// Service worker for the Neuron PWA powered by el.
//
// Caching strategy:
//   /pkg/  — WASM runtime files, cache-first (content-addressed, change on version bump)
//   *.elc  — compiled bytecode, stale-while-revalidate (instant load, background update)
//
// The WASM runtime is fetched once and cached indefinitely.
// Engram programs (.elc) are served from cache immediately, then refreshed in
// the background so the next load gets the newest version — no user action needed.

const CACHE_NAME = 'engram-v1';
const WASM_CACHE = 'engram-wasm-v1';

// Files to pre-cache during service worker installation.
const PRECACHE = [
    '/pkg/el_wasm_bg.wasm',
    '/pkg/el_wasm.js',
];

self.addEventListener('install', event => {
    event.waitUntil(
        caches.open(WASM_CACHE).then(cache => cache.addAll(PRECACHE))
    );
    // Take control immediately — don't wait for existing tabs to close.
    self.skipWaiting();
});

self.addEventListener('fetch', event => {
    const url = new URL(event.request.url);

    // WASM runtime files: cache-first.
    // These are large and rarely change; the version bump forces a new URL.
    if (url.pathname.startsWith('/pkg/')) {
        event.respondWith(
            caches.match(event.request).then(cached =>
                cached || fetch(event.request).then(response => {
                    caches.open(WASM_CACHE).then(cache =>
                        cache.put(event.request, response.clone())
                    );
                    return response;
                })
            )
        );
        return;
    }

    // Compiled bytecode (.elc): stale-while-revalidate.
    // Respond immediately from cache, update in background.
    if (url.pathname.endsWith('.elc')) {
        event.respondWith(
            caches.open(CACHE_NAME).then(async cache => {
                const cached = await cache.match(event.request);
                const fetchPromise = fetch(event.request).then(response => {
                    cache.put(event.request, response.clone());
                    return response;
                });
                return cached || fetchPromise;
            })
        );
        return;
    }
});

self.addEventListener('activate', event => {
    // Purge old cache versions to reclaim storage.
    event.waitUntil(
        caches.keys().then(keys =>
            Promise.all(
                keys
                    .filter(k => k !== CACHE_NAME && k !== WASM_CACHE)
                    .map(k => caches.delete(k))
            )
        )
    );
    // Claim all clients immediately.
    self.clients.claim();
});