#!/usr/bin/python2

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 ipalib.config import Env
from ipalib.constants import DEFAULT_CONFIG
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()

env = Env()
env._bootstrap(debug=options.debug, log=None)
env._finalize_core(**dict(DEFAULT_CONFIG))

# Initialize the API with the proper debug level
api.bootstrap(in_server=True, debug=env.debug, 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)