using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        Console.WriteLine($"Endpoint1: {ExtractEndpoint(new Uri(@"http://test.com/api"))}");

        Console.WriteLine($"Endpoint2: {ExtractEndpoint(new Uri(@"http://test.com/api/"))}");

        Console.WriteLine($"Endpoint3: {ExtractEndpoint(new Uri(@"http://test.com/api/controller"))}");

        Console.WriteLine($"Endpoint4: {ExtractEndpoint(new Uri(@"http://test.com/api/controller/"))}");

        Console.WriteLine($"Endpoint5: {ExtractEndpoint(new Uri(@"http://test.com/api/controller/endpoint"))}");

        Console.WriteLine($"Endpoint6: {ExtractEndpoint(new Uri(@"http://test.com/api/controller/endpoint/"))}");

        Console.WriteLine($"Endpoint7: {ExtractEndpoint(new Uri(@"http://test.com/api/v1/controller/endpoint"))}");

        Console.WriteLine($"Endpoint8: {ExtractEndpoint(new Uri(@"http://test.com/api/v1/controller/endpoint/"))}");

        Console.WriteLine($"Endpoint9: {ExtractEndpoint(new Uri(@"http://test.com/api/v1/controller/endpoint/extra/parms"))}");

        Console.WriteLine($"Endpoint10: {ExtractEndpoint(new Uri(@"http://test.com/api/v1/controller/endpoint/extra/parms/"))}");

        Console.WriteLine($"Endpoint11: {ExtractEndpoint(new Uri(@"http://test.com/api/v12/controller/endpoint/extra/parms"))}");

        Console.WriteLine($"Endpoint12: {ExtractEndpoint(new Uri(@"http://test.com/api/v12/controller/endpoint/extra/parms/"))}");

        Console.WriteLine($"Endpoint13: {ExtractEndpoint(new Uri(@"http://test.com/api/v1.0/controller/endpoint/extra/parms"))}");

        Console.WriteLine($"Endpoint14: {ExtractEndpoint(new Uri(@"http://test.com/api/v1.0/controller/endpoint/extra/parms/"))}");

        Console.WriteLine($"Endpoint15: {ExtractEndpoint(new Uri(@"http://test.com/api/v12.34/controller/endpoint/extra/parms"))}");

        Console.WriteLine($"Endpoint16: {ExtractEndpoint(new Uri(@"http://test.com/api/v12.34/controller/endpoint/extra/parms/"))}");

        Console.WriteLine($"Endpoint17: {ExtractEndpoint(new Uri(@"http://test.com/api/v12.34.56/controller/endpoint/extra/parms"))}");

        Console.WriteLine($"Endpoint18: {ExtractEndpoint(new Uri(@"http://test.com/api/v12.34.56/controller/endpoint/extra/parms/"))}");

    }

    private static string ExtractEndpoint(Uri requestUri)

        {

            var absolutePath = requestUri.AbsolutePath;

​

            var match = Regex.Match(absolutePath, @"^(?<EndPoint>/\w+/?([Vv]\d+(\.\d+)*)?(/?[^/]*){0,2})/?.*$");

​

            return match.Success

                ? match.Groups["EndPoint"].Value

                : string.Empty;

        }

}