timetable performance optimization

lib/state/app/modules/timetable/bloc/timetable_bloc.dart

@@ -36,7 +36,7 @@ class TimetableBloc
   TimetableState fromNothing() {
     final reference = DateTime.now().addDays(2);
     return TimetableState(
-      startDate: _startOfWeek(reference),
+      startDate: reference.mondayOfWeek,
       endDate: _endOfWeek(reference),
     );
   }
@@ -49,7 +49,7 @@ class TimetableBloc
     final stored = TimetableState.fromJson(json);
     final reference = DateTime.now().addDays(2);
     return stored.copyWith(
-      startDate: _startOfWeek(reference),
+      startDate: reference.mondayOfWeek,
       endDate: _endOfWeek(reference),
       accessibleStartDate: null,
       accessibleEndDate: null,
@@ -99,7 +99,7 @@ class TimetableBloc
 
   void resetWeek() {
     final reference = DateTime.now().addDays(2);
-    changeWeek(_startOfWeek(reference), _endOfWeek(reference));
+    changeWeek(reference.mondayOfWeek, _endOfWeek(reference));
   }
 
   void refresh() => fetch();
@@ -245,19 +245,7 @@ class TimetableBloc
   }
 
   void _writeWeekToCache(DateTime weekStart, TimetableGetWeekResponse week) {
-    final key = weekStart.weekKey();
-    add(
-      Emit((s) {
-        final updated = Map<String, TimetableGetWeekResponse>.of(s.weekCache);
-        updated[key] = week;
-        return s.copyWith(weekCache: updated, dataVersion: s.dataVersion + 1);
-      }),
-    );
-  }
-
-  static DateTime _startOfWeek(DateTime reference) {
-    final monday = reference.subtractDays(reference.weekday - 1);
-    return DateTime(monday.year, monday.month, monday.day);
+    add(Emit((s) => s.withFetchedWeek(weekStart, week)));
   }
 
   static DateTime _endOfWeek(DateTime reference) {

lib/state/app/modules/timetable/bloc/timetable_state.dart

@@ -7,6 +7,7 @@ import '../../../../../api/marianumconnect/queries/timetable_get_subjects/timeta
 import '../../../../../api/marianumconnect/queries/timetable_get_timegrid/timetable_get_timegrid_response.dart';
 import '../../../../../api/marianumconnect/queries/timetable_get_week/timetable_get_week_response.dart';
 import '../../../../../api/mhsl/custom_timetable_event/get/get_custom_timetable_event_response.dart';
+import 'week_cache.dart';
 
 part 'timetable_state.freezed.dart';
 part 'timetable_state.g.dart';
@@ -40,6 +41,23 @@ abstract class TimetableState with _$TimetableState {
   Iterable<McTimetableEntry> getAllKnownLessons() =>
       weekCache.values.expand((response) => response.entries);
 
+  /// This state with [week] cached, or `this` when its content is unchanged
+  /// (so the emit is dropped as equal).
+  TimetableState withFetchedWeek(
+    DateTime weekStart,
+    TimetableGetWeekResponse week,
+  ) {
+    final updated = mergeWeekIntoCache(
+      weekCache,
+      weekStart,
+      week,
+      viewedWeekStart: startDate,
+      now: DateTime.now(),
+    );
+    if (updated == null) return this;
+    return copyWith(weekCache: updated, dataVersion: dataVersion + 1);
+  }
+
   bool get hasReferenceData =>
       rooms != null &&
       subjects != null &&

lib/state/app/modules/timetable/bloc/week_cache.dart

@@ -0,0 +1,45 @@
+import 'package:collection/collection.dart';
+
+import '../../../../../api/marianumconnect/queries/timetable_get_week/timetable_get_week_response.dart';
+import '../../../../../extensions/date_time.dart';
+
+/// Weeks kept around the viewed week and around today's week. Everything
+/// further away is dropped: every state emit re-serializes the whole cache for
+/// HydratedBloc and the calendar rebuilds its appointments from all of it, so
+/// an unbounded cache makes week swipes slower the longer the app is used.
+const int kWeekCacheRadius = 4;
+
+/// Returns the cache with [week] stored under [weekStart], pruned to the
+/// weeks near [viewedWeekStart] or [now]. Returns null when the stored week
+/// already has identical content, so callers can skip the emit entirely.
+Map<String, TimetableGetWeekResponse>? mergeWeekIntoCache(
+  Map<String, TimetableGetWeekResponse> cache,
+  DateTime weekStart,
+  TimetableGetWeekResponse week, {
+  required DateTime viewedWeekStart,
+  required DateTime now,
+}) {
+  final key = weekStart.weekKey();
+  final existing = cache[key];
+  if (existing != null &&
+      const DeepCollectionEquality().equals(existing.toJson(), week.toJson())) {
+    return null;
+  }
+
+  final viewedMonday = viewedWeekStart.mondayOfWeek;
+  final todayMonday = now.mondayOfWeek;
+  bool isNear(DateTime monday, DateTime anchor) =>
+      monday.difference(anchor).inDays.abs() <= kWeekCacheRadius * 7 + 1;
+
+  final updated = <String, TimetableGetWeekResponse>{};
+  for (final entry in cache.entries) {
+    final monday = DateTime.tryParse(entry.key);
+    if (monday == null ||
+        isNear(monday, viewedMonday) ||
+        isNear(monday, todayMonday)) {
+      updated[entry.key] = entry.value;
+    }
+  }
+  updated[key] = week;
+  return updated;
+}