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));
            }

            byte length = IntLength(number);

            return IsPalindromicNumberCore((int)Math.Pow(10, length - 1));

            bool IsPalindromicNumberCore(int pow)
            {
                if (number < 10)
                {
                    return true;
                }

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

                number = (number % pow) / 10;

                return IsPalindromicNumberCore(pow / 100);
            }
        }

        private static byte IntLength(int number) =>
            number switch
            {
                < 10 => 1,
                < 100 => 2,
                < 1000 => 3,
                < 10000 => 4,
                < 100000 => 5,
                < 1000000 => 6,
                < 10000000 => 7,
                < 100000000 => 8,
                < 1000000000 => 9,
                _ => 10
            };
    }
}