import java.applet.Applet;

import java.awt.BorderLayout;
import java.awt.Label;
import java.awt.Choice;
import java.awt.Panel;
import java.awt.TextField;
import java.awt.TextArea;

import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;

/*
 * Applet GUI for Greatest Common Divisor functions.
 */

public class GCDApplet extends Applet implements KeyListener{
  /*
   * The init method builds the user interface. It is also responsible
   * for initializing the event handling.
   */

  // GUI elements

  Choice calc = new Choice();
  TextField a_value = new TextField(12);
  TextField b_value = new TextField(12);
  TextArea result_area = new TextArea("", 4, 30, TextArea.SCROLLBARS_VERTICAL_ONLY);

  public void init(){
    setLayout(new BorderLayout());

    Panel north = new Panel();
    add(north, BorderLayout.NORTH);

    // The north panel should start with a message to the user.
    north.add(new Label("a: "));
    north.add(a_value);
    a_value.addKeyListener(this);

    north.add(new Label("b: "));
    north.add(b_value);
    b_value.addKeyListener(this);

    // Build the function menu and add it to the north panel.
    calc.add("Recursive calulation");
    calc.add("Iterating calculation");

    north.add(calc);

    // Add the text area to the center panel. We also turn off
    // editing so that the user can read from, but not write to the area.
    result_area.setEditable(false);
    add(result_area, BorderLayout.CENTER);

  } //init

  public void keyPressed(KeyEvent event) {}
  public void keyTyped(KeyEvent event) {}

  public void keyReleased(KeyEvent event){
    if((event.getKeyCode() == KeyEvent.VK_ENTER) && ((event.getSource() == a_value) || (event.getSource() == b_value))){
      
      //Initialize
      long a = 0, b = 0;
      
      // Get a and b value from the prompt
      try{
	a = Long.valueOf(a_value.getText()).longValue();
	b = Long.valueOf(b_value.getText()).longValue();
      }catch(Exception e){};

      // Get calculation method, compute gcd and write reslt to text area.
      result_area.append("GCD(" + a + ", " + b + ") = " + GCD.gcd(a, b, (calc.getSelectedIndex() == 0) ? GCD.GCD_REC : GCD.GCD_IT) + "\n");

    } //if
  } //keyReleased
} //class GCDApplet