forked-synapse/synapse/handlers/sync.py

# -*- coding: utf-8 -*-
# Copyright 2015 - 2016 OpenMarket 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.

from ._base import BaseHandler

from synapse.streams.config import PaginationConfig
from synapse.api.constants import Membership, EventTypes
from synapse.util import unwrapFirstError
from synapse.util.logcontext import LoggingContext, preserve_fn
from synapse.util.metrics import Measure
from synapse.util.caches.response_cache import ResponseCache
from synapse.push.clientformat import format_push_rules_for_user

from twisted.internet import defer

import collections
import logging
import itertools

logger = logging.getLogger(__name__)


SyncConfig = collections.namedtuple("SyncConfig", [
    "user",
    "filter_collection",
    "is_guest",
    "request_key",
])


class TimelineBatch(collections.namedtuple("TimelineBatch", [
    "prev_batch",
    "events",
    "limited",
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if room needs to be part of the sync result.
        """
        return bool(self.events)


class JoinedSyncResult(collections.namedtuple("JoinedSyncResult", [
    "room_id",           # str
    "timeline",          # TimelineBatch
    "state",             # dict[(str, str), FrozenEvent]
    "ephemeral",
    "account_data",
    "unread_notifications",
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if room needs to be part of the sync result.
        """
        return bool(
            self.timeline
            or self.state
            or self.ephemeral
            or self.account_data
            # nb the notification count does not, er, count: if there's nothing
            # else in the result, we don't need to send it.
        )


class ArchivedSyncResult(collections.namedtuple("ArchivedSyncResult", [
    "room_id",            # str
    "timeline",           # TimelineBatch
    "state",              # dict[(str, str), FrozenEvent]
    "account_data",
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if room needs to be part of the sync result.
        """
        return bool(
            self.timeline
            or self.state
            or self.account_data
        )


class InvitedSyncResult(collections.namedtuple("InvitedSyncResult", [
    "room_id",   # str
    "invite",    # FrozenEvent: the invite event
])):
    __slots__ = []

    def __nonzero__(self):
        """Invited rooms should always be reported to the client"""
        return True


class SyncResult(collections.namedtuple("SyncResult", [
    "next_batch",  # Token for the next sync
    "presence",  # List of presence events for the user.
    "account_data",  # List of account_data events for the user.
    "joined",  # JoinedSyncResult for each joined room.
    "invited",  # InvitedSyncResult for each invited room.
    "archived",  # ArchivedSyncResult for each archived room.
])):
    __slots__ = []

    def __nonzero__(self):
        """Make the result appear empty if there are no updates. This is used
        to tell if the notifier needs to wait for more events when polling for
        events.
        """
        return bool(
            self.presence or
            self.joined or
            self.invited or
            self.archived or
            self.account_data
        )


class SyncHandler(BaseHandler):

    def __init__(self, hs):
        super(SyncHandler, self).__init__(hs)
        self.event_sources = hs.get_event_sources()
        self.clock = hs.get_clock()
        self.response_cache = ResponseCache()

    def wait_for_sync_for_user(self, sync_config, since_token=None, timeout=0,
                               full_state=False):
        """Get the sync for a client if we have new data for it now. Otherwise
        wait for new data to arrive on the server. If the timeout expires, then
        return an empty sync result.
        Returns:
            A Deferred SyncResult.
        """
        result = self.response_cache.get(sync_config.request_key)
        if not result:
            result = self.response_cache.set(
                sync_config.request_key,
                self._wait_for_sync_for_user(
                    sync_config, since_token, timeout, full_state
                )
            )
        return result

    @defer.inlineCallbacks
    def _wait_for_sync_for_user(self, sync_config, since_token, timeout,
                                full_state):
        context = LoggingContext.current_context()
        if context:
            if since_token is None:
                context.tag = "initial_sync"
            elif full_state:
                context.tag = "full_state_sync"
            else:
                context.tag = "incremental_sync"

        if timeout == 0 or since_token is None or full_state:
            # we are going to return immediately, so don't bother calling
            # notifier.wait_for_events.
            result = yield self.current_sync_for_user(
                sync_config, since_token, full_state=full_state,
            )
            defer.returnValue(result)
        else:
            def current_sync_callback(before_token, after_token):
                return self.current_sync_for_user(sync_config, since_token)

            result = yield self.notifier.wait_for_events(
                sync_config.user.to_string(), timeout, current_sync_callback,
                from_token=since_token,
            )
            defer.returnValue(result)

    def current_sync_for_user(self, sync_config, since_token=None,
                              full_state=False):
        """Get the sync for client needed to match what the server has now.
        Returns:
            A Deferred SyncResult.
        """
        if since_token is None or full_state:
            return self.full_state_sync(sync_config, since_token)
        else:
            return self.incremental_sync_with_gap(sync_config, since_token)

