There was a talk at this year’s ElixirConf about Behavior Trees that might be applicable here. They’re a concept mostly from the video game industry and NPC behavior. They were new to me, but might be worth watching the talk to see if you’d want to try them for this.

I’ve just discovered a library named Opus which allows you to create pipelines using a declarative DSL. It even supports outputting a pipeline as a graph using GraphVix.

• How to create beautiful pipelines on Elixir with Opus

I’d create a module with a single entry point and all the rules as private functions within it, pattern matching where possible. In a roughly top down order.

def send_notification(user, message)

#called from send_notifications
defp channel_muted(user, message)

#called from channel_muted
defp message_and_subscribed(user, message)
…
…

I don’t see any way to get something with that complex of a flow in a way that could easily be shown to a business owner in code so I wouldn’t put much energy into trying since a flow chart like this is a better route for that. I’d focus exclusively on trying to get it to be easy for developers to slot in new rules. So things like making sure comments show all calling functions.