# -*- coding: utf-8 -*-
# Copyright 2014-2016 OpenMarket Ltd
# Copyright 2020 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 collections.abc
import logging
from collections import namedtuple
from typing import Iterable, Optional, Set

from synapse.api.constants import EventTypes, Membership
from synapse.api.errors import NotFoundError, UnsupportedRoomVersionError
from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
from synapse.events import EventBase
from synapse.storage._base import SQLBaseStore
from synapse.storage.database import DatabasePool
from synapse.storage.databases.main.events_worker import EventsWorkerStore
from synapse.storage.databases.main.roommember import RoomMemberWorkerStore
from synapse.storage.state import StateFilter
from synapse.types import StateMap
from synapse.util.caches import intern_string
from synapse.util.caches.descriptors import cached, cachedList

logger = logging.getLogger(__name__)


MAX_STATE_DELTA_HOPS = 100


class _GetStateGroupDelta(
    namedtuple("_GetStateGroupDelta", ("prev_group", "delta_ids"))
):
    """Return type of get_state_group_delta that implements __len__, which lets
    us use the itrable flag when caching
    """

    __slots__ = []

    def __len__(self):
        return len(self.delta_ids) if self.delta_ids else 0


# this inherits from EventsWorkerStore because it calls self.get_events
class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
    """The parts of StateGroupStore that can be called from workers."""

    def __init__(self, database: DatabasePool, db_conn, hs):
        super().__init__(database, db_conn, hs)

    async def get_room_version(self, room_id: str) -> RoomVersion:
        """Get the room_version of a given room

        Raises:
            NotFoundError: if the room is unknown

            UnsupportedRoomVersionError: if the room uses an unknown room version.
                Typically this happens if support for the room's version has been
                removed from Synapse.
        """
        room_version_id = await self.get_room_version_id(room_id)
        v = KNOWN_ROOM_VERSIONS.get(room_version_id)

        if not v:
            raise UnsupportedRoomVersionError(
                "Room %s uses a room version %s which is no longer supported"
                % (room_id, room_version_id)
            )

        return v

    @cached(max_entries=10000)
    async def get_room_version_id(self, room_id: str) -> str:
        """Get the room_version of a given room

        Raises:
            NotFoundError: if the room is unknown
        """

        # First we try looking up room version from the database, but for old
        # rooms we might not have added the room version to it yet so we fall
        # back to previous behaviour and look in current state events.

        # We really should have an entry in the rooms table for every room we
        # care about, but let's be a bit paranoid (at least while the background
        # update is happening) to avoid breaking existing rooms.
        version = await self.db_pool.simple_select_one_onecol(
            table="rooms",
            keyvalues={"room_id": room_id},
            retcol="room_version",
            desc="get_room_version",
            allow_none=True,
        )

        if version is not None:
            return version

        # Retrieve the room's create event
        create_event = await self.get_create_event_for_room(room_id)
        return create_event.content.get("room_version", "1")

    async def get_room_predecessor(self, room_id: str) -> Optional[dict]:
        """Get the predecessor of an upgraded room if it exists.
        Otherwise return None.

        Args:
            room_id: The room ID.

        Returns:
            A dictionary containing the structure of the predecessor
            field from the room's create event. The structure is subject to other servers,
            but it is expected to be:
                * room_id (str): The room ID of the predecessor room
                * event_id (str): The ID of the tombstone event in the predecessor room

            None if a predecessor key is not found, or is not a dictionary.

        Raises:
            NotFoundError if the given room is unknown
        """
        # Retrieve the room's create event
        create_event = await self.get_create_event_for_room(room_id)

        # Retrieve the predecessor key of the create event
        predecessor = create_event.content.get("predecessor", None)

        # Ensure the key is a dictionary
        if not isinstance(predecessor, collections.abc.Mapping):
            return None

        return predecessor

    async def get_create_event_for_room(self, room_id: str) -> EventBase:
        """Get the create state event for a room.

        Args:
            room_id: The room ID.

        Returns:
            The room creation event.

        Raises:
            NotFoundError if the room is unknown
        """
        state_ids = await self.get_current_state_ids(room_id)
        create_id = state_ids.get((EventTypes.Create, ""))

        # If we can't find the create event, assume we've hit a dead end
        if not create_id:
            raise NotFoundError("Unknown room %s" % (room_id,))

        # Retrieve the room's create event and return
        create_event = await self.get_event(create_id)
        return create_event

    @cached(max_entries=100000, iterable=True)
    async def get_current_state_ids(self, room_id: str) -> StateMap[str]:
        """Get the current state event ids for a room based on the
        current_state_events table.

        Args:
            room_id: The room to get the state IDs of.

