Move Envoy Client to client/ subdirectory

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

@@ -0,0 +1,65 @@
+package envoy.client.data;
+
+import java.io.Serializable;
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.function.Consumer;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import envoy.util.EnvoyLog;
+
+/**
+ * Stores elements in a queue to process them later.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>Cache.java</strong><br>
+ * Created: <strong>6 Feb 2020</strong><br>
+ *
+ * @param <T> the type of cached elements
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.3-alpha
+ */
+public final class Cache<T> implements Consumer<T>, Serializable {
+
+	private final Queue<T>			elements	= new LinkedList<>();
+	private transient Consumer<T>	processor;
+
+	private static final Logger	logger				= EnvoyLog.getLogger(Cache.class);
+	private static final long	serialVersionUID	= 0L;
+
+	/**
+	 * Adds an element to the cache.
+	 *
+	 * @param element the element to add
+	 * @since Envoy Client v0.3-alpha
+	 */
+	@Override
+	public void accept(T element) {
+		logger.log(Level.FINE, String.format("Adding element %s to cache", element));
+		elements.offer(element);
+	}
+
+	@Override
+	public String toString() { return String.format("Cache[elements=" + elements + "]"); }
+
+	/**
+	 * Sets the processor to which cached elements are relayed.
+	 *
+	 * @param processor the processor to set
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void setProcessor(Consumer<T> processor) { this.processor = processor; }
+
+	/**
+	 * Relays all cached elements to the processor.
+	 *
+	 * @throws IllegalStateException if the processor is not initialized
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void relay() {
+		if (processor == null) throw new IllegalStateException("Processor is not defined");
+		elements.forEach(processor::accept);
+		elements.clear();
+	}
+}

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

@@ -0,0 +1,66 @@
+package envoy.client.data;
+
+import java.io.Serializable;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Stores a heterogeneous map of {@link Cache} objects with different type
+ * parameters.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>CacheMap.java</strong><br>
+ * Created: <strong>09.07.2020</strong><br>
+ * 
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.1-beta
+ */
+public final class CacheMap implements Serializable {
+
+	private final Map<Class<?>, Cache<?>> map = new HashMap<>();
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * Adds a cache to the map.
+	 * 
+	 * @param <T>   the type accepted by the cache
+	 * @param key   the class that maps to the cache
+	 * @param cache the cache to store
+	 * @since Envoy Client v0.1-beta
+	 */
+	public <T> void put(Class<T> key, Cache<T> cache) { map.put(key, cache); }
+
+	/**
+	 * Returns a cache mapped by a class.
+	 * 
+	 * @param <T> the type accepted by the cache
+	 * @param key the class that maps to the cache
+	 * @return the cache
+	 * @since Envoy Client v0.1-beta
+	 */
+	public <T> Cache<T> get(Class<T> key) { return (Cache<T>) map.get(key); }
+
+	/**
+	 * Returns a cache mapped by a class or any of its subclasses.
+	 * 
+	 * @param <T> the type accepted by the cache
+	 * @param key the class that maps to the cache
+	 * @return the cache
+	 * @since Envoy Client v0.1-beta
+	 */
+	public <T> Cache<? super T> getApplicable(Class<T> key) {
+		Cache<? super T> cache = get(key);
+		if (cache == null)
+			for (var e : map.entrySet())
+				if (e.getKey().isAssignableFrom(key))
+					cache = (Cache<? super T>) e.getValue();
+		return cache;
+	}
+
+	/**
+	 * @return the map in which the caches are stored
+	 * @since Envoy Client v0.1-beta
+	 */
+	public Map<Class<?>, Cache<?>> getMap() { return map; }
+}

