Release v47.2

Closes #295

app/Desktop/App.axaml

@@ -55,6 +55,42 @@
             <Setter Property="HorizontalAlignment" Value="Stretch" />
         </Style>
 
+        <Style Selector="TreeViewItem:not(:empty) /template/ Panel#PART_ExpandCollapseChevronContainer">
+            <Setter Property="Cursor" Value="Hand" />
+            <Setter Property="Margin" Value="0 0 5 0" />
+        </Style>
+        <Style Selector="TreeViewItem:empty /template/ Panel#PART_ExpandCollapseChevronContainer">
+            <Setter Property="Margin" Value="10 0" />
+        </Style>
+        <Style Selector="TreeViewItem[Level=0]:empty /template/ Panel#PART_ExpandCollapseChevronContainer">
+            <Setter Property="Margin" Value="0" />
+            <Setter Property="Width" Value="0" />
+        </Style>
+        <Style Selector="TreeViewItem /template/ ToggleButton#PART_ExpandCollapseChevron">
+            <Setter Property="Width" Value="18" />
+            <Setter Property="Height" Value="32" />
+        </Style>
+        <Style Selector="TreeViewItem /template/ ToggleButton#PART_ExpandCollapseChevron > Border">
+            <Setter Property="Padding" Value="2 10 3 10" />
+        </Style>
+
+        <Style Selector="TreeView.noSelection">
+            <Style Selector="^ TreeViewItem /template/ Border#PART_LayoutRoot">
+                <Setter Property="Background" Value="{DynamicResource TreeViewItemBackground}" />
+                <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrush}" />
+            </Style>
+            <Style Selector="^ TreeViewItem /template/ Border#PART_LayoutRoot > ContentPresenter#PART_HeaderPresenter">
+                <Setter Property="Foreground" Value="{DynamicResource TreeViewItemForeground}" />
+            </Style>
+            <Style Selector="^ TreeViewItem:disabled /template/ Border#PART_LayoutRoot">
+                <Setter Property="Background" Value="{DynamicResource TreeViewItemBackgroundDisabled}" />
+                <Setter Property="BorderBrush" Value="{DynamicResource TreeViewItemBorderBrushDisabled}" />
+            </Style>
+            <Style Selector="^ TreeViewItem:disabled /template/ Border#PART_LayoutRoot > ContentPresenter#PART_HeaderPresenter">
+                <Setter Property="Foreground" Value="{DynamicResource TreeViewItemForegroundDisabled}" />
+            </Style>
+        </Style>
+
         <Style Selector="Panel.buttons">
             <Setter Property="Margin" Value="0 20 0 0" />
         </Style>

app/Desktop/Arguments.cs

@@ -69,7 +69,7 @@ sealed class Arguments {
 						Log.Warn("Invalid concurrent downloads count: " + value);
 					}
 					else if (concurrentDownloads > 10) {
-						Log.Warn("Limiting concurrent downloads to 10");
+						Log.Warn("Limiting concurrent downloads to 10.");
 						ConcurrentDownloads = 10;
 					}
 					else {

app/Desktop/Common/AvaloniaObsevableValueExtensions.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using DHT.Utils.Observables;
+
+namespace DHT.Desktop.Common;
+
+static class AvaloniaObsevableValueExtensions {
+	public static IDisposable SubscribeLastOnUI<T>(this ObservableValue<T> observable, Action<T> action, TimeSpan delayBetweenRuns) {
+		Task Action(T value, CancellationToken cancellationToken) {
+			action(value);
+			return Task.Delay(delayBetweenRuns, cancellationToken);
+		}
+		
+		return observable.SubscribeLast(Action, TaskScheduler.FromCurrentSynchronizationContext());
+	}
+}

app/Desktop/Common/AvaloniaReflection.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Collections;
+using System.Reflection;
+using Avalonia.Interactivity;
+
+namespace DHT.Desktop.Common;
+
+static class AvaloniaReflection {
+	private static FieldInfo InteractiveEventHandlersField { get; } = typeof(Interactive).GetField("_eventHandlers", BindingFlags.Instance | BindingFlags.NonPublic)!;
+	
+	public static void Check() {
+		if (InteractiveEventHandlersField == null) {
+			throw new InvalidOperationException("Missing field: " + nameof(InteractiveEventHandlersField));
+		}
+		
+		if (InteractiveEventHandlersField.FieldType.ToString() != "System.Collections.Generic.Dictionary`2[Avalonia.Interactivity.RoutedEvent,System.Collections.Generic.List`1[Avalonia.Interactivity.Interactive+EventSubscription]]") {
+			throw new InvalidOperationException("Invalid field type: " + nameof(InteractiveEventHandlersField) + " = " + InteractiveEventHandlersField.FieldType);
+		}
+	}
+	
+	public static IList? GetEventHandler(Interactive target, RoutedEvent routedEvent) {
+		IDictionary? eventHandlers = (IDictionary?) InteractiveEventHandlersField.GetValue(target);
+		return (IList?) eventHandlers?[routedEvent];
+	}
+}

app/Desktop/Common/DatabaseGui.cs

@@ -52,7 +52,7 @@ static class DatabaseGui {
 		} catch (DatabaseTooNewException ex) {
 			await Dialog.ShowOk(window, "Database Error", "Database '" + Path.GetFileName(path) + "' was opened in a newer version of DHT (database version " + ex.DatabaseVersion + ", app version " + ex.CurrentVersion + ").");
 		} catch (Exception ex) {
-			Log.Error(ex);
+			Log.Error("Could not open database file: " + path, ex);
 			await Dialog.ShowOk(window, "Database Error", "Database '" + Path.GetFileName(path) + "' could not be opened:" + ex.Message);
 		}
 		

app/Desktop/Dialogs/CheckBox/CheckBoxDialog.axaml

@@ -8,28 +8,22 @@
         x:DataType="namespace:CheckBoxDialogModel"
         Title="{Binding Title}"
         Icon="avares://DiscordHistoryTracker/Resources/icon.ico"
-        Width="500" SizeToContent="Height" CanResize="False"
+        MinWidth="425" MinHeight="200"
+        Width="500" Height="395" CanResize="True"
         WindowStartupLocation="CenterOwner">
 
     <Window.DataContext>
         <namespace:CheckBoxDialogModel />
     </Window.DataContext>
 
-    <StackPanel Margin="20">
+    <Window.Styles>
-        <ScrollViewer MaxHeight="400">
+        <Style Selector="TreeViewItem">
-            <ItemsRepeater ItemsSource="{Binding Items}">
+            <Setter Property="IsExpanded" Value="True" />
-                <ItemsRepeater.ItemTemplate>
+        </Style>
-                    <DataTemplate>
+    </Window.Styles>
-                        <CheckBox IsChecked="{Binding IsChecked}">
+
-                            <Label>
+    <DockPanel Margin="20 17 20 20">
-                                <TextBlock Text="{Binding Title}" TextWrapping="Wrap" />
+        <Panel Classes="buttons" DockPanel.Dock="Bottom">
-                            </Label>
-                        </CheckBox>
-                    </DataTemplate>
-                </ItemsRepeater.ItemTemplate>
-            </ItemsRepeater>
-        </ScrollViewer>
-        <Panel Classes="buttons">
             <WrapPanel>
                 <Button Command="{Binding SelectAll}" IsEnabled="{Binding !AreAllSelected}">Select All</Button>
                 <Button Command="{Binding SelectNone}" IsEnabled="{Binding !AreNoneSelected}">Select None</Button>
@@ -39,6 +33,19 @@
                 <Button Click="ClickCancel">Cancel</Button>
             </WrapPanel>
         </Panel>
-    </StackPanel>
+        <ScrollViewer DockPanel.Dock="Top">
+            <TreeView Name="TreeView" Classes="noSelection" ItemsSource="{Binding RootItems}" ContainerPrepared="TreeViewOnContainerPrepared">
+                <TreeView.ItemTemplate>
+                    <TreeDataTemplate ItemsSource="{Binding Children}">
+                        <CheckBox IsChecked="{Binding IsChecked}">
+                            <Label>
+                                <TextBlock Text="{Binding Title}" TextWrapping="Wrap" />
+                            </Label>
+                        </CheckBox>
+                    </TreeDataTemplate>
+                </TreeView.ItemTemplate>
+            </TreeView>
+        </ScrollViewer>
+    </DockPanel>
 
 </Window>

app/Desktop/Dialogs/CheckBox/CheckBoxDialog.axaml.cs

@@ -1,6 +1,9 @@
 using System.Diagnostics.CodeAnalysis;
 using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Input;
 using Avalonia.Interactivity;
+using DHT.Desktop.Common;
 using DHT.Desktop.Dialogs.Message;
 
 namespace DHT.Desktop.Dialogs.CheckBox;
@@ -11,6 +14,36 @@ public sealed partial class CheckBoxDialog : Window {
 		InitializeComponent();
 	}
 	
+	private void TreeViewOnContainerPrepared(object? sender, ContainerPreparedEventArgs e) {
+		foreach (object? item in TreeView.Items) {
+			if (item != null && TreeView.ContainerFromItem(item) is TreeViewItem treeViewItem) {
+				treeViewItem.TemplateApplied += TreeViewItemOnTemplateApplied;
+				treeViewItem.GotFocus += TreeViewItemOnGotFocus;
+				treeViewItem.KeyDown += TreeViewItemOnKeyDown;
+			}
+		}
+	}
+	
+	private void TreeViewItemOnTemplateApplied(object? sender, TemplateAppliedEventArgs e) {
+		if (sender is TreeViewItem { HeaderPresenter: Interactive headerPresenter } ) {
+			// Removes support for double-clicking to expand.
+			AvaloniaReflection.GetEventHandler(headerPresenter, DoubleTappedEvent)?.Clear();
+		}
+	}
+	
+	private void TreeViewItemOnGotFocus(object? sender, GotFocusEventArgs e) {
+		if (e.NavigationMethod == NavigationMethod.Tab && sender is TreeViewItem treeViewItem && TreeView.SelectedItem == null) {
+			TreeView.SelectedItem = TreeView.ItemFromContainer(treeViewItem);
+		}
+	}
+	
+	private void TreeViewItemOnKeyDown(object? sender, KeyEventArgs e) {
+		if (e.Key == Key.Space && TreeView.SelectedItem is ICheckBoxItem item) {
+			item.IsChecked = item.IsChecked == false;
+			e.Handled = true;
+		}
+	}
+	
 	public void ClickOk(object? sender, RoutedEventArgs e) {
 		Close(DialogResult.OkCancel.Ok);
 	}

app/Desktop/Dialogs/CheckBox/CheckBoxDialogModel.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.ComponentModel;
 using System.Linq;
 using PropertyChanged.SourceGenerator;
@@ -8,64 +9,65 @@ namespace DHT.Desktop.Dialogs.CheckBox;
 partial class CheckBoxDialogModel {
 	public string Title { get; init; } = "";
 	
-	private IReadOnlyList<CheckBoxItem> items = [];
+	private ImmutableArray<ICheckBoxItem> rootItems = [];
 	
