using System;

using System.IO;

​

public abstract class MessageService

{

    public abstract string GetMessage();

}

​

public class UserInputService : MessageService

{

    public override string GetMessage()

    {

        int i = 0;

        do

        {

            try

            {

                var input = Console.ReadLine();

                if (input != null)

                {

                    return input;

                }

            }

            catch (Exception e)

            {

                return "";

            }

        }

        while (i++ < 3);

        return "";

    }

}

​

public class SMSService : MessageService

{

    public override string GetMessage()

    {

        // Not Supported

        Console.WriteLine("Operation is not supported");

        throw new NotSupportedException();

    }

}

​

public class FileService : MessageService

{

    public override string GetMessage()

    {

        var res = "";

        String s;

        StreamReader m = File.OpenText(@"C:\temp\message.txt");

        while ((s = m.ReadLine()) != null)

        {

            res += s;

        }

​

        return res;

    }

}