Planung: Stunde einer anderen Einheit zuweisen ("Einheit wechseln")

Bisher war die Einheit einer Stunde nach dem Anlegen fix - bei falscher
Auswahl im Erstellen-Dialog blieb nur Löschen+Neuanlegen. Neuer Button
öffnet einen Dialog zur Auswahl der Ziel-Einheit; die Ansicht springt
danach automatisch dorthin mit der Stunde vorausgewählt.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

LehrerApp.Desktop.Tests/PlanningTabViewModelTests.cs

@@ -93,6 +93,30 @@ public class PlanningTabViewModelTests
         Assert.Equal(new DateOnly(2025, 9, 8), byUnit[l2.Id].Date); // unverändert
     }
 
+    [Fact]
+    public async Task ChangeLessonUnit_OrdnetStundeDerZieleinheitZuUndWaehltSieAus()
+    {
+        var (vm, units, lessons, groupId) = BuildScenario();
+        var unitA = new Unit { GroupId = groupId, Title = "Mechanik" };
+        var unitB = new Unit { GroupId = groupId, Title = "Optik" };
+        units.Add(unitA); units.Add(unitB);
+        var l1 = new Lesson { UnitId = unitA.Id, GroupId = groupId, Date = new DateOnly(2025, 9, 1), Status = LessonStatus.Planned, Topic = "1" };
+        lessons.Add(l1);
+
+        vm.Initialize(groupId);
+        vm.SelectedUnit = vm.Units.Single(u => u.Id == unitA.Id);
+        vm.SelectedLesson = vm.Lessons.Single(l => l.Id == l1.Id);
+        vm.OnPickUnitChange = _ => Task.FromResult<Unit?>(unitB);
+
+        await vm.ChangeLessonUnitCommand.ExecuteAsync(null);
+
+        Assert.Empty(lessons.GetByUnit(unitA.Id));
+        var moved = Assert.Single(lessons.GetByUnit(unitB.Id));
+        Assert.Equal(l1.Id, moved.Id);
+        Assert.Equal(unitB.Id, vm.SelectedUnit?.Id);
+        Assert.Equal(l1.Id, vm.SelectedLesson?.Id);
+    }
+
     [Fact]
     public async Task CopyUnit_ErhaeltAbstaendeUndSetztGroupIdAufZielgruppe()
     {

LehrerApp.Desktop/ViewModels/Groups/PlanningViewModels.cs

@@ -5,6 +5,7 @@ using LehrerApp.Core.Interfaces;
 using LehrerApp.Core.Models;
 using LehrerApp.Core.Services;
 using LehrerApp.Desktop.Services;
+using LehrerApp.Desktop.ViewModels.Planning;
 using LehrerApp.Desktop.ViewModels.Students;
 using System.Collections.ObjectModel;
 using System.Globalization;
@@ -75,6 +76,7 @@ public partial class PlanningTabViewModel : ObservableObject
     public Func<Lesson, List<string>, List<string>, Task<bool>>? OnEditLesson { get; set; }
     public Func<LessonSummary, Task<bool>>? OnConfirmDeleteLesson { get; set; }
     public Func<Lesson, Task<MoveLessonTarget?>>? OnPickMoveTarget { get; set; }
+    public Func<Lesson, Task<Unit?>>? OnPickUnitChange { get; set; }
     public Func<Lesson, Task>? OnShowLesson { get; set; }
     public Func<Unit, Task<LessonSeriesResult?>>? OnGenerateLessonSeries { get; set; }
     public Func<Unit, Task<bool>>? OnAiAssist { get; set; }
@@ -160,6 +162,7 @@ public partial class PlanningTabViewModel : ObservableObject
         EditLessonCommand.NotifyCanExecuteChanged();
         DeleteLessonCommand.NotifyCanExecuteChanged();
         MoveLessonCommand.NotifyCanExecuteChanged();
+        ChangeLessonUnitCommand.NotifyCanExecuteChanged();
         AdvanceLessonStatusCommand.NotifyCanExecuteChanged();
     }
 
@@ -349,6 +352,23 @@ public partial class PlanningTabViewModel : ObservableObject
         new LessonSchedulingService(_lessons).Move(moved, newDate, newPeriod, shiftFollowing);
     }
 
