use strict;
use warnings;
use Class::Struct;
use XML::LibXML;
use File::Basename;
use File::Path qw(make_path rmtree);
use File::stat;
use File::Copy;
use File::Copy::Recursive qw(rcopy pathrm);
use File::Slurp;
use File::Temp;
use JSON;
use File::Find;
require List::Compare;
use POSIX;
use Cwd;

# system.build.toplevel path
my $defaultConfig = $ARGV[1] or die;

# Grub config XML generated by grubConfig function in grub.nix
my $dom = XML::LibXML->load_xml(location => $ARGV[0]);

sub get { my ($name) = @_; return $dom->findvalue("/expr/attrs/attr[\@name = '$name']/*/\@value"); }

sub getList {
    my ($name) = @_;
    my @list = ();
    foreach my $entry ($dom->findnodes("/expr/attrs/attr[\@name = '$name']/list/string/\@value")) {
        $entry = $entry->findvalue(".") or die;
        push(@list, $entry);
    }
    return @list;
}

sub readFile {
    my ($fn) = @_;
    # enable slurp mode: read entire file in one go
    local $/ = undef;
    open my $fh, "<", $fn
        or return;
    my $s = <$fh>;
    close $fh;
    # disable slurp mode
    local $/ = "\n";
    chomp $s;
    return $s;
}

sub writeFile {
    my ($fn, $s) = @_;
    open my $fh, ">", $fn or die "cannot create $fn: $!\n";
    print $fh $s or die "cannot write to $fn: $!\n";
    close $fh or die "cannot close $fn: $!\n";
}

sub runCommand {
    open(my $fh, "-|", @_) or die "Failed to execute: $@_\n";
    my @ret = $fh->getlines();
    close $fh;
    return ($?, @ret);
}

my $grub = get("grub");
my $grubTarget = get("grubTarget");
my $extraConfig = get("extraConfig");
my $extraPrepareConfig = get("extraPrepareConfig");
my $extraPerEntryConfig = get("extraPerEntryConfig");
my $extraEntries = get("extraEntries");
my $extraEntriesBeforeNixOS = get("extraEntriesBeforeNixOS") eq "true";
my $splashImage = get("splashImage");
my $splashMode = get("splashMode");
my $entryOptions = get("entryOptions");
my $subEntryOptions = get("subEntryOptions");
my $backgroundColor = get("backgroundColor");
my $configurationLimit = int(get("configurationLimit"));
my $copyKernels = get("copyKernels") eq "true";
my $timeout = int(get("timeout"));
my $timeoutStyle = get("timeoutStyle");
my $defaultEntry = get("default");
my $fsIdentifier = get("fsIdentifier");
my $grubEfi = get("grubEfi");
my $grubTargetEfi = get("grubTargetEfi");
my $bootPath = get("bootPath");
my $storePath = get("storePath");
my $canTouchEfiVariables = get("canTouchEfiVariables");
my $efiInstallAsRemovable = get("efiInstallAsRemovable");
my $efiSysMountPoint = get("efiSysMountPoint");
my $gfxmodeEfi = get("gfxmodeEfi");
my $gfxmodeBios = get("gfxmodeBios");
my $gfxpayloadEfi = get("gfxpayloadEfi");
my $gfxpayloadBios = get("gfxpayloadBios");
my $bootloaderId = get("bootloaderId");
my $forceInstall = get("forceInstall");
my $font = get("font");
my $theme = get("theme");
my $saveDefault = $defaultEntry eq "saved";
$ENV{'PATH'} = get("path");

print STDERR "updating GRUB 2 menu...\n";

make_path("$bootPath/grub", {  mode => 0700 });

# Discover whether the bootPath is on the same filesystem as / and
# /nix/store.  If not, then all kernels and initrds must be copied to
# the bootPath.
if (stat($bootPath)->dev != stat("/nix/store")->dev) {
    $copyKernels = 1;
}

