Scripting: Total food for a faction

[crzyrndm]

How do I access this value?

I want to add a dynamic bonus depending on the amount of food surplus a faction has, but to do this I need to know how much food a faction has in the first place.

The idea is to use the surplus to add bonus income/order/growth to a faction according to the size of the surplus recorded for which I'm probably going to have to hijack a bunch of traits to make the effects work (I'm assuming here that I can't just go effect.gdp_mod_all(val) to increase the income of a faction)