Koneksi WebRTC

const pc = new RTCPeerConnection({ iceServers: [ ] });

const channels = new Set();
const senders = new Map();
const remoteAudio = document.createElement("audio");
remoteAudio.controls = true; // Allow manual playback if autoplay is blocked.
remoteAudio.autoplay = true;
document.body.appendChild(remoteAudio);

let localStream = null;
let eventChannel = null;
let stopped = false;
let started = false;
let sessionCreated = false;
let updateSent = false;
let modelReady = false;
let mediaStarted = false;
const requestController = new AbortController();

const media = {
  sendAudio: true,
  receiveAudio: true,
  sendVideo: false,
  receiveVideo: false,
};

function mediaDirection(send, receive) {
  if (send && receive) return "sendrecv";
  if (send) return "sendonly";
  if (receive) return "recvonly";
  return "inactive";
}

async function configureMedia() {
  for (const kind of ["audio", "video"]) {
    const send = kind === "audio" ? media.sendAudio : media.sendVideo;
    const receive = kind === "audio" ? media.receiveAudio : media.receiveVideo;
    // Keep m=audio; the target service must support the selected directions.
    if (kind === "audio" || send || receive) {
      const transceiver = pc.addTransceiver(kind, {
        direction: mediaDirection(send, receive),
      });
      if (send) senders.set(kind, transceiver.sender);
    }
  }
  if (!media.sendAudio && !media.sendVideo) return;
  const stream = await navigator.mediaDevices.getUserMedia({
    audio: media.sendAudio,
    video: media.sendVideo ? {
      width: { ideal: 640 }, height: { ideal: 480 },
      frameRate: { ideal: 2, max: 2 },
    } : false,
  });
  // The user may end the session while the permission prompt is open.
  if (stopped) {
    stream.getTracks().forEach(track => track.stop());
    throw new Error("Session ended");
  }
  localStream = stream;
  // sender.track is still null; captured data is not sent to the model.
}

// See Send and receive events over DataChannels for bindDataChannel.
pc.ondatachannel = ({ channel }) => bindDataChannel(channel);
const clientChannel = pc.createDataChannel("oai-events");
bindDataChannel(clientChannel);

pc.onconnectionstatechange = () => {
  console.log("WebRTC state:", pc.connectionState);
  if (pc.connectionState === "connected") {
    tryInitializeModel();
  } else if (["failed", "disconnected", "closed"].includes(pc.connectionState)) {
    // This example ends the session; implement recovery as needed.
    endSession();
  }
};

function waitForIceComplete() {
  return new Promise((resolve, reject) => {
    const timer = setTimeout(() => finish(new Error("ICE gathering timed out")), 15000);
    function finish(error) {
      clearTimeout(timer);
      pc.removeEventListener("icegatheringstatechange", check);
      requestController.signal.removeEventListener("abort", cancel);
      error ? reject(error) : resolve();
    }
    function check() {
      if (pc.iceGatheringState === "complete") finish();
    }
    function cancel() { finish(new Error("Session ended")); }
    pc.addEventListener("icegatheringstatechange", check);
    requestController.signal.addEventListener("abort", cancel, { once: true });
    if (stopped) cancel();
    else check();
  });
}

function normalizeAnswerSdp(sdp) {
  return String(sdp).trim().replace(/\r?\n/g, "\r\n") + "\r\n";
}

async function startSession() {
  if (started || stopped) return;
  started = true;
  try {
    await configureMedia();
    if (stopped) return;
    const offer = await pc.createOffer();
    await pc.setLocalDescription(offer);
    await waitForIceComplete();

    // Implement this same-origin application endpoint; it is not a Model Studio API.
    // AppServer forwards SDP with the API key and returns the raw Answer SDP.
    const response = await fetch("/api/realtime/sdp", {
      method: "POST",
      headers: { "Content-Type": "application/sdp" },
      body: pc.localDescription.sdp,
      signal: requestController.signal,
    });
    if (!response.ok) {
      throw new Error(`SDP exchange failed:${response.status} ${await response.text()}`);
    }
    const answerSdp = normalizeAnswerSdp(await response.text());
    if (stopped) return;
    await pc.setRemoteDescription({ type: "answer", sdp: answerSdp });
    // Continue through connectionstatechange, DataChannel, and model events.
  } catch (error) {
    if (!stopped) console.error("Connection failed:", error);
    endSession();
  }
}

