package lrs.visitor;

import lrs.*;
/**
* Reverses the host using local anonymous inner class as a helper visitor.
* Creates the helper object each time it is called.
* @author DXN
*/
public class RevLocalInner implements IAlgo {
    public static final RevLocalInner Singleton = new RevLocalInner ();

    private RevLocalInner () {
    }

    /**
     * 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(final LRStruct host, Object input) {
        return host.getRest().execute(new IAlgo (){
            /**
             * Does nothing because the end of the original host is reached.
             * From host to h is the reverse of the original list.
             * @param h the remaining tail of the list to be reversed.
             * @param inp not used.
             * @return null.
             */
            public Object forEmpty(LRStruct h, Object inp) {
                return null;
            }

            /**
             * Removes the current list's first and insert it to the front of
             * the original host and recurs.
             * @param h the remaining tail of the list to be reversed.
             * @param inp not used.
             * @return null.
             */
            public Object forNonEmpty(LRStruct h, Object inp) {
                Object hFirst = h.removeFront(); // h has "advanced".
                host.insertFront (hFirst);
                return h.execute(this, null);
            }
        }, null);
    }

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