import java.awt.*;

import java.awt.event.*;

import java.lang.*;
import java.lang.Math;


public class Rotation1 extends java.applet.Applet 

  implements Runnable {


  Canvas oscillators;

  Label massRedLabel, massBlueLabel, massPulleyLabel,  

        massRedS, massBlueS, massPulleyS;

  Button Start;
  Thread runner;

  Scrollbar redMscroll, blueMscroll, redVscroll, blueVscroll;
  int redMass, blueMass, pulleyMass;

  double redM, blueM, pulleyM, accel, redTension, blueTension,

      theta, alpha, pulleyRadius;

  int[] xpos = new int[2];

  double[] x = new double[2];

  Image offscreenImg;

  Graphics offscreenG;



  boolean startFlag = false;


  void buildConstraints(GridBagConstraints gbc, int gx, int gy, 

      int gw, int gh,

      int wx, int wy) {

	gbc.gridx = gx;

	gbc.gridy = gy;

	gbc.gridwidth = gw;

	gbc.gridheight = gh;

	gbc.weightx = wx;

	gbc.weighty = wy;

  }



  public void init() {

    GridBagLayout gridbag = new GridBagLayout();

    GridBagConstraints constraints = new GridBagConstraints();

    setLayout(gridbag);



    xpos[0] = 300;

    xpos[1] = 300;



    // Red mass text

    buildConstraints(constraints, 0, 0, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label massRedLabel = new Label("Mass of red block (kg):", Label.CENTER);

    gridbag.setConstraints (massRedLabel, constraints);

    add(massRedLabel);



    // Red mass scrollbar label

    buildConstraints(constraints, 2, 0, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    massRedS = new Label("4", Label.LEFT);

    redMass = 4;

    gridbag.setConstraints (massRedS, constraints);

    add(massRedS);



    // Red mass scrollbar

    buildConstraints(constraints, 1, 0, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    redMscroll = new Scrollbar(Scrollbar.HORIZONTAL, 4, 1, 1, 10);

    gridbag.setConstraints (redMscroll, constraints);

    add(redMscroll);



    // Blue mass text

    buildConstraints(constraints, 0, 1, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label massBlueLabel = new Label("Mass of blue block (kg):", Label.CENTER);

    gridbag.setConstraints (massBlueLabel, constraints);

    add(massBlueLabel);



    // Blue mass scrollbar label

    buildConstraints(constraints, 2, 1, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    massBlueS = new Label("5", Label.LEFT);

    blueMass = 5;

    gridbag.setConstraints (massBlueS, constraints);

    add(massBlueS);



    // Blue mass scrollbar

    buildConstraints(constraints, 1, 1, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    blueMscroll = new Scrollbar(Scrollbar.HORIZONTAL, 5, 1, 0, 10);

    gridbag.setConstraints (blueMscroll, constraints);

    add(blueMscroll);



    // Red speed text

    buildConstraints(constraints, 0, 2, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label massPulleyLabel = new Label("Mass of the pulley (kg):", Label.CENTER);

    gridbag.setConstraints (massPulleyLabel, constraints);

    add(massPulleyLabel);



    // Red speed scrollbar label

    buildConstraints(constraints, 2, 2, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    massPulleyS = new Label("0", Label.LEFT);

    pulleyMass = 0;

    gridbag.setConstraints (massPulleyS, constraints);

    add(massPulleyS);



    // Red speed scrollbar

    buildConstraints(constraints, 1, 2, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    redVscroll = new Scrollbar(Scrollbar.HORIZONTAL, 0, 1, 0, 25);

    gridbag.setConstraints (redVscroll, constraints);

    add(redVscroll);



    // Start button

    buildConstraints(constraints, 1, 3 , 1, 1, 0, 10);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    Start = new Button("Start");

    gridbag.setConstraints (Start, constraints);

    add(Start);



    // canvas

    buildConstraints(constraints, 0, 4, 3, 1, 0, 80);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    oscillators = new Canvas();

    gridbag.setConstraints (oscillators, constraints);

    add(oscillators);



    offscreenImg = createImage(this.size().width, this.size().height);

    offscreenG = offscreenImg.getGraphics();

