DialogHost.cs

using System.Runtime.InteropServices;
using System.Security;
using System.Windows.Data;
using System.Windows.Interop;
using System.Windows.Media;
using System.Windows.Threading;

namespace MaterialDesignThemes.Wpf;

/// <summary>
/// Defines how a data context is sourced for a dialog if a <see cref="FrameworkElement"/>
/// is passed as the command parameter when using <see cref="DialogHost.OpenDialogCommand"/>.
/// </summary>
public enum DialogHostOpenDialogCommandDataContextSource
{
    /// <summary>
    /// The data context from the sender element (typically a <see cref="Button"/>) 
    /// is applied to the content.
    /// </summary>
    SenderElement,
    /// <summary>
    /// The data context from the <see cref="DialogHost"/> is applied to the content.
    /// </summary>
    DialogHostInstance,
    /// <summary>
    /// The data context is explicitly set to <c>null</c>.
    /// </summary>
    None
}

[TemplatePart(Name = PopupPartName, Type = typeof(Popup))]
[TemplatePart(Name = PopupPartName, Type = typeof(ContentControl))]
[TemplatePart(Name = ContentCoverGridName, Type = typeof(Grid))]
[TemplateVisualState(GroupName = "PopupStates", Name = OpenStateName)]
[TemplateVisualState(GroupName = "PopupStates", Name = ClosedStateName)]
public class DialogHost : ContentControl
{
    public const string PopupPartName = "PART_Popup";
    public const string PopupContentPartName = "PART_PopupContentElement";
    public const string ContentCoverGridName = "PART_ContentCoverGrid";
    public const string OpenStateName = "Open";
    public const string ClosedStateName = "Closed";

    /// <summary>
    /// Routed command to be used somewhere inside an instance to trigger showing of the dialog. Content can be passed to the dialog via a <see cref="Button.CommandParameter"/>.
    /// </summary>
    public static readonly RoutedCommand OpenDialogCommand = new();
    /// <summary>
    /// Routed command to be used inside dialog content to close a dialog. Use a <see cref="Button.CommandParameter"/> to indicate the result of the parameter.
    /// </summary>
    public static readonly RoutedCommand CloseDialogCommand = new();

    private static readonly HashSet<WeakReference<DialogHost>> LoadedInstances = [];

    private DialogOpenedEventHandler? _asyncShowOpenedEventHandler;
    private DialogClosingEventHandler? _asyncShowClosingEventHandler;
    private DialogClosedEventHandler? _asyncShowClosedEventHandler;
    private TaskCompletionSource<object?>? _dialogTaskCompletionSource;

    private Popup? _popup;
    private ContentControl? _popupContentControl;
    private Grid? _contentCoverGrid;
    private DialogOpenedEventHandler? _attachedDialogOpenedEventHandler;
    private DialogClosingEventHandler? _attachedDialogClosingEventHandler;
    private DialogClosedEventHandler? _attachedDialogClosedEventHandler;
    private IInputElement? _restoreFocusDialogClose;
    private Action? _currentSnackbarMessageQueueUnPauseAction;

    static DialogHost()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(DialogHost), new FrameworkPropertyMetadata(typeof(DialogHost)));
    }

    #region Show overloads

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content)
        => Show(content, null, null);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>        
    /// <param name="openedEventHandler">Allows access to opened event which would otherwise have been subscribed to on a instance.</param>        
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, DialogOpenedEventHandler openedEventHandler)
        => Show(content, null, openedEventHandler, null);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>
    /// <param name="closingEventHandler">Allows access to closing event which would otherwise have been subscribed to on a instance.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, DialogClosingEventHandler closingEventHandler)
        => Show(content, null, null, closingEventHandler);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>        
    /// <param name="openedEventHandler">Allows access to opened event which would otherwise have been subscribed to on a instance.</param>
    /// <param name="closingEventHandler">Allows access to closing event which would otherwise have been subscribed to on a instance.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, DialogOpenedEventHandler? openedEventHandler, DialogClosingEventHandler? closingEventHandler)
        => Show(content, null, openedEventHandler, closingEventHandler);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>        
    /// <param name="openedEventHandler">Allows access to opened event which would otherwise have been subscribed to on a instance.</param>
    /// <param name="closingEventHandler">Allows access to closing event which would otherwise have been subscribed to on a instance.</param>
    /// <param name="closedEventHandler">Allows access to closed event which would otherwise have been subscribed to on a instance.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, DialogOpenedEventHandler? openedEventHandler, DialogClosingEventHandler? closingEventHandler, DialogClosedEventHandler? closedEventHandler)
        => Show(content, null, openedEventHandler, closingEventHandler, closedEventHandler);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>
    /// <param name="dialogIdentifier"><see cref="Identifier"/> of the instance where the dialog should be shown. Typically this will match an identifier set in XAML. <c>null</c> is allowed.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, object dialogIdentifier)
        => Show(content, dialogIdentifier, null, null);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>
    /// <param name="dialogIdentifier"><see cref="Identifier"/> of the instance where the dialog should be shown. Typically this will match an identifier set in XAML. <c>null</c> is allowed.</param>
    /// <param name="openedEventHandler">Allows access to opened event which would otherwise have been subscribed to on a instance.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, object dialogIdentifier, DialogOpenedEventHandler openedEventHandler)
        => Show(content, dialogIdentifier, openedEventHandler, null);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>
    /// <param name="dialogIdentifier"><see cref="Identifier"/> of the instance where the dialog should be shown. Typically this will match an identifier set in XAML. <c>null</c> is allowed.</param>        
    /// <param name="closingEventHandler">Allows access to closing event which would otherwise have been subscribed to on a instance.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, object dialogIdentifier, DialogClosingEventHandler closingEventHandler)
        => Show(content, dialogIdentifier, null, closingEventHandler);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>
    /// <param name="dialogIdentifier"><see cref="Identifier"/> of the instance where the dialog should be shown. Typically this will match an identifier set in XAML. <c>null</c> is allowed.</param>
    /// <param name="openedEventHandler">Allows access to opened event which would otherwise have been subscribed to on a instance.</param>
    /// <param name="closingEventHandler">Allows access to closing event which would otherwise have been subscribed to on a instance.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static Task<object?> Show(object content, object? dialogIdentifier, DialogOpenedEventHandler? openedEventHandler, DialogClosingEventHandler? closingEventHandler)
        => Show(content, dialogIdentifier, openedEventHandler, closingEventHandler, null);

