client/src/main/java/envoy/client/data/Chat.java

@@ -21,11 +21,12 @@ import envoy.event.MessageStatusChange;
  */
 public class Chat implements Serializable {
 
-	protected final Contact recipient;
-
 	protected transient ObservableList<Message> messages = FXCollections.observableArrayList();
 
 	protected int		unreadAmount;
+	protected boolean	disabled;
+
+	protected final Contact recipient;
 
 	/**
 	 * Stores the last time an {@link envoy.event.IsTyping} event has been sent.
@@ -55,7 +56,15 @@ public class Chat implements Serializable {
 	}
 
 	@Override
-	public String toString() { return String.format("%s[recipient=%s,messages=%d]", getClass().getSimpleName(), recipient, messages.size()); }
+	public String toString() {
+		return String.format(
+			"%s[recipient=%s,messages=%d,disabled=%b]",
+			getClass().getSimpleName(),
+			recipient,
+			messages.size(),
+			disabled
+		);
+	}
 
 	/**
 	 * Generates a hash code based on the recipient.
@@ -90,7 +99,9 @@ public class Chat implements Serializable {
 	public void read(WriteProxy writeProxy) {
 		for (int i = messages.size() - 1; i >= 0; --i) {
 			final var m = messages.get(i);
-			if (m.getSenderID() == recipient.getID()) if (m.getStatus() == MessageStatus.READ) break;
+			if (m.getSenderID() == recipient.getID())
+				if (m.getStatus() == MessageStatus.READ)
+					break;
 				else {
 					m.setStatus(MessageStatus.READ);
 					writeProxy.writeMessageStatusChange(new MessageStatusChange(m));
@@ -168,4 +179,22 @@ public class Chat implements Serializable {
 	 * @since Envoy Client v0.2-beta
 	 */
 	public void lastWritingEventWasNow() { lastWritingEvent = System.currentTimeMillis(); }
+
+	/**
+	 * Determines whether messages can be sent in this chat. Should be {@code true}
+	 * i.e. for chats whose recipient deleted this client as a contact.
+	 *
+	 * @return whether this chat has been disabled
+	 * @since Envoy Client v0.3-beta
+	 */
+	public boolean isDisabled() { return disabled; }
+
+	/**
+	 * Determines whether messages can be sent in this chat. Should be true i.e. for
+	 * chats whose recipient deleted this client as a contact.
+	 *
+	 * @param disabled whether this chat should be disabled
+	 * @since Envoy Client v0.3-beta
+	 */
+	public void setDisabled(boolean disabled) { this.disabled = disabled; }
 }

client/src/main/java/envoy/client/data/GroupChat.java

@@ -25,7 +25,7 @@ public final class GroupChat extends Chat {
 	 * @param recipient the group whose members receive the messages
 	 * @since Envoy Client v0.1-beta
 	 */
-	public GroupChat(User sender, Contact recipient) {
+	public GroupChat(User sender, Group recipient) {
 		super(recipient);
 		this.sender = sender;
 	}

client/src/main/java/envoy/client/data/LocalDB.java

@@ -1,11 +1,14 @@
 package envoy.client.data;
 
+import static java.util.function.Predicate.not;
+
 import java.io.*;
 import java.nio.channels.*;
 import java.nio.file.StandardOpenOption;
 import java.time.Instant;
 import java.util.*;
 import java.util.logging.*;
+import java.util.stream.Stream;
 
 import javafx.application.Platform;
 import javafx.collections.*;
@@ -14,6 +17,7 @@ import envoy.client.event.*;
 import envoy.data.*;
 import envoy.data.Message.MessageStatus;
 import envoy.event.*;
+import envoy.event.contact.*;
 import envoy.exception.EnvoyException;
 import envoy.util.*;
 
@@ -39,6 +43,7 @@ public final class LocalDB implements EventListener {
 	private IDGenerator				idGenerator;
 	private CacheMap				cacheMap	= new CacheMap();
 	private String					authToken;
+	private boolean					contactsChanged;
 
 	// Auto save timer
 	private Timer	autoSaver;
@@ -137,6 +142,31 @@ public final class LocalDB implements EventListener {
 		userFile = new File(dbDir, user.getID() + ".db");
 		try (var in = new ObjectInputStream(new FileInputStream(userFile))) {
 			chats = FXCollections.observableList((List<Chat>) in.readObject());
+
+			// Some chats have changed and should not be overwritten by the saved values
+			if (contactsChanged) {
+				final var contacts = user.getContacts();
+
+				// Mark chats as disabled if a contact is no longer in this users contact list
+				final var changedUserChats = chats.stream()
+					.filter(not(chat -> contacts.contains(chat.getRecipient())))
+					.peek(chat -> { chat.setDisabled(true); logger.log(Level.INFO, String.format("Deleted chat with %s.", chat.getRecipient())); });
+
+				// Also update groups with a different member count
+				final var changedGroupChats = contacts.stream().filter(Group.class::isInstance).flatMap(group -> {
+					final var potentialChat = getChat(group.getID());
+					if (potentialChat.isEmpty()) return Stream.empty();
+					final var chat = potentialChat.get();
+					if (group.getContacts().size() != chat.getRecipient().getContacts().size()) {
+						logger.log(Level.INFO, "Removed one (or more) members from " + group);
+						return Stream.of(chat);
+					} else return Stream.empty();
+				});
+				Stream.concat(changedUserChats, changedGroupChats).forEach(chat -> chats.set(chats.indexOf(chat), chat));
+
+				// loadUserData can get called two (or more?) times during application lifecycle
+				contactsChanged = false;
+			}
 			cacheMap	= (CacheMap) in.readObject();
 			lastSync	= (Instant) in.readObject();
 		} finally {
@@ -163,7 +193,7 @@ public final class LocalDB implements EventListener {
 		user.getContacts()
 			.stream()
 			.filter(c -> !c.equals(user) && getChat(c.getID()).isEmpty())
-			.map(c -> c instanceof User ? new Chat(c) : new GroupChat(user, c))
+			.map(c -> c instanceof User ? new Chat(c) : new GroupChat(user, (Group) c))
 			.forEach(chats::add);
 	}
 
@@ -195,9 +225,9 @@ public final class LocalDB implements EventListener {
 	 * @throws IOException if the saving process failed
 	 * @since Envoy Client v0.3-alpha
 	 */
-	@Event(eventType = EnvoyCloseEvent.class, priority = 1000)
+	@Event(eventType = EnvoyCloseEvent.class, priority = 500)
 	private synchronized void save() {
-		EnvoyLog.getLogger(LocalDB.class).log(Level.INFO, "Saving local database...");
+		EnvoyLog.getLogger(LocalDB.class).log(Level.FINER, "Saving local database...");
 
 		// Save users
 		try {
@@ -217,33 +247,57 @@ public final class LocalDB implements EventListener {
 		}
 	}
 
-	@Event(priority = 150)
+	@Event(priority = 500)
 	private void onMessage(Message msg) { if (msg.getStatus() == MessageStatus.SENT) msg.nextStatus(); }
 
-	@Event(priority = 150)
+	@Event(priority = 500)
 	private void onGroupMessage(GroupMessage msg) {
 		// TODO: Cancel event once EventBus is updated
 		if (msg.getStatus() == MessageStatus.WAITING || msg.getStatus() == MessageStatus.READ)
 			logger.warning("The groupMessage has the unexpected status " + msg.getStatus());
 	}
 
-	@Event(priority = 150)
+	@Event(priority = 500)
 	private void onMessageStatusChange(MessageStatusChange evt) { getMessage(evt.getID()).ifPresent(msg -> msg.setStatus(evt.get())); }
 
