# ***** BEGIN LICENSE BLOCK *****
# Version: MPL 1.1/GPL 2.0/LGPL 2.1
#
# The contents of this file are subject to the Mozilla Public License Version
# 1.1 (the "License"); you may not use this file except in compliance with
# the License. You may obtain a copy of the License at
# http://www.mozilla.org/MPL/
#
# Software distributed under the License is distributed on an "AS IS" basis,
# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
# for the specific language governing rights and limitations under the
# License.
#
# The Original Code is Sync Server
#
# The Initial Developer of the Original Code is the Mozilla Foundation.
# Portions created by the Initial Developer are Copyright (C) 2010
# the Initial Developer. All Rights Reserved.
#
# Contributor(s):
#   Tarek Ziade (tarek@mozilla.com)
#
# Alternatively, the contents of this file may be used under the terms of
# either the GNU General Public License Version 2 or later (the "GPL"), or
# the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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# the provisions above, a recipient may use your version of this file under
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# ***** END LICENSE BLOCK *****
""" LDAP Connection Pool.
"""
import codecs
from contextlib import contextmanager
import logging
from threading import RLock
import time

import ldap
from ldap.ldapobject import ReconnectLDAPObject
import six

log = logging.getLogger(__name__)
_utf8_encoder = codecs.getencoder('utf-8')


def utf8_encode(value):
    """Encode a basestring to UTF-8.

    If the string is unicode encode it to UTF-8, if the string is
    str then assume it's already encoded. Otherwise raise a TypeError.

    :param value: A basestring
    :returns: UTF-8 encoded version of value
    :raises TypeError: If value is not basestring
    """
    if isinstance(value, six.text_type):
        return _utf8_encoder(value)[0]
    elif isinstance(value, six.binary_type):
        return value
    else:
        raise TypeError("bytes or Unicode expected, got %s"
                        % type(value).__name__)


class MaxConnectionReachedError(Exception):
    pass


class BackendError(Exception):
    def __init__(self, msg, backend):
        self.bacend = backend
        Exception.__init__(self, msg)


class StateConnector(ReconnectLDAPObject):
    """Just remembers who is connected, and if connected."""

    def __init__(self, *args, **kw):
        ReconnectLDAPObject.__init__(self, *args, **kw)
        self.connected = False
        self.who = ''
        self.cred = ''
        self._connection_time = None

    def get_lifetime(self):
        """Returns the lifetime of the connection on the server in seconds."""
        if self._connection_time is None:
            return 0
        return time.time() - self._connection_time

    def simple_bind_s(self, who='', cred='', serverctrls=None,
                      clientctrls=None):
        res = ReconnectLDAPObject.simple_bind_s(self, who, cred, serverctrls,
                                                clientctrls)
        self.connected = True
        self.who = who
        self.cred = cred
        if self._connection_time is None:
            self._connection_time = time.time()
        return res

    def unbind_ext_s(self, serverctrls=None, clientctrls=None):
        try:
            return ReconnectLDAPObject.unbind_ext_s(self, serverctrls,
                                                    clientctrls)
        finally:
            self.connected = False
            self.who = None
            self.cred = None

    def add_s(self, *args, **kwargs):
        return self._apply_method_s(ReconnectLDAPObject.add_s, *args,
                                    **kwargs)

    def modify_s(self, *args, **kwargs):
        return self._apply_method_s(ReconnectLDAPObject.modify_s, *args,
                                    **kwargs)

    def __str__(self):
        res = 'LDAP Connector'
        if self.connected:
            res += ' (connected)'
        else:
            res += ' (disconnected)'

        if self.who != '':
            res += ' - who: %r' % self.who

        if self._uri != '':
            res += ' - uri: %r' % self._uri

        return res


class ConnectionManager(object):
    """LDAP Connection Manager.

    Provides a context manager for LDAP connectors.
    """

    def __init__(self, uri, bind=None, passwd=None, size=10, retry_max=3,
                 retry_delay=.1, use_tls=False, timeout=-1,
                 connector_cls=StateConnector, use_pool=True,
                 max_lifetime=600):
        self._pool = []
        self.size = size
        self.retry_max = retry_max
        self.retry_delay = retry_delay
        self.uri = uri
        self.bind = bind
        self.passwd = passwd
        self._pool_lock = RLock()
        self.use_tls = use_tls
        self.timeout = timeout
        self.connector_cls = connector_cls
        self.use_pool = use_pool
        self.max_lifetime = max_lifetime

    def __len__(self):
        return len(self._pool)

    def _match(self, bind, passwd):
        if passwd is not None:
            passwd = utf8_encode(passwd)
        with self._pool_lock:
            inactives = []

            for conn in reversed(self._pool):
                # already in usage
                if conn.active:
                    continue

                # let's check the lifetime
                if conn.get_lifetime() > self.max_lifetime:
                    # this connector has lived for too long,
                    # we want to unbind it and remove it from the pool
                    try:
                        conn.unbind_s()
                    except Exception:
                        log.debug('Failure attempting to unbind after '
                                  'timeout; should be harmless', exc_info=True)

                    self._pool.remove(conn)
                    continue

                # we found a connector for this bind
                if conn.who == bind and conn.cred == passwd:
                    conn.active = True
                    return conn

                inactives.append(conn)

