using System;

​

class MainApp

{

    public static void Main()

    {

        var smsNotifier = new SmsNotifier();

        smsNotifier.Notify();

        var emailNotifier = new EmailNotifier();

        emailNotifier.Notify();

    }

}

​

enum StateColors

{

    Green,

    Red

}

​

abstract class AbstractState

{

    public StateColors Color { get; protected set; }

    public AbstractNotifier Notifier { get; set; }

}

​

class GreenState : AbstractState

{

    private readonly AbstractNotifier _notifier;

​

    public GreenState(AbstractNotifier notifier)

    {

        _notifier = notifier;

        Color = StateColors.Green;

    }

​

    public GreenState(AbstractState state)

    {

        _notifier = state.Notifier;

        Color = StateColors.Green;

    }

​

    public void SetColor(StateColors color)

    {

        if (color == StateColors.Red)

        {

            _notifier.State = new RedState(this);

        }

    }

}

​

class RedState : AbstractState

{

    private readonly AbstractNotifier _notifier;

​

    public RedState(AbstractState state)

    {

        _notifier = state.Notifier;

        Color = StateColors.Red;

    }

​

    public void SetColor(StateColors color)

    {

        if (color == StateColors.Green)

        {

            _notifier.State = new GreenState(this);

        }

    }

}

​

abstract class AbstractNotifier

{

    protected abstract bool Connect();

    protected abstract void Send();

    protected abstract void Disconnect();

​

    public AbstractState State { get; set; }

​

    public AbstractNotifier()

    {

        State = new GreenState(this);

    }

​

    public void Notify()

    {

        Console.WriteLine($"Current state: {State.Color}");

        if (Connect())

        {

            State = new GreenState(State);

            Console.WriteLine($"State: {State.Color}");

            Send();

            Disconnect();

        }

        else

        {

            State = new RedState(State);

            Console.WriteLine($"State: {State.Color}");

        }

    }

}

​

class SmsNotifier : AbstractNotifier

{

    public SmsNotifier()

    {

​

    }

​

    protected override bool Connect()

    {

        Console.WriteLine("Connecting to the SMS system");

        return false;

    }

    protected override void Send()

    {

        Console.WriteLine("Sending SMS");

    }

    protected override void Disconnect()

    {

        Console.WriteLine("Disconnecting from the SMS system");

    }

}

​

class EmailNotifier : AbstractNotifier

{

    public EmailNotifier()

    {

​

    }

​

    protected override bool Connect()

    {

        Console.WriteLine("Connecting to the Email system");

        return true;

    }

    protected override void Send()

    {

        Console.WriteLine("Sending email");

    }

    protected override void Disconnect()

    {

        Console.WriteLine("Disconnecting from the Email system");

    }

}

​