sw.js

/**
 * Service Worker — DE Knowledge Assistant PWA
 * Strategy: Cache-first for static assets, network-first for API calls
 * This enables "Add to Home Screen" on iOS Safari and offline shell loading
 */

const CACHE = 'de-assistant-v1';
const STATIC_ASSETS = ['/', '/index.html', '/manifest.json'];

// ── Install ──────────────────────────────────────────────────────────────────
self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(CACHE).then(cache => cache.addAll(STATIC_ASSETS))
  );
  self.skipWaiting();
});

// ── Activate ─────────────────────────────────────────────────────────────────
self.addEventListener('activate', event => {
  event.waitUntil(
    caches.keys().then(keys =>
      Promise.all(keys.filter(k => k !== CACHE).map(k => caches.delete(k)))
    )
  );
  self.clients.claim();
});

// ── Fetch ─────────────────────────────────────────────────────────────────────
self.addEventListener('fetch', event => {
  const { request } = event;
  const url = new URL(request.url);

  // API calls → always network (never cache LLM responses)
  if (url.pathname.startsWith('/api/')) {
    event.respondWith(fetch(request));
    return;
  }

  // Static assets → cache-first, fall back to network
  event.respondWith(
    caches.match(request).then(cached => {
      if (cached) return cached;
      return fetch(request).then(response => {
        if (response.ok) {
          const clone = response.clone();
          caches.open(CACHE).then(cache => cache.put(request, clone));
        }
        return response;
      });
    }).catch(() => caches.match('/index.html'))
  );
});