feat: Add service worker for offline capability (Fixes #212)

index.html

@@ -49,6 +49,19 @@
   <div id="sovereignty-msg">⚡ SOVEREIGNTY ⚡</div>
 
   <script type="module" src="app.js"></script>
+<script>
+    if ('serviceWorker' in navigator) {
+      window.addEventListener('load', () => {
+        navigator.serviceWorker.register('/sw.js')
+          .then(registration => {
+            console.log('Service Worker registered: ', registration);
+          })
+          .catch(error => {
+            console.log('Service Worker registration failed: ', error);
+          });
+      });
+    }
+  </script>
 <div id="loading" style="position: fixed; top: 0; left: 0; right: 0; height: 4px; background: #222; z-index: 1000;">
   <div id="loading-bar" style="height: 100%; background: var(--color-accent); width: 0;"></div>
 </div>

sw.js

@@ -0,0 +1,77 @@
+const CACHE_NAME = 'nexus-cache-v1';
+const ASSETS = [
+  '/',
+  '/index.html',
+  '/app.js',
+  '/style.css',
+  '/manifest.json',
+  'https://unpkg.com/three@0.183.0/build/three.module.js',
+  'https://unpkg.com/three@0.183.0/examples/jsm/' // This might need to be more specific, or handled differently
+];
+
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME)
+      .then((cache) => {
+        console.log('Opened cache');
+        return cache.addAll(ASSETS);
+      })
+  );
+});
+
+self.addEventListener('fetch', (event) => {
+  const requestUrl = new URL(event.request.url);
+
+  // Cache-first for assets
+  const isAsset = ASSETS.some(asset => event.request.url.includes(asset));
+
+  if (isAsset || requestUrl.origin === location.origin) {
+    event.respondWith(
+      caches.match(event.request)
+        .then((response) => {
+          if (response) {
+            return response;
+          }
+          return fetch(event.request)
+            .then((networkResponse) => {
+              // Only cache successful responses
+              if (networkResponse.ok) {
+                return caches.open(CACHE_NAME).then((cache) => {
+                  cache.put(event.request, networkResponse.clone());
+                  return networkResponse;
+                });
+              }
+              return networkResponse;
+            });
+        })
+        .catch(() => {
+          // Fallback for offline if no cache and no network
+          // This could be a more robust offline page if needed
+          return new Response('You are offline.');
+        })
+    );
+  } else {
+    // Network-first for other requests (e.g., API calls)
+    event.respondWith(
+      fetch(event.request)
+        .catch(() => {
+          return caches.match(event.request);
+        })
+    );
+  }
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((cacheNames) => {
+      return Promise.all(
+        cacheNames.map((cacheName) => {
+          if (cacheName !== CACHE_NAME) {
+            console.log('Deleting old cache:', cacheName);
+            return caches.delete(cacheName);
+          }
+        })
+      );
+    })
+  );
+});