# -*- 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 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.events.utils import serialize_event
from synapse.types import RoomStreamToken
from synapse.util.async_helpers import ReadWriteLock
from synapse.util.logcontext import run_in_background
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.clock = hs.get_clock()

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

    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.store.purge_history(
                    room_id, token, delete_local_events,
                )
            logger.info("[purge] complete")
            self._purges_by_id[purge_id].status = PurgeStatus.STATUS_COMPLETE
        except Exception:
            logger.error("[purge] failed: %s", Failure().getTraceback().rstrip())
            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)

    @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_room(
                    room_id=room_id
                )
            )
            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 not events:
            defer.returnValue({
                "chunk": [],
                "start": pagin_config.from_token.to_string(),
                "end": next_token.to_string(),
            })

        if event_filter:
            events = event_filter.filter(events)

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

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

            types = [
                (EventTypes.Member, state_key)
                for state_key in set(
                    event.sender  # FIXME: we also care about invite targets etc.
                    for event in events
                )
            ]

            state_ids = yield self.store.get_state_ids_for_event(
                events[0].event_id, types=types,
            )

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

        time_now = self.clock.time_msec()

        chunk = {
            "chunk": [
                serialize_event(e, time_now, as_client_event)
                for e in events
            ],
            "start": pagin_config.from_token.to_string(),
            "end": next_token.to_string(),
        }

        if state:
            chunk["state"] = [
                serialize_event(e, time_now, as_client_event)
                for e in state
            ]

        defer.returnValue(chunk)
