{ config, pkgs, lib, ... }:
{
  # Nix configuration ------------------------------------------------------------------------------

  nix.settings = {
    trusted-substituters = [
      "https://cache.nixos.org/"
      "https://hydra.iohk.io"
      "https://cache.iog.io"
      "https://nix-community.cachix.org"
      "https://mat.cachix.org"
      "https://helix.cachix.org"
      "https://pre-commit-hooks.cachix.org"
    ];
    trusted-public-keys = [
      "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
      "hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ="
      "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
      "mat.cachix.org-1:AHqv9SoBEPKlJX2DDZQnjaMcvBAgpH1j8rw5USYDZno="
      "helix.cachix.org-1:ejp9KQpR1FBI2onstMQ34yogDm4OgU2ru6lIwPvuCVs="
      "pre-commit-hooks.cachix.org-1:Pkk3Panw5AW24TOv6kz3PvLhlH8puAsJTBbOPmBo7Rc="
    ];
    trusted-users = [
      "@admin"
    ];
    auto-optimise-store = true;
    experimental-features = [ "nix-command" "flakes" ];
    extra-platforms = lib.mkIf (pkgs.system == "aarch64-darwin") [ "x86_64-darwin" "aarch64-darwin" ];
  };
  nix.configureBuildUsers = true;


  # Auto upgrade nix package and the daemon service.
  services.nix-daemon.enable = true;

  # Make Fish the default shell
  environment.shells = with pkgs; [
    bashInteractive
    fish
    zsh
  ];

  programs.fish.enable = true;
  programs.fish.useBabelfish = true;
  programs.fish.babelfishPackage = pkgs.babelfish;
  # Needed to address bug where $PATH is not properly set for fish:
  # https://github.com/LnL7/nix-darwin/issues/122
  programs.fish.shellInit = ''
    for p in (string split : ${config.environment.systemPath})
      if not contains $p $fish_user_paths
        set -Ua fish_user_paths $p
      end
    end
  '';
  environment.variables.SHELL = "${pkgs.fish}/bin/fish";
  environment.loginShell = "${pkgs.fish}/bin/fish";

  # Install and setup ZSH to work with nix(-darwin) as well
  programs.zsh.enable = true;

  # Used for backwards compatibility, please read the changelog before changing.
  # $ darwin-rebuild changelog
  system.stateVersion = 4;

}