package clist.visitor;

import clist.*;

/**
* Remove the n-th element in the host list.  n == 0 corresponds to the first
* element in the host list.
* n is passed to the visitor as the input parameter
*/
public class RemNthClockwise implements ICLVisitor
{
	public final static RemNthClockwise Singleton = new RemNthClockwise ();

	private RemNthClockwise()
	{
	}

	/**
   * Throws an exception.
	 * @param host 
	 * @param stop 
	 * @param inp  the Integer index n.
	 * @return
	 */
	public Object forEmpty (CLList host, CLList stop, Object inp)
	{
		throw new java.util.NoSuchElementException ("No such element");
	}

	/**
	 * @param host 
	 * @param stop 
	 * @param inp  the Integer index n.
	 * @return the data Obkect removed (if any).
    * @throw IllegalArgumentException if the index n > number of elements in host - 1.
	 */
	public Object forNonEmpty (CLList host, CLList stop, Object inp)
	{
      int ix = ((Integer)inp).intValue ();
      CLList tail = host.getClockwiseTail();
      if (0 == ix)
      {
         if (tail.equals (stop))
         {
            return stop.remCounterwise();
         }
         else
         {
            return host.remClockwise();
         }
      }
      else if (tail.equals (stop))
      {
		   throw new IllegalArgumentException ("No such element");
      }
      else
      {
         return tail.execClockwise (this, stop, new Integer (--ix));  // important to decrement ix first!
      }
	}
}