{ stdenv, writeText, lib, xorg, mesa, xterm, slim, metacity

, config

, # Virtual console for the X server.
  tty ? 7

, # X display number.
  display ? 0

, # List of font directories.
  fontDirectories

}:

let

  getCfg = option: config.get ["services" "xserver" option];

  optional = condition: x: if condition then [x] else [];


  videoDriver = getCfg "videoDriver";

  resolutions = map (res: "\"${toString res.x}x${toString res.y}\"") (getCfg "resolutions");

  windowManager = getCfg "windowManager";


  modules = [
    xorg.xorgserver
    xorg.xf86inputkeyboard
    xorg.xf86inputmouse
  ] 
  ++ optional (videoDriver == "vesa") xorg.xf86videovesa
  ++ optional (videoDriver == "i810") xorg.xf86videoi810;


  configFile = stdenv.mkDerivation {
    name = "xserver.conf";
    src = ./xserver.conf;
    inherit fontDirectories videoDriver resolutions;
    buildCommand = "
      buildCommand= # urgh, don't substitute this

      export fontPaths=
      for i in $fontDirectories; do
        if test \"\${i:0:\${#NIX_STORE}}\" == \"$NIX_STORE\"; then
          for j in $(find $i -name fonts.dir); do
            fontPaths=\"\${fontPaths}FontPath \\\"$(dirname $j)\\\"\\n\"
          done
        fi
      done

      export modulePaths=
      for i in $(find ${toString modules} -type d); do
        if ls $i/*.so 2> /dev/null; then
          modulePaths=\"\${modulePaths}ModulePath \\\"$i\\\"\\n\"
        fi
      done

      substituteAll $src $out
    ";
  };


  clientScript = writeText "xclient" "
    ${if windowManager == "twm" then "
    ${xorg.twm}/bin/twm &
    " else if windowManager == "metacity" then "
    ${metacity}/bin/metacity &
    " else abort ("unknown window manager "+ windowManager)}
    ${xterm}/bin/xterm -ls
  ";


  xserverArgs = [
    "-ac"
    "-nolisten tcp"
    "-terminate"
    "-logfile" "/var/log/X.${toString display}.log"
    "-config ${configFile}"
    ":${toString display}" "vt${toString tty}"
  ];

  # Note: lines must not be indented.
  slimConfig = writeText "slim.cfg" "
xauth_path ${xorg.xauth}/bin/xauth
default_xserver ${xorg.xorgserver}/bin/X
xserver_arguments ${toString xserverArgs}
login_cmd exec ${stdenv.bash}/bin/sh ${clientScript}
  ";


in


rec {
  name = "xserver";

  job = "
    #start on network-interfaces

    start script
      rm -f /var/state/opengl-driver
      ${if getCfg "driSupport"
      then "ln -sf ${mesa} /var/state/opengl-driver"
      else ""}
    end script

    env SLIM_CFGFILE=${slimConfig}
    env FONTCONFIG_FILE=/etc/fonts/fonts.conf # !!! cleanup

    ${if getCfg "driSupport"
    then "env XORG_DRI_DRIVER_PATH=${mesa}/lib/modules/dri"
    else ""}

    exec ${slim}/bin/slim
  ";
  
}