#!/usr/bin/perl

use strict;
use warnings;

my $inFile = shift || '/var/cache/bind/cancerprev.org.db';
my $outFile = shift || '/var/cache/bind/db.88.189.146';
my $ipPrefix = shift;

if (! defined $ipPrefix) {
    if ($outFile =~ /db\.([\d\.]+)$/) {
        $ipPrefix = join('.', reverse(split(/\./, $1)));
        print "Using autodetected IP prefix: $ipPrefix.\n";
    } else {
        die "No IP prefix specified, and input filename not db.0.168.192 form.\n";
    }
}

my $hostRe = qr/[[:alnum:].\-]+/;
#my $ipRe   = qr/\d{1,3}(?:\.\d{1,3}){3}/;
my $lineRe = qr/^($hostRe)\s+IN\s+A\s+\Q$ipPrefix\E\.([\d\.]+)\s*$/;

my %ipMap;

open(IN, '<', $inFile) or die($!);
while (<IN>) {
    if ($_ =~ $lineRe) {
        # For IPs that have multiple aliases, the first alias is used.
        if (! defined $ipMap{$2}) {
            $ipMap{$2} = $1;
        } else {
            print "Skipping $1 ($2 is already mapped to $ipMap{$2})\n";
        }
    }
}
close IN;

my $serialNum = sprintf '%10d', (time());

# yeah, i know this is a bit of a hack...
my $template = <<EOF;
;
; BIND reverse data file for IPs starting with $ipPrefix
; 
; THIS IS A GENERATED FILE -- DO NOT EDIT!
; ANY CHANGES WILL BE LOST!
;
; (generated from $inFile)
;
\$TTL    604800
\@       IN      SOA     office.cancerprev.org.  hostmaster.cancerprev.org. (
                     $serialNum         ; Serial
                         604800         ; Refresh
                          86400         ; Retry
                        2419200         ; Expire
                         604800 )       ; Negative Cache TTL
;
\@       IN      NS      ns1.office.cancerprev.org.
EOF

# output
open OUT, '>', $outFile or die $!;
print OUT $template;
foreach my $ip (keys %ipMap) {
    printf OUT "%s     IN      PTR     %s.office.cancerprev.org.\n", 
           ($ip, $ipMap{$ip});
}
close OUT;