allow sending username taken message

src/main/java/fr/insa/clavardator/users/PeerUser.java

@@ -166,12 +166,20 @@ public class PeerUser extends User implements Comparable<PeerUser> {
 					Log.v(this.getClass().getSimpleName(), "Received message from " + id);
 					if (msg instanceof UserInformation) {
 						assert ((UserInformation) msg).id == getId();
-						Log.v(this.getClass().getSimpleName(), "Message username: " + ((UserInformation) msg).getUsername());
-						setUsername(((UserInformation) msg).getUsername());
+						final String receivedUsername = ((UserInformation) msg).getUsername();
+						Log.v(this.getClass().getSimpleName(), "Message username: " + receivedUsername);
+						if (CurrentUser.getInstance().getUsername().equals(receivedUsername)) {
+							sendUsernameTaken(connection);
+						} else {
+							setUsername(receivedUsername);
+						}
 					} else if (msg instanceof Message) {
 						assert ((Message) msg).getRecipient().id != id;
 						Log.v(this.getClass().getSimpleName(), "Message text: " + ((Message) msg).getText());
 						history.addMessage((Message) msg);
+					} else if (msg instanceof UsernameTakenException) {
+						disconnect();
+						errorCallback.onError(new Exception("Received username already taken message"));
 					}
 				},
 				e -> {