sw.js

/**
 * sw.js — Service Worker for python-remote-sensing.com
 * Strategy:
 *   - HTML pages:   Network-first → cache fallback
 *   - CSS/JS/fonts: Cache-first (static assets, versioned by URL)
 *   - Images/icons: Stale-while-revalidate
 */

const CACHE_VERSION = 'v1';
const STATIC_CACHE  = `prs-static-${CACHE_VERSION}`;
const PAGES_CACHE   = `prs-pages-${CACHE_VERSION}`;
const IMAGE_CACHE   = `prs-images-${CACHE_VERSION}`;

const PRECACHE_ASSETS = [
  '/',
  '/assets/css/main.css',
  '/assets/css/prism-theme.css',
  '/assets/js/copy-button.js',
  '/assets/js/site.js',
  '/favicon.svg',
  '/manifest.json',
];

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

// ── Activate ─────────────────────────────────────────────────────────────────
self.addEventListener('activate', event => {
  const allowedCaches = [STATIC_CACHE, PAGES_CACHE, IMAGE_CACHE];
  event.waitUntil(
    caches.keys().then(keys =>
      Promise.all(
        keys.filter(k => !allowedCaches.includes(k)).map(k => caches.delete(k))
      )
    )
  );
  self.clients.claim();
});

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

  // Only handle same-origin GET requests
  if (request.method !== 'GET' || url.origin !== self.location.origin) return;

  const isHTML   = request.headers.get('accept') && request.headers.get('accept').includes('text/html');
  const isStatic = /\.(css|js|woff2?|ttf|otf)(\?.*)?$/.test(url.pathname);
  const isImage  = /\.(svg|png|jpg|jpeg|webp|gif|ico)(\?.*)?$/.test(url.pathname);

  if (isHTML) {
    // Network-first for HTML
    event.respondWith(networkFirst(request, PAGES_CACHE));
  } else if (isStatic) {
    // Cache-first for static assets
    event.respondWith(cacheFirst(request, STATIC_CACHE));
  } else if (isImage) {
    // Stale-while-revalidate for images
    event.respondWith(staleWhileRevalidate(request, IMAGE_CACHE));
  } else {
    // Default: network with cache fallback
    event.respondWith(networkFirst(request, PAGES_CACHE));
  }
});

// ── Strategies ────────────────────────────────────────────────────────────────
async function networkFirst(request, cacheName) {
  try {
    const response = await fetch(request);
    if (response.ok) {
      const cache = await caches.open(cacheName);
      cache.put(request, response.clone());
    }
    return response;
  } catch {
    const cached = await caches.match(request);
    return cached || caches.match('/');
  }
}

async function cacheFirst(request, cacheName) {
  const cached = await caches.match(request);
  if (cached) return cached;
  try {
    const response = await fetch(request);
    if (response.ok) {
      const cache = await caches.open(cacheName);
      cache.put(request, response.clone());
    }
    return response;
  } catch {
    return new Response('', { status: 503 });
  }
}

async function staleWhileRevalidate(request, cacheName) {
  const cache = await caches.open(cacheName);
  const cached = await cache.match(request);
  const fetchPromise = fetch(request).then(response => {
    if (response.ok) cache.put(request, response.clone());
    return response;
  });
  return cached || fetchPromise;
}