#!/usr/bin/python3

from ipaserver import dcerpc
from ipaserver.install.installutils import is_ipa_configured, ScriptError
from ipapython import config, ipautil
from ipalib import api
from ipapython.dn import DN
from ipaplatform.constants import constants
from ipaplatform.paths import paths
import sys
import os
import pwd

import six
import gssapi

from ipalib.install.kinit import kinit_keytab

if six.PY3:
    unicode = str

def retrieve_keytab(api, ccache_name, oneway_keytab_name, oneway_principal):
    getkeytab_args = ["/usr/sbin/ipa-getkeytab",
                      "-s", api.env.host,
                      "-p", oneway_principal,
                      "-k", oneway_keytab_name,
                      "-r"]
    if os.path.isfile(oneway_keytab_name):
        os.unlink(oneway_keytab_name)

    ipautil.run(getkeytab_args, env={'KRB5CCNAME': ccache_name, 'LANG': 'C'},
                raiseonerr=False)
    # Make sure SSSD is able to read the keytab
    try:
        sssd = pwd.getpwnam(constants.SSSD_USER)
        os.chown(oneway_keytab_name, sssd[2], sssd[3])
    except KeyError:
        # If user 'sssd' does not exist, we don't need to chown from root to sssd
        # because it means SSSD does not run as sssd user
        pass


def get_forest_root_domain(api_instance, trusted_domain):
    """
    retrieve trusted forest root domain for given domain name

    :param api_instance: IPA API instance
    :param trusted_domain: trusted domain name

    :returns: forest root domain DNS name
    """
    trustconfig_show = api_instance.Command.trustconfig_show
    flatname = trustconfig_show()['result']['ipantflatname'][0]

    remote_domain = dcerpc.retrieve_remote_domain(
        api_instance.env.host, flatname, trusted_domain)

    return remote_domain.info['dns_forest']


def parse_options():
    usage = "%prog <trusted domain name>\n"
    parser = config.IPAOptionParser(usage=usage,
                                    formatter=config.IPAFormatter())

    parser.add_option("-d", "--debug", action="store_true", dest="debug",
                      help="Display debugging information")

    options, args = parser.parse_args()
    safe_options = parser.get_safe_opts(options)

    return safe_options, options, args


if not is_ipa_configured():
    # LSB status code 6: program is not configured
    raise ScriptError("IPA is not configured " +
                      "(see man pages of ipa-server-install for help)", 6)

if not os.getegid() == 0:
    # LSB status code 4: user had insufficient privilege
    raise ScriptError("You must be root to run ipactl.", 4)

safe_options, options, args = parse_options()

if len(args) != 1:
    # LSB status code 2: invalid or excess argument(s)
    raise ScriptError("You must specify trusted domain name", 2)

trusted_domain = ipautil.fsdecode(args[0]).lower()

api.bootstrap(in_server=True, log=None,
              context='server', confdir=paths.ETC_IPA)
api.finalize()

# Only import trust plugin after api is initialized or internal imports
# within the plugin will not work
from ipaserver.plugins import trust

# We have to dance with two different credentials caches:
# ccache_name         --  for cifs/ipa.master@IPA.REALM to communicate with LDAP
# oneway_ccache_name  --  for IPA$@AD.REALM to communicate with AD DCs
#
# ccache_name may not exist, we'll have to initialize it from Samba's keytab
#
# oneway_ccache_name may not exist either but to initialize it, we need
# to check if oneway_keytab_name keytab exists and fetch it first otherwise.
#
# to fetch oneway_keytab_name keytab, we need to initialize ccache_name ccache first
# and retrieve our own NetBIOS domain name and use cifs/ipa.master@IPA.REALM to
# retrieve the keys to oneway_keytab_name.

keytab_name = '/etc/samba/samba.keytab'

principal = str('cifs/' + api.env.host)

oneway_ccache_name = '/var/run/ipa/krb5cc_oddjob_trusts_fetch'
ccache_name = '/var/run/ipa/krb5cc_oddjob_trusts'

# Standard sequence:
# - check if ccache exists
#   - if not, initialize it from Samba's keytab
# - check if ccache contains valid TGT
#   - if not, initialize it from Samba's keytab
# - refer the correct ccache object for further use
#
have_ccache = False
try:
    cred = kinit_keytab(principal, keytab_name, ccache_name)
    if cred.lifetime > 0:
        have_ccache = True
except gssapi.exceptions.ExpiredCredentialsError:
    pass
if not have_ccache:
    # delete stale ccache and try again
    if os.path.exists(oneway_ccache_name):
        os.unlink(ccache_name)
    cred = kinit_keytab(principal, keytab_name, ccache_name)

old_ccache = os.environ.get('KRB5CCNAME')
api.Backend.ldap2.connect(ccache_name)

# Retrieve own NetBIOS name and trusted forest's name.
# We use script's input to retrieve the trusted forest's name to sanitize input
# for file-level access as we might need to wipe out keytab in /var/lib/sss/keytabs
own_trust_dn = DN(('cn', api.env.domain),('cn','ad'), ('cn', 'etc'), api.env.basedn)
own_trust_entry = api.Backend.ldap2.get_entry(own_trust_dn, ['ipantflatname'])
own_trust_flatname = own_trust_entry.single_value.get('ipantflatname').upper()
trusted_domain_dn = DN(('cn', trusted_domain.lower()), api.env.container_adtrusts, api.env.basedn)
trusted_domain_entry = api.Backend.ldap2.get_entry(trusted_domain_dn, ['cn'])
trusted_domain = trusted_domain_entry.single_value.get('cn').lower()

# At this point if we didn't find trusted forest name, an exception will be raised
# and script will quit. This is actually intended.

oneway_keytab_name = '/var/lib/sss/keytabs/' + trusted_domain + '.keytab'
oneway_principal = str('%s$@%s' % (own_trust_flatname, trusted_domain.upper()))

# If keytab does not exist, retrieve it
if not os.path.isfile(oneway_keytab_name):
    retrieve_keytab(api, ccache_name, oneway_keytab_name, oneway_principal)

try:
    have_ccache = False
    try:
        # The keytab may have stale key material (from older trust-add run)
        cred = kinit_keytab(oneway_principal, oneway_keytab_name, oneway_ccache_name)
        if cred.lifetime > 0:
            have_ccache = True
    except gssapi.exceptions.ExpiredCredentialsError:
        pass
    if not have_ccache:
        if os.path.exists(oneway_ccache_name):
            os.unlink(oneway_ccache_name)
        kinit_keytab(oneway_principal, oneway_keytab_name, oneway_ccache_name)
except gssapi.exceptions.GSSError:
    # If there was failure on using keytab, assume it is stale and retrieve again
    retrieve_keytab(api, ccache_name, oneway_keytab_name, oneway_principal)
    if os.path.exists(oneway_ccache_name):
        os.unlink(oneway_ccache_name)
    kinit_keytab(oneway_principal, oneway_keytab_name, oneway_ccache_name)

# We are done: we have ccache with TDO credentials and can fetch domains
ipa_domain = api.env.domain
os.environ['KRB5CCNAME'] = oneway_ccache_name

# retrieve the forest root domain name and contact it to retrieve trust
# topology info
forest_root = get_forest_root_domain(api, trusted_domain)

domains = dcerpc.fetch_domains(api, ipa_domain, forest_root, creds=True)
trust_domain_object = api.Command.trust_show(trusted_domain, raw=True)['result']
trust.add_new_domains_from_trust(api, None, trust_domain_object, domains)

if old_ccache:
   os.environ['KRB5CCNAME'] = old_ccache

sys.exit(0)
