import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:syncfusion_flutter_calendar/calendar.dart';

import '../../../extensions/date_time.dart';
import '../../../routing/app_routes.dart';
import '../../../state/app/infrastructure/loadable_state/view/loadable_state_consumer.dart';
import '../../../state/app/modules/settings/bloc/settings_cubit.dart';
import '../../../state/app/modules/timetable/bloc/timetable_bloc.dart';
import '../../../state/app/modules/timetable/bloc/timetable_state.dart';
import '../../../storage/timetable_settings.dart';
import 'custom_events/custom_event_edit_dialog.dart';
import 'data/arbitrary_appointment.dart';
import 'data/lesson_period_schedule.dart';
import 'data/timetable_appointment_factory.dart';
import 'details/appointment_details_dispatcher.dart';
import 'widgets/custom_workweek_calendar.dart';
import 'widgets/special_regions_builder.dart';

enum _CalendarAction { addEvent, viewEvents }

class Timetable extends StatefulWidget {
  const Timetable({super.key});

  @override
  State<Timetable> createState() => _TimetableState();
}

class _TimetableState extends State<Timetable> {
  final GlobalKey<CustomWorkWeekCalendarState> _calendarKey =
      GlobalKey<CustomWorkWeekCalendarState>();

  List<Appointment>? _cachedAppointments;
  int? _lastDataVersion;
  TimetableSettings? _lastTimetableSettings;

  DateTime _initialDisplayDate() => DateTime.now().addDays(2);

  void _jumpToToday() {
    _calendarKey.currentState?.jumpToDate(_initialDisplayDate());
  }

  void _onAction(_CalendarAction action) {
    switch (action) {
      case _CalendarAction.addEvent:
        showDialog(
          context: context,
          builder: (_) => const CustomEventEditDialog(),
          barrierDismissible: false,
        );
      case _CalendarAction.viewEvents:
        AppRoutes.openCustomEvents(context);
    }
  }

  List<Appointment> _appointments(TimetableState state) {
    final timetableSettings = context
        .watch<SettingsCubit>()
        .val()
        .timetableSettings;
    if (_cachedAppointments != null &&
        _lastDataVersion == state.dataVersion &&
        identical(_lastTimetableSettings, timetableSettings)) {
      return _cachedAppointments!;
    }
    _lastDataVersion = state.dataVersion;
    _lastTimetableSettings = timetableSettings;

    return _cachedAppointments = TimetableAppointmentFactory(
      lessons: state.getAllKnownLessons().toList(),
      customEvents: state.customEvents?.events ?? const [],
      subjects: state.subjects?.result ?? const [],
      settings: timetableSettings,
      now: DateTime.now(),
    ).build();
  }

  bool _isCrossedOut(Appointment appointment) {
    final id = appointment.id;
    if (id is LessonAppointment) return id.entry.status == 'CANCELLED';
    return false;
  }

  bool _isOnInitialWeek(TimetableState state) =>
      state.startDate == _mondayOf(_initialDisplayDate());

  @override
  Widget build(BuildContext context) {
    final bloc = context.read<TimetableBloc>();
    final loadableState = context.watch<TimetableBloc>().state;
    final innerState = loadableState.data;
    final atToday = innerState != null && _isOnInitialWeek(innerState);
    return Scaffold(
      appBar: AppBar(
        title: const Text('Stunden & Vertretungsplan'),
        actions: [
          IconButton(
            icon: const Icon(Icons.home_outlined),
            onPressed: atToday ? null : _jumpToToday,
          ),
          PopupMenuButton<_CalendarAction>(
            icon: const Icon(Icons.edit_calendar_outlined),
            onSelected: _onAction,
            itemBuilder: (_) => const [
              PopupMenuItem(
                value: _CalendarAction.addEvent,
                child: ListTile(
                  title: Text('Kalendereintrag hinzufügen'),
                  leading: Icon(Icons.add),
                ),
              ),
              PopupMenuItem(
                value: _CalendarAction.viewEvents,
                child: ListTile(
                  title: Text('Kalendereinträge anzeigen'),
                  leading: Icon(Icons.perm_contact_calendar_outlined),
                ),
              ),
            ],
          ),
        ],
      ),
      body: LoadableStateConsumer<TimetableBloc, TimetableState>(
        // Without this predicate the consumer treats the freshly-initialised
        // empty TimetableState as "has content" and only shows the error bar
        // on top — but `_calendar` collapses to `SizedBox.shrink()` while the
        // reference data is missing, leaving the user with a blank screen.
        // Telling the consumer that "ready" means having reference data
        // flips it into the proper error-screen path instead.
        isReady: (state) => state.hasReferenceData,
        child: (state, _) => _calendar(state, bloc),
      ),
    );
  }

