#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright 2014 - 2016 OpenMarket Ltd
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
import logging
from typing import TYPE_CHECKING, cast

import attr

from twisted.python.failure import Failure

from synapse.api.constants import Direction, EventTypes, Membership
from synapse.api.errors import SynapseError
from synapse.api.filtering import Filter
from synapse.events import EventBase
from synapse.events.utils import FilteredEvent
from synapse.handlers.relations import BundledAggregations
from synapse.handlers.worker_lock import NEW_EVENT_DURING_PURGE_LOCK_NAME
from synapse.logging.opentracing import trace
from synapse.rest.admin._base import assert_user_is_admin
from synapse.streams.config import PaginationConfig
from synapse.types import (
    JsonMapping,
    Requester,
    ScheduledTask,
    StreamKeyType,
    StreamToken,
    TaskStatus,
)
from synapse.types.handlers import ShutdownRoomParams, ShutdownRoomResponse
from synapse.types.state import StateFilter
from synapse.util.async_helpers import ReadWriteLock
from synapse.util.duration import Duration
from synapse.visibility import filter_and_transform_events_for_client

if TYPE_CHECKING:
    from synapse.server import HomeServer


logger = logging.getLogger(__name__)

# How many single event gaps we tolerate returning in a `/messages` response before we
# backfill and try to fill in the history. This is an arbitrarily picked number so feel
# free to tune it in the future.
BACKFILL_BECAUSE_TOO_MANY_GAPS_THRESHOLD = 3


# This is used to avoid purging a room several time at the same moment,
# and also paginating during a purge. Pagination can trigger backfill,
# which would create old events locally, and would potentially clash with the room delete.
PURGE_PAGINATION_LOCK_NAME = "purge_pagination_lock"


PURGE_HISTORY_ACTION_NAME = "purge_history"

PURGE_ROOM_ACTION_NAME = "purge_room"

SHUTDOWN_AND_PURGE_ROOM_ACTION_NAME = "shutdown_and_purge_room"


@attr.s(slots=True, frozen=True, auto_attribs=True)
class GetMessagesResult:
    """
    Everything needed to serialize a `/messages` response.
    """

    messages_chunk: list[FilteredEvent]
    """
    A list of room events.

     - When the request is `Direction.FORWARDS`, events will be in the range:
       `start_token` < x <= `end_token`, (ascending topological_order)
     - When the request is `Direction.BACKWARDS`, events will be in the range:
       `start_token` >= x > `end_token`, (descending topological_order)

    Note that an empty chunk does not necessarily imply that no more events are
    available. Clients should continue to paginate until no `end_token` property is returned.
    """

    bundled_aggregations: dict[str, BundledAggregations]
    """
    A map of event ID to the bundled aggregations for the events in the chunk.

    If an event doesn't have any bundled aggregations, it may not appear in the map.
    """

    state: list[EventBase] | None
    """
    A list of state events relevant to showing the chunk. For example, if
    lazy_load_members is enabled in the filter then this may contain the membership
    events for the senders of events in the chunk.

    Omitted from the response when `None`.
    """

    start_token: StreamToken
    """
    Token corresponding to the start of chunk. This will be the same as the value given
    in `from` query parameter of the `/messages` request.
    """

    end_token: StreamToken | None
    """
    A token corresponding to the end of chunk. This token can be passed back to this
    endpoint to request further events.

    If no further events are available (either because we have reached the start of the
    timeline, or because the user does not have permission to see any more events), this
    property is omitted from the response.
    """


class PaginationHandler:
    """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: "HomeServer"):
        self.hs = hs
        self.server_name = hs.hostname
        self.auth = hs.get_auth()
        self.store = hs.get_datastores().main
        self._storage_controllers = hs.get_storage_controllers()
        self._state_storage_controller = self._storage_controllers.state
        self.clock = hs.get_clock()
        self._room_shutdown_handler = hs.get_room_shutdown_handler()
        self._relations_handler = hs.get_relations_handler()
        self._worker_locks = hs.get_worker_locks_handler()
        self._task_scheduler = hs.get_task_scheduler()

