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

for my $zonefile (@ARGV) {
    open my $in, '<', $zonefile;
    open my $out, '>', "$zonefile.$$";
    while (<$in>) {
        # @               SOA     ns1.wsr.ac.at. hostmaster.wsr.ac.at. 1957 14400 3600 604800 86400
        if ( my ($prefix, $master, $rp, $serial, $refresh, $retry, $expire, $negttl)
                = m/(.*)SOA\s+(\S+)\s+(\S+)\s(\d+)\s(\d+)\s(\d+)\s(\d+)\s(\d+)/
        ) {
            # maximum time recommended by RFC 2308, also enforced by
            # BIND (by default).
            if ($negttl >= 3 * 3600) {
                $negttl = 3600;
                $serial++;
            }
            print $out "${prefix}SOA\t$master $rp $serial $refresh $retry $expire $negttl\n";
        } else {
            print $out $_;
        }
    }
    rename "$zonefile.$$", $zonefile;
}