using System;

using System.Collections.Generic;

using System.Linq;

​

namespace Scratchpad

{

    public class OrderItem

    {

        public static readonly OrderItem Null = new OrderItem();

        public const string PrefixDesc = "-";

​

        public bool IsDesc { get; set; } = false;

        public string Name { get; set; } = string.Empty;

​

        public override string ToString()

        {

            if (IsDesc)

            {

                return PrefixDesc + Name;

            }

​

            return Name;

        }

​

        public static OrderItem FromString(string name)

        {

            bool isDesc = name.StartsWith(PrefixDesc);

            if (isDesc)

            {

                name = name.Substring(PrefixDesc.Length);

            }

​

            if (string.IsNullOrWhiteSpace(name))

            {

                return Null;

            }

​

            return new OrderItem

            {

                Name = name,

                IsDesc = isDesc

            };

        }

    }

​

    internal class Program

    {

        public static void Main()

        {

            string input = "hello,,world,-,-testdesc";

            IEnumerable<OrderItem> result = ParseSortBy(input);

​

            // Breakpoint here.

            Console.WriteLine(result);

        }

​

        private static IEnumerable<OrderItem> ParseSortBy(string qs)

        {

            return qs

                .Split(',', System.StringSplitOptions.RemoveEmptyEntries)

                .Select(part => OrderItem.FromString(part))

                .Where(item => item != OrderItem.Null);

        }

    }

}

​