        self.pagination_lock = ReadWriteLock()
        # IDs of rooms in which there currently an active purge *or delete* operation.
        self._purges_in_progress_by_room: set[str] = set()
        self._event_serializer = hs.get_event_client_serializer()

        self._retention_default_max_lifetime = (
            hs.config.retention.retention_default_max_lifetime
        )

        self._retention_allowed_lifetime_min = (
            hs.config.retention.retention_allowed_lifetime_min
        )
        self._retention_allowed_lifetime_max = (
            hs.config.retention.retention_allowed_lifetime_max
        )
        self._forgotten_room_retention_period = (
            hs.config.server.forgotten_room_retention_period
        )
        self._is_master = hs.config.worker.worker_app is None

        if hs.config.retention.retention_enabled and self._is_master:
            # Run the purge jobs described in the configuration file.
            for job in hs.config.retention.retention_purge_jobs:
                logger.info("Setting up purge job with config: %s", job)

                self.clock.looping_call(
                    self.hs.run_as_background_process,
                    Duration(milliseconds=job.interval),
                    "purge_history_for_rooms_in_range",
                    self.purge_history_for_rooms_in_range,
                    job.shortest_max_lifetime,
                    job.longest_max_lifetime,
                )

        self._task_scheduler.register_action(
            self._purge_history, PURGE_HISTORY_ACTION_NAME
        )
        self._task_scheduler.register_action(self._purge_room, PURGE_ROOM_ACTION_NAME)
        self._task_scheduler.register_action(
            self._shutdown_and_purge_room, SHUTDOWN_AND_PURGE_ROOM_ACTION_NAME
        )

    async def purge_history_for_rooms_in_range(
        self, min_ms: int | None, max_ms: int | None
    ) -> None:
        """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: 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: 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 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

        logger.info(
            "[purge] Running retention purge job for %s < max_lifetime <= %s (include NULLs = %s)",
            min_ms,
            max_ms,
            include_null,
        )

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

        logger.debug("[purge] Rooms to purge: %s", rooms)

        for room_id, retention_policy in rooms.items():
            logger.info("[purge] Attempting to purge messages in room %s", room_id)

            if len(await self.get_delete_tasks_by_room(room_id, only_active=True)) > 0:
                logger.warning(
                    "[purge] not purging room %s for retention as there's an ongoing purge"
                    " running for this room",
                    room_id,
                )
                continue

            # If max_lifetime is None, it means that the room has no retention policy.
            # Given we only retrieve such rooms when there's a default retention policy
            # defined in the server's configuration, we can safely assume that's the
            # case and use it for this room.
            max_lifetime = (
                retention_policy.max_lifetime or self._retention_default_max_lifetime
            )

            # Cap the effective max_lifetime to be within the range allowed in the
            # config.
            # We do this in two steps:
            #   1. Make sure it's higher or equal to the minimum allowed value, and if
            #      it's not replace it with that value. This is because the server
            #      operator can be required to not delete information before a given
            #      time, e.g. to comply with freedom of information laws.
            #   2. Make sure the resulting value is lower or equal to the maximum allowed
            #      value, and if it's not replace it with that value. This is because the
            #      server operator can be required to delete any data after a specific
            #      amount of time.
            if self._retention_allowed_lifetime_min is not None:
                max_lifetime = max(self._retention_allowed_lifetime_min, max_lifetime)

            if self._retention_allowed_lifetime_max is not None:
                max_lifetime = min(max_lifetime, self._retention_allowed_lifetime_max)

            logger.debug("[purge] max_lifetime for room %s: %s", room_id, max_lifetime)

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

            stream_ordering = await self.store.find_first_stream_ordering_after_ts(ts)

            r = await self.store.get_room_event_before_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)

            logger.info("Starting purging events in room %s", room_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.
            self.hs.run_as_background_process(
                PURGE_HISTORY_ACTION_NAME,
                self.purge_history,
                room_id,
                token,
                True,
            )

