{
  lib,
  nixpkgs,
  ...
}: {
  # to install chrome, you need to enable unfree packages
  nixpkgs.config.allowUnfree = lib.mkForce true;

  # do garbage collection weekly to keep disk usage low
  nix.gc = {
    automatic = lib.mkDefault true;
    dates = lib.mkDefault "weekly";
    options = lib.mkDefault "--delete-older-than 7d";
  };

  # Manual optimise storage: nix-store --optimise
  # https://nixos.org/manual/nix/stable/command-ref/conf-file.html#conf-auto-optimise-store
  nix.settings.auto-optimise-store = true;

  # make `nix run nixpkgs#nixpkgs` use the same nixpkgs as the one used by this flake.
  nix.registry.nixpkgs.flake = nixpkgs;
  nix.channel.enable = false; # remove nix-channel related tools & configs, we use flakes instead.

  # but NIX_PATH is still used by many useful tools, so we set it to the same value as the one used by this flake.
  # Make `nix repl '<nixpkgs>'` use the same nixpkgs as the one used by this flake.
  environment.etc."nix/inputs/nixpkgs".source = "${nixpkgs}";
  # https://github.com/NixOS/nix/issues/9574
  nix.settings.nix-path = lib.mkForce "nixpkgs=/etc/nix/inputs/nixpkgs";
}