feat: Importkonflikte gesammelt übernehmen

LehrerApp.Desktop/ViewModels/Students/StudentImportDialogViewModel.cs

@@ -30,6 +30,7 @@ public partial class StudentImportDialogViewModel : ObservableObject
     public ObservableCollection<StudentImportConflictItem> Conflicts { get; } = [];
     public bool HasMessages => Messages.Count > 0;
     public bool HasConflicts => Conflicts.Count > 0;
+    public bool CanUseExistingForAll => Conflicts.Any(conflict => conflict.HasSingleExistingStudentOption);
     public bool IsReadyWithoutConflicts => !HasConflicts && _preview.CanApply;
     public bool HasBlockingErrors => !_preview.CanApply;
     public bool CanApply => _preview.CanApply && !IsBusy;
@@ -65,6 +66,16 @@ public partial class StudentImportDialogViewModel : ObservableObject
         .ToList()
         .AsReadOnly();
 
+    /// <summary>
+    /// Wählt für alle eindeutigen Schüler-Konflikte den jeweils vorhandenen Datensatz.
+    /// Mehrdeutige Treffer und Lerngruppen-Konflikte bleiben unverändert.
+    /// </summary>
+    public void UseExistingForAll()
+    {
+        foreach (var conflict in Conflicts)
+            conflict.TrySelectSingleExistingStudent();
+    }
+
     public async Task<bool> TryApplyAsync()
     {
         Error = "";
@@ -116,6 +127,8 @@ public sealed class StudentImportMessageItem
 
 public partial class StudentImportConflictItem : ObservableObject
 {
+    private const string ExistingStudentOptionPrefix = "existing:";
+
     [ObservableProperty] private StudentImportConflictOptionItem _selectedOption;
 
     public string Id { get; }
@@ -125,6 +138,11 @@ public partial class StudentImportConflictItem : ObservableObject
     public string ExistingValue { get; }
     public string SourceReference { get; }
     public IReadOnlyList<StudentImportConflictOptionItem> Options { get; }
+    public bool HasSingleExistingStudentOption => ExistingStudentOptions.Count == 1;
+
+    private IReadOnlyList<StudentImportConflictOptionItem> ExistingStudentOptions => Options
+        .Where(option => option.Id.StartsWith(ExistingStudentOptionPrefix, StringComparison.Ordinal))
+        .ToList();
 
     public StudentImportConflictItem(ImportConflict conflict)
     {
@@ -141,6 +159,14 @@ public partial class StudentImportConflictItem : ObservableObject
             .AsReadOnly();
         _selectedOption = Options.First(option => option.Id == conflict.DefaultOptionId);
     }
+
+    public bool TrySelectSingleExistingStudent()
+    {
+        var options = ExistingStudentOptions;
+        if (options.Count != 1) return false;
+        SelectedOption = options[0];
+        return true;
+    }
 }
 
 public sealed record StudentImportConflictOptionItem(