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

with lib;

let

  cfg = config.boot.loader.grub;

  efi = config.boot.loader.efi;

  realGrub = if cfg.version == 1 then pkgs.grub
    else if cfg.zfsSupport then pkgs.grub2.override { zfsSupport = true; }
    else if cfg.trustedBoot.enable
         then if cfg.trustedBoot.isHPLaptop
              then pkgs.trustedGrub-for-HP
              else pkgs.trustedGrub
         else pkgs.grub2;

  grub =
    # Don't include GRUB if we're only generating a GRUB menu (e.g.,
    # in EC2 instances).
    if cfg.devices == ["nodev"]
    then null
    else realGrub;

  grubEfi =
    # EFI version of Grub v2
    if cfg.efiSupport && (cfg.version == 2)
    then realGrub.override { efiSupport = cfg.efiSupport; }
    else null;

  f = x: if x == null then "" else "" + x;

  grubConfig = args:
    let
      efiSysMountPoint = if args.efiSysMountPoint == null then args.path else args.efiSysMountPoint;
      efiSysMountPoint' = replaceChars [ "/" ] [ "-" ] efiSysMountPoint;
    in
    pkgs.writeText "grub-config.xml" (builtins.toXML
    { splashImage = f cfg.splashImage;
      grub = f grub;
      grubTarget = f (grub.grubTarget or "");
      shell = "${pkgs.runtimeShell}";
      fullName = (builtins.parseDrvName realGrub.name).name;
      fullVersion = (builtins.parseDrvName realGrub.name).version;
      grubEfi = f grubEfi;
      grubTargetEfi = if cfg.efiSupport && (cfg.version == 2) then f (grubEfi.grubTarget or "") else "";
      bootPath = args.path;
      storePath = config.boot.loader.grub.storePath;
      bootloaderId = if args.efiBootloaderId == null then "NixOS${efiSysMountPoint'}" else args.efiBootloaderId;
      timeout = if config.boot.loader.timeout == null then -1 else config.boot.loader.timeout;
      inherit efiSysMountPoint;
      inherit (args) devices;
      inherit (efi) canTouchEfiVariables;
      inherit (cfg)
        version extraConfig extraPerEntryConfig extraEntries forceInstall useOSProber
        extraEntriesBeforeNixOS extraPrepareConfig extraInitrd configurationLimit copyKernels
        default fsIdentifier efiSupport efiInstallAsRemovable gfxmodeEfi gfxmodeBios;
      path = (makeBinPath ([
        pkgs.coreutils pkgs.gnused pkgs.gnugrep pkgs.findutils pkgs.diffutils pkgs.btrfs-progs
        pkgs.utillinux ]
        ++ (optional (cfg.efiSupport && (cfg.version == 2)) pkgs.efibootmgr)
        ++ (optionals cfg.useOSProber [pkgs.busybox pkgs.os-prober])
      )) + ":" + (makeSearchPathOutput "bin" "sbin" [
        pkgs.mdadm pkgs.utillinux
      ]);
      font = if cfg.font == null then ""
        else (if lib.last (lib.splitString "." cfg.font) == "pf2"
             then cfg.font
             else "${convertedFont}");
    });

  bootDeviceCounters = fold (device: attr: attr // { "${device}" = (attr."${device}" or 0) + 1; }) {}
    (concatMap (args: args.devices) cfg.mirroredBoots);

  convertedFont = (pkgs.runCommand "grub-font-converted.pf2" {}
           (builtins.concatStringsSep " "
             ([ "${realGrub}/bin/grub-mkfont"
               cfg.font
               "--output" "$out"
             ] ++ (optional (cfg.fontSize!=null) "--size ${toString cfg.fontSize}")))
         );
in

