import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
import java.util.*;
import java.text.*;

public class MultiIncline extends JPanel implements MouseInputListener {

    String statusStr = "";

    boolean designMode = false;       // If in design mode, corners can be moved.
    int radius = 10;                  // Radius of bead.
    int numSegments = 2;              // Number of segments in incline.
    double maxX = 400;                // x3
    double[] segx, segy;              // Store x and y values of intermediate points.

    // Variables tied to the current segment (where the bead is now).
    int currentSeg = -1;              
    double cosineOfCurrentAngle;      
    double sineOfCurrentAngle;

    // The usual physical variables.
    double m = 1;
    double ax, ay;
    double vx, vy;
    double x,y;
    double g = 9.8;  
    int time;

    // Animation:
    int sleepTime = 100;
    int timeStep = sleepTime;
    boolean stopped = true;

    // GUI:
    String terminateMsg = "";
    DecimalFormat df = new DecimalFormat ("##.##");
    JTextField segmentsField;
    int currentBeingDragged = -1;


    public MultiIncline ()
    {
	initSegments ();
	this.addMouseListener (this);
	this.addMouseMotionListener (this);
    }


    void initSegments ()
    {
	segx = new double [numSegments + 1];
	segy = new double [numSegments + 1];
	// Initialize the x and y parts.
	double interval = maxX / numSegments;

        // Leftmost point (the start).
	segx[0] = 0;
	segy[0] = maxX;

        // Intermediate points along straight line.
	for (int i=1; i<numSegments; i++) {
	    segx[i] = i * interval;
	    segy[i] = maxX - i * interval;
	}

        // Rightmost.
	segx[numSegments] = maxX;
	segy[numSegments] = 0;
    }


    void start ()
    {
	Thread t = new Thread () {
		public void run () 
		{
		    simulate ();
		}
	    };
	t.start ();
    }


    void simulate ()
    {
	// Initialize variables.
        double a = 0;
	ax = ay = 0;
	vx = vy = 0;
	x = 0;
	y = maxX;

        // We'll set currentSeg=0 inside loop.
        currentSeg = -1;

	stopped = false;
	time = 0;

	while (! stopped) {

            // Pause animation.
	    try {
		Thread.sleep (sleepTime);
	    }
	    catch (InterruptedException e) {
	    }

	    // Update clock.
	    time += timeStep;

	    double delT = (double) timeStep / 1000.0;  // seconds.

	    if (x >= segx[currentSeg+1]) {
                // Change to new segment.
		currentSeg ++;
		double hyp = distance (segx[currentSeg],segy[currentSeg], segx[currentSeg+1],segy[currentSeg+1]);
		double yDiff = Math.abs (segy[currentSeg] - segy[currentSeg+1]);
		double xDiff = Math.abs (segx[currentSeg] - segx[currentSeg+1]);
		cosineOfCurrentAngle = xDiff / hyp;
		sineOfCurrentAngle = yDiff / hyp;
                a = g * sineOfCurrentAngle;

		// Now conserve energy
		double v = Math.sqrt (vx*vx + vy*vy);
		vx = v * cosineOfCurrentAngle;
		vy = - v * sineOfCurrentAngle;
	    }

            // Horizontal and vertical accelerations.
	    ax = a * cosineOfCurrentAngle;
            ay = - a * sineOfCurrentAngle;

            // Increase velocity accordingly.
	    vx = vx + delT * ax;
	    vy = vy + delT * ay;

            // Increase distance according to velocity.
	    x = x + delT * vx;
	    y = y + delT * vy;

            // If we're close enough to the end, stop.
	    if (x >= (maxX - 0.01)) {
		break;
	    }

	    // Redraw.
	    repaint ();
	}

    }


    public void paintComponent (Graphics g)
    {
	super.paintComponent (g);

	Dimension D = this.getSize ();

	// Background.
	g.setColor (Color.white);
	g.fillRect (0,0, D.width, D.height);

        // Draw segments.
	g.setColor (Color.lightGray);
	for (int i=0; i<numSegments; i++) {
	    // Draw i-th segment.
	    int px = (int)segx[i];
	    int py = (int)segy[i];
	    int qx = (int)segx[i+1];
	    int qy = (int)segy[i+1];
	    g.drawLine (px, D.height-py, qx, D.height-qy);
	    g.fillOval (px-2,D.height-py-2, 4, 4);
	    g.fillOval (qx-2,D.height-qy-2, 4, 4);
	}

