import java.io.*;
import java.net.*;

/**
 * This class provides location awareness to the granularity of a room
 * inside a building based on the reception of 802.11 broadcasts and the
 * corresponding detection of ultrasound.  This class is intended to be used
 * by an application running on a mobile device.  If the mobile device moves
 * close to a desktop running the ServerBeacon class/application, it will
 * know that it is in the same room as the desktop based on the information
 * provided by this MobileClient class.
 * <p>
 * An application using this class needs to provide a reference to itself in
 * the MobileClient class's constructor.  The application must also have a
 * roomChanged() method so that the MobileClient class can signal the
 * application when a room change has occurred.
 *
 * @author Tony Offer
 * @author Chris Palistrant
 * @version 1.0
 */
public class MobileClient {

    // Reference to the object/application that instantiated this MobileClient
    private Object notifyApp = null;

    // The multicast socket that will be collecting 802.11 broadcasts
    // directed toward a certain multicast group.
    private MulticastSocket socket = null;

    // The ultrasound listener object that will be responsible for
    // recording and analyzing the sound in the room in order to detect
    // the presence of ultrasound.
    private UltrasoundListener ultrasound = null;

    // This string identifies the current room in which this
    // MobileClient object perceives itself to exist.
    private String room = null;
    
    // The multicast group that this MobileClient's socket should join in
    // order to receive 802.11 broadcasts.
    public static final String GROUPADDR = "239.255.255.254";

    // The port number on which to listen for the 802.11 broadcasts.
    public static final int PORTNUM = 8019;

    /**
     * This is the only constructor for this class.  It takes a reference
     * to the object that instantiated it so that the MobileClient class
     * can notify the object when a room change has occurred.  No other
     * constructor is provided because the MobileClient class must have
     * access to a roomChanged() method.
     *
     * @param extApp    Reference to the external object/application that
     *                  instantiated this MobileClient object.
     */
    public MobileClient(Object extApp) {
	notifyApp = extApp;

	try {
	    // Instantiate a new multicast socket with the appropriate port
	    // number.
	    socket = new MulticastSocket(PORTNUM);

	    // Get the InetAddress corresponding to the string stored in
	    // GROUPADDR and make the socket join this group so that it
	    // can receive messages directed to this group address.
	    InetAddress group = InetAddress.getByName(GROUPADDR);
	    socket.joinGroup(group);
	} catch (SocketException se) {
	    se.printStackTrace();
	    System.exit(1);
	} catch (SecurityException se) {
	    se.printStackTrace();
	    System.exit(1);
	} catch (IOException ioe) {
	    ioe.printStackTrace();
	    System.exit(1);
	} catch (UnknownHostException uhe) {
	    uhe.printStackTrace();
	    System.exit(1);
	}

	// Instantiate a new UltrasoundListener for the purpose of
	// detecting ultrasound.
	ultrasound = new UltrasoundListener();

	// Start a new Listener thread so that this MobileClient class
	// can be made aware of room changes.
	new Listener(this, socket, ultrasound).start();
    }

    /**
     * This is the method that will be called by Listener threads when
     * the threads are done detecting 802.11 and ultrasound.  Based on
     * the 802.11 room string and ultrasound boolean decision it
     * receives, the update() method will decide whether a room change
     * has occurred, signalling the external application if necessary.
     * 
     * @param roomString    The 802.11 room-identifying message that was
     *                      received by the Listener thread.
     * @param ultrasoundPresent    Boolean decision indicating whether
     *                             or not ultrasound was found to be
     *                             present by the Listener thread.
     */
    public void update(String roomString, boolean ultrasoundPresent) {

        // If the room string is different and ultrasound was detected,
	// a change in room location has occurred.  Otherwise, if the
	// room string is the same and ultrasound was not detected, then
	// the device running this MobileClient class is no longer in
	// the room identified by 'room'.
	if ( !roomString.equals(room) && ultrasoundPresent ) {

	    // Update this MobileClient's 'room' identifier
            room = roomString;

	    // Notify the external application of a room change.
	    notifyApp.roomChanged(roomString);

	else if ( roomString.equals(room) && !ultrasoundPresent ) {

	    // Update this MobileClient's 'room' identifier -- the
	    // mobile device is currently not in a room.
	    room = null;

	    // Notify the external application of a room change.
	    notifyApp.roomChanged(room);
	}
    }
}