import 'package:intl/intl.dart';

import '../../../../../api/mhsl/customTimetableEvent/customTimetableEvent.dart';
import '../../../../../api/webuntis/queries/getTimetable/getTimetableResponse.dart';
import '../../../infrastructure/utilityWidgets/loadableHydratedBloc/loadable_hydrated_bloc.dart';
import '../../../infrastructure/utilityWidgets/loadableHydratedBloc/loadable_hydrated_bloc_event.dart';
import '../repository/timetable_repository.dart';
import 'timetable_event.dart';
import 'timetable_state.dart';

class TimetableBloc extends LoadableHydratedBloc<TimetableEvent, TimetableState, TimetableRepository> {
  static const Duration _weekSpan = Duration(days: 7);
  static final DateFormat _weekKeyFormat = DateFormat('yyyyMMdd');

  DateTime _lastWeekRequestStart = DateTime.fromMillisecondsSinceEpoch(0);

  @override
  TimetableRepository repository() => TimetableRepository();

  @override
  TimetableState fromNothing() {
    final reference = DateTime.now().add(const Duration(days: 2));
    return TimetableState(
      startDate: _startOfWeek(reference),
      endDate: _endOfWeek(reference),
    );
  }

  @override
  TimetableState fromStorage(Map<String, dynamic> json) => TimetableState.fromJson(json);

  @override
  Map<String, dynamic>? toStorage(TimetableState state) => state.toJson();

  @override
  Future<void> gatherData() async {
    final initial = innerState ?? fromNothing();
    await Future.wait([
      _loadCurrentWeek(initial.startDate, initial.endDate),
      _loadStaticReferenceData(),
      _loadCustomEvents(),
    ]);
    _prefetchAdjacentWeeks(initial.startDate, initial.endDate);
  }

  void changeWeek(DateTime startDate, DateTime endDate) {
    final current = innerState ?? fromNothing();
    if (current.startDate == startDate && current.endDate == endDate) return;
    add(Emit((s) => s.copyWith(startDate: startDate, endDate: endDate)));
    _loadCurrentWeek(startDate, endDate);
    _prefetchAdjacentWeeks(startDate, endDate);
  }

  void resetWeek() {
    final reference = DateTime.now().add(const Duration(days: 2));
    changeWeek(_startOfWeek(reference), _endOfWeek(reference));
  }

  void refresh() => fetch();

  Future<void> addCustomEvent(CustomTimetableEvent event) async {
    await repo.data.addCustomEvent(event);
    await _refreshCustomEvents();
  }

  Future<void> updateCustomEvent(String id, CustomTimetableEvent event) async {
    await repo.data.updateCustomEvent(id, event);
    await _refreshCustomEvents();
  }

  Future<void> removeCustomEvent(String id) async {
    await repo.data.removeCustomEvent(id);
    await _refreshCustomEvents();
  }

  Future<void> _loadCurrentWeek(DateTime startDate, DateTime endDate) async {
    final requestStart = DateTime.now();
    _lastWeekRequestStart = requestStart;
    try {
      final week = await repo.data.getWeek(startDate, endDate);
      if (_lastWeekRequestStart.isAfter(requestStart)) return;
      _writeWeekToCache(startDate, week);
    } catch (_) {
      // Errors are surfaced via LoadableHydratedBloc.fetch's catchError.
      rethrow;
    }
  }

  Future<void> _loadStaticReferenceData() async {
    final (rooms, subjects, schoolHolidays) = await (
      repo.data.getRooms(),
      repo.data.getSubjects(),
      repo.data.getSchoolHolidays(),
    ).wait;

    add(DataGathered((s) => s.copyWith(
          rooms: rooms,
          subjects: subjects,
          schoolHolidays: schoolHolidays,
          dataVersion: s.dataVersion + 1,
        )));
  }

  Future<void> _loadCustomEvents({bool renew = false}) async {
    final events = await repo.data.getCustomEvents(renew: renew);
    add(DataGathered((s) => s.copyWith(customEvents: events, dataVersion: s.dataVersion + 1)));
  }

  Future<void> _refreshCustomEvents() => _loadCustomEvents(renew: true);

  void _prefetchAdjacentWeeks(DateTime start, DateTime end) {
    _prefetchWeek(start.subtract(_weekSpan), end.subtract(_weekSpan));
    _prefetchWeek(start.add(_weekSpan), end.add(_weekSpan));
  }

  void _prefetchWeek(DateTime start, DateTime end) {
    repo.data.getWeek(start, end).then((week) => _writeWeekToCache(start, week)).catchError((_) {});
  }

  void _writeWeekToCache(DateTime weekStart, GetTimetableResponse week) {
    final key = _weekKeyFormat.format(weekStart);
    add(DataGathered((s) {
      final updated = Map<String, GetTimetableResponse>.of(s.weekCache);
      updated[key] = week;
      return s.copyWith(weekCache: updated, dataVersion: s.dataVersion + 1);
    }));
  }

  static DateTime _startOfWeek(DateTime reference) {
    final monday = reference.subtract(Duration(days: reference.weekday - 1));
    return DateTime(monday.year, monday.month, monday.day);
  }

  static DateTime _endOfWeek(DateTime reference) {
    final friday = reference.add(Duration(days: DateTime.daysPerWeek - reference.weekday - 2));
    return DateTime(friday.year, friday.month, friday.day);
  }
}