{

  ###### interface

  options = {

    boot.loader.grub = {

      enable = mkOption {
        default = !config.boot.isContainer;
        type = types.bool;
        description = ''
          Whether to enable the GNU GRUB boot loader.
        '';
      };

      version = mkOption {
        default = 2;
        example = 1;
        type = types.int;
        description = ''
          The version of GRUB to use: <literal>1</literal> for GRUB
          Legacy (versions 0.9x), or <literal>2</literal> (the
          default) for GRUB 2.
        '';
      };

      device = mkOption {
        default = "";
        example = "/dev/disk/by-id/wwn-0x500001234567890a";
        type = types.str;
        description = ''
          The device on which the GRUB boot loader will be installed.
          The special value <literal>nodev</literal> means that a GRUB
          boot menu will be generated, but GRUB itself will not
          actually be installed.  To install GRUB on multiple devices,
          use <literal>boot.loader.grub.devices</literal>.
        '';
      };

      devices = mkOption {
        default = [];
        example = [ "/dev/disk/by-id/wwn-0x500001234567890a" ];
        type = types.listOf types.str;
        description = ''
          The devices on which the boot loader, GRUB, will be
          installed. Can be used instead of <literal>device</literal> to
          install GRUB onto multiple devices.
        '';
      };

      mirroredBoots = mkOption {
        default = [ ];
        example = [
          { path = "/boot1"; devices = [ "/dev/disk/by-id/wwn-0x500001234567890a" ]; }
          { path = "/boot2"; devices = [ "/dev/disk/by-id/wwn-0x500009876543210a" ]; }
        ];
        description = ''
          Mirror the boot configuration to multiple partitions and install grub
          to the respective devices corresponding to those partitions.
        '';

        type = with types; listOf (submodule {
          options = {

            path = mkOption {
              example = "/boot1";
              type = types.str;
              description = ''
                The path to the boot directory where GRUB will be written. Generally
                this boot path should double as an EFI path.
              '';
            };

            efiSysMountPoint = mkOption {
              default = null;
              example = "/boot1/efi";
              type = types.nullOr types.str;
              description = ''
                The path to the efi system mount point. Usually this is the same
                partition as the above path and can be left as null.
              '';
            };

            efiBootloaderId = mkOption {
              default = null;
              example = "NixOS-fsid";
              type = types.nullOr types.str;
              description = ''
                The id of the bootloader to store in efi nvram.
                The default is to name it NixOS and append the path or efiSysMountPoint.
                This is only used if <literal>boot.loader.efi.canTouchEfiVariables</literal> is true.
              '';
            };

            devices = mkOption {
              default = [ ];
              example = [ "/dev/disk/by-id/wwn-0x500001234567890a" "/dev/disk/by-id/wwn-0x500009876543210a" ];
              type = types.listOf types.str;
              description = ''
                The path to the devices which will have the GRUB MBR written.
                Note these are typically device paths and not paths to partitions.
              '';
            };

          };
        });
      };

      configurationName = mkOption {
        default = "";
        example = "Stable 2.6.21";
        type = types.str;
        description = ''
          GRUB entry name instead of default.
        '';
      };

      storePath = mkOption {
        default = "/nix/store";
        type = types.str;
        description = ''
          Path to the Nix store when looking for kernels at boot.
          Only makes sense when copyKernels is false.
        '';
      };

      extraPrepareConfig = mkOption {
        default = "";
        type = types.lines;
        description = ''
          Additional bash commands to be run at the script that
          prepares the GRUB menu entries.
        '';
      };

      extraConfig = mkOption {
        default = "";
        example = "serial; terminal_output.serial";
        type = types.lines;
        description = ''
          Additional GRUB commands inserted in the configuration file
          just before the menu entries.
        '';
      };

      extraPerEntryConfig = mkOption {
        default = "";
        example = "root (hd0)";
        type = types.lines;
        description = ''
          Additional GRUB commands inserted in the configuration file
          at the start of each NixOS menu entry.
        '';
      };

      extraEntries = mkOption {
        default = "";
        type = types.lines;
        example = ''
          # GRUB 1 example (not GRUB 2 compatible)
          title Windows
            chainloader (hd0,1)+1

