My goal using the rain barrel when it has water left

Hi,
Can anyone guide me on how I can manage a rain barrel as a water source for a 3 zone drip irregation system.

Here is what I plan to do:
1) use pump start zone to activate a water pump to pull water out of barrel and pump it into the irregation manifold when there is water left in the barrel. I think I may need to integrate another sensor.

2) phase 2 , fill up the rain barrel when there is no rain and its empty

thanks for any ideas