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

public class MobiusApplet extends Applet implements Runnable
{
	gCanvas	tafel;
	iPanel	instructionPanel;
	Thread	runner;
	Date	currentTime;
	public void init() {
		setBackground(Color.white);
		GridBagLayout gridbag = new GridBagLayout();
		setLayout(gridbag);
		GridBagConstraints c = new GridBagConstraints();
		currentTime = new Date();
		tafel = new gCanvas();
		c.fill = GridBagConstraints.BOTH;
		c.gridwidth = GridBagConstraints.REMAINDER;
		c.weightx = 1.0;
		c.weighty = 20.0;
		c.anchor = GridBagConstraints.WEST;
		gridbag.setConstraints(tafel,c);
		add(tafel);
		instructionPanel = new iPanel();
		c.fill = GridBagConstraints.BOTH;
		c.gridwidth = GridBagConstraints.REMAINDER;
		c.weightx = 1.0;
		c.weighty = 0.0;
		gridbag.setConstraints(instructionPanel,c);
		add(instructionPanel);
}
	
	public void start() {
		if (runner == null) {
			runner = new Thread(this);
			runner.start();
		}
	}
	
	public void stop() {
		if (runner != null) {
			runner.stop();
			runner = null;
		}
	}
	
	public void run() {
		while (true) {
			currentTime = new Date();
			tafel.updateLocation();
			repaint();
			try {Thread.sleep(1000);}
			catch (InterruptedException e) {}
		}
	}
	
}

class iPanel extends Panel{
	iPanel() {
	  setLayout(new BorderLayout());
	  Label l = new Label("2-Dimensionsal Crab Moving in a M\u00f6bius Strip.", Label.CENTER);
	add("Center", l);
	}
}

class gCanvas extends Canvas{
	Color rectBackground,topColor,bottomColor;
	double locationx = 0.45,locationy = 0.45;
	double vx,vy;
	double crabwidth = 0.2, crabheight = 0.14;
	Point Origin;
	int xscale, yscale;
	gCanvas() {
		setBackground(new Color(255,255,192));
		rectBackground = new Color(192,255,255);
		topColor = Color.red;
		bottomColor = Color.green;
		vx = 2*Math.PI/100;
		vy = 4.0/100;
		Origin = new Point(30,20);
		xscale = 330;
		yscale = 250;
		repaint();
	}
	
	private void ConvertCoordinates(double x, double y, Point p) {
		p.x = (int)(Origin.x + xscale*x);
		p.y = (int)(Origin.y + yscale*y);
	}

	public void updateLocation() {
		Color tempColor;
		if (locationy+vy<=0) {
			locationx = locationx-(locationy/vy)*vx;
			locationy = 0;
			vy = -vy;
		}
		else if (locationy+vy >=1-crabheight) {
			locationx = locationx +((1-crabheight-locationy)/vy)*vx;
			locationy = 1-crabheight;
			vy = -vy;
		} else {
			locationx = locationx+vx;
			locationy = locationy + vy;
		}
		if (locationx >1.0) {
			locationx = locationx - 1.0;
			locationy = 1.0 - locationy - crabheight;
			vy = -vy;
			tempColor = topColor;
				topColor = bottomColor;
				bottomColor = tempColor;
			}
		repaint();
		}
	
	public void paint(Graphics g) {
		Point Coords = new Point(0,0);

		g.clipRect(Origin.x,Origin.y,xscale,yscale);
		g.setColor(rectBackground);
		g.fillRect(Origin.x,Origin.y,xscale,yscale);
		
		ConvertCoordinates(locationx, locationy, Coords);
		g.setColor(topColor);
		g.fillArc(Coords.x,Coords.y,(int)(xscale*crabwidth),(int)(yscale*crabheight),30,180);
		g.setColor(bottomColor);
		g.fillArc(Coords.x,Coords.y,(int)(xscale*crabwidth),(int)(yscale*crabheight),180,150);
		if (locationx>1-crabwidth) {
			ConvertCoordinates(locationx-1,1-locationy-crabheight,Coords);
			g.setColor(bottomColor);
			g.fillArc(Coords.x,Coords.y,(int)(xscale*crabwidth),(int)(yscale*crabheight),30,180);
			g.setColor(topColor);
			g.fillArc(Coords.x,Coords.y,(int)(xscale*crabwidth),(int)(yscale*crabheight),180,150);
		}
	}
}