text: import { timestamp, files, shell, routes } from '@sapper/service-worker'
  
  const ASSETS = `cache${timestamp}`
  
  // `shell` is an array of all the files generated by the bundler,
  // `files` is an array of everything in the `static` directory
  const to_cache = shell.concat(files)
  const cached = new Set(to_cache)
  
  self.addEventListener('install', event => {
    event.waitUntil(
      caches
        .open(ASSETS)
        .then(cache => cache.addAll(to_cache))
        .then(() => {
          self.skipWaiting()
        }),
    )
  })
  
  self.addEventListener('activate', event => {
    event.waitUntil(
      caches.keys().then(async keys => {
        // delete old caches
        for (const key of keys) {
          if (key !== ASSETS) await caches.delete(key)
        }
  
        self.clients.claim()
      }),
    )
  })
  
  self.addEventListener('fetch', event => {
    if (event.request.method !== 'GET' || event.request.headers.has('range'))
      return
  
    const url = new URL(event.request.url)
  
    // don't try to handle e.g. data: URIs
    if (!url.protocol.startsWith('http')) return
  
    // ignore dev server requests
    if (
      url.hostname === self.location.hostname &&
      url.port !== self.location.port
    )
      return
  
    // always serve static files and bundler-generated assets from cache
    if (url.host === self.location.host && cached.has(url.pathname)) {
      event.respondWith(caches.match(event.request))
      return
    }
  
    // for pages, you might want to serve a shell `service-worker-index.html` file,
    // which Sapper has generated for you. It's not right for every
    // app, but if it's right for yours then uncomment this section
    /*
  	if (url.origin === self.origin && routes.find(route => route.pattern.test(url.pathname))) {
  		event.respondWith(caches.match('/service-worker-index.html'));
  		return;
  	}
  	*/
  
    if (event.request.cache === 'only-if-cached') return
  
    // for everything else, try the network first, falling back to
    // cache if the user is offline. (If the pages never change, you
    // might prefer a cache-first approach to a network-first one.)
    event.respondWith(
      caches.open(`offline${timestamp}`).then(async cache => {
        try {
          const response = await fetch(event.request)
          cache.put(event.request, response.clone())
          return response
        } catch (err) {
          const response = await cache.match(event.request)
          if (response) return response
  
          throw err
        }
      }),
    )
  })
  