#!/usr/bin/perl
use warnings;
use strict;

use Getopt::Long;
use Net::DNS::Resolver;

my $cfg;
GetOptions('config:s' => \$cfg);

my %file2zone;
my $res;

if ($cfg) {
    # XXX - this is very simplistic
    open(my $fh, '<', $cfg) or die "cannot open $cfg: $!";
    my $currentzone;
    while (<$fh>) {
	if (/zone "(.*?)"/) {
	    $currentzone = $1;
	} elsif (m{file ".*/(.*)"}) {
	    $file2zone{$1} = $currentzone;
	}
    }
    $res = Net::DNS::Resolver->new();
}

for my $f (@ARGV) {
    my $maxserial = 0;
    if (my $zone = $file2zone{$f}) {
	my $reply = $res->send($zone, 'NS');
	my @nsnames;
	for my $ans ($reply->answer) {
	    push @nsnames, $ans->nsdname;
	}
	my @nsips;
	for (@nsnames) {
	    my $reply = $res->send($_, 'A');
	    for my $ans ($reply->answer) {
		push @nsips, $ans->address if $ans->type eq 'A';
	    }
	}
	for (@nsips) {
	    $res->nameservers($_);
	    my $reply = $res->send($zone, 'SOA');
	    for my $ans ($reply->answer) {
		if ($ans->type eq 'SOA') {
		    # XXX assume no wraparound
		    if ($ans->serial > $maxserial) {
			$maxserial = $ans->serial;
		    }
		}
	    }
	}
    }
    open (my $in, '<', "$f") or die "cannot open $f: $!";
    open (my $out, '>', "$f.new") or die "cannot open $f.new: $!";
    while (<$in>) {
	if (/(.*\bSOA\b.*?)(\d+)( \d+ \d+ \d+ \d+)/) {
	    my $serial = $2;
	    $maxserial = $serial if ($serial > $maxserial);
	    $maxserial++;
	    print $out "$1$maxserial$3\n";
	} else {
	    print $out $_;
	}
    }
    close($out) or die "cannot close $f.new: $!";
    rename "$f.new", $f || die "cannot rename $f.new to $f: $!";
}