text: # -*- coding: utf-8 -*-
  # Copyright 2014-2016 OpenMarket Ltd
  # Copyright 2018 New Vector Ltd
  #
  # Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  import logging
  from collections import namedtuple
  
  from six import iteritems, itervalues
  
  from canonicaljson import json
  
  from twisted.internet import defer
  
  from synapse.api.constants import EventTypes, Membership
  from synapse.storage.events_worker import EventsWorkerStore
  from synapse.types import get_domain_from_id
  from synapse.util.async_helpers import Linearizer
  from synapse.util.caches import intern_string
  from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
  from synapse.util.stringutils import to_ascii
  
  logger = logging.getLogger(__name__)
  
  
  RoomsForUser = namedtuple(
      "RoomsForUser", ("room_id", "sender", "membership", "event_id", "stream_ordering")
  )
  
  GetRoomsForUserWithStreamOrdering = namedtuple(
      "_GetRoomsForUserWithStreamOrdering", ("room_id", "stream_ordering")
  )
  
  
  # We store this using a namedtuple so that we save about 3x space over using a
  # dict.
  ProfileInfo = namedtuple("ProfileInfo", ("avatar_url", "display_name"))
  
  # "members" points to a truncated list of (user_id, event_id) tuples for users of
  # a given membership type, suitable for use in calculating heroes for a room.
  # "count" points to the total numberr of users of a given membership type.
  MemberSummary = namedtuple("MemberSummary", ("members", "count"))
  
  _MEMBERSHIP_PROFILE_UPDATE_NAME = "room_membership_profile_update"
  
  
  class RoomMemberWorkerStore(EventsWorkerStore):
      @cachedInlineCallbacks(max_entries=100000, iterable=True, cache_context=True)
      def get_hosts_in_room(self, room_id, cache_context):
          """Returns the set of all hosts currently in the room
          """
          user_ids = yield self.get_users_in_room(
              room_id, on_invalidate=cache_context.invalidate
          )
          hosts = frozenset(get_domain_from_id(user_id) for user_id in user_ids)
          defer.returnValue(hosts)
  
      @cached(max_entries=100000, iterable=True)
      def get_users_in_room(self, room_id):
          def f(txn):
              sql = (
                  "SELECT m.user_id FROM room_memberships as m"
                  " INNER JOIN current_state_events as c"
                  " ON m.event_id = c.event_id "
                  " AND m.room_id = c.room_id "
                  " AND m.user_id = c.state_key"
                  " WHERE c.type = 'm.room.member' AND c.room_id = ? AND m.membership = ?"
              )
  
              txn.execute(sql, (room_id, Membership.JOIN))
              return [to_ascii(r[0]) for r in txn]
  
          return self.runInteraction("get_users_in_room", f)
  
      @cached(max_entries=100000)
      def get_room_summary(self, room_id):
          """ Get the details of a room roughly suitable for use by the room
          summary extension to /sync. Useful when lazy loading room members.
          Args:
              room_id (str): The room ID to query
          Returns:
              Deferred[dict[str, MemberSummary]:
                  dict of membership states, pointing to a MemberSummary named tuple.
          """
  
          def _get_room_summary_txn(txn):
              # first get counts.
              # We do this all in one transaction to keep the cache small.
              # FIXME: get rid of this when we have room_stats
              sql = """
                  SELECT count(*), m.membership FROM room_memberships as m
                   INNER JOIN current_state_events as c
                   ON m.event_id = c.event_id
                   AND m.room_id = c.room_id
                   AND m.user_id = c.state_key
                   WHERE c.type = 'm.room.member' AND c.room_id = ?
                   GROUP BY m.membership
              """
  
              txn.execute(sql, (room_id,))
              res = {}
              for count, membership in txn:
                  summary = res.setdefault(to_ascii(membership), MemberSummary([], count))
  
              # we order by membership and then fairly arbitrarily by event_id so
              # heroes are consistent
              sql = """
                  SELECT m.user_id, m.membership, m.event_id
                  FROM room_memberships as m
                   INNER JOIN current_state_events as c
                   ON m.event_id = c.event_id
                   AND m.room_id = c.room_id
                   AND m.user_id = c.state_key
                   WHERE c.type = 'm.room.member' AND c.room_id = ?
                   ORDER BY
                      CASE m.membership WHEN ? THEN 1 WHEN ? THEN 2 ELSE 3 END ASC,
                      m.event_id ASC
                   LIMIT ?
              """
  