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

@@ -0,0 +1,153 @@
+package envoy.client.data;
+
+import java.io.IOException;
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+import envoy.client.net.WriteProxy;
+import envoy.data.*;
+import envoy.data.Message.MessageStatus;
+import envoy.event.MessageStatusChange;
+
+/**
+ * Represents a chat between two {@link User}s
+ * as a list of {@link Message} objects.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>Chat.java</strong><br>
+ * Created: <strong>19 Oct 2019</strong><br>
+ *
+ * @author Maximilian K&auml;fer
+ * @author Leon Hofmeister
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.1-alpha
+ */
+public class Chat implements Serializable {
+
+	protected final Contact			recipient;
+	protected final List<Message>	messages	= new ArrayList<>();
+
+	protected int unreadAmount;
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * Provides the list of messages that the recipient receives.
+	 * <p>
+	 * Saves the Messages in the corresponding chat at that Point.
+	 *
+	 * @param recipient the user who receives the messages
+	 * @since Envoy Client v0.1-alpha
+	 */
+	public Chat(Contact recipient) {
+		this.recipient	= recipient;
+	}
+
+	@Override
+	public String toString() { return String.format("Chat[recipient=%s,messages=%d]", recipient, messages.size()); }
+
+	/**
+	 * Generates a hash code based on the recipient.
+	 * 
+	 * @since Envoy Client v0.1-beta
+	 */
+	@Override
+	public int hashCode() { return Objects.hash(recipient); }
+
+	/**
+	 * Tests equality to another object based on the recipient.
+	 * 
+	 * @since Envoy Client v0.1-beta
+	 */
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj) return true;
+		if (!(obj instanceof Chat)) return false;
+		Chat other = (Chat) obj;
+		return Objects.equals(recipient, other.recipient);
+	}
+
+	/**
+	 * Sets the status of all chat messages received from the recipient to
+	 * {@code READ} starting from the bottom and stopping once a read message is
+	 * found.
+	 *
+	 * @param writeProxy the write proxy instance used to notify the server about
+	 *                   the message status changes
+	 * @throws IOException if a {@link MessageStatusChange} could not be
+	 *                     delivered to the server
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void read(WriteProxy writeProxy) throws IOException {
+		for (int i = messages.size() - 1; i >= 0; --i) {
+			final Message m = messages.get(i);
+			if (m.getSenderID() == recipient.getID()) if (m.getStatus() == MessageStatus.READ) break;
+			else {
+				m.setStatus(MessageStatus.READ);
+				writeProxy.writeMessageStatusChange(new MessageStatusChange(m));
+			}
+		}
+		unreadAmount = 0;
+	}
+
+	/**
+	 * @return {@code true} if the newest message received in the chat doesn't have
+	 *         the status {@code READ}
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public boolean isUnread() { return !messages.isEmpty() && messages.get(messages.size() - 1).getStatus() != MessageStatus.READ; }
+
+	/**
+	 * Inserts a message at the correct place according to its creation date.
+	 * 
+	 * @param message the message to insert
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void insert(Message message) {
+		for (int i = messages.size() - 1; i >= 0; --i)
+			if (message.getCreationDate().isAfter(messages.get(i).getCreationDate())) {
+				messages.add(i + 1, message);
+				return;
+			}
+		messages.add(0, message);
+	}
+
+	/**
+	 * Increments the amount of unread messages.
+	 * 
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void incrementUnreadAmount() { unreadAmount++; }
+
+	/**
+	 * @return the amount of unread mesages in this chat
+	 * @since Envoy Client v0.1-beta
+	 */
+	public int getUnreadAmount() { return unreadAmount; }
+
+	/**
+	 * @return all messages in the current chat
+	 * @since Envoy Client v0.1-beta
+	 */
+	public List<Message> getMessages() { return messages; }
+
+	/**
+	 * @return the recipient of a message
+	 * @since Envoy Client v0.1-alpha
+	 */
+	public Contact getRecipient() { return recipient; }
+
+	/**
+	 * @return whether this {@link Chat} points at a {@link User}
+	 * @since Envoy Client v0.1-beta
+	 */
+	public boolean isUserChat() { return recipient instanceof User; }
+
+	/**
+	 * @return whether this {@link Chat} points at a {@link Group}
+	 * @since Envoy Client v0.1-beta
+	 */
+	public boolean isGroupChat() { return recipient instanceof Group; }
+}

