package horstmann.ch08_queue;
import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.Iterator;

/**
    A first-in, first-out bounded collection of objects.
 */
public class BoundedQueue<E> extends AbstractCollection<E>
{
  /**
       Constructs an empty queue.
       @param capacity the maximum capacity of the queue
       <p><b>Precondition:</b> capacity > 0</p>
   */
  public BoundedQueue(int capacity)
  {
    elements = new ArrayList<E>(capacity);
    count = 0;
    head = 0;
    tail = 0;
  }

  public Iterator<E> iterator()
  {
    return new
        Iterator<E>()
    {
      public boolean hasNext()
      {
        return visited < count;
      }

      public E next()
      {
        int index = (head + visited) % elements.size();
        E r = elements.get(index);
        visited++;
        return r;
      }

      public void remove()
      {
        throw new UnsupportedOperationException();
      }

      private int visited = 0;
    };
  }

  /**
       Remove object at head.
       @return the object that has been removed from the queue
       <p><b>Precondition:</b> size() > 0</p>
   */
  public E remove()
  {
    E r = elements.get(head);
    head = (head + 1) % elements.size();
    count--;
    return r;
  }

  /**
       Append an object at tail.
       @param anObject the object to be appended
       @return true since this operation modifies the queue.
       (This is a requirement of the collections framework.)
       <p><b>Precondition:</b> !isFull()</p>
   */
  public boolean add(E anObject)
  {
    elements.set(tail,anObject);
    tail = (tail + 1) % elements.size();
    count++;
    return true;
  }

  public int size()
  {
    return count;
  }

  /**
       Checks whether this queue is full.
       @return true if the queue is full
   */
  public boolean isFull()
  {
    return count == elements.size();
  }

  /**
       Gets object at head.
       @return the object that is at the head of the queue
       <p><b>Precondition:</b> size() > 0</p>
   */
  public E peek()
  {
    return elements.get(head);
  }

  private ArrayList<E> elements;
  private int head;
  private int tail;
  private int count;
}