#!/usr/bin/perl

if ($#ARGV == -1) {
	print "Usage: $ARGV[-1] real-file\n";
	exit 0;
}

$RealFile = $ARGV[0];

$debug = 1;

open (RF,"$RealFile") || die "Can't open $RealFile: $!\n";
open (OF,">$RealFile.new") || die "Can't open $RealFile.new: $!\n";
while (<RF>) {
	if (/^\#/) { print OF; next; }
	if (/^[ \t]*\n$/) { print OF; next; }
	chomp;
	($host,$group,$reallist) = split(':');
	@reals = split('\|',$reallist);

	@hostbreak = split(/\./,$host);
	$domain = $hostbreak[$#hostbreak-1].".".$hostbreak[$#hostbreak];

	if ($debug) {
		print "\n\nPROCESSING: $host\n";
		print "DOMAIN: $domain\n";
		print "CURRENT: $host:$group:";
		foreach $r (@reals) { print "$r|"; }
		print "\n";
	}

	#
	# Reinit the ip hash
	#

	delete @newreals{keys %newreals};
	delete @oldreals{keys %oldreals};
	delete @noreal[0 .. $#noreal];
	delete @slbreal[0 .. $#slbreal];

#	foreach $ip (keys %newreals) { $newreals{"$ip"} = 0; }
#	foreach $ip (keys %oldreals) { $oldreals{"$ip"} = 0; }
#	foreach $i (@noreal)  { shift (@noreal); }
#	foreach $i (@slbreal) { shift (@slbreal); }


	#
	# Walk each nameserver for a given host
	# 

	foreach $nsline (`/usr/bin/host -t ns $domain`) {
		chomp($nsline);
		$ns = (split(/[ \t]+/,$nsline))[3];
		if ($debug) { print "$domain has a nameserver of $ns\n"; }
		$redo = 1;
		$tmphost = $host;
		while ($redo == 1) {
			print "Looking up A records for $tmphost\n";
			foreach $ipline (`/usr/bin/host -t a $tmphost $ns`) {
				if ($ipline =~ /nickname/) { 
					chomp ($ipline);
					@t = split(/[ \t]/,$ipline);
					$newhost = $t[-1];
					undef @t;
					print "$host is a CNAME to $newhost\n";
					$redo = 2;
					next;
				} else {
					if ($redo != 2) {
						$redo = 0;
					}
				}
				if (!($ipline =~ /has address/)) { next; }
				chomp($ipline);
				$ip = (split(/[ \t]+/,$ipline))[3];
				print "$tmphost IN A $ip\n";
				$newreals{"$ip"} = 1;
			}
			if ($redo) {
				print "Recursing down the CNAME\n";
				$tmphost = $newhost;
				$redo = 1;
			}
		}
	}
	if ($debug) { foreach $nr (keys %newreals) { print "$host is $nr\n"; } }

	#
	# Now see if that differs from what we already have.
	# If an IP that was in @reals is no longer there, remove it.
	# If a new IP is found, add it.
	#

	# First check for what isn't there anymore...

	foreach $r (@reals) {
		if ($newreals{"$r"} == 0) {
			if ($debug) { print "$r was removed for $host\n"; }
			push (@noreal,$r);
		}
		# Prepare for next foreach
		$oldreals{"$r"} = 1;
	}

	# What's been added? 

	foreach $r (keys %newreals) {
		if ($oldreals{"$r"} == 0) {
			if ($debug) { print "$r was added for $host\n"; }
			push (@slbreal,$r);
		}
	}

	#
	# Update the new reals file
	#

	$cnt = 0;
	@nrs = keys %newreals;
	print OF "$host:$group:";
	foreach $nr (@nrs) {
		$cnt++;
		print OF "$nr";
		if ($cnt <= $#nrs) { print OF "|"; }
		else { print OF "\n"; }
	}
}
close (RF);
close (OF);

rename ("$RealFile", "$RealFile.bak");
rename ("$RealFile.new", "$RealFile");