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

@@ -0,0 +1,115 @@
+package envoy.client.data;
+
+import static java.util.function.Function.identity;
+
+import java.io.File;
+import java.util.logging.Level;
+
+import envoy.client.ui.Startup;
+import envoy.data.Config;
+import envoy.data.ConfigItem;
+import envoy.data.LoginCredentials;
+
+/**
+ * Implements a configuration specific to the Envoy Client with default values
+ * and convenience methods.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>ClientConfig.java</strong><br>
+ * Created: <strong>01.03.2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.1-beta
+ */
+public class ClientConfig extends Config {
+
+	private static ClientConfig config;
+
+	/**
+	 * @return the singleton instance of the client config
+	 * @since Envoy Client v0.1-beta
+	 */
+	public static ClientConfig getInstance() {
+		if (config == null) config = new ClientConfig();
+		return config;
+	}
+
+	private ClientConfig() {
+		items.put("server", new ConfigItem<>("server", "s", identity(), null, true));
+		items.put("port", new ConfigItem<>("port", "p", Integer::parseInt, null, true));
+		items.put("localDB", new ConfigItem<>("localDB", "db", File::new, new File("localDB"), true));
+		items.put("ignoreLocalDB", new ConfigItem<>("ignoreLocalDB", "nodb", Boolean::parseBoolean, false, false));
+		items.put("homeDirectory", new ConfigItem<>("homeDirectory", "h", File::new, new File(System.getProperty("user.home"), ".envoy"), true));
+		items.put("fileLevelBarrier", new ConfigItem<>("fileLevelBarrier", "fb", Level::parse, Level.CONFIG, true));
+		items.put("consoleLevelBarrier", new ConfigItem<>("consoleLevelBarrier", "cb", Level::parse, Level.FINEST, true));
+		items.put("user", new ConfigItem<>("user", "u", identity()));
+		items.put("password", new ConfigItem<>("password", "pw", identity()));
+	}
+
+	/**
+	 * @return the host name of the Envoy server
+	 * @since Envoy Client v0.1-alpha
+	 */
+	public String getServer() { return (String) items.get("server").get(); }
+
+	/**
+	 * @return the port at which the Envoy server is located on the host
+	 * @since Envoy Client v0.1-alpha
+	 */
+	public Integer getPort() { return (Integer) items.get("port").get(); }
+
+	/**
+	 * @return the local database specific to the client user
+	 * @since Envoy Client v0.1-alpha
+	 */
+	public File getLocalDB() { return (File) items.get("localDB").get(); }
+
+	/**
+	 * @return {@code true} if the local database is to be ignored
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public Boolean isIgnoreLocalDB() { return (Boolean) items.get("ignoreLocalDB").get(); }
+
+	/**
+	 * @return the directory in which all local files are saves
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public File getHomeDirectory() { return (File) items.get("homeDirectory").get(); }
+
+	/**
+	 * @return the minimal {@link Level} to log inside the log file
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public Level getFileLevelBarrier() { return (Level) items.get("fileLevelBarrier").get(); }
+
+	/**
+	 * @return the minimal {@link Level} to log inside the console
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public Level getConsoleLevelBarrier() { return (Level) items.get("consoleLevelBarrier").get(); }
+
+	/**
+	 * @return the user name
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public String getUser() { return (String) items.get("user").get(); }
+
+	/**
+	 * @return the password
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public String getPassword() { return (String) items.get("password").get(); }
+
+	/**
+	 * @return {@code true} if user name and password are set
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public boolean hasLoginCredentials() { return getUser() != null && getPassword() != null; }
+
+	/**
+	 * @return login credentials for the specified user name and password, without
+	 *         the registration option
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public LoginCredentials getLoginCredentials() { return new LoginCredentials(getUser(), getPassword(), false, Startup.VERSION); }
+}

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

@@ -0,0 +1,55 @@
+package envoy.client.data;
+
+import java.io.IOException;
+import java.time.LocalDateTime;
+
+import envoy.client.net.WriteProxy;
+import envoy.data.Contact;
+import envoy.data.GroupMessage;
+import envoy.data.Message.MessageStatus;
+import envoy.data.User;
+import envoy.event.GroupMessageStatusChange;
+
+/**
+ * Represents a chat between a user and a group
+ * as a list of messages.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>GroupChat.java</strong><br>
+ * Created: <strong>05.07.2020</strong><br>
+ * 
+ * @author Maximilian K&auml;fer
+ * @since Envoy Client v0.1-beta
+ */
+public class GroupChat extends Chat {
+
+	private final User sender;
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * @param sender    the user sending the messages
+	 * @param recipient the group whose members receive the messages
+	 * @since Envoy Client v0.1-beta
+	 */
+	public GroupChat(User sender, Contact recipient) {
+		super(recipient);
+		this.sender = sender;
+	}
+
+	@Override
+	public void read(WriteProxy writeProxy) throws IOException {
+		for (int i = messages.size() - 1; i >= 0; --i) {
+			final GroupMessage gmsg = (GroupMessage) messages.get(i);
+			if (gmsg.getSenderID() != sender.getID()) {
+				if (gmsg.getMemberStatuses().get(sender.getID()) == MessageStatus.READ) break;
+				else {
+					gmsg.getMemberStatuses().replace(sender.getID(), MessageStatus.READ);
+					writeProxy
+						.writeMessageStatusChange(new GroupMessageStatusChange(gmsg.getID(), MessageStatus.READ, LocalDateTime.now(), sender.getID()));
+				}
+			}
+		}
+		unreadAmount = 0;
+	}
+}

