returns an observable that provides the first in a window and lets you know when the window closes and what was in the window

EarlyWarning.cs

void Main()
{
	var closer = new Subject<Tuple<WindowState, IList<long>>>();
	
	closer.Select(c => {
		if (c.Item1 == WindowState.Open)
		{
			return $"Should email, with an event of {c.Item2.Single()}";
		}
		else
		{
			return $"should do nothing but will write a checkpoint for {c.Item2.Max()}, because we had {String.Join(",", c.Item2.Select(i=>i.ToString()))}";
		}
	}).Timestamp().Dump();
	
	var outer = Observer.Create<IObservable<long>>(o =>
	{
		Console.WriteLine("Got start of window");
		var ws = new WindowInfo();
		//closer.OnNext(Tuple.Create<WindowState, IList<long>>(WindowState.Open, new List<long>()));
		var inner = Observer.Create<long>(ob => {
				ws.Add(ob);
				if (ws.GetInternal().Count() <=1) // only want to signal on the first one
					closer.OnNext( Tuple.Create<WindowState, IList<long>>(WindowState.Open, new List<long>() { ob}));
				}, e1 => Console.Error.WriteLine("Inner Exception"),
			// on complete()
			() => {
				Console.WriteLine("Closed Window");
				var closerValue = Tuple.Create<WindowState,IList<long>>(WindowState.Closed, ws.GetInternal());
				closer.OnNext(closerValue);
			});		
		var innerSub = o.Subscribe(inner);
	}, e=>Console.Error.WriteLine("Got Exception"), ()=>Console.WriteLine("Done"));
	var timer = Observable.Interval(TimeSpan.FromSeconds(1))
		.Do(o => Console.WriteLine("new value in window")) // just for debugging
		.Window(5)
		.Subscribe(outer);
		
	Console.ReadLine();	
}

public enum WindowState{
	Open,
	Closed
}

public class WindowInfo{
	protected List<long> internalValues = new List<long>();
	public void Add(long l){
		internalValues.Add(l);
	}
	public IList<long> GetInternal(){
		return internalValues;
	}
}