with (import <nixpkgs> {});
let
  env = bundlerEnv {
    name = "postfix_exporter-bundler-env";
    inherit ruby;
    gemfile  = ./Gemfile;
    lockfile = ./Gemfile.lock;
    gemset   = ./gemset.nix;
  };
in stdenv.mkDerivation {
  name = "postfix-exporter";
  buildInputs = [ pkgs.libffi pkgs.systemd pkgs.ruby env env.gems.puma ];
  buildPhase = ''
    echo "Build postfix_exporter
    mkdir -p "$out/lib"
    for f in ${pkgs.systemd}/lib/libsystemd*
    do
      ln -s "$f" "$out/lib/"
    done
  '';
}