/**
 * SERVICE WORKER FOR NAUE ROLL CALCULATOR
 * ========================================
 * Caching strategy:
 * 1. CACHE_FIRST for static assets (CSS, JS, images)
 * 2. NETWORK_FIRST for API/data (with fallback to cache)
 * 3. STALE_WHILE_REVALIDATE for article data
 */

const CACHE_NAME = 'rollcalc-v14-' + new Date().getTime();
const STATIC_CACHE = 'rollcalc-static-v14';
const DATA_CACHE = 'rollcalc-data-v14';

// Assets to cache on install
const STATIC_ASSETS = [
  '/',
  '/index.html',
  '/static/article-data.json',
  '/static/config.json'
];

// ===================================================================
// INSTALL EVENT - Cache static assets
// ===================================================================
self.addEventListener('install', event => {
  console.log('[ServiceWorker] Installing...');
  
  event.waitUntil(
    caches.open(STATIC_CACHE)
      .then(cache => {
        console.log('[ServiceWorker] Caching static assets');
        return cache.addAll(STATIC_ASSETS).catch(err => {
          console.warn('[ServiceWorker] Some assets failed to cache:', err);
          // Don't fail installation if some assets can't be cached
          return Promise.resolve();
        });
      })
      .then(() => self.skipWaiting())
  );
});

// ===================================================================
// ACTIVATE EVENT - Clean up old caches
// ===================================================================
self.addEventListener('activate', event => {
  console.log('[ServiceWorker] Activating...');
  
  event.waitUntil(
    caches.keys().then(cacheNames => {
      return Promise.all(
        cacheNames.map(cacheName => {
          if (cacheName !== STATIC_CACHE && 
              cacheName !== DATA_CACHE && 
              cacheName !== CACHE_NAME) {
            console.log('[ServiceWorker] Deleting old cache:', cacheName);
            return caches.delete(cacheName);
          }
        })
      );
    }).then(() => self.clients.claim())
  );
});

// ===================================================================
// FETCH EVENT - Intelligent caching strategy
// ===================================================================
self.addEventListener('fetch', event => {
  const { request } = event;
  const url = new URL(request.url);
  
  // Skip cross-origin requests
  if (url.origin !== location.origin) {
    return;
  }
  
  // ---------------------------------------------------------------
  // 1. JSON DATA (article-data.json, config.json)
  // STALE_WHILE_REVALIDATE: Use cache first, update in background
  // ---------------------------------------------------------------
  if (url.pathname.includes('.json')) {
    event.respondWith(
      caches.open(DATA_CACHE).then(cache => {
        return cache.match(request).then(response => {
          const fetchPromise = fetch(request).then(networkResponse => {
            // Update cache with fresh version
            if (networkResponse && networkResponse.status === 200) {
              cache.put(request, networkResponse.clone());
            }
            return networkResponse;
          }).catch(() => {
            // Network failed, return cached version
            return response || cacheNotFound('JSON data not found');
          });
          
          // Return cached response immediately, update in background
          return response || fetchPromise;
        });
      })
    );
    return;
  }
  
  // ---------------------------------------------------------------
  // 2. HTML PAGES
  // NETWORK_FIRST: Try network, fall back to cache
  // ---------------------------------------------------------------
  if (request.method === 'GET' && 
      (url.pathname === '/' || url.pathname.endsWith('.html'))) {
    event.respondWith(
      fetch(request)
        .then(response => {
          if (response && response.status === 200) {
            const cache_copy = response.clone();
            caches.open(STATIC_CACHE).then(cache => {
              cache.put(request, cache_copy);
            });
          }
          return response;
        })
        .catch(() => {
          return caches.match(request)
            .then(response => response || cacheNotFound('Page not found'));
        })
    );
    return;
  }
  
  // ---------------------------------------------------------------
  // 3. STATIC ASSETS (CSS, JS, images)
  // CACHE_FIRST: Use cache if available, fall back to network
  // ---------------------------------------------------------------
  if (request.method === 'GET') {
    event.respondWith(
      caches.open(STATIC_CACHE).then(cache => {
        return cache.match(request).then(response => {
          if (response) {
            return response;
          }
          
          return fetch(request).then(networkResponse => {
            // Only cache successful responses
            if (networkResponse && networkResponse.status === 200) {
              cache.put(request, networkResponse.clone());
            }
            return networkResponse;
          }).catch(() => {
            // Return offline placeholder
            if (request.destination === 'image') {
              return createPlaceholderImage();
            }
            return cacheNotFound('Asset not found');
          });
        });
      })
    );
    return;
  }
  
  // ---------------------------------------------------------------
  // 4. POST/PUT/DELETE (API calls)
  // NETWORK_ONLY: Do not cache, but handle errors gracefully
  // ---------------------------------------------------------------
  if (['POST', 'PUT', 'DELETE'].includes(request.method)) {
    event.respondWith(
      fetch(request)
        .catch(() => {
          return new Response(
            JSON.stringify({
              error: 'You are offline. API calls are not available.',
              status: 'offline'
            }),
            {
              status: 503,
              statusText: 'Service Unavailable',
              headers: new Headers({
                'Content-Type': 'application/json'
              })
            }
          );
        })
    );
    return;
  }
});

// ===================================================================
// HELPER FUNCTIONS
// ===================================================================

function cacheNotFound(message) {
  return new Response(
    `<html><body style="font-family: sans-serif; padding: 20px; color: #666;">
      <h2>Offline</h2>
      <p>${message}</p>
      <p style="font-size: 12px; color: #999;">Roll Calculator is offline or the resource is not cached.</p>
    </body></html>`,
    {
      status: 404,
      statusText: 'Not Found',
      headers: new Headers({
        'Content-Type': 'text/html'
      })
    }
  );
}

function createPlaceholderImage() {
  const svg = `<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
    <rect fill="#f0f0f0" width="100" height="100"/>
    <text x="50" y="50" text-anchor="middle" dy=".3em" fill="#999" font-size="12">
      Image offline
    </text>
  </svg>`;
  
  return new Response(svg, {
    headers: {
      'Content-Type': 'image/svg+xml',
      'Cache-Control': 'public, max-age=86400'
    }
  });
}

// ===================================================================
// LOG SERVICE WORKER STATUS
// ===================================================================
console.log('[ServiceWorker] Naue Roll Calculator Service Worker loaded');