MapLibreParticleLab/platform/ios/src/MLNFaux3DUserLocationAnnotationView.mm

#import "MLNFaux3DUserLocationAnnotationView.h"

#import "MLNLocationManager_Private.h"
#import "MLNMapViewDelegate.h"
#import "MLNMapView_Private.h"
#import "MLNUserLocation.h"
#import "MLNUserLocationAnnotationViewStyle.h"
#import "MLNUserLocationHeadingArrowLayer.h"
#import "MLNUserLocationHeadingBeamLayer.h"
#import "MLNUserLocationHeadingIndicator.h"

const CGFloat MLNUserLocationAnnotationDotSize = 22.0;
const CGFloat MLNUserLocationAnnotationHaloSize = 115.0;

const CGFloat MLNUserLocationAnnotationPuckSize = 45.0;
const CGFloat MLNUserLocationAnnotationArrowSize = MLNUserLocationAnnotationPuckSize * 0.5;

const CGFloat MLNUserLocationHeadingUpdateThreshold = 0.01;

const CGFloat MLNUserLocationApproximateZoomThreshold = 7.0;

@implementation MLNFaux3DUserLocationAnnotationView {
  BOOL _puckModeActivated;
  BOOL _approximateModeActivated;

  CALayer *_puckDot;
  CAShapeLayer *_puckArrow;

  CALayer<MLNUserLocationHeadingIndicator> *_headingIndicatorLayer;
  CALayer *_accuracyRingLayer;
  CALayer *_dotBorderLayer;
  CALayer *_dotLayer;
  CALayer *_haloLayer;

  CALayer *_approximateLayer;

  CLLocationDirection _oldHeadingAccuracy;
  CLLocationAccuracy _oldHorizontalAccuracy;
  double _oldZoom;
  double _oldPitch;
}

- (CALayer *)hitTestLayer {
  // Only the main dot should be interactive (i.e., exclude the accuracy ring and halo).
  return _dotBorderLayer ?: _puckDot;
}

- (void)update {
  if (CGSizeEqualToSize(self.frame.size, CGSizeZero)) {
    CGFloat frameSize = (self.mapView.userTrackingMode == MLNUserTrackingModeFollowWithCourse)
                            ? MLNUserLocationAnnotationPuckSize
                            : MLNUserLocationAnnotationDotSize;
    [self updateFrameWithSize:frameSize];
  }

  if (CLLocationCoordinate2DIsValid(self.userLocation.coordinate)) {
    if (@available(iOS 14, *)) {
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 140000
      if (![self.mapView.locationManager respondsToSelector:@selector(accuracyAuthorization)] ||
          self.mapView.locationManager.accuracyAuthorization ==
              CLAccuracyAuthorizationFullAccuracy) {
        [self drawPreciseLocationPuck];
      } else {
        [self drawApproximate];
        [self updatePitch];
      }
#endif
    } else {
      [self drawPreciseLocationPuck];
    }
  }
}

- (void)drawPreciseLocationPuck {
  if (_approximateModeActivated) {
    [_approximateLayer removeFromSuperlayer];
    _approximateLayer = nil;

    _approximateModeActivated = NO;
  }
  (self.mapView.userTrackingMode == MLNUserTrackingModeFollowWithCourse) ? [self drawPuck]
                                                                         : [self drawDot];
  [self updatePitch];
  _haloLayer.hidden = !CLLocationCoordinate2DIsValid(self.mapView.userLocation.coordinate) ||
                      self.mapView.userLocation.location.horizontalAccuracy > 10;
}

- (void)setTintColor:(UIColor *)tintColor {
  UIColor *puckArrowFillColor = tintColor;
  UIColor *puckArrowStrokeColor = tintColor;

  UIColor *approximateFillColor = tintColor;

