import 'dart:async';
import 'dart:math';

import 'package:bloc_concurrency/bloc_concurrency.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:lightmeter/data/models/exposure_pair.dart';
import 'package:lightmeter/data/models/film.dart';
import 'package:lightmeter/interactors/metering_interactor.dart';
import 'package:lightmeter/screens/metering/communication/bloc_communication_metering.dart';
import 'package:lightmeter/screens/metering/communication/event_communication_metering.dart'
    as communication_events;
import 'package:lightmeter/screens/metering/communication/state_communication_metering.dart'
    as communication_states;
import 'package:lightmeter/screens/metering/event_metering.dart';
import 'package:lightmeter/screens/metering/state_metering.dart';
import 'package:m3_lightmeter_resources/m3_lightmeter_resources.dart';

class MeteringBloc extends Bloc<MeteringEvent, MeteringState> {
  final MeteringCommunicationBloc _communicationBloc;
  final MeteringInteractor _meteringInteractor;
  late final StreamSubscription<communication_states.ScreenState> _communicationSubscription;

  List<ApertureValue> get _apertureValues =>
      _equipmentProfileData.apertureValues.whereStopType(stopType);
  List<ShutterSpeedValue> get _shutterSpeedValues =>
      _equipmentProfileData.shutterSpeedValues.whereStopType(stopType);

  EquipmentProfileData _equipmentProfileData;
  StopType stopType;

  @visibleForTesting
  late IsoValue iso = _meteringInteractor.iso;

  @visibleForTesting
  late NdValue nd = _meteringInteractor.ndFilter;

  @visibleForTesting
  late Film film = _meteringInteractor.film;

  @visibleForTesting
  double? ev100;

  MeteringBloc(
    this._communicationBloc,
    this._meteringInteractor,
    this._equipmentProfileData,
    this.stopType,
  ) : super(
          MeteringDataState(
            ev: null,
            film: _meteringInteractor.film,
            iso: _meteringInteractor.iso,
            nd: _meteringInteractor.ndFilter,
            exposurePairs: const [],
            continuousMetering: false,
          ),
        ) {
    _communicationSubscription = _communicationBloc.stream
        .where((state) => state is communication_states.ScreenState)
        .map((state) => state as communication_states.ScreenState)
        .listen(onCommunicationState);

    on<EquipmentProfileChangedEvent>(_onEquipmentProfileChanged);
    on<StopTypeChangedEvent>(_onStopTypeChanged);
    on<FilmChangedEvent>(_onFilmChanged);
    on<IsoChangedEvent>(_onIsoChanged);
    on<NdChangedEvent>(_onNdChanged);
    on<MeasureEvent>(_onMeasure, transformer: droppable());
    on<MeasuredEvent>(_onMeasured);
    on<MeasureErrorEvent>(_onMeasureError);
  }

  @override
  Future<void> close() async {
    await _communicationSubscription.cancel();
    return super.close();
  }

  @visibleForTesting
  void onCommunicationState(communication_states.ScreenState communicationState) {
    if (communicationState is communication_states.MeasuredState) {
      _handleEv100(
        communicationState.ev100,
        continuousMetering: communicationState is communication_states.MeteringInProgressState,
      );
    }
  }

  void _onStopTypeChanged(StopTypeChangedEvent event, Emitter emit) {
    if (stopType != event.stopType) {
      stopType = event.stopType;
      _updateMeasurements();
    }
  }

  void _onEquipmentProfileChanged(EquipmentProfileChangedEvent event, Emitter emit) {
    _equipmentProfileData = event.equipmentProfileData;
    bool willUpdateMeasurements = false;

    /// Update selected ISO value, if selected equipment profile
    /// doesn't contain currently selected value
    if (!event.equipmentProfileData.isoValues.any((v) => iso.value == v.value)) {
      _meteringInteractor.iso = event.equipmentProfileData.isoValues.first;
      iso = event.equipmentProfileData.isoValues.first;
      willUpdateMeasurements &= true;
    }

    /// The same for ND filter
    if (!event.equipmentProfileData.ndValues.any((v) => nd.value == v.value)) {
      _meteringInteractor.ndFilter = event.equipmentProfileData.ndValues.first;
      nd = event.equipmentProfileData.ndValues.first;
      willUpdateMeasurements &= true;
    }

    if (willUpdateMeasurements) {
      _updateMeasurements();
    }
  }

  void _onFilmChanged(FilmChangedEvent event, Emitter emit) {
    if (film.name != event.data.name) {
      film = event.data;
      _meteringInteractor.film = event.data;
      _film = event.data;

