using System;

using System.Text.RegularExpressions;

public class Program

{

            public static string ToJsonIdentifier(string s)

        {

            // special case, s is empty

            if (string.IsNullOrEmpty(s)) return s;

​

            // special case s is whitespace

            if (string.IsNullOrWhiteSpace(s)) return String.Empty;

​

            // special case s has multiple 'words' - so we remove all whitespace

            s = Regex.Replace(s, @"\s+", "");

​

            // special case s is only 1 letter

            if (!string.IsNullOrEmpty(s) && s.Length == 1) 

                return s.ToLowerInvariant();

​

            // replace _ with nothing, return empty string if that removes all

            var x = s.Replace("_", "");

            if (x.Length == 0) return string.Empty;

​

            x = Regex.Replace(x, "([A-Z])([A-Z]+)($|[A-Z])",

                m => m.Groups[1].Value + m.Groups[2].Value.ToLower() + m.Groups[3].Value);

            return char.ToLower(x[0]) + x.Substring(1);

        }

    public static void Main()

    {

        Console.WriteLine(ToJsonIdentifier("Hello World This is me"));

        Console.WriteLine(ToJsonIdentifier("HelloWorld"));

        Console.WriteLine(ToJsonIdentifier("Hello123"));

        Console.WriteLine(ToJsonIdentifier("myFriendly"));

        Console.WriteLine(ToJsonIdentifier("Customer_,ID"));

        Console.WriteLine(ToJsonIdentifier("customerId"));

    }

}