package lrs.visitor;
import lrs.*;

/**
 * Merges the sorted input list into the sorted host list.
 * In the end, host and the input list share the same nodes and are sorted.
 * @author Dung X. Nguyen - Copyright 2005 - All rights reserved.
 */
public class Merge implements IAlgo {
    public final static Merge Singleton = new Merge();
    private Merge() {
    }

    /**
     * @param host is empty.
     * @param other [0] an LRStruct
     * @return null
     */
    public Object emptyCase(LRStruct host, Object... other) {
        return host.execute (Share.Singleton, other[0]);
    }

    /**
     * @param host is not empty
     * @param other [0] an LRStruct
     * @return null
     */
    public Object nonEmptyCase(LRStruct host, Object... other) {
        return ((LRStruct)other[0]).execute (new IAlgo() {
            public Object emptyCase(LRStruct h, Object... inp) {
                return h.execute (Share.Singleton, inp[0]);
            }

            /**
             * @param host a non-empty LRStruct
             * @param inp [0] a non-empty LRStruct.
             */
            public Object nonEmptyCase(LRStruct h, Object... inp) {
                LRStruct inList = (LRStruct)inp[0];
                int hFirst = (Integer)h.getFirst();
                int inpFirst = (Integer)inList.getFirst();
                if (hFirst <= inpFirst) {
                    h.getRest().execute(this, inList);
                    return inList.execute(Share.Singleton, h);
                }
                else {
                    inList.getRest().execute (this, h);
                    return h.execute(Share.Singleton, inList);
                }
            }
        }, host);
    }
}