var roomId = getUrlQueryParameter('room');
var userId = uuidv4();
var trackId;

var pc = new RTCPeerConnection(configuration);

// send ICE candidate to engine
pc.onicecandidate = ({candidate}) => {
  rpc('trickle', [roomId, userId, trackId, JSON.stringify(candidate)]);
};

// play the audio stream when available
pc.ontrack = (event) => { 
  el = document.createElement(event.track.kind)
  el.id = aid;
  el.srcObject = stream;
  el.autoplay = true;
  document.getElementById('peers').appendChild(el)
};

// setup local audio stream from microphone
const stream = await navigator.mediaDevices.getUserMedia(constraints);
stream.getTracks().forEach((track) => {
  pc.addTrack(track, stream);
});
await pc.setLocalDescription(await pc.createOffer());

// RPC publish to roomId, with SDP offer
var res = await rpc('publish', [roomId, userId, JSON.stringify(pc.localDescription)]);
// publish should respond an SDP answer
if (res.data && res.data.sdp.type === 'answer') {
  await pc.setRemoteDescription(res.data.sdp);
  trackId = res.data.track;
  subscribe(pc);
}

// RPC subscribe to roomId periodically  
async function subscribe(pc) {
  var res = await rpc('subscribe', [roomId, userId, trackId]);

  if (res.data && res.data.type === 'offer') {
    await pc.setRemoteDescription(res.data);
    var sdp = await pc.createAnswer();
    await pc.setLocalDescription(sdp);
    // RPC anwser the subscribe offer
    await rpc('answer', [roomId, userId, trackId, JSON.stringify(sdp)]);
  }
  setTimeout(function () {
    subscribe(pc);
  }, 3000);
}

async function rpc(method, params = []) {
  const response = await fetch('http://localhost:7000', {
    method: 'POST',
    mode: 'cors', 
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({id: uuidv4(), method: method, params: params})
  });
  return response.json(); 
}