#!/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 ipapython.dnsutil import DNSName
from ipaplatform.constants import constants
from ipaplatform.paths import paths
import io
import sys
import os
import pwd
import tempfile
import textwrap

import six
import gssapi

from ipalib.install.kinit import kinit_keytab, kinit_password

if six.PY3:
    unicode = str


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",
    )
    parser.add_option(
        "-s",
        "--server",
        action="store",
        dest="server",
        help="Domain controller for the Active Directory domain (optional)",
    )
    parser.add_option(
        "-a",
        "--admin",
        action="store",
        dest="admin",
        help="Active Directory administrator (optional)",
    )
    parser.add_option(
        "-p",
        "--password",
        action="store",
        dest="password",
        help="Display debugging information",
    )

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

    # We only use first argument of the passed args but as D-BUS interface
    # in oddjobd cannot expose optional, we fill in empty slots from IPA side
    # and filter them here.
    trusted_domain = ipautil.fsdecode(args[0]).lower()

    # Accept domain names that at least have two labels. We do not support
    # single label Active Directory domains. This also catches empty args.
    if len(DNSName(trusted_domain).labels) < 2:
        # LSB status code 2: invalid or excess argument(s)
        raise ScriptError("You must specify a valid trusted domain name", 2)
    return safe_options, options, trusted_domain


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, server=None):
    """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, realm_server=server
    )

    return remote_domain.info["dns_forest"]


def generate_krb5_config(realm, server):
    """Generate override krb5 config file for trusted domain DC access

    :param realm: realm of the trusted AD domain
    :param server: server to override KDC to

    :returns: tuple (temporary config file name, KRB5_CONFIG string)
    """
    cfg = paths.KRB5_CONF
    tcfg = None
    if server:
        content = textwrap.dedent(u"""
            [realms]
               %s = {
                   kdc = %s
               }
            """) % (
            realm.upper(),
            server,
        )

        (fd, tcfg) = tempfile.mkstemp(dir="/var/run/ipa",
                prefix="krb5conf", text=True)
        with io.open(fd, mode='w', encoding='utf-8') as o:
            o.write(content)
        cfg = ":".join([tcfg, cfg])
    return (tcfg, cfg)


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, trusted_domain = parse_options()

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, gssapi.raw.misc.GSSError):
    pass
if not have_ccache:
    # delete stale ccache and try again
    if os.path.exists(ccache_name):
        os.unlink(ccache_name)
    cred = kinit_keytab(principal, keytab_name, ccache_name)

old_ccache = os.environ.get("KRB5CCNAME")
old_config = os.environ.get("KRB5_CONFIG")
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.

# Generate MIT Kerberos configuration file that potentially overlays
# the KDC to connect to for a trusted domain to allow --server option
# to take precedence.
cfg_file, cfg = generate_krb5_config(trusted_domain, options.server)

if not (options.admin and options.password):
    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,
                config=cfg,
            )
            if cred.lifetime > 0:
                have_ccache = True
        except (gssapi.exceptions.ExpiredCredentialsError, gssapi.raw.misc.GSSError):
            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,
                config=cfg,
            )
    except (gssapi.exceptions.GSSError, gssapi.raw.misc.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)
        cred = kinit_keytab(
            oneway_principal,
            oneway_keytab_name,
            oneway_ccache_name,
            config=cfg,
        )
else:
    cred = kinit_password(
        options.admin,
        options.password,
        oneway_ccache_name,
        canonicalize=True,
        enterprise=True,
        config=cfg,
    )

if cred and cred.lifetime > 0:
    have_ccache = True

if not have_ccache:
    sys.exit(1)

# We are done: we have ccache with TDO credentials and can fetch domains
ipa_domain = api.env.domain
os.environ["KRB5CCNAME"] = oneway_ccache_name
os.environ["KRB5_CONFIG"] = cfg

# retrieve the forest root domain name and contact it to retrieve trust
# topology info
forest_root = get_forest_root_domain(
    api, trusted_domain, server=options.server
)
domains = dcerpc.fetch_domains(
    api, ipa_domain, forest_root, creds=True, server=options.server
)

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

if old_config:
    os.environ["KRB5_CONFIG"] = old_config

if cfg_file:
    os.remove(cfg_file)

trust_domain_object = api.Command.trust_show(trusted_domain, raw=True)[
    "result"
]
trust.add_new_domains_from_trust(api, None, trust_domain_object, domains)

sys.exit(0)