package lrs.visitor;
import lrs.*;

/**
* Sorts by splitting the host into two sublists, sorts the sublists, then
* merges the sorted sublists.
*/
public class MergeSorter1 implements IAlgo
{
  public static final MergeSorter1 Singleton = new MergeSorter1 ();
  private MergeSorter1()
  {
  }

	/**
	 * @param host 
	 * @param input not used.
	 * @return null
	 */
	public Object nullCase(LRStruct host, Object input)
	{
		return null;  // there is nothing to sort
	}

	/**
	 * @param host 
	 * @param input not used.
	 * @return null.
	 */
	public Object nonNullCase(final LRStruct host, Object input)
	{
      return host.getRest().execute (
         new IAlgo ()
         {
            // Case host has one element (i.e. hostTail is empty).
            public Object nullCase (LRStruct hostTail, Object inputNotUsed)
            {
               return null;
            }

            public Object nonNullCase (LRStruct hostTail, Object inputNotUsed)
            {
               LRStruct sublist = (LRStruct)host.execute (EveryOther1.Singleton, null);
               host.execute (MergeSorter1.Singleton, null);
		         sublist.execute (MergeSorter1.Singleton, null);
               host.execute (Merger.Singleton, sublist);
               return null;
            }
         }
         , null);
	}

	public static void main(String[] args)
	{
      LRStruct l1 = new LRStruct ();
      System.out.println ("l1: " + l1);
      System.out.println ("Merge sort l1...");
      l1.execute(MergeSorter1.Singleton, null);
      System.out.println ("l1: " + l1);

      l1.insertFront (new Integer (-9));
      l1.insertFront (new Integer (15));
      l1.insertFront (new Integer (263));
      l1.insertFront (new Integer (-72));
      l1.insertFront (new Integer (0));
      l1.insertFront (new Integer (48));
/*
*/
      System.out.println ("l1: " + l1);
      System.out.println ("Merge sort l1...");
      l1.execute(MergeSorter1.Singleton, null);
      System.out.println ("l1: " + l1);
  }
}