-	public IReadOnlyList<CheckBoxItem> Items {
+	public ImmutableArray<ICheckBoxItem> RootItems {
-		get => items;
+		get => rootItems;
 		
 		protected set {
-			foreach (CheckBoxItem item in items) {
+			foreach (ICheckBoxItem item in ICheckBoxItem.GetAllRecursively(rootItems)) {
 				item.PropertyChanged -= OnItemPropertyChanged;
 			}
 			
-			items = value;
+			rootItems = value;
 			
-			foreach (CheckBoxItem item in items) {
+			foreach (ICheckBoxItem item in ICheckBoxItem.GetAllRecursively(rootItems)) {
 				item.PropertyChanged += OnItemPropertyChanged;
 			}
 		}
 	}
 	
-	private bool pauseCheckEvents = false;
+	protected IEnumerable<ICheckBoxItem> AllItems => ICheckBoxItem.GetAllRecursively(RootItems);
 	
-	[DependsOn(nameof(Items))]
+	[DependsOn(nameof(RootItems))]
-	public bool AreAllSelected => Items.All(static item => item.IsChecked);
+	public bool AreAllSelected => RootItems.All(static item => item.IsChecked == true);
 	
-	[DependsOn(nameof(Items))]
+	[DependsOn(nameof(RootItems))]
-	public bool AreNoneSelected => Items.All(static item => !item.IsChecked);
+	public bool AreNoneSelected => RootItems.All(static item => item.IsChecked == false);
+	
+	private bool pauseUpdatingBulkButtons = false;
 	
 	public void SelectAll() => SetAllChecked(true);
 	public void SelectNone() => SetAllChecked(false);
 	
 	private void SetAllChecked(bool isChecked) {
-		pauseCheckEvents = true;
+		pauseUpdatingBulkButtons = true;
 		
-		foreach (CheckBoxItem item in Items) {
+		foreach (ICheckBoxItem item in RootItems) {
 			item.IsChecked = isChecked;
 		}
 		
-		pauseCheckEvents = false;
+		pauseUpdatingBulkButtons = false;
 		UpdateBulkButtons();
 	}
 	
-	private void UpdateBulkButtons() {
-		OnPropertyChanged(new PropertyChangedEventArgs(nameof(Items)));
-	}
-	
 	private void OnItemPropertyChanged(object? sender, PropertyChangedEventArgs e) {
-		if (!pauseCheckEvents && e.PropertyName == nameof(CheckBoxItem.IsChecked)) {
+		if (e.PropertyName == nameof(ICheckBoxItem.IsChecked) && !pauseUpdatingBulkButtons) {
 			UpdateBulkButtons();
 		}
 	}
+	
+	private void UpdateBulkButtons() {
+		OnPropertyChanged(new PropertyChangedEventArgs(nameof(RootItems)));
+	}
 }
 
 sealed class CheckBoxDialogModel<T> : CheckBoxDialogModel {
-	private new IReadOnlyList<CheckBoxItem<T>> Items { get; }
+	public IEnumerable<T> SelectedValues => AllItems.OfType<ICheckBoxItem.Leaf<T>>()
+	                                                .Where(static item => item.IsChecked == true)
+	                                                .Select(static item => item.Value);
 	
-	public IEnumerable<CheckBoxItem<T>> SelectedItems => Items.Where(static item => item.IsChecked);
+	public CheckBoxDialogModel(ImmutableArray<ICheckBoxItem> items) {
-	
+		this.RootItems = items;
-	public CheckBoxDialogModel(IEnumerable<CheckBoxItem<T>> items) {
-		this.Items = new List<CheckBoxItem<T>>(items);
-		base.Items = Items;
 	}
 }

app/Desktop/Dialogs/CheckBox/CheckBoxItem.cs

@@ -1,20 +1,110 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.ComponentModel;
+using System.Linq;
 using PropertyChanged.SourceGenerator;
 
 namespace DHT.Desktop.Dialogs.CheckBox;
 
-partial class CheckBoxItem {
+partial interface ICheckBoxItem : INotifyPropertyChanged {
-	public string Title { get; init; } = "";
+	public string Title { get; }
-	public object? Item { get; init; } = null;
+	public bool? IsChecked { get; set; }
 	
-	[Notify]
+	public ImmutableArray<ICheckBoxItem> Children { get; }
-	private bool isChecked = false;
-}
-
-sealed class CheckBoxItem<T> : CheckBoxItem {
-	public new T Item { get; }
 	
-	public CheckBoxItem(T item) {
+	void NotifyIsCheckedChanged();
-		this.Item = item;
+	
-		base.Item = item;
+	public static IEnumerable<ICheckBoxItem> GetAllRecursively(IEnumerable<ICheckBoxItem> items) {
+		Stack<ICheckBoxItem> stack = new Stack<ICheckBoxItem>(items);
+		
+		while (stack.TryPop(out var item)) {
+			yield return item;
+			
+			foreach (ICheckBoxItem child in item.Children) {
+				stack.Push(child);
+			}
+		}
+	}
+	
+	sealed class NonLeaf : ICheckBoxItem {
+		public string Title { get; }
+		
+		public bool? IsChecked {
+			get {
+				if (Children.Count(static child => child.IsChecked == true) == Children.Length) {
+					return true;
+				}
+				else if (Children.Count(static child => child.IsChecked == false) == Children.Length) {
+					return false;
+				}
+				else {
+					return null;
+				}
+			}
+			
+			set {
+				foreach (ICheckBoxItem child in Children) {
+					if (child is Leaf leaf) {
+						leaf.SetCheckedFromParent(value);
+					}
+					else {
+						child.IsChecked = value;
+					}
+				}
+				
+				NotifyIsCheckedChanged();
+				parent?.NotifyIsCheckedChanged();
+			}
+		}
+		
+		public ImmutableArray<ICheckBoxItem> Children { get; }
+		
+		public event PropertyChangedEventHandler? PropertyChanged;
+		
+		private readonly ICheckBoxItem? parent;
+		
+		public NonLeaf(string title, ICheckBoxItem? parent, Func<ICheckBoxItem, ImmutableArray<ICheckBoxItem>> children) {
+			this.parent = parent;
+			this.Title = title;
+			this.Children = children(this);
+		}
+		
+		public void NotifyIsCheckedChanged() {
+			PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsChecked)));
+		}
+	}
+	
+	partial class Leaf(string title, ICheckBoxItem? parent, bool isChecked) : ICheckBoxItem {
+		public string Title { get; } = title;
+		
+		public ImmutableArray<ICheckBoxItem> Children => ImmutableArray<ICheckBoxItem>.Empty;
+		
+		public readonly ICheckBoxItem? parent = parent;
+		
+		[Notify]
+		private bool? isChecked = isChecked;
+		
+		private bool notifyParent = true;
+		
+		public void SetCheckedFromParent(bool? isChecked) {
+			notifyParent = false;
+			IsChecked = isChecked;
+			notifyParent = true;
+		}
+		
+		private void OnIsCheckedChanged() {
+			if (notifyParent) {
+				parent?.NotifyIsCheckedChanged();
+			}
+		}
+		
+		void ICheckBoxItem.NotifyIsCheckedChanged() {
+			OnPropertyChanged(new PropertyChangedEventArgs(nameof(IsChecked)));
+		}
+	}
+	
+	sealed class Leaf<T>(string title, ICheckBoxItem? parent, T value, bool isChecked) : Leaf(title, parent, isChecked) {
+		public T Value => value;
 	}
 }

app/Desktop/Dialogs/CheckBox/CheckBoxItemList.cs

@@ -0,0 +1,46 @@
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+
+namespace DHT.Desktop.Dialogs.CheckBox;
+
+sealed class CheckBoxItemList<TKey, TValue> where TKey : notnull {
+	private readonly List<INode> rootNodes = [];
+	private readonly Dictionary<TKey, List<INode>> parentNodes = [];
+	
+	public void AddParent(TKey key, string title) {
+		if (!parentNodes.ContainsKey(key)) {
+			List<INode> children = [];
+			rootNodes.Add(new INode.NonLeaf(title, children));
+			parentNodes[key] = children;
+		}
+	}
+	
+	public void Add(TValue value, string title, bool isChecked = false) {
+		rootNodes.Add(new INode.Leaf(title, value, isChecked));
+	}
+	
+	public void Add(TKey key, TValue value, string title, bool isChecked = false) {
+		parentNodes.GetValueOrDefault(key, rootNodes).Add(new INode.Leaf(title, value, isChecked));
+	}
+	
+	public ImmutableArray<ICheckBoxItem> ToCheckBoxItems() {
+		return [..rootNodes.Select(static node => node.ToCheckBoxItem(null))];
+	}
+	
+	private interface INode {
+		ICheckBoxItem ToCheckBoxItem(ICheckBoxItem? parent);
+		
+		sealed record NonLeaf(string Title, List<INode> Children) : INode {
+			public ICheckBoxItem ToCheckBoxItem(ICheckBoxItem? parent) {
+				return new ICheckBoxItem.NonLeaf(Title, parent, self => [..Children.Select(child => child.ToCheckBoxItem(self))]);
+			}
+		}
+		
+		sealed record Leaf(string Title, TValue Value, bool IsChecked) : INode {
+			public ICheckBoxItem ToCheckBoxItem(ICheckBoxItem? parent) {
+				return new ICheckBoxItem.Leaf<TValue>(Title, parent, Value, IsChecked);
+			}
+		}
+	}
+}

app/Desktop/Discord/DiscordAppSettings.cs

@@ -42,8 +42,7 @@ static class DiscordAppSettings {
 			JsonObject settingsJson = await ReadSettingsJson();
 			return AreDevToolsEnabled(settingsJson);
 		} catch (Exception e) {
-			Log.Error("Cannot read settings file.");
+			Log.Error("Could not read settings file.", e);
-			Log.Error(e);
 			return null;
 		}
 	}
@@ -62,7 +61,7 @@ static class DiscordAppSettings {
 		} catch (JsonException) {
 			return SettingsJsonResult.InvalidJson;
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not read settings file.", e);
 			return SettingsJsonResult.ReadError;
 		}
 		
@@ -84,16 +83,14 @@ static class DiscordAppSettings {
 			
 			await WriteSettingsJson(json);
 		} catch (Exception e) {
-			Log.Error("An error occurred when writing settings file.");
+			Log.Error("Could not write settings file.", e);
-			Log.Error(e);
 			
 			if (File.Exists(JsonBackupFilePath)) {
 				try {
 					File.Move(JsonBackupFilePath, JsonFilePath, overwrite: true);
 					Log.Info("Restored settings file from backup.");
 				} catch (Exception e2) {
-					Log.Error("Cannot restore settings file from backup.");
+					Log.Error("Could not restore settings file from backup.", e2);
-					Log.Error(e2);
 				}
 			}
 			
