package binaryTree;

/**
 * Models the binary tree structure using the state pattern and
 * the visitor pattern.
 *
 * Provides only structural behaviors and a hook to execute
 * any visitor algorithm.
 *
 * @author Alan L. Cox
 * @author Dung X. Nguyen - Copyright 1999 - All rights reserved.
 * @since 04/05/01
 */
public class BiTree
{
    /**
     * The state of this BiTree.
     */
    private ANode _rootNode;

    /**
     * Initializes this BiTree to the empty state.
     */
    public BiTree()
    {
	_rootNode = EmptyNode.Singleton;
    }

    /**
     * Get the data object at the root of this BiTree if it exists.
     *
     * @return the data object at the root of this BiTree if it exists.
     * @exception NoSuchElementException if this BiTree is empty.
     */
    public Object getRootData()
    {
	return _rootNode.getRootData();
    }

    /**
     * Set the data object at the root of this BiTree to the given data object.
     *
     * @param data the data object.
     * @exception NoSuchElementException if this BiTree is empty.
     */
    public void setRootData(Object data)
    {
	_rootNode.setRootData(data);
    }

    /**
     * Get the left subtree of this BiTree if it exists.
     *
     * @return the left subtree of this BiTree if it exists.
     * @exception NoSuchElementException if this BiTree is empty.
     */
    public BiTree getLeftSubTree()
    {
	return _rootNode.getLeftSubTree();
    }

    /**
     * Attaches a new left subtree to the left of this BiTree,
     * allowing this BiTree to grow to the left.
     *
     * @param biTree the new left subtree.
     * @exception NoSuchElementException if this BiTree is empty.
     */
    public void setLeftSubTree(BiTree biTree)
    {
	_rootNode.setLeftSubTree(biTree);
    }

    /**
     * Gets the right subtree of this BiTree if it exsists.
     *
     * @return the right subtree of this BiTree if it exists.
     * @exception NoSuchElementException if this BiTree is empty.
     */
    public BiTree getRightSubTree()
    {
	return _rootNode.getRightSubTree();
    }

    /**
     * Attaches a new right subtree to the right of this BiTree,
     * allowing this BiTree to grow to the right.
     *
     * @param biTree the new right subtree.
     * @exception NoSuchElementException if this BiTree is empty.
     */
    public void setRightSubTree(BiTree biTree)
    {
	_rootNode.setRightSubTree(biTree);
    }

    /**
     * Changes an empty BiTree into a non-empty BiTree
     * with the given data at the root of the BiTree.
     *
     * @param data the data object.
     * @exception IllegalStateException if this BiTree is non-empty.
     */
    public void insertRoot(Object data)
    {
	_rootNode.insertRoot(data, this);
    }

    /**
     * Removes and returns the data object at the root of this BiTree
     * if at least one of the subtrees is empty.  The BiTree may
     * change from a non-empty to an empty state.
     *
     * @return the data object at the root of this BiTree.
     * @exception NoSuchElementException if this BiTree is empty.
     * @exception IllegalStateException if this BiTree has two
     *     non-empty subtrees. 
     */
    public Object removeRoot()
    {
	return _rootNode.removeRoot(this);
    }

    /**
     * Hook to execute any algorithm that presents itself as a visitor
     * to this BiTree.
     *
     * @param algo a visitor to a BiTree.
     * @param input the input for the algo visitor.
     * @return the output for the execution of algo.
     */
    public Object execute(IAlgo algo, Object input)
    {
	return _rootNode.execute(algo, input, this);
    }

    /** -- Package access only: -------------------------------------------- */

    /**
     * Returns the current state of this BiTree.
     *
     * @return the current root node (i.e., state) of this BiTree.
     */
    ANode getRootNode()
    {
	return _rootNode;
    }

    /**
     * Changes this BiTree to a given new state (i.e., node).
     *
     * @param node a new root node (i.e., state) for this BiTree.
     */
    void setRootNode(ANode node)
    {
	_rootNode = node;
    }

    /**
     * Helper method for removeRoot().
     *
     * @param sibling the sibbling of this BiTree.
     * @param parent the parent of this BiTree.
     * @return the data object at the parent of this BiTree.
     */
    Object removeParent(BiTree sibling, BiTree parent)
    {
	return _rootNode.removeParent(sibling, parent, this);
    }

    /**
     * Helper method for removeParent().
     *
     * @param sibling the sibbling of this BiTree.
     * @param parent the parent of this BiTree.
     * @return the root data of the parent of this BiTree.
     */
    Object removeParentFromNonEmptyNode(BiTree sibling, BiTree parent)
    {
	return _rootNode.removeParentFromNonEmptyNode(sibling, parent);
    }
}