import 'package:xml/xml.dart';
import 'package:latlong2/latlong.dart';
import 'package:aves/model/activity/activity_track.dart';
import 'gps_smoothing.dart';

class TcxActivityParser {
  static ActivityTrack parse(String xml, {required String fileName}) {
    final doc = XmlDocument.parse(xml);

    final points = <LatLng>[];
    final elevations = <double?>[];
    final times = <DateTime?>[];

    final trackpoints = doc.findAllElements('Trackpoint');

    for (final tp in trackpoints) {
      final lat = tp.findElements('LatitudeDegrees')
          .map((e) => double.tryParse(e.text))
          .firstOrNull;

      final lon = tp.findElements('LongitudeDegrees')
          .map((e) => double.tryParse(e.text))
          .firstOrNull;

      final ele = tp.findElements('AltitudeMeters')
          .map((e) => double.tryParse(e.text))
          .firstOrNull;

      final time = tp.findElements('Time')
          .map((e) => DateTime.tryParse(e.text))
          .firstOrNull;

      if (lat != null && lon != null) {
        points.add(LatLng(lat, lon));
        elevations.add(ele);
        times.add(time);
      }
    }

    final smoothed = GpsSmoothing.douglasPeucker(points, 5.0);

    return ActivityTrack(
      name: fileName,
      format: 'TCX',
      tracks: {smoothed},
      pointCount: smoothed.length,
      distanceMeters: null,
      elevationGainMeters: null,
      duration: null,
      startTime: times.firstOrNull,
      sport: null,
    );
  }
}

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