const CACHE = 'intern-log-v1'
const CORE = ['./', './index.html']

self.addEventListener('install', event => {
  event.waitUntil(caches.open(CACHE).then(c => c.addAll(CORE)).then(() => self.skipWaiting()))
})

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

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

  // 页面导航：网络优先，离线回退缓存的应用壳
  if (req.mode === 'navigate') {
    event.respondWith(
      fetch(req)
        .then(resp => {
          const clone = resp.clone()
          caches.open(CACHE).then(c => c.put('./index.html', clone))
          return resp
        })
        .catch(() => caches.match('./index.html'))
    )
    return
  }

  // 静态资源：缓存优先，未命中时拉取并写入缓存
  event.respondWith(
    caches.match(req).then(hit => hit || fetch(req).then(resp => {
      if (resp.ok) {
        const clone = resp.clone()
        caches.open(CACHE).then(c => c.put(req, clone))
      }
      return resp
    }))
  )
})