@@ -103,8 +100,7 @@ static class DiscordAppSettings {
 		try {
 			File.Delete(JsonBackupFilePath);
 		} catch (Exception e) {
-			Log.Error("Cannot delete backup file.");
+			Log.Error("Could not delete backup file.", e);
-			Log.Error(e);
 		}
 		
 		return SettingsJsonResult.Success;

app/Desktop/Main/Controls/DownloadItemFilterPanelModel.cs

@@ -2,9 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
-using System.Reactive.Linq;
 using System.Threading.Tasks;
-using Avalonia.ReactiveUI;
 using DHT.Desktop.Common;
 using DHT.Server;
 using DHT.Server.Data.Filters;
@@ -49,7 +47,7 @@ sealed partial class DownloadItemFilterPanelModel : IAsyncDisposable {
 	private readonly State state;
 	private readonly string verb;
 	
-	private readonly DelayedThrottledTask<FilterSettings> saveFilterSettingsTask;
+	private readonly ThrottledTask<FilterSettings> saveFilterSettingsTask;
 	private bool isLoadingFilterSettings;
 	
 	private readonly RestartableTask<long> downloadItemCountTask;
@@ -65,10 +63,10 @@ sealed partial class DownloadItemFilterPanelModel : IAsyncDisposable {
 		this.state = state;
 		this.verb = verb;
 		
-		this.saveFilterSettingsTask = new DelayedThrottledTask<FilterSettings>(Log, TimeSpan.FromSeconds(5), SaveFilterSettings);
+		this.saveFilterSettingsTask = new ThrottledTask<FilterSettings>(Log, SaveFilterSettings, TimeSpan.FromSeconds(5), TaskScheduler.Default);
 		
 		this.downloadItemCountTask = new RestartableTask<long>(SetMatchingCount, TaskScheduler.FromCurrentSynchronizationContext());
-		this.downloadItemCountSubscription = state.Db.Downloads.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnDownloadItemCountChanged);
+		this.downloadItemCountSubscription = state.Db.Downloads.TotalCount.SubscribeLastOnUI(OnDownloadItemCountChanged, TimeSpan.FromMilliseconds(15));
 		
 		UpdateFilterStatistics();
 		
@@ -109,8 +107,7 @@ sealed partial class DownloadItemFilterPanelModel : IAsyncDisposable {
 				await setter.Set(SettingsKey.DownloadsMaximumSizeUnit, settings.MaximumSizeUnit.Name);
 			});
 		} catch (Exception e) {
-			Log.Error("Could not save download filter settings");
+			Log.Error("Could not save download filter settings.", e);
-			Log.Error(e);
 		}
 	}
 	

app/Desktop/Main/Controls/MessageFilterPanelModel.cs

@@ -1,12 +1,11 @@
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
-using System.Reactive.Linq;
-using System.Text;
 using System.Threading.Tasks;
 using Avalonia.Controls;
-using Avalonia.ReactiveUI;
 using DHT.Desktop.Common;
 using DHT.Desktop.Dialogs.CheckBox;
 using DHT.Desktop.Dialogs.Message;
@@ -90,9 +89,9 @@ sealed partial class MessageFilterPanelModel : IDisposable {
 		
 		this.exportedMessageCountTask = new RestartableTask<long>(SetExportedMessageCount, TaskScheduler.FromCurrentSynchronizationContext());
 		
-		this.messageCountSubscription = state.Db.Messages.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnMessageCountChanged);
+		this.messageCountSubscription = state.Db.Messages.TotalCount.SubscribeLastOnUI(OnMessageCountChanged, TimeSpan.FromMilliseconds(15));
-		this.channelCountSubscription = state.Db.Channels.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnChannelCountChanged);
+		this.channelCountSubscription = state.Db.Channels.TotalCount.SubscribeLastOnUI(OnChannelCountChanged, TimeSpan.FromMilliseconds(15));
-		this.userCountSubscription = state.Db.Users.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnUserCountChanged);
+		this.userCountSubscription = state.Db.Users.TotalCount.SubscribeLastOnUI(OnUserCountChanged, TimeSpan.FromMilliseconds(15));
 		
 		UpdateFilterStatistics();
 		UpdateChannelFilterLabel();
@@ -185,51 +184,64 @@ sealed partial class MessageFilterPanelModel : IDisposable {
 		FilterStatisticsText = verb + " " + exportedMessageCountStr + " out of " + totalMessageCountStr + " message" + (totalMessageCount is null or 1 ? "." : "s.");
 	}
 	
+	[SuppressMessage("ReSharper", "NotAccessedPositionalProperty.Local")]
+	[SuppressMessage("ReSharper", "MemberCanBePrivate.Local")]
+	private readonly record struct ChannelFilterKey(byte Type, ulong? ServerId, string Title) : IComparable<ChannelFilterKey> {
+		public static ChannelFilterKey DirectMessages { get; } = new (Type: 1, ServerId: null, Title: "Direct Messages");
+		public static ChannelFilterKey GroupMessages { get; } = new (Type: 2, ServerId: null, Title: "Group Messages");
+		public static ChannelFilterKey Unknown { get; } = new (Type: 4, ServerId: null, Title: "Unknown");
+		
+		public static ChannelFilterKey For(DHT.Server.Data.Server server) {
+			return server.Type switch {
+				ServerType.Server        => new ChannelFilterKey(Type: 3, server.Id, "Server - " + server.Name),
+				ServerType.Group         => GroupMessages,
+				ServerType.DirectMessage => DirectMessages,
+				_                        => Unknown,
+			};
+		}
+		
+		public bool Equals(ChannelFilterKey other) {
+			return Type == other.Type && ServerId == other.ServerId;
+		}
+		
+		public override int GetHashCode() {
+			return HashCode.Combine(Type, ServerId);
+		}
+		
+		public int CompareTo(ChannelFilterKey other) {
+			int result = Type.CompareTo(other.Type);
+			if (result != 0) {
+				return result;
+			}
+			else {
+				return Title.CompareTo(other.Title);
+			}
+		}
+	}
+	
 	public async Task OpenChannelFilterDialog() {
-		async Task<List<CheckBoxItem<ulong>>> PrepareChannelItems(ProgressDialog dialog) {
+		async Task<ImmutableArray<ICheckBoxItem>> PrepareChannelItems(ProgressDialog dialog) {
-			var items = new List<CheckBoxItem<ulong>>();
+			CheckBoxItemList<ChannelFilterKey, ulong> items = new CheckBoxItemList<ChannelFilterKey, ulong>();
 			Dictionary<ulong, DHT.Server.Data.Server> servers = await state.Db.Servers.Get().ToDictionaryAsync(static server => server.Id);
 			
-			await foreach (Channel channel in state.Db.Channels.Get()) {
+			foreach (ChannelFilterKey channelFilterKey in servers.Values.Select(ChannelFilterKey.For).Order()) {
-				ulong channelId = channel.Id;
+				items.AddParent(channelFilterKey, channelFilterKey.Title);
-				string channelName = channel.Name;
-				
-				string title;
-				if (servers.TryGetValue(channel.Server, out var server)) {
-					var titleBuilder = new StringBuilder();
-					ServerType? serverType = server.Type;
-					
-					titleBuilder.Append('[')
-					            .Append(ServerTypes.ToString(serverType))
-					            .Append("] ");
-					
-					if (serverType == ServerType.DirectMessage) {
-						titleBuilder.Append(channelName);
-					}
-					else {
-						titleBuilder.Append(server.Name)
-						            .Append(" - ")
-						            .Append(channelName);
-					}
-					
-					title = titleBuilder.ToString();
-				}
-				else {
-					title = channelName;
-				}
-				
-				items.Add(new CheckBoxItem<ulong>(channelId) {
-					Title = title,
-					IsChecked = IncludedChannels == null || IncludedChannels.Contains(channelId),
-				});
 			}
 			
-			return items;
+			await foreach (Channel channel in state.Db.Channels.Get().OrderBy(static channel => channel.Position ?? int.MinValue).ThenBy(static channel => channel.Name)) {
+				ChannelFilterKey key = servers.TryGetValue(channel.Server, out var server)
+					                       ? ChannelFilterKey.For(server)
+					                       : ChannelFilterKey.Unknown;
+				
+				items.Add(key, channel.Id, channel.Name, isChecked: IncludedChannels == null || IncludedChannels.Contains(channel.Id));
+			}
+			
+			return items.ToCheckBoxItems();
 		}
 		
 		const string Title = "Included Channels";
 		
-		List<CheckBoxItem<ulong>> items;
+		ImmutableArray<ICheckBoxItem> items;
 		try {
 			items = await ProgressDialog.ShowIndeterminate(window, Title, "Loading channels...", PrepareChannelItems);
 		} catch (Exception e) {
@@ -244,22 +256,27 @@ sealed partial class MessageFilterPanelModel : IDisposable {
 	}
 	
 	public async Task OpenUserFilterDialog() {
-		async Task<List<CheckBoxItem<ulong>>> PrepareUserItems(ProgressDialog dialog) {
+		async Task<ImmutableArray<ICheckBoxItem>> PrepareUserItems(ProgressDialog dialog) {
-			var checkBoxItems = new List<CheckBoxItem<ulong>>();
+			CheckBoxItemList<ulong, ulong> items = new CheckBoxItemList<ulong, ulong>();
 			
-			await foreach (User user in state.Db.Users.Get()) {
+			static string GetDisplayName(User user) {
-				checkBoxItems.Add(new CheckBoxItem<ulong>(user.Id) {
+				return user.DisplayName == null ? user.Name : $"{user.DisplayName} ({user.Name})";
-					Title = user.DisplayName == null ? user.Name : $"{user.DisplayName} ({user.Name})",
-					IsChecked = IncludedUsers == null || IncludedUsers.Contains(user.Id),
-				});
 			}
 			
-			return checkBoxItems;
+			await foreach ((ulong id, string name) in state.Db.Users.Get().Select(static user => (user.Id, GetDisplayName(user))).OrderBy(static pair => pair.Item2)) {
+				items.Add(
+					value: id,
+					title: name,
+					isChecked: IncludedUsers == null || IncludedUsers.Contains(id)
+				);
+			}
+			
+			return items.ToCheckBoxItems();
 		}
 		
 		const string Title = "Included Users";
 		
-		List<CheckBoxItem<ulong>> items;
+		ImmutableArray<ICheckBoxItem> items;
 		try {
 			items = await ProgressDialog.ShowIndeterminate(window, Title, "Loading users...", PrepareUserItems);
 		} catch (Exception e) {
@@ -273,9 +290,7 @@ sealed partial class MessageFilterPanelModel : IDisposable {
 		}
 	}
 	
-	private async Task<HashSet<ulong>?> OpenIdFilterDialog(string title, List<CheckBoxItem<ulong>> items) {
+	private async Task<HashSet<ulong>?> OpenIdFilterDialog(string title, ImmutableArray<ICheckBoxItem> items) {
-		items.Sort(static (item1, item2) => item1.Title.CompareTo(item2.Title));
-		
 		var model = new CheckBoxDialogModel<ulong>(items) {
 			Title = title,
 		};
@@ -283,7 +298,7 @@ sealed partial class MessageFilterPanelModel : IDisposable {
 		var dialog = new CheckBoxDialog { DataContext = model };
 		var result = await dialog.ShowDialog<DialogResult.OkCancel>(window);
 		
