//RandomWalkAnimation.java

import java.awt.*;
import java.awt.event.*;    //**ActionListener "interface"
import javax.swing.*;

public class RandomWalkAnimation extends JApplet implements ActionListener {
                                                 //***
    int animationDelay;        //** millisecond delay
    Timer animationTimer;      //** Timer drives animation.
    //initialize Timer object with a time in ms, it will automatically
    //fire event periodically.

    double totalDist;  //*moved from paint
    int xPrev, yPrev, xNow, yNow;  //*moved from paint
    int steps;
            
    public void init() {
	String input;
	
	input = JOptionPane.showInputDialog("Enter animation delay in ms");
	animationDelay = Integer.parseInt(input);

        //initialize (**moved from paint)
	xPrev = xNow = getWidth()/2;   //start in center
	yPrev = yNow = getHeight()/2;
        steps = 0;
        totalDist = 0;
        
	startAnimation();  //*** begin animation
   }
   
    //** will be called once every animationDelay ms.
    //**Notice there is no loop in paint.   
    public void paint( Graphics g ) {

	double avgDist=0, dist;
	int scale=5;   //conversion to screen pixels

        steps++;
        
	switch ((int)(Math.random()*4)) {
	case 0:  //up
	    yNow = yPrev - scale;
	    break;
	case 1:  //down
	    yNow = yPrev + scale;
	    break;
	case 2:  //left
	    xNow = xPrev - scale;
	    break;
	case 3:  //left
	    xNow = xPrev + scale;
	    break;
	}
	
	g.drawLine(xPrev,yPrev,xNow,yNow);
	
	xPrev = xNow;
	yPrev = yNow;
	
	int x = (xNow - getWidth()/2) / scale;
	int y = (yNow - getHeight()/2) / scale;
	dist = Math.sqrt(x*x+y*y);
	totalDist += dist;
	avgDist = totalDist / steps;
	
	showStatus("Distance from origin: " + (int)dist + 
	       "   Average distance: " + (int)avgDist);
    }


    //** Generic animation stuff:  use this as is for any animation.
    
    // respond to Timer's event.  
    //Must have this method if implementing ActionListener
    public void actionPerformed( ActionEvent actionEvent ) {
	repaint(); // repaint animator. ** calls paint method
    }
    
    // start or restart animation
    public void startAnimation() {
	if ( animationTimer == null ) {
	    animationTimer = new Timer( animationDelay, this );
	    animationTimer.start();
	}
	else // continue from last image displayed
	    if ( ! animationTimer.isRunning() )
		animationTimer.restart();
    }
    
    // stop animation timer
    public void stopAnimation() {
	animationTimer.stop();
    }
}