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'];

/// 100ms SDK provides callbacks to the client app about any change or update happening in the room after a user has joined by implementing HMSUpdateListener.
/// These updates can be used to render the video on screen or to display other info regarding the room.
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
  /// [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
  ///
  ///  [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
  /// [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
  ///  [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
  /// [error]: the error that occurred
  void onError({required HMSException 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
  /// [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
  /// [speakers] the list of speakers
  void onUpdateSpeakers({required List<HMSSpeaker> updateSpeakers});

  ///when network or some other error happens it will be called
  void onReconnecting();

  ///when you are back in the room after reconnection
  void onReconnected();

  ///when someone requests for track change of yours be it video or audio this will be triggered
  /// [hmsTrackChangeRequest] request instance consisting of all the required info about track change
  void onChangeTrackStateRequest({required HMSTrackChangeRequest hmsTrackChangeRequest});

  ///when someone kicks you out or when someone ends the room at that time it is triggered
  /// [hmsPeerRemovedFromPeer] it consists info about who removed you and why.
  void onRemovedFromRoom({required HMSPeerRemovedFromPeer hmsPeerRemovedFromPeer});
}

HMSPeerUpdate
  HMSPeerUpdate.peerJoined: A new peer joins the room
  HMSPeerUpdate.peerLeft: An existing peer leaves the room
  HMSPeerUpdate.roleUpdated
  HMSPeerUpdate.metadataChanged
  HMSPeerUpdate.nameChanged

HMSTrackUpdate
  HMSTrackUpdate.trackAdded: A new track is added by a remote peer
  HMSTrackUpdate.trackRemoved: An existing track is removed from a remote peer
  HMSTrackUpdate.trackMuted: An existing track of a remote peer is muted
  HMSTrackUpdate.trackUnMuted: An existing track of a remote peer is unmuted
  HMSTrackUpdate.trackDegraded
  HMSTrackUpdate.trackRestored

HMSRoomUpdate
  HMSRoomUpdate.roomMuted
  HMSRoomUpdate.roomUnmuted
  HMSRoomUpdate.serverRecordingStateUpdated
  HMSRoomUpdate.browserRecordingStateUpdated
  HMSRoomUpdate.rtmpStreamingStateUpdated
  HMSRoomUpdate.hlsStreamingStateUpdated

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

HMSSDK hmsSDK = HMSSDK()
hmsSDK.build()
hmsSDK.joinMeeting(config: this.config);

hmsSDK.leave() // to leave a room

// Turn on
hmsSDK.switchAudio(isOn: true)

// Turn off  
hmsSDK.switchAudio(isOn: false)

hmsSDK.startCapturing()

hmsSDK.stopCapturing()

hmsSDK.switchCamera()

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

HMSVideoView(track: videoTrack);

 hmsSDK.changeRole(peer: peer, roleName: roleName, forceChange: true);

// following is an example implementation of chat messaging

// to send a broadcast message
String message = 'Hello World!'
hmsSDK.sendBroadcastMessage(message);  // meeting is an instance of `HMSSDK` 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 HMSException 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});
}