NextExpense/static/sw.js

/* ============================================================
 * NextExpense — Service Worker
 * Version: 2.0.0
 * Cache name: nextexpense-v2
 * Strategy: Cache-first for shell assets, network-only for API
 * ============================================================ */

const CACHE_NAME = 'nextexpense-v2';

// Shell assets to pre-cache on install
const SHELL_ASSETS = [
  '/',
  '/static/css/style.css',
  '/static/favicon.svg',
  'https://unpkg.com/htmx.org@1.9.10'
];

// API path prefix pattern — requests matching these are never cached
const API_PATTERNS = [
  '/api/',
  '/auth/',
  '/login',
  '/logout',
  '/register'
];

/* ------------------------------------------------------------
 * Utility: determine whether a request targets an API endpoint
 * ------------------------------------------------------------ */
function isApiRequest(url) {
  return API_PATTERNS.some(pattern => url.pathname.startsWith(pattern));
}

/* ------------------------------------------------------------
 * Utility: determine whether a request is a shell asset eligible
 *           for cache-first strategy
 * ------------------------------------------------------------ */
function isShellAsset(url) {
  const path = url.pathname;
  const origin = url.origin;

  // Same-origin shell pages
  if (origin === self.location.origin && (path === '/' || path === '')) {
    return true;
  }

  // Same-origin CSS
  if (origin === self.location.origin && path.startsWith('/static/css/')) {
    return true;
  }

  // Same-origin JS
  if (origin === self.location.origin && path.startsWith('/static/js/')) {
    return true;
  }

  // HTMX CDN (cache-first for fast loading)
  if (url.href === 'https://unpkg.com/htmx.org@1.9.10') {
    return true;
  }

  return false;
}

/* ------------------------------------------------------------
 * INSTALL — Pre-cache shell assets
 * ------------------------------------------------------------ */
self.addEventListener('install', event => {
  console.log('[SW] Install event — caching shell assets');

  event.waitUntil(
    caches.open(CACHE_NAME)
      .then(cache => {
        // Use addAll for atomic caching — if one fails, the whole
        // install fails and the SW won't activate
        return cache.addAll(SHELL_ASSETS).catch(err => {
          console.error('[SW] Failed to cache some shell assets:', err);
          // Still attempt to activate even if caching is partially
          // unsuccessful — the fetch handler will fall back to network
          throw err;
        });
      })
      .then(() => {
        console.log('[SW] Shell assets cached successfully');
        return self.skipWaiting();
      })
      .catch(err => {
        console.error('[SW] Install failed:', err);
        // Still try to activate so the SW takes over
        return self.skipWaiting();
      })
  );
});

/* ------------------------------------------------------------
 * ACTIVATE — Clean up old caches
 * ------------------------------------------------------------ */
self.addEventListener('activate', event => {
  console.log('[SW] Activate event — cleaning old caches');

  event.waitUntil(
    caches.keys().then(cacheNames => {
      return Promise.all(
        cacheNames
          .filter(name => name !== CACHE_NAME)
          .map(name => {
            console.log('[SW] Deleting old cache:', name);
            return caches.delete(name);
          })
      );
    }).then(() => {
      console.log('[SW] Activated — taking control of all clients');
      return self.clients.claim();
    }).catch(err => {
      console.error('[SW] Activation cleanup failed:', err);
      // Continue even if cleanup fails
      return self.clients.claim();
    })
  );
});

/* ------------------------------------------------------------
 * FETCH — Hybrid strategy
 *   - Cache-first with network fallback for shell assets
 *   - Network-only for API / dynamic endpoints
 *   - Stale-while-revalidate for other same-origin assets
 * ------------------------------------------------------------ */
self.addEventListener('fetch', event => {
  const request = event.request;
  const url = new URL(request.url);

  // Ignore non-GET requests (POST, PUT, DELETE, etc.)
  if (request.method !== 'GET') {
    return;
  }

  // Ignore browser-extension and non-http(s) requests
  if (!url.protocol.startsWith('http')) {
    return;
  }

