timetable performance optimization

lib/view/pages/timetable/widgets/timetable_calendar_view.dart

@@ -55,6 +55,13 @@ class TimetableCalendarViewState extends State<TimetableCalendarView> {
   // the same identity checks the cache always used.
   (int, TimetableSettings, List<CustomTimetableEvent>, bool)? _cacheKey;
 
+  // Stable identities let the calendar reuse its per-week pages across
+  // rebuilds; rebuilding these every frame would invalidate that cache.
+  LessonPeriodSchedule? _schedule;
+  Object? _scheduleKey;
+  List<TimeRegion>? _regions;
+  Object? _regionsKey;
+
   DateTime _initialDisplayDate() => DateTime.now().addDays(2);
 
   /// Snaps the calendar back to the current week. Exposed so host pages can
@@ -90,7 +97,37 @@ class TimetableCalendarViewState extends State<TimetableCalendarView> {
     ).build();
   }
 
-  bool _isCrossedOut(Appointment appointment) {
+  LessonPeriodSchedule _scheduleFor(TimetableState state) {
+    if (_schedule != null && identical(_scheduleKey, state.timegrid)) {
+      return _schedule!;
+    }
+    _scheduleKey = state.timegrid;
+    return _schedule = LessonPeriodSchedule.fromState(state);
+  }
+
+  List<TimeRegion> _regionsFor(
+    TimetableState state,
+    LessonPeriodSchedule schedule,
+  ) {
+    final theme = Theme.of(context);
+    final key = (
+      state.schoolHolidays,
+      schedule,
+      theme.colorScheme,
+      theme.disabledColor,
+      DateTime.now().dateOnly,
+    );
+    if (_regions != null && key == _regionsKey) return _regions!;
+    _regionsKey = key;
+    return _regions = SpecialRegionsBuilder(
+      holidays: state.schoolHolidays!,
+      schedule: schedule,
+      colorScheme: theme.colorScheme,
+      disabledColor: theme.disabledColor,
+    ).build();
+  }
+
+  static bool _isCrossedOut(Appointment appointment) {
     final id = appointment.id;
     if (id is LessonAppointment) return id.entry.status == 'CANCELLED';
     return false;
@@ -104,14 +141,9 @@ class TimetableCalendarViewState extends State<TimetableCalendarView> {
     // transient null can never crash the build.
     if (state.schoolHolidays == null) return const SizedBox.shrink();
 
-    final schedule = LessonPeriodSchedule.fromState(state);
+    final schedule = _scheduleFor(state);
     final appointments = _appointments(state);
-    final regions = SpecialRegionsBuilder(
-      holidays: state.schoolHolidays!,
-      schedule: schedule,
-      colorScheme: Theme.of(context).colorScheme,
-      disabledColor: Theme.of(context).disabledColor,
-    ).build();
+    final regions = _regionsFor(state, schedule);
 
     final capabilities = context.watch<CapabilitiesCubit>();
     final (minDate, maxDate) = _scrollBounds(
@@ -171,8 +203,8 @@ class TimetableCalendarViewState extends State<TimetableCalendarView> {
               ? state.accessibleEndDate!
               : baseMax)
         : baseMax;
-    final today = _startOfDay(DateTime.now());
-    final todayMonday = _mondayOf(today);
+    final today = DateTime.now().dateOnly;
+    final todayMonday = today.mondayOfWeek;
     final currentWeekEnd = todayMonday.addDays(DateTime.daysPerWeek - 1);
     final capMin = pastDays == null
         ? null
@@ -202,11 +234,6 @@ class TimetableCalendarViewState extends State<TimetableCalendarView> {
     return (mondayMin, finalMax);
   }
 
-  static DateTime _mondayOf(DateTime d) =>
-      _startOfDay(d.subtractDays(d.weekday - 1));
-
-  static DateTime _startOfDay(DateTime d) => DateTime(d.year, d.month, d.day);
-
   static DateTime _earlier(DateTime a, DateTime b) => a.isBefore(b) ? a : b;
 
   static DateTime _later(DateTime a, DateTime b) => a.isAfter(b) ? a : b;