    /// <summary>
    /// Shows a modal dialog. To use, a <see cref="DialogHost"/> instance must be in a visual tree (typically this may be specified towards the root of a Window's XAML).
    /// </summary>
    /// <param name="content">Content to show (can be a control or view model).</param>
    /// <param name="dialogIdentifier"><see cref="Identifier"/> of the instance where the dialog should be shown. Typically this will match an identifier set in XAML. <c>null</c> is allowed.</param>
    /// <param name="openedEventHandler">Allows access to opened event which would otherwise have been subscribed to on a instance.</param>
    /// <param name="closingEventHandler">Allows access to closing event which would otherwise have been subscribed to on a instance.</param>
    /// <param name="closedEventHandler">Allows access to closed event which would otherwise have been subscribed to on a instance.</param>
    /// <returns>Task result is the parameter used to close the dialog, typically what is passed to the <see cref="CloseDialogCommand"/> command.</returns>
    public static async Task<object?> Show(object content, object? dialogIdentifier, DialogOpenedEventHandler? openedEventHandler, DialogClosingEventHandler? closingEventHandler, DialogClosedEventHandler? closedEventHandler)
    {
        if (content is null) throw new ArgumentNullException(nameof(content));
        return await GetInstance(dialogIdentifier).ShowInternal(content, openedEventHandler, closingEventHandler, closedEventHandler);
    }

    /// <summary>
    ///  Close a modal dialog.
    /// </summary>
    /// <param name="dialogIdentifier"> of the instance where the dialog should be closed. Typically this will match an identifier set in XAML. </param>
    public static void Close(object? dialogIdentifier)
        => Close(dialogIdentifier, null);

    /// <summary>
    ///  Close a modal dialog.
    /// </summary>
    /// <param name="dialogIdentifier"> of the instance where the dialog should be closed. Typically this will match an identifier set in XAML. </param>
    /// <param name="parameter"> to provide to close handler</param>
    public static void Close(object? dialogIdentifier, object? parameter)
    {
        DialogHost dialogHost = GetInstance(dialogIdentifier);
        if (dialogHost.CurrentSession is { } currentSession)
        {
            currentSession.Close(parameter);
            return;
        }
        throw new InvalidOperationException("DialogHost is not open.");
    }

    /// <summary>
    /// Retrieve the current dialog session for a DialogHost
    /// </summary>
    /// <param name="dialogIdentifier">The identifier to use to retrieve the DialogHost</param>
    /// <returns>The DialogSession if one is in process, or null</returns>
    public static DialogSession? GetDialogSession(object? dialogIdentifier)
    {
        DialogHost dialogHost = GetInstance(dialogIdentifier);
        return dialogHost.CurrentSession;
    }

    /// <summary>
    /// dialog instance exists
    /// </summary>
    /// <param name="dialogIdentifier">of the instance where the dialog should be closed. Typically this will match an identifier set in XAML.</param>
    /// <returns></returns>
    public static bool IsDialogOpen(object? dialogIdentifier) => GetDialogSession(dialogIdentifier)?.IsEnded == false;

    private static DialogHost GetInstance(object? dialogIdentifier)
    {
        if (LoadedInstances.Count == 0)
            throw new InvalidOperationException("No loaded DialogHost instances.");

        List<DialogHost> targets = [];
        foreach (var instance in LoadedInstances.ToList())
        {
            if (instance.TryGetTarget(out DialogHost? dialogInstance))
            {
                object? identifier = null;
                if (dialogInstance.CheckAccess())
                {
                    identifier = dialogInstance.Identifier;
                }
                else
                {
                    // Retrieve the identifier using the Dispatcher on the owning thread (effectively replaces the VerifyAccess() call previously used)
                    identifier = dialogInstance.Dispatcher.Invoke(() => dialogInstance.Identifier);
                }
                if (Equals(dialogIdentifier, identifier))
                {
                    targets.Add(dialogInstance);
                }
            }
            else
            {
                LoadedInstances.Remove(instance);
            }
        }

        if (targets.Count == 0)
            throw new InvalidOperationException($"No loaded DialogHost have an {nameof(Identifier)} property matching {nameof(dialogIdentifier)} ('{dialogIdentifier}') argument.");
        if (targets.Count > 1)
            throw new InvalidOperationException("Multiple viable DialogHosts. Specify a unique Identifier on each DialogHost, especially where multiple Windows are a concern.");

        return targets[0];
    }

    internal async Task<object?> ShowInternal(object content, DialogOpenedEventHandler? openedEventHandler, DialogClosingEventHandler? closingEventHandler, DialogClosedEventHandler? closedEventHandler)
    {
        if (IsOpen)
            throw new InvalidOperationException("DialogHost is already open.");

