package binaryTree;

/**
 * Represents the empty state of a BiTree.  Uses the singleton pattern
 * to model the uniqueness of "emptiness".
 *
 * @author Alan L. Cox
 * @author Dung X. Nguyen - Copyright 1999 - All rights reserved.
 * @since 4/5/01
 */
class EmptyNode extends ANode
{
    /**
     * Singleton pattern.
     */
    public final static EmptyNode Singleton = new EmptyNode();

    private EmptyNode()
    {
    }

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

    /**
     * Throws java.util.NoSuchElementException.
     */
    void setRootData(Object data)
    {
	throw new java.util.NoSuchElementException("EmptyNode.setRootData()");
    }

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

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

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

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

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

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

    /**
     * Helper method for removeRoot().  Removes the parent by
     * elevating its sibling's node to the root of the BiTree.
     * It doesn't matter whether the sibling is an empty or non-
     * empty BiTree.
     *
     * @param sibling the sibbling of the parent of this node.
     * @param parent the parent of this node.
     * @param owner the owner (i.e., context) of this node.
     * @return the data object at the parent of this node.
     */
    Object removeParent(BiTree sibling, BiTree parent, BiTree owner)
    {
	Object data = parent.getRootData();
	parent.setRootNode(sibling.getRootNode());
	return data;
    }

    /**
     * Helper method for removeParent().  This method is called only
     * if our left sibling was a non-empty BiTree.  Removes the parent
     * by elevating its sibling's node to the root of the BiTree.
     *
     * @param sibling the sibbling of this node.
     * @param parent the parent of this node.
     * @return the root data of the parent of this node.
     */
    Object removeParentFromNonEmptyNode(BiTree sibling, BiTree parent)
    {
	Object data = parent.getRootData();
	parent.setRootNode(sibling.getRootNode());
	return data;
    }

    /**
     * Calls IAlgo's method emptyCase() to execute the visiting algorithm.
     *
     * @param algo the visiting algorithm
     * @param input the input needed by the visiting algorithm.
     * @param owner the context of this node.
     * @return the output for the emptyCase() of the algorithm.
     */
    Object execute(IAlgo algo, Object input, BiTree owner)
    {
	return algo.emptyCase(owner, input);
    }
}