# Discover information about the location of the bootPath
struct(Fs => {
    device => '$',
    type => '$',
    mount => '$',
});
sub PathInMount {
    my ($path, $mount) = @_;
    my @splitMount = split /\//, $mount;
    my @splitPath = split /\//, $path;
    if ($#splitPath < $#splitMount) {
        return 0;
    }
    for (my $i = 0; $i <= $#splitMount; $i++) {
        if ($splitMount[$i] ne $splitPath[$i]) {
            return 0;
        }
    }
    return 1;
}

# Figure out what filesystem is used for the directory with init/initrd/kernel files
sub GetFs {
    my ($dir) = @_;
    my $bestFs = Fs->new(device => "", type => "", mount => "");
    foreach my $fs (read_file("/proc/self/mountinfo")) {
        chomp $fs;
        my @fields = split / /, $fs;
        my $mountPoint = $fields[4];
        my @mountOptions = split /,/, $fields[5];

        # Skip the optional fields.
        my $n = 6; $n++ while $fields[$n] ne "-"; $n++;
        my $fsType = $fields[$n];
        my $device = $fields[$n + 1];
        my @superOptions = split /,/, $fields[$n + 2];

        # Skip the bind-mount on /nix/store.
        next if $mountPoint eq "/nix/store" && (grep { $_ eq "rw" } @superOptions);
        # Skip mount point generated by systemd-efi-boot-generator?
        next if $fsType eq "autofs";

        # Ensure this matches the intended directory
        next unless PathInMount($dir, $mountPoint);

        # Is it better than our current match?
        if (length($mountPoint) > length($bestFs->mount)) {

            # -d performs a stat, which can hang forever on network file systems,
            # so we only make this call last, when it's likely that this is the mount point we need.
            next unless -d $mountPoint;

            $bestFs = Fs->new(device => $device, type => $fsType, mount => $mountPoint);
        }
    }
    return $bestFs;
}
struct (Grub => {
    path => '$',
    search => '$',
});
my $driveid = 1;
sub GrubFs {
    my ($dir) = @_;
    my $fs = GetFs($dir);
    my $path = substr($dir, length($fs->mount));
    if (substr($path, 0, 1) ne "/") {
        $path = "/$path";
    }
    my $search = "";

    # ZFS is completely separate logic as zpools are always identified by a label
    # or custom UUID
    if ($fs->type eq 'zfs') {
        my $sid = index($fs->device, '/');

        if ($sid < 0) {
            $search = '--label ' . $fs->device;
            $path = '/@' . $path;
        } else {
            $search = '--label ' . substr($fs->device, 0, $sid);
            $path = '/' . substr($fs->device, $sid) . '/@' . $path;
        }
    } else {
        my %types = ('uuid' => '--fs-uuid', 'label' => '--label');

        if ($fsIdentifier eq 'provided') {
            # If the provided dev is identifying the partition using a label or uuid,
            # we should get the label / uuid and do a proper search
            my @matches = $fs->device =~ m/\/dev\/disk\/by-(label|uuid)\/(.*)/;
            if ($#matches > 1) {
                die "Too many matched devices"
            } elsif ($#matches == 1) {
                $search = "$types{$matches[0]} $matches[1]"
            }
        } else {
            # Determine the identifying type
            $search = $types{$fsIdentifier} . ' ';

            # Based on the type pull in the identifier from the system
            my ($status, @devInfo) = runCommand("@utillinux@/bin/blkid", "-o", "export", @{[$fs->device]});
            if ($status != 0) {
                die "Failed to get blkid info (returned $status) for @{[$fs->mount]} on @{[$fs->device]}";
            }
            my @matches = join("", @devInfo) =~ m/@{[uc $fsIdentifier]}=([^\n]*)/;
            if ($#matches != 0) {
                die "Couldn't find a $types{$fsIdentifier} for @{[$fs->device]}\n"
            }
            $search .= $matches[0];
        }

