using System;

namespace ShuffleCharacters
{
    public static class StringExtension
    {
        /// <summary>
        /// Shuffles characters in source string according some rule.
        /// </summary>
        /// <param name="source">The source string.</param>
        /// <param name="count">The count of iterations.</param>
        /// <returns>Result string.</returns>
        /// <exception cref="ArgumentException">Source string is null or empty or white spaces.</exception>
        /// <exception cref="ArgumentException">Count of iterations is less than 0.</exception>
        public static string ShuffleChars(string source, int count)
        {
            if (string.IsNullOrWhiteSpace(source))
            {
                throw new ArgumentException("Source string is null or empty or white spaces.", nameof(source));
            }

            if (count < 0)
            {
                throw new ArgumentException("Count of iterations is less than 0", nameof(count));
            }

            string bufferStart = string.Empty;
            string bufferEnd = string.Empty;

            for (int i = 0; i < count; i++)
            {
                for (int j = 1; j < source.Length; j += 2)
                {
                    bufferStart = string.Concat(bufferStart, source[j]);
                }

                for (int k = 0; k < source.Length; k += 2)
                {
                    bufferEnd = string.Concat(bufferEnd, source[k]);
                }

                source = string.Concat(bufferStart, bufferEnd);
            }

            return source;
        }
    }
}