      /// If user selects 'Other' film we preserve currently selected ISO
      /// and therefore only discard reciprocity formula
      if (iso.value != event.data.iso && event.data != const Film.other()) {
        final newIso = IsoValue.values.firstWhere(
          (e) => e.value == event.data.iso,
          orElse: () => iso,
        );
        _meteringInteractor.iso = newIso;
        iso = newIso;
      }

      _updateMeasurements();
    }
  }

  void _onIsoChanged(IsoChangedEvent event, Emitter emit) {
    /// Discard currently selected film even if ISO is the same,
    /// because, for example, Fomapan 400 and any Ilford 400
    /// have different reciprocity formulas
    _meteringInteractor.film = Film.values.first;
    _film = Film.values.first;

    if (iso != event.isoValue) {
      _meteringInteractor.iso = event.isoValue;
      iso = event.isoValue;
      _updateMeasurements();
    }
  }

  void _onNdChanged(NdChangedEvent event, Emitter emit) {
    if (nd != event.ndValue) {
      _meteringInteractor.ndFilter = event.ndValue;
      nd = event.ndValue;
      _updateMeasurements();
    }
  }

  void _onMeasure(MeasureEvent _, Emitter emit) {
    _meteringInteractor.quickVibration();
    _communicationBloc.add(const communication_events.MeasureEvent());
    emit(
      LoadingState(
        film: film,
        iso: iso,
        nd: nd,
      ),
    );
  }

  void _updateMeasurements() => _handleEv100(ev100, continuousMetering: false);

  void _handleEv100(double? ev100, {required bool continuousMetering}) {
    if (ev100 == null || ev100.isNaN || ev100.isInfinite) {
      add(MeasureErrorEvent(continuousMetering: continuousMetering));
    } else {
      add(MeasuredEvent(ev100, continuousMetering: continuousMetering));
    }
  }

  void _onMeasured(MeasuredEvent event, Emitter emit) {
    _meteringInteractor.responseVibration();
    ev100 = event.ev100;
    final ev = event.ev100 + log2(iso.value / 100) - nd.stopReduction;
    emit(
      MeteringDataState(
        ev: ev,
        film: film,
        iso: iso,
        nd: nd,
        exposurePairs: buildExposureValues(ev),
        continuousMetering: event.continuousMetering,
      ),
    );
  }

  void _onMeasureError(MeasureErrorEvent event, Emitter emit) {
    _meteringInteractor.errorVibration();
    ev100 = null;
    emit(
      MeteringDataState(
        ev: null,
        film: film,
        iso: iso,
        nd: nd,
        exposurePairs: const [],
        continuousMetering: event.continuousMetering,
      ),
    );
  }

  @visibleForTesting
  List<ExposurePair> buildExposureValues(double ev) {
    if (ev.isNaN || ev.isInfinite) {
      return List.empty();
    }

    /// Depending on the `stopType` the exposure pairs list length is multiplied by 1,2 or 3
    final int evSteps = (ev * (stopType.index + 1)).round();

    /// Basically we use 1" shutter speed as an anchor point for building the exposure pairs list.
    /// But user can exclude this value from the list using custom equipment profile.
    /// So we have to restore the index of the anchor value.
    const ShutterSpeedValue anchorShutterSpeed = ShutterSpeedValue(1, false, StopType.full);
    int anchorIndex = _shutterSpeedValues.indexOf(anchorShutterSpeed);
    if (anchorIndex < 0) {
      final filteredFullList = ShutterSpeedValue.values.whereStopType(stopType);
      final customListStartIndex = filteredFullList.indexOf(_shutterSpeedValues.first);
      final fullListAnchor = filteredFullList.indexOf(anchorShutterSpeed);
      if (customListStartIndex < fullListAnchor) {
        /// This means, that user excluded anchor value at the end,
        /// i.e. all shutter speed values are shorter than 1".
        anchorIndex = fullListAnchor - customListStartIndex;
      } else {
        /// In case user excludes anchor value at the start,
        /// we can do no adjustment.
      }
    }
    final int evOffset = anchorIndex - evSteps;

    late final int apertureOffset;
    late final int shutterSpeedOffset;
    if (evOffset >= 0) {
      apertureOffset = 0;
      shutterSpeedOffset = evOffset;
    } else {
      apertureOffset = -evOffset;
      shutterSpeedOffset = 0;
    }

    final int itemsCount = min(
          _apertureValues.length + shutterSpeedOffset,
          _shutterSpeedValues.length + apertureOffset,
        ) -
        max(apertureOffset, shutterSpeedOffset);

    if (itemsCount < 0) {
      return List.empty();
    }
    return List.generate(
      itemsCount,
      (index) => ExposurePair(
        _apertureValues[index + apertureOffset],
        film.reciprocityFailure(_shutterSpeedValues[index + shutterSpeedOffset]),
      ),
      growable: false,
    );
  }
}