-	@Event(priority = 150)
+	@Event(priority = 500)
 	private void onGroupMessageStatusChange(GroupMessageStatusChange evt) {
 		this.<GroupMessage>getMessage(evt.getID()).ifPresent(msg -> msg.getMemberStatuses().replace(evt.getMemberID(), evt.get()));
 	}
 
-	@Event(priority = 150)
+	@Event(priority = 500)
 	private void onUserStatusChange(UserStatusChange evt) {
 		getChat(evt.getID()).map(Chat::getRecipient).map(User.class::cast).ifPresent(u -> u.setStatus(evt.get()));
 	}
 
-	@Event(priority = 150)
+	@Event(priority = 500)
+	private void onUserOperation(UserOperation operation) {
+		final var eventUser = operation.get();
+		switch (operation.getOperationType()) {
+			case ADD:
+				Platform.runLater(() -> chats.add(0, new Chat(eventUser)));
+				break;
+			case REMOVE:
+				getChat(eventUser.getID()).ifPresent(chat -> chat.setDisabled(true));
+				break;
+		}
+	}
+
+	@Event
+	private void onGroupCreationResult(GroupCreationResult evt) {
+		final var newGroup = evt.get();
+
+		// The group creation was not successful
+		if (newGroup == null) return;
+
+		// The group was successfully created
+		else Platform.runLater(() -> chats.add(new GroupChat(user, newGroup)));
+	}
+
+	@Event(priority = 500)
 	private void onGroupResize(GroupResize evt) { getChat(evt.getGroupID()).map(Chat::getRecipient).map(Group.class::cast).ifPresent(evt::apply); }
 
-	@Event(priority = 150)
+	@Event(priority = 500)
 	private void onNameChange(NameChange evt) {
 		chats.stream().map(Chat::getRecipient).filter(c -> c.getID() == evt.getID()).findAny().ifPresent(c -> c.setName(evt.get()));
 	}
@@ -262,7 +316,7 @@ public final class LocalDB implements EventListener {
 	 *
 	 * @since Envoy Client v0.2-beta
 	 */
-	@Event(eventType = Logout.class, priority = 100)
+	@Event(eventType = Logout.class, priority = 50)
 	private void onLogout() {
 		autoSaver.cancel();
 		autoSaveRestart = true;
@@ -296,6 +350,12 @@ public final class LocalDB implements EventListener {
 	@Event(priority = 500)
 	private void onOwnStatusChange(OwnStatusChange statusChange) { user.setStatus(statusChange.get()); }
 
+	@Event(eventType = ContactsChangedSinceLastLogin.class, priority = 500)
+	private void onContactsChangedSinceLastLogin() { contactsChanged = true; }
+
+	@Event(priority = 500)
+	private void onContactDisabled(ContactDisabled event) { getChat(event.get().getID()).ifPresent(chat -> chat.setDisabled(true)); }
+
 	/**
 	 * @return a {@code Map<String, User>} of all users stored locally with their
 	 *         user names as keys

client/src/main/java/envoy/client/data/Settings.java

@@ -68,7 +68,7 @@ public final class Settings implements EventListener {
 	 * @throws IOException if an error occurs while saving the themes
 	 * @since Envoy Client v0.2-alpha
 	 */
-	@Event(eventType = EnvoyCloseEvent.class, priority = 900)
+	@Event(eventType = EnvoyCloseEvent.class)
 	private void save() {
 		EnvoyLog.getLogger(Settings.class).log(Level.INFO, "Saving settings...");
 

client/src/main/java/envoy/client/data/shortcuts/EnvoyShortcutConfig.java

@@ -6,6 +6,7 @@ import envoy.client.data.Context;
 import envoy.client.helper.ShutdownHelper;
 import envoy.client.ui.SceneContext.SceneInfo;
 import envoy.client.util.UserUtil;
+import envoy.data.User.UserStatus;
 
 /**
  * Envoy-specific implementation of the keyboard-shortcut interaction offered by
@@ -40,5 +41,25 @@ public class EnvoyShortcutConfig {
 				() -> Context.getInstance().getSceneContext().load(SceneInfo.SETTINGS_SCENE),
 				SceneInfo.SETTINGS_SCENE,
 				SceneInfo.LOGIN_SCENE);
+
+		// Add option to change to status away
+		instance.addForNotExcluded(new KeyCodeCombination(KeyCode.A, KeyCombination.CONTROL_DOWN, KeyCombination.SHIFT_DOWN),
+				() -> UserUtil.changeStatus(UserStatus.AWAY),
+				SceneInfo.LOGIN_SCENE);
+
+		// Add option to change to status busy
+		instance.addForNotExcluded(new KeyCodeCombination(KeyCode.B, KeyCombination.CONTROL_DOWN, KeyCombination.SHIFT_DOWN),
+				() -> UserUtil.changeStatus(UserStatus.BUSY),
+				SceneInfo.LOGIN_SCENE);
+
+		// Add option to change to status offline
+		instance.addForNotExcluded(new KeyCodeCombination(KeyCode.F, KeyCombination.CONTROL_DOWN, KeyCombination.SHIFT_DOWN),
+				() -> UserUtil.changeStatus(UserStatus.OFFLINE),
+				SceneInfo.LOGIN_SCENE);
+
+		// Add option to change to status online
+		instance.addForNotExcluded(new KeyCodeCombination(KeyCode.N, KeyCombination.CONTROL_DOWN, KeyCombination.SHIFT_DOWN),
+				() -> UserUtil.changeStatus(UserStatus.ONLINE),
+				SceneInfo.LOGIN_SCENE);
 	}
 }

client/src/main/java/envoy/client/event/ContactDisabled.java

@@ -0,0 +1,21 @@
+package envoy.client.event;
+
+import envoy.data.Contact;
+import envoy.event.Event;
+
+/**
+ * Signifies that the chat of a contact should be disabled.
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Client v0.3-beta
+ */
+public class ContactDisabled extends Event<Contact> {
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * @param contact the contact that should be disabled
+	 * @since Envoy Client v0.3-beta
+	 */
+	public ContactDisabled(Contact contact) { super(contact); }
+}

client/src/main/java/envoy/client/net/Client.java

@@ -61,6 +61,7 @@ public final class Client implements EventListener, Closeable {
 	 */
 	public void performHandshake(LoginCredentials credentials, CacheMap cacheMap) throws TimeoutException, IOException, InterruptedException {
 		if (online) throw new IllegalStateException("Handshake has already been performed successfully");
+		rejected = false;
 
 		// Establish TCP connection
 		logger.log(Level.FINER, String.format("Attempting connection to server %s:%d...", config.getServer(), config.getPort()));
@@ -75,8 +76,6 @@ public final class Client implements EventListener, Closeable {
 		receiver.registerProcessor(User.class, sender -> this.sender = sender);
 		receiver.registerProcessors(cacheMap.getMap());
 
-		rejected = false;
-
 		// Start receiver
 		receiver.start();
 
@@ -95,7 +94,10 @@ public final class Client implements EventListener, Closeable {
 				return;
 			}
 
-			if (System.currentTimeMillis() - start > 5000) throw new TimeoutException("Did not log in after 5 seconds");
+			if (System.currentTimeMillis() - start > 5000) {
+				rejected = true;
+				throw new TimeoutException("Did not log in after 5 seconds");
+			}
 			Thread.sleep(500);
 		}
 
@@ -146,7 +148,7 @@ public final class Client implements EventListener, Closeable {
 		logger.log(Level.FINE, "Sending " + obj);
 		try {
 			SerializationUtils.writeBytesWithLength(obj, socket.getOutputStream());
-		} catch (IOException e) {
+		} catch (final IOException e) {
 			throw new RuntimeException(e);
 		}
 	}
@@ -177,7 +179,7 @@ public final class Client implements EventListener, Closeable {
 	private void onHandshakeRejection() { rejected = true; }
 
