/* COSC 304 section 2
   LUKE BURGESS
   luke_burgess@hotmail.com
   @00205854
   Oct 13 2000 */

// Lab task: Chapter 7, Exercise 7.30, page 314 from "Java How To Program", Deitel & Deitel
// Removes spaces and punctuation (if any) from given word(s) and 
// tests to see if result is a palindrome.

import javax.swing.JApplet;
import javax.swing.JOptionPane;
import javax.swing.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;

public class Exercise30p314 extends JApplet implements ActionListener {

   private JLabel inputLabel, outputLabel;
   private JTextField inputField;
   private JTextArea output;

   public void init () {
      Container c = getContentPane();
      c.setLayout (new FlowLayout());
      c.setBackground(Color.decode("#ccccff"));

      inputLabel = new JLabel ("Enter text:");
      inputField = new JTextField (20);
      inputField.addActionListener (this);
      c.add (inputLabel);
      c.add (inputField);

      outputLabel = new JLabel ("    Answer:");
      output = new JTextArea (1, 20);
      output.setBackground(Color.decode("#ccccff"));
      c.add (outputLabel);
      c.add (output);
   } // init()

   public void actionPerformed (ActionEvent e) {

      String s = e.getActionCommand().toString();

      if (testPalindrome (s))
         output.setText ("Is a palindrome");
      else
         output.setText ("Is not a palindrome");

   } // actionPerformed()

   public static boolean testPalindrome (String s) {
      String stripped = stripInvalidChars (s);
      int firstIndex = 0;
      int lastIndex  = stripped.length() - 1;
      char firstValidChar;
      char lastValidChar;
      boolean answer;

      if (stripped.length() < 2)
         answer = true;

      else {

         firstValidChar = Character.toLowerCase (stripped.charAt (firstIndex));
         lastValidChar = Character.toLowerCase (stripped.charAt (lastIndex));

         if (firstValidChar != lastValidChar)
            answer = false;
         else  // Test all other characters
            answer = testPalindrome (stripped.substring (firstIndex + 1, lastIndex));

      } // else

      return answer;

   } // testPalindrome()

   // Invalid characters include punctuation and spaces.
   public static String stripInvalidChars (String s) {

      int first = 0;
      int last = s.length() - 1;
      boolean validFirst;
      boolean validLast;
      boolean done = false;

      // Increment first and decrement last until each indexes a valid 
      // character, or there are no valid characters to be found.
      while ((first < last) && !done) {

         validFirst = Character.isLetterOrDigit (s.charAt (first));
         validLast = Character.isLetterOrDigit (s.charAt (last));

         if (validFirst && validLast)
            done = true;
         else {
            if (!validFirst)
               first ++;
            if (!validLast)
               last --;
         } // else

      } // while()

      if (first <= last)
         return s.substring (first, last + 1);
      else
         return "";

   } // stripInvalidChars()
} // class Exercise30p314