feat: Implement upcoming manga calendar feature

- Added UpcomingUIModel for managing upcoming manga list items with headers and items.
- Introduced CalendarDay widget to display individual days with event indicators.
- Created CalendarHeader widget for navigating between months.
- Developed CalendarIndicator for visualizing events on specific days.
- Implemented UpcomingCalendar to manage the calendar view and event loading.
- Added UpcomingItem widget for displaying individual upcoming manga with cover images.
- Introduced FetchInterval utility to calculate fetch intervals based on chapter upload dates.
- Refactored updateMangaDetail to utilize FetchInterval for smart update days.
- Enhanced MedianExtension to ensure correct median calculation.
- Removed unused imports and commented-out code for cleaner implementation.

lib/modules/calendar/calendar_screen.dart

@@ -1,24 +1,21 @@
-import 'dart:typed_data';
-
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 import 'package:isar_community/isar.dart';
 import 'package:mangayomi/models/chapter.dart';
 import 'package:mangayomi/models/manga.dart';
+import 'package:mangayomi/modules/calendar/models/upcoming_ui_model.dart';
 import 'package:mangayomi/modules/calendar/providers/calendar_provider.dart';
+import 'package:mangayomi/modules/calendar/widgets/upcoming_calendar.dart';
+import 'package:mangayomi/modules/calendar/widgets/upcoming_item.dart'
+    as widgets;
 import 'package:mangayomi/modules/more/settings/reader/providers/reader_state_provider.dart';
-import 'package:mangayomi/modules/widgets/custom_extended_image_provider.dart';
-import 'package:mangayomi/modules/widgets/custom_sliver_grouped_list_view.dart';
 import 'package:mangayomi/modules/widgets/progress_center.dart';
 import 'package:mangayomi/providers/l10n_providers.dart';
-import 'package:mangayomi/utils/constant.dart';
 import 'package:mangayomi/utils/date.dart';
-import 'package:mangayomi/utils/extensions/build_context_extensions.dart';
+import 'package:mangayomi/utils/fetch_interval.dart';
-import 'package:mangayomi/utils/headers.dart';
 import 'package:mangayomi/utils/item_type_filters.dart';
 import 'package:mangayomi/utils/item_type_localization.dart';
-import 'package:table_calendar/table_calendar.dart';
 
 class CalendarScreen extends ConsumerStatefulWidget {
   final ItemType? itemType;
@@ -29,18 +26,15 @@ class CalendarScreen extends ConsumerStatefulWidget {
 }
 
 class _CalendarScreenState extends ConsumerState<CalendarScreen> {
-  late final ValueNotifier<List<Manga>> _selectedEntries;
-  CalendarFormat _calendarFormat = CalendarFormat.month;
-  RangeSelectionMode _rangeSelectionMode = RangeSelectionMode.toggledOff;
-  final firstDay = DateTime.now();
-  final lastDay = DateTime.now().add(const Duration(days: 1000));
-  DateTime _focusedDay = DateTime.now();
-  DateTime? _selectedDay;
-  DateTime? _rangeStart;
-  DateTime? _rangeEnd;
   late ItemType? itemType;
   late List<ItemType> _visibleTypes;
 
+  /// Currently displayed year/month on the calendar.
+  late DateTime _selectedYearMonth;
+
+  /// Header GlobalKeys so clicking a calendar day scrolls to that date.
+  final Map<DateTime, GlobalKey> _headerKeys = {};
+
   @override
   void initState() {
     super.initState();
@@ -51,122 +45,54 @@ class _CalendarScreenState extends ConsumerState<CalendarScreen> {
     } else {
       itemType = _visibleTypes.isNotEmpty ? _visibleTypes.first : null;
     }
-    _selectedDay = _focusedDay;
+    final now = DateTime.now();
-    _selectedEntries = ValueNotifier([]);
+    _selectedYearMonth = DateTime(now.year, now.month);
-  }
-
-  @override
-  void dispose() {
-    _selectedEntries.dispose();
-    super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
     final l10n = context.l10n;
-    final locale = ref.watch(l10nLocaleStateProvider);
     final data = ref.watch(getCalendarStreamProvider(itemType: itemType));
+
     return Scaffold(
-      appBar: AppBar(title: Text(l10n.calendar)),
+      appBar: AppBar(
+        title: Text(l10n.calendar),
+        actions: [
+          IconButton(
+            icon: const Icon(Icons.help_outline),
+            tooltip: l10n.calendar_info,
+            onPressed: () {
+              showDialog(
+                context: context,
+                builder: (ctx) => AlertDialog(
+                  content: Text(l10n.calendar_info),
+                  actions: [
+                    TextButton(
+                      onPressed: () => Navigator.of(ctx).pop(),
+                      child: Text(MaterialLocalizations.of(ctx).okButtonLabel),
+                    ),
+                  ],
+                ),
+              );
+            },
+          ),
+        ],
+      ),
       body: data.when(
-        data: (data) {
+        data: (mangaList) {
-          if (_selectedDay != null) {
+          final upcomingData = _buildUpcomingData(mangaList);
-            _selectedEntries.value = _getEntriesForDay(_selectedDay!, data);
+          final items = upcomingData.items;
+          final events = upcomingData.events;
+
+          // Build header keys
+          _headerKeys.clear();
+          for (final date in upcomingData.headerIndexes.keys) {
+            _headerKeys[date] = GlobalKey();
           }
-          return Padding(
+
-            padding: const EdgeInsets.symmetric(horizontal: 15),
+          return _buildContent(items, events);
-            child: CustomScrollView(
-              slivers: [
-                SliverToBoxAdapter(
-                  child: Column(
-                    children: [
-                      _buildWarningTile(context),
-                      Padding(
-                        padding: const EdgeInsets.symmetric(horizontal: 15),
-                        child: Row(
-                          children: [
-                            Expanded(
-                              child: SegmentedButton(
-                                emptySelectionAllowed: true,
-                                showSelectedIcon: false,
-                                style: TextButton.styleFrom(
-                                  shape: RoundedRectangleBorder(
-                                    borderRadius: BorderRadius.circular(50),
-                                  ),
-                                ),
-                                segments: _visibleTypes.map((type) {
-                                  return ButtonSegment(
-                                    value: type.index,
-                                    label: Padding(
-                                      padding: const EdgeInsets.all(12),
-                                      child: Text(type.localized(l10n)),
-                                    ),
-                                  );
-                                }).toList(),
-                                selected: {itemType?.index},
-                                onSelectionChanged: (newSelection) {
-                                  if (newSelection.isNotEmpty &&
-                                      newSelection.first != null) {
-                                    setState(() {
-                                      itemType =
-                                          ItemType.values[newSelection.first!];
-                                    });
-                                  }
-                                },
-                              ),
-                            ),
-                          ],
-                        ),
-                      ),
-                      _buildCalendar(data, locale),
-                      const SizedBox(height: 15),
-                    ],
-                  ),
-                ),
-                ValueListenableBuilder<List<Manga>>(
-                  valueListenable: _selectedEntries,
-                  builder: (context, value, _) {
-                    return CustomSliverGroupedListView<Manga, String>(
-                      elements: value,
-                      groupBy: (element) {
-                        return dateFormat(
-                          _selectedDay?.millisecondsSinceEpoch.toString() ??
-                              DateTime.now()
-                                  .add(Duration(days: element.smartUpdateDays!))
-                                  .millisecondsSinceEpoch
-                                  .toString(),
-                          context: context,
-                          ref: ref,
-                          forHistoryValue: true,
-                          useRelativeTimesTamps: false,
-                        );
-                      },
-                      groupSeparatorBuilder: (String groupByValue) => Padding(
-                        padding: const EdgeInsets.only(bottom: 8, left: 12),
-                        child: Row(
-                          children: [
-                            Text(
-                              "${dateFormat(null, context: context, stringDate: groupByValue, ref: ref, useRelativeTimesTamps: true, showInDaysFuture: true)} - ${dateFormat(null, context: context, stringDate: groupByValue, ref: ref, useRelativeTimesTamps: false)}",
-                            ),
-                          ],
-                        ),
-                      ),
-                      itemBuilder: (context, element) {
-                        return CalendarListTileWidget(
-                          manga: element,
-                          selectedDay: _selectedDay,
-                        );
-                      },
-                      order: GroupedListOrder.ASC,
-                    );
-                  },
-                ),
-                SliverToBoxAdapter(child: const SizedBox(height: 15)),
-              ],
-            ),
-          );
         },
-        error: (Object error, StackTrace stackTrace) {
+        error: (error, stackTrace) {
           return Center(
             child: Padding(
               padding: const EdgeInsets.all(8.0),
@@ -174,254 +100,253 @@ class _CalendarScreenState extends ConsumerState<CalendarScreen> {
             ),
           );
         },
-        loading: () {
+        loading: () => const ProgressCenter(),
-          return const ProgressCenter();
-        },
       ),
     );
   }
 
