Fix time_date sensor to update at predictable intervals

[stu-gott]

Description:

Change the time_date sensor to update when the time or date actually changes. Previous behavior asserts no control over when updates occur so they happen randomly/sporadically.

Related issue (if applicable): fixes #

Pull request in home-assistant.github.io with documentation (if applicable): No docs impact

Checklist:

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[mention-bot]

@stu-gott, thanks for your PR! By analyzing the history of the files in this pull request, we identified @molobrakos, @balloob and @fabaff to be potential reviewers.

[balloob]

You can just do this:

from datetime import timedelta

return now + timedelta(seconds=interval)

[stu-gott]

The intent of this code is to have the sensor update approximately at the time that the minute/date actually changes.
I had two specific cases in mind that a straightforward timedelta fails to address.

1. Home Assistant restart: we have no way of knowing how many seconds into a minute a sensor will be instantiated. an extreme example is Home Assistant being restarted at 2 PM local time for a date sensor. waiting a full 86400 seconds to update state means the sensor will read the previous day's setting until 2 PM.
2. Time skew as Home Assistant runs. because it takes a finite amount of time for this code to run (and the system is cooperative multitasking), blindly asking for a 60-second sleep interval forever means this function will be called late. by re-computing how much time is left in the interval, we will stay on track.

[balloob]

You're right, I didn't fully copy your algorithm. I was merely trying to point out that Python has a built-in class to work with time periods.

[stu-gott]

Ah. That does make the code more readable. Thanks!

[balloob]

Thanks! 🐬 🍺 🎉 🌮