#!/usr/bin/python
import os
import sys
import re
import argparse
from subprocess import Popen, PIPE, check_call, CalledProcessError
import ipaddr
import dns.zone  # http://www.dnspython.org/


def sync_dynamic_zones():
	check_call(['rndc', 'sync'])


def ipfamily_by_ip(ip):
	if isinstance(ip, ipaddr.IPv4Address):
		return 'A'
	elif isinstance(ip, ipaddr.IPv6Address):
		return 'AAAA'
	assert False


def forward_lookup(fqdn, ip_family):
	"""Returns the ip address of the fqdn or None if none is found..

	:param fqdn: Fully qualified domain name.
	:param ip_family: 'A' or 'AAAA'"""
	filename = '/var/cache/bind/dyn.colgarra.priv.at'
	zonename = os.path.basename(filename)
	zone = dns.zone.from_file(filename, zonename, relativize=False)
	for name, ttl, rdata in zone.iterate_rdatas(ip_family):
		if str(name)[:-1] == fqdn:  # [:-1] removes trailing dot
			return ipaddr.IPAddress(rdata.address)


def reverse_lookup(ip):
	"""Returns an iterator of fqdns for the given IP address.

	:param ip: Instance of ipaddr.IPv4Address or ipaddr.IPv6Address"""
	filename = '/var/cache/bind/dyn.colgarra.priv.at'
	zonename = os.path.basename(filename)
	zone = dns.zone.from_file(filename, zonename, relativize=False)
	for name, ttl, rdata in zone.iterate_rdatas(ipfamily_by_ip(ip)):
		if ipaddr.IPAddress(rdata.address) == ip:
			yield str(name)


def nsupdate_add(fqdn, ttl, ip):
	"""
	:param fqdn: Fully qualified domain name
	:param ip_family: A or AAAA
	:raises an NsupdateError in case of errors."""
	command = "update add {fqdn} {ttl} IN {ip_family} {ip}\n\n".format(fqdn=fqdn, ttl=ttl, ip_family=ipfamily_by_ip(ip), ip=ip)
	p = Popen(['nsupdate', '-l'], stdin=PIPE)
	p.communicate(command)
	if p.returncode != 0:
		raise CalledProcessError(p.returncode, 'nsupdate -l')

def nsupdate_delete(fqdn, ip_family):
	"""
	:param fqdn: Fully qualified domain name
	:param ip_family: A or AAAA
	:raises an NsupdateError in case of errors."""
	command = "update delete {fqdn} {ip_family}\n\n".format(fqdn=fqdn, ip_family=ip_family)
	p = Popen(['nsupdate', '-l'], stdin=PIPE)
	p.communicate(command)
	if p.returncode != 0:
		raise CalledProcessError(p.returncode, 'nsupdate -l')


def blockip_whitelist_add(ip):
	"""
	:param ip: ipv4 address
	:raises a CalledProcessError in case of errors."""
	if ipfamily_by_ip(ip) == 'A':
		command = ['iptables', '-I', 'blockip', '-s', str(ip), '-j', 'ACCEPT']
		check_call(command)


def blockip_whitelist_delete(ip):
	"""
	:param ip: ipv4 address
	:raises a CalledProcessError in case of errors."""
	if ipfamily_by_ip(ip) == 'A':
		command = ['iptables', '-D', 'blockip', '-s', str(ip), '-j', 'ACCEPT']
		check_call(command)


def main(args):
	try:
		if args.delete:
			if args.ip is None:
				nsupdate_delete(args.fqdn, 'A')
				nsupdate_delete(args.fqdn, 'AAAA')
			else:
				ipfamily = ipfamily_by_ip(args.ip)
				sync_dynamic_zones()
				old_ip = forward_lookup(args.fqdn, ipfamily)
				nsupdate_delete(args.fqdn, ipfamily_by_ip(args.ip))
				if old_ip is not None:
					blockip_whitelist_delete(old_ip)
		else:
			ipfamily = ipfamily_by_ip(args.ip)
			sync_dynamic_zones()
			old_ip = forward_lookup(args.fqdn, ipfamily)
			nsupdate_delete(args.fqdn, ipfamily)
			nsupdate_add(args.fqdn, args.ttl, args.ip)
			if old_ip != args.ip:
				if old_ip is not None:
					blockip_whitelist_delete(old_ip)
				blockip_whitelist_add(args.ip)
	except CalledProcessError as e:
		sys.exit(e.returncode)



if __name__ == '__main__':
	parser = argparse.ArgumentParser(description='Add or delete a domain name from dyndns (simplifies call to nsupdate).')
	parser.add_argument('-d', '--delete', action='store_true', help='delete instead of add')
	parser.add_argument('-i', '--ip', help='IP address (either IPv4 or IPv6)')
	parser.add_argument('-t', '--ttl', type=int, default=600, help='TTL (default: 600)')
	parser.add_argument('fqdn', help='fully qualified domain name to add or delete, e.g. myserver.dyn.example.com')
	args = parser.parse_args()

	# check ip
	if not args.delete and not args.ip:
		parser.error('The IP address is mandatory')
	if args.ip:
		try:
			args.ip = ipaddr.IPAddress(args.ip) # throws an exception if the IP address is not valid
		except ValueError:
			parser.error('The IP address is not valid')

	# check fqdn
	if re.match(r'[-0-9a-z]+(\.[-0-9a-z]+)*$', args.fqdn) is None:
		parser.error('The fqdn has an invalid format.')

	main(args)