package queues;

import clist.*;
import clist.visitor.*;
import java.util.Enumeration;

/**
 * A queue implemented using CList.
 *
 * Version 1.
 *
 * @author Alan L. Cox
 * @since 03/15/01
 */
public class CListQueue implements IQueue
{
    private CList _objects = new CList();
    
    /**
     * Adds an object to the CListQueue.
     * @param object the object to enqueue
     * This enqueue method is O(1) since it has one statement.
     */
    public void enqueue(Object object)
    {
	_objects.insertFrontCounterClockwise(object);
    }

    /**
     * Removes the first object of the CListQueue.
     * @return the dequeued object
     * This dequeue method is O(1) since it has one statement.
     */
    public Object dequeue()
    {
	return _objects.removeFrontClockwise();
    }

    /**
     * Enumerates the queue in clockwise order.
     * @return an Enumeration of the queue in clockwise order.
     * This dequeue method is O(1) since it contains single statements.
     */
    public Enumeration enumeration()
    {
	/**
	 * We can't use an anonymous inner class to implement this
	 * Enumeration because of the cosntructor.
	 */
	class CListEnumeration implements Enumeration
	{
	    private CList _next;

	    private boolean last = false;
	    private boolean done = false;
	    private CList _stop;
	    CListEnumeration(CList clist)
	    {
		_next = clist;
		_stop = clist;
	    }	      

	    public boolean hasMoreElements()
	    {
		if(((Boolean)_next.executeClockwise(IsEmpty.Singleton, null)).booleanValue())
		    return false;
		else
		   {
		       if (done == true) 
			   return false;
		       
		       CList tail = _next.getRestClockwise();
		      
		       if (tail.equals(_stop))
			   {
			       last = true;
			       return true;
			   }
		       else
			   return true;
		       
		   }
	    }
	

	    public Object nextElement()
	    {
		if(((Boolean)_next.executeClockwise(IsEmpty.Singleton, null)).booleanValue())
		    return null;
		
		else
		    {
			if (done == true)
			    return null;
			    
			if (last == true) {
			    done = true;
			}
			Object object = _next.getFirstClockwise();
			
			_next = _next.getRestClockwise();
			
			return object;
		    }
	    }
	    
	}
	return new CListEnumeration(_objects);
    }
}