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

namespace Fibonacci {
    public class Fibo {
        private static int counter;
        static string _fiboReturn = string.Empty;
        static Stack<int> _temp = new Stack<int>();

        public static string FibonacciSequence(int lengthOfSequence) {
                if (_temp.Count == 0) {
                    _temp.Push(0);
                    _fiboReturn += WriteToReturn(0);
                }
                else if (_temp.Peek() == 0) {
                    _temp.Push(1);
                    _fiboReturn += WriteToReturn(1);
                }
                else {
                    var num2 = _temp.Pop();
                    var num1 = _temp.Pop();
                    _temp.Push(num2);
                    _temp.Push(num1+num2);
                    _fiboReturn += WriteToReturn(num1 + num2);
            }
            counter++;
            if (counter <= lengthOfSequence) {
                FibonacciSequence(lengthOfSequence);
            }
            return _fiboReturn;
        }

        private static string WriteToReturn(int input) {

            return $"{input}, ";
        }
    }
}