              # 6 is 5 (number of heroes) plus 1, in case one of them is the calling user.
              txn.execute(sql, (room_id, Membership.JOIN, Membership.INVITE, 6))
              for user_id, membership, event_id in txn:
                  summary = res[to_ascii(membership)]
                  # we will always have a summary for this membership type at this
                  # point given the summary currently contains the counts.
                  members = summary.members
                  members.append((to_ascii(user_id), to_ascii(event_id)))
  
              return res
  
          return self.runInteraction("get_room_summary", _get_room_summary_txn)
  
      @cached()
      def get_invited_rooms_for_user(self, user_id):
          """ Get all the rooms the user is invited to
          Args:
              user_id (str): The user ID.
          Returns:
              A deferred list of RoomsForUser.
          """
  
          return self.get_rooms_for_user_where_membership_is(user_id, [Membership.INVITE])
  
      @defer.inlineCallbacks
      def get_invite_for_user_in_room(self, user_id, room_id):
          """Gets the invite for the given user and room
  
          Args:
              user_id (str)
              room_id (str)
  
          Returns:
              Deferred: Resolves to either a RoomsForUser or None if no invite was
                  found.
          """
          invites = yield self.get_invited_rooms_for_user(user_id)
          for invite in invites:
              if invite.room_id == room_id:
                  defer.returnValue(invite)
          defer.returnValue(None)
  
      def get_rooms_for_user_where_membership_is(self, user_id, membership_list):
          """ Get all the rooms for this user where the membership for this user
          matches one in the membership list.
  
          Args:
              user_id (str): The user ID.
              membership_list (list): A list of synapse.api.constants.Membership
              values which the user must be in.
          Returns:
              A list of dictionary objects, with room_id, membership and sender
              defined.
          """
          if not membership_list:
              return defer.succeed(None)
  
          return self.runInteraction(
              "get_rooms_for_user_where_membership_is",
              self._get_rooms_for_user_where_membership_is_txn,
              user_id,
              membership_list,
          )
  
      def _get_rooms_for_user_where_membership_is_txn(
          self, txn, user_id, membership_list
      ):
  
          do_invite = Membership.INVITE in membership_list
          membership_list = [m for m in membership_list if m != Membership.INVITE]
  
          results = []
          if membership_list:
              where_clause = "user_id = ? AND (%s) AND forgotten = 0" % (
                  " OR ".join(["membership = ?" for _ in membership_list]),
              )
  
              args = [user_id]
              args.extend(membership_list)
  
              sql = (
                  "SELECT m.room_id, m.sender, m.membership, m.event_id, e.stream_ordering"
                  " FROM current_state_events as c"
                  " INNER JOIN room_memberships as m"
                  " ON m.event_id = c.event_id"
                  " INNER JOIN events as e"
                  " ON e.event_id = c.event_id"
                  " AND m.room_id = c.room_id"
                  " AND m.user_id = c.state_key"
                  " WHERE c.type = 'm.room.member' AND %s"
              ) % (where_clause,)
  
              txn.execute(sql, args)
              results = [RoomsForUser(**r) for r in self.cursor_to_dict(txn)]
  
          if do_invite:
              sql = (
                  "SELECT i.room_id, inviter, i.event_id, e.stream_ordering"
                  " FROM local_invites as i"
                  " INNER JOIN events as e USING (event_id)"
                  " WHERE invitee = ? AND locally_rejected is NULL"
                  " AND replaced_by is NULL"
              )
  
              txn.execute(sql, (user_id,))
              results.extend(
                  RoomsForUser(
                      room_id=r["room_id"],
                      sender=r["inviter"],
                      event_id=r["event_id"],
                      stream_ordering=r["stream_ordering"],
                      membership=Membership.INVITE,
                  )
                  for r in self.cursor_to_dict(txn)
              )
  
          return results
  
      @cachedInlineCallbacks(max_entries=500000, iterable=True)
      def get_rooms_for_user_with_stream_ordering(self, user_id):
          """Returns a set of room_ids the user is currently joined to
  
          Args:
              user_id (str)
  
          Returns:
              Deferred[frozenset[GetRoomsForUserWithStreamOrdering]]: Returns
              the rooms the user is in currently, along with the stream ordering
              of the most recent join for that user and room.
          """
          rooms = yield self.get_rooms_for_user_where_membership_is(
              user_id, membership_list=[Membership.JOIN]
          )
          defer.returnValue(
              frozenset(
                  GetRoomsForUserWithStreamOrdering(r.room_id, r.stream_ordering)
                  for r in rooms
              )
          )
  
