nix-user-module/flake.nix

{
  description = "C3D2 NixOS user module";

  inputs = {
    nixpkgs-lib.url = "github:nix-community/nixpkgs.lib";
    nixos-modules = {
      url = "github:SuperSandro2000/nixos-modules";
      inputs.nixpkgs-lib.follows = "nixpkgs-lib";
    };
  };

  outputs = { nixos-modules, nixpkgs-lib, ... }:
    let
      inherit (nixpkgs-lib) lib;
      ls = dir: lib.attrNames (builtins.readDir (./. + "/${dir}"));
    in
    {
      nixosModule = { config, libS, ... }@args: {
        _module.args.libS = lib.mkOverride 1001 (nixos-modules.lib { inherit lib config; });

        imports = [
          nixos-modules.nixosModules.default
        ] ++ (dir: map
          (file: ./. + "/${dir}/${file}")
          # assume that the nixos-modules repo is already imported if libS exists
          (lib.remove (lib.optionalString (lib.hasAttr "libS" args) "default.nix") (ls dir))
        ) "modules";
      };
    };
}