using System;

using System.Collections.Generic;

using System.Collections.Immutable;

using System.Linq;

using System.Threading;

using System.Threading.Tasks;

​

public enum AllowedOutOfStockOrderMode

{

    /// <summary>

    /// Default behavior - No out of stock ordering allowed

    /// </summary>

    Unknown = 0,

​

    /// <summary>

    /// Allowed back-order for Registry items

    /// </summary>

    Registry = 1,

​

    /// <summary>

    /// Out of stock purchasing

    /// </summary>

    OosPurchasing = 2

}

​

​

public class Program

{

    public static void Main()

    {

        var productAllowedModes = new Dictionary<string, HashSet<AllowedOutOfStockOrderMode>>();

​

        var productAllowedOutOfStockOrderModes = "R9-165|1,;";

        foreach (var record in productAllowedOutOfStockOrderModes.Split(';'))

        {

            //Console.WriteLine(record);

            var productModes = record.Split('|');

            var oosModes = new HashSet<AllowedOutOfStockOrderMode>();

​

             if (productModes == null || productModes.Length < 2 || productModes[0] == null || productModes[1] == null)

            {   

                 Console.WriteLine(productModes);

                 Console.WriteLine(productModes);

                Console.WriteLine("Skip this");

                continue;

            }

​

            foreach (var oos in productModes[1].Split(',', StringSplitOptions.RemoveEmptyEntries))

            {   

                if(oos == null)

                    continue;

                oosModes.Add((AllowedOutOfStockOrderMode)Int32.Parse(oos));

            }

​

            if (productAllowedModes.TryGetValue(productModes[0], out var oosModesExisting))

            {

                oosModes = oosModes.Concat(oosModesExisting).ToHashSet();

                productAllowedModes[productModes[0]] = oosModes;

            }

            else

            {

                productAllowedModes.Add(productModes[0], oosModes);

            }

        }

        /*

        foreach (var rec in productAllowedModes) {

            Console.WriteLine(rec.Key);

            Console.WriteLine(String.Join(",", rec.Value));

        }

        */

        var s = productAllowedModes.ToImmutableDictionary(

            x => x.Key,

            x => x.Value.ToImmutableHashSet()

        );

        Console.WriteLine("=========");

        foreach (var rec in s) {

            Console.WriteLine(rec.Key);

            Console.WriteLine(String.Join(",", rec.Value));

        }

    }

}