import 'dart:typed_data';

import 'package:aves/model/activity/activity_track.dart';
import 'package:fit_sdk/fit_sdk.dart' as fit;
import 'package:latlong2/latlong.dart';

class FitActivityParser {
  static final Distance _distance = Distance();

  static ActivityTrack parse(
    Uint8List bytes, {
    required String fileName,
  }) {
    final records = <_FitPoint>[];

    double? sessionDistanceMeters;
    Duration? sessionDuration;
    String? sport;

    final decoder = fit.Decode();

    decoder.onMesg = (dynamic message) {
      final messageName = '${message.name}'.toLowerCase();

      final fields = <String, dynamic>{};

      for (final dynamic field in message.fields) {
        final name = '${field.name}'.toLowerCase();
        fields[name] = field.value;
      }

      if (messageName == 'record') {
        final latRaw = _readNumber(fields, const [
          'position_lat',
          'positionlat',
          'lat',
          'latitude',
        ]);

        final lonRaw = _readNumber(fields, const [
          'position_long',
          'positionlon',
          'lon',
          'long',
          'longitude',
        ]);

        if (latRaw == null || lonRaw == null) return;

        final lat = _semicirclesToDegrees(latRaw);
        final lon = _semicirclesToDegrees(lonRaw);

        if (!lat.isFinite || !lon.isFinite) return;
        if (lat.abs() > 90 || lon.abs() > 180) return;

        final elevation = _readNumber(fields, const [
          'altitude',
          'enhanced_altitude',
        ]);

        final time = _readDateTime(fields, const [
          'timestamp',
          'time',
        ]);

        records.add(
          _FitPoint(
            latLng: LatLng(lat, lon),
            elevationMeters: elevation,
            time: time,
          ),
        );
      }

      if (messageName == 'session') {
        sessionDistanceMeters ??= _readNumber(fields, const [
          'total_distance',
          'distance',
        ]);

        final elapsedSeconds = _readNumber(fields, const [
          'total_elapsed_time',
          'total_timer_time',
        ]);

        if (elapsedSeconds != null) {
          sessionDuration = Duration(seconds: elapsedSeconds.round());
        }

        final sessionSport = fields['sport'];
        if (sessionSport != null) {
          sport = _normalizeSport('$sessionSport');
        }
      }

      if (messageName == 'sport') {
        final sportValue = fields['sport'];
        if (sportValue != null) {
          sport = _normalizeSport('$sportValue');
        }
      }
    };

    decoder.read(bytes);

    final points = records
        .where(
          (point) =>
              point.latLng.latitude.isFinite &&
              point.latLng.longitude.isFinite,
        )
        .toList();

    final tracks = <List<LatLng>>{};
    if (points.length >= 2) {
      tracks.add(points.map((point) => point.latLng).toList());
    }

    return ActivityTrack(
      name: fileName,
      format: 'FIT',
      tracks: tracks,
      pointCount: points.length,
      distanceMeters: sessionDistanceMeters ?? _computeDistanceMeters(points),
      elevationGainMeters: _computeElevationGainMeters(points),
      duration: sessionDuration ?? _computeDuration(points),
      startTime: points.map((point) => point.time).nonNulls.firstOrNull,
      sport: sport,
    );
  }

  static double? _readNumber(
    Map<String, dynamic> fields,
    List<String> names,
  ) {
    for (final name in names) {
      final value = fields[name];
      if (value == null) continue;

      if (value is num) {
        return value.toDouble();
      }

      final parsed = double.tryParse('$value');
      if (parsed != null && parsed.isFinite) {
        return parsed;
      }
    }

    return null;
  }

  static DateTime? _readDateTime(
    Map<String, dynamic> fields,
    List<String> names,
  ) {
    for (final name in names) {
      final value = fields[name];
      if (value == null) continue;

      if (value is DateTime) return value;

      if (value is int) {
        // FIT timestamp = seconds since 1989-12-31 UTC.
        return DateTime.fromMillisecondsSinceEpoch(
          (value + 631065600) * 1000,
          isUtc: true,
        );
      }

      final parsed = DateTime.tryParse('$value');
      if (parsed != null) return parsed;
    }

    return null;
  }

  static double _semicirclesToDegrees(num value) {
    return value.toDouble() * 180.0 / 2147483648.0;
  }

  static double? _computeDistanceMeters(List<_FitPoint> points) {
    if (points.length < 2) return null;

    var distanceMeters = 0.0;

    for (var i = 1; i < points.length; i++) {
      distanceMeters += _distance.as(
        LengthUnit.Meter,
        points[i - 1].latLng,
        points[i].latLng,
      );
    }

    return distanceMeters > 0 ? distanceMeters : null;
  }

  static double? _computeElevationGainMeters(List<_FitPoint> points) {
    var gain = 0.0;
    double? previousElevation;

    for (final point in points) {
      final elevation = point.elevationMeters;
      if (elevation == null) continue;

      final previous = previousElevation;
      if (previous != null) {
        final delta = elevation - previous;
        if (delta > 0) {
          gain += delta;
        }
      }

      previousElevation = elevation;
    }

    return gain > 0 ? gain : null;
  }

  static Duration? _computeDuration(List<_FitPoint> points) {
    final times = points.map((point) => point.time).nonNulls.toList();
    if (times.length < 2) return null;

    times.sort();

    final duration = times.last.difference(times.first);
    return duration.isNegative ? null : duration;
  }

  static String _normalizeSport(String raw) {
    final value = raw.trim().toLowerCase();

    switch (value) {
      case 'running':
      case 'run':
        return 'Corsa';
      case 'cycling':
      case 'biking':
      case 'bike':
        return 'Bici';
      case 'walking':
      case 'walk':
        return 'Camminata';
      case 'hiking':
      case 'trekking':
        return 'Trekking';
      case 'swimming':
        return 'Nuoto';
      default:
        return raw.trim();
    }
  }
}

class _FitPoint {
  final LatLng latLng;
  final double? elevationMeters;
  final DateTime? time;

  const _FitPoint({
    required this.latLng,
    this.elevationMeters,
    this.time,
  });
}

extension _FirstOrNull<E> on Iterable<E> {
  E? get firstOrNull {
    final iterator = this.iterator;
    if (!iterator.moveNext()) return null;
    return iterator.current;
  }
}