package edu.rice.cs.dxn.QFList;

/**
 * non-null list node
 */
class NonNullNode implements IState
{
   private Object _dat;
	private QFList _tail;

	/**
    * Initializes this NonNullNode to contain dat and an empty tail list.
	 * @param dat the data object to be stored in this NonNullNode.
	 */
	NonNullNode(Object dat)
	{
	   _dat = dat;
  	   _tail = new QFList();
   }

	/**
    * Initializes this NonNullNode to contain dat and a given tail list.
	 * @param dat the data object to be stored in this NonNullNode.
    * @param tail the QFList tail of this NoNullNode.
	 */
	NonNullNode(Object dat, QFList tail)
	{
	   _dat = dat;
  	   _tail = tail;
   }

	/**
	 * @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;
	}

	/**
    * Inserts a data object at the front of the QFList owner.
	 * @param dat the object to be inserted at the front.
	 * @param owner the QFList owner
	 */
	public void insertFront (Object dat, QFList owner)
	{
      owner.setHead (new NonNullNode (dat, new QFList (owner.getHead ())));
      /* Details:
      QFList coOwner = new QFList (owner.getHead ()); // new QFList (this);
      NonNullNode newNode = new NonNullNode (dat, coOwner);
      owner.setHead (newNode); // "old" style: owner._head = newNode - cannot be done here.
      */
   }

	/**
	 * @param owner
	 * @return the front data of the QFList owner.
	 */
	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);
   }
}