# -*- coding: utf-8 -*-
# Copyright 2014-2016 OpenMarket Ltd
# Copyright 2018-2019 New Vector Ltd
# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# 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 deque, namedtuple

from six import iteritems
from six.moves import range

from prometheus_client import Counter, Histogram

from twisted.internet import defer

from synapse.api.constants import EventTypes
from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.state import StateResolutionStore
from synapse.storage.data_stores import DataStores
from synapse.util.async_helpers import ObservableDeferred
from synapse.util.metrics import Measure

logger = logging.getLogger(__name__)

# The number of times we are recalculating the current state
state_delta_counter = Counter("synapse_storage_events_state_delta", "")

# The number of times we are recalculating state when there is only a
# single forward extremity
state_delta_single_event_counter = Counter(
    "synapse_storage_events_state_delta_single_event", ""
)

# The number of times we are reculating state when we could have resonably
# calculated the delta when we calculated the state for an event we were
# persisting.
state_delta_reuse_delta_counter = Counter(
    "synapse_storage_events_state_delta_reuse_delta", ""
)

# The number of forward extremities for each new event.
forward_extremities_counter = Histogram(
    "synapse_storage_events_forward_extremities_persisted",
    "Number of forward extremities for each new event",
    buckets=(1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"),
)

# The number of stale forward extremities for each new event. Stale extremities
# are those that were in the previous set of extremities as well as the new.
stale_forward_extremities_counter = Histogram(
    "synapse_storage_events_stale_forward_extremities_persisted",
    "Number of unchanged forward extremities for each new event",
    buckets=(0, 1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"),
)


class _EventPeristenceQueue(object):
    """Queues up events so that they can be persisted in bulk with only one
    concurrent transaction per room.
    """

    _EventPersistQueueItem = namedtuple(
        "_EventPersistQueueItem", ("events_and_contexts", "backfilled", "deferred")
    )

    def __init__(self):
        self._event_persist_queues = {}
        self._currently_persisting_rooms = set()

    def add_to_queue(self, room_id, events_and_contexts, backfilled):
        """Add events to the queue, with the given persist_event options.

        NB: due to the normal usage pattern of this method, it does *not*
        follow the synapse logcontext rules, and leaves the logcontext in
        place whether or not the returned deferred is ready.

        Args:
            room_id (str):
            events_and_contexts (list[(EventBase, EventContext)]):
            backfilled (bool):

        Returns:
            defer.Deferred: a deferred which will resolve once the events are
                persisted. Runs its callbacks *without* a logcontext.
        """
        queue = self._event_persist_queues.setdefault(room_id, deque())
        if queue:
            # if the last item in the queue has the same `backfilled` setting,
            # we can just add these new events to that item.
            end_item = queue[-1]
            if end_item.backfilled == backfilled:
                end_item.events_and_contexts.extend(events_and_contexts)
                return end_item.deferred.observe()

        deferred = ObservableDeferred(defer.Deferred(), consumeErrors=True)

        queue.append(
            self._EventPersistQueueItem(
                events_and_contexts=events_and_contexts,
                backfilled=backfilled,
                deferred=deferred,
            )
        )

        return deferred.observe()

    def handle_queue(self, room_id, per_item_callback):
        """Attempts to handle the queue for a room if not already being handled.

        The given callback will be invoked with for each item in the queue,
        of type _EventPersistQueueItem. The per_item_callback will continuously
        be called with new items, unless the queue becomnes empty. The return
        value of the function will be given to the deferreds waiting on the item,
        exceptions will be passed to the deferreds as well.

        This function should therefore be called whenever anything is added
        to the queue.

