Get a notification when someone changes the keyboard language

Example.cs

ObservableKeyboard.InputProfileChanged
    .Subscribe(_ => Console.WriteLine("Hey it changed!"));

ObservableKeyboard.cs

using System;
using System.Reactive;
using System.Reactive.Disposables;
using System.Reactive.Linq;
using System.Runtime.InteropServices;
using ReactiveUI;
using TSF.InteropTypes;
using TSF.TypeLib;

namespace Peach
{
    public static class ObservableKeyboard
    {
        static readonly Guid IID_ITfLanguageProfileNotifySink = new Guid("43C9FE15-F494-4C17-9DE2-B8A4AC350AA8");

        static ObservableKeyboard()
        {
            var inputProfileChanged = Observable.Create<Unit>((subj) => {
                var ns = new NotifySink();
                var type = Type.GetTypeFromCLSID(new Guid(CLSIDs.CLSID_TF_InputProcessorProfiles));
                var source = (ITfSource)Activator.CreateInstance(type);
                var disp = ns.Subscribe(subj);

                uint cookie = 0;
                var hr = source.AdviseSink(IID_ITfLanguageProfileNotifySink, ns, out cookie);
                if (!hr.Succeeded) {
                    subj.OnError(Marshal.GetExceptionForHR(hr.Code));
                }

                return Disposable.Create(() => {
                    if (cookie != 0) source.UnadviseSink(cookie);

                    Marshal.ReleaseComObject(source);
                    disp.Dispose();
                });
            });

            InputProfileChanged = inputProfileChanged.Publish().RefCount();
        }

        public static IObservable<Unit> InputProfileChanged { get; private set; }
    }

    public class NotifySink : ITfLanguageProfileNotifySink, IObservable<Unit>
    {
        readonly ScheduledSubject<Unit> inner = new ScheduledSubject<Unit>(RxApp.MainThreadScheduler);

        public HRESULT OnLanguageChange(LangID langid, out bool pfAccept)
        {
            // NB: This doesn't even get called most of the time
            pfAccept = true;
            return new HRESULT { Code = 0 };
        }

        public HRESULT OnLanguageChanged()
        {
            inner.OnNext(Unit.Default);
            return new HRESULT { Code = 0 };
        }

        public IDisposable Subscribe(IObserver<Unit> observer)
        {
            return inner.Subscribe(observer);
        }
    }
}