http.Response response = await http.post(Uri.parse(Constant.getTokenURL),
        body: {'room_id': room, 'user_id': user, 'role': Constant.defaultRole});

var body = json.decode(response.body);
String token = body['token'];

abstract class HMSUpdateListener {
  /// This will be called on a successful JOIN of the room by the user
  ///
  /// This is the point where applications can stop showing its loading state
  /// - Parameter room: the room which was joined
  void onJoin({required HMSRoom room});

  /// This is called when there is a change in any property of the Room
  ///
  /// - Parameters:
  ///   - room: the room which was joined
  ///   - update: the triggered update type. Should be used to perform different UI Actions
  void onRoomUpdate({required HMSRoom room, required HMSRoomUpdate update});

  /// This will be called whenever there is an update on an existing peer
  /// or a new peer got added/existing peer is removed.
  ///
  /// This callback can be used to keep a track of all the peers in the room
  /// - Parameters:
  ///   - peer: the peer who joined/left or was updated
  ///   - update: the triggered update type. Should be used to perform different UI Actions
  void onPeerUpdate({required HMSPeer peer, required HMSPeerUpdate update});

  /// This is called when there are updates on an existing track
  /// or a new track got added/existing track is removed
  ///
  /// This callback can be used to render the video on screen whenever a track gets added
  /// - Parameters:
  ///   - track: the track which was added, removed or updated
  ///   - trackUpdate: the triggered update type
  ///   - peer: the peer for which track was added, removed or updated
  void onTrackUpdate(
      {required HMSTrack track,
      required HMSTrackUpdate trackUpdate,
      required HMSPeer peer});

  /// This will be called when there is an error in the system
  ///
  /// and SDK has already retried to fix the error
  /// - Parameter error: the error that occurred
  void onError({required HMSError error});

  /// This is called when there is a new broadcast message from any other peer in the room
  ///
  /// This can be used to implement chat is the room
  /// - Parameter message: the received broadcast message
  void onMessage({required HMSMessage message});

  /// This is called when someone asks for change or role
  ///
  /// for eg. admin can ask a peer to become host from guest.
  /// this triggers this call on peer's app
  void onRoleChangeRequest({required HMSRoleChangeRequest roleChangeRequest});

  /// This is called every 1 second with list of active speakers
  ///
  ///    A HMSSpeaker object contains -
  ///    - peerId: the peer identifier of HMSPeer who is speaking
  ///    - trackId: the track identifier of HMSTrack which is emitting audio
  ///    - audioLevel: a number within range 1-100 indicating the audio volume
  ///
  /// A peer who is not present in the list indicates that the peer is not speaking
  ///
  /// This can be used to highlight currently speaking peers in the room
  /// - Parameter speakers: the list of speakers
  void onUpdateSpeakers({required List<HMSSpeaker> updateSpeakers});

  void onReconnecting();

  void onReconnected();
}

  HMSPeerUpdate
    case PEER_JOINED A new peer joins the room
    case PEER_LEFT - An existing peer leaves the room
    case BECAME_DOMINANT_SPEAKER - A peer becomes a dominant speaker
    case NO_DOMINANT_SPEAKER - There is silence in the room (No speaker is detected)
    
  HMSTrackUpdate
    case TRACK_ADDED - A new track is added by a remote peer
    case TRACK_REMOVED - An existing track is removed from a remote peer
    case TRACK_MUTED - An existing track of a remote peer is muted
    case TRACK_UNMUTED - An existing track of a remote peer is unmuted
    case TRACK_DESCRIPTION_CHANGED - The optional description of a track of a remote peer is changed

// Create a new HMSConfig
HMSConfig config = HMSConfig( userId: userId,
                              roomId: roomId,
                              authToken: token,
                              userName: userName);

HMSMeeting meeting = HMSMeeting()
meeting.joinMeeting(config: this.config);

meeting.leave() // to leave a room

// Turn on
meeting.switchAudio(isOn:true)
// Turn off  
meeting.switchAudio(isOn:false)

meeting.startCapturing()

meeting.stopCapturing()

meeting.switchCamera()

HMSTrack
    - AudioTrack
        - LocalAudioTrack
        - RemoteAudioTrack
    - VideoTrack
        - LocalVideoTrack
        - RemoteVideoTrack

VideoView(
    track: videoTrack,
    args: {
      'height': customHeight,
      'width': customWidth,
    },
  );

 meeting.changeRole(
        peerId: peerId, roleName: roleName, forceChange: forceChange);

// following is an example implementation of chat messaging

// to send a broadcast message
String message = 'Hello World!'
meeting.sendMessage(message);  // meeting is an instance of `HMSMeeting` object



// receiving messages
// the object conforming to `HMSUpdateListener` will be invoked with `on(message: HMSMessage)`, add your logic to update Chat UI within this listener
void onMessage({required HMSMessage message}){
    let messageReceived = message.message // extract message payload from `HMSMessage` object that is received
    // update your Chat UI with the messageReceived
}

abstract class HMSPreviewListener {

  //you will get all error updates here
  void onError({required HMSError error});

  //here you will get room instance where you are going to join and your own local tracks to render the video by checking the type of trackKind and then using the 
  //above mentioned VideoView widget
  void onPreview({required HMSRoom room, required List<HMSTrack> localTracks});
}

<uses-feature android:name="android.hardware.camera"/>

<uses-feature android:name="android.hardware.camera.autofocus"/>

<uses-permission android:name="android.permission.CAMERA"/>

<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>

<uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS"/>

<uses-permission android:name="android.permission.RECORD_AUDIO"/>

<uses-permission android:name="android.permission.BLUETOOTH"/>

<uses-permission android:name="android.permission.INTERNET"/>

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

<key>NSMicrophoneUsageDescription</key>
<string>{YourAppName} wants to use your microphone</string>

<key>NSCameraUsageDescription</key>
<string>{YourAppName} wants to use your camera</string>

<key>NSLocalNetworkUsageDescription</key>
<string>{YourAppName} App wants to use your local network</string>