        If another callback is currently handling the queue then it will not be
        invoked.
        """

        if room_id in self._currently_persisting_rooms:
            return

        self._currently_persisting_rooms.add(room_id)

        @defer.inlineCallbacks
        def handle_queue_loop():
            try:
                queue = self._get_drainining_queue(room_id)
                for item in queue:
                    try:
                        ret = yield per_item_callback(item)
                    except Exception:
                        with PreserveLoggingContext():
                            item.deferred.errback()
                    else:
                        with PreserveLoggingContext():
                            item.deferred.callback(ret)
            finally:
                queue = self._event_persist_queues.pop(room_id, None)
                if queue:
                    self._event_persist_queues[room_id] = queue
                self._currently_persisting_rooms.discard(room_id)

        # set handle_queue_loop off in the background
        run_as_background_process("persist_events", handle_queue_loop)

    def _get_drainining_queue(self, room_id):
        queue = self._event_persist_queues.setdefault(room_id, deque())

        try:
            while True:
                yield queue.popleft()
        except IndexError:
            # Queue has been drained.
            pass


class EventsPersistenceStorage(object):
    """High level interface for handling persisting newly received events.

    Takes care of batching up events by room, and calculating the necessary
    current state and forward extremity changes.
    """

    def __init__(self, hs, stores: DataStores):
        # We ultimately want to split out the state store from the main store,
        # so we use separate variables here even though they point to the same
        # store for now.
        self.main_store = stores.main
        self.state_store = stores.main

        self._clock = hs.get_clock()
        self.is_mine_id = hs.is_mine_id
        self._event_persist_queue = _EventPeristenceQueue()
        self._state_resolution_handler = hs.get_state_resolution_handler()

    @defer.inlineCallbacks
    def persist_events(self, events_and_contexts, backfilled=False):
        """
        Write events to the database
        Args:
            events_and_contexts: list of tuples of (event, context)
            backfilled (bool): Whether the results are retrieved from federation
                via backfill or not. Used to determine if they're "new" events
                which might update the current state etc.

        Returns:
            Deferred[int]: the stream ordering of the latest persisted event
        """
        partitioned = {}
        for event, ctx in events_and_contexts:
            partitioned.setdefault(event.room_id, []).append((event, ctx))

        deferreds = []
        for room_id, evs_ctxs in iteritems(partitioned):
            d = self._event_persist_queue.add_to_queue(
                room_id, evs_ctxs, backfilled=backfilled
            )
            deferreds.append(d)

        for room_id in partitioned:
            self._maybe_start_persisting(room_id)

        yield make_deferred_yieldable(
            defer.gatherResults(deferreds, consumeErrors=True)
        )

        max_persisted_id = yield self.main_store.get_current_events_token()

        return max_persisted_id

    @defer.inlineCallbacks
    def persist_event(self, event, context, backfilled=False):
        """

        Args:
            event (EventBase):
            context (EventContext):
            backfilled (bool):

        Returns:
            Deferred: resolves to (int, int): the stream ordering of ``event``,
            and the stream ordering of the latest persisted event
        """
        deferred = self._event_persist_queue.add_to_queue(
            event.room_id, [(event, context)], backfilled=backfilled
        )

        self._maybe_start_persisting(event.room_id)

        yield make_deferred_yieldable(deferred)

        max_persisted_id = yield self.main_store.get_current_events_token()
        return (event.internal_metadata.stream_ordering, max_persisted_id)

    def _maybe_start_persisting(self, room_id):
        @defer.inlineCallbacks
        def persisting_queue(item):
            with Measure(self._clock, "persist_events"):
                yield self._persist_events(
                    item.events_and_contexts, backfilled=item.backfilled
                )

        self._event_persist_queue.handle_queue(room_id, persisting_queue)

    @defer.inlineCallbacks
    def _persist_events(self, events_and_contexts, backfilled=False):
        """Calculates the change to current state and forward extremities, and
        persists the given events and with those updates.

