using System;

using System.Collections.Generic;

​

interface IServerStrategy

{

    string Process(string request);

}

​

class Server : IServerStrategy 

{

    private HashSet<string> modifiers;

    public Server(params string[] modifiers) 

    {

        this.modifiers = new HashSet<string>(modifiers);

    }   

    public string Process(string request) 

    {

        string respose = "";

        if (request.StartsWith("ECHO "))

        {

            respose = ProcessEchoRequest(request);

        }

        else if (request == "PING" )

        {

            respose = ProcessPingRequest();

        }

        else

        {

            return "Bad request";

        }

        return ProcessModifiers(respose);

    }

    public string ProcessModifiers(string request) 

    {

        string response = request;

        if (this.modifiers.Contains("TIME"))

        {

            response = string.Concat(DateTime.Now.ToString("HH:mm:ss")," ", response);

        }

        if (this.modifiers.Contains("TOUPPER"))

        {

            response = response.ToUpper();

        }

        return response;

    }

    private string ProcessEchoRequest(string request) 

    {

        string echoKeyword = "ECHO ";

        return request.Substring(echoKeyword.Length);

    }

    private string ProcessPingRequest() 

    {

        return "Pong";

    }

}

​

public class Program

{

    public static void Main()

    {

        var server1 = new Server();     

        Console.WriteLine(server1.Process("ECHO Hello world!"));    // Hello world!

        Console.WriteLine(server1.Process("PING"));                 // Pong

        Console.WriteLine(server1.Process("XYZV"));                 // Bad request              

        var server2 = new Server("TOUPPER");        

        Console.WriteLine(server2.Process("ECHO Hello world!"));    // HELLO WORLD!

        Console.WriteLine(server2.Process("PING"));                 // PONG

        var server3 = new Server("TIME");

        Console.WriteLine(server3.Process("ECHO Hello world!"));    // 10:20:30 Hello world!

        Console.WriteLine(server3.Process("PING"));                 // 10:20:30 Pong

​

        var server4 = new Server("TIME", "TOUPPER");

        Console.WriteLine(server4.Process("ECHO Hello world!"));    // 10:20:30 HELLO WORLD!

        Console.WriteLine(server4.Process("PING"));                 // 10:20:30 PONG        

    }

}