package binaryTree.visitor;

import binaryTree.*;

/**
 * Computes a String representation of the binary tree host so that it can be printed vertically.
 * @author Dung X. Nguyen - Copyright 2000 - All rights reserved.
 */
public class ToString implements IVisitor
{
	public final static ToString Singleton = new ToString ();

	private ToString ()
	{
	}

	/**
    * Returns "[]", a String representation of an empty binary tree.
	 * @param host an empty binary tree.
	 * @param input not used.
	 * @return "[]".
	 */
	public Object emptyCase(BiTree host, Object input)
	{
		return "[]";
	}

	/**
   * Computes a String representation of the binary tree host so that it can be printed vertically.
   * There is no '\n' at the end of the String.  Passes appropriate leftmost leading String to
   * a helper visitor to compute the String representations of the left and right subtrees. 
   * @param host a non-empty binary tree.
   * @param input not used.
   * @return (root + "\n" +
   *   left subtree + "\n" +
   *   right subtree)
   */
	public Object nonEmptyCase(BiTree host, Object input)
	{
      String ls = (String) host.getLeftSubTree().execute(ToStringHelp.Singleton, "|  ");
      String rs = (String)host.getRightSubTree().execute(ToStringHelp.Singleton, "   ");
		return (host.getRootDat() + "\n" + ls + "\n" + rs);
      // EXERCISE FOR STUDENTS: Rewrite the above using anonymous inner classes.
	}
}