I'm looking for book/course/materials recommendations for learning iOS development. Self study, not a bootcamp or other paid or ISA program

I have a fairly straightforward game/social chat concept in mind to use as my muse. It doesn't require any complex math, physics engine etc, would mostly just be a crud app with some timing elements. I do have some experience developing simple web apps with ruby (rails + sinatra) so not starting from 0, but am still very much a beginner. Especially with regards to languages like Objective-C and maybe swift that aren't as intuitive/readable to someone without a CS background.

Many thanks.