nixos/modules/light-actkbd.nix

{pkgs, ...}: let
  light = "${pkgs.light}/bin/light";
  decLight = pkgs.writeScriptBin "decrease-light-smartly" ''
    #!${pkgs.fish}/bin/fish

    set curr (${light} -G)

    if test $curr -le 5.00 -a $curr -gt 1.00
      ${light} -S 1
    else
      ${light} -U 10
    end
  '';

  incLight = pkgs.writeScriptBin "increase-light-smartly" ''
    #!${pkgs.fish}/bin/fish

    set curr (${light} -G)

    if test $curr -eq 0.00
      ${light} -S 1
    else
      ${light} -A 10
    end
  '';
in {
  programs.light.enable = true;

  environment.systemPackages = [incLight decLight pkgs.fish];

  services.actkbd = {
    enable = true;
    bindings = [
      {
        keys = [225];
        events = ["key"];
        command = "${incLight}/bin/increase-light-smartly";
      }
      {
        keys = [224];
        events = ["key"];
        command = "${decLight}/bin/decrease-light-smartly";
      }
    ];
  };
}