I have a few days off and I am trying to determine if automata theory is something I would like to learn more about in the future. I've come across mentions of semirings and monoidal categories, and this is the direction I'd go in. So I'm looking for two things:

1. A brief review of automata theory to get a general feel for the field and
2. Some papers that detail how abstract algebra and category theory are used in automata theory.

Any recommendations are welcome.