        # BTRFS is a special case in that we need to fix the referenced path based on subvolumes
        if ($fs->type eq 'btrfs') {
            my ($status, @id_info) = runCommand("@btrfsprogs@/bin/btrfs", "subvol", "show", @{[$fs->mount]});
            if ($status != 0) {
                die "Failed to retrieve subvolume info for @{[$fs->mount]}\n";
            }
            my @ids = join("\n", @id_info) =~ m/^(?!\/\n).*Subvolume ID:[ \t\n]*([0-9]+)/s;
            if ($#ids > 0) {
                die "Btrfs subvol name for @{[$fs->device]} listed multiple times in mount\n"
            } elsif ($#ids == 0) {
                my ($status, @path_info) = runCommand("@btrfsprogs@/bin/btrfs", "subvol", "list", @{[$fs->mount]});
                if ($status != 0) {
                    die "Failed to find @{[$fs->mount]} subvolume id from btrfs\n";
                }
                my @paths = join("", @path_info) =~ m/ID $ids[0] [^\n]* path ([^\n]*)/;
                if ($#paths > 0) {
                    die "Btrfs returned multiple paths for a single subvolume id, mountpoint @{[$fs->mount]}\n";
                } elsif ($#paths != 0) {
                    die "Btrfs did not return a path for the subvolume at @{[$fs->mount]}\n";
                }
                $path = "/$paths[0]$path";
            }
        }
    }
    if (not $search eq "") {
        $search = "search --set=drive$driveid " . $search;
        $path = "(\$drive$driveid)$path";
        $driveid += 1;
    }
    return Grub->new(path => $path, search => $search);
}
my $grubBoot = GrubFs($bootPath);
my $grubStore;
if ($copyKernels == 0) {
    $grubStore = GrubFs($storePath);
}

# Generate the header.
my $conf .= "# Automatically generated.  DO NOT EDIT THIS FILE!\n";

my @users = ();
foreach my $user ($dom->findnodes('/expr/attrs/attr[@name = "users"]/attrs/attr')) {
    my $name = $user->findvalue('@name') or die;
    my $hashedPassword = $user->findvalue('./attrs/attr[@name = "hashedPassword"]/string/@value');
    my $hashedPasswordFile = $user->findvalue('./attrs/attr[@name = "hashedPasswordFile"]/string/@value');
    my $password = $user->findvalue('./attrs/attr[@name = "password"]/string/@value');
    my $passwordFile = $user->findvalue('./attrs/attr[@name = "passwordFile"]/string/@value');

    if ($hashedPasswordFile) {
        open(my $f, '<', $hashedPasswordFile) or die "Can't read file '$hashedPasswordFile'!";
        $hashedPassword = <$f>;
        chomp $hashedPassword;
    }
    if ($passwordFile) {
        open(my $f, '<', $passwordFile) or die "Can't read file '$passwordFile'!";
        $password = <$f>;
        chomp $password;
    }

    if ($hashedPassword) {
        if (index($hashedPassword, "grub.pbkdf2.") == 0) {
            $conf .= "\npassword_pbkdf2 $name $hashedPassword";
        }
        else {
            die "Password hash for GRUB user '$name' is not valid!";
        }
    }
    elsif ($password) {
        $conf .= "\npassword $name $password";
    }
    else {
        die "GRUB user '$name' has no password!";
    }
    push(@users, $name);
}
if (@users) {
    $conf .= "\nset superusers=\"" . join(' ',@users) . "\"\n";
}

if ($copyKernels == 0) {
    $conf .= "
        " . $grubStore->search;
}
# FIXME: should use grub-mkconfig.
my $defaultEntryText = $defaultEntry;
if ($saveDefault) {
    $defaultEntryText = "\"\${saved_entry}\"";
}
$conf .= "
    " . $grubBoot->search . "
    if [ -s \$prefix/grubenv ]; then
      load_env
    fi