  }

  public void start() {
    if (runner == null); {
      runner = new Thread(this);
      runner.start();
    }
  }

  public void stop() {
    if (runner != null) {
      runner.stop();
      runner = null;
    }
  }

  public void run() {

    int index;

    double g, scale, t, deltat, dist;

    deltat=0.5;

    boolean beforeFlag;

    beforeFlag = true;

    startFlag = false;

    g = 9.8;

    scale = 0.01;

    pulleyRadius = 0.1;



    while (true) {

      beforeFlag = true;

      redM = (int)(redMass);

      blueM = (int)(blueMass);

      pulleyM = pulleyMass;

      t = 0.0;



      x[0] = 300.0;

      xpos[0] = (int)(x[0]);

      x[1] = 300.0;

      xpos[1] = (int)(x[1]);

     

      accel = g*(blueM-redM)/(blueM+redM+0.5*pulleyM);

      redTension = redM*(g+accel);

      blueTension = blueM*(g-accel);

      theta = 0.0;

      alpha = accel/pulleyRadius;



      while (startFlag) {



        while (startFlag) { 

          t = t + deltat; 

          dist = 0.5*accel*t*t;

          if (dist>74.0) dist = 74.0; 

          if (dist<-74.0) dist = -74.0;

          theta = scale*dist/pulleyRadius;  

          x[0] = 300.0-dist;

          xpos[0] = (int)(x[0]);

          x[1] = 300.0+dist;

          xpos[1] = (int)(x[1]);

          repaint();

          try { Thread.sleep(100); }

          catch (InterruptedException e) { }

       } 

     }
     repaint();

     try { Thread.sleep(1); }

     catch (InterruptedException e) { }

     }
  }

  public void update(Graphics g) {
    paint(g);
  }

  public void paint(Graphics g) {



  int i, yVal;



     // Draw background

    offscreenG.setColor(Color.lightGray);

    offscreenG.fillRect(0,0,400,199);

    offscreenG.setColor(Color.white);

    offscreenG.fillRect(0,200,400,200);

    

   // Draw mass

    offscreenG.setColor(Color.red);

    offscreenG.fillRect(52,xpos[0],16,16);

    offscreenG.drawLine(60,xpos[0],60,215);

    offscreenG.drawString("Tension in red string = " + redTension + " N", 130, 320);

    offscreenG.setColor(Color.blue);

    offscreenG.fillRect(72,xpos[1],16,16);

    offscreenG.drawLine(80,xpos[1],80,215);

    offscreenG.drawString("Tension in blue string = " + blueTension + " N", 130, 340);

    offscreenG.setColor(Color.darkGray);

    offscreenG.fillOval(60,205,20,20);

    offscreenG.drawString("Acceleration of the blocks = " + accel + " m/s^2", 130, 220);

    offscreenG.drawString("Angular acceleration of the pulley = " + alpha + " rad/s^2", 130, 240);

    offscreenG.drawString("Pulley radius = " + pulleyRadius + " m", 130, 260);

    offscreenG.drawString("Pulley moment of inertia = " + 0.005*pulleyM + " kg m^2", 130, 280);

    offscreenG.drawString("Net torque on the pulley = " + (blueTension-redTension)*pulleyRadius + " N m", 130, 300);

    offscreenG.setColor(Color.white);

    offscreenG.drawLine(70,215,70+(int)(10.0*Math.cos(theta)),215+(int)(10.0*Math.sin(theta)));

    offscreenG.setColor(Color.black);

    offscreenG.drawLine(50,390,90,390);

    g.drawImage(offscreenImg,0,0,this);

  }



  public void destroy() {

     offscreenG.dispose();

  }



  public boolean action (Event evt, Object arg) {



    if (evt.target instanceof Button) {

      if (Start.getLabel().equals("Start")) {

        startFlag = true;

        Start.setLabel("Reset");

      }

      else {

        startFlag = false;

        Start.setLabel("Start");

      }

    }

    else return super.action(evt, arg);

    return true;

  }



  public boolean handleEvent(Event evt) {



    if (evt.target instanceof Scrollbar) {

      if ((Scrollbar)evt.target == redMscroll) {

        redMass = ((Scrollbar)evt.target).getValue();

        massRedS.setText(String.valueOf(redMass));

      }

      else if ((Scrollbar)evt.target == blueMscroll) {

        blueMass = ((Scrollbar)evt.target).getValue();

        massBlueS.setText(String.valueOf(blueMass));

      }

      else if ((Scrollbar)evt.target == redVscroll) {

        pulleyMass = ((Scrollbar)evt.target).getValue();

        massPulleyS.setText(String.valueOf(pulleyMass));

      }

	repaint();

    }

    else return super.handleEvent(evt);

    return true;

  }

}