feat: add new Toast.

src/Ursa/Controls/Toast/IManagedToastManager.cs

@@ -0,0 +1,22 @@
+using Avalonia.Metadata;
+
+namespace Ursa.Controls;
+
+/// <summary>
+/// Represents a toast manager that can show arbitrary content.
+/// Managed toast managers can show any content.
+/// </summary>
+/// <remarks>
+/// Because toast managers of this type are implemented purely in managed code, they
+/// can display arbitrary content, as opposed to toast managers which display toasts
+/// using the host operating system's toast mechanism.
+/// </remarks>
+[NotClientImplementable]
+public interface IManagedToastManager : IToastManager
+{
+    /// <summary>
+    /// Shows a toast.
+    /// </summary>
+    /// <param name="content">The content to be displayed.</param>
+    void Show(object content);
+}

src/Ursa/Controls/Toast/IToast.cs

@@ -0,0 +1,38 @@
+using Avalonia.Controls.Notifications;
+using Avalonia.Metadata;
+
+namespace Ursa.Controls;
+
+/// <summary>
+/// Represents a toast that can be shown in a window or by the host operating system.
+/// </summary>
+[NotClientImplementable]
+public interface IToast
+{
+
+    /// <summary>
+    /// Gets the toast message.
+    /// </summary>
+    string? Content { get; }
+
+    /// <summary>
+    /// Gets the <see cref="NotificationType"/> of the toast.
+    /// </summary>
+    NotificationType Type { get; }
+
+    /// <summary>
+    /// Gets the expiration time of the toast after which it will automatically close.
+    /// If the value is <see cref="TimeSpan.Zero"/> then the toast will remain open until the user closes it.
+    /// </summary>
+    TimeSpan Expiration { get; }
+
+    /// <summary>
+    /// Gets an Action to be run when the toast is clicked.
+    /// </summary>
+    Action? OnClick { get; }
+
+    /// <summary>
+    /// Gets an Action to be run when the toast is closed.
+    /// </summary>
+    Action? OnClose { get; }
+}

src/Ursa/Controls/Toast/IToastManager.cs

@@ -0,0 +1,17 @@
+using Avalonia.Metadata;
+
+namespace Ursa.Controls;
+
+/// <summary>
+/// Represents a toast manager that can be used to show toasts in a window or using
+/// the host operating system.
+/// </summary>
+[NotClientImplementable]
+public interface IToastManager
+{
+    /// <summary>
+    /// Show a toast.
+    /// </summary>
+    /// <param name="toast">The toast to be displayed.</param>
+    void Show(IToast toast);
+}

src/Ursa/Controls/Toast/Toast.cs

@@ -0,0 +1,80 @@
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using Avalonia.Controls.Notifications;
+
+namespace Ursa.Controls;
+
+/// <summary>
+/// A toast that can be shown in a window or by the host operating system.
+/// </summary>
+/// <remarks>
+/// This class represents a toast that can be displayed either in a window using
+/// <see cref="WindowToastManager"/> or by the host operating system (to be implemented).
+/// </remarks>
+public class Toast : IToast, INotifyPropertyChanged
+{
+    private string? _content;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Toast"/> class.
+    /// </summary>
+    /// <param name="content">The content to be displayed in the toast.</param>
+    /// <param name="type">The <see cref="NotificationType"/> of the toast.</param>
+    /// <param name="expiration">The expiry time at which the toast will close. 
+    /// Use <see cref="TimeSpan.Zero"/> for toasts that will remain open.</param>
+    /// <param name="onClick">An Action to call when the toast is clicked.</param>
+    /// <param name="onClose">An Action to call when the toast is closed.</param>
+    public Toast(
+        string? content,
+        NotificationType type = NotificationType.Information,
+        TimeSpan? expiration = null,
+        Action? onClick = null,
+        Action? onClose = null)
+    {
+        Content = content;
+        Type = type;
+        Expiration = expiration ?? TimeSpan.FromSeconds(5);
+        OnClick = onClick;
+        OnClose = onClose;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Toast"/> class.
+    /// </summary>
+    public Toast() : this(null)
+    {
+    }
+
+    /// <inheritdoc/>
+    public string? Content
+    {
+        get => _content;
+        set
+        {
+            if (_content != value)
+            {
+                _content = value;
+                OnPropertyChanged();
+            }
+        }
+    }
+
+    /// <inheritdoc/>
+    public NotificationType Type { get; set; }
+
+    /// <inheritdoc/>
+    public TimeSpan Expiration { get; set; }
+
+    /// <inheritdoc/>
+    public Action? OnClick { get; set; }
+
+    /// <inheritdoc/>
+    public Action? OnClose { get; set; }
+
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null)
+    {
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+    }
+}

