using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DataStructures.Stack
{
    public class QueueBasedStack<T>
    {
        private readonly Queue<T> queue;

        public QueueBasedStack() => queue = new Queue<T>();

        /// <summary>
        ///     Clears the stack.
        /// </summary>
        public void Clear() => queue.Clear();

        public bool IsEmpty() => queue.Count == 0;

        /// <summary>
        ///     Adds an item on top of the stack.
        /// </summary>
        /// <param name="item">Item to be added on top of stack.</param>
        public void Push(T item) => queue.Enqueue(item);

        /// <summary>
        ///     Removes an item from  top of the stack and returns it.
        ///  </summary>
        /// <returns>item on top of stack.</returns>
        /// <exception cref="InvalidOperationException">Throw if stack is empty.</exception>
        public T Pop()
        {
            if (IsEmpty())
            {
                throw new InvalidOperationException("The stack contains no items.");
            }

            for (int i = 0; i < queue.Count - 1; i++)
            {
                queue.Enqueue(queue.Dequeue());
            }

            return queue.Dequeue();
        }

        /// <summary>
        ///     return an item from the top of the stack without removing it.
        /// </summary>
        /// <returns>item on top of the stack.</returns>
        /// <exception cref="InvalidOperationException">Throw if stack is empty.</exception>
        public T Peek()
        {
            if (IsEmpty())
            {
                throw new InvalidOperationException("The stack contains no items.");
            }

            for (int i = 0; i < queue.Count - 1; i++)
            {
                queue.Enqueue(queue.Dequeue());
            }

            var item = queue.Peek();
            queue.Enqueue(queue.Dequeue());
            return item;
        }

        /// <summary>
        ///     returns the count of items on the stack.
        /// </summary>
        /// <returns>number of items on the stack.</returns>
        public int Length() => queue.Count;
    }
}