/**
 * Service Worker
 * 
 * Handles caching of:
 * - App shell (HTML, CSS, JS)
 * - Map tiles (runtime caching)
 * - API responses (network-first)
 * 
 * Note: Database operations are handled by the SharedWorker (shared-db-worker.js),
 *       NOT by this service worker. They serve different purposes:
 *       - Service Worker: Caching, offline asset serving, push notifications
 *       - SharedWorker: Shared database connection across tabs
 */

const CACHE_VERSION = 'v1';
const SHELL_CACHE = `shell-${CACHE_VERSION}`;
const TILES_CACHE = `tiles-${CACHE_VERSION}`;
const MODULES_CACHE = `modules-${CACHE_VERSION}`;
const API_CACHE = `api-${CACHE_VERSION}`;

// Maximum number of tiles to cache
const MAX_TILES = 500;

// App shell assets - precached on install
// Vite will generate hashed filenames, so we cache the entry points
// and let the browser handle the hashed assets
const SHELL_ASSETS = [
  '/',
  '/index.html',
  '/offline.html',
  '/manifest.json'
];

// ============================================================================
// INSTALL EVENT
// ============================================================================

self.addEventListener('install', (event) => {
  console.log('[SW] Installing...');
  
  event.waitUntil(
    caches.open(SHELL_CACHE)
      .then((cache) => {
        console.log('[SW] Precaching app shell');
        return cache.addAll(SHELL_ASSETS);
      })
      .then(() => self.skipWaiting())
  );
});

// ============================================================================
// ACTIVATE EVENT
// ============================================================================

self.addEventListener('activate', (event) => {
  console.log('[SW] Activating...');
  
  event.waitUntil(
    caches.keys()
      .then((cacheNames) => {
        return Promise.all(
          cacheNames
            .filter((name) => {
              // Delete old version caches
              return (name.startsWith('shell-') && name !== SHELL_CACHE) ||
                     (name.startsWith('tiles-') && name !== TILES_CACHE) ||
                     (name.startsWith('modules-') && name !== MODULES_CACHE) ||
                     (name.startsWith('api-') && name !== API_CACHE);
            })
            .map((name) => {
              console.log('[SW] Deleting old cache:', name);
              return caches.delete(name);
            })
        );
      })
      .then(() => self.clients.claim())
  );
});

// ============================================================================
// FETCH EVENT
// ============================================================================

self.addEventListener('fetch', (event) => {
  const request = event.request;
  const url = new URL(request.url);
  
  // Only handle GET requests
  if (request.method !== 'GET') return;
  
  // Skip chrome-extension and other non-http(s) requests
  if (!url.protocol.startsWith('http')) return;
  
  // Route to appropriate caching strategy
  if (isMapTile(url)) {
    event.respondWith(cacheThenNetwork(request, TILES_CACHE, MAX_TILES));
  } else if (isApiRequest(url)) {
    event.respondWith(networkFirst(request, API_CACHE));
  } else if (isModuleAsset(url)) {
    event.respondWith(staleWhileRevalidate(request, MODULES_CACHE));
  } else if (isAppAsset(url)) {
    event.respondWith(cacheFirst(request, SHELL_CACHE));
  }
  // Let other requests pass through to network
});

// ============================================================================
// URL CLASSIFICATION
// ============================================================================

function isMapTile(url) {
  // Common tile server patterns for all our base maps
  return url.hostname.includes('tile.openstreetmap.org') ||
         url.hostname.includes('opentopomap.org') ||
         url.hostname.includes('arcgisonline.com') ||
         url.hostname.includes('basemaps.cartocdn.com') ||
         url.hostname.includes('tiles.') ||
         url.pathname.match(/\/\d+\/\d+\/\d+\.(png|jpg|pbf)$/) ||
         url.pathname.match(/\/tile\/\d+\/\d+\/\d+/);
}

function isApiRequest(url) {
  return url.pathname.startsWith('/api/') ||
         url.pathname.endsWith('.php');
}

function isModuleAsset(url) {
  return url.pathname.startsWith('/modules/');
}

function isAppAsset(url) {
  // Same origin, common asset extensions
  return url.origin === self.location.origin &&
         (url.pathname.endsWith('.html') ||
          url.pathname.endsWith('.css') ||
          url.pathname.endsWith('.js') ||
          url.pathname.endsWith('.wasm') ||
          url.pathname.endsWith('.json') ||
          url.pathname.match(/\.(png|jpg|jpeg|gif|svg|ico|webp)$/));
}

