/*
    Virtual Physics Lab:  Pendulum
 */

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

public class pendulum extends Applet implements Runnable{
    public MediaTracker tracker;
	public Image offScreenImage;
	public Image theBox;
	public boolean copyRight = false;
	Thread moveThread;
	private static final int MOVEPAUSE = 50;
	public boolean stopWatch = false, myGo = false, myPause = false;
	public long t0, t1, tpause;
	public String timeout = "0", timeout1 = "", timeout2 = "", timeout3 = "";
	public Color colorBack = new Color(0, 80, 0);
	public 	Color colorBob1 = new Color(120, 0, 0);
	public 	Color colorBob2 = new Color(150,0, 0);
	public 	Color colorBob3 = new Color(180,0, 0);
	public int dt = 0, minutes=0, hours=0;
	public double time=0.0;
	public int ix0 = 275, iy0 = 97, ix, iy, iPendL;
	public double pendL, x=0, y, A, omega;
	public boolean dragBob = false;

	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 init() {
		super.init();		
		// load the backgrond image
		tracker= new MediaTracker(this);
		theBox = this.getImage(getCodeBase(),"bg.jpg");
		tracker.addImage(theBox,0);
		try {
	    	tracker.waitForID(0);
		} catch (InterruptedException e) {
		}
		offScreenImage = createImage(500,350);
		pendL = 0.5+0.5*Math.random();
		y = pendL;
		iPendL = (int)(200*pendL);

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

	public void update(Graphics g){
		Graphics offg = offScreenImage.getGraphics();
		paint(offg);
		g.drawImage(offScreenImage, 0, 0, this);
	}

	public void paint(Graphics g){
		g.setColor(Color.gray);
		g.fillRect(0,0,500,350);
		g.drawImage(theBox,91,0,theBox.getWidth(this),theBox.getHeight(this),this);
		g.setColor(colorBack);
		g.fillRect(0,220,140,130);
		g.setColor(Color.white);
		g.drawRect(3,223,134,124);
		g.setColor(Color.black);
		g.fillRect(6,226,128,40);
		if (stopWatch) {
			dt = (int)(System.currentTimeMillis() - t1);
			time = dt/1000.;
			if (time >= 60) {
				time = time - 60.0;
				t1 = t1 + 60000;
				minutes++;
			}
			if (minutes == 60) {
				minutes = 0;
				hours++;
			}
			if (hours < 1) {
				if (minutes < 1) {
					timeout = ""+time;
				} else {
					if (time < 10) {
						timeout = ""+minutes+":0"+time;
					} else {
						timeout = ""+minutes+":"+time;
					}
				}
			} else {
				String outmin = ""+minutes;
				if (minutes < 10) outmin = "0"+minutes;
				String outsec = ""+time;
				if (time < 10) outsec = "0"+time;
				timeout = ""+hours+":"+outmin+":"+outsec;
			}
		}
		g.setColor(Color.red);
		g.setFont(new Font("Courier", Font.BOLD, 24));
		g.drawString(timeout,15,257);
		g.setFont(new Font("Courier", Font.BOLD, 18));
		if (!timeout1.equals("")) {
			// lap time 1 display
			g.setColor(Color.white);
			g.drawString("1>",15,290);
			g.setColor(Color.red);
			g.drawString(timeout1,45,290);
		}
		if (!timeout2.equals("")) {
			// lap time 2 display
			g.setColor(Color.white);
			g.drawString("2>",15,310);
			g.setColor(Color.red);
			g.drawString(timeout2,45,310);
		}
		if (!timeout3.equals("")) {
			// lap time 3 display
			g.setColor(Color.white);
			g.drawString("3>",15,330);
			g.setColor(Color.red);
			g.drawString(timeout3,45,330);
		}
		
		// pendulum
		// T   =   2 pi (L/g)^(1/2)
		// omega = (g/L)^(1/2) / (1 + k^2/4 + 9k^4/64 + ...) with k=sin(theta0/2)
		// theta(t) = A cos(omega t)
				
