introduce drawer header

lib/drawer/drawer.dart

@@ -20,6 +20,18 @@ class _ClassDrawerState extends State<ClassDrawer> {
   late final searchTextController = TextEditingController(text: activeQuery);
 
   List<Class> get availableClasses => widget.appContext.classes ?? [];
+  Set<Class> get selectedClasses =>
+      widget.appContext.profile.value!.selectedClasses
+          .map((id) => availableClasses.firstWhere((cls) => cls.id == id))
+          .toSet();
+
+  String get headerText {
+    final classes = selectedClasses;
+    final selectedNames =
+        classes.map((cls) => cls.codeWithoutFaculty).join(', ');
+
+    return selectedNames;
+  }
 
   @override
   void initState() {
@@ -109,13 +121,26 @@ class _ClassDrawerState extends State<ClassDrawer> {
     return Drawer(
       child: Column(
         children: [
-          Padding(
-            padding: const EdgeInsets.all(8.0),
-            child: TextField(
-              controller: searchTextController,
-              decoration: const InputDecoration(
-                hintText: 'Suche...',
-              ),
+          DrawerHeader(
+            child: Column(
+              mainAxisAlignment: MainAxisAlignment.end,
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(
+                  headerText,
+                  style: TextStyle(
+                    // fontWeight: FontWeight.bold,
+                    color: Theme.of(context).primaryColor,
+                  ),
+                ),
+                Expanded(child: Container()),
+                TextField(
+                  controller: searchTextController,
+                  decoration: const InputDecoration(
+                    hintText: 'Suche...',
+                  ),
+                ),
+              ],
             ),
           ),
           Expanded(