/*
    * @(#)LinkedList.java					0.3-3 06/05/2001
    *
    *  This file is part of the HTTPClient package
    *  Copyright (C) 1996-2001 Ronald Tschalär
    *
    *  This library is free software; you can redistribute it and/or
    *  modify it under the terms of the GNU Lesser General Public
    *  License as published by the Free Software Foundation; either
   *  version 2 of the License, or (at your option) any later version.
   *
   *  This library is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   *  Lesser General Public License for more details.
   *
   *  You should have received a copy of the GNU Lesser General Public
   *  License along with this library; if not, write to the Free
   *  Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
   *  MA 02111-1307, USA
   *
   *  For questions, suggestions, bug-reports, enhancement-requests etc.
   *  I may be contacted at:
   *
   *  ronald@innovation.ch
   *
   *  The HTTPClient's home page is located at:
   *
   *  http://www.innovation.ch/java/HTTPClient/ 
   *
   */
  
  package HTTPClient;
  
  
  /**
   * This class implements a singly linked list.
   *
   * @version	0.3-3  06/05/2001
   * @author	Ronald Tschalär
   */
  class LinkedList
  {
      /** head of list */
      private LinkElement head = null;
  
      /** tail of list (for faster adding) */
      private LinkElement tail = null;
  
  
      /**
       * Add the specified element to the head of the list.
       *
       * @param elem the object to add to the list.
       */
      public synchronized void addToHead(Object elem)
      {
  	head = new LinkElement(elem, head);
  
  	if (head.next == null)
  	    tail = head;
      }
  
  
      /**
       * Add the specified element to the end of the list.
       *
       * @param elem the object to add to the list.
       */
      public synchronized void addToEnd(Object elem)
      {
  	if (head == null)
  	    head = tail = new LinkElement(elem, null);
  	else
  	    tail = (tail.next = new LinkElement(elem, null));
      }
  
  
      /**
       * Remove the specified element from the list. Does nothing if the element
       * is not in the list.
       *
       * @param elem the object to remove from the list.
       */
      public synchronized void remove(Object elem)
      {
  	if (head == null)  return;
  
  	if (head.element == elem)
  	{
  	    head = head.next;
  	    return;
  	}
  
  	LinkElement curr = head;
  	while (curr.next != null)
  	{
  	    if (curr.next.element == elem)
  	    {
 		if (curr.next == tail)  tail = curr;
 		curr.next = curr.next.next;
 		return;
 	    }
 	    curr = curr.next;
 	}
     }
 
 
     /**
      * Return the first element in the list. The list is not modified in any
      * way.
      *
      * @return the first element
      */
     public synchronized Object getFirst()
     {
 	if (head == null)  return null;
 	return head.element;
     }
 
 
     private LinkElement next_enum = null;
 
     /**
      * Starts an enumeration of all the elements in this list. Note that only
      * one enumeration can be active at any time.
      *
      * @return the first element, or null if the list is empty
      */
     public synchronized Object enumerate()
     {
 	if (head == null)  return null;
 
 	next_enum = head.next;
 	return head.element;
     }
 
 
     /**
      * Gets the next element in the enumeration. The enumeration must have
      * been first initalized with a call to <code>enumerate()</code>.
      *
      * @return the next element, or null if none left
      * @see #enumerate()
      */
     public synchronized Object next()
     {
 	if (next_enum == null)  return null;
 
 	Object elem = next_enum.element;
 	next_enum = next_enum.next;
 
 	return elem;
     }
 
 
     public static void main(String args[])  throws Exception
     {
 	// LinkedList Test Suite
 
 	System.err.println("\n*** Linked List Tests ...");
 
 	LinkedList list = new LinkedList();
 	list.addToHead("One");
 	list.addToEnd("Last");
 	if (!list.getFirst().equals("One"))
 	    throw new Exception("First element wrong");
 	if (!list.enumerate().equals("One"))
 	    throw new Exception("First element wrong");
 	if (!list.next().equals("Last"))
 	    throw new Exception("Last element wrong");
 	if (list.next() != null)
 	    throw new Exception("End of list wrong");
 	list.remove("One");
 	if (!list.getFirst().equals("Last"))
 	    throw new Exception("First element wrong");
 	list.remove("Last");
 	if (list.getFirst() != null)
 	    throw new Exception("End of list wrong");
 
 	list = new LinkedList();
 	list.addToEnd("Last");
 	list.addToHead("One");
 	if (!list.getFirst().equals("One"))
 	    throw new Exception("First element wrong");
 	if (!list.enumerate().equals("One"))
 	    throw new Exception("First element wrong");
 	if (!list.next().equals("Last"))
 	    throw new Exception("Last element wrong");
 	if (list.next() != null)
 	    throw new Exception("End of list wrong");
 	if (!list.enumerate().equals("One"))
 	    throw new Exception("First element wrong");
 	list.remove("One");
 	if (!list.next().equals("Last"))
 	    throw new Exception("Last element wrong");
 	list.remove("Last");
 	if (list.next() != null)
 	    throw new Exception("End of list wrong");
 
 	list = new LinkedList();
 	list.addToEnd("Last");
 	list.addToHead("Two");
 	list.addToHead("One");
 	if (!list.getFirst().equals("One"))
 	    throw new Exception("First element wrong");
 	if (!list.enumerate().equals("One"))
 	    throw new Exception("First element wrong");
 	if (!list.next().equals("Two"))
 	    throw new Exception("Second element wrong");
 	if (!list.next().equals("Last"))
 	    throw new Exception("Last element wrong");
 	if (list.next() != null)
 	    throw new Exception("End of list wrong");
 	list.remove("Last");
 	list.remove("Two");
 	list.remove("One");
 	if (list.getFirst() != null)
 	    throw new Exception("Empty list wrong");
 
 	System.err.println("\n*** Tests finished successfuly");
     }
 }
 
 
 /**
  * The represents a single element in the linked list.
  */
 class LinkElement
 {
     Object      element;
     LinkElement next;
 
     LinkElement(Object elem, LinkElement next)
     {
 	this.element = elem;
 	this.next    = next;
     }
 }