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 Incline extends JPanel {

    String statusStr = "";

    double m = 1;                // Mass.
    double alpha = 30;           // Angle of incline to the horizontal.
    double a = 0;                // Acceleration along incline.
    double v = 0;                // Velocity along incline.
    double d = 0;                // Distance from top of incline.
    double g = 9.8;              // meters /second^2
    
    int time;                    // Track the current time.
    int sleepTime = 100;         // For animation.
    int timeStep = sleepTime;    // Advance the clock by this much.

    boolean showShadows = true;  // Show x and y components?

    double top = 0;              // y-value of top of incline (to be calculated).
    double inclineLength = 0;    // Total length (to be calculated).
    int tickSpacing = 30;        // Spacing of tick marks along incline.
    int tickSize = 4;            // Size of each tick mark.

    boolean stopped = true;      // Animation status.

    String terminateMsg = "";
    DecimalFormat df = new DecimalFormat ("##.##");

    // Textfields:
    JTextField angleField, massField;


    void start ()
    {
        // Make a thread and run a simulation (whenever "Go" is clicked).
	Thread t = new Thread () {
		public void run () 
		{
		    simulate ();
		}
	    };
	t.start ();
    }


    void simulate ()
    {
	runSimulation (100000);
    }


    double runSimulation (double stopTime)
    {
	// Initialize variables.
	a = 0;
	v = 0;
        d = 0;
        
	stopped = false;
	time = 0;

	while (! stopped) {

            // First pause the thread.
	    try {
		Thread.sleep (sleepTime);
	    }
	    catch (InterruptedException e) {
	    }

	    // Now we're past the sleeptime. Update clock.
	    time += timeStep;

            // Interval of time in seconds.
	    double delT = (double) timeStep / 1000.0;  

            // Acceleration along incline: g*sin(alpha).
            double angleRadians = 2*Math.PI*alpha / 360.0;
            a = g * Math.sin(angleRadians);

            // Increase velocity accordingly.
	    v = v + delT * a;

            // Increase distance according to velocity.
            d = d + delT * v;

	    if ((time >= stopTime) || (d >= inclineLength)) {
		stopped = true;
		break;
	    }

	    // Redraw screen.
	    repaint ();
	}

	// Done.
        return d;
    }


    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 X and Y ticks.
        g.setColor (Color.lightGray);
        for (int i=0; i<=D.width; i+=tickSpacing) {
            g.drawLine (i, D.height, i, D.height-tickSize);
        }
        for (int i=0; i<=D.height; i+=tickSpacing) {
            g.drawLine (0, D.height-i, tickSize, D.height-i);
        }
        
        // Draw incline.
        double angleRadians = 2*Math.PI*alpha / 360.0;
        top = D.width * Math.tan (angleRadians);
        g.drawLine (0,D.height-(int)top, D.width, D.height);

        // Draw markers on incline.
        inclineLength = D.width / Math.cos (angleRadians);
        for (double mark=0; mark<=inclineLength; mark+=tickSpacing) {
            // Distance along incline from bottom.
            double dist = inclineLength - mark;
            int xVal = D.width - (int) (dist * Math.cos (angleRadians));
            int yVal = (int) (dist * Math.sin (angleRadians));
            g.fillOval (xVal-2, D.height-yVal-2, 4, 4);
        }
        
        // Draw the bead [sic].
	g.setColor (Color.red);
        int x = (int) (D.width - (inclineLength - d) * Math.cos (angleRadians));
        int y = (int) ((inclineLength - d) * Math.sin (angleRadians));
	g.fillOval (x-10, D.height-y-10, 20, 20);

        // Draw shadows.
        if (showShadows) {
            g.setColor (Color.lightGray);
            g.fillOval (x-5, D.height-5, 10, 10);
            g.fillOval (-5, D.height-y-5, 10, 10);
        }
        

	// Status:
	g.setColor (Color.black);
	g.setFont (new Font ("Serif", Font.BOLD, 20));
	int seconds = time / 1000;
	int millis = time % 1000;
	String clockStr = "time: " + seconds + ":" + millis;
	g.drawString (clockStr, 300, 20);
        g.setColor (Color.red);
        g.drawString ("dist: " + df.format(d), 300, 40);
    }


    void go ()
    {
        try {
            // Read angle and mass from textfields.
            alpha = Double.parseDouble (angleField.getText());
            m = Double.parseDouble (massField.getText());
            stopped = false;
            // Fire off the simulation thread.
            start ();
        }
        catch (Exception e) {
        }
    }
    

    public void makeFrame ()
    {
        JFrame frame = new JFrame ();
        frame.setSize (500, 400);
        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 ();

        // Angle field.
        panel.add (new JLabel ("Angle: "));
        angleField = new JTextField (4);
        angleField.setText ("30");
        panel.add (angleField);
        panel.add (new JLabel ("   "));

        // Mass field.
        panel.add (new JLabel ("Mass: "));
        massField = new JTextField (4);
        massField.setText ("1");
        panel.add (massField);
        panel.add (new JLabel ("       "));

        // Go button.
        JButton button = new JButton ("Go");
        button.addActionListener (
           new ActionListener () 
           {
               public void actionPerformed (ActionEvent a) 
               {
                   go ();
               }
           }
        );
        panel.add (button);
        
        // Quit 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)
    {
        Incline I = new Incline ();
        I.makeFrame ();
    }

}