src/Ursa/Controls/Toast/ToastCard.cs

@@ -0,0 +1,198 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Metadata;
+using Avalonia.Controls.Notifications;
+using Avalonia.Interactivity;
+using Avalonia.LogicalTree;
+
+namespace Ursa.Controls;
+
+/// <summary>
+/// Control that represents and displays a toast.
+/// </summary>
+[PseudoClasses(PC_Information, PC_Success, PC_Warning, PC_Error)]
+public class ToastCard : ContentControl
+{
+    public const string PC_Information = ":information";
+    public const string PC_Success = ":success";
+    public const string PC_Warning = ":warning";
+    public const string PC_Error = ":error";
+
+    private bool _isClosing;
+
+    static ToastCard()
+    {
+        CloseOnClickProperty.Changed.AddClassHandler<Button>(OnCloseOnClickPropertyChanged);
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ToastCard"/> class.
+    /// </summary>
+    public ToastCard()
+    {
+        UpdateNotificationType();
+    }
+
+    /// <summary>
+    /// Determines if the toast is already closing.
+    /// </summary>
+    public bool IsClosing
+    {
+        get => _isClosing;
+        private set => SetAndRaise(IsClosingProperty, ref _isClosing, value);
+    }
+
+    /// <summary>
+    /// Defines the <see cref="IsClosing"/> property.
+    /// </summary>
+    public static readonly DirectProperty<ToastCard, bool> IsClosingProperty =
+        AvaloniaProperty.RegisterDirect<ToastCard, bool>(nameof(IsClosing), o => o.IsClosing);
+
+    /// <summary>
+    /// Determines if the toast is closed.
+    /// </summary>
+    public bool IsClosed
+    {
+        get => GetValue(IsClosedProperty);
+        set => SetValue(IsClosedProperty, value);
+    }
+
+    /// <summary>
+    /// Defines the <see cref="IsClosed"/> property.
+    /// </summary>
+    public static readonly StyledProperty<bool> IsClosedProperty =
+        AvaloniaProperty.Register<ToastCard, bool>(nameof(IsClosed));
+
+    /// <summary>
+    /// Gets or sets the type of the toast
+    /// </summary>
+    public NotificationType NotificationType
+    {
+        get => GetValue(NotificationTypeProperty);
+        set => SetValue(NotificationTypeProperty, value);
+    }
+
+    /// <summary>
+    /// Defines the <see cref="NotificationType" /> property
+    /// </summary>
+    public static readonly StyledProperty<NotificationType> NotificationTypeProperty =
+        AvaloniaProperty.Register<ToastCard, NotificationType>(nameof(NotificationType));
+
+    /// <summary>
+    /// Defines the <see cref="ToastClosed"/> event.
+    /// </summary>
+    public static readonly RoutedEvent<RoutedEventArgs> ToastClosedEvent =
+        RoutedEvent.Register<ToastCard, RoutedEventArgs>(nameof(ToastClosed), RoutingStrategies.Bubble);
+
+
+    /// <summary>
+    /// Raised when the <see cref="ToastCard"/> has closed.
+    /// </summary>
+    public event EventHandler<RoutedEventArgs>? ToastClosed