          # GRUB 2 example
          menuentry "Windows 7" {
            chainloader (hd0,4)+1
          }

          # GRUB 2 with UEFI example, chainloading another distro
          menuentry "Fedora" {
            set root=(hd1,1)
            chainloader /efi/fedora/grubx64.efi
          }
        '';
        description = ''
          Any additional entries you want added to the GRUB boot menu.
        '';
      };

      extraEntriesBeforeNixOS = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Whether extraEntries are included before the default option.
        '';
      };

      extraFiles = mkOption {
        type = types.attrsOf types.path;
        default = {};
        example = literalExample ''
          { "memtest.bin" = "''${pkgs.memtest86plus}/memtest.bin"; }
        '';
        description = ''
          A set of files to be copied to <filename>/boot</filename>.
          Each attribute name denotes the destination file name in
          <filename>/boot</filename>, while the corresponding
          attribute value specifies the source file.
        '';
      };

      extraInitrd = mkOption {
        type = types.nullOr types.path;
        default = null;
        example = "/boot/extra_initramfs.gz";
        description = ''
          The path to a second initramfs to be supplied to the kernel.
          This ramfs will not be copied to the store, so that it can
          contain secrets such as LUKS keyfiles or ssh keys.
          This implies that rolling back to a previous configuration
          won't rollback the state of this file.
        '';
      };

      useOSProber = mkOption {
        default = false;
        type = types.bool;
        description = ''
          If set to true, append entries for other OSs detected by os-prober.
        '';
      };

      splashImage = mkOption {
        type = types.nullOr types.path;
        example = literalExample "./my-background.png";
        description = ''
          Background image used for GRUB.
          Set to <literal>null</literal> to run GRUB in text mode.

          <note><para>
          For grub 1:
          It must be a 640x480,
          14-colour image in XPM format, optionally compressed with
          <command>gzip</command> or <command>bzip2</command>.
          </para></note>

          <note><para>
          For grub 2:
          File must be one of .png, .tga, .jpg, or .jpeg. JPEG images must
          not be progressive.
          The image will be scaled if necessary to fit the screen.
          </para></note>
        '';
      };

      font = mkOption {
        type = types.nullOr types.path;
        default = "${realGrub}/share/grub/unicode.pf2";
        description = ''
          Path to a TrueType, OpenType, or pf2 font to be used by Grub.
        '';
      };

      fontSize = mkOption {
        type = types.nullOr types.int;
        example = literalExample 16;
        default = null;
        description = ''
          Font size for the grub menu. Ignored unless <literal>font</literal>
          is set to a ttf or otf font.
        '';
      };

      gfxmodeEfi = mkOption {
        default = "auto";
        example = "1024x768";
        type = types.str;
        description = ''
          The gfxmode to pass to GRUB when loading a graphical boot interface under EFI.
        '';
      };

      gfxmodeBios = mkOption {
        default = "1024x768";
        example = "auto";
        type = types.str;
        description = ''
          The gfxmode to pass to GRUB when loading a graphical boot interface under BIOS.
        '';
      };

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

      copyKernels = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Whether the GRUB menu builder should copy kernels and initial
          ramdisks to /boot.  This is done automatically if /boot is
          on a different partition than /.
        '';
      };

      default = mkOption {
        default = 0;
        type = types.int;
        description = ''
          Index of the default menu item to be booted.
        '';
      };

      fsIdentifier = mkOption {
        default = "uuid";
        type = types.enum [ "uuid" "label" "provided" ];
        description = ''
          Determines how GRUB will identify devices when generating the
          configuration file. A value of uuid / label signifies that grub
          will always resolve the uuid or label of the device before using
          it in the configuration. A value of provided means that GRUB will
          use the device name as show in <command>df</command> or
          <command>mount</command>. Note, zfs zpools / datasets are ignored
          and will always be mounted using their labels.
        '';
      };

      zfsSupport = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Whether GRUB should be built against libzfs.
          ZFS support is only available for GRUB v2.
          This option is ignored for GRUB v1.
        '';
      };

      efiSupport = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Whether GRUB should be built with EFI support.
          EFI support is only available for GRUB v2.
          This option is ignored for GRUB v1.
        '';
      };

      efiInstallAsRemovable = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Whether to invoke <literal>grub-install</literal> with
          <literal>--removable</literal>.</para>