        _dialogTaskCompletionSource = new TaskCompletionSource<object?>();

        AssertTargetableContent();

        if (content != null)
            DialogContent = content;

        _asyncShowOpenedEventHandler = openedEventHandler;
        _asyncShowClosingEventHandler = closingEventHandler;
        _asyncShowClosedEventHandler = closedEventHandler;
        SetCurrentValue(IsOpenProperty, true);

        object? result = await _dialogTaskCompletionSource.Task;

        _asyncShowOpenedEventHandler = null;
        _asyncShowClosingEventHandler = null;
        _asyncShowClosedEventHandler = null;

        return result;
    }

    #endregion

    public DialogHost()
    {
        Loaded += OnLoaded;
        Unloaded += OnUnloaded;

        CommandBindings.Add(new CommandBinding(CloseDialogCommand, CloseDialogHandler, CloseDialogCanExecute));
        CommandBindings.Add(new CommandBinding(OpenDialogCommand, OpenDialogHandler));
    }

    public static readonly DependencyProperty IdentifierProperty = DependencyProperty.Register(
        nameof(Identifier), typeof(object), typeof(DialogHost), new PropertyMetadata(default(object)));

    /// <summary>
    /// Identifier which is used in conjunction with <see cref="Show(object)"/> to determine where a dialog should be shown.
    /// </summary>
    public object? Identifier
    {
        get => GetValue(IdentifierProperty);
        set => SetValue(IdentifierProperty, value);
    }

    public static readonly DependencyProperty IsOpenProperty = DependencyProperty.Register(
        nameof(IsOpen), typeof(bool), typeof(DialogHost), new FrameworkPropertyMetadata(default(bool), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, IsOpenPropertyChangedCallback));

    private static void IsOpenPropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
    {
        var dialogHost = (DialogHost)dependencyObject;

        if (dialogHost._popupContentControl != null)
            ValidationAssist.SetSuppress(dialogHost._popupContentControl, !dialogHost.IsOpen);
        VisualStateManager.GoToState(dialogHost, dialogHost.GetStateName(), !TransitionAssist.GetDisableTransitions(dialogHost));

        if (dialogHost.IsOpen)
        {
            dialogHost._currentSnackbarMessageQueueUnPauseAction = dialogHost.SnackbarMessageQueue?.Pause();
        }
        else
        {
            dialogHost._attachedDialogClosingEventHandler = null;
            if (dialogHost._currentSnackbarMessageQueueUnPauseAction != null)
            {
                dialogHost._currentSnackbarMessageQueueUnPauseAction();
                dialogHost._currentSnackbarMessageQueueUnPauseAction = null;
            }

            object? closeParameter = null;
            if (dialogHost.CurrentSession is { } session)
            {
                //multiple ways of calling back that the dialog is closed:
                // * routed event
                // * the attached property (which should be applied to the button which opened the dialog
                // * straight forward IsOpen dependency property 
                // * handler provided to the async show method
                var dialogClosedEventArgs = new DialogClosedEventArgs(dialogHost.CurrentSession, DialogClosedEvent);
                dialogHost.OnDialogClosed(dialogClosedEventArgs);
                dialogHost._attachedDialogClosedEventHandler?.Invoke(dialogHost, dialogClosedEventArgs);
                dialogHost.DialogClosedCallback?.Invoke(dialogHost, dialogClosedEventArgs);
                dialogHost._asyncShowClosedEventHandler?.Invoke(dialogHost, dialogClosedEventArgs);
                dialogHost._attachedDialogClosedEventHandler = null;

                if (!session.IsEnded)
                {
                    session.Close(session.CloseParameter);
                }
                //DialogSession.Close may attempt to cancel the closing of the dialog.
                //When the dialog is closed in this manner it is not valid
                if (!session.IsEnded)
                {
                    throw new InvalidOperationException($"Cannot cancel dialog closing after {nameof(IsOpen)} property has been set to {bool.FalseString}");
                }
                closeParameter = session.CloseParameter;
                dialogHost.CurrentSession = null;
            }

            //NB: _dialogTaskCompletionSource is only set in the case where the dialog is shown with Show
            dialogHost._dialogTaskCompletionSource?.TrySetResult(closeParameter);

