// Service Worker for Notes English PWA (Stage 2)
// Strategy: Cache-first for static assets, Network-first for API calls.

const CACHE_NAME = 'notes-v5.5';
const OFFLINE_URL = '/';

const PRECACHE_URLS = [
  '/',
  '/static/css/style.css',
  '/static/js/app.js',
  '/static/js/modules/api.js',
  '/static/js/modules/ui.js',
  '/static/js/modules/dictionary.js',
  '/static/js/modules/srs.js',
  '/static/js/modules/reader.js',
  '/static/js/modules/cefr.js',
  '/static/js/modules/grammar.js',
  '/manifest.json',
];

// -----------------------------------------------------------------------
// Install: pre-cache core assets
// -----------------------------------------------------------------------
self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then((cache) => {
      return cache.addAll(PRECACHE_URLS);
    }).then(() => self.skipWaiting())
  );
});

// -----------------------------------------------------------------------
// Activate: delete old caches
// -----------------------------------------------------------------------
self.addEventListener('activate', (event) => {
  event.waitUntil(
    caches.keys().then((keys) => {
      return Promise.all(
        keys
          .filter((key) => key !== CACHE_NAME)
          .map((key) => caches.delete(key))
      );
    }).then(() => self.clients.claim())
  );
});

// -----------------------------------------------------------------------
// Fetch: strategy based on request type
// -----------------------------------------------------------------------
self.addEventListener('fetch', (event) => {
  const { request } = event;
  const url = new URL(request.url);

  // Skip cross-origin requests
  if (url.origin !== location.origin) return;

  // API calls → Network-first (never serve API from cache)
  if (url.pathname.startsWith('/api/')) {
    event.respondWith(
      fetch(request).catch(() => {
        return new Response(
          JSON.stringify({ error: 'Offline. Please check your connection.' }),
          { status: 503, headers: { 'Content-Type': 'application/json' } }
        );
      })
    );
    return;
  }

  // Static assets (CSS, JS, icons) → Cache-first (with ignoreSearch)
  if (
    url.pathname.startsWith('/static/') ||
    url.pathname === '/manifest.json' ||
    url.pathname === '/sw.js'
  ) {
    event.respondWith(
      caches.match(request, { ignoreSearch: true }).then((cached) => {
        return cached || fetch(request).then((response) => {
          if (response.ok) {
            const clone = response.clone();
            caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
          }
          return response;
        });
      })
    );
    return;
  }

  // HTML navigation (SPA root) → Network-first with offline fallback
  event.respondWith(
    fetch(request)
      .then((response) => {
        if (response.ok) {
          const clone = response.clone();
          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
        }
        return response;
      })
      .catch(() => {
        return caches.match(OFFLINE_URL).then((cached) => {
          return cached || new Response('<h1>Offline</h1><p>Please check your connection.</p>', {
            headers: { 'Content-Type': 'text/html' },
          });
        });
      })
  );
});