 	@Override
-	@Event(eventType = EnvoyCloseEvent.class, priority = 800)
+	@Event(eventType = EnvoyCloseEvent.class, priority = 50)
 	public void close() {
 		if (online) {
 			logger.log(Level.INFO, "Closing connection...");

client/src/main/java/envoy/client/ui/control/GroupSizeLabel.java

@@ -16,5 +16,7 @@ public final class GroupSizeLabel extends Label {
 	 * @param recipient the group whose members to show
 	 * @since Envoy Client v0.3-beta
 	 */
-	public GroupSizeLabel(Group recipient) { super(recipient.getContacts().size() + " members"); }
+	public GroupSizeLabel(Group recipient) {
+		super(recipient.getContacts().size() + " member" + (recipient.getContacts().size() != 1 ? "s" : ""));
+	}
 }

client/src/main/java/envoy/client/ui/controller/ChatScene.java

@@ -37,7 +37,7 @@ import envoy.data.*;
 import envoy.data.Attachment.AttachmentType;
 import envoy.data.Message.MessageStatus;
 import envoy.event.*;
-import envoy.event.contact.ContactOperation;
+import envoy.event.contact.UserOperation;
 import envoy.exception.EnvoyException;
 import envoy.util.EnvoyLog;
 
@@ -91,9 +91,6 @@ public final class ChatScene implements EventListener, Restorable {
 	@FXML
 	private Label topBarStatusLabel;
 
-	@FXML
-	private MenuItem deleteContactMenuItem;
-
 	@FXML
 	private ImageView attachmentView;
 
@@ -165,7 +162,7 @@ public final class ChatScene implements EventListener, Restorable {
 
 		// Initialize message and user rendering
 		messageList.setCellFactory(MessageListCell::new);
-		chatList.setCellFactory(new ListCellFactory<>(ChatControl::new));
+		chatList.setCellFactory(ChatListCell::new);
 
 		// JavaFX provides an internal way of populating the context menu of a text
 		// area.
@@ -191,7 +188,6 @@ public final class ChatScene implements EventListener, Restorable {
 
 		// Set the design of the box in the upper-left corner
 		settingsButton.setAlignment(Pos.BOTTOM_RIGHT);
-		HBox.setHgrow(spaceBetweenUserAndSettingsButton, Priority.ALWAYS);
 		generateOwnStatusControl();
 
 		Platform.runLater(() -> {
@@ -271,18 +267,22 @@ public final class ChatScene implements EventListener, Restorable {
 	}
 
 	@Event
-	private void onContactOperation(ContactOperation operation) {
-		final var contact = operation.get();
-		switch (operation.getOperationType()) {
-			case ADD:
-				if (contact instanceof User) localDB.getUsers().put(contact.getName(), (User) contact);
-				final var chat = contact instanceof User ? new Chat(contact) : new GroupChat(client.getSender(), contact);
-				Platform.runLater(() -> ((ObservableList<Chat>) chats.getSource()).add(0, chat));
-				break;
-			case REMOVE:
-				Platform.runLater(() -> chats.getSource().removeIf(c -> c.getRecipient().equals(contact)));
-				break;
+	private void onUserOperation(UserOperation operation) {
+
+		// All ADD dependent logic resides in LocalDB
+		if (operation.getOperationType().equals(ElementOperation.REMOVE)) Platform.runLater(() -> disableChat(new ContactDisabled(operation.get())));
 	}
+
+	@Event
+	private void onGroupResize(GroupResize resize) {
+		final var chatFound = localDB.getChat(resize.getGroupID());
+		chatFound.ifPresent(chat -> Platform.runLater(() -> {
+			chatList.refresh();
+
+			// Update the top-bar status label if all conditions apply
+			if (currentChat != null && currentChat.getRecipient().equals(chat.getRecipient())) topBarStatusLabel
+				.setText(chat.getRecipient().getContacts().size() + " member" + (currentChat.getRecipient().getContacts().size() != 1 ? "s" : ""));
+		}));
 	}
 
 	@Event(eventType = NoAttachments.class)
@@ -298,8 +298,8 @@ public final class ChatScene implements EventListener, Restorable {
 		});
 	}
 
-	@Event
-	private void onGroupCreationResult(GroupCreationResult result) { Platform.runLater(() -> newGroupButton.setDisable(!result.get())); }
+	@Event(priority = 150)
+	private void onGroupCreationResult(GroupCreationResult result) { Platform.runLater(() -> newGroupButton.setDisable(result.get() == null)); }
 
 	@Event(eventType = ThemeChangeEvent.class)
 	private void onThemeChange() {
@@ -312,7 +312,6 @@ public final class ChatScene implements EventListener, Restorable {
 		clientProfilePic.setImage(IconUtil.loadIconThemeSensitive("user_icon", 43));
 		chatList.setCellFactory(new ListCellFactory<>(ChatControl::new));
 		messageList.setCellFactory(MessageListCell::new);
-		// TODO: cache image
 		if (currentChat != null)
 			if (currentChat.getRecipient() instanceof User) recipientProfilePic.setImage(IconUtil.loadIconThemeSensitive("user_icon", 43));
 			else recipientProfilePic.setImage(IconUtil.loadIconThemeSensitive("group_icon", 43));
@@ -332,8 +331,10 @@ public final class ChatScene implements EventListener, Restorable {
 	@FXML
 	private void chatListClicked() {
 		if (chatList.getSelectionModel().isEmpty()) return;
+		final var chat = chatList.getSelectionModel().getSelectedItem();
+		if (chat == null) return;
 
-		final var user = chatList.getSelectionModel().getSelectedItem().getRecipient();
+		final var user = chat.getRecipient();
 		if (user != null && (currentChat == null || !user.equals(currentChat.getRecipient()))) {
 
 			// LEON: JFC <===> JAVA FRIED CHICKEN <=/=> Java Foundation Classes
@@ -345,7 +346,6 @@ public final class ChatScene implements EventListener, Restorable {
 			final var scrollIndex = messageList.getItems().size() - currentChat.getUnreadAmount();
 			messageList.scrollTo(scrollIndex);
 			logger.log(Level.FINEST, "Loading chat with " + user + " at index " + scrollIndex);
-			deleteContactMenuItem.setText("Delete " + user.getName());
 
 			// Read the current chat
 			currentChat.read(writeProxy);
@@ -363,20 +363,28 @@ public final class ChatScene implements EventListener, Restorable {
 			remainingChars
 				.setText(String.format("remaining chars: %d/%d", MAX_MESSAGE_LENGTH - messageTextArea.getText().length(), MAX_MESSAGE_LENGTH));
 		}
-		messageTextArea.setDisable(currentChat == null || postingPermanentlyDisabled);
-		voiceButton.setDisable(!recorder.isSupported());
-		attachmentButton.setDisable(false);
+
+		// Enable or disable the necessary UI controls
+		final var chatEditable = currentChat == null || currentChat.isDisabled();
+		messageTextArea.setDisable(chatEditable || postingPermanentlyDisabled);
+		voiceButton.setDisable(!recorder.isSupported() || chatEditable);
+		attachmentButton.setDisable(chatEditable);
 		chatList.refresh();
 
