/*
 * Author: Wenbing Zhao
 * Last Modified: 9/18/2006
 * For EEC484/584 Project 1
 */

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

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

    private byte[] m_receiveBuffer = new byte[Frame.MAX_FRAME_SIZE]; 
    private DataLinkLayer m_datalinkLayer = null;
    
    public PhysicalLayer(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 setDataLinkLayer(DataLinkLayer dl) {
	m_datalinkLayer = dl;
    }

    public void send(byte[] payload) {
	// To be modified
	// simulate random loss of frame
	Random rand = new Random();
	int randnum = rand.nextInt(10); // range 0-10
	if(randnum < 3)
	    return; // simulate a loss

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

    // Interface provided to the data link layer to pick
    // up message received
    public byte[] receive() {
	return m_receiveBuffer;
    }

    // Thread to read frames arrived from the network and to notify
    // the data link layer
    public class ReadThread extends Thread {
	public void run() {
	    while(true) {
		DatagramPacket p = 
		    new DatagramPacket(m_receiveBuffer, 
				       m_receiveBuffer.length); 
		
		try {
		    m_socket.receive(p); 
		} catch(Exception e) {
		    System.out.println("Cannot receive from socket: "+e);
		}
		
		byte[] receivedData = p.getData();
		//System.out.println("Received frame: "+ receivedData[0]);
		
		if(m_datalinkLayer != null)
		    m_datalinkLayer.onFrameArrival();
	    }
	}
    }
}