    # ‘grub-reboot’ sets a one-time saved entry, which we process here and
    # then delete.
    if [ \"\${next_entry}\" ]; then
      set default=\"\${next_entry}\"
      set next_entry=
      save_env next_entry
      set timeout=1
      set boot_once=true
    else
      set default=$defaultEntryText
      set timeout=$timeout
    fi
    set timeout_style=$timeoutStyle

    function savedefault {
        if [ -z \"\${boot_once}\"]; then
        saved_entry=\"\${chosen}\"
        save_env saved_entry
        fi
    }

    # Setup the graphics stack for bios and efi systems
    if [ \"\${grub_platform}\" = \"efi\" ]; then
      insmod efi_gop
      insmod efi_uga
    else
      insmod vbe
    fi
";

if ($font) {
    copy $font, "$bootPath/converted-font.pf2" or die "cannot copy $font to $bootPath: $!\n";
    $conf .= "
        insmod font
        if loadfont " . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/converted-font.pf2; then
          insmod gfxterm
          if [ \"\${grub_platform}\" = \"efi\" ]; then
            set gfxmode=$gfxmodeEfi
            set gfxpayload=$gfxpayloadEfi
          else
            set gfxmode=$gfxmodeBios
            set gfxpayload=$gfxpayloadBios
          fi
          terminal_output gfxterm
        fi
    ";
}
if ($splashImage) {
    # Keeps the image's extension.
    my ($filename, $dirs, $suffix) = fileparse($splashImage, qr"\..[^.]*$");
    # The module for jpg is jpeg.
    if ($suffix eq ".jpg") {
        $suffix = ".jpeg";
    }
    if ($backgroundColor) {
        $conf .= "
        background_color '$backgroundColor'
        ";
    }
    copy $splashImage, "$bootPath/background$suffix" or die "cannot copy $splashImage to $bootPath: $!\n";
    $conf .= "
        insmod " . substr($suffix, 1) . "
        if background_image --mode '$splashMode' " . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/background$suffix; then
          set color_normal=white/black
          set color_highlight=black/white
        else
          set menu_color_normal=cyan/blue
          set menu_color_highlight=white/blue
        fi
    ";
}

rmtree("$bootPath/theme") or die "cannot clean up theme folder in $bootPath\n" if -e "$bootPath/theme";

if ($theme) {
    # Copy theme
    rcopy($theme, "$bootPath/theme") or die "cannot copy $theme to $bootPath\n";

    # Detect which modules will need to be loaded
    my $with_png = 0;
    my $with_jpeg = 0;

    find({ wanted => sub {
            if ($_ =~ /\.png$/i) {
                $with_png = 1;
            }
            elsif ($_ =~ /\.jpe?g$/i) {
                $with_jpeg = 1;
            }
    }, no_chdir => 1 }, $theme);

    if ($with_png) {
        $conf .= "
            insmod png
        "
    }
    if ($with_jpeg) {
        $conf .= "
            insmod jpeg
        "
    }

    $conf .= "
        # Sets theme.
        set theme=" . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/theme/theme.txt
        export theme
        # Load theme fonts, if any
    ";

    find( { wanted => sub {
        if ($_ =~ /\.pf2$/i) {
            $font = File::Spec->abs2rel($File::Find::name, $theme);
            $conf .= "
                loadfont " . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/theme/$font
            ";
        }
    }, no_chdir => 1 }, $theme );
}

$conf .= "$extraConfig\n";


# Generate the menu entries.
$conf .= "\n";

my %copied;
make_path("$bootPath/kernels", { mode => 0755 }) if $copyKernels;

sub copyToKernelsDir {
    my ($path) = @_;
    return $grubStore->path . substr($path, length("/nix/store")) unless $copyKernels;
    $path =~ /\/nix\/store\/(.*)/ or die;
    my $name = $1; $name =~ s/\//-/g;
    my $dst = "$bootPath/kernels/$name";
    # Don't copy the file if $dst already exists.  This means that we
    # have to create $dst atomically to prevent partially copied
    # kernels or initrd if this script is ever interrupted.
    if (! -e $dst) {
        my $tmp = "$dst.tmp";
        copy $path, $tmp or die "cannot copy $path to $tmp: $!\n";
        rename $tmp, $dst or die "cannot rename $tmp to $dst: $!\n";
    }
    $copied{$dst} = 1;
    return ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/kernels/$name";
}

sub addEntry {
    my ($name, $path, $options, $current) = @_;
    return unless -e "$path/kernel" && -e "$path/initrd";

    my $kernel = copyToKernelsDir(Cwd::abs_path("$path/kernel"));
    my $initrd = copyToKernelsDir(Cwd::abs_path("$path/initrd"));

