using System;

using System.Text.RegularExpressions;

​

#nullable enable

​

public class Program

{

     private static readonly Regex s_atLocationRegex = new Regex("(?<=^At ).*?(?=\\.  )"); // Matches "At LOCATION." pattern

     private static readonly Regex s_remoteLocationRegex = new Regex("^Remote?(?=\\.  )"); // Matches "Remote." pattern

    public static void Main()

    {

        for(int i = 0; i < 1000; i++)

        {

            TestNotes("At DMC.  At DCI. This is a test note 1. ");      

            TestNotes("Remote.  This is a test note 2. ");

            TestNotes("At Wrigley.  This is a test note 3. Remote. ");  

        }

    }

    private static void TestNotes(string notes)

    {

        var result = DecomposeNotesField(notes);

        Console.WriteLine("Location: {0},\tnotes: {1}", result?.Location, result?.NotesWithoutLocation);

    }

    private static NotesLocationRegexResult? DecomposeNotesField(string? notes)

    {

        if (notes is null)

            return null;

​

        try

        {

            var result = s_atLocationRegex.Match(notes);

            if (result.Success)

            {

                return new NotesLocationRegexResult(

                    result.Value,

                    notes[(result.Value.Length + 6)..] // Skip length of string that contains "At {location].  " prefix

                );

            }

​

            result = s_remoteLocationRegex.Match(notes);

            if (result.Success)

            {

                return new NotesLocationRegexResult(

                    result.Value,

                    notes[9..] // Skip the first 9 characters that contains "Remote.  " prefix

                );

            }

        }

        catch { return null; }

​

        return null;

    }

    private record NotesLocationRegexResult(string Location, string NotesWithoutLocation);

}