            // Don't attempt to Invoke if _restoreFocusDialogClose hasn't been assigned yet. Can occur
            // if the MainWindow has started up minimized. Even when Show() has been called, this doesn't
            // seem to have been set.
            dialogHost.Dispatcher.InvokeAsync(() => dialogHost._restoreFocusDialogClose?.Focus(), DispatcherPriority.Input);

            return;
        }

        dialogHost.CurrentSession = new DialogSession(dialogHost);
        var window = Window.GetWindow(dialogHost);
        if (!dialogHost.IsRestoreFocusDisabled)
        {
            dialogHost._restoreFocusDialogClose = window != null ? FocusManager.GetFocusedElement(window) : null;

            // Check restore focus override
            if (dialogHost._restoreFocusDialogClose is DependencyObject dependencyObj &&
                GetRestoreFocusElement(dependencyObj) is { } focusOverride)
            {
                dialogHost._restoreFocusDialogClose = focusOverride;
            }
        }

        //multiple ways of calling back that the dialog has opened:
        // * routed event
        // * the attached property (which should be applied to the button which opened the dialog
        // * straight forward dependency property 
        // * handler provided to the async show method
        var dialogOpenedEventArgs = new DialogOpenedEventArgs(dialogHost.CurrentSession, DialogOpenedEvent);
        dialogHost.OnDialogOpened(dialogOpenedEventArgs);
        dialogHost._attachedDialogOpenedEventHandler?.Invoke(dialogHost, dialogOpenedEventArgs);
        dialogHost.DialogOpenedCallback?.Invoke(dialogHost, dialogOpenedEventArgs);
        dialogHost._asyncShowOpenedEventHandler?.Invoke(dialogHost, dialogOpenedEventArgs);

        dialogHost.Dispatcher.BeginInvoke(DispatcherPriority.Background, new Action(() =>
        {
            CommandManager.InvalidateRequerySuggested();
            UIElement? child = dialogHost.FocusPopup();

            if (child != null)
            {
                //https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/issues/187
                //totally not happy about this, but on immediate validation we can get some weird looking stuff...give WPF a kick to refresh...
                Task.Delay(300).ContinueWith(t => child.Dispatcher.BeginInvoke(new Action(() => child.InvalidateVisual())));
            }
        }));
    }

    /// <summary>
    /// Returns a DialogSession for the currently open dialog for managing it programmatically. If no dialog is open, CurrentSession will return null
    /// </summary>
    public DialogSession? CurrentSession { get; private set; }

    public bool IsOpen
    {
        get => (bool)GetValue(IsOpenProperty);
        set => SetValue(IsOpenProperty, value);
    }

    public static readonly DependencyProperty PlacementProperty = DependencyProperty.Register(
        nameof(Placement), typeof(PlacementMode), typeof(DialogHost), new PropertyMetadata(PlacementMode.Center));

    public PlacementMode Placement
    {
        get => (PlacementMode)GetValue(PlacementProperty);
        set => SetValue(PlacementProperty, value);
    }

    public static readonly DependencyProperty CornerRadiusProperty = DependencyProperty.Register(
        nameof(CornerRadius), typeof(CornerRadius), typeof(DialogHost), new PropertyMetadata(default(CornerRadius)));

    public CornerRadius CornerRadius
    {
        get => (CornerRadius)GetValue(CornerRadiusProperty);
        set => SetValue(CornerRadiusProperty, value);
    }

    public static readonly DependencyProperty DialogContentProperty = DependencyProperty.Register(
        nameof(DialogContent), typeof(object), typeof(DialogHost), new PropertyMetadata(default(object)));

    public object? DialogContent
    {
        get => GetValue(DialogContentProperty);
        set => SetValue(DialogContentProperty, value);
    }

    public static readonly DependencyProperty DialogContentUniformCornerRadiusProperty = DependencyProperty.Register(
        nameof(DialogContentUniformCornerRadius), typeof(double), typeof(DialogHost), new PropertyMetadata(4d));

    public double DialogContentUniformCornerRadius
    {
        get => (double)GetValue(DialogContentUniformCornerRadiusProperty);
        set => SetValue(DialogContentUniformCornerRadiusProperty, value);
    }

    public static readonly DependencyProperty DialogContentTemplateProperty = DependencyProperty.Register(
        nameof(DialogContentTemplate), typeof(DataTemplate), typeof(DialogHost), new PropertyMetadata(default(DataTemplate)));

    public DataTemplate? DialogContentTemplate
    {
        get => (DataTemplate?)GetValue(DialogContentTemplateProperty);
        set => SetValue(DialogContentTemplateProperty, value);
    }

    public static readonly DependencyProperty DialogContentTemplateSelectorProperty = DependencyProperty.Register(
        nameof(DialogContentTemplateSelector), typeof(DataTemplateSelector), typeof(DialogHost), new PropertyMetadata(default(DataTemplateSelector)));

    public DataTemplateSelector? DialogContentTemplateSelector
    {
        get => (DataTemplateSelector?)GetValue(DialogContentTemplateSelectorProperty);
        set => SetValue(DialogContentTemplateSelectorProperty, value);
    }

    public static readonly DependencyProperty DialogContentStringFormatProperty = DependencyProperty.Register(
        nameof(DialogContentStringFormat), typeof(string), typeof(DialogHost), new PropertyMetadata(default(string)));

    public string? DialogContentStringFormat
    {
        get => (string?)GetValue(DialogContentStringFormatProperty);
        set => SetValue(DialogContentStringFormatProperty, value);
    }

    public static readonly DependencyProperty DialogMarginProperty = DependencyProperty.Register(
        "DialogMargin", typeof(Thickness), typeof(DialogHost), new PropertyMetadata(default(Thickness)));

    public Thickness DialogMargin
    {
        get => (Thickness)GetValue(DialogMarginProperty);
        set => SetValue(DialogMarginProperty, value);
    }

    public static readonly DependencyProperty OpenDialogCommandDataContextSourceProperty = DependencyProperty.Register(
        nameof(OpenDialogCommandDataContextSource), typeof(DialogHostOpenDialogCommandDataContextSource), typeof(DialogHost), new PropertyMetadata(default(DialogHostOpenDialogCommandDataContextSource)));