    @defer.inlineCallbacks
    def full_state_sync(self, sync_config, timeline_since_token):
        """Get a sync for a client which is starting without any state.

        If a 'message_since_token' is given, only timeline events which have
        happened since that token will be returned.

        Returns:
            A Deferred SyncResult.
        """
        now_token = yield self.event_sources.get_current_token()

        now_token, ephemeral_by_room = yield self.ephemeral_by_room(
            sync_config, now_token
        )

        presence_stream = self.event_sources.sources["presence"]
        # TODO (mjark): This looks wrong, shouldn't we be getting the presence
        # UP to the present rather than after the present?
        pagination_config = PaginationConfig(from_token=now_token)
        presence, _ = yield presence_stream.get_pagination_rows(
            user=sync_config.user,
            pagination_config=pagination_config.get_source_config("presence"),
            key=None
        )

        membership_list = (
            Membership.INVITE, Membership.JOIN, Membership.LEAVE, Membership.BAN
        )

        room_list = yield self.store.get_rooms_for_user_where_membership_is(
            user_id=sync_config.user.to_string(),
            membership_list=membership_list
        )

        account_data, account_data_by_room = (
            yield self.store.get_account_data_for_user(
                sync_config.user.to_string()
            )
        )

        account_data['m.push_rules'] = yield self.push_rules_for_user(
            sync_config.user
        )

        tags_by_room = yield self.store.get_tags_for_user(
            sync_config.user.to_string()
        )

        joined = []
        invited = []
        archived = []
        deferreds = []

        room_list_chunks = [room_list[i:i + 10] for i in xrange(0, len(room_list), 10)]
        for room_list_chunk in room_list_chunks:
            for event in room_list_chunk:
                if event.membership == Membership.JOIN:
                    room_sync_deferred = preserve_fn(
                        self.full_state_sync_for_joined_room
                    )(
                        room_id=event.room_id,
                        sync_config=sync_config,
                        now_token=now_token,
                        timeline_since_token=timeline_since_token,
                        ephemeral_by_room=ephemeral_by_room,
                        tags_by_room=tags_by_room,
                        account_data_by_room=account_data_by_room,
                    )
                    room_sync_deferred.addCallback(joined.append)
                    deferreds.append(room_sync_deferred)
                elif event.membership == Membership.INVITE:
                    invite = yield self.store.get_event(event.event_id)
                    invited.append(InvitedSyncResult(
                        room_id=event.room_id,
                        invite=invite,
                    ))
                elif event.membership in (Membership.LEAVE, Membership.BAN):
                    # Always send down rooms we were banned or kicked from.
                    if not sync_config.filter_collection.include_leave:
                        if event.membership == Membership.LEAVE:
                            if sync_config.user.to_string() == event.sender:
                                continue

                    leave_token = now_token.copy_and_replace(
                        "room_key", "s%d" % (event.stream_ordering,)
                    )
                    room_sync_deferred = preserve_fn(
                        self.full_state_sync_for_archived_room
                    )(
                        sync_config=sync_config,
                        room_id=event.room_id,
                        leave_event_id=event.event_id,
                        leave_token=leave_token,
                        timeline_since_token=timeline_since_token,
                        tags_by_room=tags_by_room,
                        account_data_by_room=account_data_by_room,
                    )
                    room_sync_deferred.addCallback(archived.append)
                    deferreds.append(room_sync_deferred)

            yield defer.gatherResults(
                deferreds, consumeErrors=True
            ).addErrback(unwrapFirstError)

        account_data_for_user = sync_config.filter_collection.filter_account_data(
            self.account_data_for_user(account_data)
        )

        presence = sync_config.filter_collection.filter_presence(
            presence
        )

        defer.returnValue(SyncResult(
            presence=presence,
            account_data=account_data_for_user,
            joined=joined,
            invited=invited,
            archived=archived,
            next_batch=now_token,
        ))