+		// Design the top bar
 		if (currentChat != null) {
 			topBarContactLabel.setText(currentChat.getRecipient().getName());
+			topBarContactLabel.setVisible(true);
+			topBarStatusLabel.setVisible(true);
 			if (currentChat.getRecipient() instanceof User) {
 				final var status = ((User) currentChat.getRecipient()).getStatus().toString();
 				topBarStatusLabel.setText(status);
+				topBarStatusLabel.getStyleClass().clear();
 				topBarStatusLabel.getStyleClass().add(status.toLowerCase());
 				recipientProfilePic.setImage(IconUtil.loadIconThemeSensitive("user_icon", 43));
 			} else {
-				topBarStatusLabel.setText(currentChat.getRecipient().getContacts().size() + " members");
+				topBarStatusLabel.setText(currentChat.getRecipient().getContacts().size() + " member"
+						+ (currentChat.getRecipient().getContacts().size() != 1 ? "s" : ""));
 				topBarStatusLabel.getStyleClass().clear();
 				recipientProfilePic.setImage(IconUtil.loadIconThemeSensitive("group_icon", 43));
 			}
@@ -386,7 +394,6 @@ public final class ChatScene implements EventListener, Restorable {
 			clip.setArcHeight(43);
 			clip.setArcWidth(43);
 			recipientProfilePic.setClip(clip);
-
 			messageSearchButton.setVisible(true);
 		}
 	}
@@ -665,9 +672,9 @@ public final class ChatScene implements EventListener, Restorable {
 			Platform.runLater(() -> {
 				chats.getSource().remove(currentChat);
 				((ObservableList<Chat>) chats.getSource()).add(0, currentChat);
-				chatList.getSelectionModel().select(0);
 				localDB.getChats().remove(currentChat);
 				localDB.getChats().add(0, currentChat);
+				chatList.getSelectionModel().select(0);
 			});
 			scrollToMessageListEnd();
 
@@ -712,7 +719,8 @@ public final class ChatScene implements EventListener, Restorable {
 	 * @since Envoy Client v0.1-beta
 	 */
 	private void updateAttachmentView(boolean visible) {
-		if (!attachmentView.getImage().equals(DEFAULT_ATTACHMENT_VIEW_IMAGE)) attachmentView.setImage(DEFAULT_ATTACHMENT_VIEW_IMAGE);
+		if (!(attachmentView.getImage() == null || attachmentView.getImage().equals(DEFAULT_ATTACHMENT_VIEW_IMAGE)))
+			attachmentView.setImage(DEFAULT_ATTACHMENT_VIEW_IMAGE);
 		attachmentView.setVisible(visible);
 	}
 
@@ -727,14 +735,59 @@ public final class ChatScene implements EventListener, Restorable {
 			// Else prepend it to the HBox children
 			final var ownUserControl = new ContactControl(localDB.getUser());
 			ownUserControl.setAlignment(Pos.CENTER_LEFT);
+			HBox.setHgrow(ownUserControl, Priority.NEVER);
 			ownContactControl.getChildren().add(0, ownUserControl);
 		}
 	}
 
-	// Context menu actions
+	/**
+	 * Redesigns the UI when the {@link Chat} of the given contact has been marked
+	 * as disabled.
+	 *
+	 * @param event the contact whose chat got disabled
+	 * @since Envoy Client v0.3-beta
+	 */
+	@Event
+	public void disableChat(ContactDisabled event) {
+		chatList.refresh();
+		final var recipient = event.get();
 
-	@FXML
-	private void deleteContact() { try {} catch (final NullPointerException e) {} }
+		// Decrement member count for groups
+		if (recipient instanceof Group)
+			topBarStatusLabel.setText(recipient.getContacts().size() + " member" + (recipient.getContacts().size() != 1 ? "s" : ""));
+		if (currentChat != null && currentChat.getRecipient().equals(recipient)) {
+			messageTextArea.setDisable(true);
+			voiceButton.setDisable(true);
+			attachmentButton.setDisable(true);
+			pendingAttachment = null;
+			messageList.getStyleClass().clear();
+			messageList.getStyleClass().add("disabled-chat");
+		}
+	}
+
+	/**
+	 * Resets every component back to its inital state before a chat was selected.
+	 *
+	 * @since Envoy Client v0.3-beta
+	 */
+	public void resetState() {
+		currentChat = null;
+		chatList.getSelectionModel().clearSelection();
+		messageList.getItems().clear();
+		messageTextArea.setDisable(true);
+		attachmentView.setImage(null);
+		topBarContactLabel.setVisible(false);
+		topBarStatusLabel.setVisible(false);
+		messageSearchButton.setVisible(false);
+		messageTextArea.clear();
+		messageTextArea.setDisable(true);
+		attachmentButton.setDisable(true);
+		voiceButton.setDisable(true);
+		remainingChars.setVisible(false);
+		pendingAttachment = null;
+		recipientProfilePic.setImage(null);
+		if (recorder.isRecording()) recorder.cancel();
+	}
 
 	@FXML
 	private void copyAndPostMessage() {

client/src/main/java/envoy/client/ui/controller/ContactSearchTab.java

@@ -63,7 +63,7 @@ public class ContactSearchTab implements EventListener {
 	}
 
 	@Event
-	private void onContactOperation(ContactOperation operation) {
+	private void onUserOperation(UserOperation operation) {
 		final var contact = operation.get();
 		if (operation.getOperationType() == ElementOperation.ADD) Platform.runLater(() -> {
 			userList.getItems().remove(contact);
@@ -96,7 +96,7 @@ public class ContactSearchTab implements EventListener {
 	}
 
 	/**
-	 * Sends an {@link ContactOperation} for the selected user to the
+	 * Sends an {@link UserOperation} for the selected user to the
 	 * server.
 	 *
 	 * @since Envoy Client v0.1-beta
@@ -114,7 +114,7 @@ public class ContactSearchTab implements EventListener {
 	private void addAsContact() {
 
 		// Sends the event to the server
-		final var event = new ContactOperation(currentlySelectedUser, ElementOperation.ADD);
+		final var event = new UserOperation(currentlySelectedUser, ElementOperation.ADD);
 		client.send(event);
 
 		// Removes the chosen user and updates the UI
@@ -124,5 +124,8 @@ public class ContactSearchTab implements EventListener {
 	}
 
 	@FXML
-	private void backButtonClicked() { eventBus.dispatch(new BackEvent()); }
+	private void backButtonClicked() {
+		searchBar.setText("");
+		eventBus.dispatch(new BackEvent());
+	}
 }

client/src/main/java/envoy/client/ui/controller/GroupCreationTab.java

@@ -16,7 +16,7 @@ import envoy.client.ui.control.*;
 import envoy.client.ui.listcell.ListCellFactory;
 import envoy.data.*;
 import envoy.event.GroupCreation;
-import envoy.event.contact.ContactOperation;
+import envoy.event.contact.UserOperation;
 import envoy.util.Bounds;
 
 import dev.kske.eventbus.*;
@@ -82,7 +82,7 @@ public class GroupCreationTab implements EventListener {
 				.map(User.class::cast)
 				.collect(Collectors.toList()));
 		resizeQuickSelectSpace(0);
-		quickSelectList.addEventFilter(MouseEvent.MOUSE_PRESSED, evt -> evt.consume());
+		quickSelectList.addEventFilter(MouseEvent.MOUSE_PRESSED, MouseEvent::consume);
 	}
 
 	/**
@@ -234,11 +234,11 @@ public class GroupCreationTab implements EventListener {
 	}
 