      @defer.inlineCallbacks
      def get_rooms_for_user(self, user_id, on_invalidate=None):
          """Returns a set of room_ids the user is currently joined to
          """
          rooms = yield self.get_rooms_for_user_with_stream_ordering(
              user_id, on_invalidate=on_invalidate
          )
          defer.returnValue(frozenset(r.room_id for r in rooms))
  
      @cachedInlineCallbacks(max_entries=500000, cache_context=True, iterable=True)
      def get_users_who_share_room_with_user(self, user_id, cache_context):
          """Returns the set of users who share a room with `user_id`
          """
          room_ids = yield self.get_rooms_for_user(
              user_id, on_invalidate=cache_context.invalidate
          )
  
          user_who_share_room = set()
          for room_id in room_ids:
              user_ids = yield self.get_users_in_room(
                  room_id, on_invalidate=cache_context.invalidate
              )
              user_who_share_room.update(user_ids)
  
          defer.returnValue(user_who_share_room)
  
      @defer.inlineCallbacks
      def get_joined_users_from_context(self, event, context):
          state_group = context.state_group
          if not state_group:
              # If state_group is None it means it has yet to be assigned a
              # state group, i.e. we need to make sure that calls with a state_group
              # of None don't hit previous cached calls with a None state_group.
              # To do this we set the state_group to a new object as object() != object()
              state_group = object()
  
          current_state_ids = yield context.get_current_state_ids(self)
          result = yield self._get_joined_users_from_context(
              event.room_id, state_group, current_state_ids, event=event, context=context
          )
          defer.returnValue(result)
  
      def get_joined_users_from_state(self, room_id, state_entry):
          state_group = state_entry.state_group
          if not state_group:
              # If state_group is None it means it has yet to be assigned a
              # state group, i.e. we need to make sure that calls with a state_group
              # of None don't hit previous cached calls with a None state_group.
              # To do this we set the state_group to a new object as object() != object()
              state_group = object()
  
          return self._get_joined_users_from_context(
              room_id, state_group, state_entry.state, context=state_entry
          )
  
      @cachedInlineCallbacks(
          num_args=2, cache_context=True, iterable=True, max_entries=100000
      )
      def _get_joined_users_from_context(
          self,
          room_id,
          state_group,
          current_state_ids,
          cache_context,
          event=None,
          context=None,
      ):
          # We don't use `state_group`, it's there so that we can cache based
          # on it. However, it's important that it's never None, since two current_states
          # with a state_group of None are likely to be different.
          # See bulk_get_push_rules_for_room for how we work around this.
          assert state_group is not None
  
          users_in_room = {}
          member_event_ids = [
              e_id
              for key, e_id in iteritems(current_state_ids)
              if key[0] == EventTypes.Member
          ]
  
          if context is not None:
              # If we have a context with a delta from a previous state group,
              # check if we also have the result from the previous group in cache.
              # If we do then we can reuse that result and simply update it with
              # any membership changes in `delta_ids`
              if context.prev_group and context.delta_ids:
                  prev_res = self._get_joined_users_from_context.cache.get(
                      (room_id, context.prev_group), None
                  )
                  if prev_res and isinstance(prev_res, dict):
                      users_in_room = dict(prev_res)
                      member_event_ids = [
                          e_id
                          for key, e_id in iteritems(context.delta_ids)
                          if key[0] == EventTypes.Member
                      ]
                      for etype, state_key in context.delta_ids:
                          users_in_room.pop(state_key, None)
  
          # We check if we have any of the member event ids in the event cache
          # before we ask the DB
  
          # We don't update the event cache hit ratio as it completely throws off
          # the hit ratio counts. After all, we don't populate the cache if we
          # miss it here
          event_map = self._get_events_from_cache(
              member_event_ids, allow_rejected=False, update_metrics=False
          )
  
          missing_member_event_ids = []
          for event_id in member_event_ids:
              ev_entry = event_map.get(event_id)
              if ev_entry:
                  if ev_entry.event.membership == Membership.JOIN:
                      users_in_room[to_ascii(ev_entry.event.state_key)] = ProfileInfo(
                          display_name=to_ascii(
                              ev_entry.event.content.get("displayname", None)
                          ),
                          avatar_url=to_ascii(
                              ev_entry.event.content.get("avatar_url", None)
                          ),
                      )
              else:
                  missing_member_event_ids.append(event_id)
  
