'use strict';
// Serve app files and individually selected route snapshots independently (v2).
importScripts('/js/offline-storage.js');

self.addEventListener('install', event => event.waitUntil(self.skipWaiting()));
self.addEventListener('activate', event => event.waitUntil(self.clients.claim()));

/** Audio seeks need partial responses even when the entire file is stored locally. */
async function rangedResponse(response, range) {
  const bytes = await response.arrayBuffer();
  const match = /^bytes=(\d*)-(\d*)$/.exec(range);
  if (!match || (!match[1] && !match[2])) return new Response(null, { status: 416, headers: { 'Content-Range': `bytes */${bytes.byteLength}` } });
  const start = match[1] ? Number(match[1]) : Math.max(0, bytes.byteLength - Number(match[2]));
  const end = match[1] ? (match[2] ? Math.min(Number(match[2]), bytes.byteLength - 1) : bytes.byteLength - 1) : bytes.byteLength - 1;
  if (start > end || start >= bytes.byteLength) return new Response(null, { status: 416, headers: { 'Content-Range': `bytes */${bytes.byteLength}` } });
  const headers = new Headers(response.headers);
  headers.set('Content-Range', `bytes ${start}-${end}/${bytes.byteLength}`);
  headers.set('Content-Length', String(end - start + 1));
  headers.set('Accept-Ranges', 'bytes');
  return new Response(bytes.slice(start, end + 1), { status: 206, headers });
}

self.addEventListener('fetch', event => {
  const request = event.request;
  const url = new URL(request.url);
  if (request.method !== 'GET' || url.origin !== self.location.origin
    || request.headers.has('X-Wegwichtel-Offline-Download')
    || url.pathname === '/api/offline-manifest') return;
  event.respondWith((async () => {
    // A complete snapshot is cache-first, avoiding any wait for a failing mobile network.
    const cached = await self.Wegwichtel.OfflineStore.match(request.url).catch(() => null);
    if (cached) {
      const range = request.headers.get('Range');
      return range ? rangedResponse(cached, range) : cached;
    }
    return fetch(request);
  })());
});