	// If design mode, draw circles.
	if (designMode) {
	    g.setColor (Color.black);
	    for (int i=0; i<=numSegments; i++) {
		g.drawOval ((int)segx[i]-radius, D.height-(int)segy[i]-radius, 2*radius, 2*radius);
	    }
	    return;
	}

        // Draw the bead [sic].
	g.setColor (Color.red);
	g.fillOval ((int)x-10, D.height-(int)y-10, 20, 20);


	// Time taken so far:
	g.setColor (Color.black);
	g.setFont (new Font ("Serif", Font.BOLD, 20));
	int seconds = time / 1000;
	int millis = time % 1000;
	String clockStr = "" + seconds + ":" + millis;
	g.drawString (clockStr, 300, 20);
    }


    //////////////////////////////////////////////////////////////////////
    //
    // GUI stuff below

    void go ()
    {
	designMode = false;
	stopped = false;
	start ();
    }

    void design ()
    {
        try {
            int n = Integer.parseInt (segmentsField.getText());
	    if ((n >= 2) && (n != numSegments)) {
		numSegments = n;
		initSegments ();
	    }
	    designMode = true;
	    this.repaint ();
        }
        catch (Exception e) {
        }
    }


    // These methods are for the mouse-listening interface.
    public void mouseClicked (MouseEvent e) {}
    public void mouseEntered (MouseEvent e) {}
    public void mouseMoved (MouseEvent e) {}

    public void mouseExited (MouseEvent e)  
    {
	currentBeingDragged = -1;
    }


    public void mousePressed (MouseEvent e) 
    {
	if (! designMode) {
	    return;
	}
	currentBeingDragged = nodeClick (e.getPoint());
    }

    int nodeClick (Point clickPoint) 
    {
	// See if click is within a circle.
	Dimension D = this.getSize ();
	for (int i=1; i<numSegments; i++) {
	    double d = distance (clickPoint.x, D.height-clickPoint.y, segx[i], segy[i]);
	    if (d < radius) {
		return i;
	    }
	}
	return -1;
    }
  
    double distance (double x1, double y1, double x2, double y2)
    {
	return Math.sqrt ((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
    }

    public void mouseReleased (MouseEvent e) 
    {
	if (! designMode) {
	    return;
	}
	
	currentBeingDragged = -1;
	this.repaint ();
    }
    
    public void mouseDragged (MouseEvent e) 
    {
	if ((! designMode) || (currentBeingDragged < 0)) {
	    return;
	}
	
	Dimension D = this.getSize();
	int my = e.getY();
	// Check if valid.
	double tempY = D.height - my;
	if ((tempY < segy[currentBeingDragged-1]) && 
	    (tempY > segy[currentBeingDragged+1]) ) {
	    segy[currentBeingDragged] = tempY;
	}
	this.repaint ();
    }


    public void makeFrame ()
    {
        JFrame frame = new JFrame ();
        frame.setSize (500, 500);
        frame.setResizable (true);
        Container cPane = frame.getContentPane ();
        cPane.add (this, BorderLayout.CENTER);
        cPane.add (makeBottomPanel(), BorderLayout.SOUTH);
        frame.setVisible (true);
    }
    
    JPanel makeBottomPanel ()
    {
        JPanel panel = new JPanel ();
        panel.add (new JLabel ("# Segments: "));
        segmentsField = new JTextField (4);
        segmentsField.setText ("2");
        panel.add (segmentsField);

        panel.add (new JLabel ("   "));
        JButton button = new JButton ("Design");
        button.addActionListener (
           new ActionListener () 
           {
               public void actionPerformed (ActionEvent a) 
               {
                   design ();
               }
           }
        );
        panel.add (button);

        panel.add (new JLabel ("   "));
        button = new JButton ("Go");
        button.addActionListener (
           new ActionListener () 
           {
               public void actionPerformed (ActionEvent a) 
               {
                   go ();
               }
           }
        );
        panel.add (button);
        
        panel.add (new JLabel ("       "));
        button = new JButton ("Quit");
        button.addActionListener (
           new ActionListener () 
           {
               public void actionPerformed (ActionEvent a) 
               {
                   System.exit(0);
               }
           }
        );
        panel.add (button);
        return panel;
    }
    

    public static void main (String[] argv)
    {
        MultiIncline m = new MultiIncline ();
        m.makeFrame ();
    }
    

}