorker] Cache failed:', err);
    })
  );
  // Aktiviere sofort (optional)
  self.skipWaiting();
});

// Activate Event: Cleanup alte 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) {
            console.log('[ServiceWorker] Deleting old cache:', cacheName);
            return caches.delete(cacheName);
          }
        })
      );
    })
  );
  self.clients.claim();
});

// Fetch Event: Cache First Strategy
// 1. Prüfe Cache
// 2. Wenn nicht da, frag Network
// 3. Cache die Response für nächstes Mal
self.addEventListener('fetch', event => {
  const url = event.request.url;
  
  // Skip nicht-GET Requests
  if (event.request.method !== 'GET') {
    return;
  }

  event.respondWith(
    caches.match(event.request)
      .then(response => {
        // Cache HIT
        if (response) {
          console.log('[ServiceWorker] Cache HIT:', url);
          return response;
        }

        // Cache MISS - versuche Network
        console.log('[ServiceWorker] Cache MISS, fetching:', url);
        return fetch(event.request)
          .then(response => {
            // Nur 200er Responses cachen
            if (!response || response.status !== 200 || response.type === 'error') {
              return response;
            }

            // Clone die Response (weil sie nur einmal consumable ist)
            const responseClone = response.clone();
            caches.open(CACHE_NAME).then(cache => {
              console.log('[ServiceWorker] Caching response:', url);
              cache.put(event.request, responseClone);
            });

            return response;
          })
          .catch(err => {
            // Network fail - versuche aus Cache
            console.log('[ServiceWorker] Network failed, trying cache fallback:', url);
            return caches.match(event.request).then(response => {
              if (response) return response;
              
              // Fallback für offline
              console.warn('[ServiceWorker] No cache fallback for:', url);
              return new Response('Offline - resource not available', {
                status: 503,
                statusText: 'Service Unavailable'
              });
            });
          });
      })
  );
});

console.log('[ServiceWorker] Script loaded');