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

        Args:
            room_id: The room to purge from
            token: topological token to delete events before
            delete_local_events: True to delete local events as well as
                remote ones

        Returns:
            unique ID for this purge transaction.
        """
        purge_id = await self._task_scheduler.schedule_task(
            PURGE_HISTORY_ACTION_NAME,
            resource_id=room_id,
            params={"token": token, "delete_local_events": delete_local_events},
        )

        # 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)

        return purge_id

    async def _purge_history(
        self,
        task: ScheduledTask,
    ) -> tuple[TaskStatus, JsonMapping | None, str | None]:
        """
        Scheduler action to purge some history of a room.
        """
        if (
            task.resource_id is None
            or task.params is None
            or "token" not in task.params
            or "delete_local_events" not in task.params
        ):
            return (
                TaskStatus.FAILED,
                None,
                "Not enough parameters passed to _purge_history",
            )
        err = await self.purge_history(
            task.resource_id,
            task.params["token"],
            task.params["delete_local_events"],
        )
        if err is not None:
            return TaskStatus.FAILED, None, err
        return TaskStatus.COMPLETE, None, None

    async def purge_history(
        self,
        room_id: str,
        token: str,
        delete_local_events: bool,
    ) -> str | None:
        """Carry out a history purge on a room.

        Args:
            room_id: The room to purge from
            token: topological token to delete events before
            delete_local_events: True to delete local events as well as remote ones
        """
        try:
            async with self._worker_locks.acquire_read_write_lock(
                PURGE_PAGINATION_LOCK_NAME, room_id, write=True
            ):
                await self._storage_controllers.purge_events.purge_history(
                    room_id, token, delete_local_events
                )
            logger.info("[purge] complete")
            return None
        except Exception:
            f = Failure()
            logger.error(
                "[purge] failed", exc_info=(f.type, f.value, f.getTracebackObject())
            )
            return f.getErrorMessage()

    async def get_delete_task(self, delete_id: str) -> ScheduledTask | None:
        """Get the current status of an active deleting

        Args:
            delete_id: delete_id returned by start_shutdown_and_purge_room
                or start_purge_history.
        """
        return await self._task_scheduler.get_task(delete_id)

    async def get_delete_tasks_by_room(
        self, room_id: str, only_active: bool | None = False
    ) -> list[ScheduledTask]:
        """Get complete, failed or active delete tasks by room

        Args:
            room_id: room_id that is deleted
            only_active: if True, completed&failed tasks will be omitted
        """
        statuses = [TaskStatus.ACTIVE]
        if not only_active:
            statuses += [TaskStatus.COMPLETE, TaskStatus.FAILED]

        return await self._task_scheduler.get_tasks(
            actions=[PURGE_ROOM_ACTION_NAME, SHUTDOWN_AND_PURGE_ROOM_ACTION_NAME],
            resource_id=room_id,
            statuses=statuses,
        )

    async def _purge_room(
        self,
        task: ScheduledTask,
    ) -> tuple[TaskStatus, JsonMapping | None, str | None]:
        """
        Scheduler action to purge a room.
        """
        if not task.resource_id:
            raise Exception("No room id passed to purge_room task")
        params = task.params if task.params else {}
        await self.purge_room(task.resource_id, params.get("force", False))
        return TaskStatus.COMPLETE, None, None

    async def purge_room(
        self,
        room_id: str,
        force: bool,
    ) -> None:
        """Purge the given room from the database.

