Add image viewer window

src/Decho/ViewModels/MainWindowViewModel.cs

@@ -797,7 +797,10 @@ public sealed class MainWindowViewModel : ViewModelBase
 
                 Avalonia.Threading.Dispatcher.UIThread.Post(() =>
                 {
-                    serverVm.Channels.Add(channelVm);
+                    if (!serverVm.Channels.Any(c => c.Name == channel.Name))
+                    {
+                        serverVm.Channels.Add(channelVm);
+                    }
                     serverVm.SelectedChannel = channelVm;
 
                     foreach (MessageModel msg in joinResult.History)

src/Decho/Views/ImageViewerWindow.axaml

@@ -0,0 +1,29 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        mc:Ignorable="d"
+        x:Class="Decho.Views.ImageViewerWindow"
+        Title="Image"
+        MinWidth="100"
+        MinHeight="100"
+        MaxWidth="1400"
+        MaxHeight="1000"
+        SizeToContent="WidthAndHeight"
+        WindowStartupLocation="CenterOwner"
+        Background="{DynamicResource UiTheme03}">
+    <Border Padding="8">
+        <Grid RowDefinitions="*,Auto">
+        <Image x:Name="ImageView"
+               Stretch="Uniform"
+               HorizontalAlignment="Stretch"
+               VerticalAlignment="Stretch" />
+        <Button Grid.Row="1"
+                Content="Close"
+                HorizontalAlignment="Right"
+                Width="80"
+                Margin="0 8 0 0"
+                Click="OnCloseClick" />
+        </Grid>
+    </Border>
+</Window>

src/Decho/Views/ImageViewerWindow.axaml.cs

@@ -0,0 +1,34 @@
+using Avalonia.Controls;
+using Avalonia.Media.Imaging;
+
+namespace Decho.Views;
+
+public sealed partial class ImageViewerWindow : Window
+{
+    public ImageViewerWindow()
+    {
+        InitializeComponent();
+    }
+
+    public ImageViewerWindow(Bitmap bitmap, string fileName)
+    {
+        InitializeComponent();
+        Title = fileName;
+        ImageView.Source = bitmap;
+
+        Opened += (_, _) =>
+        {
+            SizeToContent = SizeToContent.Manual;
+            if (Width > MaxWidth) Width = MaxWidth;
+            if (Height > MaxHeight) Height = MaxHeight;
+
+            MaxHeight = double.MaxValue;
+            MaxWidth = double.MaxValue;
+        };
+    }
+
+    private void OnCloseClick(object? sender, Avalonia.Interactivity.RoutedEventArgs e)
+    {
+        Close();
+    }
+}

src/Decho/Views/MessageItemView.axaml

@@ -37,7 +37,9 @@
 							<Image Loaded="OnAttachmentImageLoaded"
 								   MaxHeight="300"
 								   MaxWidth="400"
-								   HorizontalAlignment="Left" />
+								   HorizontalAlignment="Left"
+								   Cursor="Hand"
+								   PointerPressed="OnAttachmentImagePointerPressed" />
 							<TextBlock Text="{Binding FileName}"
 									   FontSize="11"
 									   Opacity="0.7" />

src/Decho/Views/MessageItemView.axaml.cs

@@ -321,4 +321,61 @@ public partial class MessageItemView : UserControl
             // Ignore if temp file cannot be deleted
         }
     }
+
+    private async void OnAttachmentImagePointerPressed(object? sender, Avalonia.Input.PointerPressedEventArgs e)
+    {
+        if (sender is not Image image)
+        {
+            return;
+        }
+
+        if (image.DataContext is not AttachmentDto att)
+        {
+            return;
+        }
+
+        if (att.Kind != AttachmentKind.Image)
+        {
+            return;
+        }
+
+        if (DataContext is not MessageViewModel msg)
+        {
+            return;
+        }
+
+        if (msg.ImageCache.TryGetValue(att.Url, out Bitmap? cached))
+        {
+            ImageViewerWindow viewer = new ImageViewerWindow(cached, att.FileName);
+            if (TopLevel.GetTopLevel(this) is Window parent)
+            {
+                await viewer.ShowDialog(parent);
+            }
+            return;
+        }
+
+        MainWindowViewModel? mainVm = this.GetMainWindowViewModel();
+        if (mainVm is null)
+        {
+            return;
+        }
+
+        byte[]? bytes = await mainVm.ConnectionService.DownloadImageBytesAsync(
+            msg.ServerUrl ?? "", msg.Model.ChannelName, att.Url);
+
+        if (bytes is null || bytes.Length == 0)
+        {
+            return;
+        }
+
+        using MemoryStream stream = new MemoryStream(bytes);
+        Bitmap bitmap = new Bitmap(stream);
+        msg.ImageCache[att.Url] = bitmap;
+
+        ImageViewerWindow viewerWindow = new ImageViewerWindow(bitmap, att.FileName);
+        if (TopLevel.GetTopLevel(this) is Window parentWindow)
+        {
+            await viewerWindow.ShowDialog(parentWindow);
+        }
+    }
 }