# -*- coding: utf-8 -*-
# Copyright 2014 - 2016 OpenMarket Ltd
# Copyright 2017 - 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 six import iteritems

from twisted.internet import defer
from twisted.python.failure import Failure

from synapse.api.constants import EventTypes, Membership
from synapse.api.errors import SynapseError
from synapse.logging.context import run_in_background
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage.state import StateFilter
from synapse.types import RoomStreamToken
from synapse.util.async_helpers import ReadWriteLock
from synapse.util.stringutils import random_string
from synapse.visibility import filter_events_for_client

logger = logging.getLogger(__name__)


class PurgeStatus(object):
    """Object tracking the status of a purge request

    This class contains information on the progress of a purge request, for
    return by get_purge_status.

    Attributes:
        status (int): Tracks whether this request has completed. One of
            STATUS_{ACTIVE,COMPLETE,FAILED}
    """

    STATUS_ACTIVE = 0
    STATUS_COMPLETE = 1
    STATUS_FAILED = 2

    STATUS_TEXT = {
        STATUS_ACTIVE: "active",
        STATUS_COMPLETE: "complete",
        STATUS_FAILED: "failed",
    }

    def __init__(self):
        self.status = PurgeStatus.STATUS_ACTIVE

    def asdict(self):
        return {"status": PurgeStatus.STATUS_TEXT[self.status]}


class PaginationHandler(object):
    """Handles pagination and purge history requests.

    These are in the same handler due to the fact we need to block clients
    paginating during a purge.
    """

    def __init__(self, hs):
        self.hs = hs
        self.auth = hs.get_auth()
        self.store = hs.get_datastore()
        self.storage = hs.get_storage()
        self.state_store = self.storage.state
        self.clock = hs.get_clock()
        self._server_name = hs.hostname

        self.pagination_lock = ReadWriteLock()
        self._purges_in_progress_by_room = set()
        # map from purge id to PurgeStatus
        self._purges_by_id = {}
        self._event_serializer = hs.get_event_client_serializer()

        self._retention_default_max_lifetime = hs.config.retention_default_max_lifetime

        if hs.config.retention_enabled:
            # Run the purge jobs described in the configuration file.
            for job in hs.config.retention_purge_jobs:
                self.clock.looping_call(
                    run_as_background_process,
                    job["interval"],
                    "purge_history_for_rooms_in_range",
                    self.purge_history_for_rooms_in_range,
                    job["shortest_max_lifetime"],
                    job["longest_max_lifetime"],
                )

    @defer.inlineCallbacks
    def purge_history_for_rooms_in_range(self, min_ms, max_ms):
        """Purge outdated events from rooms within the given retention range.

        If a default retention policy is defined in the server's configuration and its
        'max_lifetime' is within this range, also targets rooms which don't have a
        retention policy.

        Args:
            min_ms (int|None): Duration in milliseconds that define the lower limit of
                the range to handle (exclusive). If None, it means that the range has no
                lower limit.
            max_ms (int|None): Duration in milliseconds that define the upper limit of
                the range to handle (inclusive). If None, it means that the range has no
                upper limit.
        """
        # We want the storage layer to to include rooms with no retention policy in its
        # return value only if a default retention policy is defined in the server's
        # configuration and that policy's 'max_lifetime' is either lower (or equal) than
        # max_ms or higher than min_ms (or both).
        if self._retention_default_max_lifetime is not None:
            include_null = True

            if min_ms is not None and min_ms >= self._retention_default_max_lifetime:
                # The default max_lifetime is lower than (or equal to) min_ms.
                include_null = False

            if max_ms is not None and max_ms < self._retention_default_max_lifetime:
                # The default max_lifetime is higher than max_ms.
                include_null = False
        else:
            include_null = False

        rooms = yield self.store.get_rooms_for_retention_period_in_range(
            min_ms, max_ms, include_null
        )

        for room_id, retention_policy in iteritems(rooms):
            if room_id in self._purges_in_progress_by_room:
                logger.warning(
                    "[purge] not purging room %s as there's an ongoing purge running"
                    " for this room",
                    room_id,
                )
                continue

            max_lifetime = retention_policy["max_lifetime"]

            if max_lifetime is None:
                # If max_lifetime is None, it means that include_null equals True,
                # therefore we can safely assume that there is a default policy defined
                # in the server's configuration.
                max_lifetime = self._retention_default_max_lifetime

