/*
    Put an electron into orbit
 */

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

public class Orbit extends Applet implements Runnable{
	Thread moveThread;
	private static final int MOVEPAUSE = 30;
	public boolean myGo = false, inTow = false, copyRight = false;
	public boolean holdIt = false, crashed = false;;
	public Image theBack, theFront;
	public Image offScreenImage;
	public int xS=100, yS=100, vx=0, vy=0;
	public int xE=250, yE=175, rE=15;
	public double vv=0, xx=xS, yy=yS, xxV=0, yyV=0;
	public int t=0;
	
	public double vscale=10000.0, rscale=0.01;


	public void start()  {
		if(myGo) {
			if(moveThread == null){
				moveThread = new Thread(this);
				moveThread.start();
			}
		}
	}
	
	public void stop()  {
		if(moveThread != null){
			moveThread.stop();
			try {
				moveThread.join();
			}
			catch (InterruptedException e) { }
		}
		moveThread=null;
	}
		
	public void run() {
		while (true){
			try {
				moveThread.sleep(MOVEPAUSE);
			}catch(InterruptedException e) {
			}
			repaint();
		}
	}
	
	public void update(Graphics g){
		Graphics offg = offScreenImage.getGraphics();
		paint(offg);
		g.drawImage(offScreenImage, 0, 0, this);
	}

	public void init() {
		super.init();
		offScreenImage = createImage(500,350);

		//{{INIT_CONTROLS
		setLayout(null);
		resize(500,350);
		//}}
		
		repaint();
	}

	public void paint(Graphics g){
		g.setColor(Color.lightGray);
		g.fillRect(0,0,500,350);
		
		for (int i=0; i<10; i++){
			g.setColor(new Color(255,i*20,i*20));
			g.fillOval(xE-rE+i,yE-rE+i,2*rE-3*i,2*rE-3*i);
		}
		g.setColor(Color.black);
		g.setFont(new Font("Helvetica", Font.BOLD, 24));
		g.drawString("+",xE-7,yE+7);

		if (crashed) {
			g.setColor(Color.red);
			g.fillOval((int)xx-10,(int)yy-10,20,20);
			myGo = false;
			stop();
		} else {
			for (int i=0; i<10; i++){
				g.setColor(new Color(i*20,i*20,255));
				g.fillOval((int)xx-rE+i,(int)yy-rE+i,2*rE-3*i,2*rE-3*i);
			}
			g.setColor(Color.black);
			g.setFont(new Font("Helvetica", Font.BOLD, 30));
			g.drawString("-",(int)xx-6,(int)yy+6);
			
			vv = Math.sqrt(xxV*xxV + yyV*yyV);

			if (inTow){
				t=0;
				g.setColor(Color.lightGray);
				if (vv < 10) {
					g.drawLine(xS, yS, xS+vx, yS+vy);
				} else {
					drawArrow(g, xS, yS, xS+vx, yS+vy);
				}
				xx = (double)xS;
				yy = (double)yS;
				xxV = (double)vx;
				yyV = (double)vy;
			} else {
				g.setColor(Color.yellow);
				if (vv < 10) {
					g.drawLine((int)xx, (int)yy, (int)(xx+xxV), (int)(yy+yyV));
				} else {
					drawArrow(g, (int)xx, (int)yy, (int)(xx+xxV), (int)(yy+yyV));
				}
			}
			
			if (myGo) {
				t++;
				double dist = Math.sqrt((xx-xE)*(xx-xE) + (yy-yE)*(yy-yE));		
				xxV = xxV - vscale*(xx-xE)/(dist*dist*dist);
				yyV = yyV - vscale*(yy-yE)/(dist*dist*dist);
				xx = xx + rscale*xxV;
				yy = yy + rscale*yyV;
				if (dist < rE) crashed = true;
			}
		}
		
		if (xx > 520 || xx < -20 || yy > 370 || yy < -20) {
			myGo = false;
			stop();
		}

		if (myGo) {
			g.setColor(Color.red);
			g.setFont(new Font("Helvetica", Font.BOLD, 12));
			g.drawString("Running ...",430,10);
		}
				
		/*
		g.setColor(Color.white);
		g.drawString("xx ="+xx,400,30);
		g.drawString("yy ="+yy,400,60);
		g.drawString("xxV ="+xxV,400,90);
		g.drawString("yyV ="+yyV,400,120);
		g.drawString("t ="+t,400,150);
		*/
		
		// copyright notice:
		if (copyRight) {
			g.setColor(Color.green);
			g.fillRect(100,100,240,70);
			g.setColor(Color.white);
			g.setFont(new Font("Helvetica", Font.PLAIN, 18));
			g.drawString("This applet was written by:",110,120);
			g.drawString("Wolfgang Bauer",110,140);
			g.drawString("Copyright: WB 1999",110,160);
		}
	}

	public boolean handleEvent(Event event) {
		if (event.target == this && event.id == Event.KEY_PRESS) {
			String thePressedKey = ""+(char)event.key;
			if (thePressedKey.equalsIgnoreCase("w")) {
				copyRight = !copyRight;
	            repaint();
			}
			if (thePressedKey.equalsIgnoreCase("s")) {
				holdIt = !holdIt;
				if (holdIt) {
					stop();
				} else {
					start();
		            repaint();
				}
			}
		}
		if (event.target == this && event.id == Event.MOUSE_DOWN) {
			myGo = false;
			inTow = true;
			holdIt = false;
			crashed = false;
			xS = event.x;
			yS = event.y;
			vy = 0;
			vy = 0;
			repaint();
			return true;
		}
		if (event.target == this && event.id == Event.MOUSE_DRAG) {
			vx = event.x - xS;
			vy = event.y - yS;
			repaint();
			return true;
		}
		if (event.target == this && event.id == Event.MOUSE_UP) {
			myGo = true;
			inTow = false;
			vx = event.x - xS;
			vy = event.y - yS;
			start();
			repaint();
			return true;
		}
		return super.handleEvent(event);
	}
	
	public void drawArrow(Graphics g, int tailX, int tailY, int headX, int headY) {
	    double theta = Math.atan( (double)(tailY-headY)/(tailX-headX) );
	    if((tailX-headX)>=0) theta+= Math.PI;
	    int w1=8/2, w2=16/2, w3=24/2;
	    double s = Math.sin(theta);
	    double c = Math.cos(theta);	    
	    int sw1 = (int)(s*w1);
	    int sw2 = (int)(s*w2);
	    int sw3 = (int)(s*w3);
	    int cw1 = (int)(c*w1);
	    int cw2 = (int)(c*w2);
	    int cw3 = (int)(c*w3);
	    int[] exes = {tailX-sw1, headX-cw3-sw1, headX-cw3-sw2, headX, headX-cw3+sw2, headX-cw3+sw1, tailX+sw1, tailX-sw1};
	    int[] whys = {tailY+cw1, headY-sw3+cw1, headY-sw3+cw2, headY, headY-sw3-cw2, headY-sw3-cw1, tailY-cw1, tailY+cw1};
	    Polygon arrow = new Polygon(exes, whys, 8);
	    g.fillPolygon(arrow); 
	    g.setColor(Color.black);
	    g.drawPolygon(arrow);   
	}	
	
	public String outString(String inString, int l){    // returns the first l chars of string
		int ls = (int)Math.min(inString.length(),l);
		return inString.substring(0,ls);
	}

	//{{DECLARE_CONTROLS
	//}}
}