        Returns:
            The current state of the room.
        """

        def _get_current_state_ids_txn(txn):
            txn.execute(
                """SELECT type, state_key, event_id FROM current_state_events
                WHERE room_id = ?
                """,
                (room_id,),
            )

            return {(intern_string(r[0]), intern_string(r[1])): r[2] for r in txn}

        return await self.db_pool.runInteraction(
            "get_current_state_ids", _get_current_state_ids_txn
        )

    # FIXME: how should this be cached?
    async def get_filtered_current_state_ids(
        self, room_id: str, state_filter: StateFilter = StateFilter.all()
    ) -> StateMap[str]:
        """Get the current state event of a given type for a room based on the
        current_state_events table.  This may not be as up-to-date as the result
        of doing a fresh state resolution as per state_handler.get_current_state

        Args:
            room_id
            state_filter: The state filter used to fetch state
                from the database.

        Returns:
            Map from type/state_key to event ID.
        """

        where_clause, where_args = state_filter.make_sql_filter_clause()

        if not where_clause:
            # We delegate to the cached version
            return await self.get_current_state_ids(room_id)

        def _get_filtered_current_state_ids_txn(txn):
            results = {}
            sql = """
                SELECT type, state_key, event_id FROM current_state_events
                WHERE room_id = ?
            """

            if where_clause:
                sql += " AND (%s)" % (where_clause,)

            args = [room_id]
            args.extend(where_args)
            txn.execute(sql, args)
            for row in txn:
                typ, state_key, event_id = row
                key = (intern_string(typ), intern_string(state_key))
                results[key] = event_id

            return results

        return await self.db_pool.runInteraction(
            "get_filtered_current_state_ids", _get_filtered_current_state_ids_txn
        )

    async def get_canonical_alias_for_room(self, room_id: str) -> Optional[str]:
        """Get canonical alias for room, if any

        Args:
            room_id: The room ID

        Returns:
            The canonical alias, if any
        """

        state = await self.get_filtered_current_state_ids(
            room_id, StateFilter.from_types([(EventTypes.CanonicalAlias, "")])
        )

        event_id = state.get((EventTypes.CanonicalAlias, ""))
        if not event_id:
            return

        event = await self.get_event(event_id, allow_none=True)
        if not event:
            return

        return event.content.get("canonical_alias")

    @cached(max_entries=50000)
    async def _get_state_group_for_event(self, event_id: str) -> Optional[int]:
        return await self.db_pool.simple_select_one_onecol(
            table="event_to_state_groups",
            keyvalues={"event_id": event_id},
            retcol="state_group",
            allow_none=True,
            desc="_get_state_group_for_event",
        )

    @cachedList(
        cached_method_name="_get_state_group_for_event",
        list_name="event_ids",
        num_args=1,
    )
    async def _get_state_group_for_events(self, event_ids):
        """Returns mapping event_id -> state_group"""
        rows = await self.db_pool.simple_select_many_batch(
            table="event_to_state_groups",
            column="event_id",
            iterable=event_ids,
            keyvalues={},
            retcols=("event_id", "state_group"),
            desc="_get_state_group_for_events",
        )

        return {row["event_id"]: row["state_group"] for row in rows}

    async def get_referenced_state_groups(
        self, state_groups: Iterable[int]
    ) -> Set[int]:
        """Check if the state groups are referenced by events.

        Args:
            state_groups

        Returns:
            The subset of state groups that are referenced.
        """

        rows = await self.db_pool.simple_select_many_batch(
            table="event_to_state_groups",
            column="state_group",
            iterable=state_groups,
            keyvalues={},
            retcols=("DISTINCT state_group",),
            desc="get_referenced_state_groups",
        )

        return {row["state_group"] for row in rows}


class MainStateBackgroundUpdateStore(RoomMemberWorkerStore):

    CURRENT_STATE_INDEX_UPDATE_NAME = "current_state_members_idx"
    EVENT_STATE_GROUP_INDEX_UPDATE_NAME = "event_to_state_groups_sg_index"
    DELETE_CURRENT_STATE_UPDATE_NAME = "delete_old_current_state_events"

    def __init__(self, database: DatabasePool, db_conn, hs):
        super().__init__(database, db_conn, hs)

        self.server_name = hs.hostname

        self.db_pool.updates.register_background_index_update(
            self.CURRENT_STATE_INDEX_UPDATE_NAME,
            index_name="current_state_events_member_index",
            table="current_state_events",
            columns=["state_key"],
            where_clause="type='m.room.member'",
        )
        self.db_pool.updates.register_background_index_update(
            self.EVENT_STATE_GROUP_INDEX_UPDATE_NAME,
            index_name="event_to_state_groups_sg_index",
            table="event_to_state_groups",
            columns=["state_group"],
        )
        self.db_pool.updates.register_background_update_handler(
            self.DELETE_CURRENT_STATE_UPDATE_NAME,
            self._background_remove_left_rooms,
        )

    async def _background_remove_left_rooms(self, progress, batch_size):
        """Background update to delete rows from `current_state_events` and
        `event_forward_extremities` tables of rooms that the server is no
        longer joined to.
        """

        last_room_id = progress.get("last_room_id", "")

        def _background_remove_left_rooms_txn(txn):
            # get a batch of room ids to consider
            sql = """
                SELECT DISTINCT room_id FROM current_state_events
                WHERE room_id > ? ORDER BY room_id LIMIT ?
            """

            txn.execute(sql, (last_room_id, batch_size))
            room_ids = [row[0] for row in txn]
            if not room_ids:
                return True, set()

