package binaryTree;

/**
 * Represents the state of the parent binary tree structure.
 *
 * This is an instance of the Union pattern.
 *
 * @author Alan L. Cox
 * @author Dung X. Nguyen - Copyright 1999 - All rights reserved.
 * @since 04/05/01
 */
abstract class ANode
{
    /**
     * Get the data object at this node if it exists.
     *
     * @return the data object at this node if it exists.
     * @exception NoSuchElementException if the node is empty.
     */
    abstract Object getRootData();

    /**
     * Set the data object at this node to the given data object.
     *
     * @param data the new data object for this node.
     * @exception NoSuchElementException if the node is empty.
     */
    abstract void setRootData(Object data);

    /**
     * Get the left subtree of this node.
     *
     * @return the left subtree of this node if it exists.
     * @exception NoSuchElementException if the owner is empty.
     */
    abstract BiTree getLeftSubTree();

    /**
     * Set the left subtree of this node to the given tree.
     *
     * @param biTree != null.
     * @exception NoSuchElementException if the owner is empty.
     */
    abstract void setLeftSubTree(BiTree biTree);

    /**
     * Get the right subtree of this node.
     *
     * @return the right subtree of this node if it exists.
     * @exception NoSuchElementException if the owner is empty.
     */
    abstract BiTree getRightSubTree();

    /**
     * Set the right subtree of this node to the given tree.
     *
     * @param biTree != null.
     * @exception NoSuchElementException if the owner is empty.
     */
    abstract void setRightSubTree(BiTree 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.
     * @param owner the context of this state.
     * @exception IllegaStateException if the owner is not empty.
     */
    abstract void insertRoot(Object data, BiTree owner);

    /**
     * Removes and returns the data object at this node if at least
     * one of the subtrees is empty.  The node may change from a
     * non-empty to an empty state. 
     *
     * @param owner the context of this state.
     * @exception NoSuchElementException if this node is empty.
     * @exception IllegalStateException if this node has two non-empty
     *     subtrees. 
     */
    abstract Object removeRoot(BiTree owner);

    /**
     * Helper method for removeRoot().
     *
     * @param sibling the sibbling of this node.
     * @param parent the parent of this node.
     * @param owner the owner of this node.
     * @return the root data of the parent of this node.
     */
    abstract Object removeParent(BiTree sibling, BiTree parent, BiTree owner);

    /**
     * Helper method for removeParent().
     *
     * @param parent the parent of this node.
     * @return the data object at the parent of this node.
     */
    abstract Object removeParentFromNonEmptyNode(BiTree sibling, BiTree parent);

    /**
     * Calls IAlgo's appropriate method 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 algorithm's output.
     */
    abstract Object execute(IAlgo algo, Object input, BiTree owner);
}