-		return result == DialogResult.OkCancel.Ok ? model.SelectedItems.Select(static item => item.Item).ToHashSet() : null;
+		return result == DialogResult.OkCancel.Ok ? model.SelectedValues.ToHashSet() : null;
 	}
 	
 	public MessageFilter CreateFilter() {

app/Desktop/Main/Controls/ServerConfigurationPanelModel.cs

@@ -62,7 +62,7 @@ sealed partial class ServerConfigurationPanelModel : IDisposable {
 		try {
 			await server.Start(ServerConfiguration.Port, ServerConfiguration.Token);
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not start internal server.", e);
 			await Dialog.ShowOk(window, "Internal Server Error", e.Message);
 		}
 		
@@ -76,7 +76,7 @@ sealed partial class ServerConfigurationPanelModel : IDisposable {
 		try {
 			await server.Stop();
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not stop internal server.", e);
 			await Dialog.ShowOk(window, "Internal Server Error", e.Message);
 		}
 		

app/Desktop/Main/Controls/StatusBarModel.cs

@@ -1,7 +1,6 @@
 using System;
-using System.Reactive.Linq;
-using Avalonia.ReactiveUI;
 using Avalonia.Threading;
+using DHT.Desktop.Common;
 using DHT.Server;
 using DHT.Server.Service;
 using PropertyChanged.SourceGenerator;
@@ -41,9 +40,9 @@ sealed partial class StatusBarModel : IDisposable {
 	public StatusBarModel(State state) {
 		this.state = state;
 		
-		serverCountSubscription = state.Db.Servers.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(newServerCount => ServerCount = newServerCount);
+		serverCountSubscription = state.Db.Servers.TotalCount.SubscribeLastOnUI(newServerCount => ServerCount = newServerCount, TimeSpan.FromMilliseconds(15));
-		channelCountSubscription = state.Db.Channels.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(newChannelCount => ChannelCount = newChannelCount);
+		channelCountSubscription = state.Db.Channels.TotalCount.SubscribeLastOnUI(newChannelCount => ChannelCount = newChannelCount, TimeSpan.FromMilliseconds(15));
-		messageCountSubscription = state.Db.Messages.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(newMessageCount => MessageCount = newMessageCount);
+		messageCountSubscription = state.Db.Messages.TotalCount.SubscribeLastOnUI(newMessageCount => MessageCount = newMessageCount, TimeSpan.FromMilliseconds(15));
 		
 		state.Server.StatusChanged += OnStateServerStatusChanged;
 		serverStatus = state.Server.IsRunning ? ServerManager.Status.Started : ServerManager.Status.Stopped;

app/Desktop/Main/MainWindowModel.cs

@@ -89,14 +89,21 @@ sealed partial class MainWindowModel : IAsyncDisposable {
 		try {
 			await state.Server.Start(ServerConfiguration.Port, ServerConfiguration.Token);
 		} catch (Exception ex) {
-			Log.Error(ex);
+			Log.Error("Could not start internal server.", ex);
 			await Dialog.ShowOk(window, "Internal Server Error", ex.Message);
 		}
 		
-		mainContentScreenModel = new MainContentScreenModel(window, state);
+		try {
-		mainContentScreenModel.DatabaseClosed += MainContentScreenModelOnDatabaseClosed;
+			mainContentScreenModel = new MainContentScreenModel(window, state);
-		
+			mainContentScreenModel.DatabaseClosed += MainContentScreenModelOnDatabaseClosed;
-		await mainContentScreenModel.Initialize();
+			await mainContentScreenModel.Initialize();
+		} catch (Exception ex) {
+			Log.Error("Could not initialize content screen.", ex);
+			await Dialog.ShowOk(window, "Initialization Error", ex.Message);
+			await DisposeContent();
+			await DisposeState();
+			return;
+		}
 		
 		Title = Path.GetFileName(state.Db.Path) + " - " + DefaultTitle;
 		CurrentScreen = new MainContentScreen { DataContext = mainContentScreenModel };

app/Desktop/Main/Pages/DatabasePageModel.cs

@@ -55,11 +55,11 @@ sealed class DatabasePageModel {
 				break;
 			
 			case PlatformID.Unix:
-				Process.Start("xdg-open", [ folder ]);
+				Process.Start("xdg-open", [folder]);
 				break;
 			
 			case PlatformID.MacOSX:
-				Process.Start("open", [ folder ]);
+				Process.Start("open", [folder]);
 				break;
 			
 			default:
@@ -80,22 +80,25 @@ sealed class DatabasePageModel {
 		
 		const string Title = "Database Merge";
 		
-		ImportResult? result;
+		var result = new TaskCompletionSource<ImportResult?>();
 		try {
-			result = await ProgressDialog.Show(window, Title, async (dialog, callback) => await MergeWithDatabaseFromPaths(Db, paths, dialog, callback));
+			var dialog = new ProgressDialog();
+			dialog.DataContext = new ProgressDialogModel(Title, async callbacks => result.SetResult(await MergeWithDatabaseFromPaths(Db, paths, dialog, callbacks)), progressItems: 2);
+			await dialog.ShowProgressDialog(window);
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not merge databases.", e);
 			await Dialog.ShowOk(window, Title, "Could not merge databases: " + e.Message);
 			return;
 		}
 		
-		await Dialog.ShowOk(window, Title, GetImportDialogMessage(result, "database file"));
+		await Dialog.ShowOk(window, Title, GetImportDialogMessage(result.Task.Result, "database file"));
 	}
 	
-	private static async Task<ImportResult?> MergeWithDatabaseFromPaths(IDatabaseFile target, string[] paths, ProgressDialog dialog, IProgressCallback callback) {
+	private static async Task<ImportResult?> MergeWithDatabaseFromPaths(IDatabaseFile target, string[] paths, ProgressDialog dialog, IReadOnlyList<IProgressCallback> callbacks) {
-		var schemaUpgradeCallbacks = new SchemaUpgradeCallbacks(dialog, paths.Length);
+		var schemaUpgradeCallbacks = new SchemaUpgradeCallbacks(dialog, callbacks[1], paths.Length);
+		var databaseMergeProgressCallback = new DatabaseMergeProgressCallback(callbacks[1]);
 		
-		return await PerformImport(target, paths, dialog, callback, "Database Merge", async path => {
+		return await PerformImport(target, paths, dialog, callbacks[0], "Database Merge", async path => {
 			IDatabaseFile? db = await DatabaseGui.TryOpenOrCreateDatabaseFromPath(path, dialog, schemaUpgradeCallbacks);
 			
 			if (db == null) {
@@ -103,7 +106,7 @@ sealed class DatabasePageModel {
 			}
 			
 			try {
-				await target.AddFrom(db);
+				await target.Merge(db, databaseMergeProgressCallback);
 				return true;
 			} finally {
 				await db.DisposeAsync();
@@ -111,7 +114,7 @@ sealed class DatabasePageModel {
 		});
 	}
 	
-	private sealed class SchemaUpgradeCallbacks(ProgressDialog dialog, int total) : ISchemaUpgradeCallbacks {
+	private sealed class SchemaUpgradeCallbacks(ProgressDialog dialog, IProgressCallback callback, int total) : ISchemaUpgradeCallbacks {
 		private bool? decision;
 		
 		public Task<InitialDatabaseSettings?> GetInitialDatabaseSettings() {
@@ -125,6 +128,7 @@ sealed class DatabasePageModel {
 		}
 		
 		public Task Start(int versionSteps, Func<ISchemaUpgradeCallbacks.IProgressReporter, Task> doUpgrade) {
+			callback.UpdateIndeterminate("Upgrading database...");
 			return doUpgrade(new NullReporter());
 		}
 		
@@ -143,6 +147,20 @@ sealed class DatabasePageModel {
 		}
 	}
 	
+	private sealed class DatabaseMergeProgressCallback(IProgressCallback callback) : DatabaseMerging.IProgressCallback {
+		public void OnImportingMetadata() {
+			callback.UpdateIndeterminate("Importing metadata...");
+		}
+		
+		public void OnMessagesImported(long finished, long total) {
+			callback.Update("Importing messages...", finished, total);
+		}
+		
+		public void OnDownloadsImported(long finished, long total) {
+			callback.Update("Importing downloaded files...", finished, total);
+		}
+	}
+	
 	public async Task ImportLegacyArchive() {
 		string[] paths = await window.StorageProvider.OpenFiles(new FilePickerOpenOptions {
 			Title = "Open Legacy DHT Archive",
@@ -160,7 +178,7 @@ sealed class DatabasePageModel {
 		try {
 			result = await ProgressDialog.Show(window, Title, async (dialog, callback) => await ImportLegacyArchiveFromPaths(Db, paths, dialog, callback));
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not import legacy archives.", e);
 			await Dialog.ShowOk(window, Title, "Could not import legacy archives: " + e.Message);
 			return;
 		}
@@ -223,7 +241,7 @@ sealed class DatabasePageModel {
 		int finished = 0;
 		
 		foreach (string path in paths) {
-			await callback.Update(Path.GetFileName(path), finished, total);
+			await callback.Update("File: " + Path.GetFileName(path), finished, total);
 			++finished;
 			
 			if (!File.Exists(path)) {
@@ -236,7 +254,7 @@ sealed class DatabasePageModel {
 					++successful;
 				}
 			} catch (Exception ex) {
-				Log.Error(ex);
+				Log.Error("Could not import file: " + path, ex);
 				await Dialog.ShowOk(dialog, dialogTitle, "File '" + Path.GetFileName(path) + "' could not be imported: " + ex.Message);
 			}
 		}
@@ -302,7 +320,7 @@ sealed class DatabasePageModel {
 		try {
 			await ProgressDialog.ShowIndeterminate(window, Title, "Vacuuming database...", _ => Db.Vacuum());
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not vacuum database.", e);
 			await Dialog.ShowOk(window, Title, "Could not vacuum database: " + e.Message);
 			return;
 		}

app/Desktop/Main/Pages/DebugPage.axaml

@@ -45,5 +45,8 @@
                 </StackPanel>
             </WrapPanel>
         </Expander>
+        <Expander Header="About" IsExpanded="True">
+            <TextBlock Text="{Binding SqliteVersion, StringFormat=Sqlite Version: {0}}" />
+        </Expander>
     </StackPanel>
 </UserControl>

app/Desktop/Main/Pages/DebugPageModel.cs

@@ -9,14 +9,18 @@ using DHT.Desktop.Dialogs.Progress;
 using DHT.Server;
 using DHT.Server.Data;
 using DHT.Server.Service;
+using PropertyChanged.SourceGenerator;
 
 namespace DHT.Desktop.Main.Pages;
 
-sealed class DebugPageModel {
+sealed partial class DebugPageModel {
 	public string GenerateChannels { get; set; } = "0";
 	public string GenerateUsers { get; set; } = "0";
 	public string GenerateMessages { get; set; } = "0";
 	
