Is anyone well-versed enough in Flakes internals to know how Nix turns a flakeref string (i.e. "github:nixos/nixpkgs") into a URL? Or, if it doesn't do that, how it works with the input without having an intermediary URL stage?

I have a project where I take the flake.lock data and reconstruct the input data into a URL, so I can use git ls-remote and see if the input has changed at all (so I can see which inputs would be updated, without waiting the 15-30 seconds for nix flake update to run). However, I've run into less easy input types to work with, and it's made me question whether I'm reinventing the wheel here.