    @defer.inlineCallbacks
    def full_state_sync_for_joined_room(self, room_id, sync_config,
                                        now_token, timeline_since_token,
                                        ephemeral_by_room, tags_by_room,
                                        account_data_by_room):
        """Sync a room for a client which is starting without any state
        Returns:
            A Deferred JoinedSyncResult.
        """

        batch = yield self.load_filtered_recents(
            room_id, sync_config, now_token, since_token=timeline_since_token
        )

        room_sync = yield self.incremental_sync_with_gap_for_room(
            room_id, sync_config,
            now_token=now_token,
            since_token=timeline_since_token,
            ephemeral_by_room=ephemeral_by_room,
            tags_by_room=tags_by_room,
            account_data_by_room=account_data_by_room,
            batch=batch,
            full_state=True,
        )

        defer.returnValue(room_sync)

    @defer.inlineCallbacks
    def push_rules_for_user(self, user):
        user_id = user.to_string()
        rawrules = yield self.store.get_push_rules_for_user(user_id)
        enabled_map = yield self.store.get_push_rules_enabled_for_user(user_id)
        rules = format_push_rules_for_user(user, rawrules, enabled_map)
        defer.returnValue(rules)

    def account_data_for_user(self, account_data):
        account_data_events = []

        for account_data_type, content in account_data.items():
            account_data_events.append({
                "type": account_data_type,
                "content": content,
            })

        return account_data_events

    def account_data_for_room(self, room_id, tags_by_room, account_data_by_room):
        account_data_events = []
        tags = tags_by_room.get(room_id)
        if tags is not None:
            account_data_events.append({
                "type": "m.tag",
                "content": {"tags": tags},
            })

        account_data = account_data_by_room.get(room_id, {})
        for account_data_type, content in account_data.items():
            account_data_events.append({
                "type": account_data_type,
                "content": content,
            })

        return account_data_events

    @defer.inlineCallbacks
    def ephemeral_by_room(self, sync_config, now_token, since_token=None):
        """Get the ephemeral events for each room the user is in
        Args:
            sync_config (SyncConfig): The flags, filters and user for the sync.
            now_token (StreamToken): Where the server is currently up to.
            since_token (StreamToken): Where the server was when the client
                last synced.
        Returns:
            A tuple of the now StreamToken, updated to reflect the which typing
            events are included, and a dict mapping from room_id to a list of
            typing events for that room.
        """

        with Measure(self.clock, "ephemeral_by_room"):
            typing_key = since_token.typing_key if since_token else "0"

            rooms = yield self.store.get_rooms_for_user(sync_config.user.to_string())
            room_ids = [room.room_id for room in rooms]

            typing_source = self.event_sources.sources["typing"]
            typing, typing_key = yield typing_source.get_new_events(
                user=sync_config.user,
                from_key=typing_key,
                limit=sync_config.filter_collection.ephemeral_limit(),
                room_ids=room_ids,
                is_guest=sync_config.is_guest,
            )
            now_token = now_token.copy_and_replace("typing_key", typing_key)

            ephemeral_by_room = {}

            for event in typing:
                # we want to exclude the room_id from the event, but modifying the
                # result returned by the event source is poor form (it might cache
                # the object)
                room_id = event["room_id"]
                event_copy = {k: v for (k, v) in event.iteritems()
                              if k != "room_id"}
                ephemeral_by_room.setdefault(room_id, []).append(event_copy)

            receipt_key = since_token.receipt_key if since_token else "0"

            receipt_source = self.event_sources.sources["receipt"]
            receipts, receipt_key = yield receipt_source.get_new_events(
                user=sync_config.user,
                from_key=receipt_key,
                limit=sync_config.filter_collection.ephemeral_limit(),
                room_ids=room_ids,
                is_guest=sync_config.is_guest,
            )
            now_token = now_token.copy_and_replace("receipt_key", receipt_key)

            for event in receipts:
                room_id = event["room_id"]
                # exclude room id, as above
                event_copy = {k: v for (k, v) in event.iteritems()
                              if k != "room_id"}
                ephemeral_by_room.setdefault(room_id, []).append(event_copy)

        defer.returnValue((now_token, ephemeral_by_room))

    def full_state_sync_for_archived_room(self, room_id, sync_config,
                                          leave_event_id, leave_token,
                                          timeline_since_token, tags_by_room,
                                          account_data_by_room):
        """Sync a room for a client which is starting without any state
        Returns:
            A Deferred ArchivedSyncResult.
        """

        return self.incremental_sync_for_archived_room(
            sync_config, room_id, leave_event_id, timeline_since_token, tags_by_room,
            account_data_by_room, full_state=True, leave_token=leave_token,
        )

