/**
  * Generic Queue example
  * Immutable Version, without specifications
  * SWE 619, Fall 2009
  * @author Paul Ammann
  * September 23, 2009
  */

import java.util.*;

public class IQueue <E> {

   private List<E> elements;
   private int size;

   public IQueue() {   
      this.elements = new ArrayList<E>();
      this.size = 0;
   }

   // Note: Added private constructor
   private IQueue(IQueue <E> current) {   
      this.elements = new ArrayList<E>(current.elements);
      this.size = current.size;
   }

   // Note:  Producer version of enQueue
   public IQueue<E> enQueue (E e) {
     IQueue<E> result = new IQueue<E>(this);
     result.elements.add(e);
     result.size++;
     return result;
   }

   // Note:  Observer split from deQueue
   public E peek () {
     if (size == 0) throw new IllegalStateException("IQueue.peek");
     E result = elements.get(0);
     return result;
   }

   // Note:  Producer version of deQueue
   public IQueue<E> deQueue () {
     if (size == 0) throw new IllegalStateException("IQueue.deQueue");
     IQueue<E> result = new IQueue<E>(this);
     result.elements.remove(0);
     result.size--;
     return result;
   }

   public boolean isEmpty() {
      return size == 0;
   }

  public static void main(String[] args) {
     // Simple exercise to enQueue/deQueue cmd line args
     // Usage:  java Queue item1 item2 item3 ...
     IQueue <String> q = new IQueue <String>();
     for (String arg : args)
        q = q.enQueue(arg);
     while (!q.isEmpty() ) {
        System.out.println(q.peek().toUpperCase());
        q = q.deQueue();
     }

  }

}