          if missing_member_event_ids:
              rows = yield self._simple_select_many_batch(
                  table="room_memberships",
                  column="event_id",
                  iterable=missing_member_event_ids,
                  retcols=('user_id', 'display_name', 'avatar_url'),
                  keyvalues={"membership": Membership.JOIN},
                  batch_size=500,
                  desc="_get_joined_users_from_context",
              )
  
              users_in_room.update(
                  {
                      to_ascii(row["user_id"]): ProfileInfo(
                          avatar_url=to_ascii(row["avatar_url"]),
                          display_name=to_ascii(row["display_name"]),
                      )
                      for row in rows
                  }
              )
  
          if event is not None and event.type == EventTypes.Member:
              if event.membership == Membership.JOIN:
                  if event.event_id in member_event_ids:
                      users_in_room[to_ascii(event.state_key)] = ProfileInfo(
                          display_name=to_ascii(event.content.get("displayname", None)),
                          avatar_url=to_ascii(event.content.get("avatar_url", None)),
                      )
  
          defer.returnValue(users_in_room)
  
      @cachedInlineCallbacks(max_entries=10000)
      def is_host_joined(self, room_id, host):
          if '%' in host or '_' in host:
              raise Exception("Invalid host name")
  
          sql = """
              SELECT state_key FROM current_state_events AS c
              INNER JOIN room_memberships USING (event_id)
              WHERE membership = 'join'
                  AND type = 'm.room.member'
                  AND c.room_id = ?
                  AND state_key LIKE ?
              LIMIT 1
          """
  
          # We do need to be careful to ensure that host doesn't have any wild cards
          # in it, but we checked above for known ones and we'll check below that
          # the returned user actually has the correct domain.
          like_clause = "%:" + host
  
          rows = yield self._execute("is_host_joined", None, sql, room_id, like_clause)
  
          if not rows:
              defer.returnValue(False)
  
          user_id = rows[0][0]
          if get_domain_from_id(user_id) != host:
              # This can only happen if the host name has something funky in it
              raise Exception("Invalid host name")
  
          defer.returnValue(True)
  
      @cachedInlineCallbacks()
      def was_host_joined(self, room_id, host):
          """Check whether the server is or ever was in the room.
  
          Args:
              room_id (str)
              host (str)
  
          Returns:
              Deferred: Resolves to True if the host is/was in the room, otherwise
              False.
          """
          if '%' in host or '_' in host:
              raise Exception("Invalid host name")
  
          sql = """
              SELECT user_id FROM room_memberships
              WHERE room_id = ?
                  AND user_id LIKE ?
                  AND membership = 'join'
              LIMIT 1
          """
  
          # We do need to be careful to ensure that host doesn't have any wild cards
          # in it, but we checked above for known ones and we'll check below that
          # the returned user actually has the correct domain.
          like_clause = "%:" + host
  
          rows = yield self._execute("was_host_joined", None, sql, room_id, like_clause)
  
          if not rows:
              defer.returnValue(False)
  
          user_id = rows[0][0]
          if get_domain_from_id(user_id) != host:
              # This can only happen if the host name has something funky in it
              raise Exception("Invalid host name")
  
          defer.returnValue(True)
  
      def get_joined_hosts(self, room_id, state_entry):
          state_group = state_entry.state_group
          if not state_group:
              # If state_group is None it means it has yet to be assigned a
              # state group, i.e. we need to make sure that calls with a state_group
              # of None don't hit previous cached calls with a None state_group.
              # To do this we set the state_group to a new object as object() != object()
              state_group = object()
  
          return self._get_joined_hosts(
              room_id, state_group, state_entry.state, state_entry=state_entry
          )
  
      @cachedInlineCallbacks(num_args=2, max_entries=10000, iterable=True)
      # @defer.inlineCallbacks
      def _get_joined_hosts(self, room_id, state_group, current_state_ids, state_entry):
          # We don't use `state_group`, its there so that we can cache based
          # on it. However, its important that its never None, since two current_state's
          # with a state_group of None are likely to be different.
          # See bulk_get_push_rules_for_room for how we work around this.
          assert state_group is not None
  
          cache = self._get_joined_hosts_cache(room_id)
          joined_hosts = yield cache.get_destinations(state_entry)
  
          defer.returnValue(joined_hosts)
  
      @cached(max_entries=10000)
      def _get_joined_hosts_cache(self, room_id):
          return _JoinedHostsCache(self, room_id)
  
      @cachedInlineCallbacks(num_args=2)
      def did_forget(self, user_id, room_id):
          """Returns whether user_id has elected to discard history for room_id.
  