 	@Event
-	private void onContactOperation(ContactOperation operation) {
-		if (operation.get() instanceof User) Platform.runLater(() -> {
+	private void onUserOperation(UserOperation operation) {
+		Platform.runLater(() -> {
 			switch (operation.getOperationType()) {
 				case ADD:
-					userList.getItems().add((User) operation.get());
+					userList.getItems().add(operation.get());
 					break;
 				case REMOVE:
 					userList.getItems().removeIf(operation.get()::equals);

client/src/main/java/envoy/client/ui/listcell/AbstractListCell.java

@@ -33,6 +33,7 @@ public abstract class AbstractListCell<T, U extends Node> extends ListCell<T> {
 			setGraphic(renderItem(item));
 		} else {
 			setGraphic(null);
+			setCursor(Cursor.DEFAULT);
 		}
 	}
 

client/src/main/java/envoy/client/ui/listcell/ChatListCell.java

@@ -0,0 +1,46 @@
+package envoy.client.ui.listcell;
+
+import javafx.scene.control.*;
+
+import envoy.client.data.*;
+import envoy.client.net.Client;
+import envoy.client.ui.control.ChatControl;
+import envoy.client.util.UserUtil;
+import envoy.data.User;
+
+/**
+ * A list cell containing chats represented as chat controls.
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Client v0.3-beta
+ */
+public class ChatListCell extends AbstractListCell<Chat, ChatControl> {
+
+	private static final Client client = Context.getInstance().getClient();
+
+	/**
+	 * @param listView the list view inside of which the cell will be displayed
+	 * @since Envoy Client v0.3-beta
+	 */
+	public ChatListCell(ListView<? extends Chat> listView) { super(listView); }
+
+	@Override
+	protected ChatControl renderItem(Chat chat) {
+		if (client.isOnline()) {
+			final var	menu		= new ContextMenu();
+			final var	removeMI	= new MenuItem();
+			removeMI.setText(
+					chat.isDisabled() ? "Delete " : chat.getRecipient() instanceof User ? "Block " : "Leave group " + chat.getRecipient().getName());
+			removeMI.setOnAction(
+					chat.isDisabled() ? e -> UserUtil.deleteContact(chat.getRecipient()) : e -> UserUtil.disableContact(chat.getRecipient()));
+			menu.getItems().add(removeMI);
+			setContextMenu(menu);
+		} else setContextMenu(null);
+
+		// TODO: replace with icon in ChatControl
+		final var chatControl = new ChatControl(chat);
+		if (chat.isDisabled()) chatControl.getStyleClass().add("disabled-chat");
+		else chatControl.getStyleClass().remove("disabled-chat");
+		return chatControl;
+	}
+}

client/src/main/java/envoy/client/util/UserUtil.java

@@ -1,6 +1,6 @@
 package envoy.client.util;
 
-import java.util.logging.Level;
+import java.util.logging.*;
 
 import javafx.scene.control.Alert;
 import javafx.scene.control.Alert.AlertType;
@@ -9,8 +9,11 @@ import envoy.client.data.Context;
 import envoy.client.event.*;
 import envoy.client.helper.*;
 import envoy.client.ui.SceneContext.SceneInfo;
+import envoy.client.ui.controller.ChatScene;
+import envoy.data.*;
 import envoy.data.User.UserStatus;
-import envoy.event.UserStatusChange;
+import envoy.event.*;
+import envoy.event.contact.UserOperation;
 import envoy.util.EnvoyLog;
 
 import dev.kske.eventbus.EventBus;
@@ -23,6 +26,9 @@ import dev.kske.eventbus.EventBus;
  */
 public final class UserUtil {
 
+	private static final Context	context	= Context.getInstance();
+	private static final Logger		logger	= EnvoyLog.getLogger(UserUtil.class);
+
 	private UserUtil() {}
 
 	/**
@@ -40,7 +46,8 @@ public final class UserUtil {
 			EnvoyLog.getLogger(ShutdownHelper.class).log(Level.INFO, "A logout was requested");
 			EventBus.getInstance().dispatch(new EnvoyCloseEvent());
 			EventBus.getInstance().dispatch(new Logout());
-			Context.getInstance().getSceneContext().load(SceneInfo.LOGIN_SCENE);
+			context.getSceneContext().load(SceneInfo.LOGIN_SCENE);
+			logger.log(Level.INFO, "A logout occurred.");
 		});
 	}
 
@@ -54,11 +61,56 @@ public final class UserUtil {
 	public static void changeStatus(UserStatus newStatus) {
 
 		// Sending the already active status is a valid action
-		if (newStatus.equals(Context.getInstance().getLocalDB().getUser().getStatus())) return;
+		if (newStatus.equals(context.getLocalDB().getUser().getStatus())) return;
 		else {
 			EventBus.getInstance().dispatch(new OwnStatusChange(newStatus));
-			if (Context.getInstance().getClient().isOnline())
-				Context.getInstance().getClient().send(new UserStatusChange(Context.getInstance().getLocalDB().getUser().getID(), newStatus));
+			if (context.getClient().isOnline()) context.getClient().send(new UserStatusChange(context.getLocalDB().getUser().getID(), newStatus));
+			logger.log(Level.INFO, "A manual status change occurred.");
+		}
+	}
+
+	/**
+	 * Removes the given contact.
+	 *
+	 * @param block the contact that should be removed
+	 * @since Envoy Client v0.3-beta
+	 */
+	public static void disableContact(Contact block) {
+		if (!context.getClient().isOnline() || block == null) return;
+		else {
+			final var alert = new Alert(AlertType.CONFIRMATION);
+			alert.setContentText("Are you sure you want to " + (block instanceof User ? "block " : "leave group ") + block.getName() + "?");
+			AlertHelper.confirmAction(alert, () -> {
+				final var isUser = block instanceof User;
+				context.getClient()
+					.send(isUser ? new UserOperation((User) block, ElementOperation.REMOVE)
+							: new GroupResize(context.getLocalDB().getUser(), (Group) block, ElementOperation.REMOVE));
+				if (!isUser) block.getContacts().remove(context.getLocalDB().getUser());
+				EventBus.getInstance().dispatch(new ContactDisabled(block));
+				logger.log(Level.INFO, isUser ? "A user was blocked." : "The user left a group.");
+			});
+		}
+	}
+
+	/**
+	 * Deletes the given contact with all his messages entirely.
+	 *
+	 * @param delete the contact to delete
+	 * @since Envoy Client v0.3-beta
+	 */
+	public static void deleteContact(Contact delete) {
+		if (delete == null) return;
+		else {
+			final var alert = new Alert(AlertType.CONFIRMATION);
+			alert.setContentText("Are you sure you want to delete " + delete.getName()
+					+ " entirely? All messages with this contact will be deleted. This action cannot be undone.");
+			AlertHelper.confirmAction(alert, () -> {
+				context.getLocalDB().getUsers().remove(delete.getName());
+				context.getLocalDB().getChats().removeIf(chat -> chat.getRecipient().equals(delete));
+				if (context.getSceneContext().getController() instanceof ChatScene)
+					((ChatScene) context.getSceneContext().getController()).resetState();
+				logger.log(Level.INFO, "A contact with all his messages was deleted.");
+			});
 		}
 	}
 }

client/src/main/resources/css/base.css

@@ -140,19 +140,24 @@
 .tab-pane {
     -fx-tab-max-height: 0.0 ;
 }
+
 .tab-pane .tab-header-area {
     visibility: hidden ;
     -fx-padding: -20.0 0.0 0.0 0.0;
 }
 
+.disabled-chat {
+	-fx-background-color: #0000FF;
+}
+
 #quick-select-list .scroll-bar:horizontal{
-	-fx-pref-height: 0;
-	-fx-max-height: 0;
-	-fx-min-height: 0; 
+	-fx-pref-height: 0.0;
+	-fx-max-height: 0.0;
+	-fx-min-height: 0.0; 
 }
 
