OS X/macOS's HID stack is called IOHIDFamily, and much of it is open source. This includes kernel and userspace components. You can find the code for various different OS X/macOS releases at
https://opensource.apple.com/
For 10.12.2 (latest code released at time of writing) you can browse the IOHIDFamily code here:
https://opensource.apple.com/source/IOHIDFamily/IOHIDFamily-870.31.1/
or download it as a zip file here:
https://opensource.apple.com/tarballs/IOHIDFamily/IOHIDFamily-870.31.1.tar.gz
The "tools" directory contains some userspace sample/test code which might help with what you're trying to do.
As for sample code not being updated, documentation being incomplete/outdated/missing, and provided code requiring a lot of effort to build: welcome to Mac systems & driver development. That's unfortunately how it is. I've been doing OS X kernel/driver work for 7 years, and while some things get easier with experience, downloading code from Apple and building it still feels like playing the lottery.