#!/usr/bin/env python3

"""Update HS DNS settings behind Google WiFi systems."""

import argparse
import json
import urllib.request
import urllib.parse
import sys

import dns.resolver


WIFI_STATUS_URI = 'http://192.168.86.1/api/v1/status'


def get_wan_ip():
    with urllib.request.urlopen(WIFI_STATUS_URI) as req:
        data = req.read()
    status = json.loads(data)
    return status['wan']['localIpAddress']


def update_ip(hostname, password, ip=None):
    """Update HE DNS with new settings."""
    params = {
        'hostname': hostname,
        'password': password,
    }
    if ip:
        params['myip'] = ip
    body = urllib.parse.urlencode(params).encode()

    url = 'https://dyn.dns.he.net/nic/update'
    req = urllib.request.Request(url, body)

    with urllib.request.urlopen(req) as response:
        return response.read()


def get_parser():
    """Get CLI parser."""
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--hostname', required=True)
    parser.add_argument('-p', '--password', '--key', required=True)
    parser.add_argument('-a', '--address', '--ip')
    parser.add_argument('-q', '--quiet', action='store_true')
    return parser


def main(argv):
    """The main entry point for scripts."""
    parser = get_parser()
    opts = parser.parse_args(argv)

    if opts.quiet:
        p = lambda *args: None
    else:
        p = print

    curr_ip = get_wan_ip()
    p('Current IP', curr_ip)

    p('Looking up', opts.hostname, '...')
    answers = dns.resolver.resolve(opts.hostname, 'A')
    for msg in answers:
        p('Current DNS', msg.to_text())
        if curr_ip != msg.to_text():
            p('Updating IP')
            resp = update_ip(opts.hostname, opts.password, opts.address)
            p(resp)
        else:
            p('Up-to-date!')
        break


if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))