          Returns False if they have since re-joined."""
  
          def f(txn):
              sql = (
                  "SELECT"
                  "  COUNT(*)"
                  " FROM"
                  "  room_memberships"
                  " WHERE"
                  "  user_id = ?"
                  " AND"
                  "  room_id = ?"
                  " AND"
                  "  forgotten = 0"
              )
              txn.execute(sql, (user_id, room_id))
              rows = txn.fetchall()
              return rows[0][0]
  
          count = yield self.runInteraction("did_forget_membership", f)
          defer.returnValue(count == 0)
  
  
  class RoomMemberStore(RoomMemberWorkerStore):
      def __init__(self, db_conn, hs):
          super(RoomMemberStore, self).__init__(db_conn, hs)
          self.register_background_update_handler(
              _MEMBERSHIP_PROFILE_UPDATE_NAME, self._background_add_membership_profile
          )
  
      def _store_room_members_txn(self, txn, events, backfilled):
          """Store a room member in the database.
          """
          self._simple_insert_many_txn(
              txn,
              table="room_memberships",
              values=[
                  {
                      "event_id": event.event_id,
                      "user_id": event.state_key,
                      "sender": event.user_id,
                      "room_id": event.room_id,
                      "membership": event.membership,
                      "display_name": event.content.get("displayname", None),
                      "avatar_url": event.content.get("avatar_url", None),
                  }
                  for event in events
              ],
          )
  
          for event in events:
              txn.call_after(
                  self._membership_stream_cache.entity_has_changed,
                  event.state_key,
                  event.internal_metadata.stream_ordering,
              )
              txn.call_after(
                  self.get_invited_rooms_for_user.invalidate, (event.state_key,)
              )
  
              # We update the local_invites table only if the event is "current",
              # i.e., its something that has just happened. If the event is an
              # outlier it is only current if its an "out of band membership",
              # like a remote invite or a rejection of a remote invite.
              is_new_state = not backfilled and (
                  not event.internal_metadata.is_outlier()
                  or event.internal_metadata.is_out_of_band_membership()
              )
              is_mine = self.hs.is_mine_id(event.state_key)
              if is_new_state and is_mine:
                  if event.membership == Membership.INVITE:
                      self._simple_insert_txn(
                          txn,
                          table="local_invites",
                          values={
                              "event_id": event.event_id,
                              "invitee": event.state_key,
                              "inviter": event.sender,
                              "room_id": event.room_id,
                              "stream_id": event.internal_metadata.stream_ordering,
                          },
                      )
                  else:
                      sql = (
                          "UPDATE local_invites SET stream_id = ?, replaced_by = ? WHERE"
                          " room_id = ? AND invitee = ? AND locally_rejected is NULL"
                          " AND replaced_by is NULL"
                      )
  
                      txn.execute(
                          sql,
                          (
                              event.internal_metadata.stream_ordering,
                              event.event_id,
                              event.room_id,
                              event.state_key,
                          ),
                      )
  
      @defer.inlineCallbacks
      def locally_reject_invite(self, user_id, room_id):
          sql = (
              "UPDATE local_invites SET stream_id = ?, locally_rejected = ? WHERE"
              " room_id = ? AND invitee = ? AND locally_rejected is NULL"
              " AND replaced_by is NULL"
          )
  
          def f(txn, stream_ordering):
              txn.execute(sql, (stream_ordering, True, room_id, user_id))
  
          with self._stream_id_gen.get_next() as stream_ordering:
              yield self.runInteraction("locally_reject_invite", f, stream_ordering)
  
      def forget(self, user_id, room_id):
          """Indicate that user_id wishes to discard history for room_id."""
  
          def f(txn):
              sql = (
                  "UPDATE"
                  "  room_memberships"
                  " SET"
                  "  forgotten = 1"
                  " WHERE"
                  "  user_id = ?"
                  " AND"
                  "  room_id = ?"
              )
              txn.execute(sql, (user_id, room_id))
  
              self._invalidate_cache_and_stream(txn, self.did_forget, (user_id, room_id))
  
          return self.runInteraction("forget_membership", f)
  
