import java.applet.*;
import java.awt.*;
import java.util.*;

public class Comet extends Applet implements Runnable{
	Thread drawOval;
	boolean done;
	int Wwidth, Wheight;
	int numBalls = 20;
	ballType ball[];

	class ballType{
		Color colour;
		int x, y, radius, xi, yi, xii, yii, oldx, oldy;

		ballType(){
			oldx = oldy = x = y = radius = 10;
			xi = yi = 0;
			xii = yii = 1;
		}

		ballType(int newx, int newy, int r){
			oldx = newx;
			oldy = y = newy;
			radius = r;
			xi = yi = 0;
			xii = yii = 1;
		}

		void move(){
			oldx = x;
			oldy = y;

			if(x + xi <= 0){
				xi = - xi;
				xii = -1;
				yii = 2;
			}else if(x + xi >= Wwidth - radius){
				xi = - xi;
				xii = 1;
				yii = -2;
			}

			if(y + yi <= 0){
				yi = - yi;
				yii = -1;
				xii = 2;
			}else if(y + yi >= Wheight - radius){
				yi = - yi;
				yii = 1;
				xii = -2;
			}

			x += xi;
			y += yi;
			xi += xii;
			yi += yii;
		}

		public void trail(ballType leader){
			float deltax, deltay, length, ratio;
			oldx = x;
			oldy = y;
			deltax = x - leader.x;
			deltay = y - leader.y;
			length = (float)Math.sqrt(deltax * deltax + deltay * deltay) * 2;
			if(length > radius + leader.radius){
				ratio = (float)(radius + leader.radius) / length;
				deltax *= ratio;
				deltay *= ratio;
				x = (int)(leader.x + deltax);
				y = (int)(leader.y + deltay);
			}
		}

	}

	public void init(){
		int n;

		//////// find out what the width and height of the window is. ////////
		Wwidth = (new Integer(getParameter("width"))).intValue();
		Wheight = (new Integer(getParameter("height"))).intValue();

		//////// initialize the balls //////////
		ball = new ballType[numBalls];
		for(n = 0; n < numBalls; n++){
			ball[n] = new ballType();
		}
		ball[0].xii = 1;
		ball[0].yii = -1;
		ball[0].y = Wheight >> 1;
		ball[0].x = Wwidth >> 2;

		for(n = 1; n < numBalls; n++){
			ball[n].radius = (int)((float)(numBalls - n) * 
					       ((float)ball[0].radius / (float)numBalls));

		}

		for(n = 0; n < numBalls; n++){
			ball[n].colour = new Color(
				255 - (n + 1) * (255 / numBalls),
				192 / (n + 1),
				0
			);
		}


		///////// initialize the drawing area //////////
		setBackground(Color.black);
		setForeground(Color.black);


		///////// start the animation thread /////////
		drawOval = new Thread(this);
		drawOval.start();
	}

	public void run(){
		int n;

		while(true){
			ball[0].move();
			for(n = 1; n < numBalls; n++){
				ball[n].trail(ball[n - 1]);
			}

			repaint();

			try{
				Thread.sleep(30);
			}

			catch(Exception e){
				showStatus("Error: " + e.getMessage());
			}
		}
	}

	public void paint(Graphics g){
		int n;
		for(n = numBalls - 1; n >= 0; n--){
			g.setColor(ball[n].colour);
			g.fillOval(ball[n].x, ball[n].y, ball[n].radius << 1, ball[n].radius << 1);
		}
	}

}