        Args:
            room_id: room to be purged
            force: set true to skip checking for joined users.
        """
        logger.info("starting purge room_id=%s force=%s", room_id, force)

        async with self._worker_locks.acquire_multi_read_write_lock(
            [
                (PURGE_PAGINATION_LOCK_NAME, room_id),
                (NEW_EVENT_DURING_PURGE_LOCK_NAME, room_id),
            ],
            write=True,
        ):
            # first check that we have no users in this room
            joined = await self.store.is_host_joined(room_id, self.server_name)
            if joined:
                if force:
                    logger.info(
                        "force-purging room %s with some local users still joined",
                        room_id,
                    )
                else:
                    raise SynapseError(400, "Users are still joined to this room")

            await self._storage_controllers.purge_events.purge_room(room_id)

        logger.info("purge complete for room_id %s", room_id)

    @trace
    async def get_messages(
        self,
        requester: Requester,
        room_id: str,
        pagin_config: PaginationConfig,
        as_client_event: bool = True,
        event_filter: Filter | None = None,
        use_admin_priviledge: bool = False,
    ) -> GetMessagesResult:
        """Get messages in a room.

        Args:
            requester: The user requesting messages.
            room_id: The room they want messages from.
            pagin_config: The pagination config rules to apply, if any.
            as_client_event: True to get events in client-server format.
            event_filter: Filter to apply to results or None
            use_admin_priviledge: if `True`, return all events, regardless
                of whether `user` has access to them. To be used **ONLY**
                from the admin API.

        Returns:
            Pagination API results
        """
        if use_admin_priviledge:
            await assert_user_is_admin(self.auth, requester)

        user_id = requester.user.to_string()

        if pagin_config.from_token:
            from_token = pagin_config.from_token
        elif pagin_config.direction == Direction.FORWARDS:
            from_token = (
                await self.hs.get_event_sources().get_start_token_for_pagination(
                    room_id
                )
            )
        else:
            from_token = (
                await self.hs.get_event_sources().get_current_token_for_pagination(
                    room_id
                )
            )
            # We expect `/messages` to use historic pagination tokens by default but
            # `/messages` should still works with live tokens when manually provided.
            assert from_token.room_key.topological is not None

        room_token = from_token.room_key

        (membership, member_event_id) = (None, None)
        if not use_admin_priviledge:
            (
                membership,
                member_event_id,
            ) = await self.auth.check_user_in_room_or_world_readable(
                room_id, requester, allow_departed_users=True
            )

        if pagin_config.direction == Direction.BACKWARDS:
            # if we're going backwards, we might need to backfill. This
            # requires that we have a topo token.
            if room_token.topological:
                curr_topo = room_token.topological
            else:
                curr_topo = await self.store.get_current_topological_token(
                    room_id, room_token.stream
                )

        # 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.
        if (
            pagin_config.direction == Direction.BACKWARDS
            and not use_admin_priviledge
            and membership == Membership.LEAVE
        ):
            # This is only None if the room is world_readable, in which case
            # "Membership.JOIN" would have been returned and we should never hit
            # this branch.
            assert member_event_id

            leave_token = await self.store.get_topological_token_for_event(
                member_event_id
            )
            assert leave_token.topological is not None

            if leave_token.topological < curr_topo:
                from_token = from_token.copy_and_replace(
                    StreamKeyType.ROOM, leave_token
                )

        to_room_key = None
        if pagin_config.to_token:
            to_room_key = pagin_config.to_token.room_key

        # Initially fetch the events from the database. With any luck, we can return
        # these without blocking on backfill (handled below).
        (
            events,
            next_key,
            limited,
        ) = await self.store.paginate_room_events_by_topological_ordering(
            room_id=room_id,
            from_key=from_token.room_key,
            to_key=to_room_key,
            direction=pagin_config.direction,
            limit=pagin_config.limit,
            event_filter=event_filter,
        )

        if pagin_config.direction == Direction.BACKWARDS:
            # We use a `Set` because there can be multiple events at a given depth
            # and we only care about looking at the unique continum of depths to
            # find gaps.
            event_depths: set[int] = {event.depth for event in events}
            sorted_event_depths = sorted(event_depths)

