package rebelsky.exam2.solutions;

import rebelsky.linear.Queue;

/**
 * An implementation of queues using arrays.  Currently incomplete.
 *
 * @author Samuel A. Rebelsky
 * @author Kevin Conor
 * @author CSC152 2004F
 * @version 1.01 of October 2004.
 */
public class NewArrayBasedQueue
	implements Queue
{
// +--------+--------------------------------------------------
// | Fields |
// +--------+

	/** The index of the "last" thing. */
	int last;

	/** The index of the "first" thing. */
	int first;

	/** The stuff actually in the queue. */
	Object[] contents;

// +--------------+--------------------------------------------
// | Constructors |
// +--------------+
	
	public NewArrayBasedQueue()
	{
		this.last = -1;
		this.first = 0;
		this.contents = new Object[3];
	} // NewArrayBasedQueue()

// +---------+-------------------------------------------------
// | Methods |
// +---------+

	public void put(Object addMe)
	{
		this.last = this.last + 1;
		// Have we run off the end?  If so, wrap around to
		// the beginning.
		if (this.last == this.contents.length)
			this.last = 0;
		if ((this.last == this.first) && (!this.isEmpty()))
			this.expand();
		this.contents[this.last] = addMe;
	} // put(Object)

	public Object get()
		throws Exception
	{
		// Note that the following line throws an exception
		// if the queue is empty.  Hence, the remaining lines
		// will not be executed.
		Object returnMe = this.peek(); 

		this.contents[this.first] = null; // Actually remove it.
		++this.first;
		if (this.first == this.contents.length)
			this.first = 0;
		return returnMe;
	} // get()

	public Object peek()
		throws Exception
	{
		if (this.contents[this.first] == null)
			throw new Exception("It's empty!");
		return this.contents[this.first];
	} // peek()

	private void expand()
	{
		// Allocate the new array
		Object[] newcontents = new Object[2*this.contents.length];
/*
		// Copy the elements incorrectly
		for (int i = 0; i < this.contents.length; i++)
		{
			newcontents[i] = contents[i];
		} // for
 */
		// Copy the elements
		for (int i = 0; i < this.contents.length; i++)
		{
			newcontents[i] = contents[this.first];
			++this.first;
			if (this.first == this.contents.length)
				this.first = 0;
		}

		// Update fields
		this.last = this.contents.length;
		this.contents = newcontents;
		this.first = 0;
	} // expand()

	public boolean isEmpty()
	{
		return this.contents[this.first] == null;
	} // isEmpty()

} // class NewArrayBasedQueue