    /// <summary>
    /// Defines how a data context is sourced for a dialog if a <see cref="FrameworkElement"/>
    /// is passed as the command parameter when using <see cref="DialogHost.OpenDialogCommand"/>.
    /// </summary>
    public DialogHostOpenDialogCommandDataContextSource OpenDialogCommandDataContextSource
    {
        get => (DialogHostOpenDialogCommandDataContextSource)GetValue(OpenDialogCommandDataContextSourceProperty);
        set => SetValue(OpenDialogCommandDataContextSourceProperty, value);
    }

    public static readonly DependencyProperty CloseOnClickAwayProperty = DependencyProperty.Register(
        "CloseOnClickAway", typeof(bool), typeof(DialogHost), new PropertyMetadata(default(bool)));

    /// <summary>
    /// Indicates whether the dialog will close if the user clicks off the dialog, on the obscured background.
    /// </summary>
    public bool CloseOnClickAway
    {
        get => (bool)GetValue(CloseOnClickAwayProperty);
        set => SetValue(CloseOnClickAwayProperty, value);
    }

    public static readonly DependencyProperty CloseOnClickAwayParameterProperty = DependencyProperty.Register(
        "CloseOnClickAwayParameter", typeof(object), typeof(DialogHost), new PropertyMetadata(default(object)));

    /// <summary>
    /// Parameter to provide to close handlers if an close due to click away is instigated.
    /// </summary>
    public object? CloseOnClickAwayParameter
    {
        get => GetValue(CloseOnClickAwayParameterProperty);
        set => SetValue(CloseOnClickAwayParameterProperty, value);
    }

    public static readonly DependencyProperty SnackbarMessageQueueProperty = DependencyProperty.Register(
        "SnackbarMessageQueue", typeof(SnackbarMessageQueue), typeof(DialogHost), new PropertyMetadata(default(SnackbarMessageQueue), SnackbarMessageQueuePropertyChangedCallback));

    private static void SnackbarMessageQueuePropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
    {
        var dialogHost = (DialogHost)dependencyObject;
        if (dialogHost._currentSnackbarMessageQueueUnPauseAction != null)
        {
            dialogHost._currentSnackbarMessageQueueUnPauseAction();
            dialogHost._currentSnackbarMessageQueueUnPauseAction = null;
        }

        if (!dialogHost.IsOpen) return;
        var snackbarMessageQueue = dependencyPropertyChangedEventArgs.NewValue as SnackbarMessageQueue;
        dialogHost._currentSnackbarMessageQueueUnPauseAction = snackbarMessageQueue?.Pause();
    }

    /// <summary>
    /// Allows association of a snackbar, so that notifications can be paused whilst a dialog is being displayed.
    /// </summary>
    public SnackbarMessageQueue? SnackbarMessageQueue
    {
        get => (SnackbarMessageQueue?)GetValue(SnackbarMessageQueueProperty);
        set => SetValue(SnackbarMessageQueueProperty, value);
    }

    public static readonly DependencyProperty DialogThemeProperty =
        DependencyProperty.Register(nameof(DialogTheme), typeof(BaseTheme), typeof(DialogHost), new PropertyMetadata(default(BaseTheme)));

    /// <summary>
    /// Set the theme (light/dark) for the dialog.
    /// </summary>
    public BaseTheme DialogTheme
    {
        get => (BaseTheme)GetValue(DialogThemeProperty);
        set => SetValue(DialogThemeProperty, value);
    }

    public static readonly DependencyProperty PopupStyleProperty = DependencyProperty.Register(
        nameof(PopupStyle), typeof(Style), typeof(DialogHost), new PropertyMetadata(default(Style)));

    public Style? PopupStyle
    {
        get => (Style?)GetValue(PopupStyleProperty);
        set => SetValue(PopupStyleProperty, value);
    }

    public static readonly DependencyProperty OverlayBackgroundProperty = DependencyProperty.Register(
        nameof(OverlayBackground), typeof(Brush), typeof(DialogHost), new PropertyMetadata(Brushes.Black));

    /// <summary>
    /// Represents the overlay brush that is used to dim the background behind the dialog
    /// </summary>
    public Brush? OverlayBackground
    {
        get => (Brush?)GetValue(OverlayBackgroundProperty);
        set => SetValue(OverlayBackgroundProperty, value);
    }

    public static readonly DependencyProperty DialogBackgroundProperty = DependencyProperty.Register(
        nameof(DialogBackground), typeof(Brush), typeof(DialogHost), new PropertyMetadata(null));

