sw.js

const CACHE_NAME = 'cidr-calc-v1';
const ASSETS = [
  './',
  './index.html',
  './style.css',
  './app.js',
  './manifest.json',
  './icons/icon-192.png',
  './icons/icon-512.png'
];

self.addEventListener('install', (e) => {
  e.waitUntil(
    caches.open(CACHE_NAME).then((cache) => {
      return cache.addAll(ASSETS);
    }).then(() => self.skipWaiting())
  );
});

self.addEventListener('activate', (e) => {
  e.waitUntil(
    caches.keys().then((keys) => {
      return Promise.all(
        keys.map((key) => {
          if (key !== CACHE_NAME) {
            return caches.delete(key);
          }
        })
      );
    }).then(() => self.clients.claim())
  );
});

self.addEventListener('fetch', (e) => {
  e.respondWith(
    caches.match(e.request).then((cachedResponse) => {
      if (cachedResponse) {
        // Fetch fresh in background and update cache
        fetch(e.request)
          .then((networkResponse) => {
            if (networkResponse.status === 200) {
              caches.open(CACHE_NAME).then((cache) => cache.put(e.request, networkResponse));
            }
          })
          .catch(() => {/* Ignore network failures, use cached */});
        return cachedResponse;
      }
      return fetch(e.request).then((networkResponse) => {
        if (!networkResponse || networkResponse.status !== 200 || networkResponse.type !== 'basic') {
          return networkResponse;
        }
        const responseToCache = networkResponse.clone();
        caches.open(CACHE_NAME).then((cache) => {
          cache.put(e.request, responseToCache);
        });
        return networkResponse;
      });
    })
  );
});