+	[Notify(Setter.Private)]
+	private string? sqliteVersion = string.Empty;
+	
 	private readonly Window window;
 	private readonly State state;
 	
@@ -28,6 +32,10 @@ sealed class DebugPageModel {
 		this.state = state;
 	}
 	
+	public async Task Initialize() {
+		SqliteVersion = await state.Db.GetVersion() ?? "<unknown>";
+	}
+	
 	public async void OnClickAddRandomDataToDatabase() {
 		if (!int.TryParse(GenerateChannels, out int channels) || channels < 1) {
 			await Dialog.ShowOk(window, "Generate Random Data", "Amount of channels must be at least 1!");
@@ -169,6 +177,8 @@ sealed class DebugPageModel {
 	public string GenerateUsers { get; set; } = "0";
 	public string GenerateMessages { get; set; } = "0";
 
+	public string SqliteVersion => string.Empty;
+	
 	public void OnClickAddRandomDataToDatabase() {}
 }
 #endif

app/Desktop/Main/Pages/DownloadsPageModel.cs

@@ -2,11 +2,9 @@ using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.ComponentModel;
-using System.Reactive.Linq;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Platform.Storage;
-using Avalonia.ReactiveUI;
 using DHT.Desktop.Common;
 using DHT.Desktop.Dialogs.File;
 using DHT.Desktop.Dialogs.Message;
@@ -19,6 +17,7 @@ using DHT.Server.Data.Filters;
 using DHT.Server.Data.Settings;
 using DHT.Server.Download;
 using DHT.Utils.Logging;
+using DHT.Utils.Observables;
 using DHT.Utils.Tasks;
 using PropertyChanged.SourceGenerator;
 
@@ -82,8 +81,8 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 			statisticsSkipped,
 		];
 		
-		downloadStatisticsTask = new ThrottledTask<DownloadStatusStatistics>(Log, UpdateStatistics, TaskScheduler.FromCurrentSynchronizationContext());
+		downloadStatisticsTask = new ThrottledTask<DownloadStatusStatistics>(Log, UpdateStatistics, TimeSpan.FromMilliseconds(100), TaskScheduler.FromCurrentSynchronizationContext());
-		downloadItemCountSubscription = state.Db.Downloads.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnDownloadCountChanged);
+		downloadItemCountSubscription = state.Db.Downloads.TotalCount.SubscribeLastOnUI(OnDownloadCountChanged, TimeSpan.FromMilliseconds(15));
 		
 		RecomputeDownloadStatistics();
 	}
@@ -92,7 +91,12 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 		await FilterModel.Initialize();
 		
 		if (await state.Db.Settings.Get(SettingsKey.DownloadsAutoStart, defaultValue: false)) {
-			await StartDownload();
+			try {
+				await StartDownload();
+			} catch (Exception e) {
+				Log.Error("Could not automatically start downloads.", e);
+				await Dialog.ShowOk(window, "Database Error", "Could not automatically start downloads: " + e.Message);
+			}
 		}
 	}
 	
@@ -111,23 +115,43 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 	
 	public async Task OnClickToggleDownload() {
 		IsToggleDownloadButtonEnabled = false;
-		
+		try {
-		if (IsDownloading) {
+			if (IsDownloading) {
-			await StopDownload();
+				await StopDownload();
+			}
+			else {
+				try {
+					await StartDownload();
+				} catch (Exception e) {
+					Log.Error("Could not start downloads.", e);
+					await Dialog.ShowOk(window, "Database Error", "Could not start downloads: " + e.Message);
+					return;
+				}
+			}
+			
+			try {
+				await state.Db.Settings.Set(SettingsKey.DownloadsAutoStart, IsDownloading);
+			} catch (Exception e) {
+				Log.Error("Could not update auto-start setting in database.", e);
+			}
+		} finally {
+			IsToggleDownloadButtonEnabled = true;
 		}
-		else {
-			await StartDownload();
-		}
-		
-		await state.Db.Settings.Set(SettingsKey.DownloadsAutoStart, IsDownloading);
-		IsToggleDownloadButtonEnabled = true;
 	}
 	
 	private async Task StartDownload() {
 		await state.Db.Downloads.MoveDownloadingItemsBackToQueue();
 		
-		IObservable<DownloadItem> finishedItems = await state.Downloader.Start(currentDownloadFilter = FilterModel.CreateFilter());
+		try {
-		finishedItemsSubscription = finishedItems.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnItemFinished);
+			currentDownloadFilter = FilterModel.CreateFilter();
+			ObservableValue<DownloadItem> finishedItems = await state.Downloader.Start(currentDownloadFilter);
+			finishedItemsSubscription = finishedItems.SubscribeLastOnUI(OnItemFinished, TimeSpan.FromMilliseconds(15));
+		} catch (Exception) {
+			finishedItemsSubscription?.Dispose();
+			finishedItemsSubscription = null;
+			currentDownloadFilter = null;
+			throw;
+		}
 		
 		OnDownloadStateChanged();
 	}
@@ -138,8 +162,8 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 		
 		finishedItemsSubscription?.Dispose();
 		finishedItemsSubscription = null;
-		
 		currentDownloadFilter = null;
+		
 		OnDownloadStateChanged();
 	}
 	
@@ -155,12 +179,12 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 	
 	public async Task OnClickRetryFailed() {
 		IsRetryingFailedDownloads = true;
-		
 		try {
 			await state.Db.Downloads.RetryFailed();
 			RecomputeDownloadStatistics();
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not retry failed downloads.", e);
+			await Dialog.ShowOk(window, "Retry Failed", "Could not retry failed downloads: " + e.Message);
 		} finally {
 			IsRetryingFailedDownloads = false;
 		}
@@ -212,7 +236,7 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 				await state.Db.Vacuum();
 			});
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not delete orphaned downloads.", e);
 			await Dialog.ShowOk(window, Title, "Could not delete orphaned downloads: " + e.Message);
 		}
 	}
@@ -239,7 +263,7 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 				return await exporter.Export(new ExportProgressReporter(callback));
 			});
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not export downloaded files.", e);
 			await Dialog.ShowOk(window, Title, "Could not export downloaded files: " + e.Message);
 			return;
 		}
@@ -260,7 +284,7 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 		}
 	}
 	
-	private void UpdateStatistics(DownloadStatusStatistics statusStatistics) {
+	private Task UpdateStatistics(DownloadStatusStatistics statusStatistics) {
 		statisticsPending.Items = statusStatistics.PendingCount;
 		statisticsPending.Size = statusStatistics.PendingTotalSize;
 		statisticsPending.HasFilesWithUnknownSize = statusStatistics.PendingWithUnknownSizeCount > 0;
@@ -279,6 +303,8 @@ sealed partial class DownloadsPageModel : IAsyncDisposable {
 		
 		HasSuccessfulDownloads = statusStatistics.SuccessfulCount > 0;
 		HasFailedDownloads = statusStatistics.FailedCount > 0;
+		
+		return Task.CompletedTask;
 	}
 	
 	public sealed partial class StatisticsRow(string state) {

app/Desktop/Main/Pages/TrackingPageModel.cs

@@ -146,7 +146,7 @@ sealed partial class TrackingPageModel {
 			await clipboard.SetTextAsync(script);
 			return true;
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not copy to clipboard.", e);
 			await Dialog.ShowOk(window, errorDialogTitle, "An error occurred while copying to clipboard.");
 			return false;
 		}

app/Desktop/Main/Pages/ViewerPageModel.cs

@@ -75,7 +75,7 @@ sealed partial class ViewerPageModel : IDisposable {
 				}
 			}
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not apply filters.", e);
 			await Dialog.ShowOk(window, "Apply Filters", "Could not apply filters: " + e.Message);
 		}
 	}

app/Desktop/Main/Screens/MainContentScreenModel.cs

@@ -70,6 +70,10 @@ sealed class MainContentScreenModel : IAsyncDisposable {
 	
 	public async Task Initialize() {
 		await DownloadsPageModel.Initialize();
+		
+		#if DEBUG
+		await DebugPageModel.Initialize();
+		#endif
 	}
 	
 	public async ValueTask DisposeAsync() {

app/Desktop/Main/Screens/WelcomeScreenModel.cs

@@ -131,7 +131,7 @@ sealed partial class WelcomeScreenModel {
 			await Dialog.ShowOk(window, "Check Updates", "Request timed out.");
 			return;
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not check for updates.", e);
 			await Dialog.ShowOk(window, "Check Updates", "Error checking for updates: " + e.Message);
 			return;
 		}

app/Desktop/Program.cs

@@ -2,6 +2,7 @@
 using System.Globalization;
 using System.Reflection;
 using Avalonia;
+using DHT.Desktop.Common;
 using DHT.Utils.Logging;
 using DHT.Utils.Resources;
 
@@ -57,6 +58,8 @@ static class Program {
 	}
 	
 	private static AppBuilder BuildAvaloniaApp() {
+		AvaloniaReflection.Check();
+		
 		return AppBuilder.Configure<App>()
 		                 .UsePlatformDetect()
 		                 .WithInterFont()

app/Resources/Tracker/scripts/discord.js

@@ -67,7 +67,7 @@ class DISCORD {
 	/**
 	 * @type {function(String): MessageData}
 	 */
-	static #getMessages = WEBPACK.findFunction("getMessages");
+	static #getMessages = WEBPACK.findFunction("getMessages", [ "isLoadingMessages" ]);
 	
 	/**
 	 * @type {function(String): void}

app/Resources/Tracker/scripts/webpack.js

@@ -88,7 +88,7 @@ class WEBPACK {
 			return modules[0];
 		}
 		
-		console.error("[DHT] Cannot find module " + name + ", results found:", modules.length);
+		console.error("[DHT] Cannot find module " + name + ", results found:", modules.length, modules);
 		return null;
 	}
 	

app/Resources/Viewer/scripts/discord.mjs

@@ -107,7 +107,7 @@ export default (function() {
 	const isImageUrl = function(url) {
 		const dot = url.pathname.lastIndexOf(".");
 		const ext = dot === -1 ? "" : url.pathname.substring(dot).toLowerCase();
-		return ext === ".png" || ext === ".gif" || ext === ".jpg" || ext === ".jpeg";
+		return ext === ".png" || ext === ".gif" || ext === ".jpg" || ext === ".jpeg" || ext === ".webp" || ext === ".avif";
 	};
 	
 	return {

app/Server/Database/DatabaseExtensions.cs

@@ -1,34 +0,0 @@
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
-using DHT.Server.Data;
-
-namespace DHT.Server.Database;
-
-public static class DatabaseExtensions {
-	public static async Task AddFrom(this IDatabaseFile target, IDatabaseFile source) {
-		await target.Users.Add(await source.Users.Get().ToListAsync());
-		await target.Servers.Add(await source.Servers.Get().ToListAsync());
-		await target.Channels.Add(await source.Channels.Get().ToListAsync());
-		
-		const int MessageBatchSize = 100;
-		List<Message> batchedMessages = new (MessageBatchSize);
-		
-		await foreach (Message message in source.Messages.Get()) {
-			batchedMessages.Add(message);
-			
-			if (batchedMessages.Count >= MessageBatchSize) {
-				await target.Messages.Add(batchedMessages);
-				batchedMessages.Clear();
-			}
-		}
-		
-		await target.Messages.Add(batchedMessages);
-		
-		await foreach (Data.Download download in source.Downloads.Get()) {
-			if (download.Status != DownloadStatus.Success || !await source.Downloads.GetDownloadData(download.NormalizedUrl, stream => target.Downloads.AddDownload(download, stream))) {
-				await target.Downloads.AddDownload(download, stream: null);
-			}
-		}
-	}
-}

app/Server/Database/DummyDatabaseFile.cs

@@ -19,6 +19,10 @@ sealed class DummyDatabaseFile : IDatabaseFile {
 	
 	private DummyDatabaseFile() {}
 	
+	public Task<string?> GetVersion() {
+		return Task.FromResult<string?>(null);
+	}
+	
 	public Task Vacuum() {
 		return Task.CompletedTask;
 	}

app/Server/Database/IDatabaseFile.cs

@@ -14,5 +14,6 @@ public interface IDatabaseFile : IAsyncDisposable {
 	IMessageRepository Messages { get; }
 	IDownloadRepository Downloads { get; }
 	