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

@@ -0,0 +1,205 @@
+package envoy.client.data;
+
+import java.util.*;
+
+import envoy.data.*;
+import envoy.event.GroupResize;
+import envoy.event.MessageStatusChange;
+import envoy.event.NameChange;
+
+/**
+ * Stores information about the current {@link User} and their {@link Chat}s.
+ * For message ID generation a {@link IDGenerator} is stored as well.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>LocalDB.java</strong><br>
+ * Created: <strong>3 Feb 2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.3-alpha
+ */
+public abstract class LocalDB {
+
+	protected User					user;
+	protected Map<String, Contact>	users		= new HashMap<>();
+	protected List<Chat>			chats		= new ArrayList<>();
+	protected IDGenerator			idGenerator;
+	protected CacheMap				cacheMap	= new CacheMap();
+
+	{
+		cacheMap.put(Message.class, new Cache<>());
+		cacheMap.put(MessageStatusChange.class, new Cache<>());
+	}
+
+	/**
+	 * Initializes a storage space for a user-specific list of chats.
+	 *
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void initializeUserStorage() {}
+
+	/**
+	 * Stores all users. If the client user is specified, their chats will be stored
+	 * as well. The message id generator will also be saved if present.
+	 *
+	 * @throws Exception if the saving process failed
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void save() throws Exception {}
+
+	/**
+	 * Loads all user data.
+	 *
+	 * @throws Exception if the loading process failed
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void loadUsers() throws Exception {}
+
+	/**
+	 * Loads all data of the client user.
+	 *
+	 * @throws Exception if the loading process failed
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void loadUserData() throws Exception {}
+
+	/**
+	 * Loads the ID generator. Any exception thrown during this process is ignored.
+	 *
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void loadIDGenerator() {}
+
+	/**
+	 * Synchronizes the contact list of the client user with the chat and user
+	 * storage.
+	 * 
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void synchronize() {
+		user.getContacts().stream().filter(u -> u instanceof User && !users.containsKey(u.getName())).forEach(u -> users.put(u.getName(), u));
+		users.put(user.getName(), user);
+
+		// Synchronize user status data
+		for (Contact contact : users.values())
+			if (contact instanceof User)
+				getChat(contact.getID()).ifPresent(chat -> { ((User) chat.getRecipient()).setStatus(((User) contact).getStatus()); });
+
+		// Create missing chats
+		user.getContacts()
+			.stream()
+			.filter(c -> !c.equals(user) && getChat(c.getID()).isEmpty())
+			.map(c -> c instanceof User ? new Chat(c) : new GroupChat(user, c))
+			.forEach(chats::add);
+	}
+
+	/**
+	 * @return a {@code Map<String, User>} of all users stored locally with their
+	 *         user names as keys
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public Map<String, Contact> getUsers() { return users; }
+
+	/**
+	 * @return all saved {@link Chat} objects that list the client user as the
+	 *         sender
+	 * @since Envoy Client v0.1-alpha
+	 **/
+	public List<Chat> getChats() { return chats; }
+
+	/**
+	 * @param chats the chats to set
+	 */
+	public void setChats(List<Chat> chats) { this.chats = chats; }
+
+	/**
+	 * @return the {@link User} who initialized the local database
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public User getUser() { return user; }
+
+	/**
+	 * @param user the user to set
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public void setUser(User user) { this.user = user; }
+
+	/**
+	 * @return the message ID generator
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public IDGenerator getIDGenerator() { return idGenerator; }
+
+	/**
+	 * @param idGenerator the message ID generator to set
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void setIDGenerator(IDGenerator idGenerator) { this.idGenerator = idGenerator; }
+
+	/**
+	 * @return {@code true} if an {@link IDGenerator} is present
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public boolean hasIDGenerator() { return idGenerator != null; }
+
+	/**
+	 * @return the cache map for messages and message status changes
+	 * @since Envoy Client v0.1-beta
+	 */
+	public CacheMap getCacheMap() { return cacheMap; }
+
+	/**
+	 * Searches for a message by ID.
+	 *
+	 * @param id the ID of the message to search for
+	 * @return an optional containing the message
+	 * @since Envoy Client v0.1-beta
+	 */
+	public Optional<Message> getMessage(long id) {
+		return chats.stream().map(Chat::getMessages).flatMap(List::stream).filter(m -> m.getID() == id).findAny();
+	}
+
+	/**
+	 * Searches for a chat by recipient ID.
+	 * 
+	 * @param recipientID the ID of the chat's recipient
+	 * @return an optional containing the chat
+	 * @since Envoy Client v0.1-beta
+	 */
+	public Optional<Chat> getChat(long recipientID) { return chats.stream().filter(c -> c.getRecipient().getID() == recipientID).findAny(); }
+
+	/**
+	 * Performs a contact name change if the corresponding contact is present.
+	 *
+	 * @param event the {@link NameChange} to process
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void replaceContactName(NameChange event) {
+		chats.stream().map(Chat::getRecipient).filter(c -> c.getID() == event.getID()).findAny().ifPresent(c -> c.setName(event.get()));
+	}
+
+	/**
+	 * Performs a group resize operation if the corresponding group is present.
+	 *
+	 * @param event the {@link GroupResize} to process
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void updateGroup(GroupResize event) {
+		chats.stream()
+			.map(Chat::getRecipient)
+			.filter(Group.class::isInstance)
+			.filter(g -> g.getID() == event.getGroupID() && g.getID() != user.getID())
+			.map(Group.class::cast)
+			.findAny()
+			.ifPresent(group -> {
+				switch (event.getOperation()) {
+					case ADD:
+						group.getContacts().add(event.get());
+						break;
+					case REMOVE:
+						group.getContacts().remove(event.get());
+						break;
+				}
+			});
+	}
+}

