package envoy.client.data;

import java.io.*;
import java.nio.channels.*;
import java.nio.file.StandardOpenOption;
import java.time.Instant;
import java.util.*;
import java.util.logging.Level;

import envoy.client.event.EnvoyCloseEvent;
import envoy.data.*;
import envoy.event.*;
import envoy.exception.EnvoyException;
import envoy.util.*;

import dev.kske.eventbus.Event;
import dev.kske.eventbus.EventBus;
import dev.kske.eventbus.EventListener;

/**
 * Stores information about the current {@link User} and their {@link Chat}s.
 * For message ID generation a {@link IDGenerator} is stored as well.
 * <p>
 * The managed objects are stored inside a folder in the local file system.
 * <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 final class LocalDB implements EventListener {

	// Data
	private User				user;
	private Map<String, User>	users		= Collections.synchronizedMap(new HashMap<>());
	private List<Chat>			chats		= Collections.synchronizedList(new ArrayList<>());
	private IDGenerator			idGenerator;
	private CacheMap			cacheMap	= new CacheMap();
	private String				authToken;

	// State management
	private Instant lastSync = Instant.EPOCH;

	// Persistence
	private File		userFile;
	private FileLock	instanceLock;

	private final File dbDir, idGeneratorFile, lastLoginFile, usersFile;

	/**
	 * Constructs an empty local database.
	 *
	 * @param dbDir the directory in which to persist data
	 * @throws IOException    if {@code dbDir} is a file (and not a directory)
	 * @throws EnvoyException if {@code dbDir} is in use by another Envoy instance
	 * @since Envoy Client v0.2-beta
	 */
	public LocalDB(File dbDir) throws IOException, EnvoyException {
		this.dbDir = dbDir;
		EventBus.getInstance().registerListener(this);

		// Ensure that the database directory exists
		if (!dbDir.exists()) dbDir.mkdirs();
		else if (!dbDir.isDirectory()) throw new IOException(String.format("LocalDBDir '%s' is not a directory!", dbDir.getAbsolutePath()));

		// Lock the directory
		lock();

		// Initialize global files
		idGeneratorFile	= new File(dbDir, "id_gen.db");
		lastLoginFile	= new File(dbDir, "last_login.db");
		usersFile		= new File(dbDir, "users.db");

		// Load global files
		loadGlobalData();

		// Initialize offline caches
		cacheMap.put(Message.class, new Cache<>());
		cacheMap.put(MessageStatusChange.class, new Cache<>());
	}

	/**
	 * Ensured that only one Envoy instance is using this local database by creating
	 * a lock file.
	 * The lock file is deleted on application exit.
	 *
	 * @throws EnvoyException if the lock cannot by acquired
	 * @since Envoy Client v0.2-beta
	 */
	private synchronized void lock() throws EnvoyException {
		final var file = new File(dbDir, "instance.lock");
		try {
			final var fc = FileChannel.open(file.toPath(), StandardOpenOption.CREATE, StandardOpenOption.WRITE);
			instanceLock = fc.tryLock();
			if (instanceLock == null) throw new EnvoyException("Another Envoy instance is using this local database!");
		} catch (final IOException e) {
			throw new EnvoyException("Could not create lock file!", e);
		}
	}

	/**
	 * Loads the local user registry {@code users.db}, the id generator
	 * {@code id_gen.db} and last login file {@code last_login.db}.
	 *
	 * @since Envoy Client v0.2-beta
	 */
	private synchronized void loadGlobalData() {
		try {
			try (var in = new ObjectInputStream(new FileInputStream(usersFile))) {
				users = (Map<String, User>) in.readObject();
			}
			idGenerator = SerializationUtils.read(idGeneratorFile, IDGenerator.class);
			try (var in = new ObjectInputStream(new FileInputStream(lastLoginFile))) {
				user		= (User) in.readObject();
				authToken	= (String) in.readObject();
			}
		} catch (IOException | ClassNotFoundException e) {}
	}

	/**
	 * Loads all data of the client user.
	 *
	 * @throws ClassNotFoundException if the loading process failed
	 * @throws IOException            if the loading process failed
	 * @since Envoy Client v0.3-alpha
	 */
	public synchronized void loadUserData() throws ClassNotFoundException, IOException {
		if (user == null) throw new IllegalStateException("Client user is null, cannot initialize user storage");
		userFile = new File(dbDir, user.getID() + ".db");
		try (var in = new ObjectInputStream(new FileInputStream(userFile))) {
			chats		= (List<Chat>) in.readObject();
			cacheMap	= (CacheMap) in.readObject();
			lastSync	= (Instant) in.readObject();
		}
		synchronize();
	}

	/**
	 * Synchronizes the contact list of the client user with the chat and user
	 * storage.
	 *
	 * @since Envoy Client v0.1-beta
	 */
	private void synchronize() {
		user.getContacts().stream().filter(u -> u instanceof User && !users.containsKey(u.getName())).forEach(u -> users.put(u.getName(), (User) u));
		users.put(user.getName(), user);

		// Synchronize user status data
		for (final var contact : users.values())
			if (contact instanceof User) getChat(contact.getID()).ifPresent(chat -> { ((User) chat.getRecipient()).setStatus(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);
	}

	/**
	 * 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 IOException if the saving process failed
	 * @since Envoy Client v0.3-alpha
	 */
	@Event(eventType = EnvoyCloseEvent.class, priority = 1000)
	private synchronized void save() {
		EnvoyLog.getLogger(LocalDB.class).log(Level.INFO, "Saving local database...");

		// Save users
		try {
			SerializationUtils.write(usersFile, users);

			// Save user data and last sync time stamp
			if (user != null)
				SerializationUtils.write(userFile, chats, cacheMap, Context.getInstance().getClient().isOnline() ? Instant.now() : lastSync);

			// Save last login information
			if (authToken != null) SerializationUtils.write(lastLoginFile, user, authToken);

			// Save ID generator
			if (hasIDGenerator()) SerializationUtils.write(idGeneratorFile, idGenerator);
		} catch (final IOException e) {
			EnvoyLog.getLogger(LocalDB.class).log(Level.SEVERE, "Unable to save local database: ", e);
		}
	}

	@Event
	private void onNewAuthToken(NewAuthToken evt) { authToken = evt.get(); }

	/**
	 * @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, User> 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; }

	/**
	 * @return the time stamp when the database was last saved
	 * @since Envoy Client v0.2-beta
	 */
	public Instant getLastSync() { return lastSync; }

	/**
	 * @return the authentication token of the user
	 * @since Envoy Client v0.2-beta
	 */
	public String getAuthToken() { return authToken; }

	/**
	 * 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;
				}
			});
	}
}