Packer Module Support

Our team has a number of AWS AMI packer builds, written in JSON.
They are all essentially copy/paste of each other with some key variables adjusted.
As my team are heavy users of terraform and HCL packer is (imo) the best way to enable my team, I was hoping to create a reusable module in packer that could then be used going forward, and to replace the JSON implementations with having to copy/paste anymore.

I cannot find any documentation to support this feature.

Does anyone know:
a) if it exists - where the docs are
b) if it doesn’t exist - the best way to replicate this kind of DRY setup