package jsjf;

import jsjf.exceptions.*;

/**
 * CircularArrayQueue represents an array implementation of a queue in 
 * which the indexes for the front and rear of the queue circle back to 0
 * when they reach the end of the array.
 * 
 * @author Lewis and Chase
 * @version 4.0
 */
public class CircularArrayQueue<T> implements QueueADT<T>
{
    private final static int DEFAULT_CAPACITY = 100;
    private int front, rear, count;
    private T[] queue; 
  
    /**
     * Creates an empty queue using the specified capacity.
     * @param initialCapacity the initial size of the circular array queue
     */
    public CircularArrayQueue (int initialCapacity)
    {
        front = rear = count = 0;
        queue = (T[]) (new Object[initialCapacity]);
    }
  
    /**
     * Creates an empty queue using the default capacity.
     */
    public CircularArrayQueue()
    {
        this(DEFAULT_CAPACITY);
    }    
	
	/**
     * Adds the specified element to the rear of this queue, expanding
     * the capacity of the queue array if necessary.
     * @param element the element to add to the rear of the queue
     */
    public void enqueue(T element)
    {
        if (size() == queue.length) 
            expandCapacity();
    
        queue[rear] = element;
        rear = (rear+1) % queue.length;
    
        count++;
    }
	
	/**
     * Creates a new array to store the contents of this queue with
     * twice the capacity of the old one.
     */
    private void expandCapacity()
    {
        T[] larger = (T[]) (new Object[queue.length *2]);
    
        for (int scan = 0; scan < count; scan++)
        {
            larger[scan] = queue[front];
            front = (front + 1) % queue.length;
        }
    
        front = 0;
        rear = count;
        queue = larger;
    }
	
    /**
     * Removes the element at the front of this queue and returns a
     * reference to it. 
	 * @return the element removed from the front of the queue
     * @throws EmptyCollectionException  if the queue is empty
     */
    public T dequeue() throws EmptyCollectionException
    {
        if (isEmpty())
            throw new EmptyCollectionException("queue");
    
        T result = queue[front];
        queue[front] = null;
        front = (front+1) % queue.length;
    
        count--;
    
        return result;
    }
  
    /** 
     * Returns a reference to the element at the front of this queue.
     * The element is not removed from the queue.  
     * @return the first element in the queue
     * @throws EmptyCollectionException if the queue is empty
     */
    public T first() throws EmptyCollectionException
    {
        if (isEmpty())
            throw new EmptyCollectionException("queue");
    
        return queue[front];
    }
  
    /**
     * Returns true if this queue is empty and false otherwise.
     * @return true if this queue is empty 
     */
    public boolean isEmpty()
    {
	return (count == 0);
    }
  
    /**
     * Returns the number of elements currently in this queue.
     * @return the size of the queue
     */
    public int size()
    {
	return count;
    }
  
    /**
     * Returns a string representation of this queue. 
     * @return the string representation of the queue
     */
    public String toString()
    {
	// To be completed as a programming project
        return " ";
    }
}