    # Include second initrd with secrets
    if (-e -x "$path/append-initrd-secrets") {
        # Name the initrd secrets after the system from which they're derived.
        my $systemName = basename(Cwd::abs_path("$path"));
        my $initrdSecretsPath = "$bootPath/kernels/$systemName-secrets";

        make_path(dirname($initrdSecretsPath), { mode => 0755 });
        my $oldUmask = umask;
        # Make sure initrd is not world readable (won't work if /boot is FAT)
        umask 0137;
        my $initrdSecretsPathTemp = File::Temp::mktemp("$initrdSecretsPath.XXXXXXXX");
        if (system("$path/append-initrd-secrets", $initrdSecretsPathTemp) != 0) {
          if ($current) {
              die "failed to create initrd secrets $!\n";
          } else {
              say STDERR "warning: failed to create initrd secrets for \"$name\", an older generation";
              say STDERR "note: this is normal after having removed or renamed a file in `boot.initrd.secrets`";
          }
        }
        # Check whether any secrets were actually added
        if (-e $initrdSecretsPathTemp && ! -z _) {
            rename $initrdSecretsPathTemp, $initrdSecretsPath or die "failed to move initrd secrets into place: $!\n";
            $copied{$initrdSecretsPath} = 1;
            $initrd .= " " . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/kernels/$systemName-secrets";
        } else {
            unlink $initrdSecretsPathTemp;
            rmdir dirname($initrdSecretsPathTemp);
        }
        umask $oldUmask;
    }

    my $xen = -e "$path/xen.gz" ? copyToKernelsDir(Cwd::abs_path("$path/xen.gz")) : undef;

    # FIXME: $confName

    my $kernelParams =
        "init=" . Cwd::abs_path("$path/init") . " " .
        readFile("$path/kernel-params");
    my $xenParams = $xen && -e "$path/xen-params" ? readFile("$path/xen-params") : "";

    $conf .= "menuentry \"$name\" " . $options . " {\n";
    if ($saveDefault) {
        $conf .= "  savedefault\n";
    }
    $conf .= $grubBoot->search . "\n";
    if ($copyKernels == 0) {
        $conf .= $grubStore->search . "\n";
    }
    $conf .= "  $extraPerEntryConfig\n" if $extraPerEntryConfig;
    $conf .= "  multiboot $xen $xenParams\n" if $xen;
    $conf .= "  " . ($xen ? "module" : "linux") . " $kernel $kernelParams\n";
    $conf .= "  " . ($xen ? "module" : "initrd") . " $initrd\n";
    $conf .= "}\n\n";
}

sub addGeneration {
    my ($name, $nameSuffix, $path, $options, $current) = @_;

    # Do not search for grand children
    my @links = sort (glob "$path/specialisation/*");

    if ($current != 1 && scalar(@links) != 0) {
        $conf .= "submenu \"$name$nameSuffix\" --class submenu {\n";
    }

    addEntry("$name" . (scalar(@links) == 0 ? "" : " - Default") . $nameSuffix, $path, $options, $current);