-  Widget _buildWarningTile(BuildContext context) {
+  Widget _buildContent(List<UpcomingUIModel> items, Map<DateTime, int> events) {
-    return ListTile(
+    final l10n = context.l10n;
-      title: Padding(
+
-        padding: const EdgeInsets.symmetric(vertical: 3),
+    return CustomScrollView(
-        child: Row(
+      slivers: [
-          children: [
+        // Item type selector
-            Icon(Icons.warning_amber_outlined, color: context.secondaryColor),
+        if (_visibleTypes.length > 1)
-            const SizedBox(width: 10),
+          SliverToBoxAdapter(
-            Flexible(
+            child: Padding(
-              child: Text(
+              padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
-                context.l10n.calendar_info,
+              child: SegmentedButton(
-                softWrap: true,
+                emptySelectionAllowed: true,
-                overflow: TextOverflow.clip,
+                showSelectedIcon: false,
-                style: TextStyle(fontSize: 13, color: context.secondaryColor),
+                style: TextButton.styleFrom(
+                  shape: RoundedRectangleBorder(
+                    borderRadius: BorderRadius.circular(50),
+                  ),
+                ),
+                segments: _visibleTypes.map((type) {
+                  return ButtonSegment(
+                    value: type.index,
+                    label: Padding(
+                      padding: const EdgeInsets.all(12),
+                      child: Text(type.localized(l10n)),
+                    ),
+                  );
+                }).toList(),
+                selected: {itemType?.index},
+                onSelectionChanged: (newSelection) {
+                  if (newSelection.isNotEmpty && newSelection.first != null) {
+                    setState(() {
+                      itemType = ItemType.values[newSelection.first!];
+                    });
+                  }
+                },
               ),
             ),
-          ],
+          ),
+
+        SliverToBoxAdapter(
+          child: UpcomingCalendar(
+            selectedYearMonth: _selectedYearMonth,
+            events: events,
+            setSelectedYearMonth: (yearMonth) {
+              setState(() {
+                _selectedYearMonth = yearMonth;
+              });
+            },
+            onClickDay: (date) => _scrollToDate(date),
+          ),
         ),
-      ),
+
+        const SliverToBoxAdapter(child: SizedBox(height: 8)),
+
+        // All upcoming items (date headers + manga tiles)
+        if (items.isEmpty)
+          SliverToBoxAdapter(
+            child: Padding(
+              padding: const EdgeInsets.all(32),
+              child: Center(
+                child: Text(
+                  l10n.calendar_no_data,
+                  style: Theme.of(context).textTheme.bodyLarge?.copyWith(
+                    color: Theme.of(context).colorScheme.onSurfaceVariant,
+                  ),
+                ),
+              ),
+            ),
+          )
+        else
+          SliverList(
+            delegate: SliverChildBuilderDelegate((context, index) {
+              final item = items[index];
+              return switch (item) {
+                UpcomingHeader(:final date, :final mangaCount) => _DateHeading(
+                  key: _headerKeys[date],
+                  date: date,
+                  mangaCount: mangaCount,
+                ),
+                UpcomingItem(:final manga) => widgets.UpcomingItem(
+                  manga: manga,
+                  onTap: () =>
+                      context.push('/manga-reader/detail', extra: manga.id),
+                ),
+              };
+            }, childCount: items.length),
+          ),
+
+        const SliverToBoxAdapter(child: SizedBox(height: 16)),
+      ],
     );
   }
 
