# /usr/bin/env python2
# coding: utf-8

"""
Solution from:
<name 1> (<matriculation 1>)
<name 2> (<matriculation 2>)
"""


def ex06_task():
    """
    Your task is to use DNSSEC to walk the `example.com.` DNS zone. For each domain encountered, print the third level label.
    You do not need to import any modules. You can query any name server with the
        `query_nameserver(ip, port, domain, rdtype)`
    function defined below. The exact specification for the `rdtype` parameter can found in the dnspython documentation.

    A third level label looks like this:
        XXX.example.com

    A correct solution will be obvious.
    """

    # HINT:
    # You can extract the relevant part of the responses like this (for any valid i)
    # query_nameserver( ... )[i].next.to_text()

    # TODO implement
    domain = 'example.com.'

    while 1:
        domain = query_nameserver('139.19.117.15', 53535, domain, 'NSEC')[0].next.to_text()
        if domain == 'example.com.':
            break
        print domain.split('.')[0]
    pass

########################################################################################################################
# DO NOT MODIFY ANYTHING BELOW THIS LINE
########################################################################################################################


def query_nameserver(ip, port, domain, rdtype):
    """
    Queries the name server at ip:port for a certain domain and resource type.

    :param ip: str, IPv4 in dotted notation of the name server
    :param port: int, Port of the name server
    :param domain: str, The domain you want the resource records from.
    :param rdtype: int or str, The type of resource records. Examples: 1, 'A'
    :return: List of answers with matching resource record.
    """

    import dns.resolver

    r = dns.resolver.Resolver()
    r.nameservers = [ ip ]
    r.port = port
    try:
        tmp = r.query(domain, rdtype=rdtype, raise_on_no_answer=False)
        return [x for x in tmp.rrset] + [x for x in tmp.response.authority]
    except (dns.resolver.NXDOMAIN, TypeError) as e:
        return []


if __name__ == '__main__':
    ex06_task()