// ============================================================================
// CACHING STRATEGIES
// ============================================================================

/**
 * Cache First - Use cache, fallback to network
 * Best for: App shell, static assets
 */
async function cacheFirst(request, cacheName) {
  const cached = await caches.match(request);
  if (cached) return cached;
  
  try {
    const response = await fetch(request);
    if (response.ok) {
      const cache = await caches.open(cacheName);
      cache.put(request, response.clone());
    }
    return response;
  } catch (error) {
    // Return offline page for navigation requests
    if (request.mode === 'navigate') {
      return caches.match('/offline.html');
    }
    throw error;
  }
}

/**
 * Network First - Try network, fallback to cache
 * Best for: API requests, dynamic content
 */
async function networkFirst(request, cacheName) {
  try {
    const response = await fetch(request);
    if (response.ok) {
      const cache = await caches.open(cacheName);
      cache.put(request, response.clone());
    }
    return response;
  } catch (error) {
    const cached = await caches.match(request);
    if (cached) return cached;
    throw error;
  }
}

/**
 * Stale While Revalidate - Return cache immediately, update in background
 * Best for: Module assets, frequently updated content
 */
async function staleWhileRevalidate(request, cacheName) {
  const cache = await caches.open(cacheName);
  const cached = await cache.match(request);
  
  const fetchPromise = fetch(request).then((response) => {
    if (response.ok) {
      cache.put(request, response.clone());
    }
    return response;
  }).catch(() => cached);
  
  return cached || fetchPromise;
}

/**
 * Cache Then Network with limit - Cache tiles with size limit
 * Best for: Map tiles
 */
async function cacheThenNetwork(request, cacheName, maxItems) {
  const cache = await caches.open(cacheName);
  const cached = await cache.match(request);
  
  if (cached) return cached;
  
  try {
    const response = await fetch(request);
    
    if (response.ok) {
      // Check cache size and trim if needed
      const keys = await cache.keys();
      if (keys.length >= maxItems) {
        // Remove oldest entries (first 10%)
        const toDelete = keys.slice(0, Math.ceil(maxItems * 0.1));
        await Promise.all(toDelete.map(key => cache.delete(key)));
      }
      
      cache.put(request, response.clone());
    }
    
    return response;
  } catch (error) {
    // For tiles, just fail silently - map will show blank tile
    return new Response('', { status: 408, statusText: 'Offline' });
  }
}

// ============================================================================
// MESSAGE HANDLING
// ============================================================================

self.addEventListener('message', (event) => {
  const { type, payload } = event.data || {};
  
  switch (type) {
    case 'SKIP_WAITING':
      self.skipWaiting();
      break;
      
    case 'CACHE_MODULES':
      cacheModules(payload.modules);
      break;
      
    case 'CLEAR_USER_CACHE':
      clearUserCaches();
      break;
      
    case 'GET_CACHE_STATUS':
      getCacheStatus().then(status => {
        event.source.postMessage({ type: 'CACHE_STATUS', status });
      });
      break;
  }
});

/**
 * Cache specific modules on demand
 */
async function cacheModules(moduleNames) {
  const cache = await caches.open(MODULES_CACHE);
  
  for (const moduleName of moduleNames) {
    try {
      const moduleAssets = [
        `/modules/${moduleName}/index.js`,
        `/modules/${moduleName}/index.css`,
        `/modules/${moduleName}/index.html`
      ];
      
      await cache.addAll(moduleAssets.filter(async (url) => {
        // Only cache assets that exist
        try {
          const response = await fetch(url, { method: 'HEAD' });
          return response.ok;
        } catch {
          return false;
        }
      }));
      
      console.log('[SW] Cached module:', moduleName);
    } catch (error) {
      console.warn('[SW] Failed to cache module:', moduleName, error);
    }
  }
}

/**
 * Clear user-specific caches (call on logout)
 */
async function clearUserCaches() {
  await caches.delete(API_CACHE);
  await caches.delete(MODULES_CACHE);
  console.log('[SW] Cleared user caches');
}

/**
 * Get cache status information
 */
async function getCacheStatus() {
  const cacheNames = await caches.keys();
  const status = {};
  
  for (const name of cacheNames) {
    const cache = await caches.open(name);
    const keys = await cache.keys();
    status[name] = keys.length;
  }
  
  return status;
}