package lrs.visitor;

import lrs.*;
/**
* Reverses the host.
* @since 10/05/01
* @author DXN
*/
public class Reverse implements IAlgo {
    public static final Reverse Singleton = new Reverse();

    private Reverse() {
    }

    /**
     * Does nothing: the empty host is the reverse of itself.
     * @return null
     */
    public Object forEmpty(LRStruct host, Object input) {
        return null;
    }

    /**
     * Asks for help to recursively move down the host, removes one element at
     * a time and inserting it to the front of the host.  In the end, the host
     * is reversed.
     * @return null
     */
    public Object forNonEmpty(LRStruct host, Object input) {
        return host.getRest().execute(ReverseHelp.Singleton, host);
    }

    public static void main (String[] args) {
        LRStruct p = new LRStruct ();
        testVisitor (p, Reverse.Singleton, null);
        p.insertFront(new Integer (-1));
        testVisitor (p, Reverse.Singleton, null);
        p.insertFront (new Integer (3));
        testVisitor (p, Reverse.Singleton, null);
        p.insertFront(new Integer (5));
        testVisitor (p, Reverse.Singleton, null);
        p.insertFront(new Integer (99));
        testVisitor (p, Reverse.Singleton, null);
    }

    private static void testVisitor(LRStruct p, IAlgo algo, Object input) {
    // NOTE the use of Object.getClass ()!!!
    // Also watch what happens when input == null!!!

        try {
            System.out.println (p + " execute " + algo.getClass ()
                                + ", " + input + "...");
            System.out.println ("   ---> " + p.execute (algo, input) + " " + p);
        }
        catch (Exception e) {
            System.out.println (e);
        }
    }
}