            # no connector was available, let's rebind the latest inactive one
            if len(inactives) > 0:
                for conn in inactives:
                    try:
                        self._bind(conn, bind, passwd)
                        return conn
                    except Exception:
                        log.debug('Removing connection from pool after '
                                  'failure to rebind', exc_info=True)
                        self._pool.remove(conn)

                return None

        # There are no connector that match
        return None

    def _bind(self, conn, bind, passwd):
        # let's bind
        if self.use_tls:
            try:
                conn.start_tls_s()
            except Exception:
                raise BackendError('Could not activate TLS on established '
                                   'connection with %s' % self.uri,
                                   backend=conn)

        if bind is not None:
            conn.simple_bind_s(bind, passwd)

        conn.active = True

    def _create_connector(self, bind, passwd):
        """Creates a connector, binds it, and returns it.

        :param bind: user login
        :type bind: string
        :param passwd: user password
        :type passwd: string
        :returns: StateConnector
        :raises BackendError: If unable to connect to LDAP
        """
        tries = 0
        connected = False
        if passwd is not None:
            passwd = utf8_encode(passwd)
        exc = None
        conn = None

        # trying retry_max times in a row with a fresh connector
        while tries < self.retry_max and not connected:
            try:
                conn = self.connector_cls(self.uri, retry_max=self.retry_max,
                                          retry_delay=self.retry_delay)
                conn.timeout = self.timeout
                self._bind(conn, bind, passwd)
                connected = True
            except ldap.LDAPError as error:
                exc = error
                time.sleep(self.retry_delay)
                if tries < self.retry_max:
                    log.info('Failure attempting to create and bind '
                             'connector; will retry after %r seconds',
                             self.retry_delay, exc_info=True)
                else:
                    log.error('Failure attempting to create and bind '
                              'connector', exc_info=True)
                tries += 1

        if not connected:
            if isinstance(exc, (ldap.NO_SUCH_OBJECT,
                                ldap.INVALID_CREDENTIALS,
                                ldap.SERVER_DOWN)):
                raise exc

            # that's something else
            raise BackendError(str(exc), backend=conn)
        return conn

    def _get_connection(self, bind=None, passwd=None):
        if bind is None:
            bind = self.bind
        if passwd is None:
            passwd = self.passwd

        if self.use_pool:
            # let's try to recycle an existing one
            conn = self._match(bind, passwd)
            if conn is not None:
                return conn

            # the pool is full
            if len(self._pool) >= self.size:
                raise MaxConnectionReachedError(self.uri)

        # we need to create a new connector
        conn = self._create_connector(bind, passwd)

        # adding it to the pool
        if self.use_pool:
            with self._pool_lock:
                self._pool.append(conn)
        else:
            # with no pool, the connector is always active
            conn.active = True

        return conn

    def _release_connection(self, connection):
        if self.use_pool:
            with self._pool_lock:
                if not connection.connected:
                    # unconnected connector, let's drop it
                    self._pool.remove(connection)
                else:
                    # can be reused - let's mark is as not active
                    connection.active = False

                    # done.
                    return
        else:
            connection.active = False

        # let's try to unbind it
        try:
            connection.unbind_ext_s()
        except ldap.LDAPError:
            # avoid error on invalid state
            log.debug('Failure attempting to unbind on release; '
                      'should be harmless', exc_info=True)

    @contextmanager
    def connection(self, bind=None, passwd=None):
        """Creates a context'ed connector, binds it, and returns it.

        :param bind: user login
        :type bind: string
        :param passwd: user password
        :type passwd: string
        :returns: StateConnector
        :raises MaxConnectionReachedError: If unable to connect to LDAP
        """
        tries = 0
        conn = None
        while tries < self.retry_max:
            try:
                conn = self._get_connection(bind, passwd)
            except MaxConnectionReachedError:
                tries += 1
                time.sleep(0.1)

                # removing the first inactive connector going backward
                with self._pool_lock:
                    reversed_list = reversed(list(enumerate(self._pool)))
                    for index, conn_ in reversed_list:
                        if not conn_.active:
                            self._pool.pop(index)
                            break
            else:
                break

        if conn is None:
            raise MaxConnectionReachedError(self.uri)

        try:
            yield conn
        finally:
            self._release_connection(conn)

    def purge(self, bind, passwd=None):
        """Purge a connector.

        :param bind: user login
        :type bind: string
        :param passwd: user password
        :type passwd: string
        """
        if self.use_pool:
            return

        if passwd is not None:
            passwd = utf8_encode(passwd)

        with self._pool_lock:
            for conn in list(self._pool):
                if conn.who != bind:
                    continue

                if passwd is not None and conn.cred == passwd:
                    continue
                # let's drop it
                try:
                    conn.unbind_ext_s()
                except ldap.LDAPError:
                    # invalid state
                    log.debug('Failure attempting to unbind on purge; '
                              'should be harmless', exc_info=True)
                self._pool.remove(conn)