    /// <summary>
    /// Represents the brush for the Dialog's background
    /// </summary>
    public Brush? DialogBackground
    {
        get => (Brush?)GetValue(DialogBackgroundProperty);
        set => SetValue(DialogBackgroundProperty, value);
    }

    public bool ApplyBlurBackground
    {
        get => (bool)GetValue(ApplyBlurBackgroundProperty);
        set => SetValue(ApplyBlurBackgroundProperty, value);
    }
    public static readonly DependencyProperty ApplyBlurBackgroundProperty = DependencyProperty.Register(
        nameof(ApplyBlurBackground), typeof(bool), typeof(DialogHost), new PropertyMetadata(default(bool)));


    public const double DefaultBlurRadius = 16.0;
    public double BlurRadius
    {
        get => (double)GetValue(BlurRadiusProperty);
        set => SetValue(BlurRadiusProperty, value);
    }
    public static readonly DependencyProperty BlurRadiusProperty = DependencyProperty.Register(
        nameof(BlurRadius), typeof(double), typeof(DialogHost), new PropertyMetadata(DefaultBlurRadius));

    public override void OnApplyTemplate()
    {
        if (_contentCoverGrid != null)
            _contentCoverGrid.MouseLeftButtonUp -= ContentCoverGridOnMouseLeftButtonUp;

        _popup = GetTemplateChild(PopupPartName) as Popup;
        _popupContentControl = GetTemplateChild(PopupContentPartName) as ContentControl;
        _contentCoverGrid = GetTemplateChild(ContentCoverGridName) as Grid;

        if (_contentCoverGrid != null)
            _contentCoverGrid.MouseLeftButtonUp += ContentCoverGridOnMouseLeftButtonUp;

        VisualStateManager.GoToState(this, GetStateName(), false);

        base.OnApplyTemplate();
    }

    #region restore focus properties

    public static readonly DependencyProperty RestoreFocusElementProperty = DependencyProperty.RegisterAttached(
        "RestoreFocusElement", typeof(IInputElement), typeof(DialogHost), new PropertyMetadata(default(IInputElement)));

    public static void SetRestoreFocusElement(DependencyObject element, IInputElement value)
        => element.SetValue(RestoreFocusElementProperty, value);

    public static IInputElement GetRestoreFocusElement(DependencyObject element)
        => (IInputElement)element.GetValue(RestoreFocusElementProperty);

    public static readonly DependencyProperty IsRestoreFocusDisabledProperty = DependencyProperty.Register(
        nameof(IsRestoreFocusDisabled), typeof(bool), typeof(DialogHost), new PropertyMetadata(false));

    public bool IsRestoreFocusDisabled
    {
        get => (bool)GetValue(IsRestoreFocusDisabledProperty);
        set => SetValue(IsRestoreFocusDisabledProperty, value);
    }

    #endregion

    #region open dialog events/callbacks

    public static readonly RoutedEvent DialogOpenedEvent =
        EventManager.RegisterRoutedEvent(
            "DialogOpened",
            RoutingStrategy.Bubble,
            typeof(DialogOpenedEventHandler),
            typeof(DialogHost));

    /// <summary>
    /// Raised when a dialog is opened.
    /// </summary>
    public event DialogOpenedEventHandler DialogOpened
    {
        add => AddHandler(DialogOpenedEvent, value);
        remove => RemoveHandler(DialogOpenedEvent, value);
    }

    /// <summary>
    /// Attached property which can be used on the <see cref="Button"/> which instigated the <see cref="OpenDialogCommand"/> to process the event.
    /// </summary>
    public static readonly DependencyProperty DialogOpenedAttachedProperty = DependencyProperty.RegisterAttached(
        "DialogOpenedAttached", typeof(DialogOpenedEventHandler), typeof(DialogHost), new PropertyMetadata(default(DialogOpenedEventHandler)));

    public static void SetDialogOpenedAttached(DependencyObject element, DialogOpenedEventHandler value)
        => element.SetValue(DialogOpenedAttachedProperty, value);

    public static DialogOpenedEventHandler GetDialogOpenedAttached(DependencyObject element)
        => (DialogOpenedEventHandler)element.GetValue(DialogOpenedAttachedProperty);

    public static readonly DependencyProperty DialogOpenedCallbackProperty = DependencyProperty.Register(
        nameof(DialogOpenedCallback), typeof(DialogOpenedEventHandler), typeof(DialogHost), new PropertyMetadata(default(DialogOpenedEventHandler)));

    /// <summary>
    /// Callback fired when the <see cref="DialogOpened"/> event is fired, allowing the event to be processed from a binding/view model.
    /// </summary>
    public DialogOpenedEventHandler? DialogOpenedCallback
    {
        get => (DialogOpenedEventHandler?)GetValue(DialogOpenedCallbackProperty);
        set => SetValue(DialogOpenedCallbackProperty, value);
    }

    protected void OnDialogOpened(DialogOpenedEventArgs eventArgs)
        => RaiseEvent(eventArgs);

    #endregion

    #region close dialog events/callbacks

    public static readonly RoutedEvent DialogClosingEvent =
        EventManager.RegisterRoutedEvent(
            "DialogClosing",
            RoutingStrategy.Bubble,
            typeof(DialogClosingEventHandler),
            typeof(DialogHost));

