/**
 * Mutable quasi-functional linear recursive structure.
 * @author Dung X. Nguyen - Copyright 1999 - All rights reserved.
 * @since 10/01/99
 * @dependency IAlgo 
 */
public class QFList
{
	/** @SBGen Variable (,head,,128)   */
	private IState _head;

	/** @SBGen Constructor   */
	 public QFList()
	{
		_head = NullNode.singleton;
   }

	/**
	 * @param dat data to insert at this node
	 */
	public final void insertFront(Object dat)
	{
		_head.insertFront(dat, this);
	}

	/**
	 * @return Returns this node's first
	 */
	public final Object removeFront()
	{
		return _head.removeFront(this);
	}

	/**
	 * @return Gets the data from this node
	 */
	public final Object getFirst()
	{
		return _head.getFirst(this);
	}

	/**
	 * @param dat new data for this node
	 */
	public final void setFirst(Object dat)
	{
		_head.setFirst(dat, this);
	}

	/**
	 * @return gets the rest of the structure
	 */
	public final QFList getRest()
	{
		return _head.getRest(this);
	}

	/**
	 * @param tail sets a new tail for this node
	 */
	public final void setRest(QFList tail)
	{
		_head.setRest(tail, this);
	}

	public final Object execute(IAlgo visitor, Object param)
	{
	    return _head.execute(visitor, param, this);
	}

	/**
	 * @param head
	 */
	private final void setHead(IState head)
	{
		_head = head;
	}

	/**
	 * @return
	 */
	private final IState getHead()
	{
		return(_head);
	}

  /**
   * null list node. singleton pattern.
  */
  private static class NullNode implements IState
  {
	  public final static NullNode singleton = new NullNode();

	  private NullNode()
	  {
     }

	  /**
	  * @param owner
	  * @return null
	  */
	  public QFList getRest(QFList owner)
	  {
		  throw new java.util.NoSuchElementException ("Empty list has no first.");
	  }

	  /**
	  * @param owner
	  * @return null
	  */
	  public Object getFirst(QFList owner)
	  {
		  throw new java.util.NoSuchElementException ("Empty list has no first.");
	  }

	  /**
	  * @param tail
	  * @param owner
	  */
	  public void setRest(QFList tail, QFList owner)
	  {
		  throw new java.util.NoSuchElementException ("Empty list has no tail.");
	  }

	  /**
	   * @param dat
	   * @param owner
	   */
	  public void setFirst(Object dat, QFList owner)
	  {
		  throw new java.util.NoSuchElementException ("Empty list has no first.");
	  }

	  /**
	   * @param dat
	   * @param owner
	   */
	  public void insertFront(Object dat, QFList owner)
	  {
	      owner.setHead(new NonNullNode(dat));
	  }

	  /**
	   * @param owner
	   * @return
	   */
	  public Object removeFront(QFList owner)
	  {
		  throw new java.util.NoSuchElementException ("Empty list has no front.");
	  }

     public Object execute(IAlgo visitor, Object param, QFList owner)
     {
        return visitor.nullCase(owner, param);
     }
  
		public String toString()
		{
         return "";
		}
}

   /**
   * non-null list node
   */
   private static class NonNullNode implements IState
   {
      /** @SBGen Variable (,tail,,64)   */
	   private Object _dat;
		/** @SBGen Variable (,tail,,64)   */
		private QFList _tail;

	   /**
	   * @param _dat
	   */
	   public NonNullNode(Object dat)
	   {
		   _dat = dat;
  	      _tail = new QFList();
	   }

	   /**
	   * @param owner
	   * @return n
	   */
	   public QFList getRest(QFList owner)
	   {
		   return(_tail);
	   }

	   /**
	   * @param owner
	   * @return n
	   */
	   public Object getFirst(QFList owner)
	   {
		   return(_dat);
	   }

	   /**
	   * @param tail
	   * @param owner
	   */
	   public void setRest(QFList tail, QFList owner)
	   {
		   _tail = tail;
	   }

	   /**
	   * @param first
	   * @param owner
	   */
	   public void setFirst(Object first, QFList owner)
	   {
		   _dat = first;
	   }

	   /**
	   * @param dat
	   * @param owner
	   */
	   public void insertFront (Object dat, QFList owner)
	   {
         NonNullNode newNode = new NonNullNode (dat);
         IState tmpHead = owner.getHead();    // tmpHead = owner._head
         owner.setHead(newNode);              // owner._head = newNode
         owner.getRest().setHead(tmpHead);    // newNode._tail._head = tmpHead
 	   }

	   /**
	   * @param owner
	   * @return the front data.
	   */
	   public Object removeFront(QFList owner)
	   {
         Object dat = owner.getFirst();       // dat = _dat
    	   owner.setHead(owner.getRest().getHead()); // owner._head = _tail._head
    	   return(dat);
	   }

      /**
      * @returns the output object resulting from executing the visitor.
      */
      public Object execute(IAlgo visitor, Object input, QFList owner)
      {
         return visitor.nonNullCase(owner, input);
      }
   
		public String toString()
		{
         return _dat.toString () + " " + _tail.toString ();
		}
}

	public String toString()
	{
      return _head.toString ();
	}
}