package bjc.utils.esodata;

import java.util.Deque;
import java.util.LinkedList;

/**
 * A FIFO implementation of a stack.
 * 
 * Basically, a stack that actually acts like a queue.
 *
 * @param <T>
 *        The datatype stored in the stack.
 *
 * @author Ben Culkin
 */
public class QueueStack<T> extends Stack<T> {
	/* Our backing queue. */
	private final Deque<T> backing;

	/** Create a new empty stack queue. */
	public QueueStack() {
		backing = new LinkedList<>();
	}

	@Override
	public void push(final T elm) {
		backing.add(elm);
	}

	@Override
	public T pop() {
		if(backing.isEmpty()) throw new StackUnderflowException();

		return backing.remove();
	}

	@Override
	public T top() {
		if(backing.isEmpty()) throw new StackUnderflowException();

		return backing.peek();
	}

	@Override
	public int size() {
		return backing.size();
	}

	@Override
	public boolean empty() {
		return backing.size() == 0;
	}

	@SuppressWarnings("unchecked")
	@Override
	public T[] toArray() {
		return (T[]) backing.toArray();
	}

	@Override
	public String toString() {
		return String.format("QueueStack [backing=%s]", backing);
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;

		result = prime * result + (backing == null ? 0 : backing.hashCode());

		return result;
	}

	@Override
	public boolean equals(final Object obj) {
		if(this == obj) return true;
		if(obj == null) return false;
		if(!(obj instanceof QueueStack<?>)) return false;

		final QueueStack<?> other = (QueueStack<?>) obj;

		if(backing == null) {
			if(other.backing != null) return false;
		} else if(!backing.equals(other.backing)) return false;

		return true;
	}
}