    /// <summary>
    /// Raised just before a dialog is closed.
    /// </summary>
    public event DialogClosingEventHandler DialogClosing
    {
        add => AddHandler(DialogClosingEvent, value);
        remove => RemoveHandler(DialogClosingEvent, value);
    }

    /// <summary>
    /// Attached property which can be used on the <see cref="Button"/> which instigated the <see cref="OpenDialogCommand"/> to process the closing event.
    /// </summary>
    public static readonly DependencyProperty DialogClosingAttachedProperty = DependencyProperty.RegisterAttached(
        "DialogClosingAttached", typeof(DialogClosingEventHandler), typeof(DialogHost), new PropertyMetadata(default(DialogClosingEventHandler)));

    public static void SetDialogClosingAttached(DependencyObject element, DialogClosingEventHandler value)
        => element.SetValue(DialogClosingAttachedProperty, value);

    public static DialogClosingEventHandler GetDialogClosingAttached(DependencyObject element)
        => (DialogClosingEventHandler)element.GetValue(DialogClosingAttachedProperty);

    public static readonly DependencyProperty DialogClosingCallbackProperty = DependencyProperty.Register(
        nameof(DialogClosingCallback), typeof(DialogClosingEventHandler), typeof(DialogHost), new PropertyMetadata(default(DialogClosingEventHandler)));

    /// <summary>
    /// Callback fired when the <see cref="DialogClosing"/> event is fired, allowing the event to be processed from a binding/view model.
    /// </summary>
    public DialogClosingEventHandler? DialogClosingCallback
    {
        get => (DialogClosingEventHandler?)GetValue(DialogClosingCallbackProperty);
        set => SetValue(DialogClosingCallbackProperty, value);
    }

    protected void OnDialogClosing(DialogClosingEventArgs eventArgs)
        => RaiseEvent(eventArgs);

    public static readonly RoutedEvent DialogClosedEvent =
        EventManager.RegisterRoutedEvent(
            "DialogClosed",
            RoutingStrategy.Bubble,
            typeof(DialogClosedEventHandler),
            typeof(DialogHost));

    /// <summary>
    /// Raised when a dialog is closed.
    /// </summary>
    public event DialogClosedEventHandler DialogClosed
    {
        add => AddHandler(DialogClosedEvent, value);
        remove => RemoveHandler(DialogClosedEvent, value);
    }

    /// <summary>
    /// Attached property which can be used on the <see cref="Button"/> which instigated the <see cref="OpenDialogCommand"/> to process the closed event.
    /// </summary>
    public static readonly DependencyProperty DialogClosedAttachedProperty = DependencyProperty.RegisterAttached(
        "DialogClosedAttached", typeof(DialogClosedEventHandler), typeof(DialogHost), new PropertyMetadata(default(DialogClosedEventHandler)));

    public static void SetDialogClosedAttached(DependencyObject element, DialogClosedEventHandler value)
        => element.SetValue(DialogClosedAttachedProperty, value);

    public static DialogClosedEventHandler GetDialogClosedAttached(DependencyObject element)
        => (DialogClosedEventHandler)element.GetValue(DialogClosedAttachedProperty);

    public static readonly DependencyProperty DialogClosedCallbackProperty = DependencyProperty.Register(
        nameof(DialogClosedCallback), typeof(DialogClosedEventHandler), typeof(DialogHost), new PropertyMetadata(default(DialogClosedEventHandler)));

    /// <summary>
    /// Callback fired when the <see cref="DialogClosed"/> event is fired, allowing the event to be processed from a binding/view model.
    /// </summary>
    public DialogClosedEventHandler? DialogClosedCallback
    {
        get => (DialogClosedEventHandler?)GetValue(DialogClosedCallbackProperty);
        set => SetValue(DialogClosedCallbackProperty, value);
    }

    protected void OnDialogClosed(DialogClosedEventArgs eventArgs)
        => RaiseEvent(eventArgs);

    #endregion

    internal void AssertTargetableContent()
    {
        var existingBinding = BindingOperations.GetBindingExpression(this, DialogContentProperty);
        if (existingBinding != null)
            throw new InvalidOperationException(
                "Content cannot be passed to a dialog via the OpenDialog if DialogContent already has a binding.");
    }

    internal void InternalClose(object? parameter)
    {
        var currentSession = CurrentSession ?? throw new InvalidOperationException($"{nameof(DialogHost)} does not have a current session");

        currentSession.CloseParameter = parameter;
        currentSession.IsEnded = true;

        //multiple ways of calling back that the dialog is closing:
        // * routed event
        // * the attached property (which should be applied to the button which opened the dialog
        // * straight forward IsOpen dependency property 
        // * handler provided to the async show method
        var dialogClosingEventArgs = new DialogClosingEventArgs(currentSession, DialogClosingEvent);
        OnDialogClosing(dialogClosingEventArgs);
        _attachedDialogClosingEventHandler?.Invoke(this, dialogClosingEventArgs);
        DialogClosingCallback?.Invoke(this, dialogClosingEventArgs);
        _asyncShowClosingEventHandler?.Invoke(this, dialogClosingEventArgs);

        if (dialogClosingEventArgs.IsCancelled)
        {
            currentSession.IsEnded = false;
            return;
        }

