package binaryTree.visitor;

import binaryTree.*;

/**
 * Computes a String representation of the binary tree host so that it can be printed vertically,
 * given a leftmost leading string for the two subtrees.
 * Called by ToString.
 * Can be implemented as an anonymous inner class in the call by ToString.
 * @author Dung X. Nguyen - Copyright 2000 - All rights reserved.
 */
public class ToStringHelp implements IVisitor
{
   public static final ToStringHelp Singleton = new ToStringHelp ();
	private ToStringHelp ()
	{
   }

	/**
    * Returns "|_[]" to denote an empty tree subtree.
	 * @param host an empty binary (sub)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.
   * @param host a non-empty binary (sub)tree.
   * @param input appropriate leftmost leading String to help compute the String representations
   * of the left and right subtrees.
   * @return ("|_" + root + "\n" +
   *  input + left subtree + "\n" +
   *  input + right subtree)
   */
	public Object nonEmptyCase(BiTree host, Object input)
	{
      String ls = (String)host.getLeftSubTree().execute(this, input + "|  ");
      String rs = (String) host.getRightSubTree().execute(this, input + "   ");
		return ("|_ " + host.getRootDat()+ "\n" + input + ls + "\n" + input + rs);
	}
}