    # Find all the children of the current default configuration
    # Do not search for grand children
    foreach my $link (@links) {

        my $entryName = "";

        my $cfgName = readFile("$link/configuration-name");

        my $date = strftime("%F", localtime(lstat($link)->mtime));
        my $version =
            -e "$link/nixos-version"
            ? readFile("$link/nixos-version")
            : basename((glob(dirname(Cwd::abs_path("$link/kernel")) . "/lib/modules/*"))[0]);

        if ($cfgName) {
            $entryName = $cfgName;
        } else {
            my $linkname = basename($link);
            $entryName = "($linkname - $date - $version)";
        }
        addEntry("$name - $entryName", $link, "", 1);
    }

    if ($current != 1 && scalar(@links) != 0) {
        $conf .= "}\n";
    }
}

# Add default entries.
$conf .= "$extraEntries\n" if $extraEntriesBeforeNixOS;

addGeneration("@distroName@", "", $defaultConfig, $entryOptions, 1);

$conf .= "$extraEntries\n" unless $extraEntriesBeforeNixOS;

my $grubBootPath = $grubBoot->path;
# extraEntries could refer to @bootRoot@, which we have to substitute
$conf =~ s/\@bootRoot\@/$grubBootPath/g;

# Emit submenus for all system profiles.
sub addProfile {
    my ($profile, $description) = @_;

    # Add entries for all generations of this profile.
    $conf .= "submenu \"$description\" --class submenu {\n";

    sub nrFromGen { my ($x) = @_; $x =~ /\/\w+-(\d+)-link/; return $1; }

    my @links = sort
        { nrFromGen($b) <=> nrFromGen($a) }
        (glob "$profile-*-link");

    my $curEntry = 0;
    foreach my $link (@links) {
        last if $curEntry++ >= $configurationLimit;
        if (! -e "$link/nixos-version") {
            warn "skipping corrupt system profile entry ‘$link’\n";
            next;
        }
        my $date = strftime("%F", localtime(lstat($link)->mtime));
        my $version =
            -e "$link/nixos-version"
            ? readFile("$link/nixos-version")
            : basename((glob(dirname(Cwd::abs_path("$link/kernel")) . "/lib/modules/*"))[0]);
        addGeneration("@distroName@ - Configuration " . nrFromGen($link), " ($date - $version)", $link, $subEntryOptions, 0);
    }

    $conf .= "}\n";
}

addProfile "/nix/var/nix/profiles/system", "@distroName@ - All configurations";

for my $profile (glob "/nix/var/nix/profiles/system-profiles/*") {
    my $name = basename($profile);
    next unless $name =~ /^\w+$/;
    addProfile $profile, "@distroName@ - Profile '$name'";
}

# extraPrepareConfig could refer to @bootPath@, which we have to substitute
$extraPrepareConfig =~ s/\@bootPath\@/$bootPath/g;

# Run extraPrepareConfig in sh
if ($extraPrepareConfig ne "") {
    system((get("shell"), "-c", $extraPrepareConfig));
}

# write the GRUB config.
my $confFile = "$bootPath/grub/grub.cfg";
my $tmpFile = $confFile . ".tmp";
writeFile($tmpFile, $conf);


# check whether to install GRUB EFI or not
sub getEfiTarget {
    if (($grub ne "") && ($grubEfi ne "")) {
        # EFI can only be installed when target is set;
        # A target is also required then for non-EFI grub
        if (($grubTarget eq "") || ($grubTargetEfi eq "")) { die }
        else { return "both" }
    } elsif (($grub ne "") && ($grubEfi eq "")) {
        # TODO: It would be safer to disallow non-EFI grub installation if no target is given.
        #       If no target is given, then grub auto-detects the target which can lead to errors.
        #       E.g. it seems as if grub would auto-detect a EFI target based on the availability
        #       of a EFI partition.
        #       However, it seems as auto-detection is currently relied on for non-x86_64 and non-i386
        #       architectures in NixOS. That would have to be fixed in the nixos modules first.
        return "no"
    } elsif (($grub eq "") && ($grubEfi ne "")) {
        # EFI can only be installed when target is set;
        if ($grubTargetEfi eq "") { die }
        else {return "only" }
    } else {
        # prevent an installation if neither grub nor grubEfi is given
        return "neither"
    }
}

my $efiTarget = getEfiTarget();

