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

public class Winch extends JPanel {

    // Set this to true to make vertical case with gravity.
    static boolean isVertical = false;

    double g = 9.8;              // Set g=0 for horizonal case.

    // Time variables
    double t = 0;                // Current time.
    double delT = 0.1;           // Time increment.

    // Winch variables
    double winchY = 450;         // (x,y) location of wheel center.
    double winchX = 300;
    double mw = 1;               // Mass.
    double R = 50;               // Radius
    double angularVel = 0;       // angular velocity.

    // Load variables (initial y = 0). The location is determined from the wheel.
    double m = 10;               // Mass.          
    double y = 3*R;              // Height of top edge.
    double yVel = 0;             // Track load velocity.
    double yMax = 250;           // Target.
    double prevY = 0;            // Record previous y value to estimate y'(t)


    // Control variables and parameters.
    double V = 10000;              // Voltage.
    double kP = 5;               // Constant for proportional term.
    double kD = 0;               // Constant for differential term.
    double kI = 0;               // Constant for integral term.
    double S = 0;                // For integration.
        
    // GUI variables.
    int sleepTime = 100;
    String terminateMsg = "";
    Thread currentThread;



    // When the "go" button is pressed, make a thread and fire off a simulation run.

    void go ()
    {
        if (currentThread != null) {
            currentThread.interrupt ();
            currentThread = null;
        }
        
	currentThread = new Thread () {
		public void run () 
		{
		    simulate ();
		}
	    };
	currentThread.start ();
    }
    


    // Perform one simulation run.

    void simulate ()
    {
        reset ();
        while (y < winchY-R) {   // Stop if it collides with the winch.
	    try {
		Thread.sleep (sleepTime);
	    }
	    catch (InterruptedException e) {
                break;
	    }

            nextStep ();
            repaint ();
        }
        terminateMsg = "Final velocity: " + yVel;
    }
    

    // Initialize variables at t=0

    void reset ()
    {
        t = 0;
        // Initial y = height of load = 2R (by design).
        y = 3 * R; 
        prevY = y;

        angularVel = 0;

        if (! isVertical) {
            g = 0;           // No gravity.
        }
        else {
            g = 9.8;
        }
    }
    

    void nextStep ()
    {
        // Current time.
        t = t + delT;

        // PID.
        // V = kP * (yMax - y) - kD * (yVel) + kI * S;

        // Assume that torque is proportional to voltage with const=1
        double torque = V;

        // Compute current mu(t) = angular acceleration.
        double angularAcc = (torque - m*g*R) / (m*R*R + mw*R*R);

        // Update angular velocity.
        angularVel = angularVel + angularAcc * delT;

        // We need the change in angle to compute change in Y because y(t)=R*theta(t)
        double delAngle = angularVel * delT;
        double delY = delAngle * R;
        y = y + delY;

        // Estimate y'(t) - for use in control.
        yVel = (y-prevY) / delT;
        prevY = y;

        // Accumulate errors - for use in control.
        S = S + (yMax - y);
    }
    

    ////////////////////////////////////////////////////////////////////////
    // GUI stuff


    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);
        
        Graphics2D g2 = (Graphics2D) g;
        AffineTransform originalTrans = g2.getTransform ();
        // Rotate for horizontal case.
        if (! isVertical) {
            g2.setTransform (AffineTransform.getRotateInstance(Math.PI/2,D.width/2,D.height/2));
        }
        
        // Winch.
        int drawX = (int) (winchX - R);
        int drawY = (int) (winchY + R);
        g.setColor (Color.blue);
        g.fillOval (drawX,D.height-drawY, (int)R*2, (int)R*2);
        
        // Load.
        drawX = (int) winchX;
        drawY = (int) y;
        g.setColor (Color.red);
        g.fillRect (drawX,D.height-drawY, (int)R*2, (int)R*2);

        // Cable.
        int drawX1 = (int) (winchX + R);
        int drawY1 = (int) winchY;
        int drawY2 = (int) y;
        g.setColor (Color.black);
        g.drawLine (drawX1, D.height-drawY1, drawX1, D.height-drawY2);

        // Goal line.
        g.setColor (Color.lightGray);
        g.drawLine (0, D.height-(int)yMax, D.width, D.height-(int)yMax);

        g2.setTransform (originalTrans);
        // Message.
	g.setColor (Color.black);
	g.drawString (terminateMsg, 500, 500);
    }
    


    JPanel makeBottomPanel ()
    {
        JPanel panel = new JPanel ();
        
        panel.add (new JLabel ("  "));
	JButton goB = new JButton ("Go");
	goB.addActionListener (
	   new ActionListener () {
		   public void actionPerformed (ActionEvent a)
		   {
		       go ();
		   }
           }
        );
	panel.add (goB);

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


    void makeFrame ()
    {
        JFrame frame = new JFrame ();
        frame.setSize (800, 600);
        frame.setTitle ("Winch");
        Container cPane = frame.getContentPane();
        cPane.add (makeBottomPanel(), BorderLayout.SOUTH);
        cPane.add (this, BorderLayout.CENTER);
        frame.setVisible (true);
    }


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

}