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

@@ -0,0 +1,88 @@
+package envoy.client.data;
+
+import java.io.*;
+import java.util.ArrayList;
+import java.util.HashMap;
+
+import envoy.data.IDGenerator;
+import envoy.util.SerializationUtils;
+
+/**
+ * Implements a {@link LocalDB} in a way that stores all information inside a
+ * folder on the local file system.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>PersistentLocalDB.java</strong><br>
+ * Created: <strong>27.10.2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @author Maximilian K&auml;fer
+ * @since Envoy Client v0.1-alpha
+ */
+public final class PersistentLocalDB extends LocalDB {
+
+	private File dbDir, userFile, idGeneratorFile, usersFile;
+
+	/**
+	 * Constructs an empty local database. To serialize any user-specific data to
+	 * the file system, call {@link PersistentLocalDB#initializeUserStorage()} first
+	 * and then {@link PersistentLocalDB#save()}.
+	 *
+	 * @param dbDir the directory in which to persist data
+	 * @throws IOException if {@code dbDir} is a file (and not a directory)
+	 * @since Envoy Client v0.1-alpha
+	 */
+	public PersistentLocalDB(File dbDir) throws IOException {
+		this.dbDir = dbDir;
+
+		// Test if the database directory is actually a directory
+		if (dbDir.exists() && !dbDir.isDirectory())
+			throw new IOException(String.format("LocalDBDir '%s' is not a directory!", dbDir.getAbsolutePath()));
+
+		// Initialize global files
+		idGeneratorFile	= new File(dbDir, "id_gen.db");
+		usersFile		= new File(dbDir, "users.db");
+	}
+
+	/**
+	 * Creates a database file for a user-specific list of chats.
+	 *
+	 * @throws IllegalStateException if the client user is not specified
+	 * @since Envoy Client v0.1-alpha
+	 */
+	@Override
+	public void initializeUserStorage() {
+		if (user == null) throw new IllegalStateException("Client user is null, cannot initialize user storage");
+		userFile = new File(dbDir, user.getID() + ".db");
+	}
+
+	@Override
+	public void save() throws IOException {
+		// Save users
+		SerializationUtils.write(usersFile, users);
+
+		// Save user data
+		if (user != null) SerializationUtils.write(userFile, chats, cacheMap);
+
+		// Save id generator
+		if (hasIDGenerator()) SerializationUtils.write(idGeneratorFile, idGenerator);
+	}
+
+	@Override
+	public void loadUsers() throws ClassNotFoundException, IOException { users = SerializationUtils.read(usersFile, HashMap.class); }
+
+	@Override
+	public void loadUserData() throws ClassNotFoundException, IOException {
+		try (var in = new ObjectInputStream(new FileInputStream(userFile))) {
+			chats		= (ArrayList<Chat>) in.readObject();
+			cacheMap	= (CacheMap) in.readObject();
+		}
+	}
+
+	@Override
+	public void loadIDGenerator() {
+		try {
+			idGenerator = SerializationUtils.read(idGeneratorFile, IDGenerator.class);
+		} catch (ClassNotFoundException | IOException e) {}
+	}
+}

