#!/usr/bin/ruby
# a script to try and parse /var/lib/arpwatch/arp.dat 
# into DHCP/DNS configuration snippets
# Copyleft 2006 by Michael Shigorin <mike@osdn.org.ua>

DEBUG  = false		# -v
DEBUG2 = true			# -vv

ARPDAT = "arp.dat"
#ARPDAT = "arp.test"
IGNORE = "arp.ignore"		# one MAC per line to ignore

PREFIX = "192.168"
OLDNET = "#{PREFIX}.0"
NEWNET = "#{PREFIX}.10"
OLDPAT = Regexp.new(OLDNET)

ZONE = NEWNET.split(".").reverse.join(".") + ".in-addr.arpa_ADD"
DHCP = "dhcpd.conf_ADD"

data = Hash.new
result = Hash.new
ignored = Array.new

begin
	File.open(IGNORE) do |f|
		f.each do |mac| ignored << mac.chomp end
	end
rescue
	puts "** unable to open #{IGNORE}, accepting all MACs" if DEBUG
end

p ignored if DEBUG

File.open(ARPDAT) do |f|
	f.each do |line|
		mac,ip,tstamp,host = line.split
		next if mac.nil? or ip.nil? or tstamp.nil?	# broken line
		next if ignored.include?(mac)
		# host might be empty...
		begin
			data[mac][tstamp] = { ip => host }
		rescue	# new MAC
			data[mac] = Hash.new
			retry
		end
	end
end

# let's look closer into different "alias" ip/hosts for the same mac
# 
# note that due to DDNS enabled, "last" IP has a better chance
# to have a proper _hostname_ in the corresponding data[] record;
# still we prefer "first" _IP_ since these were given out by hand
# which seems slightly more honorable than dhcp pool

data.each do |mac,tstamps|
	first_ip = nil
	last_ip  = nil
	lastname = nil
	puts "* #{mac}" if DEBUG2
	tstamps.sort.each do |tstamp,host|
		host.each do |ip,hostname|
			puts "  + #{tstamp}\t#{ip}\t#{hostname}" if DEBUG2
			first_ip = ip if ip =~ OLDPAT and first_ip.nil?
			last_ip  = ip
			lastname = hostname
		end
	end
	begin
		new_ip = first_ip.sub(OLDNET, NEWNET)
	rescue	# mac never seen on oldnet, probably fresh/only one
		new_ip = last_ip
	end
	if lastname.nil?
		lastname = new_ip.sub(/^#{PREFIX}.(\d+).(\d+)/,'ws\1-\2')
	end
	puts "#{mac}\t#{new_ip}\t#{lastname}" if DEBUG
	result[new_ip] = {
		'mac' => mac,
		'host' => lastname
	}
end

# need something like: result.sort!
#
# NEED to check hostnames for uniq! (dhcpd chokes otherwise)

# finally, construct conf file snippets in question

File.open(ZONE, "w") do |f|
	result.each do |ip,res|
		f << "#{res['host']}		IN	A	#{ip}\n"
	end
end		# output file should be sorted by hostname...

File.open(DHCP, "w") do |f|
	result.each do |ip,res|
		f << "  host #{res['host']} {\n"
		f << "    hardware ethernet #{res['mac']};\n"
		f << "    fixed-address #{res['host']};\n"
		f << "  }\n\n"
	end
end		# output file should be sorted somehow