Getting value since noon with deltaSince

Setup, Configuration and Use Scripts & Rules
1

I am on latest stable OH4.x and am struggling with a rule:

I have an number item which gets updated with a metering value every 5-10 sec. I want to keep track of the usage (here divided by 1000) since midnight and since noon.
Since midnight works - both since noon only keeps the right value until midnight - and then gets reset to 0 and stays 0 until noon. How can I mitigate this ? Do I need to add logic to swap the now.with(LocalTime to .MIN after midnight and LocalTime.NOON before? There must be a simpler way ?

		var Number todayKWh
        todayKWh = (wattslive_positive_active_energy.deltaSince(now.with(LocalTime.MIN), "rrd4j")) / 1000
		electricity_meter_dailyTotalKWh.postUpdate(todayKWh)

		var Number noonKWh
		noonKWh = (wattslive_positive_active_energy.deltaSince(now.with(LocalTime.NOON), "rrd4j")) / 1000 
		electricity_meter_noonTotalKWh.postUpdate(noonKWh)
2

Check the current time. If it’s before noon, start from the previous day’s noon

3

what would such an “if” statement look like ?

4 
var noon = now.with(LocalTime.NOON)
if (now.isBefore(noon)) {
  noon = noon.minusDays(1)
}
5

Thanks for leading me on the right track. This is how it looked in the end (working):

		var Number noonKWh
		if (now.isBefore(now.with(LocalTime.NOON))) {
			noonKWh = (wattslive_positive_active_energy.deltaSince(now.with(LocalTime.NOON).minusDays(1), "rrd4j")) / 1000 
		} else {
			noonKWh = (wattslive_positive_active_energy.deltaSince(now.with(LocalTime.NOON), "rrd4j")) / 1000 
		}
		electricity_meter_noonTotalKWh.postUpdate(noonKWh)
6 
var noon = now.with(LocalTime.NOON)
if (now.isBefore(noon)) {
  noon = noon.minusDays(1)
}
		
var noonKWh = wattslive_positive_active_energy.deltaSince(noon, "rrd4j") / 1000 
electricity_meter_noonTotalKWh.postUpdate(noonKWh)

Additional note: rrd4j isn’t the best backend for doing these sorts of things. Pick influxdb or something, anything other than rrd4j (or mapdb). rrd4j is lossy.