package envoy.client;

import java.io.*;
import java.time.Instant;
import java.util.*;
import java.util.logging.Logger;

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;

import envoy.client.event.EventBus;
import envoy.client.event.MessageCreationEvent;
import envoy.client.util.EnvoyLog;
import envoy.exception.EnvoyException;
import envoy.schema.*;
import envoy.schema.Message.Metadata.MessageState;

/**
 * Project: <strong>envoy-client</strong><br>
 * File: <strong>LocalDB.java</strong><br>
 * Created: <strong>27.10.2019</strong><br>
 *
 * @author Kai S. K. Engelbart
 * @author Maximilian K&auml;fer
 * @since Envoy v0.1-alpha
 */
public class LocalDB {

	private File				localDBDir, localDBFile, usersFile;
	private User				user;
	private Map<String, User>	users	= new HashMap<>();
	private List<Chat>			chats	= new ArrayList<>();

	private ObjectFactory	objectFactory	= new ObjectFactory();
	private DatatypeFactory	datatypeFactory;

	private Sync	unreadMessagesSync	= objectFactory.createSync();
	private Sync	sync				= objectFactory.createSync();
	private Sync	readMessages		= objectFactory.createSync();

  private static final Logger logger = EnvoyLog.getLogger(LocalDB.class.getSimpleName());

	/**
	 * Constructs an empty local database. To serialize any chats to the file
	 * system, call {@link LocalDB#initializeDBFile()}.
	 *
	 * @param localDBDir the directory in which to store users and chats
	 * @throws IOException if the LocalDB could not be initialized
	 * @since Envoy v0.1-alpha
	 */
	public LocalDB(File localDBDir) throws IOException {
		this.localDBDir = localDBDir;

		try {
			datatypeFactory = DatatypeFactory.newInstance();
		} catch (DatatypeConfigurationException e) {
			e.printStackTrace();
		}

		// Initialize local database directory
		if (localDBDir.exists() && !localDBDir.isDirectory())
			throw new IOException(String.format("LocalDBDir '%s' is not a directory!", localDBDir.getAbsolutePath()));
		usersFile = new File(localDBDir, "users.db");
	}

	/**
	 * Creates a database file for a user-specific list of chats.
	 *
	 * @throws NullPointerException if the client user is not yet specified
	 * @since Envoy v0.1-alpha
	 */
	public void initializeDBFile() {
		if (user == null) throw new NullPointerException("Client user is null");
		localDBFile = new File(localDBDir, user.getID() + ".db");
	}

	/**
	 * Stores all users to the local database. If the client user is specified, the
	 * chats related to this user are stored as well.
	 *
	 * @throws IOException if something went wrong during saving
	 * @since Envoy v0.1-alpha
	 */
	public void save() throws IOException {
		// Save users
		write(usersFile, users);

		// Save chats
		write(localDBFile, chats);
	}

	/**
	 * Loads all users that are stored in the local database.
	 *
	 * @throws EnvoyException if the loading process failed
	 * @since Envoy v0.2-alpha
	 */
	@SuppressWarnings("unchecked")
	public void loadUsers() throws EnvoyException { users = read(usersFile, HashMap.class); }

	/**
	 * Loads all chats saved by Envoy for the client user.
	 *
	 * @throws EnvoyException if the loading process failed
	 * @since Envoy v0.1-alpha
	 */
	@SuppressWarnings("unchecked")
	public void loadChats() throws EnvoyException { chats = read(localDBFile, ArrayList.class); }

	private <T> T read(File file, Class<T> serializedClass) throws EnvoyException {
		if (file == null) throw new NullPointerException("File is null");
		try (ObjectInputStream in = new ObjectInputStream(new FileInputStream(file))) {
			return serializedClass.cast(in.readObject());
		} catch (ClassNotFoundException | IOException e) {
			throw new EnvoyException("Could not load serialized object", e);
		}
	}

	private <T> void write(File file, T obj) throws IOException {
		if (file == null) throw new NullPointerException("File is null");
		if (obj == null) throw new NullPointerException("Object to serialize is null");
		if (!file.exists()) {
			file.getParentFile().mkdirs();
			file.createNewFile();
		}
		try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file))) {
			out.writeObject(obj);
		} catch (IOException e) {
			throw e;
		}
	}

	/**
	 * Creates a {@link Message} object serializable to XML.
	 *
	 * @param textContent The content (text) of the message
	 * @param recipientID The recipient of the message
	 * @return prepared {@link Message} object
	 * @since Envoy v0.1-alpha
	 */
	public Message createMessage(String textContent, long recipientID) {
		Message.Metadata metaData = objectFactory.createMessageMetadata();
		metaData.setSender(user.getID());
		metaData.setRecipient(recipientID);
		metaData.setState(MessageState.WAITING);
		metaData.setDate(datatypeFactory.newXMLGregorianCalendar(Instant.now().toString()));

		Message.Content content = objectFactory.createMessageContent();
		content.setType("text");
		content.setText(textContent);

		Message message = objectFactory.createMessage();
		message.setMetadata(metaData);
		message.getContent().add(content);

		return message;
	}

	/**
	 * Creates a {@link Sync} object filled with the changes that occurred to the
	 * local database since the last synchronization.
	 *
	 * @param userId the ID of the user that is synchronized by this client
	 * @return {@link Sync} object filled with the current changes
	 * @since Envoy v0.1-alpha
	 */
	public Sync fillSync(long userId) {
		addWaitingMessagesToSync();

		sync.getMessages().addAll(readMessages.getMessages());
		readMessages.getMessages().clear();

		logger.finest(String.format("Filled sync with %d messages.", sync.getMessages().size()));
		return sync;
	}

