{ lib, pkgs, nixpkgs, ... }: {
  # optimizations
  nix.settings.auto-optimise-store = true;

  # garbage collection
  nix.gc = {
    automatic = true;
    dates = "weekly";
    options = "--delete-older-than 30d";
  };

  # experimental features
  nix.settings.experimental-features = [ "nix-command" "flakes" ];

  # pin nixpkgs registry
  nix.registry.nixpkgs.flake = nixpkgs;

  # print diff between two generations
  system.activationScripts.nvd-report-changes = ''
    PATH=$PATH:${lib.makeBinPath [ pkgs.nvd pkgs.nix ]}
    nvd diff $(ls -dv /nix/var/nix/profiles/system-*-link | tail -2)
  '';
}