            ###########################################################################
            #
            # exclude rooms where we have active members

            sql = """
                SELECT room_id
                FROM local_current_membership
                WHERE
                    room_id > ? AND room_id <= ?
                    AND membership = 'join'
                GROUP BY room_id
            """

            txn.execute(sql, (last_room_id, room_ids[-1]))
            joined_room_ids = {row[0] for row in txn}
            to_delete = set(room_ids) - joined_room_ids

            ###########################################################################
            #
            # exclude rooms which we are in the process of constructing; these otherwise
            # qualify as "rooms with no local users", and would have their
            # forward extremities cleaned up.

            # the following query will return a list of rooms which have forward
            # extremities that are *not* also the create event in the room - ie
            # those that are not being created currently.

            sql = """
                SELECT DISTINCT efe.room_id
                FROM event_forward_extremities efe
                LEFT JOIN current_state_events cse ON
                    cse.event_id = efe.event_id
                    AND cse.type = 'm.room.create'
                    AND cse.state_key = ''
                WHERE
                    cse.event_id IS NULL
                    AND efe.room_id > ? AND efe.room_id <= ?
            """

            txn.execute(sql, (last_room_id, room_ids[-1]))

            # build a set of those rooms within `to_delete` that do not appear in
            # the above, leaving us with the rooms in `to_delete` that *are* being
            # created.
            creating_rooms = to_delete.difference(row[0] for row in txn)
            logger.info("skipping rooms which are being created: %s", creating_rooms)

            # now remove the rooms being created from the list of those to delete.
            #
            # (we could have just taken the intersection of `to_delete` with the result
            # of the sql query, but it's useful to be able to log `creating_rooms`; and
            # having done so, it's quicker to remove the (few) creating rooms from
            # `to_delete` than it is to form the intersection with the (larger) list of
            # not-creating-rooms)

            to_delete -= creating_rooms

            ###########################################################################
            #
            # now clear the state for the rooms

            logger.info("Deleting current state left rooms: %r", to_delete)

            # First we get all users that we still think were joined to the
            # room. This is so that we can mark those device lists as
            # potentially stale, since there may have been a period where the
            # server didn't share a room with the remote user and therefore may
            # have missed any device updates.
            rows = self.db_pool.simple_select_many_txn(
                txn,
                table="current_state_events",
                column="room_id",
                iterable=to_delete,
                keyvalues={"type": EventTypes.Member, "membership": Membership.JOIN},
                retcols=("state_key",),
            )

            potentially_left_users = {row["state_key"] for row in rows}

            # Now lets actually delete the rooms from the DB.
            self.db_pool.simple_delete_many_txn(
                txn,
                table="current_state_events",
                column="room_id",
                iterable=to_delete,
                keyvalues={},
            )

            self.db_pool.simple_delete_many_txn(
                txn,
                table="event_forward_extremities",
                column="room_id",
                iterable=to_delete,
                keyvalues={},
            )

            self.db_pool.updates._background_update_progress_txn(
                txn,
                self.DELETE_CURRENT_STATE_UPDATE_NAME,
                {"last_room_id": room_ids[-1]},
            )

            return False, potentially_left_users

        finished, potentially_left_users = await self.db_pool.runInteraction(
            "_background_remove_left_rooms", _background_remove_left_rooms_txn
        )

        if finished:
            await self.db_pool.updates._end_background_update(
                self.DELETE_CURRENT_STATE_UPDATE_NAME
            )

        # Now go and check if we still share a room with the remote users in
        # the deleted rooms. If not mark their device lists as stale.
        joined_users = await self.get_users_server_still_shares_room_with(
            potentially_left_users
        )

        for user_id in potentially_left_users - joined_users:
            await self.mark_remote_user_device_list_as_unsubscribed(user_id)

        return batch_size


class StateStore(StateGroupWorkerStore, MainStateBackgroundUpdateStore):
    """Keeps track of the state at a given event.

    This is done by the concept of `state groups`. Every event is a assigned
    a state group (identified by an arbitrary string), which references a
    collection of state events. The current state of an event is then the
    collection of state events referenced by the event's state group.

    Hence, every change in the current state causes a new state group to be
    generated. However, if no change happens (e.g., if we get a message event
    with only one parent it inherits the state group from its parent.)

    There are three tables:
      * `state_groups`: Stores group name, first event with in the group and
        room id.
      * `event_to_state_groups`: Maps events to state groups.
      * `state_groups_state`: Maps state group to state events.
    """

    def __init__(self, database: DatabasePool, db_conn, hs):
        super().__init__(database, db_conn, hs)
