#!/usr/bin/python3
# Authors:
#   Christian Heimes <cheimes@redhat.com>
#
# Copyright (C) 2015  Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
"""ipa-httpd-kdproxy

This script creates or removes the symlink from /etc/ipa/ipa-kdc-proxy.conf
to /etc/httpd/conf.d/. It's called from ExecStartPre hook in httpd.service.
"""
import logging
import os
import socket
import sys

from ipalib import api, errors
from ipapython.ipa_log_manager import standard_logging_setup
from ipapython.ipaldap import LDAPClient
from ipapython.dn import DN
from ipaplatform.paths import paths

logger = logging.getLogger(os.path.basename(__file__))


DEBUG = False
TIME_LIMIT = 2


class Error(Exception):
    """Base error class"""


class ConfigFileError(Error):
    """Something is wrong with the config file"""


class CheckError(Error):
    """An unrecoverable error has occured

    The exit code is 0.
    """


class FatalError(Error):
    """A fatal error has occured

    Fatal errors cause the command to exit with a non-null exit code.
    """


class KDCProxyConfig(object):
    ipaconfig_flag = 'ipaKDCProxyEnabled'

    def __init__(self, time_limit=TIME_LIMIT):
        self.time_limit = time_limit
        self.con = None
        self.ldap_uri = api.env.ldap_uri
        self.kdc_dn = DN(('cn', 'KDC'), ('cn', api.env.host),
                         ('cn', 'masters'), ('cn', 'ipa'), ('cn', 'etc'),
                         api.env.basedn)
        self.conf = paths.HTTPD_IPA_KDCPROXY_CONF
        self.conflink = paths.HTTPD_IPA_KDCPROXY_CONF_SYMLINK

    def _ldap_con(self):
        """Establish LDAP connection"""
        logger.debug('ldap_uri: %s', self.ldap_uri)
        try:
            self.con = LDAPClient(self.ldap_uri)
            self.con.external_bind()
        except (errors.NetworkError, socket.timeout) as e:
            msg = 'Unable to connect to dirsrv: %s' % e
            raise CheckError(msg)
        except errors.AuthorizationError as e:
            msg = 'Authorization error: %s' % e
            raise CheckError(msg)
        except Exception as e:
            msg = ('Unknown error while retrieving setting from %s: %s' %
                   (self.ldap_uri, e))
            logger.exception('%s', msg)
            raise FatalError(msg)

    def _find_entry(self, dn, attrs, filter, scope=LDAPClient.SCOPE_BASE):
        """Find an LDAP entry, handles NotFound and Limit"""
        try:
            entries = self.con.get_entries(
                dn, scope, filter, attrs, time_limit=self.time_limit)
        except errors.NotFound:
            logger.debug('Entry not found: %s', dn)
            return None
        except Exception as e:
            msg = ('Unknown error while retrieving setting from %s: %s' %
                   (self.ldap_uri, e))
            logger.exception('%s', msg)
            raise FatalError(msg)
        return entries[0]

    def is_host_enabled(self):
        """Check replica specific flag"""
        logger.debug('Read settings from dn: %s', self.kdc_dn)
        srcfilter = self.con.make_filter(
            {'ipaConfigString': u'kdcProxyEnabled'}
        )
        entry = self._find_entry(self.kdc_dn, ['cn'], srcfilter)
        logger.debug('%s ipaConfigString: %s', self.kdc_dn, entry)
        return entry is not None

    def validate_symlink(self):
        """Validate symlink in Apache conf.d"""
        if not os.path.exists(self.conflink):
            return False
        if not os.path.islink(self.conflink):
            raise ConfigFileError(
                "'%s' already exists, but it is not a symlink"
                % self.conflink)
        dest = os.readlink(self.conflink)
        if dest != self.conf:
            raise ConfigFileError(
                "'%s' points to '%s', expected '%s'"
                % (self.conflink, dest, self.conf))
        return True

    def create_symlink(self):
        """Create symlink to enable KDC proxy support"""
        try:
            valid = self.validate_symlink()
        except ConfigFileError as e:
            logger.warning("Cannot enable KDC proxy: %s ", e)
            return False

        if valid:
            logger.debug("Symlink exists and is valid")
            return True

        if not os.path.isfile(self.conf):
            logger.warning("'%s' does not exist", self.conf)
            return False

        # create the symbolic link
        logger.debug("Creating symlink from '%s' to '%s'",
                     self.conf, self.conflink)
        os.symlink(self.conf, self.conflink)
        return True

    def remove_symlink(self):
        """Delete symlink to disable KDC proxy support"""
        try:
            valid = self.validate_symlink()
        except CheckError as e:
            logger.warning("Cannot disable KDC proxy: %s ", e)
            return False

        if valid:
            logger.debug("Removing symlink '%s'", self.conflink)
            os.unlink(self.conflink)
        else:
            logger.debug("Symlink '%s' has already been removed.",
                         self.conflink)

        return True

    def __enter__(self):
        self._ldap_con()
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        if self.con is not None:
            self.con.unbind()
            self.con = None


def main(debug=DEBUG, time_limit=TIME_LIMIT):
    # initialize API without file logging
    if not api.isdone('bootstrap'):
        api.bootstrap(context='server', confdir=paths.ETC_IPA,
                      log=None, debug=debug)
        standard_logging_setup(verbose=True, debug=debug)

    try:
        cfg = KDCProxyConfig(time_limit)
        with cfg:
            if cfg.is_host_enabled():
                if cfg.create_symlink():
                    logger.info('KDC proxy enabled')
                    return 0
            else:
                if cfg.remove_symlink():
                    logger.info('KDC proxy disabled')
                    return 0
    except CheckError as e:
        logger.warning('%s', str(e))
        logger.warning('Disabling KDC proxy')
        cfg.remove_symlink()
        return 0
    except Exception as e:
        logger.error('%s', str(e))
        return 1


if __name__ == '__main__':
    sys.exit(main())