# Append entries detected by os-prober
if (get("useOSProber") eq "true") {
    if ($saveDefault) {
        # os-prober will read this to determine if "savedefault" should be added to generated entries
        $ENV{'GRUB_SAVEDEFAULT'} = "true";
    }

    my $targetpackage = ($efiTarget eq "no") ? $grub : $grubEfi;
    system(get("shell"), "-c", "pkgdatadir=$targetpackage/share/grub $targetpackage/etc/grub.d/30_os-prober >> $tmpFile");
}

# Atomically switch to the new config
rename $tmpFile, $confFile or die "cannot rename $tmpFile to $confFile: $!\n";


# Remove obsolete files from $bootPath/kernels.
foreach my $fn (glob "$bootPath/kernels/*") {
    next if defined $copied{$fn};
    print STDERR "removing obsolete file $fn\n";
    unlink $fn;
}


#
# Install GRUB if the parameters changed from the last time we installed it.
#

struct(GrubState => {
    name => '$',
    version => '$',
    efi => '$',
    devices => '$',
    efiMountPoint => '$',
    grub => '$',
    grubEfi => '$',
    extraGrubInstallArgs => '@',
});
# If you add something to the state file, only add it to the end
# because it is read line-by-line.
sub readGrubState {
    my $defaultGrubState = GrubState->new(name => "", version => "", efi => "", devices => "", efiMountPoint => "", grub => "", grubEfi => "", extraGrubInstallArgs => () );
    open my $fh, "<", "$bootPath/grub/state" or return $defaultGrubState;
    local $/ = "\n";
    my $name = <$fh>;
    chomp($name);
    my $version = <$fh>;
    chomp($version);
    my $efi = <$fh>;
    chomp($efi);
    my $devices = <$fh>;
    chomp($devices);
    my $efiMountPoint = <$fh>;
    chomp($efiMountPoint);
    # Historically, arguments in the state file were one per each line, but that
    # gets really messy when newlines are involved, structured arguments
    # like lists are needed (they have to have a separator encoding), or even worse,
    # when we need to remove a setting in the future. Thus, the 6th line is a JSON
    # object that can store structured data, with named keys, and all new state
    # should go in there.
    my $jsonStateLine = <$fh>;
    # For historical reasons we do not check the values above for un-definedness
    # (that is, when the state file has too few lines and EOF is reached),
    # because the above come from the first version of this logic and are thus
    # guaranteed to be present.
    $jsonStateLine = defined $jsonStateLine ? $jsonStateLine : '{}'; # empty JSON object
    chomp($jsonStateLine);
    if ($jsonStateLine eq "") {
        $jsonStateLine = '{}'; # empty JSON object
    }
    my %jsonState = %{decode_json($jsonStateLine)};
    my @extraGrubInstallArgs = exists($jsonState{'extraGrubInstallArgs'}) ? @{$jsonState{'extraGrubInstallArgs'}} : ();
    my $grubValue = exists($jsonState{'grub'}) ? $jsonState{'grub'} : "";
    my $grubEfiValue = exists($jsonState{'grubEfi'}) ? $jsonState{'grubEfi'} : "";
    close $fh;
    my $grubState = GrubState->new(name => $name, version => $version, efi => $efi, devices => $devices, efiMountPoint => $efiMountPoint, extraGrubInstallArgs => \@extraGrubInstallArgs, grub => $grubValue, grubEfi => $grubEfiValue );
    return $grubState
}

my @deviceTargets = getList('devices');
my $prevGrubState = readGrubState();
my @prevDeviceTargets = split/,/, $prevGrubState->devices;
my @extraGrubInstallArgs = getList('extraGrubInstallArgs');
my @prevExtraGrubInstallArgs = @{$prevGrubState->extraGrubInstallArgs};

