#!/usr/bin/perl -w

use strict;
use Fcntl qw/SEEK_CUR O_CREAT O_TRUNC O_WRONLY O_RDONLY/;
use Data::Dumper;
use Capture::Tiny qw/capture/;
use JSON;

my $image=$ARGV[0];
my $output=$ARGV[1];

if (!defined($image) || !defined($output) || $image eq '' || $output eq '') {
        printf("extractefi input.iso efi.img\n");
        exit 1;
}

printf("Using sfdisk to get partition layout\n");
my ($stdout, $stderr, $exit)=capture {
        system(sprintf("/usr/sbin/sfdisk -J %s", $image));
};

if ($exit != 0) {
        printf("Failed to execute sfdisk on image\n%s\n", $stderr);
        exit 1;
}

my $sf=from_json($stdout);

my $efipart;
if ($sf->{partitiontable}{label} eq 'dos') {
        my @efis=grep { $_->{type} eq 'ef' } @{$sf->{partitiontable}{partitions}};
        $efipart=shift @efis;
} elsif ($sf->{partitiontable}{label} eq 'gpt') {
        my @efis=grep { $_->{type} eq 'C12A7328-F81F-11D2-BA4B-00A0C93EC93B' } @{$sf->{partitiontable}{partitions}};
        $efipart=shift @efis;
}

if (!defined($efipart)) {
        printf("Could not find EFI System Partition with UUID C12A7328-F81F-11D2-BA4B-00A0C93EC93B\n");
        exit 1;
}

my $start=$sf->{partitiontable}{sectorsize}*$efipart->{start};
my $size=$sf->{partitiontable}{sectorsize}*$efipart->{size};

printf("Opening file %s to read efi image from offset %d length %d\n", $image, $start, $size);

my $img;
sysopen(my $i, $image, O_RDONLY);
sysseek($i, $start, SEEK_CUR);
my $j=sysread($i, $img, $size);

if ($j != $size) {
        printf("Short read while trying to read EFI system partition\n");
        exit 1;
}
close($i);

printf("Writing efi image %s size %d\n", $output, $size);
sysopen(my $o, $output, O_CREAT|O_TRUNC|O_WRONLY);
syswrite($o, $img, $size);
close($o);