import java.awt.*;
import java.awt.event.*;
import java.lang.*;
import java.lang.Math;

public class RelVa extends java.applet.Applet 
  implements Runnable {

  Canvas oscillators;
  Label riverSpeedLabel, boatSpeedLabel, boatAngleLabel,
        riverSpeedS, boatSpeedS, boatAngleS;
  Button Start;
  Thread runner;
  Scrollbar riverSpeedscroll, boatSpeedscroll, boatAnglescroll;
  int riverSpeed, boatSpeed, ballDiameter;
  int[] xpos = new int[5];
  double[] x = new double[5];
  int[] ypos = new int[5];
  double[] y = new double[5];
  int[] vectorX = new int[6];
  double vectorXpos = new double[6];
  int[] vectorY = new int[6];
  double vectorYpos = new double[6];
  double riverV, boatV, boatA, vRSX, vRSY, vBRX, vBRY, vBSX, vBSY,
          crossTime, xDistance;
  double pi = 3.141592653589793238468;

  Image offscreenImg;
  Graphics offscreenG;

  boolean startFlag;

  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);


    // River speed text
    buildConstraints(constraints, 0, 0, 1, 1, 20, 5);
    constraints.fill = GridBagConstraints.NONE;
    constraints.anchor = GridBagConstraints.EAST;
    Label riverSpeedLabel = new Label("Speed of the river (m/s):", Label.CENTER);
    gridbag.setConstraints (riverSpeedLabel, constraints);
    add(riverSpeedLabel);

    // River speed scrollbar label
    buildConstraints(constraints, 2, 0, 1, 1, 20, 0);
    constraints.fill = GridBagConstraints.HORIZONTAL;
    riverSpeedS = new Label("2", Label.LEFT);
    riverSpeed = 2;
    gridbag.setConstraints (riverSpeedS, constraints);
    add(riverSpeedS);

    // River speed scrollbar
    buildConstraints(constraints, 1, 0, 1, 1, 20, 0);
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.anchor = GridBagConstraints.WEST;
    riverSpeedscroll = new Scrollbar(Scrollbar.HORIZONTAL, 0, 0, 0, 5);
    riverSpeedscroll.setValue (riverSpeed);
    gridbag.setConstraints (riverSpeedscroll, constraints);
    add(riverSpeedscroll);

    // boat speed text
    buildConstraints(constraints, 0, 1, 1, 1, 20, 5);
    constraints.fill = GridBagConstraints.NONE;
    constraints.anchor = GridBagConstraints.EAST;
    Label boatSpeedLabel = new Label("Speed of the boat (m/s):", Label.CENTER);
    gridbag.setConstraints (boatSpeedLabel, constraints);
    add(boatSpeedLabel);

    // boat speed scrollbar label
    buildConstraints(constraints, 2, 1, 1, 1, 20, 0);
    constraints.fill = GridBagConstraints.HORIZONTAL;
    boatSpeedS = new Label("5", Label.LEFT);
    boatSpeed = 5;
    gridbag.setConstraints (boatSpeedS, constraints);
    add(boatSpeedS);

    // boat speed scrollbar
    buildConstraints(constraints, 1, 2, 1, 1, 20, 0);
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.anchor = GridBagConstraints.WEST;
    boatSpeedscroll = new Scrollbar(Scrollbar.HORIZONTAL, 0, 0, 1, 12);
    boatSpeedscroll.setValue (boatSpeed);
    gridbag.setConstraints (boatSpeedscroll, constraints);
    add(boatSpeedscroll);

    // boat angle text
    buildConstraints(constraints, 0, 2, 1, 1, 20, 5);
    constraints.fill = GridBagConstraints.NONE;
    constraints.anchor = GridBagConstraints.EAST;
    Label boatAngleLabel = new Label("Boat angle (degrees):", Label.CENTER);
    gridbag.setConstraints (boatAngleLabel, constraints);
    add(boatAngleLabel);

    // boat angle scrollbar label
    buildConstraints(constraints, 2, 2, 1, 1, 20, 0);
    constraints.fill = GridBagConstraints.HORIZONTAL;
    boatAngleS = new Label("0", Label.LEFT);
    boatAngle = 0;
    gridbag.setConstraints (boatAngleS, constraints);
    add(boatAngleS);

    // boat angle scrollbar
    buildConstraints(constraints, 1, 2, 1, 1, 20, 0);
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.anchor = GridBagConstraints.WEST;
    boatAnglescroll = new Scrollbar(Scrollbar.HORIZONTAL, 0, 0, -30, 30);
    boatAnglescroll.setValue (boatAngle);
    gridbag.setConstraints (boatAnglescroll, constraints);
    add(boatAnglescroll);

