How can I compile cuda code (nvcc) using Bazel

I would like to compile a simple cu file using bazel. I've created a/third_party folder which looks like this:

opencv.bzl
opencv.BUILD
qt.bzl
qt.BUILD
...
...
...

for qt I've created a macro qt_cc_library in qt.bzl to handle qt files, and I would like to add a similar library/binary for cuda

I don't understand what I should add to the WORKSPACE/cuda.bzl/cuda.BUILD files, and all the online references are old and broken (e.g. this,this). I've look at the extension page but when trying to compile I get errors and cannot debug the bzl file.

This should be pretty basic but for there is no working example for compiling cuda (nvcc) Code with bazel.