niveum/modules/power-action.nix

{
  config,
  lib,
  pkgs,
  ...
}:
with lib; let
  cfg = config.services.power-action;

  out = {
    options.services.power-action = api;
    config = lib.mkIf cfg.enable imp;
  };

  api = {
    enable = mkEnableOption "power-action";
    battery = mkOption {
      type = types.str;
      default = "BAT0";
    };
    user = mkOption {
      type = types.str;
      default = "power-action";
    };
    startAt = mkOption {
      type = types.str;
      default = "*:0/1";
    };
    plans = mkOption {
      type = with types;
        attrsOf (submodule {
          options = {
            charging = mkOption {
              type = nullOr bool;
              default = null;
              description = ''
                check for charging status.
                null = don't care
                true = only if system is charging or unknown
                false = only if system is discharging
              '';
            };
            upperLimit = mkOption {
              type = int;
            };
            lowerLimit = mkOption {
              type = int;
            };
            action = mkOption {
              type = path;
            };
          };
        });
    };
  };

  imp = {
    systemd.services.power-action = {
      serviceConfig = rec {
        ExecStart = startScript;
        User = cfg.user;
      };
      startAt = cfg.startAt;
    };
  };

  startScript = pkgs.writers.writeDash "power-action" ''
    set -euf

    power="$(${powerlvl})"
    state="$(${state})"
    ${concatStringsSep "\n" (mapAttrsToList writeRule cfg.plans)}
  '';
  charging_check = plan:
    if (plan.charging == null)
    then ""
    else if plan.charging
    then ''&& [ "$state" = "true" ]''
    else ''&& ! [ "$state" = "true" ]'';

  writeRule = _: plan: "if [ $power -ge ${toString plan.lowerLimit} ] && [ $power -le ${toString plan.upperLimit} ] ${charging_check plan}; then ${plan.action}; fi";

  powerlvl = pkgs.writers.writeDash "powerlvl" ''
    cat /sys/class/power_supply/${cfg.battery}/capacity
  '';

  state = pkgs.writers.writeDash "state" ''
    if [ "$(cat /sys/class/power_supply/${cfg.battery}/status)" = "Discharging" ]
      then echo "false"
      else echo "true"
    fi
  '';
in
  out