      @defer.inlineCallbacks
      def _background_add_membership_profile(self, progress, batch_size):
          target_min_stream_id = progress.get(
              "target_min_stream_id_inclusive", self._min_stream_order_on_start
          )
          max_stream_id = progress.get(
              "max_stream_id_exclusive", self._stream_order_on_start + 1
          )
  
          INSERT_CLUMP_SIZE = 1000
  
          def add_membership_profile_txn(txn):
              sql = """
                  SELECT stream_ordering, event_id, events.room_id, event_json.json
                  FROM events
                  INNER JOIN event_json USING (event_id)
                  INNER JOIN room_memberships USING (event_id)
                  WHERE ? <= stream_ordering AND stream_ordering < ?
                  AND type = 'm.room.member'
                  ORDER BY stream_ordering DESC
                  LIMIT ?
              """
  
              txn.execute(sql, (target_min_stream_id, max_stream_id, batch_size))
  
              rows = self.cursor_to_dict(txn)
              if not rows:
                  return 0
  
              min_stream_id = rows[-1]["stream_ordering"]
  
              to_update = []
              for row in rows:
                  event_id = row["event_id"]
                  room_id = row["room_id"]
                  try:
                      event_json = json.loads(row["json"])
                      content = event_json['content']
                  except Exception:
                      continue
  
                  display_name = content.get("displayname", None)
                  avatar_url = content.get("avatar_url", None)
  
                  if display_name or avatar_url:
                      to_update.append((display_name, avatar_url, event_id, room_id))
  
              to_update_sql = """
                  UPDATE room_memberships SET display_name = ?, avatar_url = ?
                  WHERE event_id = ? AND room_id = ?
              """
              for index in range(0, len(to_update), INSERT_CLUMP_SIZE):
                  clump = to_update[index : index + INSERT_CLUMP_SIZE]
                  txn.executemany(to_update_sql, clump)
  
              progress = {
                  "target_min_stream_id_inclusive": target_min_stream_id,
                  "max_stream_id_exclusive": min_stream_id,
              }
  
              self._background_update_progress_txn(
                  txn, _MEMBERSHIP_PROFILE_UPDATE_NAME, progress
              )
  
              return len(rows)
  
          result = yield self.runInteraction(
              _MEMBERSHIP_PROFILE_UPDATE_NAME, add_membership_profile_txn
          )
  
          if not result:
              yield self._end_background_update(_MEMBERSHIP_PROFILE_UPDATE_NAME)
  
          defer.returnValue(result)
  
  
  class _JoinedHostsCache(object):
      """Cache for joined hosts in a room that is optimised to handle updates
      via state deltas.
      """
  
      def __init__(self, store, room_id):
          self.store = store
          self.room_id = room_id
  
          self.hosts_to_joined_users = {}
  
          self.state_group = object()
  
          self.linearizer = Linearizer("_JoinedHostsCache")
  
          self._len = 0
  
      @defer.inlineCallbacks
      def get_destinations(self, state_entry):
          """Get set of destinations for a state entry
  
          Args:
              state_entry(synapse.state._StateCacheEntry)
          """
          if state_entry.state_group == self.state_group:
              defer.returnValue(frozenset(self.hosts_to_joined_users))
  
          with (yield self.linearizer.queue(())):
              if state_entry.state_group == self.state_group:
                  pass
              elif state_entry.prev_group == self.state_group:
                  for (typ, state_key), event_id in iteritems(state_entry.delta_ids):
                      if typ != EventTypes.Member:
                          continue
  
                      host = intern_string(get_domain_from_id(state_key))
                      user_id = state_key
                      known_joins = self.hosts_to_joined_users.setdefault(host, set())
  
                      event = yield self.store.get_event(event_id)
                      if event.membership == Membership.JOIN:
                          known_joins.add(user_id)
                      else:
                          known_joins.discard(user_id)
  
                          if not known_joins:
                              self.hosts_to_joined_users.pop(host, None)
              else:
                  joined_users = yield self.store.get_joined_users_from_state(
                      self.room_id, state_entry
                  )
  
                  self.hosts_to_joined_users = {}
                  for user_id in joined_users:
                      host = intern_string(get_domain_from_id(user_id))
                      self.hosts_to_joined_users.setdefault(host, set()).add(user_id)
  
              if state_entry.state_group:
                  self.state_group = state_entry.state_group
              else:
                  self.state_group = object()
              self._len = sum(len(v) for v in itervalues(self.hosts_to_joined_users))
          defer.returnValue(frozenset(self.hosts_to_joined_users))
  
      def __len__(self):
          return self._len
  