 #quick-select-list .scroll-bar:vertical{
-	-fx-pref-width: 0;
-	-fx-max-width: 0;
-	-fx-min-width: 0; 
+	-fx-pref-width: 0.0;
+	-fx-max-width: 0.0;
+	-fx-min-width: 0.0; 
 }

client/src/main/resources/fxml/ChatScene.fxml

@@ -126,15 +126,6 @@
 										<ListView id="chat-list" fx:id="chatList"
 											focusTraversable="false" onMouseClicked="#chatListClicked"
 											prefWidth="316.0" VBox.vgrow="ALWAYS">
-											<contextMenu>
-												<ContextMenu anchorLocation="CONTENT_TOP_LEFT">
-													<items>
-														<MenuItem fx:id="deleteContactMenuItem"
-															mnemonicParsing="false" onAction="#deleteContact"
-															text="Delete" />
-													</items>
-												</ContextMenu>
-											</contextMenu>
 											<padding>
 												<Insets bottom="5.0" left="5.0" right="2.0" top="5.0" />
 											</padding>
@@ -167,7 +158,7 @@
 				<HBox id="transparent-background" fx:id="ownContactControl">
 					<children>
 						<Region id="transparent-background" prefWidth="120"
-							fx:id="spaceBetweenUserAndSettingsButton" />
+							fx:id="spaceBetweenUserAndSettingsButton" HBox.hgrow="ALWAYS" />
 						<Button fx:id="settingsButton" mnemonicParsing="false"
 							onAction="#settingsButtonClicked" prefHeight="30.0"
 							prefWidth="30.0" text="" alignment="CENTER">

common/src/main/java/envoy/event/GroupCreation.java

@@ -17,14 +17,14 @@ public final class GroupCreation extends Event<String> {
 	private static final long serialVersionUID = 0L;
 
 	/**
-	 * @param value            the name of this group at creation time
+	 * @param name             the name of this group at creation time
 	 * @param initialMemberIDs the IDs of all {@link User}s that should be group
 	 *                         members from the beginning on (excluding the creator
 	 *                         of this group)
 	 * @since Envoy Common v0.1-beta
 	 */
-	public GroupCreation(String value, Set<Long> initialMemberIDs) {
-		super(value);
+	public GroupCreation(String name, Set<Long> initialMemberIDs) {
+		super(name);
 		this.initialMemberIDs = initialMemberIDs != null ? initialMemberIDs : new HashSet<>();
 	}
 

common/src/main/java/envoy/event/GroupCreationResult.java

@@ -1,5 +1,7 @@
 package envoy.event;
 
+import envoy.data.Group;
+
 /**
  * Used to communicate with a client that his request to create a group might
  * have been rejected as it might be disabled on his current server.
@@ -7,15 +9,23 @@ package envoy.event;
  * @author Leon Hofmeister
  * @since Envoy Common v0.2-beta
  */
-public class GroupCreationResult extends Event<Boolean> {
+public class GroupCreationResult extends Event<Group> {
 
 	private static final long serialVersionUID = 1L;
 
 	/**
-	 * Creates a new {@code GroupCreationResult}.
+	 * Creates a new {@code GroupCreationResult} that implies the failure of this
+	 * {@link GroupCreationResult}.
 	 *
-	 * @param success whether the GroupCreation sent before was successful
 	 * @since Envoy Common v0.2-beta
 	 */
-	public GroupCreationResult(boolean success) { super(success); }
+	public GroupCreationResult() { super(null); }
+
+	/**
+	 * Creates a new {@code GroupCreationResult}.
+	 *
+	 * @param resultGroup the group the server created
+	 * @since Envoy Common v0.2-beta
+	 */
+	public GroupCreationResult(Group resultGroup) { super(resultGroup); }
 }

common/src/main/java/envoy/event/GroupResize.java

@@ -34,11 +34,10 @@ public final class GroupResize extends Event<User> {
 	public GroupResize(User user, Group group, ElementOperation operation) {
 		super(user);
 		this.operation = operation;
-		if (group.getContacts().contains(user)) {
-			if (operation.equals(ADD))
+		final var contained = group.getContacts().contains(user);
+		if (contained && operation.equals(ADD))
 			throw new IllegalArgumentException(String.format("Cannot add %s to %s!", user, group));
-		} else if (operation.equals(REMOVE))
-			throw new IllegalArgumentException(String.format("Cannot remove %s from %s!", user, group));
+		else if (operation.equals(REMOVE) && !contained) throw new IllegalArgumentException(String.format("Cannot remove %s from %s!", user, group));
 		groupID = group.getID();
 	}
 
@@ -72,5 +71,5 @@ public final class GroupResize extends Event<User> {
 	}
 
 	@Override
-	public String toString() { return String.format("GroupResize[userid=%d,groupid=%d,operation=%s]", get(), groupID, operation); }
+	public String toString() { return String.format("GroupResize[user=%s,groupid=%d,operation=%s]", get(), groupID, operation); }
 }

common/src/main/java/envoy/event/contact/ContactsChangedSinceLastLogin.java

@@ -0,0 +1,15 @@
+package envoy.event.contact;
+
+import envoy.event.Event.Valueless;
+
+/**
+ * Conveys that either a direct contact or a group member has been deleted while
+ * the user has been offline.
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.3-beta
+ */
+public class ContactsChangedSinceLastLogin extends Valueless {
+
+	private static final long serialVersionUID = 1L;
+}

common/src/main/java/envoy/event/contact/UserOperation.java

@@ -1,35 +1,38 @@
 package envoy.event.contact;
 
-import envoy.data.Contact;
+import envoy.data.User;
 import envoy.event.*;
 
 /**
  * Signifies the modification of a contact list.
  *
  * @author Maximilian Käfer
- * @since Envoy Common v0.2-alpha
+ * @since Envoy Common v0.3-beta
  */
-public final class ContactOperation extends Event<Contact> {
+public final class UserOperation extends Event<User> {
 
 	private final ElementOperation operationType;
 
 	private static final long serialVersionUID = 1L;
 
 	/**
-	 * Initializes a {@link ContactOperation}.
+	 * Initializes a {@link UserOperation}.
 	 *
 	 * @param contact       the user on which the operation is performed
 	 * @param operationType the type of operation to perform
-	 * @since Envoy Common v0.2-alpha
+	 * @since Envoy Common v0.3-beta
 	 */
-	public ContactOperation(Contact contact, ElementOperation operationType) {
+	public UserOperation(User contact, ElementOperation operationType) {
 		super(contact);
 		this.operationType = operationType;
 	}
 
 	/**
 	 * @return the type of operation to perform
-	 * @since Envoy Common v0.2-alpha
+	 * @since Envoy Common v0.3-beta
 	 */
 	public ElementOperation getOperationType() { return operationType; }
+
+	@Override
+	public String toString() { return String.format("%s[contact=%s, operation=%s]", UserOperation.class.getSimpleName(), value, operationType); }
 }

server/src/main/java/envoy/server/Startup.java

@@ -49,9 +49,10 @@ public final class Startup {
 						new MessageStatusChangeProcessor(),
 						new GroupMessageStatusChangeProcessor(),
 						new UserStatusChangeProcessor(),
+						new GroupResizeProcessor(),
 						new IDGeneratorRequestProcessor(),
 						new UserSearchProcessor(),
-						new ContactOperationProcessor(),
+						new UserOperationProcessor(),
 						new IsTypingProcessor(),
 						new NameChangeProcessor(),
 						new ProfilePicChangeProcessor(),

server/src/main/java/envoy/server/data/Message.java

@@ -51,11 +51,11 @@ public class Message {
 	@Id
 	protected long id;
 
-	@ManyToOne
+	@ManyToOne(cascade = CascadeType.REMOVE)
 	@JoinColumn
 	protected User sender;
 
