using System;
using System.Collections.Generic;

/// <summary>
/// This interface defines an action observer. It implements a generic observer pattern and can be reused,
/// but its main usage in this project is to make the view update whenever the shop model changes.
/// </summary>
public interface IShopModelObserver<T>
{
    void OnSelected(T item);
    void OnRemoved(T item);
    void OnAdded(T item);
    void OnTransaction(int balance);     // Called when a transaction happens that changes the balance of the model, contains total new balance
}

// Unsubscriber, so the observer can self-unsubscribe from this observable without any coupling
public class Unsubscriber<T> : IDisposable
{
    private List<IShopModelObserver<T>> _observers;
    private IShopModelObserver<T> _observer;

    internal Unsubscriber(List<IShopModelObserver<T>> observers, IShopModelObserver<T> observer)
    {
        this._observers = observers;
        this._observer = observer;
    }

    public void Dispose()
    {
        if (_observers.Contains(_observer))
            _observers.Remove(_observer);
    }
}