  UIColor *accuracyFillColor = tintColor;
  UIColor *haloFillColor = tintColor;
  UIColor *dotFillColor = tintColor;
  UIColor *headingFillColor = tintColor;

  if ([self.mapView.delegate
          respondsToSelector:@selector(mapViewStyleForDefaultUserLocationAnnotationView:)]) {
    MLNUserLocationAnnotationViewStyle *style =
        [self.mapView.delegate mapViewStyleForDefaultUserLocationAnnotationView:self.mapView];

    puckArrowFillColor = style.puckArrowFillColor ? style.puckArrowFillColor : puckArrowFillColor;

    if (@available(iOS 14, *)) {
      approximateFillColor =
          style.approximateHaloFillColor ? style.approximateHaloFillColor : approximateFillColor;
    }

    haloFillColor = style.haloFillColor ? style.haloFillColor : haloFillColor;
    dotFillColor = style.puckFillColor ? style.puckFillColor : dotFillColor;
    headingFillColor = style.puckFillColor ? style.puckFillColor : headingFillColor;
  }

  if (_puckModeActivated) {
    _puckArrow.fillColor = [puckArrowFillColor CGColor];
    _puckArrow.strokeColor = [puckArrowStrokeColor CGColor];
  } else if (_approximateModeActivated) {
    _approximateLayer.backgroundColor = [approximateFillColor CGColor];
  } else {
    _accuracyRingLayer.backgroundColor = [accuracyFillColor CGColor];
    _haloLayer.backgroundColor = [haloFillColor CGColor];
    _dotLayer.backgroundColor = [dotFillColor CGColor];
    [_headingIndicatorLayer updateTintColor:[headingFillColor CGColor]];
  }
}

- (void)updatePitch {
  if (self.mapView.camera.pitch != _oldPitch) {
    // disable implicit animation
    [CATransaction begin];
    [CATransaction setDisableActions:YES];

    CATransform3D t = CATransform3DRotate(
        CATransform3DIdentity, MLNRadiansFromDegrees(self.mapView.camera.pitch), 1.0, 0, 0);
    self.layer.sublayerTransform = t;

    [self updateFaux3DEffect];

    [CATransaction commit];

    _oldPitch = self.mapView.camera.pitch;
  }
}

- (void)updateFaux3DEffect {
  CGFloat pitch = MLNRadiansFromDegrees(self.mapView.camera.pitch);

  if (_puckDot) {
    _puckDot.shadowOffset = CGSizeMake(0, fmaxf(pitch * 10.f, 1.f));
    _puckDot.shadowRadius = fmaxf(pitch * 5.f, 0.75f);
  }

  if (_dotBorderLayer) {
    _dotBorderLayer.shadowOffset = CGSizeMake(0.f, pitch * 10.f);
    _dotBorderLayer.shadowRadius = fmaxf(pitch * 5.f, 3.f);
  }

  if (_dotLayer) {
    _dotLayer.zPosition = pitch * 2.f;
  }
}

- (void)updateFrameWithSize:(CGFloat)size {
  CGSize newSize = CGSizeMake(size, size);
  if (CGSizeEqualToSize(self.frame.size, newSize)) {
    return;
  }

  // Update frame size, keeping the existing center point.
  CGPoint oldCenter = self.center;
  CGRect newFrame = self.frame;
  newFrame.size = newSize;
  [self setFrame:newFrame];
  [self setCenter:oldCenter];
}

- (void)drawPuck {
  if (!_puckModeActivated) {
    self.layer.sublayers = nil;

    _headingIndicatorLayer = nil;
    _accuracyRingLayer = nil;
    _haloLayer = nil;
    _dotBorderLayer = nil;
    _dotLayer = nil;

    [self updateFrameWithSize:MLNUserLocationAnnotationPuckSize];
  }

  UIColor *arrowColor = self.mapView.tintColor;
  UIColor *puckShadowColor = UIColor.blackColor;
  CGFloat shadowOpacity = 0.25;

  if ([self.mapView.delegate
          respondsToSelector:@selector(mapViewStyleForDefaultUserLocationAnnotationView:)]) {
    MLNUserLocationAnnotationViewStyle *style =
        [self.mapView.delegate mapViewStyleForDefaultUserLocationAnnotationView:self.mapView];
    arrowColor = style.puckArrowFillColor ? style.puckArrowFillColor : arrowColor;
    puckShadowColor = style.puckShadowColor ? style.puckShadowColor : puckShadowColor;
    shadowOpacity = style.puckShadowOpacity;
  }

  // background dot (white with black shadow)
  //
  if (!_puckDot) {
    _puckDot = [self circleLayerWithSize:MLNUserLocationAnnotationPuckSize];
    _puckDot.backgroundColor = [[UIColor whiteColor] CGColor];
    _puckDot.shadowColor = [puckShadowColor CGColor];
    _puckDot.shadowOpacity = shadowOpacity;
    _puckDot.shadowPath = [[UIBezierPath bezierPathWithOvalInRect:_puckDot.bounds] CGPath];

    if (self.mapView.camera.pitch) {
      [self updateFaux3DEffect];
    } else {
      _puckDot.shadowOffset = CGSizeMake(0, 1);
      _puckDot.shadowRadius = 0.75;
    }

