Ability to know when an expunge has finished

At the company I work for, we do nightly expunges to clear down deleted docs (providing the threshold is above 5% in our case).

Whilst this has been okay for us, we want the ability to know when an expunge has completed. At the moment we do some calculations to estimate how long it would take.

it would be nice if there was a way to see when an expunge has completed. This could either be by assigning an async id to the call, or any other means of having visibility.

I started to look into this issue, but saw that the underlying call for expunging starts to use the lucene side of the code base, so thought I was digging to deep, so any advice on this issue would be much appreciated (as I'm trying to contribute more to OOS).