function tryInitializeModel() {
  if (stopped || updateSent || !sessionCreated ||
      pc.connectionState !== "connected" ||
      eventChannel?.readyState !== "open") return;
  sendModelEvent({
    event_id: `event_${crypto.randomUUID()}`,
    type: "session.update",
    session: {
      modalities: media.receiveAudio ? ["text", "audio"] : ["text"],
      input_audio_format: "pcm",
      output_audio_format: "pcm",
      turn_detection: { type: "server_vad", threshold: 0.5,
                        silence_duration_ms: 800 },
    },
  });
  updateSent = true;
}

async function handleModelEvent(event, channel) {
  if (stopped) return;
  if (event.type === "session.created") {
    sessionCreated = true;
    eventChannel = channel; // Send configuration on the channel that delivered the session event.
    tryInitializeModel();
  } else if (event.type === "session.updated" && updateSent) {
    modelReady = true;
    await startSendingMedia();
  } else if (event.type === "error") {
    console.error("Model error:", event.error);
    endSession();
  } else {
    // Handle text, transcripts, and response state; receive audio on media tracks.
    console.log("Model event:", event);
  }
}

async function startSendingMedia() {
  if (stopped || !modelReady || mediaStarted) return;
  mediaStarted = true;

  for (const track of localStream?.getTracks() ?? []) {

    if (stopped) return;
    const sender = senders.get(track.kind);
    if (sender) await sender.replaceTrack(track);
  }
}

// Register before startSession(); also handle tracks with no streams.
const remoteAudioStream = new MediaStream();
const remoteVideo = media.receiveVideo ? document.createElement("video") : null;
if (remoteVideo) {
  remoteVideo.autoplay = true;
  remoteVideo.playsInline = true;
  remoteVideo.controls = true;
  document.body.appendChild(remoteVideo);
}
pc.ontrack = ({ track }) => {
  if (stopped) return;
  if (track.kind === "audio" && media.receiveAudio) {
    remoteAudioStream.addTrack(track);
    remoteAudio.srcObject = remoteAudioStream;
    remoteAudio.play().catch(() => {
      console.info("Autoplay blocked. Use the audio controls to play.");
    });
  }
  if (track.kind === "video" && remoteVideo) {
    remoteVideo.srcObject = new MediaStream([track]);
    remoteVideo.play().catch(() => console.info("Use the video controls to play."));
  }
};

function endSession() {
  if (stopped) return;
  stopped = true;
  modelReady = false;
  sessionCreated = false;
  updateSent = false;
  mediaStarted = false;
  requestController.abort(); // Cancel the pending SDP request and ICE wait.
  localStream?.getTracks().forEach(track => track.stop());
  localStream = null;
  channels.forEach(channel => channel.close());
  channels.clear();
  eventChannel = null;
  pc.close();
  senders.clear();
  remoteAudioStream.getTracks().forEach(track => track.stop());
  remoteAudio.pause();
  remoteAudio.srcObject = null;
  remoteAudio.remove();
  if (remoteVideo) {
    remoteVideo.srcObject?.getTracks().forEach(track => track.stop());
    remoteVideo.pause();
    remoteVideo.srcObject = null;
    remoteVideo.remove();
  }
}

function sendModelEvent(event, channel = eventChannel) {
  if (stopped || pc.connectionState !== "connected" ||
      channel?.readyState !== "open") {
    throw new Error("Data channel is not ready");
  }
  channel.send(JSON.stringify(event));
}

function bindDataChannel(channel) {
  channels.add(channel);
  channel.onopen = () => {
    if (stopped) return;
    console.log("DataChannel opened:", channel.label);
    tryInitializeModel();
  };
  channel.onmessage = ({ data }) => {
    if (stopped) return;
    let event;
    try { event = JSON.parse(data); }
    catch (error) {
      console.warn("Cannot parse model event:", error);
      return;
    }
    if (!event || typeof event !== "object") return;
    handleModelEvent(event, channel).catch(error => {
      if (!stopped) console.error("Model event handling failed:", error);
      endSession();
    });
  };
  channel.onerror = error => console.error("DataChannel error:", error);
  channel.onclose = () => {
    channels.delete(channel);
    if (channel === eventChannel) endSession();
  };
  if (channel.readyState === "open") channel.onopen();
}