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

import '../../../../api/mhsl/custom_timetable_event/custom_timetable_event.dart';
import '../../../../extensions/date_time.dart';
import '../../../../state/app/modules/settings/bloc/settings_cubit.dart';
import '../../../../state/app/modules/timetable/bloc/timetable_state.dart';
import '../../../../storage/timetable_settings.dart';
import '../data/arbitrary_appointment.dart';
import '../data/lesson_period_schedule.dart';
import '../data/timetable_appointment_factory.dart';
import 'custom_workweek_calendar.dart';
import 'special_regions_builder.dart';

/// Renders a weekly timetable from a [TimetableState]. Shared by the user's own
/// plan and the foreign-element view; the only differences are which custom
/// events to overlay (none for foreign plans) and whether tapping an empty slot
/// can create an event ([onCreateEvent] is null for read-only foreign plans).
///
/// The week navigation and appointment-tap callbacks are supplied by the host
/// page so each can route them to its own bloc.
class TimetableCalendarView extends StatefulWidget {
  final TimetableState state;
  final void Function(DateTime weekStart, DateTime weekEnd) onWeekChanged;
  final void Function(Appointment appointment) onAppointmentTap;
  final void Function(DateTime start, DateTime end)? onCreateEvent;
  final List<CustomTimetableEvent> customEvents;

  const TimetableCalendarView({
    super.key,
    required this.state,
    required this.onWeekChanged,
    required this.onAppointmentTap,
    this.onCreateEvent,
    this.customEvents = const [],
  });

  @override
  State<TimetableCalendarView> createState() => TimetableCalendarViewState();
}

class TimetableCalendarViewState extends State<TimetableCalendarView> {
  final GlobalKey<CustomWorkWeekCalendarState> _calendarKey =
      GlobalKey<CustomWorkWeekCalendarState>();

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

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

  /// Snaps the calendar back to the current week. Exposed so host pages can
  /// wire it to a "today" AppBar action.
  void jumpToToday() {
    _calendarKey.currentState?.jumpToDate(_initialDisplayDate());
  }

  bool isOnInitialWeek() =>
      widget.state.startDate == _mondayOf(_initialDisplayDate());

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

    return _cachedAppointments = TimetableAppointmentFactory(
      lessons: state.getAllKnownLessons().toList(),
      customEvents: widget.customEvents,
      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;
  }

  @override
  Widget build(BuildContext context) {
    final state = widget.state;
    // Reference data is gated by the host's LoadableStateConsumer isReady
    // predicate, but guard the one hard dereference (schoolHolidays) so a
    // transient null can never crash the build.
    if (state.schoolHolidays == null) 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();

    final (minDate, maxDate) = _scrollBounds(state);

    return CustomWorkWeekCalendar(
      key: _calendarKey,
      schedule: schedule,
      appointments: appointments,
      timeRegions: regions,
      initialDate: _initialDisplayDate(),
      minDate: minDate,
      maxDate: maxDate,
      onAppointmentTap: widget.onAppointmentTap,
      onWeekChanged: widget.onWeekChanged,
      isCrossedOut: _isCrossedOut,
      onCreateEvent: widget.onCreateEvent,
    );
  }

  /// 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.
  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 past denials,
  /// and finally clamps to a fixed window around today.
  (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);
  }
}