{pkgs, config, ...}:

###### interface
let
  inherit (pkgs.lib) mkOption;

  options = {

    services.xserver.displayManager.kdm = {
      enable = mkOption {
        default = false;
        description = "
          Whether to enable the KDE display manager.
        ";
      };
    };

  };

in

###### implementation
let
  xcfg = config.services.xserver;
  dmcfg = xcfg.displayManager;
  cfg = dmcfg.kdm;

  inherit (pkgs.lib) mkIf;
  inherit (pkgs) stdenv;
  inherit (pkgs.kde42) kdebase_workspace;

  kdmrc = stdenv.mkDerivation {
    name = "kdmrc";
    # -e "s|Session=${kdebase_workspace}/share/config/kdm/Xsession|Session=${dmcfg.session.script}|" \
    buildCommand = ''
      cp ${kdebase_workspace}/share/config/kdm/kdmrc .
      sed -i -e "s|#HaltCmd=|HaltCmd=${pkgs.upstart}/sbin/halt|" \
             -e "s|#RebootCmd=|RebootCmd=${pkgs.upstart}/sbin/reboot|" \
	     -e "s|#Xrdb=|Xrdb=${pkgs.xlibs.xrdb}/bin/xrdb|" \
	     -e "s|#HiddenUsers=root|HiddenUsers=root,nixbld1,nixbld2,nixbld3,nixbld4,nixbld5,nixbld6,nixbld7,nixbld8,nixbld9,nixbld10|" \
	     -e "s|ServerCmd=/FOO/bin/X|ServerCmd=${dmcfg.xserverBin} ${dmcfg.xserverArgs}|" \
 	     -e "s|^SessionsDirs=.*$|SessionsDirs=${dmcfg.session.desktops}|" \
	     -e "s|#FailsafeClient=|FailsafeClient=${pkgs.xterm}/bin/xterm|" \
	     -e "s|#PluginsLogin=sign|PluginsLogin=${kdebase_workspace}/lib/kde4/kgreet_classic.so|" \
      kdmrc
      ensureDir $out
      cp kdmrc $out
    '';
  };

in

mkIf cfg.enable {
  require = [
    options
  ];

  services = {
    xserver = {
      displayManager = {
        job = {
          beforeScript = "";
          env = "";
          execCmd = "${kdebase_workspace}/bin/kdm -config ${kdmrc}/kdmrc";
        };
      };
    };
  };
}