using System.Reactive.Linq;
using System.Runtime.InteropServices;

using Avalonia;
using Avalonia.Controls;

namespace InkForge.Desktop.Services;

public class TopLevels
{
	public static readonly AttachedProperty<object?> RegisterProperty
		= AvaloniaProperty.RegisterAttached<TopLevels, Visual, object?>("Register");
	private static readonly Dictionary<object, Visual> RegistrationMapper = [];

	public static TopLevel? ActiveTopLevel { get; private set; }

	static TopLevels()
	{
		RegisterProperty.Changed.AddClassHandler<Visual>(RegisterChanged);
		WindowBase.IsActiveProperty.Changed.Subscribe(WindowActiveChanged);
	}

	public static object? GetRegister(AvaloniaObject element)
	{
		return element.GetValue(RegisterProperty);
	}

	public static TopLevel? GetTopLevelForContext(object context)
	{
		return TopLevel.GetTopLevel(GetVisualForContext(context));
	}

	public static Visual? GetVisualForContext(object context)
	{
		return RegistrationMapper.TryGetValue(context, out var result) ? result : null;
	}

	public static void SetRegister(AvaloniaObject element, object value)
	{
		element.SetValue(RegisterProperty, value);
	}

	private static void RegisterChanged(Visual sender, AvaloniaPropertyChangedEventArgs e)
	{
		ArgumentNullException.ThrowIfNull(sender);

		// Unregister any old registered context
		if (e.OldValue != null)
		{
			RegistrationMapper.Remove(e.OldValue);
		}

		// Register any new context
		if (e.NewValue != null)
		{
			CollectionsMarshal.GetValueRefOrAddDefault(RegistrationMapper, e.NewValue, out _) = sender;
		}
	}

	private static void WindowActiveChanged(AvaloniaPropertyChangedEventArgs<bool> e)
	{
		ActiveTopLevel = (e.GetOldAndNewValue<bool>(), e.Sender) switch
		{
			((false, true), TopLevel topLevel) => topLevel,
			((true, false), { } topLevel) when topLevel == ActiveTopLevel => null,
			_ => ActiveTopLevel,
		};
	}
}