/// <summary>
/// A proxy class that supports the implementation of <see cref="INotifyPropertyChanged"/>.
/// It helps manage property changes and notifications efficiently.
///</summary>
public class PropertyChangeProxy {

	/// <summary>
	/// Initializes a new instance of the <see cref="PropertyChangeProxy"/> class
	/// that delegates notifications to the specified event handler.
	/// </summary>
	/// <param name="sender">The object that owns this proxy.</param>
	/// <param name="handlerGetter">A function that retrieves the event handler for notifications.</param>
	public PropertyChangeProxy(object? sender, Func<PropertyChangedEventHandler?> handlerGetter) { }

	/// <summary>
	/// Initializes a new instance of the <see cref="PropertyChangeProxy"/> class
	/// that delegates notifications using a specified action.
	/// </summary>
	/// <param name="raiseAction">An action to invoke property change notifications.</param>
	public PropertyChangeProxy(Action<PropertyChangedEventArgs> raiseAction) { }

	/// <summary>
	/// Sets the given storage value and sends a property change notification if the value has changed.
	/// </summary>
	/// <typeparam name="T">The type of the property.</typeparam>
	/// <param name="storage">A reference to the backing field of the property.</param>
	/// <param name="value">The new value to set.</param>
	/// <param name="propertyName">The name of the property (automatically determined).</param>
	/// <returns>A result indicating whether the value was changed.</returns>
	public ResultWithValue<PropertyChangeProxy> TrySetAndNotify<T>(ref T storage, T value, [CallerMemberName] string? propertyName = null) { }

	/// <summary>
	/// Sends a property change notification for the specified property name.
	/// </summary>
	/// <param name="propertyName">The name of the property (automatically determined).</param>
	/// <returns>The current instance of <see cref="PropertyChangeProxy"/>.</returns>
	public PropertyChangeProxy Notify([CallerMemberName] string? propertyName = null) { }

	/// <summary>
	/// Retrieves a cached <see cref="PropertyChangedEventArgs"/> instance for the specified property name.
	/// If no cached instance exists, a new one is created and stored.
	/// </summary>
	/// <param name="name">The name of the property for which to retrieve an event args instance.</param>
	/// <returns>A cached <see cref="PropertyChangedEventArgs"/> instance associated with the given property name.</returns>
	public static PropertyChangedEventArgs GetOrAddCachedEventArgs(string name) { }
}

public class NotifierBase : INotifyPropertyChanged {
	public NotiferBase () {
		PropertyChangeNotifier = new PropertyChangeProxy(this, () => PropertyChanged);
	}
	protected readonly PropertyChangeProxy PropertyChangeNotifier;
	public event PropertyChangedEventHandler? PropertyChanged;
}
public class NotifierPerson : NotifierBase {
	string _firstName = "";
	string _lastName = "";
	public string FirstName {
		get => _fistName;
		set => PropertyChangeNotifier.TrySetAndNotify(ref _firstName, value).When(o => o.Notify(nameof(FullName)));
	}
	public string LastName {
		get => _lastName;
		set => PropertyChangeNotifier.TrySetAndNotify(ref _lastName, value).When(o => o.Notify(nameof(FullName)));
	}
	public string FullName => FistName + " " + LastName;
}

public class NotifierBase : INotifyPropertyChanged {
	public NotifierBase() {
		propChangeNotifier = new PropertyChangeProxy(RaisePropertyChangedEvent);
	}
	private readonly PropertyChangeProxy propChangeNotifier;

	protected virtual void RaisePropertyChangedEvent(PropertyChangedEventArgs e) {
		PropertyChanged?.Invoke(this, e);
	}
	public virtual event PropertyChangedEventHandler? PropertyChanged;

	protected bool SetProperty<T>(ref T storage, T value, [CallerMemberName]string? propName = null) 
		=> propChangeNotifier.TrySetAndNotify(ref storage, value, propName);

	protected void OnPropertyChanged([CallerMemberName]string? propName = null)
		=> propChangeNotifier.Notify(propName);

}
public class NotifierPerson : NotifierBase {
	string _firstName = "";
	string _lastName = "";
	public string FirstName {
		get => _fistName;
		set {
			if (SetProperty(ref _firstName, value)) OnPropertyChanged(nameof(FullName));
		}
	}
	public string LastName {
		get => _lastName;
		set {
			if (SetProperty(ref _lastName, value)) OnPropertyChanged(nameof(FullName));
		}
	}
	public string FullName => FirstName + " " + LastName;

    // override members
	protected override void RaisePropertyChangedEvent(PropertyChangedEventArgs e) {
		Console.WriteLine("Raise Event.");
		base.RaisePropertyChangedEvent(e);
	}
	public override event PropertyChangedEventHandler? PropertyChanged {
		add {
			base.PropertyChanged += value;
			Console.WriteLine("Handler added.");
		}
		remove {
			base.PropertyChanged -= value;
			Console.WriteLine("Handler removed.");
		}
	}
}