import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Point2D;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JPanel;


class Sistema{
	double g=10;//9.81;
	double m1 = 1;
	double th1 = Math.PI/2;
	double w1=0;
	double L1=1;

	double dt=0.001;

	final int N = 2;

	double energiaIniziale, yPotenziale0;

	ArrayList<Point2D.Double> tracciato = new ArrayList<Point2D.Double>();

	public Sistema(){
		double y0 = getY();

		yPotenziale0 = m1*L1;
		energiaIniziale = energiaCinetica()+energiaPotenziale();

		System.out.println("y0:"+y0);
		System.out.println("y:"+yPotenziale0 + " Tot."+energiaIniziale+" = C:"+energiaCinetica()+" P:"+energiaPotenziale());

	}

	synchronized ArrayList<Point2D.Double> getTracciato(){
		return tracciato;
	}

	synchronized double energiaCinetica(){
		return m1*L1*L1*w1*w1/2;
	}

	synchronized double energiaPotenziale(){
		return m1*g*yPotenziale0+g*m1*getY();
	}

	synchronized double getX(){ 
		double x1 = L1*Math.sin(th1);
		return x1; 
	}

	synchronized double getY(){ 
		double y1 = -L1*Math.cos(th1);
		return y1; 
	}



	void simulate(){
		
		synchronized(this){
			double yin[] = new double[N];
			yin[0] = th1;
			yin[1] = w1;
			double yout[] = runge_kutta(0, yin, dt);
			this.th1 = yout[0];
			this.w1 = yout[1];
			
			//System.out.println(""+Math.toDegrees(th1)+" "+w1);

			tracciato.add(new Point2D.Double(getX(), getY()));
		}
	}

	double[] derivs(double xin, double yin[])
	{
		/*
		    yin[0] = th1[i];
			yin[1] = w1[i];
			yin[2] = th2[i];
			yin[3] = w2[i];
		 */

		double dydx[] = new double[N];
		/* function to fill array of derivatives dydx at xin */

		dydx[0] = yin[1]; 
		dydx[1] = -g/L1*Math.sin(th1);

		return dydx;

	}

	double[] runge_kutta(double xin, double yin[], double h)
	{
		double yout[] = new double[N];
		/* fourth order Runge-Kutta - see e.g. Numerical Recipes */

		int i;
		double hh, xh;
		double dydx[] = new double[N];
		double dydxt[] = new double[N];
		double yt[] = new double[N];
		double k1[] = new double[N];
		double k2[] = new double[N];
		double k3[] = new double[N];
		double k4[] = new double[N];

		hh = 0.5*h;
		xh = xin + hh; 

		dydx = derivs(xin, yin); /* first step */
//		System.out.print("a:");
		for (i = 0; i < N; i++) 
		{
			k1[i] = h*dydx[i];
			yt[i] = yin[i] + 0.5*k1[i];
//			System.out.printf(" %5.2f ",k1[i]);
		}

		dydxt = derivs(xh, yt); /* second step */ 
//		System.out.print("\nb:");
		for (i = 0; i < N; i++)
		{
			k2[i] = h*dydxt[i];
			yt[i] = yin[i] + 0.5*k2[i];
//			System.out.printf(" %5.2f ",k2[i]);
		}   

		dydxt = derivs(xh, yt); /* third step */
//		System.out.print("\nc:");
		for (i = 0; i < N; i++)
		{
			k3[i] = h*dydxt[i];
			yt[i] = yin[i] + k3[i];
//			System.out.printf(" %5.2f ",k3[i]);
		}

		dydxt = derivs(xin + h, yt); /* fourth step */
//		System.out.print("\nd:");
		for (i = 0; i < N; i++)
		{
			k4[i] = h*dydxt[i];
			yout[i] = yin[i] + k1[i]/6. + k2[i]/3. + k3[i]/3. + k4[i]/6.;
//			System.out.printf(" %5.2f ",k4[i]);
		}
//		System.out.println();
		return yout;