    [self.layer addSublayer:_puckDot];
  }

  // arrow
  //
  if (!_puckArrow) {
    _puckArrow = [CAShapeLayer layer];
    _puckArrow.path = [[self puckArrow] CGPath];
    _puckArrow.fillColor = [arrowColor CGColor];
    _puckArrow.bounds = CGRectMake(0, 0, round(MLNUserLocationAnnotationArrowSize),
                                   round(MLNUserLocationAnnotationArrowSize));
    _puckArrow.position = CGPointMake(CGRectGetMidX(super.bounds), CGRectGetMidY(super.bounds));
    _puckArrow.shouldRasterize = YES;
    _puckArrow.rasterizationScale = [UIScreen mainScreen].scale;
    _puckArrow.drawsAsynchronously = YES;

    _puckArrow.lineJoin = @"round";
    _puckArrow.lineWidth = 1.f;
    _puckArrow.strokeColor = _puckArrow.fillColor;

    [self.layer addSublayer:_puckArrow];
  }
  if (self.userLocation.location.course >= 0) {
    _puckArrow.affineTransform = CGAffineTransformRotate(
        CGAffineTransformIdentity,
        -MLNRadiansFromDegrees(self.mapView.direction - self.userLocation.location.course));
  }

  if (!_puckModeActivated) {
    _puckModeActivated = YES;

    [self updateFaux3DEffect];
  }
}

- (UIBezierPath *)puckArrow {
  CGFloat max = MLNUserLocationAnnotationArrowSize;

  UIBezierPath *bezierPath = UIBezierPath.bezierPath;
  [bezierPath moveToPoint:CGPointMake(max * 0.5, 0)];
  [bezierPath addLineToPoint:CGPointMake(max * 0.1, max)];
  [bezierPath addLineToPoint:CGPointMake(max * 0.5, max * 0.65)];
  [bezierPath addLineToPoint:CGPointMake(max * 0.9, max)];
  [bezierPath addLineToPoint:CGPointMake(max * 0.5, 0)];
  [bezierPath closePath];

  return bezierPath;
}

- (void)drawDot {
  if (_puckModeActivated) {
    self.layer.sublayers = nil;

    _puckDot = nil;
    _puckArrow = nil;

    [self updateFrameWithSize:MLNUserLocationAnnotationDotSize];
  }

  UIColor *haloColor = self.mapView.tintColor;
  UIColor *puckBackgroundColor = self.mapView.tintColor;
  UIColor *puckShadowColor = UIColor.blackColor;
  CGFloat shadowOpacity = 0.25;

  if ([self.mapView.delegate
          respondsToSelector:@selector(mapViewStyleForDefaultUserLocationAnnotationView:)]) {
    MLNUserLocationAnnotationViewStyle *style =
        [self.mapView.delegate mapViewStyleForDefaultUserLocationAnnotationView:self.mapView];
    haloColor = style.haloFillColor ? style.haloFillColor : haloColor;
    puckBackgroundColor = style.puckFillColor ? style.puckFillColor : puckBackgroundColor;
    puckShadowColor = style.puckShadowColor ? style.puckShadowColor : puckShadowColor;
    shadowOpacity = style.puckShadowOpacity;
  }

  // heading indicator (tinted, beam or arrow)
  //
  BOOL headingTrackingModeEnabled =
      self.mapView.userTrackingMode == MLNUserTrackingModeFollowWithHeading;
  BOOL showHeadingIndicator = self.mapView.showsUserHeadingIndicator || headingTrackingModeEnabled;

  if (showHeadingIndicator) {
    _headingIndicatorLayer.hidden = NO;
    CLLocationDirection headingAccuracy = self.userLocation.heading.headingAccuracy;

    if (([_headingIndicatorLayer isMemberOfClass:[MLNUserLocationHeadingBeamLayer class]] &&
         !headingTrackingModeEnabled) ||
        ([_headingIndicatorLayer isMemberOfClass:[MLNUserLocationHeadingArrowLayer class]] &&
         headingTrackingModeEnabled)) {
      [_headingIndicatorLayer removeFromSuperlayer];
      _headingIndicatorLayer = nil;
      _oldHeadingAccuracy = -1;
    }