-  Widget _buildCalendar(List<Manga> data, Locale locale) {
+  /// Scrolls to the header for [date] using Scrollable.ensureVisible.
-    return TableCalendar(
+  void _scrollToDate(DateTime date) {
-      firstDay: firstDay,
+    final key = _headerKeys[date];
-      lastDay: lastDay,
+    if (key?.currentContext != null) {
-      focusedDay: _focusedDay,
+      Scrollable.ensureVisible(
-      locale: locale.toLanguageTag(),
+        key!.currentContext!,
-      selectedDayPredicate: (day) => isSameDay(_selectedDay, day),
+        duration: const Duration(milliseconds: 300),
-      rangeStartDay: _rangeStart,
+        curve: Curves.easeInOut,
-      rangeEndDay: _rangeEnd,
+      );
-      calendarFormat: _calendarFormat,
+    }
-      rangeSelectionMode: _rangeSelectionMode,
+  }
-      eventLoader: (day) => _getEntriesForDay(day, data),
+
-      startingDayOfWeek: StartingDayOfWeek.monday,
+  /// Builds the upcoming UI model list, events map, and header indexes
-      calendarStyle: CalendarStyle(
+  /// from the raw manga list.
-        outsideDaysVisible: true,
+  _UpcomingData _buildUpcomingData(List<Manga> mangaList) {
-        weekendTextStyle: TextStyle(color: context.primaryColor),
+    // 1. Compute expected next update date for each manga
-      ),
+    final List<({Manga manga, DateTime expectedDate})> mangaWithDates = [];
-      onDaySelected: (selectedDay, focusedDay) =>
+    for (final manga in mangaList) {
-          _onDaySelected(selectedDay, focusedDay, data),
+      final expectedDate = _computeExpectedDate(manga);
-      onRangeSelected: (start, end, focusedDay) =>
+      if (expectedDate != null) {
-          _onRangeSelected(start, end, focusedDay, data),
+        mangaWithDates.add((manga: manga, expectedDate: expectedDate));
-      onFormatChanged: (format) {
+      }
-        if (_calendarFormat != format) {
+    }
-          setState(() => _calendarFormat = format);
+
+    // 2. Sort by date ascending
+    mangaWithDates.sort((a, b) => a.expectedDate.compareTo(b.expectedDate));
+
+    // 3. Group by date and build UI models with headers
+    final List<UpcomingUIModel> items = [];
+    final Map<DateTime, int> events = {};
+    final Map<DateTime, int> headerIndexes = {};
+
+    DateTime? lastDate;
+    int countForGroup = 0;
+    int headerIndex = -1;
+
+    for (final entry in mangaWithDates) {
+      final date = DateTime(
+        entry.expectedDate.year,
+        entry.expectedDate.month,
+        entry.expectedDate.day,
+      );
+
+      if (lastDate == null || date != lastDate) {
+        // Finalize count for previous group
+        if (headerIndex >= 0) {
+          final prevHeader = items[headerIndex] as UpcomingHeader;
+          items[headerIndex] = UpcomingHeader(
+            date: prevHeader.date,
+            mangaCount: countForGroup,
+          );
+          events[prevHeader.date] = countForGroup;
         }
-      },
+
-      onPageChanged: (focusedDay) => _focusedDay = focusedDay,
+        // Start new group
+        headerIndex = items.length;
+        headerIndexes[date] = headerIndex;
+        items.add(UpcomingHeader(date: date, mangaCount: 0));
+        countForGroup = 0;
+        lastDate = date;
+      }
+
+      items.add(UpcomingItem(manga: entry.manga, expectedDate: date));
+      countForGroup++;
+    }
+
+    // Finalize last group
+    if (headerIndex >= 0 && headerIndex < items.length) {
+      final lastHeader = items[headerIndex] as UpcomingHeader;
+      items[headerIndex] = UpcomingHeader(
+        date: lastHeader.date,
+        mangaCount: countForGroup,
+      );
+      events[lastHeader.date] = countForGroup;
+    }
+
+    return _UpcomingData(
+      items: items,
+      events: events,
+      headerIndexes: headerIndexes,
     );
   }
 
-  final Map<String, List<Manga>> _dayCache = {};
+  /// Computes the expected next update date for a mang
-
+  DateTime? _computeExpectedDate(Manga manga) {
-  List<Manga> _getEntriesForDay(DateTime day, List<Manga> data) {
+    if (manga.smartUpdateDays == null || manga.smartUpdateDays! <= 0) {
-    final key = "${day.year}-${day.month}-${day.day}";
+      return null;
-    if (_dayCache.containsKey(key)) return _dayCache[key]!;
-    final result = data.where((e) {
-      final lastChapter = e.chapters
-          .filter()
-          .sortByDateUploadDesc()
-          .findFirstSync();
-      final lastDate = int.tryParse(lastChapter?.dateUpload ?? "");
-      final start = lastDate != null
-          ? DateTime.fromMillisecondsSinceEpoch(lastDate)
-          : DateTime.now();
-      final temp = start.add(Duration(days: e.smartUpdateDays!));
-      return temp.year == day.year &&
-          temp.month == day.month &&
-          temp.day == day.day;
-    }).toList();
-    _dayCache[key] = result;
-    return result;
-  }
-
-  List<Manga> _getEntriesForRange(
-    DateTime start,
-    DateTime end,
-    List<Manga> data,
-  ) {
-    final days = _daysInRange(start, end);
-
-    return [for (final d in days) ..._getEntriesForDay(d, data)];
-  }
-
-  void _onDaySelected(
-    DateTime selectedDay,
-    DateTime focusedDay,
-    List<Manga> data,
-  ) {
-    if (!isSameDay(_selectedDay, selectedDay)) {
-      setState(() {
-        _selectedDay = selectedDay;
-        _focusedDay = focusedDay;
-        _rangeStart = null;
-        _rangeEnd = null;
-        _rangeSelectionMode = RangeSelectionMode.toggledOff;
-      });
-
-      _selectedEntries.value = _getEntriesForDay(selectedDay, data);
     }
-  }
+    final lastChapter = manga.chapters
-
+        .filter()
-  void _onRangeSelected(
+        .sortByDateUploadDesc()
-    DateTime? start,
+        .findFirstSync();
-    DateTime? end,
+    final lastChapterMs = int.tryParse(lastChapter?.dateUpload ?? '');
-    DateTime focusedDay,
+    return FetchInterval.computeExpectedDate(
-    List<Manga> data,
+      lastChapterDateMs: lastChapterMs,
-  ) {
+      lastUpdateMs: manga.lastUpdate,
-    setState(() {
+      interval: manga.smartUpdateDays,
-      _selectedDay = null;
-      _focusedDay = focusedDay;
-      _rangeStart = start;
-      _rangeEnd = end;
-      _rangeSelectionMode = RangeSelectionMode.toggledOn;
-    });
-
-    if (start != null && end != null) {
-      _selectedEntries.value = _getEntriesForRange(start, end, data);
-    } else if (start != null) {
-      _selectedEntries.value = _getEntriesForDay(start, data);
-    } else if (end != null) {
-      _selectedEntries.value = _getEntriesForDay(end, data);
-    }
-  }
-
-  List<DateTime> _daysInRange(DateTime first, DateTime last) {
-    final dayCount = last.difference(first).inDays + 1;
-    return List.generate(
-      dayCount,
-      (index) => DateTime.utc(first.year, first.month, first.day + index),
     );
   }
 }
 
