position_tracker.dart

import 'dart:async';


class PositionTracker {
  PositionTracker(this._currentLat, this._currentLong, [this.minimumDelta = 100.0]);
  
  final double minimumDelta;
  final StreamController<void> _onUpdate = new StreamController<void>();
  double _currentLat;
  double _currentLatDelta = 0.0;
  double _currentLong;
  double _currentLongDelta = 0.0;

  Stream<void> get onUpdated => _onUpdate.stream;
  
  double get lat => _currentLat;
  
  double get long => _currentLong;
  
  void updatePosition(double lat, double long) {
    // compute delta somehow, pretty sure this isn't correct XD
    double deltaLat = (_currentLat - lat).abs();
    double deltaLong = (_currentLong - long).abs();
    _currentLat = lat;
    _currentLong = long;
    _currentLatDelta += deltaLat;
    _currentLongDelta += deltaLong;
    // Probablt not a linear combination, but thats not the point!
    if (_currentLatDelta + _currentLongDelta > minimumDelta) {
      _onUpdate.add(null);
      _currentLatDelta = 0.0;
      _currentLongDelta = 0.0;
    }
  }
}

Future<void> main() async {
  final PositionTracker tracker = new PositionTracker(0.0, 10.0);
  tracker.onUpdated.listen((_) => print('updated!'));
  tracker.updatePosition(100.0, 200.0);
}