            # Figure out what token we should start purging at.
            ts = self.clock.time_msec() - max_lifetime

            stream_ordering = yield self.store.find_first_stream_ordering_after_ts(ts)

            r = yield self.store.get_room_event_after_stream_ordering(
                room_id, stream_ordering,
            )
            if not r:
                logger.warning(
                    "[purge] purging events not possible: No event found "
                    "(ts %i => stream_ordering %i)",
                    ts,
                    stream_ordering,
                )
                continue

            (stream, topo, _event_id) = r
            token = "t%d-%d" % (topo, stream)

            purge_id = random_string(16)

            self._purges_by_id[purge_id] = PurgeStatus()

            logger.info(
                "Starting purging events in room %s (purge_id %s)" % (room_id, purge_id)
            )

            # We want to purge everything, including local events, and to run the purge in
            # the background so that it's not blocking any other operation apart from
            # other purges in the same room.
            run_as_background_process(
                "_purge_history", self._purge_history, purge_id, room_id, token, True,
            )

    def start_purge_history(self, room_id, token, delete_local_events=False):
        """Start off a history purge on a room.

        Args:
            room_id (str): The room to purge from

            token (str): topological token to delete events before
            delete_local_events (bool): True to delete local events as well as
                remote ones

        Returns:
            str: unique ID for this purge transaction.
        """
        if room_id in self._purges_in_progress_by_room:
            raise SynapseError(
                400, "History purge already in progress for %s" % (room_id,)
            )

        purge_id = random_string(16)

        # we log the purge_id here so that it can be tied back to the
        # request id in the log lines.
        logger.info("[purge] starting purge_id %s", purge_id)

        self._purges_by_id[purge_id] = PurgeStatus()
        run_in_background(
            self._purge_history, purge_id, room_id, token, delete_local_events
        )
        return purge_id

    @defer.inlineCallbacks
    def _purge_history(self, purge_id, room_id, token, delete_local_events):
        """Carry out a history purge on a room.

        Args:
            purge_id (str): The id for this purge
            room_id (str): The room to purge from
            token (str): topological token to delete events before
            delete_local_events (bool): True to delete local events as well as
                remote ones

        Returns:
            Deferred
        """
        self._purges_in_progress_by_room.add(room_id)
        try:
            with (yield self.pagination_lock.write(room_id)):
                yield self.storage.purge_events.purge_history(
                    room_id, token, delete_local_events
                )
            logger.info("[purge] complete")
            self._purges_by_id[purge_id].status = PurgeStatus.STATUS_COMPLETE
        except Exception:
            f = Failure()
            logger.error(
                "[purge] failed", exc_info=(f.type, f.value, f.getTracebackObject())
            )
            self._purges_by_id[purge_id].status = PurgeStatus.STATUS_FAILED
        finally:
            self._purges_in_progress_by_room.discard(room_id)

            # remove the purge from the list 24 hours after it completes
            def clear_purge():
                del self._purges_by_id[purge_id]

            self.hs.get_reactor().callLater(24 * 3600, clear_purge)

    def get_purge_status(self, purge_id):
        """Get the current status of an active purge

        Args:
            purge_id (str): purge_id returned by start_purge_history

        Returns:
            PurgeStatus|None
        """
        return self._purges_by_id.get(purge_id)

    async def purge_room(self, room_id):
        """Purge the given room from the database"""
        with (await self.pagination_lock.write(room_id)):
            # check we know about the room
            await self.store.get_room_version(room_id)

            # first check that we have no users in this room
            joined = await defer.maybeDeferred(
                self.store.is_host_joined, room_id, self._server_name
            )

            if joined:
                raise SynapseError(400, "Users are still joined to this room")

            await self.storage.purge_events.purge_room(room_id)

    @defer.inlineCallbacks
    def get_messages(
        self,
        requester,
        room_id=None,
        pagin_config=None,
        as_client_event=True,
        event_filter=None,
    ):
        """Get messages in a room.