my $devicesDiffer = scalar (List::Compare->new( '-u', '-a', \@deviceTargets, \@prevDeviceTargets)->get_symmetric_difference());
my $extraGrubInstallArgsDiffer = scalar (List::Compare->new( '-u', '-a', \@extraGrubInstallArgs, \@prevExtraGrubInstallArgs)->get_symmetric_difference());
my $efiDiffer = $efiTarget ne $prevGrubState->efi;
my $efiMountPointDiffer = $efiSysMountPoint ne $prevGrubState->efiMountPoint;
# re-installing grub once the package store path changes is necessary, because
# introducing patches or adjusting builds does not always bump the version number
my $grubStorePathsDiffer = ($grub ne $prevGrubState->grub) || ($grubEfi ne $prevGrubState->grubEfi);
if (($ENV{'NIXOS_INSTALL_GRUB'} // "") eq "1") {
    warn "NIXOS_INSTALL_GRUB env var deprecated, use NIXOS_INSTALL_BOOTLOADER";
    $ENV{'NIXOS_INSTALL_BOOTLOADER'} = "1";
}
my $requireNewInstall = $devicesDiffer || $extraGrubInstallArgsDiffer || $efiDiffer || $efiMountPointDiffer || $grubStorePathsDiffer || (($ENV{'NIXOS_INSTALL_BOOTLOADER'} // "") eq "1");

# install a symlink so that grub can detect the boot drive
my $tmpDir = File::Temp::tempdir(CLEANUP => 1) or die "Failed to create temporary space: $!";
symlink "$bootPath", "$tmpDir/boot" or die "Failed to symlink $tmpDir/boot: $!";

# install non-EFI GRUB
if (($requireNewInstall != 0) && ($efiTarget eq "no" || $efiTarget eq "both")) {
    foreach my $dev (@deviceTargets) {
        next if $dev eq "nodev";
        print STDERR "installing the GRUB 2 boot loader on $dev...\n";
        my @command = ("$grub/sbin/grub-install", "--recheck", "--root-directory=$tmpDir", Cwd::abs_path($dev), @extraGrubInstallArgs);
        if ($forceInstall eq "true") {
            push @command, "--force";
        }
        if ($grubTarget ne "") {
            push @command, "--target=$grubTarget";
        }
        (system @command) == 0 or die "$0: installation of GRUB on $dev failed: $!\n";
    }
}


# install EFI GRUB
if (($requireNewInstall != 0) && ($efiTarget eq "only" || $efiTarget eq "both")) {
    print STDERR "installing the GRUB 2 boot loader into $efiSysMountPoint...\n";
    my @command = ("$grubEfi/sbin/grub-install", "--recheck", "--target=$grubTargetEfi", "--boot-directory=$bootPath", "--efi-directory=$efiSysMountPoint", @extraGrubInstallArgs);
    if ($forceInstall eq "true") {
        push @command, "--force";
    }
    push @command, "--bootloader-id=$bootloaderId";
    if ($canTouchEfiVariables ne "true") {
        push @command, "--no-nvram";
        push @command, "--removable" if $efiInstallAsRemovable eq "true";
    }

    (system @command) == 0 or die "$0: installation of GRUB EFI into $efiSysMountPoint failed: $!\n";
}


# update GRUB state file
if ($requireNewInstall != 0) {
    # Temp file for atomic rename.
    my $stateFile = "$bootPath/grub/state";
    my $stateFileTmp = $stateFile . ".tmp";

    open my $fh, ">", "$stateFileTmp" or die "cannot create $stateFileTmp: $!\n";
    print $fh get("fullName"), "\n" or die;
    print $fh get("fullVersion"), "\n" or die;
    print $fh $efiTarget, "\n" or die;
    print $fh join( ",", @deviceTargets ), "\n" or die;
    print $fh $efiSysMountPoint, "\n" or die;
    my %jsonState = (
        extraGrubInstallArgs => \@extraGrubInstallArgs,
        grub => $grub,
        grubEfi => $grubEfi
    );
    my $jsonStateLine = encode_json(\%jsonState);
    print $fh $jsonStateLine, "\n" or die;
    close $fh or die;

    # Atomically switch to the new state file
    rename $stateFileTmp, $stateFile or die "cannot rename $stateFileTmp to $stateFile: $!\n";
}