'use strict';

const CACHE_VERSION = 'v1.0.1';
const STATIC_CACHE_NAME = `static-cache-${CACHE_VERSION}`;
const IMAGE_CACHE_NAME = `image-cache-${CACHE_VERSION}`;

// App Shell: files that are critical for the app to work offline
const APP_SHELL_FILES = [
    '/index.html',
    '/styles.css',
    '/app.js',
    '/manifest.webmanifest',
    '/icons/icon-192x192.png',
    '/icons/icon-512x512.png'
];

// --- INSTALL Event ---
// Caches the App Shell
self.addEventListener('install', event => {
    console.log('[Service Worker] Install');
    event.waitUntil(
        caches.open(STATIC_CACHE_NAME)
            .then(cache => {
                console.log('[Service Worker] Caching App Shell');
                return cache.addAll(APP_SHELL_FILES);
            })
    );
});

// --- ACTIVATE Event ---
// Cleans up old caches
self.addEventListener('activate', event => {
    console.log('[Service Worker] Activate');
    event.waitUntil(
        caches.keys().then(cacheNames => {
            return Promise.all(
                cacheNames.map(cacheName => {
                    if (cacheName !== STATIC_CACHE_NAME && cacheName !== IMAGE_CACHE_NAME) {
                        console.log('[Service Worker] Deleting old cache:', cacheName);
                        return caches.delete(cacheName);
                    }
                })
            );
        })
    );
    return self.clients.claim();
});

// --- FETCH Event ---
// Intercepts network requests and serves from cache if available
self.addEventListener('fetch', event => {
    const { request } = event;
    const url = new URL(request.url);

    // Strategy 1: Stale-While-Revalidate for App Shell (static assets)
    // Serves from cache immediately for speed, then updates the cache in the background.
    if (APP_SHELL_FILES.includes(url.pathname) || url.origin === self.location.origin) {
        event.respondWith(
            caches.open(STATIC_CACHE_NAME).then(cache => {
                return cache.match(request).then(response => {
                    const fetchPromise = fetch(request).then(networkResponse => {
                        cache.put(request, networkResponse.clone());
                        return networkResponse;
                    });
                    // Return cached response immediately, or wait for network if not in cache
                    return response || fetchPromise;
                });
            })
        );
        return;
    }
    
    // Strategy 2: Cache-First for images from external origins (e.g., Pexels)
    // If the image is in the cache, serve it. Otherwise, fetch from network,
    // cache it, and then serve it.
    if (url.hostname === 'images.pexels.com') {
        event.respondWith(
            caches.open(IMAGE_CACHE_NAME).then(cache => {
                return cache.match(request).then(response => {
                    if (response) {
                        return response; // Found in cache
                    }
                    // Not in cache, fetch and then cache it
                    return fetch(request).then(networkResponse => {
                        cache.put(request, networkResponse.clone());
                        return networkResponse;
                    });
                });
            })
        );
        return;
    }

    // For any other requests, just fetch from the network.
    event.respondWith(fetch(request));
});