          <para>Unless you turn this on, GRUB will install itself somewhere in
          <literal>boot.loader.efi.efiSysMountPoint</literal> (exactly where
          depends on other config variables). If you've set
          <literal>boot.loader.efi.canTouchEfiVariables</literal> *AND* you
          are currently booted in UEFI mode, then GRUB will use
          <literal>efibootmgr</literal> to modify the boot order in the
          EFI variables of your firmware to include this location. If you are
          *not* booted in UEFI mode at the time GRUB is being installed, the
          NVRAM will not be modified, and your system will not find GRUB at
          boot time. However, GRUB will still return success so you may miss
          the warning that gets printed ("<literal>efibootmgr: EFI variables
          are not supported on this system.</literal>").</para>

          <para>If you turn this feature on, GRUB will install itself in a
          special location within <literal>efiSysMountPoint</literal> (namely
          <literal>EFI/boot/boot$arch.efi</literal>) which the firmwares
          are hardcoded to try first, regardless of NVRAM EFI variables.</para>

          <para>To summarize, turn this on if:
          <itemizedlist>
            <listitem><para>You are installing NixOS and want it to boot in UEFI mode,
            but you are currently booted in legacy mode</para></listitem>
            <listitem><para>You want to make a drive that will boot regardless of
            the NVRAM state of the computer (like a USB "removable" drive)</para></listitem>
            <listitem><para>You simply dislike the idea of depending on NVRAM
            state to make your drive bootable</para></listitem>
          </itemizedlist>
        '';
      };

      enableCryptodisk = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Enable support for encrypted partitions. GRUB should automatically
          unlock the correct encrypted partition and look for filesystems.
        '';
      };

      forceInstall = mkOption {
        default = false;
        type = types.bool;
        description = ''
          Whether to try and forcibly install GRUB even if problems are
          detected. It is not recommended to enable this unless you know what
          you are doing.
        '';
      };

      trustedBoot = {

        enable = mkOption {
          default = false;
          type = types.bool;
          description = ''
            Enable trusted boot. GRUB will measure all critical components during
            the boot process to offer TCG (TPM) support.
          '';
        };

        systemHasTPM = mkOption {
          default = "";
          example = "YES_TPM_is_activated";
          type = types.string;
          description = ''
            Assertion that the target system has an activated TPM. It is a safety
            check before allowing the activation of 'trustedBoot.enable'. TrustedBoot
            WILL FAIL TO BOOT YOUR SYSTEM if no TPM is available.
          '';
        };

        isHPLaptop = mkOption {
          default = false;
          type = types.bool;
          description = ''
            Use a special version of TrustedGRUB that is needed by some HP laptops
            and works only for the HP laptops.
          '';
        };

      };

    };

  };


  ###### implementation

  config = mkMerge [

    { boot.loader.grub.splashImage = mkDefault (
        if cfg.version == 1 then pkgs.fetchurl {
          url = http://www.gnome-look.org/CONTENT/content-files/36909-soft-tux.xpm.gz;
          sha256 = "14kqdx2lfqvh40h6fjjzqgff1mwk74dmbjvmqphi6azzra7z8d59";
        }
        # GRUB 1.97 doesn't support gzipped XPMs.
        else "${pkgs.nixos-artwork.wallpapers.gnome-dark}/share/artwork/gnome/Gnome_Dark.png");
    }

    (mkIf cfg.enable {

      boot.loader.grub.devices = optional (cfg.device != "") cfg.device;

      boot.loader.grub.mirroredBoots = optionals (cfg.devices != [ ]) [
        { path = "/boot"; inherit (cfg) devices; inherit (efi) efiSysMountPoint; }
      ];

      system.build.installBootLoader =
        let
          install-grub-pl = pkgs.substituteAll {
            src = ./install-grub.pl;
            inherit (pkgs) utillinux;
            btrfsprogs = pkgs.btrfs-progs;
          };
        in pkgs.writeScript "install-grub.sh" (''
        #!${pkgs.runtimeShell}
        set -e
        export PERL5LIB=${makePerlPath (with pkgs.perlPackages; [ FileSlurp XMLLibXML XMLSAX XMLSAXBase ListCompare ])}
        ${optionalString cfg.enableCryptodisk "export GRUB_ENABLE_CRYPTODISK=y"}
      '' + flip concatMapStrings cfg.mirroredBoots (args: ''
        ${pkgs.perl}/bin/perl ${install-grub-pl} ${grubConfig args} $@
      ''));

      system.build.grub = grub;