    if (!_headingIndicatorLayer && headingAccuracy) {
      if (headingTrackingModeEnabled) {
        _headingIndicatorLayer =
            [[MLNUserLocationHeadingBeamLayer alloc] initWithUserLocationAnnotationView:self];
        [_headingIndicatorLayer updateTintColor:[haloColor CGColor]];
        [self.layer insertSublayer:_headingIndicatorLayer below:_dotBorderLayer];
      } else {
        _headingIndicatorLayer =
            [[MLNUserLocationHeadingArrowLayer alloc] initWithUserLocationAnnotationView:self];
        [_headingIndicatorLayer updateTintColor:[puckBackgroundColor CGColor]];
        [self.layer addSublayer:_headingIndicatorLayer];
        _headingIndicatorLayer.zPosition = 1;
      }
    }

    if (_oldHeadingAccuracy != headingAccuracy) {
      [_headingIndicatorLayer updateHeadingAccuracy:headingAccuracy];
      _oldHeadingAccuracy = headingAccuracy;
    }

    CLLocationDirection headingDirection =
        (self.userLocation.heading.trueHeading >= 0 ? self.userLocation.heading.trueHeading
                                                    : self.userLocation.heading.magneticHeading);
    if (headingDirection >= 0) {
      CGFloat rotation = -MLNRadiansFromDegrees(self.mapView.direction - headingDirection);

      // Don't rotate if the change is imperceptible.
      if (fabs(rotation) > MLNUserLocationHeadingUpdateThreshold) {
        [CATransaction begin];
        [CATransaction setDisableActions:YES];

        _headingIndicatorLayer.affineTransform =
            CGAffineTransformRotate(CGAffineTransformIdentity, rotation);

        [CATransaction commit];
      }
    }
  } else {
    [_headingIndicatorLayer removeFromSuperlayer];
    _headingIndicatorLayer = nil;
  }

  // update accuracy ring (if zoom or horizontal accuracy have changed)
  //
  if (_accuracyRingLayer &&
      (_oldZoom != self.mapView.zoomLevel ||
       _oldHorizontalAccuracy != self.userLocation.location.horizontalAccuracy)) {
    CGFloat accuracyRingSize = [self calculateAccuracyRingSize:self.mapView.zoomLevel];

    // only show the accuracy ring if it won't be obscured by the location dot
    if (accuracyRingSize > MLNUserLocationAnnotationDotSize + 15) {
      _accuracyRingLayer.hidden = NO;

      // disable implicit animation of the accuracy ring, unless triggered by a change in accuracy
      BOOL shouldDisableActions =
          _oldHorizontalAccuracy == self.userLocation.location.horizontalAccuracy;

      [CATransaction begin];
      [CATransaction setDisableActions:shouldDisableActions];

      _accuracyRingLayer.bounds = CGRectMake(0, 0, accuracyRingSize, accuracyRingSize);
      _accuracyRingLayer.cornerRadius = accuracyRingSize / 2.0;

      // match the halo to the accuracy ring
      _haloLayer.bounds = _accuracyRingLayer.bounds;
      _haloLayer.cornerRadius = _accuracyRingLayer.cornerRadius;
      _haloLayer.shouldRasterize = NO;

      [CATransaction commit];
    } else {
      _accuracyRingLayer.hidden = YES;

      _haloLayer.bounds =
          CGRectMake(0, 0, MLNUserLocationAnnotationHaloSize, MLNUserLocationAnnotationHaloSize);
      _haloLayer.cornerRadius = MLNUserLocationAnnotationHaloSize / 2.0;
      _haloLayer.shouldRasterize = YES;
      _haloLayer.rasterizationScale = [UIScreen mainScreen].scale;
    }

    // store accuracy and zoom so we're not redrawing unchanged location updates
    _oldHorizontalAccuracy = self.userLocation.location.horizontalAccuracy;
    _oldZoom = self.mapView.zoomLevel;
  }

  // accuracy ring (circular, tinted, mostly-transparent)
  //
  if (!_accuracyRingLayer && self.userLocation.location.horizontalAccuracy) {
    CGFloat accuracyRingSize = [self calculateAccuracyRingSize:self.mapView.zoomLevel];
    _accuracyRingLayer = [self circleLayerWithSize:accuracyRingSize];
    _accuracyRingLayer.backgroundColor = [self.mapView.tintColor CGColor];
    _accuracyRingLayer.opacity = 0.1;
    _accuracyRingLayer.shouldRasterize = NO;
    _accuracyRingLayer.allowsGroupOpacity = NO;