	}
}

class Pannello extends JPanel implements Runnable, MouseMotionListener{

	double x[];
	double y[];
	int offX, offY;
	double scale;
	final int DIM_BARRA_EN = 400;

	Sistema sistema;

	public Pannello(Sistema sistema){
		this.sistema=sistema;
		x = new double[2];
		y = new double[2];
	}

	@Override
	protected void paintComponent(Graphics g) {
		super.paintComponent(g);
		int raggioPallina=20;
		offX=this.getWidth()/2;
		offY=this.getHeight()/2;
		scale=(getHeight()-100)/sistema.L1/2;
		ArrayList<Point2D.Double> tracciato;
		synchronized(sistema){

			x[0]=sistema.getX()*scale;
			y[0]=-sistema.getY()*scale;
			tracciato = sistema.getTracciato();
		}


		Graphics2D g2 = (Graphics2D)g;        
		g2.setStroke(new BasicStroke(3.0f));

		for(int i=0; i<tracciato.size()-1; i++){
			int x1 = (int) (tracciato.get(i).x*scale+offX);
			int y1 = (int) (-tracciato.get(i).y*scale+offY);
			int x2 = (int) (tracciato.get(i+1).x*scale+offX);
			int y2 = (int) (-tracciato.get(i+1).y*scale+offY);
			int c = (int) (255.0/tracciato.size()*i);
			//			System.out.println("i: "+i+" colore: "+c+" n."+sistema.tracciato.size()*i);
			g2.setPaint(new Color(c, 0, 0));
			g.drawLine(x1,y1,x2,y2);
		}

		g2.setPaint(new Color(0, 0, 0));
		g2.setStroke(new BasicStroke(2.0f));

		//bracci e palline
		g.drawLine(offX,offY, (int)x[0]+offX,(int)y[0]+offY);
		g.fillOval((int)x[0]-raggioPallina/2+offX, (int)y[0]-raggioPallina/2+offY, raggioPallina, raggioPallina);

		//energia
		g2.setStroke(new BasicStroke(1.0f));
		g2.setPaint(new Color(0.5f, 0.5f, 0.5f));
		g.fillRect(10,10,DIM_BARRA_EN,10);//tot
		g2.setPaint(new Color(0f, 1f, 0f));

		double e = sistema.energiaCinetica();
		double v = sistema.energiaPotenziale();
		double m = sistema.energiaIniziale;
		g.fillRect(10,20,(int)(e/sistema.energiaIniziale*DIM_BARRA_EN),10);//cinetica
		g2.setPaint(new Color(1f, 0f, 0f));
		g.fillRect(10+(int)(e/sistema.energiaIniziale*DIM_BARRA_EN),20,
				(int)(v/sistema.energiaIniziale*DIM_BARRA_EN),10);//potenziale


	}

	@Override
	public void mouseDragged(MouseEvent arg0) {
		// TODO Auto-generated method stub

	}
	@Override
	public void mouseMoved(MouseEvent arg0) {

		x[0]=(double)arg0.getX()-offX;
		y[0]=(double)arg0.getY()-offY;

	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		while(true){
			sistema.simulate();

			System.out.format("EnIni:%8.2f Tot.%8.2f = C: %8.2f P: %8.2f\n",
					sistema.energiaIniziale,
					sistema.energiaCinetica()+sistema.energiaPotenziale(),
					sistema.energiaCinetica(),sistema.energiaPotenziale());

			repaint();
			try {
				Thread.sleep((long) (sistema.dt*1000));
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

}


public class Pendolo {


	public static void main(String[] args) {
		JFrame frame = new JFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setSize(600, 600);
		frame.setLayout(null);

		Sistema s = new Sistema();

		Pannello p = new Pannello(s);
		p.setBounds(0,0,600,600);
		frame.add(p);
		p.addMouseMotionListener(p);
		new Thread(p).start();

		s.simulate();

		frame.setVisible(true);
	}


}