        Args:
            requester (Requester): The user requesting messages.
            room_id (str): The room they want messages from.
            pagin_config (synapse.api.streams.PaginationConfig): The pagination
                config rules to apply, if any.
            as_client_event (bool): True to get events in client-server format.
            event_filter (Filter): Filter to apply to results or None
        Returns:
            dict: Pagination API results
        """
        user_id = requester.user.to_string()

        if pagin_config.from_token:
            room_token = pagin_config.from_token.room_key
        else:
            pagin_config.from_token = (
                yield self.hs.get_event_sources().get_current_token_for_pagination()
            )
            room_token = pagin_config.from_token.room_key

        room_token = RoomStreamToken.parse(room_token)

        pagin_config.from_token = pagin_config.from_token.copy_and_replace(
            "room_key", str(room_token)
        )

        source_config = pagin_config.get_source_config("room")

        with (yield self.pagination_lock.read(room_id)):
            (
                membership,
                member_event_id,
            ) = yield self.auth.check_in_room_or_world_readable(room_id, user_id)

            if source_config.direction == "b":
                # if we're going backwards, we might need to backfill. This
                # requires that we have a topo token.
                if room_token.topological:
                    max_topo = room_token.topological
                else:
                    max_topo = yield self.store.get_max_topological_token(
                        room_id, room_token.stream
                    )

                if membership == Membership.LEAVE:
                    # If they have left the room then clamp the token to be before
                    # they left the room, to save the effort of loading from the
                    # database.
                    leave_token = yield self.store.get_topological_token_for_event(
                        member_event_id
                    )
                    leave_token = RoomStreamToken.parse(leave_token)
                    if leave_token.topological < max_topo:
                        source_config.from_key = str(leave_token)

                yield self.hs.get_handlers().federation_handler.maybe_backfill(
                    room_id, max_topo
                )

            events, next_key = yield self.store.paginate_room_events(
                room_id=room_id,
                from_key=source_config.from_key,
                to_key=source_config.to_key,
                direction=source_config.direction,
                limit=source_config.limit,
                event_filter=event_filter,
            )

            next_token = pagin_config.from_token.copy_and_replace("room_key", next_key)

        if events:
            if event_filter:
                events = event_filter.filter(events)

            events = yield filter_events_for_client(
                self.storage, user_id, events, is_peeking=(member_event_id is None)
            )

        if not events:
            return {
                "chunk": [],
                "start": pagin_config.from_token.to_string(),
                "end": next_token.to_string(),
            }

        state = None
        if event_filter and event_filter.lazy_load_members() and len(events) > 0:
            # TODO: remove redundant members

            # FIXME: we also care about invite targets etc.
            state_filter = StateFilter.from_types(
                (EventTypes.Member, event.sender) for event in events
            )

            state_ids = yield self.state_store.get_state_ids_for_event(
                events[0].event_id, state_filter=state_filter
            )

            if state_ids:
                state = yield self.store.get_events(list(state_ids.values()))
                state = state.values()

        time_now = self.clock.time_msec()

        chunk = {
            "chunk": (
                yield self._event_serializer.serialize_events(
                    events, time_now, as_client_event=as_client_event
                )
            ),
            "start": pagin_config.from_token.to_string(),
            "end": next_token.to_string(),
        }

        if state:
            chunk["state"] = yield self._event_serializer.serialize_events(
                state, time_now, as_client_event=as_client_event
            )

        return chunk
