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));
            }

            char[] sourceArray = source.ToCharArray();
            char[] startBufferArray = new char[source.Length / 2];
            char[] endBufferArray = new char[(source.Length + 1) / 2];

            int bufferIndex = 0;
            int r = 0;

            for (int i = 0; i < count; i++)
            {
                for (int k = 1; i < source.Length; i += 2, bufferIndex++)
                {
                    startBufferArray[bufferIndex] = sourceArray[k];
                }

                bufferIndex = 0;

                for (int k = 0; i < source.Length; i += 2, bufferIndex++)
                {
                    endBufferArray[bufferIndex] = sourceArray[k];
                }

                for (int j = 0; j < source.Length / 2; j++)
                {
                    sourceArray[j] = startBufferArray[j];
                }

                r = 0;

                for (int e = source.Length / 2; e < source.Length; e++, r++)
                {
                    sourceArray[e] = startBufferArray[r];
                }
            }

            string startBuffer = new string(startBufferArray);
            string endBuffer = new string(endBufferArray);

            return startBuffer + endBuffer;
        }
    }
}