+    /// Ordnet eine bereits angelegte Stunde einer anderen Einheit derselben Gruppe zu (Korrektur
+    /// einer im Erstellen-Dialog falsch gewählten Einheit, Nutzer-Feedback) — bisher war das nur
+    /// über Löschen + Neuanlegen möglich. Datum/Stundennummer bleiben unverändert, nur UnitId ändert
+    /// sich. Nach dem Speichern springt die Ansicht direkt zur Ziel-Einheit mit der Stunde
+    /// vorausgewählt, damit sichtbar bleibt, wohin sie verschoben wurde.
+    [RelayCommand(CanExecute = nameof(HasSelectedLesson))]
+    private async Task ChangeLessonUnit()
+    {
+        if (OnPickUnitChange is null || SelectedLesson is null) return;
+        var lesson = SelectedLesson.Model;
+        var targetUnit = await OnPickUnitChange(lesson);
+        if (targetUnit is null) return;
+        lesson.UnitId = targetUnit.Id;
+        _lessons.Save(lesson);
+        RefreshPlanning(selectUnitId: targetUnit.Id, selectLessonId: lesson.Id);
+    }
+
     [RelayCommand(CanExecute = nameof(HasSelectedLesson))]
     private void AdvanceLessonStatus()
     {
@@ -1206,6 +1226,38 @@ public partial class MoveLessonDialogViewModel : ObservableObject
     }
 }
 
+// ── Dialog: Stunde einer anderen Einheit zuweisen (Korrektur der Einheit) ────
+
+public partial class ChangeLessonUnitDialogViewModel : ObservableObject
+{
+    [ObservableProperty] private TimetableUnitOption? _selectedUnit;
+    [ObservableProperty] private string _error = "";
+
+    public string CurrentUnitLabel { get; }
+    public ObservableCollection<TimetableUnitOption> Units { get; } = [];
+    public bool HasUnits => Units.Count > 0;
+    public Unit? Result { get; private set; }
+
+    public ChangeLessonUnitDialogViewModel(IUnitRepository units, Guid groupId, Guid currentUnitId,
+        string currentUnitTitle)
+    {
+        CurrentUnitLabel = currentUnitTitle;
+        foreach (var unit in units.GetByGroup(groupId).Where(u => u.Id != currentUnitId)
+                     .OrderBy(u => u.Status == UnitStatus.Active ? 0 : u.Status == UnitStatus.Planned ? 1 : 2)
+                     .ThenByDescending(u => u.StartDate)
+                     .ThenBy(u => u.Title, StringComparer.CurrentCultureIgnoreCase))
+            Units.Add(new TimetableUnitOption(unit));
+    }
+
+    [RelayCommand]
+    private void Save()
+    {
+        Error = "";
+        if (SelectedUnit is null) { Error = "Bitte eine Ziel-Einheit auswählen."; return; }
+        Result = SelectedUnit.Model;
+    }
+}
+
 // ── Dialog: Stunden serienweise aus dem Stundenplan erzeugen (4.2.5) ────────
 
 public partial class GenerateLessonSeriesDialogViewModel : ObservableObject

LehrerApp.Desktop/Views/Groups/ChangeLessonUnitDialog.axaml

@@ -0,0 +1,47 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="clr-namespace:LehrerApp.Desktop.ViewModels.Groups"
+        xmlns:vmp="clr-namespace:LehrerApp.Desktop.ViewModels.Planning"
+        x:Class="LehrerApp.Desktop.Views.Groups.ChangeLessonUnitDialog"
+        x:DataType="vm:ChangeLessonUnitDialogViewModel"
+        Title="Einheit wechseln"
+        Width="440" Height="360" MinWidth="400" MinHeight="320"
+        CanResize="False" WindowStartupLocation="CenterOwner">
+
+  <Grid RowDefinitions="*,Auto" Margin="24">
+    <StackPanel Grid.Row="0" Spacing="14">
+      <TextBlock Text="Einheit wechseln" Classes="dialogtitle"/>
+      <TextBlock FontSize="12" Opacity="0.6">
+        <Run Text="Bisherige Einheit: "/>
+        <Run Text="{Binding CurrentUnitLabel}"/>
+      </TextBlock>
+
+      <StackPanel Spacing="5" IsVisible="{Binding HasUnits}">
+        <TextBlock Text="Neue Einheit" FontSize="12" Opacity="0.7"/>
+        <ComboBox ItemsSource="{Binding Units}" SelectedItem="{Binding SelectedUnit}"
+                  HorizontalAlignment="Stretch">
+          <ComboBox.ItemTemplate>
+            <DataTemplate x:DataType="vmp:TimetableUnitOption">
+              <StackPanel>
+                <TextBlock Text="{Binding Label}" FontWeight="SemiBold"/>
+                <TextBlock Text="{Binding Detail}" FontSize="11" Opacity="0.6"/>
+              </StackPanel>
+            </DataTemplate>
+          </ComboBox.ItemTemplate>
+        </ComboBox>
+      </StackPanel>
+
+      <TextBlock Text="Keine andere Einheit in dieser Gruppe vorhanden."
+                 FontSize="12" Opacity="0.7" TextWrapping="Wrap"
+                 IsVisible="{Binding !HasUnits}"/>
+
+      <TextBlock Text="{Binding Error}" Foreground="Red" FontSize="11"
+                 IsVisible="{Binding Error, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"/>
+    </StackPanel>
+    <Grid Grid.Row="1" ColumnDefinitions="*,8,*" Margin="0,20,0,0">
+      <Button Grid.Column="0" Content="Abbrechen" HorizontalAlignment="Stretch" Click="OnCancel"/>
+      <Button Grid.Column="2" Content="Verschieben" HorizontalAlignment="Stretch" Click="OnSave"
+              IsEnabled="{Binding HasUnits}"/>
+    </Grid>
+  </Grid>
+</Window>

