/*
 * Author: Wenbing Zhao
 * Last Modified: 11/10/2006
 * For EEC484/584 Project 2
 */

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

public class NetworkLayer {
    private InetAddress m_IPAddress;
    private DatagramSocket m_socket = null;
    private int m_localport = 0;
    private int m_remoteport = 0;

    private Vector m_receiveBuffer = new Vector(10);
    private TransportLayer m_transportLayer = null;
    
    public NetworkLayer() { }

    public NetworkLayer(int localport, int remoteport) {
	m_localport = localport;
	m_remoteport = remoteport;
	try {
	    m_IPAddress = InetAddress.getByName("localhost"); 
	    m_socket = new DatagramSocket(localport); 
	} catch(Exception e) {
	    System.out.println("Cannot create UDP socket: "+e);
	}

	// start the reading thread
	new ReadThread().start();
    }

    public void setTransportLayer(TransportLayer tl) {
	m_transportLayer = tl;
    }

    public void send(byte[] payload) {
	// simulate random loss of packet
	Random rand = new Random();
	int randnum = rand.nextInt(10); // range 0-10
	if(randnum < 3) {
	    //System.out.println("X");
	    return; // simulate a loss
	}

	try {
	    DatagramPacket p = 
		new DatagramPacket(payload, payload.length, 
				   m_IPAddress, m_remoteport); 
	    m_socket.send(p);
	} catch(Exception e) {
	    System.out.println("Error sending packet: "+e);
	}
    }

    // Interface provided to the data link layer to pick
    // up message received
    public byte[] receive() {
	if(m_receiveBuffer.size() > 0)
	    return ((DatagramPacket)m_receiveBuffer.remove(0)).getData();
	else
	    return null;
    }

    // Thread to read packets arrived from the network and to notify
    // the data link layer
    public class ReadThread extends Thread {
	public void run() {
	    while(true) {
		// if there is buffered received packets, notify
		// the transport layer instead of blocking reading
		if(m_receiveBuffer.size() > 0) {
		    if(m_transportLayer != null)
			m_transportLayer.onPacketArrival();
		    continue;
		}

		byte[] buffer = new byte[Packet.MAX_PACKET_SIZE]; 
		DatagramPacket p = 
		    new DatagramPacket(buffer, buffer.length);  
		
		try {
		    m_socket.receive(p); 
		} catch(Exception e) {
		    System.out.println("Cannot receive from socket: "+e);
		}
		
		m_receiveBuffer.add(p);

		if(m_transportLayer != null)
		    m_transportLayer.onPacketArrival();
	    }
	}
    }
}