    [self.layer addSublayer:_accuracyRingLayer];
  }

  // expanding sonar-like pulse (circular, tinted, fades out)
  //
  if (!_haloLayer) {
    _haloLayer = [self circleLayerWithSize:MLNUserLocationAnnotationHaloSize];
    _haloLayer.backgroundColor = [haloColor CGColor];
    _haloLayer.allowsGroupOpacity = NO;
    _haloLayer.zPosition = -0.1f;

    // set defaults for the animations
    CAAnimationGroup *animationGroup = [self loopingAnimationGroupWithDuration:3.0];

    // scale out radially with initial acceleration
    CAKeyframeAnimation *boundsAnimation =
        [CAKeyframeAnimation animationWithKeyPath:@"transform.scale.xy"];
    boundsAnimation.values = @[ @0, @0.35, @1 ];
    boundsAnimation.keyTimes = @[ @0, @0.2, @1 ];

    // go transparent as scaled out, start semi-opaque
    CAKeyframeAnimation *opacityAnimation = [CAKeyframeAnimation animationWithKeyPath:@"opacity"];
    opacityAnimation.values = @[ @0.4, @0.4, @0 ];
    opacityAnimation.keyTimes = @[ @0, @0.2, @1 ];

    animationGroup.animations = @[ boundsAnimation, opacityAnimation ];

    [_haloLayer addAnimation:animationGroup forKey:@"animateTransformAndOpacity"];

    [self.layer addSublayer:_haloLayer];
  }

  // background dot (white with black shadow)
  //
  if (!_dotBorderLayer) {
    _dotBorderLayer = [self circleLayerWithSize:MLNUserLocationAnnotationDotSize];
    _dotBorderLayer.backgroundColor = [[UIColor whiteColor] CGColor];
    _dotBorderLayer.shadowColor = [puckShadowColor CGColor];
    _dotBorderLayer.shadowOpacity = shadowOpacity;
    _dotBorderLayer.shadowPath =
        [[UIBezierPath bezierPathWithOvalInRect:_dotBorderLayer.bounds] CGPath];

    if (self.mapView.camera.pitch) {
      [self updateFaux3DEffect];
    } else {
      _dotBorderLayer.shadowOffset = CGSizeMake(0, 0);
      _dotBorderLayer.shadowRadius = 3;
    }

    [self.layer addSublayer:_dotBorderLayer];
  }

  // inner dot (pulsing, tinted)
  //
  if (!_dotLayer) {
    _dotLayer = [self circleLayerWithSize:MLNUserLocationAnnotationDotSize * 0.75];
    _dotLayer.backgroundColor = [puckBackgroundColor CGColor];

    // set defaults for the animations
    CAAnimationGroup *animationGroup = [self loopingAnimationGroupWithDuration:1.5];
    animationGroup.autoreverses = YES;
    animationGroup.fillMode = kCAFillModeBoth;

    // scale the dot up and down
    CABasicAnimation *pulseAnimation =
        [CABasicAnimation animationWithKeyPath:@"transform.scale.xy"];
    pulseAnimation.fromValue = @0.8;
    pulseAnimation.toValue = @1;

    // fade opacity in and out, subtly
    CABasicAnimation *opacityAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
    opacityAnimation.fromValue = @0.8;
    opacityAnimation.toValue = @1;

    animationGroup.animations = @[ pulseAnimation, opacityAnimation ];

    [_dotLayer addAnimation:animationGroup forKey:@"animateTransformAndOpacity"];

    [self.layer addSublayer:_dotLayer];
  }

  if (_puckModeActivated) {
    _puckModeActivated = NO;

    [self updateFaux3DEffect];
  }
}

- (void)drawApproximate {
  if (!_approximateModeActivated) {
    self.layer.sublayers = nil;

    _headingIndicatorLayer = nil;
    _dotBorderLayer = nil;
    _dotLayer = nil;
    _accuracyRingLayer = nil;
    _haloLayer = nil;
    _puckDot = nil;
    _puckArrow = nil;