    @defer.inlineCallbacks
    def incremental_sync_with_gap(self, sync_config, since_token):
        """ Get the incremental delta needed to bring the client up to
        date with the server.
        Returns:
            A Deferred SyncResult.
        """
        now_token = yield self.event_sources.get_current_token()

        rooms = yield self.store.get_rooms_for_user(sync_config.user.to_string())
        room_ids = [room.room_id for room in rooms]

        presence_source = self.event_sources.sources["presence"]
        presence, presence_key = yield presence_source.get_new_events(
            user=sync_config.user,
            from_key=since_token.presence_key,
            limit=sync_config.filter_collection.presence_limit(),
            room_ids=room_ids,
            is_guest=sync_config.is_guest,
        )
        now_token = now_token.copy_and_replace("presence_key", presence_key)

        now_token, ephemeral_by_room = yield self.ephemeral_by_room(
            sync_config, now_token, since_token
        )

        rm_handler = self.hs.get_handlers().room_member_handler
        app_service = yield self.store.get_app_service_by_user_id(
            sync_config.user.to_string()
        )
        if app_service:
            rooms = yield self.store.get_app_service_rooms(app_service)
            joined_room_ids = set(r.room_id for r in rooms)
        else:
            joined_room_ids = yield rm_handler.get_joined_rooms_for_user(
                sync_config.user
            )

        user_id = sync_config.user.to_string()

        timeline_limit = sync_config.filter_collection.timeline_limit()

        tags_by_room = yield self.store.get_updated_tags(
            user_id,
            since_token.account_data_key,
        )

        account_data, account_data_by_room = (
            yield self.store.get_updated_account_data_for_user(
                user_id,
                since_token.account_data_key,
            )
        )

        push_rules_changed = yield self.store.have_push_rules_changed_for_user(
            user_id, int(since_token.push_rules_key)
        )

        if push_rules_changed:
            account_data["m.push_rules"] = yield self.push_rules_for_user(
                sync_config.user
            )

        # Get a list of membership change events that have happened.
        rooms_changed = yield self.store.get_membership_changes_for_user(
            user_id, since_token.room_key, now_token.room_key
        )

        mem_change_events_by_room_id = {}
        for event in rooms_changed:
            mem_change_events_by_room_id.setdefault(event.room_id, []).append(event)

        newly_joined_rooms = []
        archived = []
        invited = []
        for room_id, events in mem_change_events_by_room_id.items():
            non_joins = [e for e in events if e.membership != Membership.JOIN]
            has_join = len(non_joins) != len(events)

            # We want to figure out if we joined the room at some point since
            # the last sync (even if we have since left). This is to make sure
            # we do send down the room, and with full state, where necessary
            if room_id in joined_room_ids or has_join:
                old_state = yield self.get_state_at(room_id, since_token)
                old_mem_ev = old_state.get((EventTypes.Member, user_id), None)
                if not old_mem_ev or old_mem_ev.membership != Membership.JOIN:
                        newly_joined_rooms.append(room_id)

                if room_id in joined_room_ids:
                    continue

            if not non_joins:
                continue

            # Only bother if we're still currently invited
            should_invite = non_joins[-1].membership == Membership.INVITE
            if should_invite:
                room_sync = InvitedSyncResult(room_id, invite=non_joins[-1])
                if room_sync:
                    invited.append(room_sync)

            # Always include leave/ban events. Just take the last one.
            # TODO: How do we handle ban -> leave in same batch?
            leave_events = [
                e for e in non_joins
                if e.membership in (Membership.LEAVE, Membership.BAN)
            ]

            if leave_events:
                leave_event = leave_events[-1]
                room_sync = yield self.incremental_sync_for_archived_room(
                    sync_config, room_id, leave_event.event_id, since_token,
                    tags_by_room, account_data_by_room,
                    full_state=room_id in newly_joined_rooms
                )
                if room_sync:
                    archived.append(room_sync)