  // ── Strategy 1: Network-only for API calls ──
  if (isApiRequest(url)) {
    event.respondWith(
      fetch(request).catch(err => {
        console.warn('[SW] API fetch failed (offline?):', url.pathname, err);
        // Return a lightweight JSON error so the app can handle it gracefully
        return new Response(
          JSON.stringify({ error: 'You are offline. Please check your connection.' }),
          {
            status: 503,
            statusText: 'Service Unavailable',
            headers: { 'Content-Type': 'application/json' }
          }
        );
      })
    );
    return;
  }

  // ── Strategy 2: Cache-first with network fallback for shell assets ──
  if (isShellAsset(url)) {
    event.respondWith(
      caches.match(request)
        .then(cachedResponse => {
          if (cachedResponse) {
            // Cache hit — return immediately
            return cachedResponse;
          }

          // Cache miss — fetch from network, then cache for future
          return fetch(request)
            .then(networkResponse => {
              // Only cache valid responses
              if (!networkResponse || networkResponse.status !== 200) {
                return networkResponse;
              }

              // Clone the response so we can cache one and return the other
              const responseToCache = networkResponse.clone();
              caches.open(CACHE_NAME)
                .then(cache => {
                  cache.put(request, responseToCache).catch(err => {
                    console.error('[SW] Failed to cache asset:', url.pathname, err);
                  });
                })
                .catch(err => {
                  console.error('[SW] Failed to open cache for storing:', err);
                });

              return networkResponse;
            })
            .catch(err => {
              console.warn('[SW] Network fetch failed for shell asset:', url.pathname, err);
              // Return a minimal offline fallback for navigations
              if (request.mode === 'navigate') {
                return new Response(
                  '<!DOCTYPE html><html><head><title>Offline — NextExpense</title><meta name="viewport" content="width=device-width, initial-scale=1"><style>body{font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,sans-serif;display:flex;flex-direction:column;align-items:center;justify-content:center;min-height:100vh;margin:0;padding:2rem;text-align:center;background:#0f172a;color:#f8fafc}h1{font-size:1.5rem;margin-bottom:0.5rem}p{color:#94a3b8;max-width:24rem}</style></head><body><h1>You\'re offline</h1><p>NextExpense needs an internet connection to load. Please check your connection and try again.</p></body></html>',
                  {
                    status: 503,
                    statusText: 'Service Unavailable',
                    headers: { 'Content-Type': 'text/html; charset=utf-8' }
                  }
                );
              }

              return new Response(
                'Offline — resource not available',
                {
                  status: 503,
                  statusText: 'Service Unavailable',
                  headers: { 'Content-Type': 'text/plain; charset=utf-8' }
                }
              );
            });
        })
        .catch(err => {
          console.error('[SW] Cache match error:', err);
          // Fall through to network
          return fetch(request).catch(() => {
            return new Response(
              'An unexpected error occurred.',
              { status: 502, headers: { 'Content-Type': 'text/plain' } }
            );
          });
        })
    );
    return;
  }

  // ── Strategy 3: Network-first for all other (non-shell, non-API) assets ──
  // This covers images, fonts, etc. — try network first, fall back to cache
  event.respondWith(
    fetch(request)
      .then(networkResponse => {
        // Cache successful responses for offline fallback
        if (networkResponse && networkResponse.status === 200) {
          const responseToCache = networkResponse.clone();
          caches.open(CACHE_NAME)
            .then(cache => {
              cache.put(request, responseToCache).catch(err => {
                console.error('[SW] Failed to cache dynamic asset:', url.pathname, err);
              });
            })
            .catch(err => {
              console.error('[SW] Failed to open cache for dynamic asset:', err);
            });
        }
        return networkResponse;
      })
      .catch(err => {
        console.warn('[SW] Network failed, trying cache for:', url.pathname, err);
        return caches.match(request).then(cachedResponse => {
          if (cachedResponse) {
            return cachedResponse;
          }
          // Nothing in cache either — return a basic error
          return new Response(
            'Resource unavailable offline.',
            { status: 503, headers: { 'Content-Type': 'text/plain' } }
          );
        });
      })
  );
});