from typing import Optional

import dns.resolver
import ldap3
from zope import component
from zope.interface import implementer

from ceo_common.interfaces import IADLDAPService, IConfig
from ceo_common.logger_factory import logger_factory
from ceo_common.model import ADLDAPRecord
from ceo_common.utils import is_in_development

logger = logger_factory(__name__)


@implementer(IADLDAPService)
class ADLDAPService:
    def __init__(self):
        cfg = component.getUtility(IConfig)
        if is_in_development():
            self.adldap_dns_srv_name = None
            self.adldap_server_url = cfg.get('adldap_server_url')
        else:
            self.adldap_dns_srv_name = cfg.get('adldap_dns_srv_name')
            # Perform the actual DNS query later so that we don't delay startup
            self.adldap_server_url = None
        self.adldap_base = cfg.get('adldap_base')

    def _get_server_url(self) -> str:
        assert self.adldap_dns_srv_name is not None
        answers = dns.resolver.resolve(self.adldap_dns_srv_name, 'SRV')
        target = answers[0].target.to_text()
        # Strip the trailing '.'
        target = target[:-1]
        logger.debug('Using AD LDAP server %s', target)
        # ldaps doesn't seem to work
        return 'ldap://' + target

    def _get_conn(self) -> ldap3.Connection:
        if self.adldap_server_url is None:
            self.adldap_server_url = self._get_server_url()
        # When get_info=ldap3.SCHEMA (the default), ldap3 tries to search
        # for schema information in 'CN=Schema,CN=Configuration,DC=ds,DC=uwaterloo,DC=ca',
        # which doesn't exist so a LDAPNoSuchObjectResult exception is raised.
        # To avoid this, we tell ldap3 not to look up any server info.
        server = ldap3.Server(self.adldap_server_url, get_info=ldap3.NONE)
        return ldap3.Connection(
            server, auto_bind=True, read_only=True, raise_exceptions=True)

    def get_user(self, username: str) -> Optional[ADLDAPRecord]:
        conn = self._get_conn()
        conn.search(
            self.adldap_base, f'(sAMAccountName={username})',
            attributes=ADLDAPRecord.ldap_attributes, size_limit=1)
        if not conn.entries:
            return None
        return ADLDAPRecord.deserialize_from_ldap(conn.entries[0])