using Avalonia;
using ReactiveUI;

namespace AtomUI.Desktop.Controls;

/// <summary>
/// A ReactiveUI <see cref="Window"/> that implements the <see cref="IViewFor"/> interface and will
/// activate your ViewModel automatically if the view model implements <see cref="IActivatableViewModel"/>. When
/// the DataContext property changes, this class will update the ViewModel property with the new DataContext value,
/// and vice versa.
/// </summary>
/// <typeparam name="TViewModel">ViewModel type.</typeparam>
public class ReactiveWindow<TViewModel> : Window, IViewFor<TViewModel> where TViewModel : class
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("AvaloniaProperty", "AVP1002",
        Justification = "Generic avalonia property is expected here.")]
    public static readonly StyledProperty<TViewModel?> ViewModelProperty = 
        AvaloniaProperty.Register<ReactiveWindow<TViewModel>, TViewModel?>(nameof(ViewModel));

    /// <summary>
    /// Initializes a new instance of the <see cref="ReactiveWindow{TViewModel}"/> class.
    /// </summary>
    public ReactiveWindow()
    {
        // This WhenActivated block calls ViewModel's WhenActivated
        // block if the ViewModel implements IActivatableViewModel.
        this.WhenActivated(disposables => { });
    }

    /// <summary>
    /// The ViewModel.
    /// </summary>
    public TViewModel? ViewModel
    {
        get => GetValue(ViewModelProperty);
        set => SetValue(ViewModelProperty, value);
    }

    object? IViewFor.ViewModel
    {
        get => ViewModel;
        set => ViewModel = (TViewModel?)value;
    }

    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
    {
        base.OnPropertyChanged(change);

        if (change.Property == DataContextProperty)
        {
            if (ReferenceEquals(change.OldValue, ViewModel)
                && change.NewValue is null or TViewModel)
            {
                SetCurrentValue(ViewModelProperty, change.NewValue);
            }
        }
        else if (change.Property == ViewModelProperty)
        {
            if (ReferenceEquals(change.OldValue, DataContext))
            {
                SetCurrentValue(DataContextProperty, change.NewValue);
            }
        }
    }
}