import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
/**
 * Demonstrates use of a doubly-linked list
 *
 * @author Mr J
 * @version 20050208
 */
public class NameList extends Applet implements ActionListener
{
	// GUI objects
	private TextField name = new TextField("Type a name here!");
	private Button add = new Button("Add name");
	private Button next = new Button("Next");
	private Button prev = new Button("Previous");
	private TextArea display = new TextArea(20, 30);
	private Label messages = new Label("Messages will appear here");

    // data members
    DoubleNode head = null;
    DoubleNode current = null;
    
	/** 
	 * Add objects to the Applet
	 */
	public void init()
	{
        add(name);
        add(add);
        add(next);
        add(prev);
        add(display);
        add(display);
        add(messages);
        // Causes button presses to be detected
        add.addActionListener(this);
        next.addActionListener(this);
        prev.addActionListener(this);
	}
	/** 
	 * When an event occurs on an object with an ActionListener attached, this
	 * method is carried out.  
	 * 
	 * @param e carries details about the event that occurred
	 */
		public void actionPerformed(ActionEvent e)
	{
	    messages.setText("");
	    // Check the button presses
	    if (e.getSource() == add)
	    {
	        addName();
	    }
	    else if (e.getSource() == next)
	    {
	        displayList( 1 );
	    }
	    else
	    {
	        displayList( -1 );
	    }
	}
	public void addName()
	{
	    // get the name and create a new node at the head
	    String theName = name.getText();
	    DoubleNode newOne = new DoubleNode( theName, head, null);
	    // if head is pointing to a node, set it's previous pointer 
	    if (head != null)
	    {
	        head.setPrev(newOne);
	    }
	    head = newOne;
	    // if no currently selected name, point to head
	    if (current == null)
	    {
	        current = head;
	    }
	    displayList( 0 );
	}
	public void displayList(int move)
	{
	     display.setText("start\n-----\n");
	    // Move the currently selected, if required
	    if (move == 1)
	    {
	        if (current.getNext() != null)
	        {
	            current = current.getNext();
	        }
	        else
	        {
	            messages.setText("At last name");
	        }
	    }
	    else if (move == -1)
	    {
	        if (current.getPrev() != null)
	        {
	            current = current.getPrev();
	        }
	        else
	        {
	            messages.setText("At first name");
	        }
	    }
	    DoubleNode temp = head;
	    // "walk" down the list, using the temp pointer
	    while (temp != null)
	    {
	      if (temp == current)
	      {
	          display.append(temp.getName()  + "<< current\n");
	      }
	      else
	      {
		      display.append(temp.getName()  + "\n");
	      }
		  temp = temp.getNext();
		}
	}
}