		if (dragBob) {
			g.setColor(Color.blue);
			g.drawLine(ix0,iy0,ix0,iy0+100);
			double angle = 90.0 - 180.0*Math.atan2(y,x)/Math.PI;
			A = angle*Math.PI/180.;  // initial angular amplitude
			//g.drawString("sA = "+sA,10,30);
			//g.drawString("theFactor = "+theFactor,10,50);
			//g.drawString("omega ="+omega,10,70);
			if (angle > 0) {
				g.drawString(outString(""+angle,4),ix0+2,iy0+30);
			} else {
				g.drawString(outString(""+angle,5),ix0+2,iy0+30);
			}
		} else {
			int it = (int)(System.currentTimeMillis() - t0);
			double t = it/1000.;
			A = A*0.9998;					// damping of amplitude
			double sA = Math.sin(A/2.);		// calculate large amplitude corrections
			double theFactor = 1.0 + sA*sA/4.0 + 9.0*sA*sA*sA*sA/64.0;
			omega = Math.sqrt(9.81/pendL) / theFactor;	// omega with large amplitude corrections
			double thetanow = A * Math.cos(omega*t);
			x = pendL*Math.sin(thetanow);
			y = pendL*Math.cos(thetanow);
		}
		ix = (int)(200*x);
		iy = (int)(200*y);
		g.setColor(Color.black);
		g.drawLine(ix0,iy0,ix0+ix,iy0+iy);
		g.setColor(colorBob1);
		g.fillOval(ix0+ix-8,iy0+iy-8,17,17);
		g.setColor(colorBob2);
		g.fillOval(ix0+ix-7,iy0+iy-7,13,13);
		g.setColor(colorBob3);
		g.fillOval(ix0+ix-6,iy0+iy-6, 9, 9);
		g.setColor(Color.white);
		g.fillOval(ix0+ix-4,iy0+iy-4, 2, 2);

		// 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.id == Event.KEY_PRESS){
			String thePressedKey = ""+(char)event.key;
			if (thePressedKey.equalsIgnoreCase("w")) {
				copyRight = !copyRight;
	            repaint();
			}
			if (thePressedKey.equalsIgnoreCase("s")) {
				stopWatch = !stopWatch;
	            if (stopWatch) {
		            t1 = System.currentTimeMillis();
		            minutes = 0;
		            hours = 0;
		            timeout = "0";
		            timeout1 = "";
		            timeout2 = "";
		            timeout3 = "";
					myGo = true;
					myPause = false;
					start();
				} else {
					myGo= false;
					myPause = false;
					stop();
				}
	            repaint();
			}
			if (thePressedKey.equalsIgnoreCase("p")) {
				myPause = !myPause;
	            if (!myPause) {
		            t1 = t1 + System.currentTimeMillis() - tpause;
					stopWatch = true;
					myGo = true;
					start();
				} else {
					tpause = System.currentTimeMillis();
					stopWatch = false;
					myGo= false;
					stop();
				}
	            repaint();
			}
			if (thePressedKey.equalsIgnoreCase("c")) {
		        minutes = 0;
		        hours = 0;
		        timeout = "0";
		        timeout1 = "";
		        timeout2 = "";
		        timeout3 = "";
				myPause = false;
				myGo = false;
				stopWatch = false;
				stop();
	            repaint();
			}
			if (thePressedKey.equals("1")) {
				timeout1 = timeout;
	            repaint();
			}
			if (thePressedKey.equals("2")) {
				timeout2 = timeout;
	            repaint();
			}
			if (thePressedKey.equals("3")) {
				timeout3 = timeout;
	            repaint();
			}
		}
		if (event.target == this && event.id == Event.MOUSE_DOWN) {
			pendulum_MouseDown(event);
			return true;
		}
		if (event.target == this && event.id == Event.MOUSE_DRAG) {
			pendulum_MouseDrag(event);
			return true;
		}
		if (event.target == this && event.id == Event.MOUSE_UP) {
			pendulum_MouseUp(event);
			return true;
		}
		return super.handleEvent(event);
	}

	//{{DECLARE_CONTROLS
	//}}

	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);
	}

	void pendulum_MouseDown(Event event) {
		int xx = event.x;
		int yy = event.y;
		if (Math.abs(xx-ix-ix0)<10 && Math.abs(yy-iy-iy0)<10) {
			dragBob = true;
			repaint();
		}
	}

	void pendulum_MouseDrag(Event event) {
		int xx = event.x;
		int yy = event.y;
		if (dragBob) {
			ix = Math.min(iPendL,Math.max((xx-ix0),-iPendL));
			iy = (int)(Math.sqrt(-1.0*ix*ix + 1.0*iPendL*iPendL));
			x = ix/200.;
			y = iy/200.;
			repaint();
		}
	}

	void pendulum_MouseUp(Event event) {
		dragBob = false;
		t1 = System.currentTimeMillis();
		t0 = t1;
		myGo = true;
		stopWatch = true;
		start();
		repaint();
	}

}