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

let

  cfg = config.programs.htop;

  fmt = value:
    if builtins.isList value then builtins.concatStringsSep " " (builtins.map fmt value) else
    if builtins.isString value then value else
    if builtins.isBool value then if value then "1" else "0" else
    if builtins.isInt value then builtins.toString value else
    throw "Unrecognized type ${builtins.typeOf value} in htop settings";

in

{

  options.programs.htop = {
    package = lib.mkPackageOption pkgs "htop" { };

    enable = lib.mkEnableOption "htop process monitor";

    settings = lib.mkOption {
      type = with lib.types; attrsOf (oneOf [ str int bool (listOf (oneOf [ str int bool ])) ]);
      default = {};
      example = {
        hide_kernel_threads = true;
        hide_userland_threads = true;
      };
      description = ''
        Extra global default configuration for htop
        which is read on first startup only.
        Htop subsequently uses ~/.config/htop/htoprc
        as configuration source.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    environment.systemPackages = [
      cfg.package
    ];

    environment.etc."htoprc".text = ''
      # Global htop configuration
      # To change set: programs.htop.settings.KEY = VALUE;
    '' + builtins.concatStringsSep "\n" (lib.mapAttrsToList (key: value: "${key}=${fmt value}") cfg.settings);
  };

}