  Widget _calendar(TimetableState state, TimetableBloc bloc) {
    if (!state.hasReferenceData) return const SizedBox.shrink();

    final schedule = LessonPeriodSchedule.fromState(state);
    final appointments = _appointments(state);
    final regions = SpecialRegionsBuilder(
      holidays: state.schoolHolidays!,
      schedule: schedule,
      colorScheme: Theme.of(context).colorScheme,
      disabledColor: Theme.of(context).disabledColor,
    ).build();

    // Scroll bounds follow the Webuntis school-year API: the calendar lets
    // the user navigate every week the server has data for. A two-week
    // fallback is used only while the school-year payload hasn't loaded yet
    // (first launch / offline), so the calendar still mounts.
    final (minDate, maxDate) = _scrollBounds(state);

    return CustomWorkWeekCalendar(
      key: _calendarKey,
      schedule: schedule,
      appointments: appointments,
      timeRegions: regions,
      initialDate: _initialDisplayDate(),
      minDate: minDate,
      maxDate: maxDate,
      onAppointmentTap: (apt) =>
          AppointmentDetailsDispatcher.show(context, bloc, apt),
      onWeekChanged: (start, end) => bloc.changeWeek(start, end),
      isCrossedOut: _isCrossedOut,
      onCreateEvent: _onCreateEventAt,
    );
  }

  void _onCreateEventAt(DateTime start, DateTime end) {
    showDialog(
      context: context,
      builder: (_) =>
          CustomEventEditDialog(initialStart: start, initialEnd: end),
      barrierDismissible: false,
    );
  }

  /// Hard caps applied on top of whatever Webuntis would allow. Even if the
  /// school year (or a stale persisted bound) would let the user scroll
  /// further, we never expose more than this much around the current week —
  /// containment for any future date-math bug that might otherwise teleport
  /// the user months away from today.
  static const int _maxWeeksBack = 4;
  static const int _maxWeeksForward = 2;

  /// Returns the (minDate, maxDate) the user is allowed to scroll between.
  /// Starts from the Webuntis school year (or a tight window when that
  /// hasn't loaded yet), tightens by anything the bloc has learned from
  /// `-7004 no allowed date` errors during scroll — so the user can't
  /// slide off into territory Webuntis would refuse anyway — and finally
  /// clamps to a fixed window around today.
  ///
  /// minDate is snapped *forward* to the next Monday because the calendar's
  /// internal `_mondayOf()` would otherwise pull a mid-week minDate back
  /// into the just-rejected week. maxDate is passed through unsnapped —
  /// `_mondayOf()` correctly walks back to the Monday of its own week,
  /// which is the last fully-allowed week.
  (DateTime, DateTime) _scrollBounds(TimetableState state) {
    final year = state.schoolyear;
    final DateTime baseMin;
    final DateTime baseMax;
    if (year != null) {
      baseMin = year.startDate;
      baseMax = year.endDate;
    } else {
      final now = DateTime.now();
      baseMin = now.subtractDays(14);
      baseMax = now.addDays(7);
    }
    final effectiveMin = state.accessibleStartDate != null
        ? (state.accessibleStartDate!.isAfter(baseMin)
              ? state.accessibleStartDate!
              : baseMin)
        : baseMin;
    final effectiveMax = state.accessibleEndDate != null
        ? (state.accessibleEndDate!.isBefore(baseMax)
              ? state.accessibleEndDate!
              : baseMax)
        : baseMax;
    final todayMonday = _mondayOf(DateTime.now());
    final cappedMin = effectiveMin.isBefore(
      todayMonday.subtractDays(_maxWeeksBack * 7),
    )
        ? todayMonday.subtractDays(_maxWeeksBack * 7)
        : effectiveMin;
    final cappedMax = effectiveMax.isAfter(
      todayMonday.addDays(_maxWeeksForward * 7 + 6),
    )
        ? todayMonday.addDays(_maxWeeksForward * 7 + 6)
        : effectiveMax;
    final daysToMonday =
        (DateTime.monday - cappedMin.weekday) % DateTime.daysPerWeek;
    final mondayMin = cappedMin.addDays(daysToMonday);
    return (mondayMin, cappedMax);
  }

  static DateTime _mondayOf(DateTime d) {
    final monday = d.subtractDays(d.weekday - 1);
    return DateTime(monday.year, monday.month, monday.day);
  }
}