// Assuming https://github.com/slightlyoff/ServiceWorker/issues/421 gets
// resolved this gives access to the API both from main pages and from within
// the service worker itself, and seems cleaner than exposing this on the
// service worker global scope.
partial interface ServiceWorkerRegistration {
  readonly attribute GeofencingController geofencing;
};

partial interface ServiceWorkerGlobalScope {
  attribute EventHandler ongeofenceenter;
  attribute EventHandler ongeofenceleave;
  attribute EventHandler ongeofenceerror;
};

interface GeofencingEvent : ExtendableEvent {
  readonly attribute GeofenceRegistration registration;
  readonly attribute Position? position;
};

// Not sure about specific error conditions. But some way of telling service
// workers about error conditions is needed.
interface GeofencingErrorEvent : GeofencingEvent {
  readonly attribute GeofencingError error;
};

interface GeofencingController {
  Promise<GeofenceRegistration> registerRegion( GeofencingRegion initialRegion, optional GeofenceRegisterOptions options );
  Promise<sequence<GeofenceRegistration>> getRegisteredRegions(optional GeofencingRegistrationQueryOptions options);
  Promise<GeofenceRegistration> getRegisteredRegion(DOMString id);
};

dictionary GeofenceRegisterOptions {
  bool includePosition = false;
};

// Similar API to ServiceWorkerClients.getAll(), nice to have, but I could
// live without it as well.
dictionary GeofencingRegistrationQueryOptions {
  DOMString? name; // optionally filter by name
};

interface GeofenceRegistration {
  readonly attribute DOMString id;     // SWRegistration-unique ID
  readonly attribute DOMString name;   // optional user-supplied name
  readonly GeofencingRegion region;
  
  Promise<undefined> unregister();
};

dictionary GeofencingRegionInit {
  DOMString name = ""; // optional user-supplied name
};

[NoInterfaceObject]
interface GeofencingRegion {
  readonly attribute DOMString name;
};

dictionary GeolocationPoint {
  double latitude;
  double longitude;
};

dictionary CircularGeofencingRegionInit : GeofencingRegionInit {
  double latitude;
  double longitude;
  double radius;
};

[Constructor(CircularGeofencingRegionInit), exposed=Worker]
interface CircularGeofencingRegion : GeofencingRegion {
  readonly attribute GeolocationPoint center;
  readonly attribute double radius;
};
 
// Other potential region types:
// Polygon of nonintersecting line segments.
[Constructor(dictionary options), exposed=Worker]
interface PolygonRegion : GeofencingRegion {
  readonly attribute sequence<GeolocationPoint> points;
};



Use case test:

Promise<GeofenceRegistration> registerRegion(
    new CircularRegion( {
      name: "myfence",
      latitude: 123,
      longitude: -1000,
      radius: 1
    }));

Promise<sequence<GeofenceRegistration> > getRegisteredRegions(
    {name: "myfence"});