-	@ManyToOne
+	@ManyToOne(cascade = CascadeType.REMOVE)
 	@JoinColumn
 	protected Contact recipient;
 

server/src/main/java/envoy/server/data/PersistenceManager.java

@@ -2,11 +2,13 @@ package envoy.server.data;
 
 import java.time.Instant;
 import java.util.List;
+import java.util.logging.Level;
 
 import javax.persistence.*;
 
 import envoy.data.User.UserStatus;
 import envoy.server.net.ConnectionManager;
+import envoy.util.EnvoyLog;
 
 /**
  * Contains operations used for persistence.
@@ -97,7 +99,15 @@ public final class PersistenceManager {
 	 * @param contact the {@link Contact} to delete
 	 * @since Envoy Server Standalone v0.1-alpha
 	 */
-	public void deleteContact(Contact contact) { remove(contact); }
+	public void deleteContact(Contact contact) {
+		transaction(() -> {
+
+			// Remove this contact from the contact list of his contacts
+			for (final var remainingContact : contact.getContacts())
+				remainingContact.getContacts().remove(contact);
+		});
+		remove(contact);
+	}
 
 	/**
 	 * Deletes a {@link Message} in the database.
@@ -227,17 +237,52 @@ public final class PersistenceManager {
 	 * @since Envoy Server Standalone v0.1-alpha
 	 */
 	public void addContactBidirectional(long contactID1, long contactID2) {
+		addContactBidirectional(getContactByID(contactID1), getContactByID(contactID2));
+	}
 
-		// Get users by ID
-		final var	c1	= getContactByID(contactID1);
-		final var	c2	= getContactByID(contactID2);
+	/**
+	 * Adds a contact to the contact list of another contact and vice versa.
+	 *
+	 * @param contact1 the first contact
+	 * @param contact2 the second contact
+	 * @since Envoy Server v0.3-beta
+	 */
+	public void addContactBidirectional(Contact contact1, Contact contact2) {
 
-		// Add users to each others contact lists
-		c1.getContacts().add(c2);
-		c2.getContacts().add(c1);
+		// Add users to each others contact list
+		contact1.getContacts().add(contact2);
+		contact2.getContacts().add(contact1);
 
 		// Synchronize changes with the database
-		transaction(() -> { entityManager.merge(c1); entityManager.merge(c2); });
+		transaction(() -> { entityManager.merge(contact1); entityManager.merge(contact2); });
+	}
+
+	/**
+	 * Removes a contact from the contact list of another contact and vice versa.
+	 *
+	 * @param contactID1 the ID of the first contact
+	 * @param contactID2 the ID of the second contact
+	 * @since Envoy Server v0.3-beta
+	 */
+	public void removeContactBidirectional(long contactID1, long contactID2) {
+		removeContactBidirectional(getContactByID(contactID1), getContactByID(contactID2));
+	}
+
+	/**
+	 * Removes a contact from the contact list of another contact and vice versa.
+	 *
+	 * @param contact1 the first contact
+	 * @param contact2 the second contact
+	 * @since Envoy Server v0.3-beta
+	 */
+	public void removeContactBidirectional(Contact contact1, Contact contact2) {
+
+		// Remove users from each others contact list
+		contact1.getContacts().remove(contact2);
+		contact2.getContacts().remove(contact1);
+
+		// Synchronize changes with the database
+		transaction(() -> { entityManager.merge(contact1); entityManager.merge(contact2); });
 	}
 
 	/**
@@ -277,6 +322,14 @@ public final class PersistenceManager {
 				entityManagerRelatedAction.run();
 				transaction.commit();
 			}
+		} catch (final RollbackException e2) {
+
+			// Apparently a major problem exists. Discard faulty transaction and then go on.
+			if (transaction.isActive()) {
+				transaction.rollback();
+				EnvoyLog.getLogger(PersistenceManager.class)
+					.log(Level.SEVERE, "Could not perform transaction, hence discarding it. It's likely that a serious issue exists.");
+			} else throw e2;
 		}
 	}
 }

server/src/main/java/envoy/server/data/User.java

@@ -70,6 +70,9 @@ public final class User extends Contact {
 	@Column(name = "last_seen")
 	private Instant lastSeen;
 
+	@Column(name = "latest_contact_deletion")
+	private Instant latestContactDeletion;
+
 	private UserStatus status;
 
 	@Override
@@ -140,4 +143,16 @@ public final class User extends Contact {
 	 * @since Envoy Server Standalone v0.1-alpha
 	 */
 	public void setStatus(UserStatus status) { this.status = status; }
+
+	/**
+	 * @return the latestContactDeletion
+	 * @since Envoy Server v0.3-beta
+	 */
+	public Instant getLatestContactDeletion() { return latestContactDeletion; }
+
+	/**
+	 * @param latestContactDeletion the latestContactDeletion to set
+	 * @since Envoy Server v0.3-beta
+	 */
+	public void setLatestContactDeletion(Instant latestContactDeletion) { this.latestContactDeletion = latestContactDeletion; }
 }

server/src/main/java/envoy/server/processors/ContactOperationProcessor.java

@@ -1,39 +0,0 @@
-package envoy.server.processors;
-
-import java.util.logging.Logger;
-
-import envoy.event.ElementOperation;
-import envoy.event.contact.ContactOperation;
-import envoy.server.data.PersistenceManager;
-import envoy.server.net.*;
-import envoy.util.EnvoyLog;
-
-/**
- * @author Kai S. K. Engelbart
- * @since Envoy Server Standalone v0.1-alpha
- */
-public final class ContactOperationProcessor implements ObjectProcessor<ContactOperation> {
-
-	private static final ConnectionManager connectionManager = ConnectionManager.getInstance();
-	private static final Logger				logger				= EnvoyLog.getLogger(ContactOperationProcessor.class);
-
-	@Override
-	public void process(ContactOperation evt, long socketId, ObjectWriteProxy writeProxy) {
-		switch (evt.getOperationType()) {
-			case ADD:
-				final long userID = ConnectionManager.getInstance().getUserIDBySocketID(socketId);
-				final long contactId = evt.get().getID();
-
-				logger.fine(String.format("Adding user %s to the contact list of user %d.%n", evt.get(), userID));
-				PersistenceManager.getInstance().addContactBidirectional(userID, contactId);
-
-				// Notify the contact if online
-				if (ConnectionManager.getInstance().isOnline(contactId))
-					writeProxy.write(connectionManager.getSocketID(contactId),
-							new ContactOperation(PersistenceManager.getInstance().getUserByID(userID).toCommon(), ElementOperation.ADD));
-				break;
-			default:
-				logger.warning(String.format("Received %s with an unsupported operation.", evt));
-		}
-	}
-}

server/src/main/java/envoy/server/processors/GroupCreationProcessor.java

@@ -5,8 +5,7 @@ import static envoy.server.Startup.config;
 import java.util.HashSet;
 
 import envoy.event.*;
-import envoy.event.contact.ContactOperation;
-import envoy.server.data.*;
+import envoy.server.data.PersistenceManager;
 import envoy.server.net.*;
 
