Charles Stross' Laundry series is basically this concept set in the present day: magic is a branch of mathematics, which means it can be computed and programmed.
It is perhaps worth noting at this point the series genre is cosmic horror.
You know fun fact I learned recently from a let's play: tentacles only refer to the appendages which end in suckers, but along the rest of their length, have no suckers. The other appendages are called arms. So, octopuses actually have no tentacles, they have arms. Squids have 8 arms, and 2 extra tentacles, which are the long ones that have little spade shaped sucker hands on them. So, probably when you pictured tentacles, you were actually picturing cephalopod arms.
This series seems to check more boxes than I thought I had...
i'm adding it to the top of the list. Except i don't have a list, so I'm creating a list and adding it to that and therefore it automatically finds itself at the top of it.
So that explains the apparent undead working for them...I only read the first book or three and it's been a minute. This is the sign for me to go back and finish the series.