package binaryTree.visitor;

import binaryTree.*;

/**
 * Returns the leftmost non-empty subtree of the host.
 */
public class LeftmostTreeFinder implements IAlgo
{
    public final static LeftmostTreeFinder Singleton =
	new LeftmostTreeFinder();

    private LeftmostTreeFinder()
    {
    }

    /**
     * @param 
     * @param 
     * @return 
     */
    public Object emptyCase(BiTree host, Object input)
    {
	throw new IllegalArgumentException("The host is an empty tree.");
    }

    /**
     * @param host
     * @param input
     * @return 
     */
    public Object nonEmptyCase(BiTree host, Object input)
    {
	return host.getLeftSubTree().execute(new IAlgo() {

	    public Object emptyCase(BiTree host, Object input)
	    {
		return input;
	    }

	    public Object nonEmptyCase(BiTree host, Object input)
	    {
		return host.getLeftSubTree().execute(this, host);
	    }
	}, host);
    }
}