const CACHE_NAME = 'offline-cache-v1'
const ASSETS = [
    '/',
    '/index.html',
    '/styles.css',
    '/styles3.css',
    '/tempo.md',
    '/bell.png',
    '/bell.svg',
    '/by-sa.png',
    '/cc-by-sa-legalcode.txt',
    '/symbols.txt'
]

self.addEventListener('install', e => {
    console.log('installing sw')
    e.waitUntil(caches.open(CACHE_NAME).then(cache => cache.addAll(ASSETS)))
    self.skipWaiting()
})

self.addEventListener('activate', e => {
    console.log('sw activated')
    e.waitUntil(self.clients.claim())
})

const checkChange = (r1, r2) => {
    const h1 = r1.headers
    const h2 = r2.headers
    if (h1.get('etag') && h2.get('etag')) return h1.get('etag') !== h2.get('etag')
    if (h1.get('last-modified') && h2.get('last-modified')) return h1.get('last-modified') !== h2.get('last-modified')
    return h1.get('content-length') !== h2.get('content-length')
}

self.addEventListener('fetch', e => {
    const url = new URL(e.request.url)
    const isTarget = ASSETS.includes(url.pathname) || url.pathname.startsWith('/fonts/')

    if (!isTarget) return

    e.respondWith((async () => {
        const cache = await caches.open(CACHE_NAME)
        const cachedResponse = await cache.match(e.request)

        const networkFetch = fetch(e.request, { cache: 'no-cache' }).then(async networkResponse => {
            if (!networkResponse.ok) return networkResponse

            const freshCopy = networkResponse.clone()
            let changed = false

            if (cachedResponse) {
                changed = checkChange(cachedResponse, networkResponse)
            } else {
                console.log(`fetch ${url.pathname}`)
            }

            await cache.put(e.request, freshCopy)

            if (changed) {
                console.log(`content changed, signaling refresh: ${url.pathname}`)
                const clients = await self.clients.matchAll()
                clients.forEach(client => {
                    client.postMessage({
                        type: 'REFRESH',
                        url: url.pathname
                    })
                })
            }
            return networkResponse
        }).catch(err => {
            console.error(`failed ${url.pathname}:`, err)
        })

        if (cachedResponse) {
            console.log(`cache ${url.pathname}`)
            e.waitUntil(networkFetch)
            return cachedResponse
        }

        return networkFetch
    })())
})