feat: Teilnehmerlisten in Lerngruppen importieren

LehrerApp.Desktop/Views/Groups/GroupDetailView.axaml

@@ -23,6 +23,8 @@
           <CheckBox Content="Ausgetretene anzeigen" IsChecked="{Binding ShowFormerStudents}"
                     VerticalAlignment="Center"/>
           <Button Content="＋ Schüler" Command="{Binding AddStudentCommand}" IsEnabled="{Binding IsEditable}"/>
+          <Button Content="⇩ Teilnehmer importieren…" Click="OnImportParticipantsClick"
+                  IsEnabled="{Binding IsEditable}"/>
           <Button Content="{Binding SelectedStudent.WithdrawActionLabel}"
                   Command="{Binding WithdrawStudentCommand}"
                   IsVisible="{Binding SelectedStudent, Converter={x:Static ObjectConverters.IsNotNull}}"/>

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

@@ -1,15 +1,23 @@
 using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Platform.Storage;
+using LehrerApp.Core.Importing;
 using LehrerApp.Core.Interfaces;
 using LehrerApp.Core.Models;
 using LehrerApp.Core.Services;
 using LehrerApp.Desktop.ViewModels.Groups;
+using LehrerApp.Desktop.ViewModels.Students;
+using LehrerApp.Desktop.Services;
 using LehrerApp.Desktop.Views.Shared;
+using LehrerApp.Desktop.Views.Students;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace LehrerApp.Desktop.Views.Groups;
 
 public partial class GroupDetailView : UserControl
 {
+    private const int MaximumImportFileSize = 20 * 1024 * 1024;
+
     public GroupDetailView() => InitializeComponent();
 
     protected override void OnDataContextChanged(EventArgs e)
@@ -60,6 +68,61 @@ public partial class GroupDetailView : UserControl
         return await dialog.ShowDialog<bool>(owner);
     }
 
+    private async void OnImportParticipantsClick(object? sender, RoutedEventArgs e)
+    {
+        var owner = TopLevel.GetTopLevel(this) as Window;
+        if (owner is null || DataContext is not GroupDetailViewModel vm || vm.Group is null) return;
+
+        var service = App.Services.GetRequiredService<StudentImportService>();
+        var patterns = service.SupportedExtensions.Select(extension => $"*{extension}").ToArray();
+        var files = await owner.StorageProvider.OpenFilePickerAsync(new FilePickerOpenOptions
+        {
+            Title = $"Teilnehmer für {vm.Group.Name} importieren",
+            AllowMultiple = false,
+            FileTypeFilter =
+            [
+                new FilePickerFileType("Unterstützte Schülerlisten")
+                {
+                    Patterns = patterns.Length > 0 ? patterns : ["*.csv"],
+                },
+            ],
+        });
+        if (files.Count == 0) return;
+
+        try
+        {
+            await using var source = await files[0].OpenReadAsync();
+            if (source.CanSeek && source.Length > MaximumImportFileSize)
+                throw new InvalidDataException("Die Importdatei ist größer als 20 MB.");
+
+            using var buffer = new MemoryStream();
+            await source.CopyToAsync(buffer);
+            if (buffer.Length > MaximumImportFileSize)
+                throw new InvalidDataException("Die Importdatei ist größer als 20 MB.");
+
+            var importFile = new ImportFile(files[0].Name, buffer.ToArray());
+            var preview = await Task.Run(async () =>
+                await service.AnalyzeAsync(importFile, vm.Group.Id).ConfigureAwait(false));
+            var dialogVm = new StudentImportDialogViewModel(service, preview, files[0].Name);
+            var dialog = new StudentImportDialog { DataContext = dialogVm };
+            if (!await dialog.ShowDialog<bool>(owner)) return;
+
+            vm.LoadStudents();
+            vm.ParticipationTab.RefreshCurrentGrid();
+            var result = dialogVm.Result!;
+            App.Services.GetRequiredService<NotificationService>().ShowSuccess(
+                $"Teilnehmerimport abgeschlossen: {result.CreatedStudents} neu, "
+                + $"{result.UpdatedStudents} ergänzt, {result.CreatedMemberships} zugeordnet.");
+        }
+        catch (Exception ex) when (ex is ImportFormatException
+                                   or InvalidDataException
+                                   or IOException
+                                   or UnauthorizedAccessException)
+        {
+            App.Services.GetRequiredService<NotificationService>().ShowError(ex.Message);
+        }
+    }
+
     private async Task<bool> ShowWithdrawStudentDialog(StudentSummary student)
     {
         if (DataContext is not GroupDetailViewModel vm || vm.Group is null) return false;