/// <reference types="@sveltejs/kit" />
/// <reference no-default-lib="true"/>
/// <reference lib="esnext" />
/// <reference lib="webworker" />

// Offline-first: the app shell and static assets are cached on install.
// GitHub API calls are never cached (sync needs live data).

import { build, files, version } from '$service-worker';

const sw = self as unknown as ServiceWorkerGlobalScope;
const CACHE = `papure-${version}`;
const ASSETS = [...build, ...files, '/'];

sw.addEventListener('install', (event) => {
	event.waitUntil(
		caches
			.open(CACHE)
			// Bypass the HTTP cache: hashed assets are cached as immutable, so a bad
			// response (e.g. a wrong MIME type) would otherwise be copied in forever.
			.then((c) => c.addAll(ASSETS.map((url) => new Request(url, { cache: 'reload' }))))
			.then(() => sw.skipWaiting())
	);
});

sw.addEventListener('activate', (event) => {
	event.waitUntil(
		caches
			.keys()
			.then((keys) => Promise.all(keys.filter((k) => k !== CACHE).map((k) => caches.delete(k))))
			.then(() => sw.clients.claim())
	);
});

sw.addEventListener('fetch', (event) => {
	const req = event.request;
	if (req.method !== 'GET') return;
	const url = new URL(req.url);
	if (url.origin !== sw.location.origin) return;

	// Navigations: network first, fall back to the cached shell (SPA).
	if (req.mode === 'navigate') {
		event.respondWith(
			fetch(req).catch(async () => (await caches.match('/')) ?? Response.error())
		);
		return;
	}

	// Assets: cache first (they're versioned or fixed).
	event.respondWith(
		caches.match(req).then(
			(hit) =>
				hit ??
				fetch(req).then((res) => {
					if (res.ok && ASSETS.includes(url.pathname)) {
						const copy = res.clone();
						void caches.open(CACHE).then((c) => c.put(req, copy));
					}
					return res;
				})
		)
	);
});