import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;

public class Tower extends Applet {
  CurvePanel mainpanel;
  Button restartButton;
  Panel buttonPanel = new Panel();
  Checkbox tangentBox, secantBox;
  int numTanPts = 0; int numSecPts = 0; 
  double slope,y0d,y1d;
  int x0,y0,x1,y1,x2,y2,x3,y3;
  CheckboxGroup cbg;
  public Point clickPoint = null;
  int[] tangentPt = new int[11];
  int[] secantPt = new int[11];
  private static final int RADIUS = 3;
  Color tan_col = new Color(.7f,.6f,.4f);
  boolean clickFlag = false;
boolean tangentLast;
  int slopeInt,slopeFrac;
  String slopeString;

  ActionListener restartListener = new ActionListener() {
    public void actionPerformed (ActionEvent e) {
      numTanPts = 0; numSecPts = 0;
      tangentBox.setState(false); secantBox.setState(true);
      mainpanel.repaint();
    }
  };

  double f(double x) {return 320-(10-5*(x-50)*(x-50)/250/250)*30 ;}

  public void init()
  {
    setBackground(Color.white);
    int numTanPts = 0; int numSecPts = 0;
    mainpanel = new CurvePanel();
    setLayout(new BorderLayout());
    add("Center",mainpanel);
    mainpanel.init();
    add("South",buttonPanel);
    buttonPanel.setLayout(new GridLayout(1,3));

    cbg = new CheckboxGroup();
    tangentBox = new Checkbox("Tangent Lines", cbg, false);
    secantBox = new Checkbox("Secant Lines", cbg, true);
    restartButton = new Button("restart");
    restartButton.addActionListener(restartListener);
    buttonPanel.add(tangentBox);
    buttonPanel.add(secantBox);
    buttonPanel.add(restartButton);
  }

  public class CurvePanel extends Panel {

    public void init(){ addMouseListener(new TowerMouseAdapter());    }

    class TowerMouseAdapter extends MouseAdapter {
      public void mouseClicked(MouseEvent e){
        clickPoint = e.getPoint();
        clickFlag = true; 
        if ((clickPoint.x>=50) && (clickPoint.x<404)){
          if (tangentBox.getState() && numTanPts<10) {
 	    numTanPts++; tangentPt[numTanPts] = clickPoint.x; tangentLast=true;
          }
          else {
	      if (secantBox.getState() && numSecPts<10) {
		 if ((numSecPts%2==0) || (secantPt[numSecPts]!=clickPoint.x)){ //avoid double pt.
		   numSecPts++; secantPt[numSecPts] = clickPoint.x; 
		   if(numSecPts%2==0) tangentLast=false;
	        }
	      }
	    }
	  }    
        repaint(); 
	} 
    }

    public void paint(Graphics g){
      g.setColor(Color.black);
	g.drawRect(0,0,499,399);
      g.drawLine(0, 320, 485, 320);  //t-axis
      g.drawLine(50, 0, 50, 340); //y-axis
      for (int i = 0; i<=10; i++) {   //y-ticks
        int y=320-i*30;
        g.drawLine(45, y, 55, y);
        g.drawString(""+i,34,y);
      }
      for (int i=1; i<18; i++) {     //t-ticks
        int x=i*25+50;
        g.drawLine(x,315,x,325);
        int tenths = i%10; int ones = i/10;
	  g.drawString(""+ones+"."+tenths,x-7,335); 
      }
      g.drawString("t",485,310);
      g.drawString("y",55,10);
  
      g.setColor(Color.yellow);
  	for (int i = 1; i<=10; i++) {  //y-grid
        int y=320-i*30;
        g.drawLine(55, y, 485, y);
	}
      for (int i=1; i<18; i++) {     //t-grid
        int x=i*25+50;
        g.drawLine(x,315,x,0);
      }
      g.setColor(Color.blue);
      for (int x = 50 ; x < 404 ; x=x+5) {   //curve
        g.drawLine(x, (int)f(x), x+5, (int)f(x+5)); 
        g.drawLine(x, (int)f(x)+1, x+5, (int)f(x+5)+1);
	  g.drawLine(x, (int)f(x)-1, x+5, (int)f(x+5)-1);
 	 }
	g.setColor(tan_col);
	for (int i = 1; i <= numTanPts; i++) { //tangent lines        
	  x0 = tangentPt[i]; y0 = (int) f(tangentPt[i]);
	  g.fillOval(x0-RADIUS,y0-RADIUS,2*RADIUS,2*RADIUS);
	  slope = 6*(x0-50.0)/1250.0; x1=50; y1=(int) (y0 + slope*(x1-x0)); 
	  x2=500;y2=(int) (y0 + slope*(x2-x0)); 
	  g.drawLine(x1,y1,x2,y2);
	}
	g.setColor(Color.red);
	for (int i = 1; i <= numSecPts; i++) { //secant lines        
	  g.fillOval(secantPt[i]-RADIUS,(int) f(secantPt[i])-RADIUS,2*RADIUS,2*RADIUS);
	  if (i%2==0){x0 = secantPt[i-1]; y0d = f(secantPt[i-1]);   //two pts. per secant
	    x1 = secantPt[i]; y1d = f(secantPt[i]); slope = (y1d-y0d)/(x1-x0); 
	    x2 = 50; y2 = (int) (y0d+slope*(x2-x0)); x3=500; y3=(int) (y0d+slope*(x3-x0));
	    g.drawLine(x2,y2,x3,y3);
	  }
	}
	g.setColor(Color.black);
	if (numTanPts>0 || numSecPts>1) {
        if (tangentLast) {
	  x0 = tangentPt[numTanPts]; slope = 6*(x0-50.0)/1250.0;
	  }
	  else{
	    if (numSecPts%2==0){
	      x0 = secantPt[numSecPts-1]; y0d = f(secantPt[numSecPts-1]); 
	      x1 = secantPt[numSecPts]; y1d = f(secantPt[numSecPts]); slope = (y1d-y0d)/(x1-x0);
	    }
	  }
	  g.drawString("Slope of last line drawn = "+String.valueOf(((int)(-slope*100*25/3))/100.0)+"  ",30,375);
	}
    }
  }