{
  system ? builtins.currentSystem,
  sources ? import ../npins,
  pkgs ? import sources.nixpkgs {
    inherit system;
    config = { };
    overlays = [ (import ./nix/overlay.nix) ];
  },
}:
let
  inherit (pkgs) lib;
  manage = pkgs.writeScriptBin "manage" ''
    exec ${pkgs.lib.getExe pkgs.python3} ${toString ./src/manage.py} $@
  '';
  package = pkgs.callPackage ./nix/package.nix { };
in
{
  shell = pkgs.mkShellNoCC {
    inputsFrom = [ package ];
    packages = [
      pkgs.npins
      manage
    ];
    env =
      let
        inherit (builtins) toString;
      in
      import ./env.nix { inherit lib pkgs; }
      // {
        NPINS_DIRECTORY = toString ../npins;
        CREDENTIALS_DIRECTORY = toString ./.credentials;
        DATABASE_URL = "sqlite:///${toString ./src}/db.sqlite3";
        # locally: use a fixed relative reference, so we can use our newest files without copying to the store
        REPO_DIR = toString ../.;
      };
    shellHook = ''
      ${lib.concatStringsSep "\n" (
        map (file: "ln -sf ${file.from} ${toString ./src/${file.to}}") package.generated
      )}

      # in production, secrets are passed via CREDENTIALS_DIRECTORY by systemd.
      # use this directory for testing with local secrets
      mkdir -p $CREDENTIALS_DIRECTORY
      echo secret > ${builtins.toString ./.credentials}/SECRET_KEY
    '';
  };

  module = import ./nix/configuration.nix;
  tests = pkgs.callPackage ./nix/tests.nix { };

  # re-export inputs so they can be overridden granularly
  # (they can't be accessed from the outside any other way)
  inherit
    sources
    system
    pkgs
    ;
}