const CACHE = 'music-box-v5';
const AUDIO_CACHE = 'zen-audio-cache';

function isAudioRequest(request) {
  return request.url.includes('.mp3') || request.url.includes('oss');
}

async function buildPartialAudioResponse(request, cachedResponse) {
  const rangeHeader = request.headers.get('range');
  if (!rangeHeader) return cachedResponse;

  const match = /bytes=(\d*)-(\d*)/.exec(rangeHeader);
  if (!match) return cachedResponse;

  const blob = await cachedResponse.blob();
  const size = blob.size;
  let start = match[1] ? Number(match[1]) : 0;
  let end = match[2] ? Number(match[2]) : size - 1;

  if (!Number.isFinite(start) || start < 0) start = 0;
  if (!Number.isFinite(end) || end >= size) end = size - 1;

  if (start >= size || start > end) {
    return new Response(null, {
      status: 416,
      headers: {
        'Accept-Ranges': 'bytes',
        'Content-Range': `bytes */${size}`
      }
    });
  }

  const partialBlob = blob.slice(start, end + 1, blob.type || cachedResponse.headers.get('content-type') || 'audio/mpeg');
  return new Response(partialBlob, {
    status: 206,
    headers: {
      'Accept-Ranges': 'bytes',
      'Content-Length': String(end - start + 1),
      'Content-Range': `bytes ${start}-${end}/${size}`,
      'Content-Type': partialBlob.type || cachedResponse.headers.get('content-type') || 'audio/mpeg'
    }
  });
}

async function handleAudioRequest(request) {
  const audioCache = await caches.open(AUDIO_CACHE);
  const cached = await audioCache.match(request.url);

  if (cached) {
    return buildPartialAudioResponse(request, cached);
  }

  return fetch(request);
}

self.addEventListener('install', e => {
  self.skipWaiting();
  e.waitUntil(
    caches.open(CACHE).then(c => c.addAll([
      './',
      './index.html',
      './zen_box.js',
      './zen_box.css'
    ]))
  );
});

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

self.addEventListener('fetch', e => {
  // 音频文件：优先命中 zen-audio-cache（离线播放必需），否则走网络
  if (isAudioRequest(e.request)) {
    e.respondWith(
      handleAudioRequest(e.request).catch(() => fetch(e.request))
    );
    return;
  }

  // playlist.json 使用 Network First
  if (e.request.url.includes('playlist.json')) {
    e.respondWith(
      fetch(e.request)
        .then(networkResponse => {
          return caches.open(CACHE).then(cache => {
            cache.put(e.request, networkResponse.clone());
            return networkResponse;
          });
        })
        .catch(() => {
          return caches.match(e.request);
        })
    );
    return;
  }

  // 其他文件（App Shell）使用 Cache First
  e.respondWith(
    caches.match(e.request).then(r => r || fetch(e.request))
  );
});