-class CalendarListTileWidget extends ConsumerWidget {
+/// Internal data class for computed upcoming state.
-  final Manga manga;
+class _UpcomingData {
-  final DateTime? selectedDay;
+  final List<UpcomingUIModel> items;
-  const CalendarListTileWidget({
+  final Map<DateTime, int> events;
-    required this.manga,
+  final Map<DateTime, int> headerIndexes;
-    required this.selectedDay,
+
-    super.key,
+  const _UpcomingData({
+    required this.items,
+    required this.events,
+    required this.headerIndexes,
   });
+}
+
+/// Date heading with relative date text + count badge.
+class _DateHeading extends ConsumerWidget {
+  final DateTime date;
+  final int mangaCount;
+
+  const _DateHeading({super.key, required this.date, required this.mangaCount});
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    return Material(
+    final theme = Theme.of(context);
-      borderRadius: BorderRadius.circular(5),
+
-      color: Colors.transparent,
+    return Padding(
-      clipBehavior: Clip.antiAliasWithSaveLayer,
+      padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 4),
-      child: InkWell(
+      child: Row(
-        onTap: () => context.push('/manga-reader/detail', extra: manga.id),
+        children: [
-        onLongPress: () {},
+          Text(
-        onSecondaryTap: () {},
+            dateFormat(
-        child: Padding(
+              date.millisecondsSinceEpoch.toString(),
-          padding: const EdgeInsets.symmetric(horizontal: 13, vertical: 5),
+              context: context,
-          child: Container(
+              ref: ref,
-            height: 45,
+              useRelativeTimesTamps: true,
-            decoration: BoxDecoration(borderRadius: BorderRadius.circular(5)),
+              showInDaysFuture: true,
-            child: Row(
+            ),
-              mainAxisAlignment: MainAxisAlignment.spaceBetween,
+            style: theme.textTheme.bodyMedium?.copyWith(
-              children: [
+              fontWeight: FontWeight.w600,
-                Expanded(
+              color: theme.colorScheme.onSurfaceVariant,
-                  child: Row(
-                    children: [
-                      ClipRRect(
-                        borderRadius: BorderRadius.circular(5),
-                        child: Material(
-                          child: GestureDetector(
-                            onTap: () {
-                              context.push(
-                                '/manga-reader/detail',
-                                extra: manga.id,
-                              );
-                            },
-                            child: Ink.image(
-                              fit: BoxFit.cover,
-                              width: 40,
-                              height: 45,
-                              image: manga.customCoverImage != null
-                                  ? MemoryImage(
-                                          manga.customCoverImage as Uint8List,
-                                        )
-                                        as ImageProvider
-                                  : CustomExtendedNetworkImageProvider(
-                                      toImgUrl(
-                                        manga.customCoverFromTracker ??
-                                            manga.imageUrl!,
-                                      ),
-                                      headers: ref.watch(
-                                        headersProvider(
-                                          source: manga.source!,
-                                          lang: manga.lang!,
-                                          sourceId: manga.sourceId,
-                                        ),
-                                      ),
-                                    ),
-                              child: InkWell(child: Container()),
-                            ),
-                          ),
-                        ),
-                      ),
-                      Expanded(
-                        child: Padding(
-                          padding: const EdgeInsets.symmetric(horizontal: 10),
-                          child: Column(
-                            mainAxisAlignment: MainAxisAlignment.center,
-                            crossAxisAlignment: CrossAxisAlignment.start,
-                            children: [
-                              Text(
-                                manga.name!,
-                                overflow: TextOverflow.ellipsis,
-                                style: TextStyle(
-                                  fontSize: 14,
-                                  color: Theme.of(
-                                    context,
-                                  ).textTheme.bodyLarge!.color,
-                                ),
-                              ),
-                              Text(
-                                context.l10n.n_chapters(
-                                  manga.chapters.countSync(),
-                                ),
-                                overflow: TextOverflow.ellipsis,
-                                style: TextStyle(
-                                  fontSize: 11,
-                                  fontStyle: FontStyle.italic,
-                                  color: context.secondaryColor,
-                                ),
-                              ),
-                            ],
-                          ),
-                        ),
-                      ),
-                    ],
-                  ),
-                ),
-              ],
             ),
           ),
-        ),
+          const SizedBox(width: 8),
+          Badge(
+            backgroundColor: theme.colorScheme.primary,
+            textColor: theme.colorScheme.onPrimary,
+            label: Text('$mangaCount'),
+          ),
+        ],
       ),
     );
   }

