{pkgs, config, ...}:

let
  inherit (pkgs.lib) mkOption mkIf singleton;
  inherit (pkgs) stdenv;
  
  kernelPackages = config.boot.kernelPackages;
  splashutils = kernelPackages.splashutils;
  requiredTTYs = config.requiredTTYs;
  
  backgrounds =
    let
    
      specificThemes =
        config.services.ttyBackgrounds.defaultSpecificThemes
        ++ config.services.ttyBackgrounds.specificThemes;
        
      overridenTTYs = map (x: x.tty) specificThemes;

      # Use the default theme for all the mingetty ttys and for the
      # syslog tty, except those for which a specific theme is
      # specified.
      defaultTTYs =
        pkgs.lib.filter (x: !(pkgs.lib.elem x overridenTTYs)) requiredTTYs;

    in      
      (map (ttyNumber: {
        tty = ttyNumber;
        theme = config.services.ttyBackgrounds.defaultTheme;
      }) defaultTTYs)
      ++ specificThemes;

  themesUnpacked = stdenv.mkDerivation {
    name = "splash-themes";
    builder = ./tty-backgrounds-combine.sh;
    # !!! Should use XML here.
    ttys = map (x: x.tty) backgrounds;
    themes = map (x: if x ? theme then (unpackTheme x.theme) else "default") backgrounds;
  };

  unpackTheme = theme: import ../../lib/unpack-theme.nix {
    inherit stdenv theme;
  };

in

{

  ###### interface
  
  options = {
  
    services.ttyBackgrounds = {

      enable = mkOption {
        default = true;
        description = ''
          Whether to enable graphical backgrounds for the virtual consoles.
        '';
      };

      defaultTheme = mkOption {
        default = pkgs.fetchurl {
          #url = http://www.bootsplash.de/files/themes/Theme-BabyTux.tar.bz2;
          url = mirror://gentoo/distfiles/Theme-BabyTux.tar.bz2;
          md5 = "a6d89d1c1cff3b6a08e2f526f2eab4e0";
        };
        description = ''
          The default theme for the virtual consoles.  Themes can be found
          at <link xlink:href='http://www.bootsplash.de/' />.
        '';
      };

      defaultSpecificThemes = mkOption {
        default = [
          /*
          { tty = 6;
            theme = pkgs.fetchurl { # Yeah!
              url = mirror://gentoo/distfiles/Theme-Pativo.tar.bz2;
              md5 = "9e13beaaadf88d43a5293e7ab757d569";
            };
          }
          */
          { tty = 10;
            theme = pkgs.themes "theme-gnu";
          }
        ];
        description = ''
          This option sets specific themes for virtual consoles.  If you
          just want to set themes for additional consoles, use
          <option>services.ttyBackgrounds.specificThemes</option>.
        '';
      };

      specificThemes = mkOption {
        default = [
        ];
        description = ''
          This option allows you to set specific themes for virtual
          consoles.
        '';
      };
      
    };
    
  };


  ###### implementation

  config = mkIf config.services.ttyBackgrounds.enable {

    assertions = singleton
      { assertion = kernelPackages.splashutils != null;
        message = "kernelPackages.splashutils may not be false";
      };

    environment.etc = singleton
      { source = themesUnpacked;
        target = "splash";
      };

    jobs = singleton {
      name = "tty-backgrounds";

      startOn = "udev";

      preStart =
        ''
          # Critical: tell the kernel where to find splash_helper.  It calls
          # this program every time we switch between consoles.
          helperProcFile=${splashutils.helperProcFile}
          if test -e /proc/sys/fbcondecor; then helperProcFile=/proc/sys/fbcondecor; fi
          echo ${splashutils}/${splashutils.helperName} > $helperProcFile

          # For each console...
          for tty in ${toString (map (x: x.tty) backgrounds)}; do
              # Make sure that the console exists.
              echo -n "" > /dev/tty$tty 

              # Set the theme as determined by tty-backgrounds-combine.sh
              # above.
              theme=$(readlink ${themesUnpacked}/$tty)
              ${splashutils}/${splashutils.controlName} --tty $tty -c setcfg -t $theme || true
              ${splashutils}/${splashutils.controlName} --tty $tty -c setpic -t $theme || true
              ${splashutils}/${splashutils.controlName} --tty $tty -c on || true
          done
        '';

      postStop =
        ''
          /var/run/current-system/sw/bin/ps -axuw > /tmp/ps
        
          # Disable the theme on each console.
          for tty in ${toString (map (x: x.tty) backgrounds)}; do
              ${splashutils}/${splashutils.controlName} --tty $tty -c off || true
          done
        '';
    };
    
  };
  
}