Neue Funktion Schüler austragen statt aus Kurs löschen.

LehrerApp.Desktop/ViewModels/Groups/ParticipationViewModels.cs

@@ -2,6 +2,7 @@ using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using LehrerApp.Core.Interfaces;
 using LehrerApp.Core.Models;
+using LehrerApp.Core.Services;
 using System.Collections.ObjectModel;
 using System.Collections.Generic;
 
@@ -140,7 +141,7 @@ public partial class ParticipationTabViewModel : ObservableObject
         foreach (var s in students)
         {
             var membership = memberships.FirstOrDefault(e => e.StudentId == s.Id);
-            if (membership is not null && !IsMemberAtDate(membership, sessionDate))
+            if (membership is not null && !GroupMembershipService.IsActiveOn(membership, sessionDate))
                 continue;
 
             var entry = entries.FirstOrDefault(e => e.StudentId == s.Id)
@@ -157,15 +158,6 @@ public partial class ParticipationTabViewModel : ObservableObject
         RebuildColumnsSignal++;
     }
 
-    private static bool IsMemberAtDate(GroupMembership membership, DateOnly date) => membership.Period switch
-    {
-        MembershipPeriod.H1Only => date.Month >= 8 || date.Month <= 1,
-        MembershipPeriod.H2Only => date.Month >= 2 && date.Month <= 7,
-        MembershipPeriod.Custom => (membership.JoinedAt is null || date >= membership.JoinedAt.Value)
-                                && (membership.LeftAt  is null || date <= membership.LeftAt.Value),
-        _                       => true,
-    };
-
     private void SaveRating(Guid sessionId, Guid studentId, string key, int? value)
     {
         var entry = _entries.GetBySessionAndStudent(sessionId, studentId)