	/**
	 * Applies the changes carried by a {@link Sync} object to the local database
	 *
	 * @param returnSync the {@link Sync} object to apply
	 * @since Envoy v0.1-alpha
	 */
	public void applySync(Sync returnSync) {
		for (int i = 0; i < returnSync.getMessages().size(); i++) {

			// The message has an ID
			if (returnSync.getMessages().get(i).getMetadata().getMessageId() != 0) {

				// Messages are processes differently corresponding to their state
				switch (returnSync.getMessages().get(i).getMetadata().getState()) {
					case SENT:
						// Update previously waiting and now sent messages that were assigned an ID by
						// the server
						sync.getMessages().get(i).getMetadata().setMessageId(returnSync.getMessages().get(i).getMetadata().getMessageId());
						sync.getMessages().get(i).getMetadata().setState(returnSync.getMessages().get(i).getMetadata().getState());
						break;
					case RECEIVED:
						if (returnSync.getMessages().get(i).getMetadata().getSender() != 0) {
							// these are the unread Messages from the server
							unreadMessagesSync.getMessages().add(returnSync.getMessages().get(i));

							// Create and dispatch message creation event
							EventBus.getInstance().dispatch(new MessageCreationEvent(returnSync.getMessages().get(i)));
						} else {
							// Update Messages in localDB to state RECEIVED
							for (Chat chat : getChats())
								if (chat.getRecipient().getID() == returnSync.getMessages().get(i).getMetadata().getRecipient())
									for (int j = 0; j < chat.getModel().getSize(); j++)
									if (chat.getModel().get(j).getMetadata().getMessageId() == returnSync.getMessages()
										.get(i)
										.getMetadata()
										.getMessageId())
										chat.getModel().get(j).getMetadata().setState(returnSync.getMessages().get(i).getMetadata().getState());
						}
						break;
					case READ:
						// Update local Messages to state READ
						logger.info("Message with ID: " + returnSync.getMessages().get(i).getMetadata().getMessageId()
								+ "was initialized to be set to READ in localDB.");
						for (Chat chat : getChats())
							if (chat.getRecipient().getID() == returnSync.getMessages().get(i).getMetadata().getRecipient()) {
								logger.info("Chat with: " + chat.getRecipient().getID() + "was selected.");
								for (int k = 0; k < chat.getModel().getSize(); k++)
									if (chat.getModel().get(k).getMetadata().getMessageId() == returnSync.getMessages()
										.get(i)
										.getMetadata()
										.getMessageId()) {
										logger.info("Message with ID: " + chat.getModel().get(k).getMetadata().getMessageId() + "was selected.");
										chat.getModel().get(k).getMetadata().setState(returnSync.getMessages().get(i).getMetadata().getState());
										logger.info("Message State is now: " + chat.getModel().get(k).getMetadata().getState());
									}
							}
						break;
				}
			}
		}

		// Updating UserStatus of all users in LocalDB
		for (User user : returnSync.getUsers())
			for (Chat chat : getChats())
				if (user.getID() == chat.getRecipient().getID())
					chat.getRecipient().setStatus(user.getStatus());

		sync.getMessages().clear();
		sync.getUsers().clear();
	}

	/**
	 * Adds the unread messages returned from the server in the latest sync to the
	 * right chats in the LocalDB.
	 *
	 * @since Envoy v0.1-alpha
	 */
	public void addUnreadMessagesToLocalDB() {
		for (Message message : unreadMessagesSync.getMessages())
			for (Chat chat : getChats())
				if (message.getMetadata().getSender() == chat.getRecipient().getID()) {
					chat.appendMessage(message);
					break;
				}
	}

	/**
	 * Changes all messages with state {@code RECEIVED} of a specific chat to state
	 * {@code READ}.
	 * <br>
	 * Adds these messages to the {@code readMessages} {@link Sync} object.
	 *
	 * @param currentChat the {@link Chat} that was just opened
	 * @since Envoy v0.1-alpha
	 */
	public void setMessagesToRead(Chat currentChat) {
		for (int i = currentChat.getModel().size() - 1; i >= 0; --i)
			if (currentChat.getModel().get(i).getMetadata().getRecipient() != currentChat.getRecipient().getID())
				if (currentChat.getModel().get(i).getMetadata().getState() == MessageState.RECEIVED) {
					currentChat.getModel().get(i).getMetadata().setState(MessageState.READ);
					readMessages.getMessages().add(currentChat.getModel().get(i));
				} else break;
	}

	/**
	 * Adds all messages with state {@code WAITING} from the {@link LocalDB} to the
	 * {@link Sync} object.
	 *
	 * @since Envoy v0.1-alpha
	 */
	private void addWaitingMessagesToSync() {
		for (Chat chat : getChats())
			for (int i = 0; i < chat.getModel().size(); i++)
				if (chat.getModel().get(i).getMetadata().getState() == MessageState.WAITING) {
					logger.info("Got Waiting Message");
					sync.getMessages().add(chat.getModel().get(i));
				}
	}

	/**
	 * Clears the {@code unreadMessagesSync} {@link Sync} object.
	 *
	 * @since Envoy v0.1-alpha
	 */
	public void clearUnreadMessagesSync() { unreadMessagesSync.getMessages().clear(); }

	/**
	 * @return a {@code Map<String, User>} of all users stored locally with their user names as keys
	 * @since Envoy v0.2-alpha
	 */
	public Map<String, User> getUsers() { return users; }

	/**
	 * @param users the users to set
	 */
	public void setUsers(Map<String, User> users) { this.users = users; }

	/**
	 * @return all saved {@link Chat} objects that list the client user as the
	 *         sender
	 * @since Envoy 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 v0.2-alpha
	 */
	public User getUser() { return user; }

	/**
	 * @param user the user to set
	 * @since Envoy v0.2-alpha
	 */
	public void setUser(User user) { this.user = user; }
}