#!/usr/bin/env python3

import argparse
import ipaddress
import netifaces
import logging
import logging.handlers
import os.path
import socket
import subprocess
import sys


def build_ip(ip_string):
	try:
		ip = ipaddress.ip_address(ip_string)
	except ValueError:
		log.error("manually specified address is invalid format: %s" % ip_string)
		sys.exit(1)
	except:
		log.error(str(e))
		sys.exit(1)

	return ip

def get_interface_addrs(iface, addrtype):
	try:
		iaddrs = netifaces.ifaddresses(iface)
		i = iaddrs[addrtype]
		log.debug("interface {} addrs of type {}: {}".format(iface,addrtype,i))
	except ValueError as e:
		log.debug("Exception class: {}".format(e.__class__))
		log.error("No interface named {} found".format(iface))
		sys.exit(1)
	except KeyError as e:
		log.debug("Exception class: {}".format(e.__class__))
		log.error("No address of type {} found on interface {}".format(addrtype, iface))
		sys.exit(1)
	except Exception as e:
		log.debug("Exception class: {}".format(e.__class__))
		log.error(str(e))
		sys.exit(1)

	return i

def build_nsupdate_cmd(server, zone, record, rrtype, ttl, addr):
		log.debug("BNC: server: {}".format(server))
		log.debug("BNC: zone: {}".format(zone))
		log.debug("BNC: record: {}".format(record))
		log.debug("BNC: rrtype: {}".format(rrtype))
		log.debug("BNC: ttl: {}".format(ttl))
		log.debug("BNC: addr: {}".format(addr))

		cmdstr =  "server {}\n".format(server)
		cmdstr += "zone {}\n".format(zone)
		cmdstr += "update delete {} {}\n".format(record, rrtype)
		cmdstr += "update add {} {} {} {}\n".format(record, ttl, rrtype, addr)
		cmdstr += "send\n"
		cmdstr += "quit\n"

		return cmdstr

def main():
	ap = argparse.ArgumentParser(description="Update dynamic DNS records using RFC2136")
	ap.add_argument("interface", help="interface to obtain IP from (for IPv6, takes the numerically first global address on the interface)")
	ap.add_argument("record", help="DNS record to update")
	ap.add_argument("zone", help="Zone name to update (e.g. example.com)")
	ap.add_argument("server", help="Server to update (IP or FQDN)")
	ap.add_argument("--v4", help="Update IPv4 A record", action="store_true", default=False)
	ap.add_argument("--v6", help="Update IPv6 AAAA record (default)", action="store_true", default=True)
	ap.add_argument("--addr4", help="Update A record with provided IP rather than detected IP (causes 'interface' to be ignored)")
	ap.add_argument("--addr6", help="Update AAAA record with provided IP rather than detected IP (causes 'interface' to be ignored)")
	ap.add_argument("--ttl", help="TTL to assign to record (default 300)", default=300)
	ap.add_argument("--keyfile", help="Alternate location for key config file (default /etc/ddns-RECORD.key where RECORD is the record name provided as the argument)")
	ap.add_argument("--debug", help="Enable debug logging", action="store_true", default=False)
	args = ap.parse_args()

	if args.debug:
		log.setLevel(logging.DEBUG)
	else:
		log.setLevel(logging.ERROR)

	if args.keyfile:
		keyfile = args.keyfile
	else:
		keyfile = "/etc/ddns-{}.key".format(args.record)
	log.debug("KEYFILE: {}".format(keyfile))

	if args.v4:
		addrtype = netifaces.AF_INET
	else:
		addrtype = netifaces.AF_INET6

	ip = False
	if args.addr4:
		ip = build_ip(args.addr4)	

	if args.addr6:
		ip = build_ip(args.addr6)

	try:
		if not os.path.exists(keyfile):
			raise Exception("missing key file {}".format(keyfile))

		if ip:
			addr = ip
			log.debug("Manual IP: {}".format(addr))
		else:
			addrarr = get_interface_addrs(args.interface, addrtype)
			addr = addrarr.pop(0)['addr']
			log.debug("Found IP: {}".format(addr))

		rrtype = "AAAA"
		if args.v4:
			rrtype = "A"

		nsupdatecmd = build_nsupdate_cmd(args.server, args.zone, args.record, rrtype, args.ttl, addr)

		nsupdate = subprocess.run(
			"nsupdate -k {}".format(keyfile),
			shell=True,
			check=True,
			input = bytes(nsupdatecmd,'utf-8'),
			capture_output = True
		)
		
		log.debug("nsupdate return code: {}".format(nsupdate.returncode))

	except subprocess.CalledProcessError as e:
		log.debug("Exception class: {}".format(e.__class__))
		log.error("Error executing: " + e.cmd)
		log.error("nsupdate stderr: " + e.stderr.decode("utf-8").strip())
		sys.exit(1)
	
	except Exception as e:
		log.debug("Exception class: {}".format(e.__class__))
		log.error(str(e))    
		sys.exit(1)

if __name__ == "__main__":
	log = logging.getLogger("ddns-update-rfc2136")
	lh = logging.StreamHandler()
	lf = logging.Formatter(fmt='%(name)s: %(levelname)s: %(message)s')
	lh.setFormatter(lf)
	log.addHandler(lh)
	main()
	sys.exit(0)