web/sw.js

/* ==========================================================================
   CHASSIS OCR PWA - SERVICE WORKER
   ========================================================================== */

const CACHE_NAME = 'chassis-ocr-pwa-v1';
const ASSETS_TO_CACHE = [
    '/',
    '/index.html',
    '/app.css',
    '/app.js',
    '/manifest.json',
    '/icons/icon-192.png',
    '/icons/icon-512.png'
];

// Install Service Worker and Cache Assets
self.addEventListener('install', (event) => {
    event.waitUntil(
        caches.open(CACHE_NAME)
            .then((cache) => {
                console.log('[Service Worker] Caching App Shell...');
                return cache.addAll(ASSETS_TO_CACHE);
            })
            .then(() => self.skipWaiting())
    );
});

// Activate event (clean up old caches)
self.addEventListener('activate', (event) => {
    event.waitUntil(
        caches.keys().then((keyList) => {
            return Promise.all(keyList.map((key) => {
                if (key !== CACHE_NAME) {
                    console.log('[Service Worker] Removing old cache:', key);
                    return caches.delete(key);
                }
            }));
        }).then(() => self.clients.claim())
    );
});

// Fetch events (Network-first with Cache Fallback for API / Cache-first for Assets)
self.addEventListener('fetch', (event) => {
    const requestUrl = new URL(event.request.url);

    // Bypass caching for backend API requests and other HTTP methods (POST, PUT, DELETE)
    if (event.request.method !== 'GET' || requestUrl.pathname.startsWith('/api/')) {
        return;
    }

    event.respondWith(
        caches.match(event.request)
            .then((cachedResponse) => {
                if (cachedResponse) {
                    // Serve cached asset immediately, but fetch fresh version in the background
                    fetch(event.request).then((networkResponse) => {
                        if (networkResponse && networkResponse.status === 200) {
                            caches.open(CACHE_NAME).then((cache) => {
                                cache.put(event.request, networkResponse);
                            });
                        }
                    }).catch(() => {/* Ignore network failures in background */});
                    
                    return cachedResponse;
                }

                // If not cached, fetch from network
                return fetch(event.request).then((networkResponse) => {
                    if (!networkResponse || networkResponse.status !== 200 || networkResponse.type !== 'basic') {
                        return networkResponse;
                    }
                    
                    // Cache the newly fetched asset
                    const responseToCache = networkResponse.clone();
                    caches.open(CACHE_NAME).then((cache) => {
                        cache.put(event.request, responseToCache);
                    });
                    
                    return networkResponse;
                });
            })
    );
});