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

@@ -0,0 +1,146 @@
+package envoy.client.data;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.prefs.Preferences;
+
+import envoy.util.SerializationUtils;
+
+/**
+ * Manages all application settings, which are different objects that can be
+ * changed during runtime and serialized them by using either the file system or
+ * the {@link Preferences} API.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>Settings.java</strong><br>
+ * Created: <strong>11 Nov 2019</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @author Maximilian K&auml;fer
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.2-alpha
+ */
+public class Settings {
+
+	// Actual settings accessible by the rest of the application
+	private Map<String, SettingsItem<?>> items;
+
+	/**
+	 * Settings are stored in this file.
+	 */
+	private static final File settingsFile = new File(ClientConfig.getInstance().getHomeDirectory(), "settings.ser");
+
+	/**
+	 * Singleton instance of this class.
+	 */
+	private static Settings settings = new Settings();
+
+	/**
+	 * The way to instantiate the settings. Is set to private to deny other
+	 * instances of that object.
+	 *
+	 * @since Envoy Client v0.2-alpha
+	 */
+	private Settings() {
+		// Load settings from settings file
+		try {
+			items = SerializationUtils.read(settingsFile, HashMap.class);
+		} catch (ClassNotFoundException | IOException e) {
+			items = new HashMap<>();
+		}
+		supplementDefaults();
+	}
+
+	/**
+	 * This method is used to ensure that there is only one instance of Settings.
+	 *
+	 * @return the instance of Settings
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public static Settings getInstance() { return settings; }
+
+	/**
+	 * Updates the preferences when the save button is clicked.
+	 *
+	 * @throws IOException if an error occurs while saving the themes
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public void save() throws IOException {
+
+		// Save settings to settings file
+		SerializationUtils.write(settingsFile, items);
+	}
+
+	private void supplementDefaults() {
+		items.putIfAbsent("enterToSend", new SettingsItem<>(true, "Enter to send", "Sends a message by pressing the enter key."));
+		items.putIfAbsent("onCloseMode", new SettingsItem<>(true, "Hide on close", "Hides the chat window when it is closed."));
+		items.putIfAbsent("currentTheme", new SettingsItem<>("dark", "Current Theme Name", "The name of the currently selected theme."));
+	}
+
+	/**
+	 * @return the name of the currently active theme
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public String getCurrentTheme() { return (String) items.get("currentTheme").get(); }
+
+	/**
+	 * Sets the name of the current theme.
+	 *
+	 * @param themeName the name to set
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public void setCurrentTheme(String themeName) { ((SettingsItem<String>) items.get("currentTheme")).set(themeName); }
+
+	/**
+	 * @return true if the currently used theme is one of the default themes
+	 * @since Envoy Client v0.1-beta
+	 */
+	public boolean isUsingDefaultTheme() {
+		final var theme = getCurrentTheme();
+		return theme.equals("dark") || theme.equals("light");
+	}
+
+	/**
+	 * @return {@code true}, if pressing the {@code Enter} key suffices to send a
+	 *         message. Otherwise it has to be pressed in conjunction with the
+	 *         {@code Control} key.
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public Boolean isEnterToSend() { return (Boolean) items.get("enterToSend").get(); }
+
+	/**
+	 * Changes the keystrokes performed by the user to send a message.
+	 *
+	 * @param enterToSend If set to {@code true} a message can be sent by pressing
+	 *                    the {@code Enter} key. Otherwise it has to be pressed in
+	 *                    conjunction with the {@code Control} key.
+	 * @since Envoy Client v0.2-alpha
+	 */
+	public void setEnterToSend(boolean enterToSend) { ((SettingsItem<Boolean>) items.get("enterToSend")).set(enterToSend); }
+
+	/**
+	 * @return the current on close mode.
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public Boolean getCurrentOnCloseMode() { return (Boolean) items.get("onCloseMode").get(); }
+
+	/**
+	 * Sets the current on close mode.
+	 *
+	 * @param currentOnCloseMode the on close mode that should be set.
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void setCurrentOnCloseMode(boolean currentOnCloseMode) { ((SettingsItem<Boolean>) items.get("onCloseMode")).set(currentOnCloseMode); }
+
+	/**
+	 * @return the items
+	 */
+	public Map<String, SettingsItem<?>> getItems() { return items; }
+
+	/**
+	 * @param items the items to set
+	 */
+	public void setItems(Map<String, SettingsItem<?>> items) { this.items = items; }
+}