        Args:
            events_and_contexts (list[(EventBase, EventContext)]):
            backfilled (bool):
            delete_existing (bool):

        Returns:
            Deferred: resolves when the events have been persisted
        """
        if not events_and_contexts:
            return

        chunks = [
            events_and_contexts[x : x + 100]
            for x in range(0, len(events_and_contexts), 100)
        ]

        for chunk in chunks:
            # We can't easily parallelize these since different chunks
            # might contain the same event. :(

            # NB: Assumes that we are only persisting events for one room
            # at a time.

            # map room_id->list[event_ids] giving the new forward
            # extremities in each room
            new_forward_extremeties = {}

            # map room_id->(type,state_key)->event_id tracking the full
            # state in each room after adding these events.
            # This is simply used to prefill the get_current_state_ids
            # cache
            current_state_for_room = {}

            # map room_id->(to_delete, to_insert) where to_delete is a list
            # of type/state keys to remove from current state, and to_insert
            # is a map (type,key)->event_id giving the state delta in each
            # room
            state_delta_for_room = {}

            if not backfilled:
                with Measure(self._clock, "_calculate_state_and_extrem"):
                    # Work out the new "current state" for each room.
                    # We do this by working out what the new extremities are and then
                    # calculating the state from that.
                    events_by_room = {}
                    for event, context in chunk:
                        events_by_room.setdefault(event.room_id, []).append(
                            (event, context)
                        )

                    for room_id, ev_ctx_rm in iteritems(events_by_room):
                        latest_event_ids = yield self.main_store.get_latest_event_ids_in_room(
                            room_id
                        )
                        new_latest_event_ids = yield self._calculate_new_extremities(
                            room_id, ev_ctx_rm, latest_event_ids
                        )

                        latest_event_ids = set(latest_event_ids)
                        if new_latest_event_ids == latest_event_ids:
                            # No change in extremities, so no change in state
                            continue

                        # there should always be at least one forward extremity.
                        # (except during the initial persistence of the send_join
                        # results, in which case there will be no existing
                        # extremities, so we'll `continue` above and skip this bit.)
                        assert new_latest_event_ids, "No forward extremities left!"

                        new_forward_extremeties[room_id] = new_latest_event_ids

                        len_1 = (
                            len(latest_event_ids) == 1
                            and len(new_latest_event_ids) == 1
                        )
                        if len_1:
                            all_single_prev_not_state = all(
                                len(event.prev_event_ids()) == 1
                                and not event.is_state()
                                for event, ctx in ev_ctx_rm
                            )
                            # Don't bother calculating state if they're just
                            # a long chain of single ancestor non-state events.
                            if all_single_prev_not_state:
                                continue

                        state_delta_counter.inc()
                        if len(new_latest_event_ids) == 1:
                            state_delta_single_event_counter.inc()

                            # This is a fairly handwavey check to see if we could
                            # have guessed what the delta would have been when
                            # processing one of these events.
                            # What we're interested in is if the latest extremities
                            # were the same when we created the event as they are
                            # now. When this server creates a new event (as opposed
                            # to receiving it over federation) it will use the
                            # forward extremities as the prev_events, so we can
                            # guess this by looking at the prev_events and checking
                            # if they match the current forward extremities.
                            for ev, _ in ev_ctx_rm:
                                prev_event_ids = set(ev.prev_event_ids())
                                if latest_event_ids == prev_event_ids:
                                    state_delta_reuse_delta_counter.inc()
                                    break

                        logger.info("Calculating state delta for room %s", room_id)
                        with Measure(
                            self._clock, "persist_events.get_new_state_after_events"
                        ):
                            res = yield self._get_new_state_after_events(
                                room_id,
                                ev_ctx_rm,
                                latest_event_ids,
                                new_latest_event_ids,
                            )
                            current_state, delta_ids = res

                        # If either are not None then there has been a change,
                        # and we need to work out the delta (or use that
                        # given)
                        if delta_ids is not None:
                            # If there is a delta we know that we've
                            # only added or replaced state, never
                            # removed keys entirely.
                            state_delta_for_room[room_id] = ([], delta_ids)
                        elif current_state is not None:
                            with Measure(
                                self._clock, "persist_events.calculate_state_delta"
                            ):
                                delta = yield self._calculate_state_delta(
                                    room_id, current_state
                                )
                            state_delta_for_room[room_id] = delta

                        # If we have the current_state then lets prefill
                        # the cache with it.
                        if current_state is not None:
                            current_state_for_room[room_id] = current_state

            yield self.main_store._persist_events_and_state_updates(
                chunk,
                current_state_for_room=current_state_for_room,
                state_delta_for_room=state_delta_for_room,
                new_forward_extremeties=new_forward_extremeties,
                backfilled=backfilled,
            )

    @defer.inlineCallbacks
    def _calculate_new_extremities(self, room_id, event_contexts, latest_event_ids):
        """Calculates the new forward extremities for a room given events to
        persist.

