how to make a parallel bezier curve heuristically in Swift 2.2+

I want to draw an object that becomes a SKShapeNode that will be a path that a player could walk on.

I saw a pretty reasonable solution for this problem here

but since it's a few years old, its not in the latest Swift... it may also not be taking advantage of new OS features.

Would anybody be interested in updating the answer to be compatible with Swift 2.2/ios 9 or later?

I'd love to see!