/**
 * CircularList.
 * 
 * @author rpj 
 * @version 24x08
 */
public class CircularList <T>  
{
    
    protected Node <T>  tail;
    /*  
     * We maintain a pointer to the tail which, in turn, points to the head
     * If we ever need the head, it is simply tail.getNext()
     *   head                                  tail
     *    1   ->   2  ->  3   ->   ...      -> 42   -|
     *   ^                                           |
     *   |-------------------------------------------|
     */


    public CircularList()
    {
        tail = null;
    }

    /**
     * add
     * 
     * @param  stuff   to be added
     */
    public void add(T stuff)
    {
        if (tail == null) {   // we're adding to an empty list
            tail = new Node <T> (stuff, null);  // make a new node
            tail.setNext(tail);   // link it to itself
        }
        else {
            // make a new node whose successor is the head
            tail.setNext(new Node <T> (stuff, tail.getNext()));
            // link it in at the tail of the existing list
            tail = tail.getNext();
        }
    }
    
    /**
     * peek
     * 
     * @return  thing at head, or null if empty
     */ 
    public T peek()
    {
        return (tail == null) ? null : tail.getNext().getData();
    }
    
    /**
     * rotate
     * 
     * advance to point to next item
     */
    public void rotate() 
    {
        // be careful of the empty list
    }
    
    /**
     * removeFromHead
     * remove item at head of list
     */
    public void removeFromHead() {
        if (tail.getNext() == tail) tail = null; // removed last item
        else {
            Node <T>  head = tail.getNext();
            tail.setNext(head.getNext());
        }
    }
}