/**
 * The Nexus Service Worker
 * Provides offline capability and home screen install support
 * Strategy: Cache-first for local assets, stale-while-revalidate for CDN
 */

const CACHE_VERSION = 'nexus-v1';
const STATIC_CACHE = `${CACHE_VERSION}-static`;
const CDN_CACHE = `${CACHE_VERSION}-cdn`;
const OFFLINE_PAGE = '/offline.html';

// Core local assets that must be cached
const CORE_ASSETS = [
  '/',
  '/index.html',
  '/style.css',
  '/app.js',
  '/manifest.json',
  '/icons/nexus-icon.svg',
  '/icons/nexus-maskable.svg',
  OFFLINE_PAGE
];

// CDN resources that benefit from caching but can be stale
const CDN_PATTERNS = [
  /^https:\/\/unpkg\.com/,
  /^https:\/\/cdn\.jsdelivr\.net/,
  /^https:\/\/fonts\.googleapis\.com/,
  /^https:\/\/fonts\.gstatic\.com/,
  /^https:\/\/cdn\.threejs\.org/
];

/**
 * Check if a URL matches any CDN pattern
 */
function isCdnResource(url) {
  return CDN_PATTERNS.some(pattern => pattern.test(url));
}

/**
 * Install event - cache core assets
 */
self.addEventListener('install', (event) => {
  console.log('[Nexus SW] Installing...');
  
  event.waitUntil(
    caches.open(STATIC_CACHE)
      .then(cache => {
        console.log('[Nexus SW] Caching core assets');
        return cache.addAll(CORE_ASSETS);
      })
      .then(() => {
        console.log('[Nexus SW] Core assets cached');
        return self.skipWaiting();
      })
      .catch(err => {
        console.error('[Nexus SW] Cache failed:', err);
      })
  );
});

/**
 * Activate event - clean up old caches
 */
self.addEventListener('activate', (event) => {
  console.log('[Nexus SW] Activating...');
  
  event.waitUntil(
    caches.keys()
      .then(cacheNames => {
        return Promise.all(
          cacheNames
            .filter(name => name.startsWith('nexus-') && name !== STATIC_CACHE && name !== CDN_CACHE)
            .map(name => {
              console.log('[Nexus SW] Deleting old cache:', name);
              return caches.delete(name);
            })
        );
      })
      .then(() => {
        console.log('[Nexus SW] Activated');
        return self.clients.claim();
      })
  );
});

/**
 * Fetch event - handle requests with appropriate strategy
 */
self.addEventListener('fetch', (event) => {
  const { request } = event;
  const url = new URL(request.url);
  
  // Skip non-GET requests
  if (request.method !== 'GET') {
    return;
  }
  
  // Skip cross-origin requests that aren't CDN resources
  if (url.origin !== self.location.origin && !isCdnResource(url.href)) {
    return;
  }
  
  // Handle CDN resources with stale-while-revalidate
  if (isCdnResource(url.href)) {
    event.respondWith(handleCdnRequest(request));
    return;
  }
  
  // Handle local assets with cache-first strategy
  event.respondWith(handleLocalRequest(request));
});

/**
 * Cache-first strategy for local assets
 * Fastest response, updates cache in background
 */
async function handleLocalRequest(request) {
  try {
    const cache = await caches.open(STATIC_CACHE);
    const cached = await cache.match(request);
    
    // Return cached version immediately if available
    if (cached) {
      // Revalidate in background for next time
      fetch(request)
        .then(response => {
          if (response.ok) {
            cache.put(request, response.clone());
          }
        })
        .catch(() => {
          // Network failed, cached version is already being used
        });
      
      return cached;
    }
    
    // Not in cache - fetch from network
    const response = await fetch(request);
    
    if (response.ok) {
      cache.put(request, response.clone());
    }
    
    return response;
  } catch (error) {
    console.error('[Nexus SW] Local request failed:', error);
    
    // Return offline page for navigation requests
    if (request.mode === 'navigate') {
      const cache = await caches.open(STATIC_CACHE);
      const offlinePage = await cache.match(OFFLINE_PAGE);
      if (offlinePage) {
        return offlinePage;
      }
    }
    
    throw error;
  }
}

/**
 * Stale-while-revalidate strategy for CDN resources
 * Serves stale content while updating in background
 */
async function handleCdnRequest(request) {
  const cache = await caches.open(CDN_CACHE);
  const cached = await cache.match(request);
  
  // Always try to fetch fresh version
  const fetchPromise = fetch(request)
    .then(response => {
      if (response.ok) {
        cache.put(request, response.clone());
      }
      return response;
    })
    .catch(error => {
      console.error('[Nexus SW] CDN fetch failed:', error);
      throw error;
    });
  
  // Return cached version immediately if available, otherwise wait for network
  if (cached) {
    // Return stale but revalidate for next time
    fetchPromise.catch(() => {}); // Swallow errors, we have cached version
    return cached;
  }
  
  // No cache - must wait for network
  return fetchPromise;
}

/**
 * Message handler for runtime cache updates
 */
self.addEventListener('message', (event) => {
  if (event.data && event.data.type === 'SKIP_WAITING') {
    self.skipWaiting();
  }
  
  if (event.data && event.data.type === 'GET_VERSION') {
    event.ports[0].postMessage({ version: CACHE_VERSION });
  }
});

/**
 * Background sync for deferred actions (future enhancement)
 */
self.addEventListener('sync', (event) => {
  if (event.tag === 'nexus-sync') {
    console.log('[Nexus SW] Background sync triggered');
    // Future: sync chat messages, state updates, etc.
  }
});

console.log('[Nexus SW] Service worker loaded');