        SetCurrentValue(IsOpenProperty, false);
    }

    /// <summary>
    /// Attempts to focus the content of a popup.
    /// </summary>
    /// <returns>The popup content.</returns>
    internal UIElement? FocusPopup()
    {
        var child = _popup?.Child ?? _popupContentControl;
        if (child is null) return null;

        if (PresentationSource.FromVisual(child) is HwndSource hwndSource)
        {
            SetFocus(hwndSource.Handle);
        }

        CommandManager.InvalidateRequerySuggested();
        var focusable = child.VisualDepthFirstTraversal().OfType<UIElement>().FirstOrDefault(ui => ui.Focusable);
        if (focusable is null) return null;

        if (focusable.IsVisible)
        {
            MoveFocus(focusable);
        }
        else
        {
            focusable.IsVisibleChanged += FocusableOnIsVisibleChanged;
        }

        return child;

        void FocusableOnIsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
        {
            if (sender is UIElement focusable)
            {
                MoveFocus(focusable);
                focusable.IsVisibleChanged -= FocusableOnIsVisibleChanged;
            }
        }

        void MoveFocus(UIElement focusable)
        {
            focusable.Dispatcher.BeginInvoke(() =>
            {
                if (!focusable.Focus()) return;
                focusable.MoveFocus(new TraversalRequest(FocusNavigationDirection.First));
            }, DispatcherPriority.Background);
        }
    }

    protected override void OnPreviewMouseDown(MouseButtonEventArgs e)
    {
        if (Window.GetWindow(this) is { } window && !window.IsActive && window.OwnedWindows.OfType<Window>().All(x => !x.IsActive))
        {
            window.Activate();
        }
        base.OnPreviewMouseDown(e);
    }

    private void ContentCoverGridOnMouseLeftButtonUp(object sender, MouseButtonEventArgs mouseButtonEventArgs)
    {
        if (CloseOnClickAway && CurrentSession != null)
            InternalClose(CloseOnClickAwayParameter);
    }

    private void OpenDialogHandler(object sender, ExecutedRoutedEventArgs executedRoutedEventArgs)
    {
        if (executedRoutedEventArgs.Handled) return;

        if (executedRoutedEventArgs.OriginalSource is DependencyObject dependencyObject)
        {
            _attachedDialogOpenedEventHandler = GetDialogOpenedAttached(dependencyObject);
            _attachedDialogClosingEventHandler = GetDialogClosingAttached(dependencyObject);
            _attachedDialogClosedEventHandler = GetDialogClosedAttached(dependencyObject);
        }

        if (executedRoutedEventArgs.Parameter != null)
        {
            AssertTargetableContent();

            if (_popupContentControl != null)
            {
                _popupContentControl.DataContext = OpenDialogCommandDataContextSource switch
                {
                    DialogHostOpenDialogCommandDataContextSource.SenderElement
                        => (executedRoutedEventArgs.OriginalSource as FrameworkElement)?.DataContext,
                    DialogHostOpenDialogCommandDataContextSource.DialogHostInstance => DataContext,
                    DialogHostOpenDialogCommandDataContextSource.None => null,
                    _ => throw new ArgumentOutOfRangeException(),
                };
            }

            DialogContent = executedRoutedEventArgs.Parameter;
        }

        SetCurrentValue(IsOpenProperty, true);

        executedRoutedEventArgs.Handled = true;
    }

    private void CloseDialogCanExecute(object sender, CanExecuteRoutedEventArgs canExecuteRoutedEventArgs)
        => canExecuteRoutedEventArgs.CanExecute = CurrentSession != null;

    private void CloseDialogHandler(object sender, ExecutedRoutedEventArgs executedRoutedEventArgs)
    {
        if (executedRoutedEventArgs.Handled) return;

        InternalClose(executedRoutedEventArgs.Parameter);

        executedRoutedEventArgs.Handled = true;
    }

    private string GetStateName()
        => IsOpen ? OpenStateName : ClosedStateName;

    private void OnUnloaded(object sender, RoutedEventArgs routedEventArgs)
    {
        foreach (var weakRef in LoadedInstances.ToList())
        {
            if (!weakRef.TryGetTarget(out DialogHost? dialogHost) || ReferenceEquals(dialogHost, this))
            {
                LoadedInstances.Remove(weakRef);
                break;
            }
        }
    }

    private void OnLoaded(object sender, RoutedEventArgs routedEventArgs)
    {
        foreach (var weakRef in LoadedInstances.ToList())
        {
            if (weakRef.TryGetTarget(out DialogHost? dialogHost) && ReferenceEquals(dialogHost, this))
            {
                return;
            }
        }

        LoadedInstances.Add(new WeakReference<DialogHost>(this));

        if (IsOpen && _popup is { } popup)
        {
            if (!popup.IsOpen)
            {
                popup.IsOpen = true;
                (popup as PopupEx)?.RefreshPosition();
            }
        }
    }

    private void OnPreviewGotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
    {

    }

    [SecurityCritical]
    [DllImport("user32.dll", EntryPoint = "SetFocus", SetLastError = true)]
    private static extern IntPtr SetFocus(IntPtr hWnd);
}