package binaryTree;

/**
 * Represents the empty state of a BiTree.  Uses the singleton pattern to model
 * the uniqueness of "emptiness".
 * @author Dung X. Nguyen - Copyright 1999 - All rights reserved.
 * @since 11/10/99
 */
class EmptyNode extends ANode
{
   /**
   * Singleton pattern.
   */
	final static EmptyNode Singleton = new EmptyNode ();

	private EmptyNode()
	{
   }

	/**
    * Throws java.util.NoSuchElementException.
	 */
	Object getRootDat(BiTree parent)
	{
		throw new java.util.NoSuchElementException ("EmptyNode.getRootDat ()");
	}

	/**
    * Throws java.util.NoSuchElementException.
	 */
	void setRootDat(Object dat, BiTree parent)
	{
		throw new java.util.NoSuchElementException ("EmptyNode.setRootDat ()");
	}

	/**
    * Throws java.util.NoSuchElementException.
	 */
	BiTree getLeftSubTree(BiTree parent)
	{
		throw new java.util.NoSuchElementException ("EmptyNode.getLeftSubTree ()");
	}

	/**
    * Throws java.util.NoSuchElementException.
	 */
	BiTree getRightSubTree(BiTree parent)
	{
		throw new java.util.NoSuchElementException ("EmptyNode.getRightSubTree ()");
	}

	/**
    * Throws java.util.NoSuchElementException.
	 */
	void setLeftSubTree(BiTree biTree, BiTree parent)
	{
		throw new java.util.NoSuchElementException ("EmptyNode.setLeftSubTree ()");
	}

	/**
    * Throws java.util.NoSuchElementException.
	 */
	void setRightSubTree(BiTree biTree, BiTree parent)
	{
		throw new java.util.NoSuchElementException ("EmptyNode.setRightSubTree ()");
	}

	/**
    * Asks the parent tree to set the root node to a new DatNode containing dat,
    * resulting in a state change from empty to non-empty.
	 * @param dat
	 * @param parent the context of this state.
	 */
	void insertRoot(Object dat, BiTree parent)
	{
      parent.setRootNode(new DatNode (dat));
	}

	/**
    * Throws java.util.NoSuchElementException.
	 */
	Object remRoot(BiTree parent)
	{
		throw new java.util.NoSuchElementException ("EmptyNode.remRoot ()");
	}

	/**
    * Removes and return the root element of the grandparent of this node,
    * asking the sibbling of the parent tree to do it if necessary.
	 * @param aunt the sibbling of the parent of this node.
	 * @param grandPo the grand parent of this node.
	 * @param mom the parent (i.e. context) of this node.
    * @return the root data of the grandparent of this node.
	 */
	Object remParent(BiTree aunt, BiTree grandPo, BiTree mom)
	{
      return aunt.remOurParent (grandPo);
	}

	/**
    * Removes and return the root element of the grandparent of this node,
    * <I>knowing</I> the sibbling of the parent tree is empty.
	 * @param grandParent the grand parent of this BiTree.
    * @param parent the context of this node.
    * @return the root data of the grandparent of this node.
	 */
	Object remOurParent(BiTree grandParent, BiTree parent)
	{
      Object dat = grandParent.getRootDat();
      grandParent.setRootNode(EmptyNode.Singleton);
		return dat;
	}

	/**
    * Calls the visitor's nullCase () method to execute the visiting algorithm.
	 * @param algo the visiting algorithm
	 * @param input the input the algorithm needs.
	 * @param parent the context of this node.
	 * @return the output for the nullCase() of the algorithm.
	 */
	Object execute(IVisitor algo, Object input, BiTree parent)
	{
		return algo.emptyCase(parent, input);
	}
}