 /**
@@ -21,21 +20,19 @@ public final class GroupCreationProcessor implements ObjectProcessor<GroupCreati
 	@Override
 	public void process(GroupCreation groupCreation, long socketID, ObjectWriteProxy writeProxy) {
 		// Don't allow the creation of groups if manually disabled
-		writeProxy.write(socketID, new GroupCreationResult(config.isGroupSupportEnabled()));
-		if (!config.isGroupSupportEnabled()) return;
+		if (!config.isGroupSupportEnabled()) {
+			writeProxy.write(socketID, new GroupCreationResult());
+			return;
+		}
 		final envoy.server.data.Group group = new envoy.server.data.Group();
 		group.setName(groupCreation.get());
 		group.setContacts(new HashSet<>());
-		groupCreation.getInitialMemberIDs().stream().map(persistenceManager::getUserByID).forEach(group.getContacts()::add);
-		group.getContacts().add(persistenceManager.getContactByID(connectionManager.getUserIDBySocketID(socketID)));
-		group.getContacts().forEach(c -> c.getContacts().add(group));
-		group.getContacts().add(persistenceManager.getUserByID(connectionManager.getUserIDBySocketID(socketID)));
 		persistenceManager.addContact(group);
-		group.getContacts()
+		groupCreation.getInitialMemberIDs()
 			.stream()
-			.map(Contact::getID)
-			.filter(connectionManager::isOnline)
-			.map(connectionManager::getSocketID)
-			.forEach(memberSocketID -> writeProxy.write(memberSocketID, new ContactOperation(group.toCommon(), ElementOperation.ADD)));
+			.map(persistenceManager::getUserByID)
+			.forEach(member -> persistenceManager.addContactBidirectional(member, group));
+		persistenceManager.addContactBidirectional(persistenceManager.getUserByID(connectionManager.getUserIDBySocketID(socketID)), group);
+		writeProxy.writeToOnlineContacts(group.getContacts(), new GroupCreationResult(group.toCommon()));
 	}
 }

server/src/main/java/envoy/server/processors/GroupResizeProcessor.java

@@ -1,8 +1,12 @@
 package envoy.server.processors;
 
+import java.time.Instant;
+import java.util.logging.Level;
+
 import envoy.event.GroupResize;
 import envoy.server.data.*;
-import envoy.server.net.*;
+import envoy.server.net.ObjectWriteProxy;
+import envoy.util.EnvoyLog;
 
 /**
  * @author Maximilian Käfer
@@ -11,34 +15,37 @@ import envoy.server.net.*;
 public final class GroupResizeProcessor implements ObjectProcessor<GroupResize> {
 
 	private static final PersistenceManager persistenceManager = PersistenceManager.getInstance();
-	private static final ConnectionManager	connectionManager	= ConnectionManager.getInstance();
 
 	@Override
 	public void process(GroupResize groupResize, long socketID, ObjectWriteProxy writeProxy) {
 
 		// Acquire the group to resize from the database
-		var group = persistenceManager.getGroupByID(groupResize.getGroupID());
+		final var	group	= persistenceManager.getGroupByID(groupResize.getGroupID());
+		final var	sender	= persistenceManager.getUserByID(groupResize.get().getID());
 
 		// Perform the desired operation
 		switch (groupResize.getOperation()) {
 			case ADD:
-				group.getContacts().add(persistenceManager.getUserByID(groupResize.get().getID()));
-				break;
+				persistenceManager.addContactBidirectional(sender, group);
+				writeProxy.writeToOnlineContacts(group.getContacts(), group.toCommon());
+				return;
 			case REMOVE:
+				persistenceManager.removeContactBidirectional(sender, group);
+				sender.setLatestContactDeletion(Instant.now());
+
+				// The group has no more members and hence will be deleted
+				if (group.getContacts().isEmpty()) {
+					EnvoyLog.getLogger(GroupResizeProcessor.class).log(Level.INFO, "Deleting now empty group " + group.getName());
+					persistenceManager.deleteContact(group);
+				} else {
+
+					// Informing the other members
+					writeProxy.writeToOnlineContacts(group.getContacts(), groupResize);
+					group.getContacts().forEach(c -> ((User) c).setLatestContactDeletion(Instant.now()));
+				}
+
 				group.getContacts().remove(persistenceManager.getUserByID(groupResize.get().getID()));
-				break;
-		}
-
-		// Update the group in the database
-		persistenceManager.updateContact(group);
-
-		// Send the updated group to all of its members
-		var commonGroup = group.toCommon();
-		group.getContacts()
-			.stream()
-			.map(Contact::getID)
-			.filter(connectionManager::isOnline)
-			.map(connectionManager::getSocketID)
-			.forEach(memberSocketID -> writeProxy.write(memberSocketID, commonGroup));
+				return;
+		}
 	}
 }

server/src/main/java/envoy/server/processors/LoginCredentialProcessor.java

@@ -13,6 +13,7 @@ import javax.persistence.NoResultException;
 
 import envoy.data.LoginCredentials;
 import envoy.event.*;
+import envoy.event.contact.ContactsChangedSinceLastLogin;
 import envoy.server.data.*;
 import envoy.server.net.*;
 import envoy.server.util.*;
@@ -104,6 +105,7 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 				user.setStatus(ONLINE);
 				user.setPasswordHash(PasswordUtil.hash(credentials.getPassword()));
 				user.setContacts(new HashSet<>());
+				user.setLatestContactDeletion(Instant.EPOCH);
 				persistenceManager.addContact(user);
 				logger.info("Registered new " + user);
 			}
@@ -205,6 +207,8 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 					writeProxy.write(socketID, new MessageStatusChange(gmsgCommon));
 			}
 		}
+		// Notify the user if a contact deletion has happened since he last logged in
+		if (user.getLatestContactDeletion().isAfter(user.getLastSeen())) writeProxy.write(socketID, new ContactsChangedSinceLastLogin());
 
 		// Complete the handshake
 		writeProxy.write(socketID, user.toCommon());

server/src/main/java/envoy/server/processors/UserOperationProcessor.java

@@ -0,0 +1,52 @@
+package envoy.server.processors;
+
+import java.time.Instant;
+import java.util.logging.*;
+
+import envoy.event.ElementOperation;
+import envoy.event.contact.UserOperation;
+import envoy.server.data.PersistenceManager;
+import envoy.server.net.*;
+import envoy.util.EnvoyLog;
+
+/**
+ * @author Kai S. K. Engelbart
+ * @since Envoy Server Standalone v0.1-alpha
+ */
+public final class UserOperationProcessor implements ObjectProcessor<UserOperation> {
+
+	private static final ConnectionManager	connectionManager	= ConnectionManager.getInstance();
+	private static final Logger				logger				= EnvoyLog.getLogger(UserOperationProcessor.class);
+	private static final PersistenceManager	persistenceManager	= PersistenceManager.getInstance();
+
+	@Override
+	public void process(UserOperation evt, long socketId, ObjectWriteProxy writeProxy) {
+		final long	userID		= ConnectionManager.getInstance().getUserIDBySocketID(socketId);
+		final long	contactID	= evt.get().getID();
+		final var	sender		= persistenceManager.getUserByID(userID);
+		switch (evt.getOperationType()) {
+			case ADD:
+				logger.log(Level.FINE, String.format("Adding %s to the contact list of user %d.", evt.get(), userID));
+				persistenceManager.addContactBidirectional(userID, contactID);
+
+				// Notify the contact if online
+				if (connectionManager.isOnline(contactID))
+					writeProxy.write(connectionManager.getSocketID(contactID), new UserOperation(sender.toCommon(), ElementOperation.ADD));
+				break;
+			case REMOVE:
+
+				// Remove the relationships and notify sender if he logs in using another
+				// LocalDB
+				persistenceManager.removeContactBidirectional(userID, contactID);
+				sender.setLatestContactDeletion(Instant.now());
+
+				// Notify the removed contact on next startup(s) of this deletion
+				persistenceManager.getUserByID(contactID).setLatestContactDeletion(Instant.now());
+
+				// Notify the removed contact if online
+				if (connectionManager.isOnline(contactID))
+					writeProxy.write(connectionManager.getSocketID(contactID), new UserOperation(sender.toCommon(), ElementOperation.REMOVE));
+				break;
+		}
+	}
+}