+	Task<string?> GetVersion();
 	Task Vacuum();
 }

app/Server/Database/Import/DatabaseMerging.cs

@@ -0,0 +1,77 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using DHT.Server.Data;
+
+namespace DHT.Server.Database.Import;
+
+public static class DatabaseMerging {
+	public static async Task Merge(this IDatabaseFile target, IDatabaseFile source, IProgressCallback callback) {
+		// Import downloads first, otherwise automatic downloads would try to re-download files from other imported data.
+		await MergeDownloads(target, source, callback);
+		
+		callback.OnImportingMetadata();
+		await target.Users.Add(await source.Users.Get().ToListAsync());
+		await target.Servers.Add(await source.Servers.Get().ToListAsync());
+		await target.Channels.Add(await source.Channels.Get().ToListAsync());
+		
+		await MergeMessages(target, source, callback);
+	}
+	
+	private static async Task MergeDownloads(IDatabaseFile target, IDatabaseFile source, IProgressCallback callback) {
+		const int ReportBatchSize = 100;
+		
+		long totalDownloads = await source.Downloads.Count();
+		long importedDownloads = 0;
+		
+		callback.OnDownloadsImported(importedDownloads, totalDownloads);
+		
+		await foreach (Data.Download download in source.Downloads.Get()) {
+			if (download.Status != DownloadStatus.Success || !await source.Downloads.GetDownloadData(download.NormalizedUrl, stream => target.Downloads.AddDownload(download, stream))) {
+				await target.Downloads.AddDownload(download, stream: null);
+			}
+			
+			if (++importedDownloads % ReportBatchSize == 0) {
+				callback.OnDownloadsImported(importedDownloads, totalDownloads);
+			}
+		}
+		
+		callback.OnDownloadsImported(totalDownloads, totalDownloads);
+	}
+	
+	private static async Task MergeMessages(IDatabaseFile target, IDatabaseFile source, IProgressCallback callback) {
+		const int MessageBatchSize = 100;
+		const int ReportEveryBatches = 10;
+		List<Message> batchedMessages = new (MessageBatchSize);
+		
+		long totalMessages = await source.Messages.Count();
+		long importedMessages = 0;
+		
+		callback.OnMessagesImported(importedMessages, totalMessages);
+		
+		await foreach (Message message in source.Messages.Get()) {
+			batchedMessages.Add(message);
+			
+			if (batchedMessages.Count >= MessageBatchSize) {
+				await target.Messages.Add(batchedMessages);
+				
+				importedMessages += batchedMessages.Count;
+				
+				if (importedMessages % (MessageBatchSize * ReportEveryBatches) == 0) {
+					callback.OnMessagesImported(importedMessages, totalMessages);
+				}
+				
+				batchedMessages.Clear();
+			}
+		}
+		
+		await target.Messages.Add(batchedMessages);
+		callback.OnMessagesImported(totalMessages, totalMessages);
+	}
+	
+	public interface IProgressCallback {
+		void OnImportingMetadata();
+		void OnMessagesImported(long finished, long total);
+		void OnDownloadsImported(long finished, long total);
+	}
+}

app/Server/Database/Repositories/IChannelRepository.cs

@@ -1,15 +1,14 @@
-using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using DHT.Server.Data;
+using DHT.Utils.Observables;
 
 namespace DHT.Server.Database.Repositories;
 
 public interface IChannelRepository {
-	IObservable<long> TotalCount { get; }
+	ObservableValue<long> TotalCount { get; }
 	
 	Task Add(IReadOnlyList<Channel> channels);
 	
@@ -20,7 +19,7 @@ public interface IChannelRepository {
 	Task<int> RemoveUnreachable();
 	
 	internal sealed class Dummy : IChannelRepository {
-		public IObservable<long> TotalCount { get; } = Observable.Return(0L);
+		public ObservableValue<long> TotalCount { get; } = new (0L);
 		
 		public Task Add(IReadOnlyList<Channel> channels) {
 			return Task.CompletedTask;

app/Server/Database/Repositories/IDownloadRepository.cs

@@ -2,22 +2,22 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
-using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using DHT.Server.Data;
 using DHT.Server.Data.Aggregations;
 using DHT.Server.Data.Filters;
 using DHT.Server.Download;
+using DHT.Utils.Observables;
 
 namespace DHT.Server.Database.Repositories;
 
 public interface IDownloadRepository {
-	IObservable<long> TotalCount { get; }
+	ObservableValue<long> TotalCount { get; }
 	
 	Task AddDownload(Data.Download item, Stream? stream);
 	
-	Task<long> Count(DownloadItemFilter filter, CancellationToken cancellationToken = default);
+	Task<long> Count(DownloadItemFilter? filter = null, CancellationToken cancellationToken = default);
 	
 	Task<DownloadStatusStatistics> GetStatistics(DownloadItemFilter nonSkippedFilter, CancellationToken cancellationToken = default);
 	
@@ -38,13 +38,13 @@ public interface IDownloadRepository {
 	IAsyncEnumerable<FileUrl> FindReachableFiles(CancellationToken cancellationToken = default);
 	
 	internal sealed class Dummy : IDownloadRepository {
-		public IObservable<long> TotalCount { get; } = Observable.Return(0L);
+		public ObservableValue<long> TotalCount { get; } = new (0L);
 		
 		public Task AddDownload(Data.Download item, Stream? stream) {
 			return Task.CompletedTask;
 		}
 		
-		public Task<long> Count(DownloadItemFilter filter, CancellationToken cancellationToken) {
+		public Task<long> Count(DownloadItemFilter? filter, CancellationToken cancellationToken) {
 			return Task.FromResult(0L);
 		}
 		

app/Server/Database/Repositories/IMessageRepository.cs

@@ -1,16 +1,15 @@
-using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using DHT.Server.Data;
 using DHT.Server.Data.Filters;
+using DHT.Utils.Observables;
 
 namespace DHT.Server.Database.Repositories;
 
 public interface IMessageRepository {
-	IObservable<long> TotalCount { get; }
+	ObservableValue<long> TotalCount { get; }
 	
 	Task Add(IReadOnlyList<Message> messages);
 	
@@ -25,7 +24,7 @@ public interface IMessageRepository {
 	Task<int> RemoveUnreachableAttachments();
 	
 	internal sealed class Dummy : IMessageRepository {
-		public IObservable<long> TotalCount { get; } = Observable.Return(0L);
+		public ObservableValue<long> TotalCount { get; } = new (0L);
 		
 		public Task Add(IReadOnlyList<Message> messages) {
 			return Task.CompletedTask;

app/Server/Database/Repositories/IServerRepository.cs

@@ -1,14 +1,13 @@
-using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using DHT.Utils.Observables;
 
 namespace DHT.Server.Database.Repositories;
 
 public interface IServerRepository {
-	IObservable<long> TotalCount { get; }
+	ObservableValue<long> TotalCount { get; }
 	
 	Task Add(IReadOnlyList<Data.Server> servers);
 	
@@ -19,7 +18,7 @@ public interface IServerRepository {
 	Task<int> RemoveUnreachable();
 	
 	internal sealed class Dummy : IServerRepository {
-		public IObservable<long> TotalCount { get; } = Observable.Return(0L);
+		public ObservableValue<long> TotalCount { get; } = new (0L);
 		
 		public Task Add(IReadOnlyList<Data.Server> servers) {
 			return Task.CompletedTask;

app/Server/Database/Repositories/IUserRepository.cs

@@ -1,15 +1,14 @@
-using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using DHT.Server.Data;
+using DHT.Utils.Observables;
 
 namespace DHT.Server.Database.Repositories;
 
 public interface IUserRepository {
-	IObservable<long> TotalCount { get; }
+	ObservableValue<long> TotalCount { get; }
 	
 	Task Add(IReadOnlyList<User> users);
 	
@@ -20,7 +19,7 @@ public interface IUserRepository {
 	Task<int> RemoveUnreachable();
 	
 	internal sealed class Dummy : IUserRepository {
-		public IObservable<long> TotalCount { get; } = Observable.Return(0L);
+		public ObservableValue<long> TotalCount { get; } = new (0L);
 		
 		public Task Add(IReadOnlyList<User> users) {
 			return Task.CompletedTask;

app/Server/Database/Sqlite/Repositories/BaseSqliteRepository.cs

@@ -1,23 +1,27 @@
 using System;
-using System.Reactive.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using DHT.Utils.Logging;
+using DHT.Utils.Observables;
 using DHT.Utils.Tasks;
 
 namespace DHT.Server.Database.Sqlite.Repositories;
 
 abstract class BaseSqliteRepository : IDisposable {
-	private readonly ObservableThrottledTask<long> totalCountTask;
+	private readonly ThrottledTask<long> totalCountTask;
 	
-	public IObservable<long> TotalCount { get; }
+	public ObservableValue<long> TotalCount { get; } = new (0L);
 	
 	protected BaseSqliteRepository(Log log) {
-		totalCountTask = new ObservableThrottledTask<long>(log, TaskScheduler.Default);
+		totalCountTask = new ThrottledTask<long>(log, SetTotalCount, TimeSpan.Zero, TaskScheduler.Default);
-		TotalCount = totalCountTask.DistinctUntilChanged();
 		UpdateTotalCount();
 	}
 	