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

@@ -0,0 +1,99 @@
+package envoy.client.data;
+
+import java.io.Serializable;
+import java.util.function.Consumer;
+
+import javax.swing.JComponent;
+
+/**
+ * Encapsulates a persistent value that is directly or indirectly mutable by the
+ * user.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>SettingsItem.java</strong><br>
+ * Created: <strong>23.12.2019</strong><br>
+ *
+ * @param <T> the type of this {@link SettingsItem}'s value
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.3-alpha
+ */
+public class SettingsItem<T> implements Serializable {
+
+	private T		value;
+	private String	userFriendlyName, description;
+
+	private transient Consumer<T> changeHandler;
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * Initializes a {@link SettingsItem}. The default value's class will be mapped
+	 * to a {@link JComponent} that can be used to display this {@link SettingsItem}
+	 * to the user.
+	 *
+	 * @param value            the default value
+	 * @param userFriendlyName the user friendly name (short)
+	 * @param description      the description (long)
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public SettingsItem(T value, String userFriendlyName, String description) {
+		this.value				= value;
+		this.userFriendlyName	= userFriendlyName;
+		this.description		= description;
+	}
+
+	/**
+	 * @return the value
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public T get() { return value; }
+
+	/**
+	 * Changes the value of this {@link SettingsItem}. If a {@code ChangeHandler} if
+	 * defined, it will be invoked with this value.
+	 *
+	 * @param value the value to set
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void set(T value) {
+		if (changeHandler != null && value != this.value) changeHandler.accept(value);
+		this.value = value;
+	}
+
+	/**
+	 * @return the userFriendlyName
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public String getUserFriendlyName() { return userFriendlyName; }
+
+	/**
+	 * @param userFriendlyName the userFriendlyName to set
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void setUserFriendlyName(String userFriendlyName) { this.userFriendlyName = userFriendlyName; }
+
+	/**
+	 * @return the description
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public String getDescription() { return description; }
+
+	/**
+	 * @param description the description to set
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void setDescription(String description) { this.description = description; }
+
+	/**
+	 * Sets a {@code ChangeHandler} for this {@link SettingsItem}. It will be
+	 * invoked with the current value once during the registration and every time
+	 * when the value changes.
+	 *
+	 * @param changeHandler the changeHandler to set
+	 * @since Envoy Client v0.3-alpha
+	 */
+	public void setChangeHandler(Consumer<T> changeHandler) {
+		this.changeHandler = changeHandler;
+		changeHandler.accept(value);
+	}
+}

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

@@ -0,0 +1,15 @@
+package envoy.client.data;
+
+/**
+ * Implements a {@link LocalDB} in a way that does not persist any information
+ * after application shutdown.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>TransientLocalDB.java</strong><br>
+ * Created: <strong>3 Feb 2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.3-alpha
+ */
+public final class TransientLocalDB extends LocalDB {
+}

client/src/main/java/envoy/client/data/audio/AudioPlayer.java

@@ -0,0 +1,64 @@
+package envoy.client.data.audio;
+
+import javax.sound.sampled.*;
+
+import envoy.exception.EnvoyException;
+
+/**
+ * Plays back audio from a byte array.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>AudioPlayer.java</strong><br>
+ * Created: <strong>05.07.2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.1-beta
+ */
+public final class AudioPlayer {
+
+	private final AudioFormat	format;
+	private final DataLine.Info	info;
+
+	private Clip clip;
+
+	/**
+	 * Initializes the player with the default audio format.
+	 *
+	 * @since Envoy Client v0.1-beta
+	 */
+	public AudioPlayer() { this(AudioRecorder.DEFAULT_AUDIO_FORMAT); }
+
+	/**
+	 * Initializes the player with a given audio format.
+	 *
+	 * @param format the audio format to use
+	 * @since Envoy Client v0.1-beta
+	 */
+	public AudioPlayer(AudioFormat format) {
+		this.format	= format;
+		info		= new DataLine.Info(Clip.class, format);
+	}
+
+	/**
+	 * @return {@code true} if audio play back is supported
+	 * @since Envoy Client v0.1-beta
+	 */
+	public boolean isSupported() { return AudioSystem.isLineSupported(info); }
+
+	/**
+	 * Plays back an audio clip.
+	 *
+	 * @param data the data of the clip
+	 * @throws EnvoyException if the play back failed
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void play(byte[] data) throws EnvoyException {
+		try {
+			clip = (Clip) AudioSystem.getLine(info);
+			clip.open(format, data, 0, data.length);
+			clip.start();
+		} catch (final LineUnavailableException e) {
+			throw new EnvoyException("Cannot play back audio", e);
+		}
+	}
+}

