What is the recommended way to implement a new encoder in the VESC firmware?

I am looking to implement a new absolute encoder via the hardware SPI interface.

For encoder details see: https://www.rls.si/eng/orbis-true-absolute-rotary-encoder

What is the recommended way to implement that:

1. Add to the  "encoder.c" and "encoder.h" code
2. Add the code in a separate file included/referenced in the "encoder.c" and "encoder.h" files
3. Create a custom application

Thanks,

Toma