nixpkgs/modules/installer/grub/grub.nix

{pkgs, config, ...}:

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

  options = {
    boot = {
      loader = {
        grub = {

          enable = mkOption {
            default = true;
            description = ''
              Whether to enable the GRUB boot loader.
            '';
          };

          grubDevice = mkOption {
            default = "";
            example = "/dev/hda";
            description = "
              The device on which the boot loader, Grub, will be installed.
              If empty, Grub won't be installed and it's your responsibility
              to make the system bootable.
            ";
          };

          bootMount = mkOption {
            default = "";
            example = "(hd0,0)";
            description = "
              If the system partition may be wiped on reinstall, it is better
              to have /boot on a small partition. To do it, we need to explain
              to GRUB where the kernels live. Specify the partition here (in 
              GRUB notation.
            ";
          };

          configurationName = mkOption {
            default = "";
            example = "Stable 2.6.21";
            description = "
              Grub entry name instead of default.
            ";
          };

          extraGrubEntries = mkOption {
            default = "";
            example = "
              title Windows
                chainloader (hd0,1)+1
            ";
            description = "
              Any additional entries you want added to the Grub boot menu.
            ";
          };

          extraGrubEntriesBeforeNixos = mkOption {
            default = false;
            description = "
              Wheter extraGrubEntries are put before the Nixos-default option
            ";
          };

          grubSplashImage = mkOption {
            default = pkgs.fetchurl {
              url = http://www.gnome-look.org/CONTENT/content-files/36909-soft-tux.xpm.gz;
              sha256 = "14kqdx2lfqvh40h6fjjzqgff1mwk74dmbjvmqphi6azzra7z8d59";
            };
            example = null;
            description = "
              Background image used for Grub.  It must be a 640x480,
              14-colour image in XPM format, optionally compressed with
              <command>gzip</command> or <command>bzip2</command>.  Set to
              <literal>null</literal> to run Grub in text mode.
            ";
          };

          configurationLimit = mkOption {
            default = 100;
            example = 120;
            description = "
              Maximum of configurations in boot menu. GRUB has problems when
              there are too many entries.
            ";
          };

          copyKernels = mkOption {
            default = false;
            description = "
              Whether the Grub menu builder should copy kernels and initial
              ramdisks to /boot.  This is necessary when /nix is on a
              different file system than /boot.
            ";
          };
        };
      };
    };
  };
in


###### implementation
let

  grubMenuBuilder = pkgs.substituteAll {
    src = ./grub-menu-builder.sh;
    isExecutable = true;
    inherit (pkgs) bash;
    path = [pkgs.coreutils pkgs.gnused pkgs.gnugrep];
    inherit (config.boot.loader.grub) copyKernels extraGrubEntries extraGrubEntriesBeforeNixos
      grubSplashImage bootMount configurationLimit;
  };
in

{
  require = [
    options

    # config.system.build
    # ../system/system-options.nix
  ];

  system = mkIf config.boot.loader.grub.enable {
    build = {
      menuBuilder = grubMenuBuilder;
    };

    # Common attribute for boot loaders so only one of them can be
    # set at once
    boot.loader.id = "grub";
    boot.loader.kernelFile = "vmlinuz";
  };

  environment.extraPackages = mkIf config.boot.loader.grub.enable [ pkgs.grub ];

  # and many other things that have to be moved inside this file.
}