+    {
+        add => AddHandler(ToastClosedEvent, value);
+        remove => RemoveHandler(ToastClosedEvent, value);
+    }
+
+    public static bool GetCloseOnClick(Button obj)
+    {
+        _ = obj ?? throw new ArgumentNullException(nameof(obj));
+        return obj.GetValue(CloseOnClickProperty);
+    }
+
+    public static void SetCloseOnClick(Button obj, bool value)
+    {
+        _ = obj ?? throw new ArgumentNullException(nameof(obj));
+        obj.SetValue(CloseOnClickProperty, value);
+    }
+
+    /// <summary>
+    /// Defines the CloseOnClick property.
+    /// </summary>
+    public static readonly AttachedProperty<bool> CloseOnClickProperty =
+        AvaloniaProperty.RegisterAttached<ToastCard, Button, bool>("CloseOnClick", defaultValue: false);
+
+    private static void OnCloseOnClickPropertyChanged(AvaloniaObject d, AvaloniaPropertyChangedEventArgs e)
+    {
+        var button = (Button)d;
+        var value = (bool)e.NewValue!;
+        if (value)
+        {
+            button.Click += Button_Click;
+        }
+        else
+        {
+            button.Click -= Button_Click;
+        }
+    }
+
+    /// <summary>
+    /// Called when a button inside the Toast is clicked.
+    /// </summary>
+    private static void Button_Click(object? sender, RoutedEventArgs e)
+    {
+        var btn = sender as ILogical;
+        var toast = btn?.GetLogicalAncestors().OfType<ToastCard>().FirstOrDefault();
+        toast?.Close();
+    }
+
+    /// <summary>
+    /// Closes the <see cref="ToastCard"/>.
+    /// </summary>
+    public void Close()
+    {
+        if (IsClosing)
+        {
+            return;
+        }
+
+        IsClosing = true;
+    }
+
+    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs e)
+    {
+        base.OnPropertyChanged(e);
+
+        if (e.Property == ContentProperty && e.NewValue is IToast toast)
+        {
+            SetValue(NotificationTypeProperty, toast.Type);
+        }
+
+        if (e.Property == NotificationTypeProperty)
+        {
+            UpdateNotificationType();
+        }
+
+        if (e.Property == IsClosedProperty)
+        {
+            if (!IsClosing && !IsClosed)
+            {
+                return;
+            }
+
+            RaiseEvent(new RoutedEventArgs(ToastClosedEvent));
+        }
+    }
+
+    private void UpdateNotificationType()
+    {
+        switch (NotificationType)
+        {
+            case NotificationType.Error:
+                PseudoClasses.Add(":error");
+                break;
+
+            case NotificationType.Information:
+                PseudoClasses.Add(":information");
+                break;
+
+            case NotificationType.Success:
+                PseudoClasses.Add(":success");
+                break;
+
+            case NotificationType.Warning:
+                PseudoClasses.Add(":warning");
+                break;
+        }
+    }
+}

