Make derivative sensor unavailable when source sensor is unavailable

[karwosts]

Proposed change

Make the derivative sensor unknown when its source sensor is non-numeric. The previous behavior just persists the previous value from the most recent time before the sensor had a bad value.

While the derivative sensor state is Unknown during the period its source sensor is non-numeric, as soon as the source sensor becomes available again, it calculates the derivative as if there was no gap in the source sensor, allowing brief periods of unavailability to not distort longer term derivative calculations.

Based on this revert PR this feature is one of the last missing pieces to re-enable statistics for Derivative sensor, which was previously reverted partially for this reason.

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[home-assistant]

Hey there @afaucogney, mind taking a look at this pull request as it has been labeled with an integration (derivative) you are listed as a code owner for? Thanks!

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[karwosts]

I can't figure out why this was here or what would ever thrown this Error.

[karwosts]

I initially started out with Unavailable instead of Unknown, but that didn't seem to work as well with the RestoreSensor.

For some reason when I shutdown HA and the sensor was Unavailable, when I booted it up again it would always restore to it's last-known-good-state, which doesn't seem like the right thing to do as the source sensor was still unavailable on boot, and it didn't seem right to put a valid-looking value there.

When I shutdown HA and the value is Unknown, then it correctly restores as Unknown, which I think is what I want.

[frenck]

This is not the correct behavior IMHO, I think we should make this sensor unavailable when the source sensor is unavailable as well.

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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[karwosts]

Ok, changed to make it unavailable instead of unknown.

Behavior is something like this:

• When added to hass, if source sensor is not setup, unavailable, or unknown, derivative is unavailable.

• When source sensor becomes available for the first time, derivative sensor becomes available and equal to the RestoreSensor state.

• When already added and source sensor becomes unavailable, derivative becomes unavailable.

• When already added and source sensor becomes unknown or non-numeric, derivative becomes unknown.

I think that's my best idea of how the rules should work, but let me know if I've misunderstood anything.

[frenck]

Thanks, @karwosts 👍

../Frenck