Hello

I am completely new to electronics and microcontrollers so please bear 
with me while I try to explain.

My current working project controls my plant grow light depending on the 
brightness (eg. sun is up/very cloudy/blinds are down).
It does so by using an AZDelivery Nano V3.0 with Atmega328 CH340 
(Arduino compatible) to poll a light sensor on an analog pin.
It then compares that value to a calibrated value to decide whether the 
plant light should be on or off. This then gets sent by means of serial 
communication with a ESP-01s over WiFi to my RaspberryPi** which 
switches a TP-Link HS100 smart switch on or off.

Although convoluted, it works fairly well but uses a lot of power as I 
never put anything in sleep mode and it's constantly connected to WiFi.

Now I would like to implement some means of saving power so that I can 
maybe even run this thing on a 9V battery for, I don't know, weeks at a 
time?

Additionally I would like to compare the value from the light sensor not 
against a single value because a cloud moving in for a few seconds would 
unnecessarily switch the light quickly. I thought that maybe I instead 
use an upper and lower bound and only switch when the value exceeds 
either, and do nothing in the middle range. I could easily do this in 
code however with the power saving I thought that maybe there is a nice 
way to do this with some additional parts.

Here are some of the points I'm having trouble with as I have no 
experience in electronics:

1. I've read that putting the ATmega328 in sleep disables the ADC, 
enabling the ADC in sleep so that it can be used as interrupt consumes a 
lot of power. Is there a way to make the lower/upper bound check in 
discrete* parts (while not using a lot of power?) so that I just use one 
or two digital pins which can wake up the ATmega328 for processing the 
brightness change.
2. I've also read that the ESP-01s does not have the means to wake up 
from deep sleep without soldering to the extremely tiny chip or by doing 
a reset (RST to GND). I would maybe just trigger a reset by pulling the 
RST pin of the ESP-01s to LOW through a 330 Ohm resistor and through an 
ATmega328 digital pin. Does that make sense?
3. Maybe there is even a way to accomplish the whole thing without even 
having to use the ATmega328***. The ESP-01s has a fairly capable 
microcontroller that can be programmed and two GPIO pins, so if I was 
able to do the brightness comparison in discrete* parts and then use one 
or two GPIO pins of the ESP-01s I could technically read the light level 
(not the exact value, just whether its below or above the lower and 
upper bounds) directly on the ESP-01s and then trigger the RaspberryPi** 
from there. Although that leaves the problem with the ESP-01s not being 
able to wake up from deep sleep without a reset, or maybe this can be 
implemented in discrete* logic too?

I hope that I have explained my issue in a comprehensible manner and 
that maybe you guys could give me some pointers what could be possible 
or even a completely different and more power saving approach. My main 
concern is the ability to save power to be able to run the whole thing 
on battery power, although the lower-upper-bound-thing would be a 
necessary addition in the future anyways.

For the lulz I have added a picture of the thing that I've made so you 
can point and laugh at some shitty beginners project ;) Note that right 
now I am using USB to supply power as the 9V battery has already 
drained.

Thank you for your time,
Gachl

\* Excuse my probably misuse of the term "discrete logic" or "discrete 
parts" - I don't just mean and/or gates and the likes but rather 
comparators and other parts outside of the two microcontrollers that I 
am currently using.

\*\* I'll probably be able to implement talking to the HS100 directly 
from a microcontroller so I can even skip having to talk to the RPi 
first but that should not be of concern right now. The Pi right now is 
necessary as it contains a real time clock which checks whether the time 
is between 8am and 8pm because the plant light should not be on outside 
of these hours.

\*\*\* I suppose an even better approach would be to use a variant of 
the ESP8266 that has more pins available but I already have three 
ESP-01s so I'd like to stick with them now.