lib/modules/calendar/models/upcoming_ui_model.dart

@@ -0,0 +1,41 @@
+import 'package:mangayomi/models/manga.dart';
+
+/// Sealed model for upcoming manga list items.
+///
+/// The list alternates between [Header] (date separator with count badge)
+/// and [Item] (individual manga) entries.
+sealed class UpcomingUIModel {
+  const UpcomingUIModel();
+}
+
+class UpcomingHeader extends UpcomingUIModel {
+  final DateTime date;
+  final int mangaCount;
+
+  const UpcomingHeader({required this.date, required this.mangaCount});
+
+  @override
+  bool operator ==(Object other) =>
+      identical(this, other) ||
+      other is UpcomingHeader &&
+          date == other.date &&
+          mangaCount == other.mangaCount;
+
+  @override
+  int get hashCode => Object.hash(date, mangaCount);
+}
+
+class UpcomingItem extends UpcomingUIModel {
+  final Manga manga;
+  final DateTime expectedDate;
+
+  const UpcomingItem({required this.manga, required this.expectedDate});
+
+  @override
+  bool operator ==(Object other) =>
+      identical(this, other) ||
+      other is UpcomingItem && manga.id == other.manga.id;
+
+  @override
+  int get hashCode => manga.id.hashCode;
+}

lib/modules/calendar/widgets/calendar_day.dart

@@ -0,0 +1,73 @@
+import 'package:flutter/material.dart';
+import 'package:mangayomi/modules/calendar/widgets/calendar_indicator.dart';
+
+const _maxEvents = 3;
+
+class CalendarDay extends StatelessWidget {
+  final DateTime date;
+  final int events;
+  final VoidCallback onDayClick;
+  final bool isToday;
+  final bool isPast;
+
+  const CalendarDay({
+    required this.date,
+    required this.events,
+    required this.onDayClick,
+    required this.isToday,
+    required this.isPast,
+    super.key,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final primaryColor = theme.colorScheme.primary;
+    final onBgColor = theme.colorScheme.onSurface;
+
+    return InkWell(
+      onTap: onDayClick,
+      customBorder: const CircleBorder(),
+      child: AspectRatio(
+        aspectRatio: 1,
+        child: Container(
+          decoration: isToday
+              ? BoxDecoration(
+                  shape: BoxShape.circle,
+                  border: Border.all(color: onBgColor, width: 1),
+                )
+              : null,
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              Text(
+                '${date.day}',
+                textAlign: TextAlign.center,
+                style: TextStyle(
+                  fontSize: 16,
+                  fontWeight: FontWeight.w600,
+                  color: isPast ? onBgColor.withValues(alpha: 0.38) : onBgColor,
+                ),
+              ),
+              if (events > 0) ...[
+                const SizedBox(height: 2),
+                Row(
+                  mainAxisAlignment: MainAxisAlignment.center,
+                  mainAxisSize: MainAxisSize.min,
+                  children: List.generate(
+                    events.clamp(0, _maxEvents),
+                    (index) => CalendarIndicator(
+                      index: index,
+                      size: 56,
+                      color: primaryColor,
+                    ),
+                  ),
+                ),
+              ],
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}

lib/modules/calendar/widgets/calendar_header.dart

@@ -0,0 +1,63 @@
+import 'package:flutter/material.dart';
+import 'package:intl/intl.dart';
+
+class CalendarHeader extends StatelessWidget {
+  final DateTime yearMonth;
+  final VoidCallback onPreviousClick;
+  final VoidCallback onNextClick;
+
+  const CalendarHeader({
+    required this.yearMonth,
+    required this.onPreviousClick,
+    required this.onNextClick,
+    super.key,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final locale = Localizations.localeOf(context);
+    final formatter = DateFormat('MMMM yyyy', locale.toLanguageTag());
+    final title = formatter.format(yearMonth);
+
+    return Padding(
+      padding: const EdgeInsets.symmetric(vertical: 8, horizontal: 16),
+      child: Row(
+        mainAxisAlignment: MainAxisAlignment.spaceBetween,
+        children: [
+          AnimatedSwitcher(
+            duration: const Duration(milliseconds: 200),
+            transitionBuilder: (child, animation) => FadeTransition(
+              opacity: animation,
+              child: SlideTransition(
+                position: Tween<Offset>(
+                  begin: const Offset(0, 0.3),
+                  end: Offset.zero,
+                ).animate(animation),
+                child: child,
+              ),
+            ),
+            child: Text(
+              title,
+              key: ValueKey(title),
+              style: theme.textTheme.titleLarge,
+            ),
+          ),
+          Row(
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              IconButton(
+                icon: const Icon(Icons.keyboard_arrow_left),
+                onPressed: onPreviousClick,
+              ),
+              IconButton(
+                icon: const Icon(Icons.keyboard_arrow_right),
+                onPressed: onNextClick,
+              ),
+            ],
+          ),
+        ],
+      ),
+    );
+  }
+}

lib/modules/calendar/widgets/calendar_indicator.dart

@@ -0,0 +1,30 @@
+import 'package:flutter/material.dart';
+
+const _indicatorScale = 12;
+const _indicatorAlphaMultiplier = 0.3;
+
+class CalendarIndicator extends StatelessWidget {
+  final int index;
+  final double size;
+  final Color color;
+
+  const CalendarIndicator({
+    required this.index,
+    required this.size,
+    required this.color,
+    super.key,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      margin: const EdgeInsets.symmetric(horizontal: 1),
+      width: size / _indicatorScale,
+      height: size / _indicatorScale,
+      decoration: BoxDecoration(
+        shape: BoxShape.circle,
+        color: color.withValues(alpha: (index + 1) * _indicatorAlphaMultiplier),
+      ),
+    );
+  }
+}