    // 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() {

    double xOrigin, yOrigin, kAngle, scale;
    ballDiameter = 16;
    kAngle = pi/180.0;
    yOrigin = 380.0;
    xOrigin = 100.0;

    while (true) {
      startFlag = false;
      index = 0;
      currentX = 0.0;
      currentY = 0.0;
      dropTime = 0.0;
      riverV = riverSpeed;
      boatV = boatSpeed;
      boatA = kAngle*boatAngle;

      x[0] = xOrigin-ballDiameter;
      xpos[0] = (int)(x[0]);
      y[0] = yOrigin;
      ypos[0] = (int)(y[0]);

	vRSX = riverV;
      vRSY = 0.0;
      vBRX = boatV*Math.sin(boatA);
      vBRY = boatV*Math.cos(boatA);
      vBSX = vBRX + vRSX;
      vBSY = vBRY + vRSY;

      crossTime = 50.0/vBSY;
      xDistance = vBSX*crossTime;
      
      maxHeight = -0.5*vIntY*vIntY/g;
      maxTime = -2.0*vIntY/g;
      range = vIntX*maxTime;

      while (startFlag) {

        while (startFlag) { 
          currentX = vIntX*dropTime;
          x[index] = x[0]+scale*currentX;
          currentY = dropTime*(vIntY+0.5*g*dropTime);
          y[index] = y[0]-scale*currentY;
          vY = vIntY+g*dropTime;

          xpos[index] = (int)(x[index]);
          ypos[index] = (int)(y[index]);
          repaint();
          try { Thread.sleep(300); }
          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;

     // Draw background
   offscreenG.setColor(Color.lightGray);
   offscreenG.fillRect(0,0,500,200);
   offscreenG.setColor(Color.white);
   offscreenG.fillRect(0,200,500,430);

   // Draw mass
    offscreenG.setColor(Color.black);
    offscreenG.drawLine(10, 220, 290, 220);
    offscreenG.drawLine(10, 380, 290, 380);
    offscreenG.drawLine(150, 210, 150, 220);
    offscreenG.drawLine(150, 380, 150, 390);
    offscreenG.setColor(Color.blue);
    offscreenG.drawString("Velocity of the river relative to the shore", 300, 210);
    offscreenG.drawString("X component : Vrsx = " + vRSX + " m/s", 310, 228);
    offscreenG.drawString("Y component : Vrsy = " + vRSY + " m/s", 310, 246);
    offscreenG.setColor(Color.red);
    offscreenG.fillOval(xpos[index],ypos[index],ballDiameter,ballDiameter);
    offscreenG.drawString("Velocity of the boat relative to the river", 300, 266);
    offscreenG.drawString("X component : Vbrx = " + vBRX + " m/s", 310, 284);
    offscreenG.drawString("Y component : Vbry = " + vBRY + " m/s", 310, 302);
    offscreenG.setColor(Color.black);
    offscreenG.drawString("Velocity of the boat relative to the shore", 300, 322);
    offscreenG.drawString("X component : Vbsx = " + vBSX + " m/s", 310, 340);
    offscreenG.drawString("Y component : Vbsy = " + vBSY + " m/s", 310, 358);
    offscreenG.drawString("Time to cross river = " + crossTime + " s", 300, 378);
    offscreenG.drawString("Distance traveled in x direction = " + xDistance + " m", 300, 396);
    offscreenG.drawString("(when the boat reaches the far shore) ", 310, 414);
    g.drawImage(offscreenImg,0,0,this);
  }

  public void destroy() {
     offscreenG.dispose();
  }

  public boolean action (Event evt, Object arg) {

    if (evt.target instanceof Button) {

      if ((Button)evt.target == Start) {

        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 == riverSpeedscroll) {
        riverSpeed = ((Scrollbar)evt.target).getValue();
        riverSpeedS.setText(String.valueOf(riverSpeed));
      }
      else if ((Scrollbar)evt.target == boatSpeedscroll) {
        boatSpeed = ((Scrollbar)evt.target).getValue();
        boatSpeedS.setText(String.valueOf(boatSpeed));
      }
      else if ((Scrollbar)evt.target == boatAnglescroll) {
        boatAngle = ((Scrollbar)evt.target).getValue();
        boatAngleS.setText(String.valueOf(boatAngle));
      }
	repaint();
    }
    else return super.handleEvent(evt);
    return true;
  }
}