+	private Task SetTotalCount(long newCount) {
+		TotalCount.Set(newCount);
+		return Task.CompletedTask;
+	}
+	
 	public void Dispose() {
 		totalCountTask.Dispose();
 	}

app/Server/Database/Sqlite/Repositories/SqliteDownloadRepository.cs

@@ -306,12 +306,14 @@ sealed class SqliteDownloadRepository(SqliteConnectionPool pool) : BaseSqliteRep
 			await using var reader = await cmd.ExecuteReaderAsync(cancellationToken);
 			
 			while (await reader.ReadAsync(cancellationToken)) {
-				found.Add(new DownloadItem {
+				var item = new DownloadItem(
-					NormalizedUrl = reader.GetString(0),
+					NormalizedUrl: reader.GetString(0),
-					DownloadUrl = reader.GetString(1),
+					DownloadUrl: reader.GetString(1),
-					Type = reader.IsDBNull(2) ? null : reader.GetString(2),
+					Type: reader.IsDBNull(2) ? null : reader.GetString(2),
-					Size = reader.IsDBNull(3) ? null : reader.GetUint64(3),
+					Size: reader.IsDBNull(3) ? null : reader.GetUint64(3)
-				});
+				);
+				
+				found.Add(item);
 			}
 		}
 		

app/Server/Database/Sqlite/SqliteDatabaseFile.cs

@@ -80,6 +80,11 @@ public sealed class SqliteDatabaseFile : IDatabaseFile {
 		await pool.DisposeAsync();
 	}
 	
+	public async Task<string?> GetVersion() {
+		await using var conn = await pool.Take();
+		return await conn.ExecuteReaderAsync("SELECT sqlite_version()", static reader => reader?.GetString(0));
+	}
+	
 	public async Task Vacuum() {
 		await using var conn = await pool.Take();
 		

app/Server/Download/DownloadExporter.cs

@@ -95,7 +95,7 @@ public sealed partial class DownloadExporter(IDatabaseFile db, string folderPath
 				} catch (FileAlreadyExistsException) {
 					success = false;
 				} catch (Exception e) {
-					Log.Error(e);
+					Log.Error("Could not export downloaded file: " + download.NormalizedUrl, e);
 					success = false;
 				}
 				

app/Server/Download/DownloadItem.cs

@@ -4,12 +4,7 @@ using DHT.Server.Data;
 
 namespace DHT.Server.Download;
 
-public readonly struct DownloadItem {
+public sealed record DownloadItem(string NormalizedUrl, string DownloadUrl, string? Type, ulong? Size) {
-	public string NormalizedUrl { get; init; }
-	public string DownloadUrl { get; init; }
-	public string? Type { get; init; }
-	public ulong? Size { get; init; }
-	
 	internal Data.Download ToSuccess(long size) {
 		return new Data.Download(NormalizedUrl, DownloadUrl, DownloadStatus.Success, Type, (ulong) Math.Max(size, val2: 0));
 	}

app/Server/Download/Downloader.cs

@@ -1,8 +1,8 @@
-using System;
 using System.Threading;
 using System.Threading.Tasks;
 using DHT.Server.Data.Filters;
 using DHT.Server.Database;
+using DHT.Utils.Observables;
 
 namespace DHT.Server.Download;
 
@@ -19,11 +19,11 @@ public sealed class Downloader {
 		this.concurrentDownloads = concurrentDownloads;
 	}
 	
-	public async Task<IObservable<DownloadItem>> Start(DownloadItemFilter filter) {
+	public async Task<ObservableValue<DownloadItem>> Start(DownloadItemFilter filter) {
 		await semaphore.WaitAsync();
 		try {
 			current ??= new DownloaderTask(db, filter, concurrentDownloads);
-			return current.FinishedItems;
+			return current.LastFinishedItem;
 		} finally {
 			semaphore.Release();
 		}

app/Server/Download/DownloaderTask.cs

@@ -2,14 +2,15 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Net;
 using System.Net.Http;
-using System.Reactive.Subjects;
 using System.Threading;
 using System.Threading.Channels;
 using System.Threading.Tasks;
 using DHT.Server.Data.Filters;
 using DHT.Server.Database;
 using DHT.Utils.Logging;
+using DHT.Utils.Observables;
 using DHT.Utils.Tasks;
 
 namespace DHT.Server.Download;
@@ -37,12 +38,11 @@ sealed class DownloaderTask : IAsyncDisposable {
 	
 	private readonly IDatabaseFile db;
 	private readonly DownloadItemFilter filter;
-	private readonly ISubject<DownloadItem> finishedItemPublisher = Subject.Synchronize(new Subject<DownloadItem>());
 	
 	private readonly Task queueWriterTask;
 	private readonly Task[] downloadTasks;
 	
-	public IObservable<DownloadItem> FinishedItems => finishedItemPublisher;
+	public ObservableValue<DownloadItem> LastFinishedItem { get; } = new (null);
 	
 	internal DownloaderTask(IDatabaseFile db, DownloadItemFilter filter, int? concurrentDownloads) {
 		this.db = db;
@@ -94,15 +94,13 @@ sealed class DownloaderTask : IAsyncDisposable {
 			} catch (TaskCanceledException e) when (e.InnerException is TimeoutException) {
 				await db.Downloads.AddDownload(item.ToFailure(), stream: null);
 				log.Error("Download timed out: " + item.DownloadUrl);
-			} catch (HttpRequestException e) {
-				await db.Downloads.AddDownload(item.ToFailure(e.StatusCode), stream: null);
-				log.Error(e);
 			} catch (Exception e) {
-				await db.Downloads.AddDownload(item.ToFailure(), stream: null);
+				HttpStatusCode? statusCode = e is HttpRequestException hre ? hre.StatusCode : null;
-				log.Error(e);
+				await db.Downloads.AddDownload(item.ToFailure(statusCode), stream: null);
+				log.Error("Could not download file: " + item.DownloadUrl, e);
 			} finally {
 				try {
-					finishedItemPublisher.OnNext(item);
+					LastFinishedItem.Set(item);
 				} catch (Exception e) {
 					log.Error("Caught exception in event handler: " + e);
 				}
@@ -146,7 +144,6 @@ sealed class DownloaderTask : IAsyncDisposable {
 			await Task.WhenAll(downloadTasks).WaitIgnoringCancellation();
 		} finally {
 			cancellationTokenSource.Dispose();
-			finishedItemPublisher.OnCompleted();
 		}
 	}
 }

app/Server/Endpoints/BaseEndpoint.cs

@@ -33,7 +33,7 @@ abstract class BaseEndpoint {
 				await response.WriteAsync(e.Message);
 			}
 		} catch (Exception e) {
-			Log.Error(e);
+			Log.Error("Could not handle request.", e);
 			response.StatusCode = (int) HttpStatusCode.InternalServerError;
 		}
 	}

app/Server/Server.csproj

@@ -11,7 +11,7 @@
   </ItemGroup>
   
   <ItemGroup>
-    <PackageReference Include="Microsoft.Data.Sqlite" Version="8.0.7" />
+    <PackageReference Include="Microsoft.Data.Sqlite" Version="9.0.6" />
     <PackageReference Include="System.Linq.Async" Version="6.0.1" />
   </ItemGroup>
   

app/Server/Service/Middlewares/ServerLoggingMiddleware.cs

@@ -30,11 +30,11 @@ sealed class ServerLoggingMiddleware(RequestDelegate next) {
 		long elapsedMs = stopwatch.ElapsedMilliseconds;
 		
 		if (context.RequestAborted.IsCancellationRequested) {
-			Log.Debug("Request to " + request.GetEncodedPathAndQuery() + " (" + requestLength + " B) was cancelled after " + elapsedMs + " ms");
+			Log.Debug("Request to " + request.GetEncodedPathAndQuery() + " (" + requestLength + " B) was cancelled after " + elapsedMs + " ms.");
 		}
 		else {
 			int responseStatus = context.Response.StatusCode;
-			Log.Debug("Request to " + request.GetEncodedPathAndQuery() + " (" + requestLength + " B) returned " + responseStatus + ", took " + elapsedMs + " ms");
+			Log.Debug("Request to " + request.GetEncodedPathAndQuery() + " (" + requestLength + " B) returned " + responseStatus + ", took " + elapsedMs + " ms.");
 		}
 	}
 }

app/Server/Service/ServerManager.cs

@@ -88,7 +88,7 @@ public sealed class ServerManager {
 			throw;
 		}
 		
-		Log.Info("Server started");
+		Log.Info("Server started.");
 		
 		server = newServer;
 		
@@ -104,7 +104,7 @@ public sealed class ServerManager {
 		
 		Log.Info("Stopping server...");
 		await server.StopAsync();
-		Log.Info("Server stopped");
+		Log.Info("Server stopped.");
 		
 		server.Dispose();
 		server = null;

app/Utils/Logging/Log.cs

@@ -88,6 +88,11 @@ public sealed class Log {
 		LogLevel(ConsoleColor.Red, "ERROR", e.ToString());
 	}
 	
+	public void Error(string message, Exception e) {
+		Error(message);
+		Error(e);
+	}
+	
 	public Perf Start(string? context = null, [CallerMemberName] string callerMemberName = "") {
 		return Perf.Start(this, context, callerMemberName);
 	}

app/Utils/Observables/LastValueObserver.cs

@@ -0,0 +1,63 @@
+using System;
+using System.Threading;
+using System.Threading.Channels;
+using System.Threading.Tasks;
+
+namespace DHT.Utils.Observables;
+
+sealed class LastValueObserver<T> : IDisposable {
+	private readonly ObservableValue<T> observable;
+	private readonly Func<T, CancellationToken, Task> action;
+	private readonly TaskScheduler scheduler;
+	
+	private readonly Channel<T> channel = Channel.CreateBounded<T>(new BoundedChannelOptions(capacity: 1) {
+		AllowSynchronousContinuations = false,
+		FullMode = BoundedChannelFullMode.DropOldest,
+		SingleReader = true,
+		SingleWriter = false,
+	});
+	
+	private readonly CancellationTokenSource cancellationTokenSource = new ();
+	
+	public LastValueObserver(ObservableValue<T> observable, Func<T, CancellationToken, Task> action, TaskScheduler scheduler) {
+		this.observable = observable;
+		this.action = action;
+		this.scheduler = scheduler;
+		
+		_ = ReadNextValue();
+	}
+	
+	private async Task ReadNextValue() {
+		CancellationToken cancellationToken = cancellationTokenSource.Token;
+		
+		try {
+			await foreach (T value in channel.Reader.ReadAllAsync(cancellationToken)) {
+				try {
+					await Task.Factory.StartNew(UseValue, value, CancellationToken.None, TaskCreationOptions.None, scheduler).WaitAsync(cancellationToken);
+				} catch (Exception) {
+					// Ignore.
+				}
+			}
+		} finally {
+			cancellationTokenSource.Dispose();
+		}
+	}
+	
+	private Task UseValue(object? value) {
+		return action((T) value!, cancellationTokenSource.Token);
+	}
+	
+	public void Notify(T value) {
+		channel.Writer.TryWrite(value);
+	}
+	
+	public void Dispose() {
+		observable.Unsubscribe(this);
+		
+		try {
+			cancellationTokenSource.Cancel();
+		} catch (ObjectDisposedException) {}
+		
+		channel.Writer.TryComplete();
+	}
+}