        # Get all events for rooms we're currently joined to.
        room_to_events = yield self.store.get_room_events_stream_for_rooms(
            room_ids=joined_room_ids,
            from_key=since_token.room_key,
            to_key=now_token.room_key,
            limit=timeline_limit + 1,
        )

        joined = []
        # We loop through all room ids, even if there are no new events, in case
        # there are non room events taht we need to notify about.
        for room_id in joined_room_ids:
            room_entry = room_to_events.get(room_id, None)

            if room_entry:
                events, start_key = room_entry

                prev_batch_token = now_token.copy_and_replace("room_key", start_key)

                newly_joined_room = room_id in newly_joined_rooms
                full_state = newly_joined_room

                batch = yield self.load_filtered_recents(
                    room_id, sync_config, prev_batch_token,
                    since_token=since_token,
                    recents=events,
                    newly_joined_room=newly_joined_room,
                )
            else:
                batch = TimelineBatch(
                    events=[],
                    prev_batch=since_token,
                    limited=False,
                )
                full_state = False

            room_sync = yield self.incremental_sync_with_gap_for_room(
                room_id=room_id,
                sync_config=sync_config,
                since_token=since_token,
                now_token=now_token,
                ephemeral_by_room=ephemeral_by_room,
                tags_by_room=tags_by_room,
                account_data_by_room=account_data_by_room,
                batch=batch,
                full_state=full_state,
            )
            if room_sync:
                joined.append(room_sync)

        # For each newly joined room, we want to send down presence of
        # existing users.
        presence_handler = self.hs.get_handlers().presence_handler
        extra_presence_users = set()
        for room_id in newly_joined_rooms:
            users = yield self.store.get_users_in_room(event.room_id)
            extra_presence_users.update(users)

        # For each new member, send down presence.
        for joined_sync in joined:
            it = itertools.chain(joined_sync.timeline.events, joined_sync.state.values())
            for event in it:
                if event.type == EventTypes.Member:
                    if event.membership == Membership.JOIN:
                        extra_presence_users.add(event.state_key)

        states = yield presence_handler.get_states(
            [u for u in extra_presence_users if u != user_id],
            as_event=True,
        )
        presence.extend(states)

        account_data_for_user = sync_config.filter_collection.filter_account_data(
            self.account_data_for_user(account_data)
        )

        presence = sync_config.filter_collection.filter_presence(
            presence
        )

        defer.returnValue(SyncResult(
            presence=presence,
            account_data=account_data_for_user,
            joined=joined,
            invited=invited,
            archived=archived,
            next_batch=now_token,
        ))

    @defer.inlineCallbacks
    def load_filtered_recents(self, room_id, sync_config, now_token,
                              since_token=None, recents=None, newly_joined_room=False):
        """
        :returns a Deferred TimelineBatch
        """
        with Measure(self.clock, "load_filtered_recents"):
            filtering_factor = 2
            timeline_limit = sync_config.filter_collection.timeline_limit()
            load_limit = max(timeline_limit * filtering_factor, 10)
            max_repeat = 5  # Only try a few times per room, otherwise
            room_key = now_token.room_key
            end_key = room_key

            if recents is None or newly_joined_room or timeline_limit < len(recents):
                limited = True
            else:
                limited = False

            if recents is not None:
                recents = sync_config.filter_collection.filter_room_timeline(recents)
                recents = yield self._filter_events_for_client(
                    sync_config.user.to_string(),
                    recents,
                )
            else:
                recents = []

            since_key = None
            if since_token and not newly_joined_room:
                since_key = since_token.room_key

            while limited and len(recents) < timeline_limit and max_repeat:
                events, end_key = yield self.store.get_room_events_stream_for_room(
                    room_id,
                    limit=load_limit + 1,
                    from_key=since_key,
                    to_key=end_key,
                )
                loaded_recents = sync_config.filter_collection.filter_room_timeline(
                    events
                )
                loaded_recents = yield self._filter_events_for_client(
                    sync_config.user.to_string(),
                    loaded_recents,
                )
                loaded_recents.extend(recents)
                recents = loaded_recents

                if len(events) <= load_limit:
                    limited = False
                    break
                max_repeat -= 1

            if len(recents) > timeline_limit:
                limited = True
                recents = recents[-timeline_limit:]
                room_key = recents[0].internal_metadata.before

            prev_batch_token = now_token.copy_and_replace(
                "room_key", room_key
            )

        defer.returnValue(TimelineBatch(
            events=recents,
            prev_batch=prev_batch_token,
            limited=limited or newly_joined_room
        ))

