package envoy.client.data;

import java.io.*;
import java.time.Instant;
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(boolean)}.
	 *
	 * @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(boolean isOnline) throws IOException {
		// Save users
		SerializationUtils.write(usersFile, users);

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

		// 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();
			lastSync	= (Instant) in.readObject();
		}
	}

	@Override
	public void loadIDGenerator() {
		try {
			idGenerator = SerializationUtils.read(idGeneratorFile, IDGenerator.class);
		} catch (ClassNotFoundException | IOException e) {}
	}
}