import 'package:latlong2/latlong.dart';

class GpsSmoothing {
  static List<LatLng> douglasPeucker(List<LatLng> points, double epsilon) {
    if (points.length < 3) return points;

    final first = points.first;
    final last = points.last;

    double maxDistance = 0;
    int index = 0;

    for (int i = 1; i < points.length - 1; i++) {
      final d = _perpendicularDistance(points[i], first, last);
      if (d > maxDistance) {
        maxDistance = d;
        index = i;
      }
    }

    if (maxDistance > epsilon) {
      final left = douglasPeucker(points.sublist(0, index + 1), epsilon);
      final right = douglasPeucker(points.sublist(index, points.length), epsilon);

      return [...left, ...right.skip(1)];
    } else {
      return [first, last];
    }
  }

  static double _perpendicularDistance(LatLng p, LatLng start, LatLng end) {
    final x = p.longitude;
    final y = p.latitude;
    final x1 = start.longitude;
    final y1 = start.latitude;
    final x2 = end.longitude;
    final y2 = end.latitude;

    final dx = x2 - x1;
    final dy = y2 - y1;

    if (dx == 0 && dy == 0) {
      return ((x - x1) * (x - x1) + (y - y1) * (y - y1)).abs();
    }

    final t = ((x - x1) * dx + (y - y1) * dy) / (dx * dx + dy * dy);
    final projX = x1 + t * dx;
    final projY = y1 + t * dy;

    return ((x - projX) * (x - projX) + (y - projY) * (y - projY)).abs();
  }
}