    @defer.inlineCallbacks
    def incremental_sync_with_gap_for_room(self, room_id, sync_config,
                                           since_token, now_token,
                                           ephemeral_by_room, tags_by_room,
                                           account_data_by_room,
                                           batch, full_state=False):
        state = yield self.compute_state_delta(
            room_id, batch, sync_config, since_token, now_token,
            full_state=full_state
        )

        account_data = self.account_data_for_room(
            room_id, tags_by_room, account_data_by_room
        )

        account_data = sync_config.filter_collection.filter_room_account_data(
            account_data
        )

        ephemeral = sync_config.filter_collection.filter_room_ephemeral(
            ephemeral_by_room.get(room_id, [])
        )

        unread_notifications = {}
        room_sync = JoinedSyncResult(
            room_id=room_id,
            timeline=batch,
            state=state,
            ephemeral=ephemeral,
            account_data=account_data,
            unread_notifications=unread_notifications,
        )

        if room_sync:
            notifs = yield self.unread_notifs_for_room_id(
                room_id, sync_config
            )

            if notifs is not None:
                unread_notifications["notification_count"] = notifs["notify_count"]
                unread_notifications["highlight_count"] = notifs["highlight_count"]

        logger.debug("Room sync: %r", room_sync)

        defer.returnValue(room_sync)

    @defer.inlineCallbacks
    def incremental_sync_for_archived_room(self, sync_config, room_id, leave_event_id,
                                           since_token, tags_by_room,
                                           account_data_by_room, full_state,
                                           leave_token=None):
        """ Get the incremental delta needed to bring the client up to date for
        the archived room.
        Returns:
            A Deferred ArchivedSyncResult
        """

        if not leave_token:
            stream_token = yield self.store.get_stream_token_for_event(
                leave_event_id
            )

            leave_token = since_token.copy_and_replace("room_key", stream_token)

        if since_token and since_token.is_after(leave_token):
            defer.returnValue(None)

        batch = yield self.load_filtered_recents(
            room_id, sync_config, leave_token, since_token,
        )

        logger.debug("Recents %r", batch)

        state_events_delta = yield self.compute_state_delta(
            room_id, batch, sync_config, since_token, leave_token,
            full_state=full_state
        )

        account_data = self.account_data_for_room(
            room_id, tags_by_room, account_data_by_room
        )

        account_data = sync_config.filter_collection.filter_room_account_data(
            account_data
        )

        room_sync = ArchivedSyncResult(
            room_id=room_id,
            timeline=batch,
            state=state_events_delta,
            account_data=account_data,
        )

        logger.debug("Room sync: %r", room_sync)

        defer.returnValue(room_sync)

    @defer.inlineCallbacks
    def get_state_after_event(self, event):
        """
        Get the room state after the given event

        :param synapse.events.EventBase event: event of interest
        :return: A Deferred map from ((type, state_key)->Event)
        """
        state = yield self.store.get_state_for_event(event.event_id)
        if event.is_state():
            state = state.copy()
            state[(event.type, event.state_key)] = event
        defer.returnValue(state)

    @defer.inlineCallbacks
    def get_state_at(self, room_id, stream_position):
        """ Get the room state at a particular stream position
        :param str room_id: room for which to get state
        :param StreamToken stream_position: point at which to get state
        :returns: A Deferred map from ((type, state_key)->Event)
        """
        last_events, token = yield self.store.get_recent_events_for_room(
            room_id, end_token=stream_position.room_key, limit=1,
        )

        if last_events:
            last_event = last_events[-1]
            state = yield self.get_state_after_event(last_event)

        else:
            # no events in this room - so presumably no state
            state = {}
        defer.returnValue(state)

    @defer.inlineCallbacks
    def compute_state_delta(self, room_id, batch, sync_config, since_token, now_token,
                            full_state):
        """ Works out the differnce in state between the start of the timeline
        and the previous sync.

