//
// IMPORTANT NOTE:
// This code is not meant to serve as an example of good coding style.
// In fact, it is an ugly hack of some very old code written for DOS
// and ported to Java.
//

import java.applet.Applet;
import java.awt.*;  // for Graphics, Color, Image, Point, ...
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.lang.Math;

public class HilbertCurve extends Applet implements MouseListener {

   int width, height;
   Color fgcolor = Color.black, bgcolor = Color.white;
   int maxGeneration = 6;
   int generation = 1;
   double x, y; // current plotting position
   double s; // segment length
   double page; // the size of the square viewport
   Graphics global_g;
   int x0, y0; // upper left pixel of square viewport

   public void init() {
      width = getSize().width;
      height = getSize().height;

      try {
         maxGeneration = Integer.parseInt( getParameter("max_generation") );
      } catch (Exception E) { }
      try {
         fgcolor = new Color(Integer.parseInt( getParameter("fgcolor"), 16 ));
      } catch (Exception E) { }
      try {
         bgcolor = new Color(Integer.parseInt( getParameter("bgcolor"), 16 ));
      } catch (Exception E) { }

      setBackground( bgcolor );
      setForeground( fgcolor );

      setup();

      addMouseListener( this );
   }

   void setup() {
      if (width > height) {
         page = width;
         x0 = (int)(width-page)/2;
         y0 = 0;
      }
      else {
         page = height;
         x0 = 0;
         y0 = (int)(height-page)/2;
      }
      s = page / Math.round( Math.pow( 2, generation ) );
   }

   public void mouseEntered( MouseEvent e ) { }
   public void mouseExited( MouseEvent e ) { }
   public void mouseClicked( MouseEvent e ) {
      ++ generation;
      if ( generation > maxGeneration ) {
         generation = 1;
      }
      setup();

      repaint();
      e.consume();
   }
   public void mousePressed( MouseEvent e ) { }
   public void mouseReleased( MouseEvent e ) { }

   void plot( double x_new, double y_new ) {
      global_g.drawLine(
         x0 + (int)Math.round( x ), y0 + (int)Math.round( y ),
         x0 + (int)Math.round( x_new ), y0 + (int)Math.round( y_new )
      );
      x = x_new;
      y = y_new;
   }

   void A( int g ) {
      if ( g > 0 ) {
         --g;
         D( g );  plot(x,y-s);
         A( g );  plot(x+s,y);
         A( g );  plot(x,y+s);
         B( g );
      }
   }
   void B( int g ) {
      if ( g > 0 ) {
         --g;
         C( g );  plot(x-s,y);
         B( g );  plot(x,y+s);
         B( g );  plot(x+s,y);
         A( g );
      }
   }
   void C( int g ) {
      if ( g > 0 ) { 
         --g;
         B( g );  plot(x,y+s);
         C( g );  plot(x-s,y);
         C( g );  plot(x,y-s);
         D( g );
      }  
   }  
   void D( int g ) {
      if ( g > 0 ) { 
         --g;
         A( g );  plot(x+s,y);
         D( g );  plot(x,y-s);
         D( g );  plot(x-s,y);
         C( g );
      }  
   }  

   public void paint( Graphics g ) {
      global_g = g; // this is a hack to avoid having to pass g around
      int tmp = s*( (int)Math.round( Math.pow(2,generation) ) - 1 ) + 1;
      x = ( page - tmp ) / 2;
      y = x + tmp;
      A( generation );
   }

   public String getAppletInfo() {
      return "Written by Michael McGuffin";
   }
}