#!/usr/bin/perl

use warnings;
use strict;

use IO::File;
use POSIX qw(strftime);

for my $file (@ARGV) {
    my $fh = IO::File->new($file,'r');
    my $fh_new = IO::File->new($file.".new",'w');
    local $/;
    my $fh_contents = <$fh>;
    # rip out old serial
    my ($old_serial) = $fh_contents =~ /IN\s+SOA\s+\S+\s+\S+\s*(?:\s*\;.+\n)*\((?:\s*\;.+\n)*\s*(\d+)/;
    my ($ymd,$iter) = $old_serial =~ /(\d{4}\d{2}\d{2})(\d{2})/;
    my $new_serial = strftime("%Y%m%d",gmtime)."01"
    if ($ymd == strftime("%Y%m%d",gmtime)) {
	$new_serial = $ymd.($iter+1);
    }
    $fh_contents =~ s/(IN\s+SOA\s+\S+\s+\S+\s*(?:\s*\;.+\n)*\((?:\s*\;.+\n)*\s*)(\d+)/${1}${new_serial}/;
    print {$fh_new} $fh_contents;
    close $fh_new;
    close $fh;
    rename($file,"${file}.bak") or die "Unable to rename $file to ${file}.bak: $!";
    rename("${file}.new",$file) or die "Unable to rename ${file}.new to ${file}: $!";
    unlink("${file}.bak") or die "Unable to unlink ${file}.bak: $!";
}