        Assumes that we are only persisting events for one room at a time.
        """

        # we're only interested in new events which aren't outliers and which aren't
        # being rejected.
        new_events = [
            event
            for event, ctx in event_contexts
            if not event.internal_metadata.is_outlier()
            and not ctx.rejected
            and not event.internal_metadata.is_soft_failed()
        ]

        latest_event_ids = set(latest_event_ids)

        # start with the existing forward extremities
        result = set(latest_event_ids)

        # add all the new events to the list
        result.update(event.event_id for event in new_events)

        # Now remove all events which are prev_events of any of the new events
        result.difference_update(
            e_id for event in new_events for e_id in event.prev_event_ids()
        )

        # Remove any events which are prev_events of any existing events.
        existing_prevs = yield self.main_store._get_events_which_are_prevs(result)
        result.difference_update(existing_prevs)

        # Finally handle the case where the new events have soft-failed prev
        # events. If they do we need to remove them and their prev events,
        # otherwise we end up with dangling extremities.
        existing_prevs = yield self.main_store._get_prevs_before_rejected(
            e_id for event in new_events for e_id in event.prev_event_ids()
        )
        result.difference_update(existing_prevs)

        # We only update metrics for events that change forward extremities
        # (e.g. we ignore backfill/outliers/etc)
        if result != latest_event_ids:
            forward_extremities_counter.observe(len(result))
            stale = latest_event_ids & result
            stale_forward_extremities_counter.observe(len(stale))

        return result

    @defer.inlineCallbacks
    def _get_new_state_after_events(
        self, room_id, events_context, old_latest_event_ids, new_latest_event_ids
    ):
        """Calculate the current state dict after adding some new events to
        a room

        Args:
            room_id (str):
                room to which the events are being added. Used for logging etc

            events_context (list[(EventBase, EventContext)]):
                events and contexts which are being added to the room

            old_latest_event_ids (iterable[str]):
                the old forward extremities for the room.

            new_latest_event_ids (iterable[str]):
                the new forward extremities for the room.

        Returns:
            Deferred[tuple[dict[(str,str), str]|None, dict[(str,str), str]|None]]:
            Returns a tuple of two state maps, the first being the full new current
            state and the second being the delta to the existing current state.
            If both are None then there has been no change.

            If there has been a change then we only return the delta if its
            already been calculated. Conversely if we do know the delta then
            the new current state is only returned if we've already calculated
            it.
        """
        # map from state_group to ((type, key) -> event_id) state map
        state_groups_map = {}

        # Map from (prev state group, new state group) -> delta state dict
        state_group_deltas = {}

        for ev, ctx in events_context:
            if ctx.state_group is None:
                # This should only happen for outlier events.
                if not ev.internal_metadata.is_outlier():
                    raise Exception(
                        "Context for new event %s has no state "
                        "group" % (ev.event_id,)
                    )
                continue

            if ctx.state_group in state_groups_map:
                continue

            # We're only interested in pulling out state that has already
            # been cached in the context. We'll pull stuff out of the DB later
            # if necessary.
            current_state_ids = ctx.get_cached_current_state_ids()
            if current_state_ids is not None:
                state_groups_map[ctx.state_group] = current_state_ids

            if ctx.prev_group:
                state_group_deltas[(ctx.prev_group, ctx.state_group)] = ctx.delta_ids

        # We need to map the event_ids to their state groups. First, let's
        # check if the event is one we're persisting, in which case we can
        # pull the state group from its context.
        # Otherwise we need to pull the state group from the database.

