nixos-config/nixos/modules/services/light-control.nix

{ config, lib, pkgs, ... }:

with lib;

let

  cfg = config.services.mqtt.light-control;

  mkMagicMergeOption = { description ? "", example ? { }, default ? { }, ... }:
    mkOption {
      inherit example description default;
      type = with lib.types;
        let
          valueType = nullOr (oneOf [
            bool
            int
            float
            str
            (attrsOf valueType)
            (listOf valueType)
          ]) // {
            description = "";
            emptyValue.value = { };
          };
        in valueType;
    };

  lightControlConfig =
    pkgs.writeText "light-control.json" (builtins.toJSON cfg.config);

in {

  options.services.mqtt.light-control = {
    enable = mkEnableOption "enable mqtt.light-control";
    loglevel = mkOption {
      default = "info";
      type = with types; enum [ "info" "trace" "debug" "error" "warning" ];
    };
    config =
      mkMagicMergeOption { description = "configuration of light-control"; };
  };

  config = mkIf cfg.enable {
    systemd.services."light-control" = {
      wantedBy = [ "multi-user.target" ];
      environment = { RUST_LOG = "light_control=${cfg.loglevel}"; };
      script = ''
        ${pkgs.light-control}/bin/light-control ${lightControlConfig}
      '';
    };
  };
}