client/src/main/java/envoy/client/data/audio/AudioRecorder.java

@@ -0,0 +1,122 @@
+package envoy.client.data.audio;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import javax.sound.sampled.*;
+
+import envoy.exception.EnvoyException;
+
+/**
+ * Records audio and exports it as a byte array.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>AudioRecorder.java</strong><br>
+ * Created: <strong>02.07.2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.1-beta
+ */
+public final class AudioRecorder {
+
+	/**
+	 * The default audio format used for recording and play back.
+	 *
+	 * @since Envoy Client v0.1-beta
+	 */
+	public static final AudioFormat DEFAULT_AUDIO_FORMAT = new AudioFormat(16000, 16, 1, true, false);
+
+	private final AudioFormat	format;
+	private final DataLine.Info	info;
+
+	private TargetDataLine	line;
+	private Path			tempFile;
+
+	/**
+	 * Initializes the recorder with the default audio format.
+	 *
+	 * @since Envoy Client v0.1-beta
+	 */
+	public AudioRecorder() { this(DEFAULT_AUDIO_FORMAT); }
+
+	/**
+	 * Initializes the recorder with a given audio format.
+	 *
+	 * @param format the audio format to use
+	 * @since Envoy Client v0.1-beta
+	 */
+	public AudioRecorder(AudioFormat format) {
+		this.format	= format;
+		info		= new DataLine.Info(TargetDataLine.class, format);
+	}
+
+	/**
+	 * @return {@code true} if audio recording is supported
+	 * @since Envoy Client v0.1-beta
+	 */
+	public boolean isSupported() { return AudioSystem.isLineSupported(info); }
+
+	/**
+	 * @return {@code true} if the recorder is active
+	 * @since Envoy Client v0.1-beta
+	 */
+	public boolean isRecording() { return line != null && line.isActive(); }
+
+	/**
+	 * Starts the audio recording.
+	 *
+	 * @throws EnvoyException if starting the recording failed
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void start() throws EnvoyException {
+		try {
+
+			// Open the line
+			line = (TargetDataLine) AudioSystem.getLine(info);
+			line.open(format);
+			line.start();
+
+			// Prepare temp file
+			tempFile = Files.createTempFile("recording", "wav");
+
+			// Start the recording
+			final var ais = new AudioInputStream(line);
+			AudioSystem.write(ais, AudioFileFormat.Type.WAVE, tempFile.toFile());
+		} catch (IOException | LineUnavailableException e) {
+			throw new EnvoyException("Cannot record voice", e);
+		}
+	}
+
+	/**
+	 * Stops the recording.
+	 *
+	 * @return the finished recording
+	 * @throws EnvoyException if finishing the recording failed
+	 * @since Envoy Client v0.1-beta
+	 */
+	public byte[] finish() throws EnvoyException {
+		try {
+			line.stop();
+			line.close();
+			final byte[] data = Files.readAllBytes(tempFile);
+			Files.delete(tempFile);
+			return data;
+		} catch (final IOException e) {
+			throw new EnvoyException("Cannot save voice recording", e);
+		}
+	}
+
+	/**
+	 * Cancels the active recording.
+	 *
+	 * @since Envoy Client v0.1-beta
+	 */
+	public void cancel() {
+		line.stop();
+		line.close();
+		try {
+			Files.deleteIfExists(tempFile);
+		} catch (IOException e) {}
+	}
+}

client/src/main/java/envoy/client/data/audio/package-info.java

@@ -0,0 +1,11 @@
+/**
+ * Contains classes related to recording and playing back audio clips.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>package-info.java</strong><br>
+ * Created: <strong>05.07.2020</strong><br>
+ * 
+ * @author Kai S. K. Engelbart
+ * @since Envoy Client v0.1-beta
+ */
+package envoy.client.data.audio;

client/src/main/java/envoy/client/data/package-info.java

@@ -0,0 +1,9 @@
+/**
+ * This package contains all data classes and classes related to persistence.
+ *
+ * @author Kai S. K. Engelbart
+ * @author Leon Hofmeister
+ * @author Maximilian Käfer
+ * @since Envoy Client v0.1-beta
+ */
+package envoy.client.data;