const cacheName = "stale-with-revalidate"

// import workbox
importScripts(
  "https://storage.googleapis.com/workbox-cdn/releases/5.1.2/workbox-sw.js"
)
const { routing, strategies } = workbox

// implements staleWhileRevalidate to all routes
routing.registerRoute(
  () => true,
  new strategies.StaleWhileRevalidate({ cacheName })
)

// removes all caches not named <cacheName>
const invalidateOldCache = async () => {
  const keys = await caches.keys()
  const isOldCache = key => key !== cacheName
  const oldKeys = keys.filter(isOldCache)

  return Promise.all(oldKeys.map(key => caches.delete(key)))
}

// runs invalidateOldCache on activation
self.addEventListener("activate", e => e.waitUntil(invalidateOldCache()))