{
  inputs,
  pkgs,
  hostname,
  ...
}: {
  # NixOS version.
  system.stateVersion = "25.05";

  # nix config.
  nix = {
    # Set $NIX_PATH.
    nixPath = ["nixpkgs=${inputs.nixpkgs}"];

    # Optimise store.
    optimise = {
      automatic = true;
      dates = ["daily"];
    };

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

  # Install nh + enable autocleanup of store.
  programs.nh = {
    enable = true;
    clean = {
      enable = true;
      extraArgs = "--keep 3";
      dates = "daily";
    };
  };

  # Enable redistributable firmware.
  hardware.enableRedistributableFirmware = true;

  # Enable firmware updates.
  services.fwupd.enable = true;

  # Set time zone.
  time.timeZone = "Australia/Perth";

  # Select internationalisation properties.
  i18n.defaultLocale = "en_AU.UTF-8";

  i18n.extraLocaleSettings = {
    LC_ADDRESS = "en_AU.UTF-8";
    LC_IDENTIFICATION = "en_AU.UTF-8";
    LC_MEASUREMENT = "en_AU.UTF-8";
    LC_MONETARY = "en_AU.UTF-8";
    LC_NAME = "en_AU.UTF-8";
    LC_NUMERIC = "en_AU.UTF-8";
    LC_PAPER = "en_AU.UTF-8";
    LC_TELEPHONE = "en_AU.UTF-8";
    LC_TIME = "en_AU.UTF-8";
  };

  # Configure keymap in X11.
  services.xserver.xkb = {
    layout = "us";
    variant = "";
  };

  # Enable networking.
  networking.networkmanager.enable = true;
  users.groups.networkmanager.members = ["fern"];

  # Set hostname
  networking.hostName = hostname;

  # Define a user account.
  users.users.fern = {
    isNormalUser = true;
    uid = 1000;
    description = "Fern Garden";
    extraGroups = ["wheel"];
  };

  # Set fish as default shell (https://nixos.wiki/wiki/Fish#Setting_fish_as_your_shell).
  programs.bash = {
    interactiveShellInit = ''
      if [[ $(ps --no-header --pid=$PPID --format=comm) != "fish" && -z ''${BASH_EXECUTION_STRING} ]]
      then
        shopt -q login_shell && LOGIN_OPTION='--login' || LOGIN_OPTION=""
        exec ${pkgs.fish}/bin/fish $LOGIN_OPTION
      fi
    '';
  };

  documentation.man.generateCaches = false; # https://discourse.nixos.org/t/slow-build-at-building-man-cache/52365/2

  # Enable all terminfo (for ghostty).
  environment.enableAllTerminfo = true;

  # Enable avahi hostname resolution.
  services.avahi = {
    enable = true;
    nssmdns4 = true;
    publish = {
      enable = true;
      addresses = true;
      domain = true;
      userServices = true;
    };
  };
}