sw.js

const CACHE_VERSION = 'np-v1';
const STATIC_CACHE  = `${CACHE_VERSION}-static`;
const CONTENT_CACHE = `${CACHE_VERSION}-content`;

const PRECACHE_ASSETS = [
  '/',
  '/assets/css/tokens.css',
  '/assets/css/global.css',
  '/assets/css/components.css',
  '/assets/js/nav.js',
  '/assets/js/copy-button.js',
  '/assets/js/accordions.js',
  '/assets/js/checkboxes.js',
  '/assets/js/tables.js',
  '/assets/img/logo.svg',
  '/manifest.json',
];

// Install — pre-cache shell assets
self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(STATIC_CACHE).then((cache) => cache.addAll(PRECACHE_ASSETS))
  );
  self.skipWaiting();
});

// Activate — clean up old caches
self.addEventListener('activate', (event) => {
  event.waitUntil(
    caches.keys().then((keys) =>
      Promise.all(
        keys
          .filter((k) => k.startsWith('np-') && k !== STATIC_CACHE && k !== CONTENT_CACHE)
          .map((k) => caches.delete(k))
      )
    )
  );
  self.clients.claim();
});

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

  // Only handle same-origin requests
  if (url.origin !== location.origin) return;

  const isHtml = request.headers.get('accept')?.includes('text/html');
  const isStatic = /\.(css|js|svg|png|ico|woff2?|webp|jpg|jpeg|gif|webmanifest|json)$/.test(url.pathname);

  if (isStatic) {
    // Cache-first for static assets
    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(STATIC_CACHE).then((c) => c.put(request, clone));
          }
          return response;
        });
      })
    );
  } else if (isHtml) {
    // Network-first (stale-while-revalidate) for HTML pages
    event.respondWith(
      caches.open(CONTENT_CACHE).then(async (cache) => {
        try {
          const response = await fetch(request);
          if (response.ok) cache.put(request, response.clone());
          return response;
        } catch {
          const cached = await cache.match(request);
          return cached || caches.match('/');
        }
      })
    );
  }
});