default.nix

{ pkgs, lib, makeWrapper, ... }:
let
  python = pkgs.python3;
  # This is a python envionment that has the dependencies
  # for the development python scripts we use, and the
  # helper library.
  python-env = python.buildEnv.override {
    extraLibs = [ python.pkgs.httpx ];
    # Add `.pth` file pointing at the directory containg our helper library.
    # This will get added to `sys.path` by `site.py`.
    # See https://docs.python.org/3/library/site.html
    postBuild = ''
      echo ${lib.escapeShellArg ./pylib} > $out/${lib.escapeShellArg python.sitePackages}/tools.pth
    '';
  };
in
# This derivation creates a package that wraps our tools to setup an environment
# with there dependencies available.
pkgs.runCommand "ps_tools" {
  nativeBuildInputs = [ makeWrapper ];
  shellHook = ''
    if [[ $- == *i* ]]; then
      cat <<MOTD
    Tools (pass --help for details):
    - update-nixpkgs
    MOTD
    fi
  '';
} ''
  mkdir -p $out/bin
  # makeWrapper <executable> <wrapperfile> <args>
  # See https://nixos.org/manual/nixpkgs/stable/#fun-makeWrapper
  makeWrapper ${python-env}/bin/python $out/bin/update-nixpkgs --add-flags ${toString ./update-nixpkgs}
''