https://github.com/mongodb/mongo/blob/4941c446e9091caa1f7151bd874c8d5b72c39bb8/src/mongo/db/s/resharding/resharding_metrics.cpp#L226

This algorithm estimates remaining operation time.

I believe it's incorrect in the case of (bytesCopied>0 && oplogEntriesApplied==0), which would be the forward-looking estimate made from within the copy phase.

It also has significant numerical issues in the granularity of the integer math. Integer division takes place too eagerly via operator/ and via duration casting.

Let's review, improve, and test it.