lib/modules/calendar/widgets/upcoming_calendar.dart

@@ -0,0 +1,153 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+import 'package:mangayomi/modules/calendar/widgets/calendar_indicator.dart';
+import 'package:table_calendar/table_calendar.dart';
+
+const _maxEventDots = 3;
+
+class UpcomingCalendar extends StatefulWidget {
+  final DateTime selectedYearMonth;
+  final Map<DateTime, int> events;
+  final ValueChanged<DateTime> setSelectedYearMonth;
+  final ValueChanged<DateTime> onClickDay;
+
+  const UpcomingCalendar({
+    required this.selectedYearMonth,
+    required this.events,
+    required this.setSelectedYearMonth,
+    required this.onClickDay,
+    super.key,
+  });
+
+  @override
+  State<UpcomingCalendar> createState() => _UpcomingCalendarState();
+}
+
+class _UpcomingCalendarState extends State<UpcomingCalendar> {
+  CalendarFormat _calendarFormat = CalendarFormat.month;
+  late DateTime _focusedDay;
+
+  @override
+  void initState() {
+    super.initState();
+    _focusedDay = widget.selectedYearMonth;
+  }
+
+  @override
+  void didUpdateWidget(covariant UpcomingCalendar oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (oldWidget.selectedYearMonth != widget.selectedYearMonth) {
+      _focusedDay = widget.selectedYearMonth;
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final locale = Localizations.localeOf(context);
+
+    return TableCalendar(
+      firstDay: DateTime.now().subtract(const Duration(days: 365)),
+      lastDay: DateTime.now().add(const Duration(days: 1000)),
+      focusedDay: _focusedDay,
+      locale: locale.toLanguageTag(),
+      calendarFormat: _calendarFormat,
+      startingDayOfWeek: StartingDayOfWeek.monday,
+      headerStyle: HeaderStyle(
+        formatButtonVisible: true,
+        titleCentered: true,
+        formatButtonShowsNext: false,
+        titleTextStyle: theme.textTheme.titleMedium!.copyWith(
+          fontWeight: FontWeight.w600,
+        ),
+        leftChevronIcon: Icon(
+          Icons.keyboard_arrow_left,
+          color: theme.colorScheme.onSurface,
+        ),
+        rightChevronIcon: Icon(
+          Icons.keyboard_arrow_right,
+          color: theme.colorScheme.onSurface,
+        ),
+      ),
+      daysOfWeekStyle: DaysOfWeekStyle(
+        weekdayStyle: TextStyle(
+          fontWeight: FontWeight.w600,
+          fontSize: 13,
+          color: theme.colorScheme.onSurface,
+        ),
+        weekendStyle: TextStyle(
+          fontWeight: FontWeight.w600,
+          fontSize: 13,
+          color: theme.colorScheme.primary,
+        ),
+      ),
+      calendarStyle: CalendarStyle(
+        outsideDaysVisible: true,
+        todayDecoration: BoxDecoration(
+          shape: BoxShape.circle,
+          border: Border.all(color: theme.colorScheme.primary, width: 1.5),
+        ),
+        todayTextStyle: TextStyle(
+          fontWeight: FontWeight.w600,
+          color: theme.colorScheme.primary,
+        ),
+        defaultTextStyle: TextStyle(
+          fontWeight: FontWeight.w500,
+          color: theme.colorScheme.onSurface,
+        ),
+        weekendTextStyle: TextStyle(
+          fontWeight: FontWeight.w500,
+          color: theme.colorScheme.primary,
+        ),
+        outsideTextStyle: TextStyle(
+          fontWeight: FontWeight.w500,
+          color: theme.colorScheme.onSurface.withValues(alpha: 0.38),
+        ),
+        // Disable default marker so we use our custom builder
+        markersMaxCount: 0,
+      ),
+      eventLoader: (day) {
+        final key = DateTime(day.year, day.month, day.day);
+        final count = widget.events[key] ?? 0;
+        return List.generate(count, (_) => day);
+      },
+      calendarBuilders: CalendarBuilders(
+        markerBuilder: (context, date, events) {
+          final key = DateTime(date.year, date.month, date.day);
+          final count = widget.events[key] ?? 0;
+          if (count == 0) return null;
+          return Positioned(
+            bottom: 4,
+            child: Row(
+              mainAxisSize: MainAxisSize.min,
+              children: List.generate(
+                min(count, _maxEventDots),
+                (index) => CalendarIndicator(
+                  index: index,
+                  size: 48,
+                  color: theme.colorScheme.primary,
+                ),
+              ),
+            ),
+          );
+        },
+      ),
+      onDaySelected: (selectedDay, focusedDay) {
+        setState(() => _focusedDay = focusedDay);
+        widget.onClickDay(
+          DateTime(selectedDay.year, selectedDay.month, selectedDay.day),
+        );
+      },
+      onFormatChanged: (format) {
+        setState(() => _calendarFormat = format);
+      },
+      onPageChanged: (focusedDay) {
+        _focusedDay = focusedDay;
+        widget.setSelectedYearMonth(
+          DateTime(focusedDay.year, focusedDay.month),
+        );
+      },
+    );
+  }
+}

lib/modules/calendar/widgets/upcoming_item.dart

@@ -0,0 +1,79 @@
+import 'dart:typed_data';
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:mangayomi/models/manga.dart';
+import 'package:mangayomi/modules/widgets/custom_extended_image_provider.dart';
+import 'package:mangayomi/utils/constant.dart';
+import 'package:mangayomi/utils/headers.dart';
+
+const _upcomingItemHeight = 96.0;
+
+class UpcomingItem extends ConsumerWidget {
+  final Manga manga;
+  final VoidCallback onTap;
+
+  const UpcomingItem({required this.manga, required this.onTap, super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final theme = Theme.of(context);
+
+    return InkWell(
+      onTap: onTap,
+      child: SizedBox(
+        height: _upcomingItemHeight,
+        child: Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
+          child: Row(
+            children: [
+              // Cover image
+              ClipRRect(
+                borderRadius: BorderRadius.circular(4),
+                child: SizedBox(
+                  width: 56,
+                  height: _upcomingItemHeight - 16,
+                  child: Image(
+                    image: _getImageProvider(ref),
+                    fit: BoxFit.cover,
+                    errorBuilder: (_, _, _) => Container(
+                      color: theme.colorScheme.surfaceContainerHighest,
+                      child: const Icon(Icons.broken_image, size: 24),
+                    ),
+                  ),
+                ),
+              ),
+              const SizedBox(width: 16),
+              // Title
+              Expanded(
+                child: Text(
+                  manga.name ?? '',
+                  maxLines: 2,
+                  overflow: TextOverflow.ellipsis,
+                  style: theme.textTheme.bodyMedium?.copyWith(
+                    fontWeight: FontWeight.w600,
+                  ),
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+
+  ImageProvider _getImageProvider(WidgetRef ref) {
+    if (manga.customCoverImage != null) {
+      return MemoryImage(manga.customCoverImage as Uint8List);
+    }
+    return CustomExtendedNetworkImageProvider(
+      toImgUrl(manga.customCoverFromTracker ?? manga.imageUrl ?? ''),
+      headers: ref.watch(
+        headersProvider(
+          source: manga.source ?? '',
+          lang: manga.lang ?? '',
+          sourceId: manga.sourceId,
+        ),
+      ),
+    );
+  }
+}