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

      environment.systemPackages = optional (grub != null) grub;

      boot.loader.grub.extraPrepareConfig =
        concatStrings (mapAttrsToList (n: v: ''
          ${pkgs.coreutils}/bin/cp -pf "${v}" "/boot/${n}"
        '') config.boot.loader.grub.extraFiles);

      assertions = [
        {
          assertion = !cfg.zfsSupport || cfg.version == 2;
          message = "Only GRUB version 2 provides ZFS support";
        }
        {
          assertion = cfg.mirroredBoots != [ ];
          message = "You must set the option ‘boot.loader.grub.devices’ or "
            + "'boot.loader.grub.mirroredBoots' to make the system bootable.";
        }
        {
          assertion = cfg.efiSupport || all (c: c < 2) (mapAttrsToList (_: c: c) bootDeviceCounters);
          message = "You cannot have duplicated devices in mirroredBoots";
        }
        {
          assertion = !cfg.trustedBoot.enable || cfg.version == 2;
          message = "Trusted GRUB is only available for GRUB 2";
        }
        {
          assertion = !cfg.efiSupport || !cfg.trustedBoot.enable;
          message = "Trusted GRUB does not have EFI support";
        }
        {
          assertion = !cfg.zfsSupport || !cfg.trustedBoot.enable;
          message = "Trusted GRUB does not have ZFS support";
        }
        {
          assertion = !cfg.trustedBoot.enable || cfg.trustedBoot.systemHasTPM == "YES_TPM_is_activated";
          message = "Trusted GRUB can break the system! Confirm that the system has an activated TPM by setting 'systemHasTPM'.";
        }
        {
          assertion = cfg.efiInstallAsRemovable -> cfg.efiSupport;
          message = "If you wish to to use boot.loader.grub.efiInstallAsRemovable, then turn on boot.loader.grub.efiSupport";
        }
        {
          assertion = cfg.efiInstallAsRemovable -> !config.boot.loader.efi.canTouchEfiVariables;
          message = "If you wish to to use boot.loader.grub.efiInstallAsRemovable, then turn off boot.loader.efi.canTouchEfiVariables";
        }
      ] ++ flip concatMap cfg.mirroredBoots (args: [
        {
          assertion = args.devices != [ ];
          message = "A boot path cannot have an empty devices string in ${args.path}";
        }
        {
          assertion = hasPrefix "/" args.path;
          message = "Boot paths must be absolute, not ${args.path}";
        }
        {
          assertion = if args.efiSysMountPoint == null then true else hasPrefix "/" args.efiSysMountPoint;
          message = "EFI paths must be absolute, not ${args.efiSysMountPoint}";
        }
      ] ++ flip map args.devices (device: {
        assertion = device == "nodev" || hasPrefix "/" device;
        message = "GRUB devices must be absolute paths, not ${device} in ${args.path}";
      }));
    })

  ];


  imports =
    [ (mkRemovedOptionModule [ "boot" "loader" "grub" "bootDevice" ] "")
      (mkRenamedOptionModule [ "boot" "copyKernels" ] [ "boot" "loader" "grub" "copyKernels" ])
      (mkRenamedOptionModule [ "boot" "extraGrubEntries" ] [ "boot" "loader" "grub" "extraEntries" ])
      (mkRenamedOptionModule [ "boot" "extraGrubEntriesBeforeNixos" ] [ "boot" "loader" "grub" "extraEntriesBeforeNixOS" ])
      (mkRenamedOptionModule [ "boot" "grubDevice" ] [ "boot" "loader" "grub" "device" ])
      (mkRenamedOptionModule [ "boot" "bootMount" ] [ "boot" "loader" "grub" "bootDevice" ])
      (mkRenamedOptionModule [ "boot" "grubSplashImage" ] [ "boot" "loader" "grub" "splashImage" ])
    ];

}