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 + 1) / 2];
            char[] endBufferArray = new char[source.Length / 2];

            int bufferIndex = 0;

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

            bufferIndex = 0;

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

            string startBuffer = startBufferArray.ToString();
            string endBuffer = endBufferArray.ToString();

            return startBuffer + endBuffer;
        }
    }
}