using System;
using System.Reflection.Metadata.Ecma335;

namespace PalindromicNumberTask
{
    /// <summary>
    /// Provides static method for working with integers.
    /// </summary>
    public static class NumbersExtension
    {
        /// <summary>
        /// Determines if a number is a palindromic number, see https://en.wikipedia.org/wiki/Palindromic_number.
        /// </summary>
        /// <param name="number">Verified number.</param>
        /// <returns>true if the verified number is palindromic number; otherwise, false.</returns>
        /// <exception cref="ArgumentException"> Thrown when source number is less than zero. </exception>
        public static bool IsPalindromicNumber(int number)
        {
            if (number < 0)
            {
                throw new ArgumentException("number is less than 0", nameof(number));
            }

            int length = IntLength(number);

            return IsPalindromicNumber(number, (int)Math.Pow(10, length - 1));
        }

        private static int IntLength(int number)
        {
            int length = 0;
            do
            {
                length++;
                number /= 10;
            }
            while (number != 0);

            return length;
        }

        private static bool IsPalindromicNumber(int number, int pow)
        {
            if (number < 10)
            {
                return true;
            }

            if (number / pow != number % 10)
            {
                return false;
            }

            return IsPalindromicNumber((number % pow) / 10, pow / 100);
        }
    }
}