GeolocatorServiceExtensions.cs

using System;
using System.Linq;
using System.Reactive.Linq;
using System.Threading;
using System.Threading.Tasks;
using Windows.Devices.Geolocation;

namespace GeolocatorService
{
	public static class GeolocatorServiceExtensions
	{
		/// <summary>
		/// Observes the user's location.
		/// </summary>
		public static IObservable<Geocoordinate> ObserveLocation(this IGeolocatorService service)
		{
			return Observable.FromEventPattern<LocationChangedEventHandler, LocationChangedEventArgs> (
				h => service.LocationChanged += h,
				h => service.LocationChanged -= h
			)
			.Select(p => p.EventArgs.Coordinate);
		}

		/// <summary>
		/// Gets and observes the user's location (or null if it's unavailable). Requests the permission if this was not already done.
		/// The location becomes null as soon as the location permission is denied.
		/// </summary>
		public static IObservable<Geocoordinate> GetAndObserveLocationOrDefault(this IGeolocatorService service)
		{
			var initialLocationOrNull = Observable.Create<Geocoordinate>(service.GetInitialLocationOrDefault);
			var locationObservable = ObserveLocation(service);
			var locationUnavailableObservable = ObserveIsPermissionGranted(service)
				.Where(isGranted => !isGranted)
				.Select(_ => default(Geocoordinate));

			return Observable.Merge(initialLocationOrNull, locationObservable, locationUnavailableObservable);
		}

		private static async Task GetInitialLocationOrDefault(this IGeolocatorService service, IObserver<Geocoordinate> observer, CancellationToken ct)
		{
			var isPermissionGranted = await service.RequestPermission(ct);
			var currentLocationOrNull = isPermissionGranted ? await service.GetLocationOrDefault(ct) : null;
			observer.OnNext(currentLocationOrNull);
		}

		/// <summary>
		/// Observes the location permission.
		/// </summary>
		public static IObservable<bool> ObserveIsPermissionGranted(this IGeolocatorService service)
		{
			return Observable.FromEventPattern<LocationPermissionChangedEventHandler, LocationPermissionChangedEventArgs>(
				h => service.LocationPermissionChanged += h,
				h => service.LocationPermissionChanged -= h
			)
			.Select(p => p.EventArgs.IsLocationPermissionGranted);
		}

		/// <summary>
		/// Gets and observes the location permission. Requests the permission if this was not already done.
		/// </summary>
		public static IObservable<bool> GetAndObserveIsPermissionGranted(this IGeolocatorService service)
		{
			var initialPermission = Observable.Create<bool>(service.GetInitialPermission);

			return ObserveIsPermissionGranted(service).Merge(initialPermission);
		}

		private static async Task GetInitialPermission(this IGeolocatorService service, IObserver<bool> observer, CancellationToken ct)
		{
			var isPermissionGranted = await service.RequestPermission(ct);
			observer.OnNext(isPermissionGranted);
		}
	}
}