using System;

​

public class Program

{

    public static void Main()

    {

        var (rel, wet) = ParseGroupName("R0000");

        Console.WriteLine($"R0000 = {rel}, {wet}");

​

        (rel, wet) = ParseGroupName("R0001_");

        Console.WriteLine($"R0001_ = {rel}, {wet}");

​

        (rel, wet) = ParseGroupName("R0002_JW");

        Console.WriteLine($"R0002_JW = {rel}, {wet}");

​

        (rel, wet) = ParseGroupName("R0003_WLZ");

        Console.WriteLine($"R0003_WLZ = {rel}, {wet}");

​

        (rel, wet) = ParseGroupName("R0004_GEMWMO");

        Console.WriteLine($"R0004_GEMWMO = {rel}, {wet}");

    }

​

    public enum WetType { NVT, WLZ, JW, WMO, }

​

    private static (string, WetType?) ParseGroupName(string groupname)

    {

        if (string.IsNullOrWhiteSpace(groupname))

        {

            return (null, null);

        }

​

        WetType? wet = null;

        var index = groupname.IndexOf('_');

        if (index >= 0)

        {

            if (groupname[^2..] == "JW")

            {

                wet = WetType.JW;

            }

            else if (groupname[^3..] == "WMO")

            {

                wet = WetType.WMO;

            }

        }

        else

        {

            index = groupname.Length;

        }

        return int.TryParse(groupname[1..index], out var relatienummer)

            ? (relatienummer.ToString(), wet)

            : (null, wet);

}}