lib/modules/manga/detail/providers/update_manga_detail_providers.dart

@@ -1,5 +1,3 @@
-import 'dart:math';
-
 import 'package:mangayomi/eval/model/m_bridge.dart';
 import 'package:mangayomi/eval/model/m_manga.dart';
 import 'package:mangayomi/main.dart';
@@ -7,8 +5,8 @@ import 'package:mangayomi/models/chapter.dart';
 import 'package:mangayomi/models/update.dart';
 import 'package:mangayomi/models/manga.dart';
 import 'package:mangayomi/services/get_detail.dart';
-import 'package:mangayomi/utils/extensions/others.dart';
 import 'package:mangayomi/utils/extensions/string_extensions.dart';
+import 'package:mangayomi/utils/fetch_interval.dart';
 import 'package:mangayomi/utils/utils.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 part 'update_manga_detail_providers.g.dart';
@@ -140,27 +138,15 @@ Future<dynamic> updateMangaDetail(
           oldChap.manga.saveSync();
         }
       }
-      final List<int> daysBetweenUploads = [];
+      // Calculate fetch interval:
-      for (var i = 0; i + 1 < chaps.length; i++) {
+      // median of gaps between recent distinct chapter dates, clamped [1, 28].
-        if (chaps[i].dateUpload != null && chaps[i + 1].dateUpload != null) {
+      final allChapters = isar.mangas.getSync(mangaId)!.chapters.toList();
-          final date1 = DateTime.fromMillisecondsSinceEpoch(
+      if (allChapters.isNotEmpty) {
-            int.parse(chaps[i].dateUpload!),
+        final interval = FetchInterval.calculateInterval(allChapters);
-          );
-          final date2 = DateTime.fromMillisecondsSinceEpoch(
-            int.parse(chaps[i + 1].dateUpload!),
-          );
-          daysBetweenUploads.add(date1.difference(date2).abs().inDays);
-        }
-      }
-      if (daysBetweenUploads.isNotEmpty) {
-        final median = daysBetweenUploads.median();
         isar.mangas.putSync(
           manga
             ..id = mangaId
-            ..smartUpdateDays = max(
+            ..smartUpdateDays = interval,
-              median,
-              daysBetweenUploads.arithmeticMean(),
-            ),
         );
       }
     });

lib/modules/manga/reader/reader_view.dart

@@ -401,11 +401,11 @@ class _MangaChapterPageGalleryState
                               chapterName: widget.chapter.name!,
                             ),
                             onFailedToLoadImage: (value) {
-                              // Handle failed image loading
+                              // // Handle failed image loading
-                              if (_failedToLoadImage.value != value &&
+                              // if (_failedToLoadImage.value != value &&
-                                  context.mounted) {
+                              //     context.mounted) {
-                                _failedToLoadImage.value = value;
+                              //   _failedToLoadImage.value = value;
-                              }
+                              // }
                             },
                             backgroundColor: backgroundColor,
                             isDoublePageMode:

lib/utils/extensions/others.dart

@@ -38,11 +38,12 @@ extension LetExtension<T> on T {
 
 extension MedianExtension on List<int> {
   int median() {
-    var middle = length ~/ 2;
+    final sorted = List<int>.from(this)..sort();
-    if (length % 2 == 1) {
+    var middle = sorted.length ~/ 2;
-      return this[middle];
+    if (sorted.length % 2 == 1) {
+      return sorted[middle];
     } else {
-      return ((this[middle - 1] + this[middle]) / 2).round();
+      return ((sorted[middle - 1] + sorted[middle]) / 2).round();
     }
   }
 