app/Utils/Observables/ObservableValue.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace DHT.Utils.Observables;
+
+public sealed class ObservableValue<T>(T? value) {
+	private readonly List<LastValueObserver<T>> observers = [];
+	private T? value = value;
+	
+	public void Set(T value) {
+		lock (this) {
+			if (EqualityComparer<T>.Default.Equals(value, this.value)) {
+				return;
+			}
+			
+			this.value = value;
+			
+			foreach (var observer in observers) {
+				observer.Notify(value);
+			}
+		}
+	}
+	
+	public IDisposable SubscribeLast(Func<T, CancellationToken, Task> action, TaskScheduler scheduler) {
+		var observer = new LastValueObserver<T>(this, action, scheduler);
+		
+		lock (this) {
+			observers.Add(observer);
+			
+			if (value is not null) {
+				observer.Notify(value);
+			}
+		}
+		
+		return observer;
+	}
+	
+	internal void Unsubscribe(LastValueObserver<T> observer) {
+		lock (this) {
+			observers.Remove(observer);
+		}
+	}
+}

app/Utils/Tasks/DelayedThrottledTask.cs

@@ -1,64 +0,0 @@
-using System;
-using System.Threading;
-using System.Threading.Channels;
-using System.Threading.Tasks;
-using DHT.Utils.Logging;
-
-namespace DHT.Utils.Tasks;
-
-public sealed class DelayedThrottledTask<T> : IDisposable {
-	private readonly Channel<T> taskChannel = Channel.CreateBounded<T>(new BoundedChannelOptions(capacity: 1) {
-		SingleReader = true,
-		SingleWriter = false,
-		AllowSynchronousContinuations = false,
-		FullMode = BoundedChannelFullMode.DropOldest,
-	});
-	
-	private readonly CancellationTokenSource cancellationTokenSource = new ();
-	private readonly Log log;
-	private readonly TimeSpan delay;
-	private readonly Func<T, Task> inputProcessor;
-	
-	public DelayedThrottledTask(Log log, TimeSpan delay, Func<T, Task> inputProcessor) {
-		this.log = log;
-		this.delay = delay;
-		this.inputProcessor = inputProcessor;
-		
-		Task.Run(ReaderTask);
-	}
-	
-	private async Task ReaderTask() {
-		CancellationToken cancellationToken = cancellationTokenSource.Token;
-		
-		try {
-			while (await taskChannel.Reader.WaitToReadAsync(cancellationToken)) {
-				await Task.Delay(delay, cancellationToken);
-				
-				T input = await taskChannel.Reader.ReadAsync(cancellationToken);
-				try {
-					await inputProcessor(input);
-				} catch (OperationCanceledException) {
-					throw;
-				} catch (Exception e) {
-					log.Error("Caught exception in task: " + e);
-				}
-			}
-		} catch (OperationCanceledException) {
-			// Ignore.
-		} finally {
-			cancellationTokenSource.Dispose();
-		}
-	}
-	
-	public void Post(T input) {
-		taskChannel.Writer.TryWrite(input);
-	}
-	
-	public void Dispose() {
-		try {
-			cancellationTokenSource.Cancel();
-		} catch (ObjectDisposedException) {}
-		
-		taskChannel.Writer.Complete();
-	}
-}

app/Utils/Tasks/ObservableThrottledTask.cs

@@ -1,32 +0,0 @@
-using System;
-using System.Reactive.Subjects;
-using System.Threading;
-using System.Threading.Tasks;
-using DHT.Utils.Logging;
-
-namespace DHT.Utils.Tasks;
-
-public sealed class ObservableThrottledTask<T> : IObservable<T>, IDisposable {
-	private readonly ReplaySubject<T> subject;
-	private readonly ThrottledTask<T> task;
-	
-	public ObservableThrottledTask(Log log, TaskScheduler resultScheduler) {
-		this.subject = new ReplaySubject<T>(bufferSize: 1);
-		this.task = new ThrottledTask<T>(log, subject.OnNext, resultScheduler);
-	}
-	
-	public void Post(Func<CancellationToken, Task<T>> resultComputer) {
-		task.Post(resultComputer);
-	}
-	
-	public IDisposable Subscribe(IObserver<T> observer) {
-		return subject.Subscribe(observer);
-	}
-	
-	public void Dispose() {
-		task.Dispose();
-		
-		subject.OnCompleted();
-		subject.Dispose();
-	}
-}

app/Utils/Tasks/ThrottledTask.cs

@@ -14,11 +14,13 @@ public abstract class ThrottledTaskBase<T> : IDisposable {
 		FullMode = BoundedChannelFullMode.DropOldest,
 	});
 	
-	private readonly CancellationTokenSource cancellationTokenSource = new ();
 	private readonly Log log;
+	private readonly TimeSpan delayBetweenRuns;
+	private readonly CancellationTokenSource cancellationTokenSource = new ();
 	
-	internal ThrottledTaskBase(Log log) {
+	internal ThrottledTaskBase(Log log, TimeSpan delayBetweenRuns) {
 		this.log = log;
+		this.delayBetweenRuns = delayBetweenRuns;
 	}
 	
 	protected async Task ReaderTask() {
@@ -33,9 +35,9 @@ public abstract class ThrottledTaskBase<T> : IDisposable {
 				} catch (Exception e) {
 					log.Error("Caught exception in task: " + e);
 				}
+				
+				await Task.Delay(delayBetweenRuns, cancellationToken);
 			}
-		} catch (OperationCanceledException) {
-			// Ignore.
 		} finally {
 			cancellationTokenSource.Dispose();
 		}
@@ -48,20 +50,20 @@ public abstract class ThrottledTaskBase<T> : IDisposable {
 	}
 	
 	public void Dispose() {
-		taskChannel.Writer.Complete();
 		cancellationTokenSource.Cancel();
+		taskChannel.Writer.Complete();
 	}
 }
 
 public sealed class ThrottledTask : ThrottledTaskBase<Task> {
-	private readonly Action resultProcessor;
+	private readonly Func<Task> resultProcessor;
 	private readonly TaskScheduler resultScheduler;
 	
-	public ThrottledTask(Log log, Action resultProcessor, TaskScheduler resultScheduler) : base(log) {
+	public ThrottledTask(Log log, Func<Task> resultProcessor, TimeSpan delayBetweenRuns, TaskScheduler resultScheduler) : base(log, delayBetweenRuns) {
 		this.resultProcessor = resultProcessor;
 		this.resultScheduler = resultScheduler;
 		
-		Task.Run(ReaderTask);
+		_ = ReaderTask();
 	}
 	
 	protected override async Task Run(Func<CancellationToken, Task> func, CancellationToken cancellationToken) {
@@ -71,18 +73,22 @@ public sealed class ThrottledTask : ThrottledTaskBase<Task> {
 }
 
 public sealed class ThrottledTask<T> : ThrottledTaskBase<Task<T>> {
-	private readonly Action<T> resultProcessor;
+	private readonly Func<T, Task> resultProcessor;
 	private readonly TaskScheduler resultScheduler;
 	
-	public ThrottledTask(Log log, Action<T> resultProcessor, TaskScheduler resultScheduler) : base(log) {
+	public ThrottledTask(Log log, Func<T, Task> resultProcessor, TimeSpan delayBetweenRuns, TaskScheduler resultScheduler) : base(log, delayBetweenRuns) {
 		this.resultProcessor = resultProcessor;
 		this.resultScheduler = resultScheduler;
 		
-		Task.Run(ReaderTask);
+		_ = ReaderTask();
 	}
 	
 	protected override async Task Run(Func<CancellationToken, Task<T>> func, CancellationToken cancellationToken) {
 		T result = await func(cancellationToken);
 		await Task.Factory.StartNew(() => resultProcessor(result), cancellationToken, TaskCreationOptions.None, resultScheduler);
 	}
+	
+	public void Post(T result) {
+		base.Post(_ => Task.FromResult(result));
+	}
 }

app/Utils/Utils.csproj

@@ -16,7 +16,6 @@
   
   <ItemGroup>
     <PackageReference Include="JetBrains.Annotations" Version="2023.2.0" />
-    <PackageReference Include="System.Reactive" Version="6.0.0" />
   </ItemGroup>
   
   <ItemGroup>

app/Version.cs

@@ -8,5 +8,5 @@ using DHT.Utils;
 namespace DHT.Utils;
 
 static class Version {
-	public const string Tag = "47.0.0.0";
+	public const string Tag = "47.2.0.0";
 }

web/index.php

@@ -22,7 +22,6 @@ define('LATEST_VERSION', $version === false ? '_' : $version);
       <h1>Discord History Tracker&nbsp;<span class="bar">|</span>&nbsp;<span class="notes"><a href="https://github.com/chylex/Discord-History-Tracker/releases">Release&nbsp;Notes</a></span></h1>
       <p>Discord History Tracker lets you save chat history in your servers, groups, and private conversations, and view it offline.</p>
       <img src="img/tracker.png" width="851" class="dht bordered">
-      <p>This page explains how to use the desktop app. If you are looking for the older version of Discord History Tracker which only needs a browser or the Discord app, visit the page for the <a href="https://dht.chylex.com/browser-only">browser-only version</a>, however keep in mind that this version has <strong>significant limitations and fewer features</strong>.</p>
       
       <h2>How to Use</h2>
       <p>Download the latest version of the desktop app here, or visit <a href="https://github.com/chylex/Discord-History-Tracker/releases">All Releases</a> for older versions and release notes.</p>
@@ -71,9 +70,9 @@ define('LATEST_VERSION', $version === false ? '_' : $version);
       
       <h2>External Links</h2>
       <p class="links">
-        <a href="https://github.com/chylex/Discord-History-Tracker/issues">Issues&nbsp;&amp;&nbsp;Suggestions</a>&nbsp;&nbsp;&mdash;&nbsp;
+        <a href="https://github.com/chylex/Discord-History-Tracker/issues">Issues&nbsp;&amp;&nbsp;Suggestions</a>&nbsp;&nbsp;&bullet;&nbsp;
-        <a href="https://github.com/chylex/Discord-History-Tracker">Source&nbsp;Code</a>&nbsp;&nbsp;&mdash;&nbsp;
+        <a href="https://github.com/chylex/Discord-History-Tracker">Source&nbsp;Code</a>&nbsp;&nbsp;&bullet;&nbsp;
-        <a href="https://twitter.com/chylexmc">Follow&nbsp;Dev&nbsp;on&nbsp;Twitter</a>&nbsp;&nbsp;&mdash;&nbsp;
+        <a href="https://chylex.com">Developer's&nbsp;Website</a>&nbsp;&nbsp;&bullet;&nbsp;
         <a href="https://ko-fi.com/chylex">Support&nbsp;via&nbsp;Ko-fi</a>
       </p>
       

web/style.css

@@ -165,7 +165,7 @@ code {
 
 .downloads svg {
   margin: 1px 4px;
-  vertical-align: -25%;
+  vertical-align: -30%;
 }
 
 .downloads svg.icon-large {