        :param str room_id
        :param TimelineBatch batch: The timeline batch for the room that will
            be sent to the user.
        :param sync_config
        :param str since_token: Token of the end of the previous batch. May be None.
        :param str now_token: Token of the end of the current batch.
        :param bool full_state: Whether to force returning the full state.

        :returns A new event dictionary
        """
        # TODO(mjark) Check if the state events were received by the server
        # after the previous sync, since we need to include those state
        # updates even if they occured logically before the previous event.
        # TODO(mjark) Check for new redactions in the state events.

        with Measure(self.clock, "compute_state_delta"):
            if full_state:
                if batch:
                    current_state = yield self.store.get_state_for_event(
                        batch.events[-1].event_id
                    )

                    state = yield self.store.get_state_for_event(
                        batch.events[0].event_id
                    )
                else:
                    current_state = yield self.get_state_at(
                        room_id, stream_position=now_token
                    )

                    state = current_state

                timeline_state = {
                    (event.type, event.state_key): event
                    for event in batch.events if event.is_state()
                }

                state = _calculate_state(
                    timeline_contains=timeline_state,
                    timeline_start=state,
                    previous={},
                    current=current_state,
                )
            elif batch.limited:
                state_at_previous_sync = yield self.get_state_at(
                    room_id, stream_position=since_token
                )

                current_state = yield self.store.get_state_for_event(
                    batch.events[-1].event_id
                )

                state_at_timeline_start = yield self.store.get_state_for_event(
                    batch.events[0].event_id
                )

                timeline_state = {
                    (event.type, event.state_key): event
                    for event in batch.events if event.is_state()
                }

                state = _calculate_state(
                    timeline_contains=timeline_state,
                    timeline_start=state_at_timeline_start,
                    previous=state_at_previous_sync,
                    current=current_state,
                )
            else:
                state = {}

            defer.returnValue({
                (e.type, e.state_key): e
                for e in sync_config.filter_collection.filter_room_state(state.values())
            })

    def check_joined_room(self, sync_config, state_delta):
        """
        Check if the user has just joined the given room (so should
        be given the full state)

        :param sync_config:
        :param dict[(str,str), synapse.events.FrozenEvent] state_delta: the
           difference in state since the last sync

        :returns A deferred Tuple (state_delta, limited)
        """
        join_event = state_delta.get((
            EventTypes.Member, sync_config.user.to_string()), None)
        if join_event is not None:
            if join_event.content["membership"] == Membership.JOIN:
                return True
        return False

    @defer.inlineCallbacks
    def unread_notifs_for_room_id(self, room_id, sync_config):
        with Measure(self.clock, "unread_notifs_for_room_id"):
            last_unread_event_id = yield self.store.get_last_receipt_event_id_for_user(
                user_id=sync_config.user.to_string(),
                room_id=room_id,
                receipt_type="m.read"
            )

            notifs = []
            if last_unread_event_id:
                notifs = yield self.store.get_unread_event_push_actions_by_room_for_user(
                    room_id, sync_config.user.to_string(), last_unread_event_id
                )
                defer.returnValue(notifs)

            # There is no new information in this period, so your notification
            # count is whatever it was last time.
            defer.returnValue(None)


def _action_has_highlight(actions):
    for action in actions:
        try:
            if action.get("set_tweak", None) == "highlight":
                return action.get("value", True)
        except AttributeError:
            pass

    return False


def _calculate_state(timeline_contains, timeline_start, previous, current):
    """Works out what state to include in a sync response.

    Args:
        timeline_contains (dict): state in the timeline
        timeline_start (dict): state at the start of the timeline
        previous (dict): state at the end of the previous sync (or empty dict
            if this is an initial sync)
        current (dict): state at the end of the timeline

    Returns:
        dict
    """
    event_id_to_state = {
        e.event_id: e
        for e in itertools.chain(
            timeline_contains.values(),
            previous.values(),
            timeline_start.values(),
            current.values(),
        )
    }

    c_ids = set(e.event_id for e in current.values())
    tc_ids = set(e.event_id for e in timeline_contains.values())
    p_ids = set(e.event_id for e in previous.values())
    ts_ids = set(e.event_id for e in timeline_start.values())

    state_ids = ((c_ids | ts_ids) - p_ids) - tc_ids

    evs = (event_id_to_state[e] for e in state_ids)
    return {
        (e.type, e.state_key): e
        for e in evs
    }