LehrerApp.Desktop/Views/Groups/ChangeLessonUnitDialog.axaml.cs

@@ -0,0 +1,21 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using LehrerApp.Desktop.ViewModels.Groups;
+
+namespace LehrerApp.Desktop.Views.Groups;
+
+public partial class ChangeLessonUnitDialog : Window
+{
+    public ChangeLessonUnitDialog() => InitializeComponent();
+
+    private void OnSave(object? s, RoutedEventArgs e)
+    {
+        if (DataContext is ChangeLessonUnitDialogViewModel vm && vm.SaveCommand.CanExecute(null))
+        {
+            vm.SaveCommand.Execute(null);
+            if (vm.Result is not null) Close(true);
+        }
+    }
+
+    private void OnCancel(object? s, RoutedEventArgs e) => Close(false);
+}

LehrerApp.Desktop/Views/Groups/PlanningTabView.axaml

@@ -91,6 +91,8 @@
                 ToolTip.Tip="Verlaufsplan schreibgeschützt und größer anzeigen — zum Mitnehmen in den Unterricht."/>
         <Button Content="Bearbeiten"             Command="{Binding EditLessonCommand}" IsEnabled="{Binding !IsReadOnly}"/>
         <Button Content="Verschieben"            Command="{Binding MoveLessonCommand}" IsEnabled="{Binding !IsReadOnly}"/>
+        <Button Content="Einheit wechseln"       Command="{Binding ChangeLessonUnitCommand}" IsEnabled="{Binding !IsReadOnly}"
+                ToolTip.Tip="Ordnet die ausgewählte Stunde einer anderen Einheit derselben Gruppe zu."/>
         <Button Content="Status weiter" Command="{Binding AdvanceLessonStatusCommand}" IsEnabled="{Binding !IsReadOnly}"
                 ToolTip.Tip="Entwurf/Geplant → Bereit → Durchgeführt"/>
         <Button Content="Sitzung erzeugen"       Command="{Binding CreateParticipationSessionCommand}"

LehrerApp.Desktop/Views/Groups/PlanningTabView.axaml.cs

@@ -38,6 +38,7 @@ public partial class PlanningTabView : UserControl
                 ShowLessonDialog(lesson.UnitId, lesson.GroupId, materials, shorthands, editingLesson: lesson);
             vm.OnConfirmDeleteLesson = ShowDeleteLessonDialog;
             vm.OnPickMoveTarget      = ShowMoveLessonDialog;
+            vm.OnPickUnitChange      = ShowChangeLessonUnitDialog;
             vm.OnShowLesson          = ShowLessonViewerDialog;
             vm.OnGenerateLessonSeries = ShowGenerateLessonSeriesDialog;
             vm.OnAiAssist = ShowAiAssistDialog;
@@ -136,6 +137,20 @@ public partial class PlanningTabView : UserControl
         return ok ? dialogVm.Result : null;
     }
 
+    private async Task<Unit?> ShowChangeLessonUnitDialog(Lesson lesson)
+    {
+        var dialogVm = new ChangeLessonUnitDialogViewModel(
+            App.Services.GetRequiredService<IUnitRepository>(),
+            lesson.GroupId, lesson.UnitId,
+            (DataContext as PlanningTabViewModel)?.SelectedUnit?.Title ?? "");
+        var dialog = new ChangeLessonUnitDialog { DataContext = dialogVm };
+        var owner = TopLevel.GetTopLevel(this) as Window;
+        if (owner is null) return null;
+
+        var ok = await dialog.ShowDialog<bool>(owner);
+        return ok ? dialogVm.Result : null;
+    }
+
     private async Task ShowLessonViewerDialog(Lesson lesson)
     {
         var viewerVm = new LessonViewerViewModel(lesson,