lib/utils/fetch_interval.dart

@@ -0,0 +1,233 @@
+import 'dart:math';
+
+import 'package:mangayomi/models/chapter.dart';
+
+/// Computes the fetch interval and next expected update date for a manga.
+///
+/// Uses the median of intervals between recent chapter upload dates
+/// (falling back to fetch/updatedAt dates) to determine a reliable
+/// release cadence. The interval is clamped to [1, maxInterval] days.
+class FetchInterval {
+  FetchInterval._();
+
+  /// Maximum interval in days.
+  static const int maxInterval = 28;
+
+  /// Grace period in days for the fetch window.
+  static const int _gracePeriod = 1;
+
+  /// Calculates the fetch interval in days from a list of chapters.
+  ///
+  /// - Takes the last N **distinct** dates (N = 3 if ≤8 chapters, else 10)
+  /// - Computes pairwise day-gaps, sorts them, picks the **median**
+  /// - Falls back to fetch dates (`updatedAt`) if upload dates are insufficient
+  /// - Defaults to 7 days if still insufficient
+  /// - Clamps to [1, [maxInterval]]
+  static int calculateInterval(List<Chapter> chapters) {
+    final chapterWindow = chapters.length <= 8 ? 3 : 10;
+
+    // ── Upload dates (primary signal) ──
+    final uploadDates =
+        chapters
+            .where((c) {
+              final ms = int.tryParse(c.dateUpload ?? '');
+              return ms != null && ms > 0;
+            })
+            .map((c) => int.parse(c.dateUpload!))
+            .toList()
+          ..sort((a, b) => b.compareTo(a)); // descending
+
+    final distinctUploadDays = _distinctDays(
+      uploadDates,
+    ).take(chapterWindow).toList();
+
+    if (distinctUploadDays.length >= 3) {
+      return _medianInterval(distinctUploadDays);
+    }
+
+    // ── Fetch / updatedAt dates (fallback signal) ──
+    final fetchDates =
+        chapters
+            .where((c) => c.updatedAt != null && c.updatedAt! > 0)
+            .map((c) => c.updatedAt!)
+            .toList()
+          ..sort((a, b) => b.compareTo(a)); // descending
+
+    final distinctFetchDays = _distinctDays(
+      fetchDates,
+    ).take(chapterWindow).toList();
+
+    if (distinctFetchDays.length >= 3) {
+      return _medianInterval(distinctFetchDays);
+    }
+
+    // ── Not enough data → default 7 days ──
+    return 7;
+  }
+
+  /// Computes the next expected update timestamp (milliseconds since epoch)
+  /// for a manga.
+  ///
+  /// [lastUpdate]    – epoch millis when chapters were last synced
+  /// [interval]      – fetch interval in days (from [calculateInterval])
+  /// [currentNextUpdate] – previously stored next-update epoch millis (0 if none)
+  /// [now]           – current DateTime (injectable for testing)
+  static int calculateNextUpdate({
+    required int lastUpdate,
+    required int interval,
+    int currentNextUpdate = 0,
+    DateTime? now,
+  }) {
+    final dateTime = now ?? DateTime.now();
+
+    // If existing nextUpdate is within the grace window, keep it.
+    if (currentNextUpdate > 0) {
+      final window = getWindow(dateTime);
+      if (currentNextUpdate >= window.$1 &&
+          currentNextUpdate <= window.$2 + 1) {
+        return currentNextUpdate;
+      }
+    }
+
+    final latestDate = lastUpdate > 0
+        ? DateTime.fromMillisecondsSinceEpoch(lastUpdate)
+        : dateTime;
+    final latestDay = DateTime(
+      latestDate.year,
+      latestDate.month,
+      latestDate.day,
+    );
+
+    final nowDay = DateTime(dateTime.year, dateTime.month, dateTime.day);
+    final timeSinceLatest = nowDay.difference(latestDay).inDays;
+
+    final effectiveInterval = interval < 0
+        ? interval.abs()
+        : _increaseInterval(interval, timeSinceLatest, increaseWhenOver: 10);
+
+    final cycle = effectiveInterval > 0
+        ? timeSinceLatest ~/ effectiveInterval
+        : 0;
+
+    return latestDay
+        .add(Duration(days: (cycle + 1) * interval.abs()))
+        .millisecondsSinceEpoch;
+  }
+
+  /// Computes the expected next update [DateTime] for a manga, suitable
+  /// for the calendar screen.
+  ///
+  /// [lastChapterDateMs] – epoch millis of last chapter upload date
+  /// [lastUpdateMs]      – epoch millis of when manga was last updated/synced
+  /// [interval]          – fetch interval in days
+  static DateTime? computeExpectedDate({
+    required int? lastChapterDateMs,
+    required int? lastUpdateMs,
+    required int? interval,
+    DateTime? now,
+  }) {
+    if (interval == null || interval <= 0) return null;
+
+    final dateTime = now ?? DateTime.now();
+
+    // Use the most recent of: last chapter upload date, last manga update
+    final referenceMs = [
+      if (lastChapterDateMs != null && lastChapterDateMs > 0) lastChapterDateMs,
+      if (lastUpdateMs != null && lastUpdateMs > 0) lastUpdateMs,
+    ];
+    if (referenceMs.isEmpty) return null;
+
+    final latestMs = referenceMs.reduce(max);
+    final latestDate = DateTime.fromMillisecondsSinceEpoch(latestMs);
+    final latestDay = DateTime(
+      latestDate.year,
+      latestDate.month,
+      latestDate.day,
+    );
+
+    final nowDay = DateTime(dateTime.year, dateTime.month, dateTime.day);
+    final timeSinceLatest = nowDay.difference(latestDay).inDays;
+
+    if (timeSinceLatest < 0) {
+      // Latest date is in the future, next update = latestDay + interval
+      return latestDay.add(Duration(days: interval));
+    }
+
+    // Find which cycle we're in and return start of next cycle
+    final effectiveInterval = _increaseInterval(
+      interval,
+      timeSinceLatest,
+      increaseWhenOver: 10,
+    );
+    final cycle = effectiveInterval > 0
+        ? timeSinceLatest ~/ effectiveInterval
+        : 0;
+    return latestDay.add(Duration(days: (cycle + 1) * interval));
+  }
+
+  /// Returns the fetch window as (lowerBound, upperBound) in epoch millis.
+  /// Today ± [_gracePeriod] day(s).
+  static (int, int) getWindow(DateTime dateTime) {
+    final today = DateTime(dateTime.year, dateTime.month, dateTime.day);
+    final lower = today.subtract(Duration(days: _gracePeriod));
+    final upper = today.add(Duration(days: _gracePeriod));
+    return (lower.millisecondsSinceEpoch, upper.millisecondsSinceEpoch - 1);
+  }
+
+  // ── Private helpers ──
+
+  /// Doubles the interval progressively if too many check cycles
+  /// have been missed (>10).
+  static int _increaseInterval(
+    int delta,
+    int timeSinceLatest, {
+    required int increaseWhenOver,
+  }) {
+    if (delta >= maxInterval) return maxInterval;
+
+    final cycle = (timeSinceLatest ~/ delta) + 1;
+    if (cycle > increaseWhenOver) {
+      return _increaseInterval(
+        min(delta * 2, maxInterval),
+        timeSinceLatest,
+        increaseWhenOver: increaseWhenOver,
+      );
+    }
+    return delta;
+  }
+
+  /// Deduplicates epoch-millis timestamps to distinct calendar days,
+  /// preserving order. Returns day-start epoch millis.
+  static Iterable<int> _distinctDays(List<int> epochMillis) sync* {
+    final seen = <int>{};
+    for (final ms in epochMillis) {
+      final day = DateTime.fromMillisecondsSinceEpoch(ms);
+      final dayKey = DateTime(
+        day.year,
+        day.month,
+        day.day,
+      ).millisecondsSinceEpoch;
+      if (seen.add(dayKey)) {
+        yield dayKey;
+      }
+    }
+  }
+
+  /// Computes pairwise day-gaps from a list of distinct day-start
+  /// epoch-millis (descending order), sorts them, and returns the median.
+  /// Clamps to [1, [maxInterval]].
+  static int _medianInterval(List<int> distinctDays) {
+    final ranges = <int>[];
+    for (var i = 0; i + 1 < distinctDays.length; i++) {
+      final daysDiff =
+          (DateTime.fromMillisecondsSinceEpoch(distinctDays[i]).difference(
+            DateTime.fromMillisecondsSinceEpoch(distinctDays[i + 1]),
+          )).inDays.abs();
+      ranges.add(daysDiff);
+    }
+    ranges.sort();
+    // Median: middle element (upper-median for even length)
+    final median = ranges[(ranges.length - 1) ~/ 2];
+    return median.clamp(1, maxInterval);
+  }
+}