[chore:] implemented symmetric difference (combiner) and its usage

MainWindow.axaml

@@ -186,6 +186,7 @@
                                 </Button>
                                 <Button HorizontalAlignment="Stretch" MinWidth="240"
                                         HorizontalContentAlignment="Center" x:Name="BtnCombineSymmetric"
+                                        Click="BtnCombineSymmetricDifference_OnClick"
                                         Margin="0,0,0,10">
                                     <StackPanel Orientation="Horizontal">
                                         <LucideIcon Kind="SquaresExclude" Width="36" Height="36" />

MainWindow.axaml.cs

@@ -522,4 +522,14 @@ public partial class MainWindow : Window
 
         StartCombine(list, Convert.ToInt32(LstCustomers.SelectedItem.ToString().Split(" - ")[0]), "intersection");
     }
+
+    private void BtnCombineSymmetricDifference_OnClick(object? sender, RoutedEventArgs e)
+    {
+        var list = new List<KasAddressList>();
+        foreach (var item in LstCustomerAdressSets.SelectedItems)
+            list.Add(Settings._instance.addressSets.GetAddressSetByID(
+                Convert.ToInt32(item.ToString().Split(" - ")[0])));
+
+        StartCombine(list, Convert.ToInt32(LstCustomers.SelectedItem.ToString().Split(" - ")[0]), "symdiff");
+    }
 }

Tasks/CombineAddresses.cs

@@ -23,6 +23,7 @@ public class CombineAddresses
             if (type == "difference") return Difference(address_lists);
             if (type == "union") return Union(address_lists);
             if (type == "intersection") return Intersection(address_lists);
+            if (type == "symdiff") return SymmetricDifference(address_lists);
 
             return null;
         });
@@ -205,9 +206,56 @@ public class CombineAddresses
     }
 
 
-    public async Task<KasAddressList> SymmetricDifference()
+    public async Task<KasAddressList> SymmetricDifference(List<KasAddressList> address_lists, Progress progress = null)
     {
-        return null;
+        var result = new KasAddressList("symmetric_difference");
+
+        if (address_lists == null || address_lists.Count == 0)
+            return result;
+
+        var total = address_lists.Sum(l => l.KasPersons.Count);
+        var processed = 0;
+
+        // Wir sammeln alle Personen + zählen, wie oft sie vorkommen
+        var allPersons = new List<(KasPerson person, int count)>();
+
+        foreach (var list in address_lists)
+        foreach (var person in list.KasPersons)
+        {
+            // Prüfen, ob schon vorhanden
+            var existing = allPersons.FirstOrDefault(p => CompareAddresses(p.person, person));
+            if (existing.person != null)
+            {
+                // Falls schon drin → Vorkommen erhöhen
+                var index = allPersons.IndexOf(existing);
+                allPersons[index] = (existing.person, existing.count + 1);
+            }
+            else
+            {
+                // Neu hinzufügen
+                allPersons.Add((person, 1));
+            }
+
+            processed++;
+            var percent = processed / (double)total * 100;
+            var logMessage =
+                $"{percent:F1}%: Person mit {person.refsid} verarbeitet (Zwischengröße {allPersons.Count})";
+
+            if (progress != null)
+            {
+                if (Dispatcher.UIThread.CheckAccess())
+                    progress.LogAction?.Invoke(logMessage);
+                else
+                    Dispatcher.UIThread.Post(() => progress.LogAction?.Invoke(logMessage));
+            }
+        }
+
+        // Nur diejenigen übernehmen, die *genau einmal* vorkamen
+        foreach (var (person, count) in allPersons)
+            if (count == 1)
+                result.KasPersons.Add(person);
+
+        return result;
     }