Recognize a sequence of elements with minimum and maximum duration - system.reactive

Question

Given a IObservable<bool>,and two TimeSpan thresholds, minDuration and maxDuration, I need to transform the sequence so that:
A sequence of true values that spans a time between minDuration and maxDuration transforms to "x"
A sequence of true values that spans more than maxDuration transforms to "y"; "y" should be emitted after maxDuration time passed since the first true value was emitted
To make things clearer, assuming minDuration = 3, maxDuration = 6, and assuming items are emitted at the speed of one per second:
fffttffttfftttttttttttffftttffffttttf
------------------y--------x-------x-
My guess is that I need to implement a custom operator, but as a RX newbie I don't know how, and I'm having a hard time finding examples that go beyond composing the existing operator with an extension method.
Links to tutorials and examples on implementing custom operators are welcome.

Answer 1

If I understand this right:
When you get consecutive true values for more than the minDuration but less than the maxDuration, you want to emit x.
When you get consecutive true values for more than the maxDuration, you want to emit y.
In any other scenario, emit nothing.
If that's the case, your marble diagram should look more like this:
fffttffttfftttttttttttffftttffffttttf
1234567 123 1234 (numbers for counting guidance)
-----------------y----------x-------x (mine)
------------------y--------x-------x- (yours)
The x can only come out on the false. You can't emit it on the true, because you don't know what a future value will be! No custom operator can solve that for you.
The rest could be solved with this:
var values = new List<bool> // matches fffttffttfftttttttttttffftttffffttttf
{
false,
false,
false,
true,
true,
false,
false,
true,
true,
false,
false,
true,
true,
true,
true,
true,
true,
true,
true,
true,
true,
true,
false,
false,
false,
true,
true,
true,
false,
false,
false,
false,
true,
true,
true,
true,
false,
};
var original = Observable.Interval(TimeSpan.FromSeconds(1))
.Where(i => i < values.Count)
.Select(i => values[(int)i]);
TimeSpan minDuration = TimeSpan.FromSeconds(3);
TimeSpan maxDuration = TimeSpan.FromSeconds(6);
var trueWindows = original
.TimeInterval()
.Scan(TimeSpan.Zero, (a, t) => t.Value
? a + t.Interval
: TimeSpan.Zero);
var coupledWindows = trueWindows.Scan(new {Previous = TimeSpan.Zero, Current = TimeSpan.Zero},
(o, t) => new {Previous = o.Current, Current = t})
.Publish()
.RefCount();
var xS = coupledWindows.Where(o => o.Previous < maxDuration && o.Previous >= minDuration && o.Current == TimeSpan.Zero).Select(t => "X");
var yS = coupledWindows.Where(o => o.Current >= maxDuration && o.Previous < maxDuration).Select(t => "Y");
As for tutorials, the best resource is http://introtorx.com/. Another somewhat good one is http://rxmarbles.com, though it uses non-.NET function names.