// Minimal Service Worker to expose a streaming endpoint: /mjpeg?key=...
// Page sends {type:'start'|'chunk'|'eof', key, ...} via postMessage.

const sessions = new Map(); // key -> {headers, status, controller, queue:[], started, ended, waiter}

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

self.addEventListener('message', (e) => {
  const d = e.data || {};
  const key = d.key || 'default';
  let s = sessions.get(key);
  if (!s) {
    s = {headers:null, status:200, controller:null, queue:[], started:false, ended:false, waiter:null};
    sessions.set(key, s);
  }
  if (d.type === 'start') {
    s.headers = d.headers || {};
    s.status = d.status || 200;
    s.started = true;
    if (s.waiter) { s.waiter(); s.waiter = null; }
  } else if (d.type === 'chunk') {
    if (s.controller) {
      s.controller.enqueue(new Uint8Array(d.chunk));
    } else {
      s.queue.push(d.chunk);
    }
  } else if (d.type === 'eof') {
    s.ended = true;
    if (s.controller) s.controller.close();
  }
});

self.addEventListener('fetch', (e) => {
  const url = new URL(e.request.url);
  if (url.pathname === '/mjpeg') {
    const key = url.searchParams.get('key') || 'default';
    let s = sessions.get(key);
    if (!s) {
      s = {headers:null, status:200, controller:null, queue:[], started:false, ended:false, waiter:null};
      sessions.set(key, s);
    }

    const stream = new ReadableStream({
      start(controller) {
        s.controller = controller;
        if (s.queue.length) {
          for (const q of s.queue) controller.enqueue(new Uint8Array(q));
          s.queue = [];
        }
        if (s.ended) controller.close();
      },
      cancel() {
        sessions.delete(key);
      }
    });

    const waitHeaders = s.started ? Promise.resolve() : new Promise((resolve) => { s.waiter = resolve; setTimeout(resolve, 5000); });

    e.respondWith((async () => {
      await waitHeaders;
      const h = new Headers();
      // 받은 헤더를 그대로 복사(다중값 지원)
      if (s.headers) {
        for (const k in s.headers) {
          const v = s.headers[k];
          if (Array.isArray(v)) { v.forEach(x => h.append(k, x)); }
          else if (v != null) { h.set(k, String(v)); }
        }
      }
      if (!h.has('Content-Type')) {
        // MJPEG 기본값(필요 시 실제 헤더에서 boundary가 전달됨)
        h.set('Content-Type', 'multipart/x-mixed-replace; boundary=--frame');
      }
      return new Response(stream, {status: s.status || 200, headers: h});
    })());
  }
});