{ pkgs, user, ... } :
  {
  nix.settings = {
  # enable flakes
  experimental-features = ["nix-command" "flakes"];

  # add a cache that speed up new applications by downloading binaries
  # from the trusted cache instead of compiling from sourcer
  substituters = [
    "https://nix-community.cachix.org"
  ];
  # trust the cache public key
  trusted-public-keys = [
    "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
  ];
  };

  # allow proprietary software on this machine. I'm not a purist.
  nixpkgs.config.allowUnfree = true;

  # this declares how often old configurations are cleared up.
  # i cleanup anything older than a week, every week.
  nix.gc = {
  automatic = true;
  options = "--delete-older-than 7d";
  dates = "weekly";
  };

  programs = {
  # command line utility that makes applying changes easy and pretty
  nh = {
    enable = true;
    flake = "/home/${user.username}/system";
  };
  };
  }