namespace UpdatedOne;

public interface IObserver<TSubject>
{
   void Update(TSubject subject);
}

public abstract class Subject<TSubject>
{
   private readonly List<IObserver<TSubject>> _observers = new();

   public void Subscribe(IObserver<TSubject> observer)
   {
      if (!_observers.Contains(observer))
         _observers.Add(observer);
   }

   public void Unsubscribe(IObserver<TSubject> observer)
   {
      _observers.Remove(observer);
   }

   protected void Notify(TSubject subject)
   {
      foreach (IObserver<TSubject> observer in _observers.ToArray())
         observer.Update(subject);
   }
}

public class Data : Subject<Data>
{
   private int _value;

   public Data(int value)
   {
      _value = value;
   }

   public void SetData(int value)
   {
      if (_value == value)
         return;

      _value = value;

      Console.WriteLine($"Data changed to {_value}");

      Notify(this);
   }

   public int GetData()
   {
      return _value;
   }
}

public class BarGraph : IObserver<Data>
{
   public void Update(Data subject)
   {
      int value = subject.GetData();

      Console.WriteLine($"Bar Graph updated: {value}");
   }
}

public class PieChart : IObserver<Data>
{
   public void Update(Data subject)
   {
      int value = subject.GetData();

      Console.WriteLine($"Pie Chart updated: {value}");
   }
}

internal static class Program
{
   private static void Main()
   {
      Data data = new Data(2);

      BarGraph barGraph = new BarGraph();
      PieChart pieChart = new PieChart();

      data.Subscribe(barGraph);
      data.Subscribe(pieChart);

      data.SetData(3);

      data.Unsubscribe(barGraph);
      data.Unsubscribe(pieChart);
   }
}