    _approximateModeActivated = YES;
  }

  UIColor *backgroundColor = self.mapView.tintColor;
  UIColor *strokeColor = UIColor.blackColor;
  CGFloat borderSize = 2.0;
  CGFloat opacity = 0.25;

  if ([self.mapView.delegate
          respondsToSelector:@selector(mapViewStyleForDefaultUserLocationAnnotationView:)]) {
    MLNUserLocationAnnotationViewStyle *style =
        [self.mapView.delegate mapViewStyleForDefaultUserLocationAnnotationView:self.mapView];
    if (@available(iOS 14, *)) {
      backgroundColor =
          style.approximateHaloFillColor ? style.approximateHaloFillColor : backgroundColor;
      strokeColor =
          style.approximateHaloBorderColor ? style.approximateHaloBorderColor : strokeColor;
      opacity = style.approximateHaloOpacity;
      borderSize = style.approximateHaloBorderWidth;
    }
  }

  // approximate ring
  if (!_approximateLayer && self.userLocation.location.horizontalAccuracy) {
    CGFloat accuracyRingSize =
        [self calculateAccuracyRingSize:MAX(self.mapView.zoomLevel,
                                            MLNUserLocationApproximateZoomThreshold)];
    _approximateLayer = [self circleLayerWithSize:accuracyRingSize];
    _approximateLayer.backgroundColor = [backgroundColor CGColor];
    _approximateLayer.opacity = opacity;
    _approximateLayer.shouldRasterize = NO;
    _approximateLayer.allowsGroupOpacity = NO;
    _approximateLayer.borderWidth = borderSize;
    _approximateLayer.borderColor = [strokeColor CGColor];

    [self.layer addSublayer:_approximateLayer];
  }

  // update approximate ring (if zoom or horizontal accuracy have changed)
  if (_approximateLayer &&
      (_oldZoom != self.mapView.zoomLevel ||
       _oldHorizontalAccuracy != self.userLocation.location.horizontalAccuracy)) {
    if (self.mapView.zoomLevel < MLNUserLocationApproximateZoomThreshold) {
      borderSize = 1.0;
    }
    _approximateLayer.borderWidth = borderSize;

    if (self.mapView.zoomLevel >= MLNUserLocationApproximateZoomThreshold) {
      CGFloat accuracyRingSize = [self calculateAccuracyRingSize:self.mapView.zoomLevel];

      _approximateLayer.hidden = NO;

      // disable implicit animation of the accuracy ring, unless triggered by a change in accuracy
      BOOL shouldDisableActions =
          _oldHorizontalAccuracy == self.userLocation.location.horizontalAccuracy;

      [CATransaction begin];
      [CATransaction setDisableActions:shouldDisableActions];

      _approximateLayer.bounds = CGRectMake(0, 0, accuracyRingSize, accuracyRingSize);
      _approximateLayer.cornerRadius = accuracyRingSize / 2.0;

      [CATransaction commit];
    }

    // store accuracy and zoom so we're not redrawing unchanged location updates
    _oldHorizontalAccuracy = self.userLocation.location.horizontalAccuracy;
    _oldZoom = self.mapView.zoomLevel;
  }
}

- (CALayer *)circleLayerWithSize:(CGFloat)layerSize {
  layerSize = round(layerSize);

  CALayer *circleLayer = [CALayer layer];
  circleLayer.bounds = CGRectMake(0, 0, layerSize, layerSize);
  circleLayer.position = CGPointMake(CGRectGetMidX(super.bounds), CGRectGetMidY(super.bounds));
  circleLayer.cornerRadius = layerSize / 2.0;
  circleLayer.shouldRasterize = YES;
  circleLayer.rasterizationScale = [UIScreen mainScreen].scale;
  circleLayer.drawsAsynchronously = YES;

  return circleLayer;
}

- (CAAnimationGroup *)loopingAnimationGroupWithDuration:(CGFloat)animationDuration {
  CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
  animationGroup.duration = animationDuration;
  animationGroup.repeatCount = INFINITY;
  animationGroup.removedOnCompletion = NO;
  animationGroup.timingFunction =
      [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault];

  return animationGroup;
}

- (CGFloat)calculateAccuracyRingSize:(double)zoomLevel {
  // diameter in screen points
  return round(self.userLocation.location.horizontalAccuracy /
               [self.mapView metersPerPointAtLatitude:self.userLocation.coordinate.latitude
                                            zoomLevel:zoomLevel] *
               2.0);
}

@end