        # Set of events we need to fetch groups for. (We know none of the old
        # extremities are going to be in events_context).
        missing_event_ids = set(old_latest_event_ids)

        event_id_to_state_group = {}
        for event_id in new_latest_event_ids:
            # First search in the list of new events we're adding.
            for ev, ctx in events_context:
                if event_id == ev.event_id and ctx.state_group is not None:
                    event_id_to_state_group[event_id] = ctx.state_group
                    break
            else:
                # If we couldn't find it, then we'll need to pull
                # the state from the database
                missing_event_ids.add(event_id)

        if missing_event_ids:
            # Now pull out the state groups for any missing events from DB
            event_to_groups = yield self.main_store._get_state_group_for_events(
                missing_event_ids
            )
            event_id_to_state_group.update(event_to_groups)

        # State groups of old_latest_event_ids
        old_state_groups = set(
            event_id_to_state_group[evid] for evid in old_latest_event_ids
        )

        # State groups of new_latest_event_ids
        new_state_groups = set(
            event_id_to_state_group[evid] for evid in new_latest_event_ids
        )

        # If they old and new groups are the same then we don't need to do
        # anything.
        if old_state_groups == new_state_groups:
            return None, None

        if len(new_state_groups) == 1 and len(old_state_groups) == 1:
            # If we're going from one state group to another, lets check if
            # we have a delta for that transition. If we do then we can just
            # return that.

            new_state_group = next(iter(new_state_groups))
            old_state_group = next(iter(old_state_groups))

            delta_ids = state_group_deltas.get((old_state_group, new_state_group), None)
            if delta_ids is not None:
                # We have a delta from the existing to new current state,
                # so lets just return that. If we happen to already have
                # the current state in memory then lets also return that,
                # but it doesn't matter if we don't.
                new_state = state_groups_map.get(new_state_group)
                return new_state, delta_ids

        # Now that we have calculated new_state_groups we need to get
        # their state IDs so we can resolve to a single state set.
        missing_state = new_state_groups - set(state_groups_map)
        if missing_state:
            group_to_state = yield self.state_store._get_state_for_groups(missing_state)
            state_groups_map.update(group_to_state)

        if len(new_state_groups) == 1:
            # If there is only one state group, then we know what the current
            # state is.
            return state_groups_map[new_state_groups.pop()], None

        # Ok, we need to defer to the state handler to resolve our state sets.

        state_groups = {sg: state_groups_map[sg] for sg in new_state_groups}

        events_map = {ev.event_id: ev for ev, _ in events_context}

        # We need to get the room version, which is in the create event.
        # Normally that'd be in the database, but its also possible that we're
        # currently trying to persist it.
        room_version = None
        for ev, _ in events_context:
            if ev.type == EventTypes.Create and ev.state_key == "":
                room_version = ev.content.get("room_version", "1")
                break

        if not room_version:
            room_version = yield self.main_store.get_room_version(room_id)

        logger.debug("calling resolve_state_groups from preserve_events")
        res = yield self._state_resolution_handler.resolve_state_groups(
            room_id,
            room_version,
            state_groups,
            events_map,
            state_res_store=StateResolutionStore(self.main_store),
        )

        return res.state, None

    @defer.inlineCallbacks
    def _calculate_state_delta(self, room_id, current_state):
        """Calculate the new state deltas for a room.

        Assumes that we are only persisting events for one room at a time.

        Returns:
            tuple[list, dict] (to_delete, to_insert): where to_delete are the
            type/state_keys to remove from current_state_events and `to_insert`
            are the updates to current_state_events.
        """
        existing_state = yield self.main_store.get_current_state_ids(room_id)

        to_delete = [key for key in existing_state if key not in current_state]

        to_insert = {
            key: ev_id
            for key, ev_id in iteritems(current_state)
            if ev_id != existing_state.get(key)
        }

        return to_delete, to_insert