src/Ursa/Controls/Toast/WindowToastManager.cs

@@ -0,0 +1,188 @@
+using System.Collections;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Metadata;
+using Avalonia.Controls.Notifications;
+using Avalonia.Controls.Primitives;
+using Avalonia.Layout;
+using Avalonia.Threading;
+using Avalonia.VisualTree;
+
+namespace Ursa.Controls;
+
+/// <summary>
+/// An <see cref="IToastManager"/> that displays toasts in a <see cref="Window"/>.
+/// </summary>
+[TemplatePart("PART_Items", typeof(Panel))]
+public class WindowToastManager : TemplatedControl, IManagedToastManager
+{
+    private IList? _items;
+
+    /// <summary>
+    /// Defines the <see cref="MaxItems"/> property.
+    /// </summary>
+    public static readonly StyledProperty<int> MaxItemsProperty =
+        AvaloniaProperty.Register<WindowToastManager, int>(nameof(MaxItems), 5);
+
+    /// <summary>
+    /// Defines the maximum number of toasts visible at once.
+    /// </summary>
+    public int MaxItems
+    {
+        get => GetValue(MaxItemsProperty);
+        set => SetValue(MaxItemsProperty, value);
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="WindowToastManager"/> class.
+    /// </summary>
+    /// <param name="host">The TopLevel that will host the control.</param>
+    public WindowToastManager(TopLevel? host) : this()
+    {
+        if (host is not null)
+        {
+            InstallFromTopLevel(host);
+        }
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="WindowToastManager"/> class.
+    /// </summary>
+    public WindowToastManager()
+    {
+    }
+
+    static WindowToastManager()
+    {
+        HorizontalAlignmentProperty.OverrideDefaultValue<WindowToastManager>(HorizontalAlignment.Stretch);
+        VerticalAlignmentProperty.OverrideDefaultValue<WindowToastManager>(VerticalAlignment.Stretch);
+    }
+
+    /// <inheritdoc/>
+    protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
+    {
+        base.OnApplyTemplate(e);
+
+        var itemsControl = e.NameScope.Find<Panel>("PART_Items");
+        _items = itemsControl?.Children;
+    }
+
+    /// <inheritdoc/>
+    public void Show(IToast content)
+    {
+        Show(content, content.Type, content.Expiration, content.OnClick, content.OnClose);
+    }
+
+    /// <inheritdoc/>
+    public void Show(object content)
+    {
+        if (content is IToast toast)
+        {
+            Show(toast, toast.Type, toast.Expiration, toast.OnClick, toast.OnClose);
+        }
+        else
+        {
+            Show(content, NotificationType.Information);
+        }
+    }
+
+    /// <summary>
+    /// Shows a Toast
+    /// </summary>
+    /// <param name="content">the content of the toast</param>
+    /// <param name="type">the type of the toast</param>
+    /// <param name="expiration">the expiration time of the toast after which it will automatically close. If the value is Zero then the toast will remain open until the user closes it</param>
+    /// <param name="onClick">an Action to be run when the toast is clicked</param>
+    /// <param name="onClose">an Action to be run when the toast is closed</param>
+    /// <param name="classes">style classes to apply</param>
+    public async void Show(object content,
+        NotificationType type,
+        TimeSpan? expiration = null,
+        Action? onClick = null,
+        Action? onClose = null,
+        string[]? classes = null)
+    {
+        Dispatcher.UIThread.VerifyAccess();
+
+        var toastControl = new ToastCard
+        {
+            Content = content,
+            NotificationType = type
+        };
+
+        // Add style classes if any
+        if (classes != null)
+        {
+            foreach (var @class in classes)
+            {
+                toastControl.Classes.Add(@class);
+            }
+        }
+
+        toastControl.ToastClosed += (sender, args) =>
+        {
+            onClose?.Invoke();
+
+            _items?.Remove(sender);
+        };
+
+        toastControl.PointerPressed += (sender, args) =>
+        {
+            onClick?.Invoke();
+
+            (sender as ToastCard)?.Close();
+        };
+
+        Dispatcher.UIThread.Post(() =>
+        {
+            _items?.Add(toastControl);
+
+            if (_items?.OfType<ToastCard>().Count(i => !i.IsClosing) > MaxItems)
+            {
+                _items.OfType<ToastCard>().First(i => !i.IsClosing).Close();
+            }
+        });
+
+        if (expiration == TimeSpan.Zero)
+        {
+            return;
+        }
+
+        await Task.Delay(expiration ?? TimeSpan.FromSeconds(5));
+
+        toastControl.Close();
+    }
+
+    protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+    {
+        base.OnPropertyChanged(change);
+    }
+
+    /// <summary>
+    /// Installs the <see cref="WindowToastManager"/> within the <see cref="AdornerLayer"/>
+    /// </summary>
+    private void InstallFromTopLevel(TopLevel topLevel)
+    {
+        topLevel.TemplateApplied += TopLevelOnTemplateApplied;
+        var adorner = topLevel.FindDescendantOfType<VisualLayerManager>()?.AdornerLayer;
+        if (adorner is not null)
+        {
+            adorner.Children.Add(this);
+            AdornerLayer.SetAdornedElement(this, adorner);
+        }
+    }
+
+    private void TopLevelOnTemplateApplied(object? sender, TemplateAppliedEventArgs e)
+    {
+        if (Parent is AdornerLayer adornerLayer)
+        {
+            adornerLayer.Children.Remove(this);
+            AdornerLayer.SetAdornedElement(this, null);
+        }
+
+        // Reinstall toast manager on template reapplied.
+        var topLevel = (TopLevel)sender!;
+        topLevel.TemplateApplied -= TopLevelOnTemplateApplied;
+        InstallFromTopLevel(topLevel);
+    }
+}