[Dart] Decoder for google encoded polyline

decode_google_polyline.dart

import 'model.dart';

void main() {
  List<LatLng> decodeEncodedPolyline({@required String encoded}) {
    List<LatLng> polyline = [];
    int index = 0, len = encoded.length;
    int lat = 0, lng = 0;
    int decode(int positon) {
      int shift = 0, result = 0;
      do {
        positon = encoded.codeUnitAt(index++) - 63;
        result |= (positon & 0x1f) << shift;
        shift += 5;
      } while (positon >= 0x20);
      return ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
    }
    while (index < len) {
      int positon;
      lat += decode(positon);
      lng += decode(positon);
      LatLng point = LatLng((lat / 1E5).toDouble(), (lng / 1E5).toDouble());
      polyline.add(point);
    }
    return polyline;
  }

  List<LatLng> polyline = decodeEncodedPolyline(
          encoded:
              "qw{DnsdeN]}Ac@HsFt@eK~AqBeN}IrAkIrAcC`@cMrBoDl@kDj@Ec@OeAMq@So@AQMmBIwA]wDsA@Ag@PbF@zAs@F{@BRx@VbARx@RJiO|BsIrAmDj@{AyB}ByCm@w@qDyEs@y@y@k@q@So@Gu@A_AJs@Xk@\\]`@[l@Wn@IvAKlDUxJOfJMrF");

  polyline.forEach((element) => print(element.toString()));
}

class LatLng {
  LatLng(this.latitude, this.longitude)
      : assert(latitude != null || longitude != null,
            "latitude and longitude can't be null");
  final double latitude;
  final double longitude;
  @override
  String toString() {
    return "$latitude,$longitude";
  }
}