            # Inspect the depths of the returned events to see if there are any gaps
            found_big_gap = False
            number_of_gaps = 0
            previous_event_depth = (
                sorted_event_depths[0] if len(sorted_event_depths) > 0 else 0
            )
            for event_depth in sorted_event_depths:
                # We don't expect a negative depth but we'll just deal with it in
                # any case by taking the absolute value to get the true gap between
                # any two integers.
                depth_gap = abs(event_depth - previous_event_depth)
                # A `depth_gap` of 1 is a normal continuous chain to the next event
                # (1 <-- 2 <-- 3) so anything larger indicates a missing event (it's
                # also possible there is no event at a given depth but we can't ever
                # know that for sure)
                if depth_gap > 1:
                    number_of_gaps += 1

                # We only tolerate a small number single-event long gaps in the
                # returned events because those are most likely just events we've
                # failed to pull in the past. Anything longer than that is probably
                # a sign that we're missing a decent chunk of history and we should
                # try to backfill it.
                #
                # XXX: It's possible we could tolerate longer gaps if we checked
                # that a given events `prev_events` is one that has failed pull
                # attempts and we could just treat it like a dead branch of history
                # for now or at least something that we don't need the block the
                # client on to try pulling.
                #
                # XXX: If we had something like MSC3871 to indicate gaps in the
                # timeline to the client, we could also get away with any sized gap
                # and just have the client refetch the holes as they see fit.
                if depth_gap > 2:
                    found_big_gap = True
                    break
                previous_event_depth = event_depth

            # Backfill in the foreground if we found a big gap, have too many holes,
            # or we don't have enough events to fill the limit that the client asked
            # for.
            missing_too_many_events = (
                number_of_gaps > BACKFILL_BECAUSE_TOO_MANY_GAPS_THRESHOLD
            )
            not_enough_events_to_fill_response = len(events) < pagin_config.limit
            if (
                found_big_gap
                or missing_too_many_events
                or not_enough_events_to_fill_response
            ):
                did_backfill = await self.hs.get_federation_handler().maybe_backfill(
                    room_id,
                    curr_topo,
                    limit=pagin_config.limit,
                )

                # If we did backfill something, refetch the events from the database to
                # catch anything new that might have been added since we last fetched.
                if did_backfill:
                    (
                        events,
                        next_key,
                        limited,
                    ) = await self.store.paginate_room_events_by_topological_ordering(
                        room_id=room_id,
                        from_key=from_token.room_key,
                        to_key=to_room_key,
                        direction=pagin_config.direction,
                        limit=pagin_config.limit,
                        event_filter=event_filter,
                    )
            else:
                # Otherwise, we can backfill in the background for eventual
                # consistency's sake but we don't need to block the client waiting
                # for a costly federation call and processing.
                self.hs.run_as_background_process(
                    "maybe_backfill_in_the_background",
                    self.hs.get_federation_handler().maybe_backfill,
                    room_id,
                    curr_topo,
                    limit=pagin_config.limit,
                )

        next_token = from_token.copy_and_replace(StreamKeyType.ROOM, next_key)

        # if no events are returned from pagination (this page is empty)
        # and there aren't any more pages (not limited),
        # that implies we have reached the end of the available events.
        # In that case we do not return end, to tell the client
        # there is no need for further queries.
        if not limited and not events:
            return GetMessagesResult(
                messages_chunk=[],
                bundled_aggregations={},
                state=None,
                start_token=from_token,
                end_token=None,
            )

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

        if not use_admin_priviledge:
            filtered_events = await filter_and_transform_events_for_client(
                self._storage_controllers,
                user_id,
                events,
                is_peeking=(member_event_id is None),
            )
        else:
            filtered_events = [FilteredEvent.admin_override(e) for e in events]

        # if after the filter applied there are no more events
        # return immediately - but there might be more in next_token batch
        if not filtered_events:
            return GetMessagesResult(
                messages_chunk=[],
                bundled_aggregations={},
                state=None,
                start_token=from_token,
                end_token=next_token,
            )

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

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

            state_ids = await self._state_storage_controller.get_state_ids_for_event(
                filtered_events[0].event.event_id, state_filter=state_filter
            )

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

        aggregations = await self._relations_handler.get_bundled_aggregations(
            filtered_events, user_id
        )

        return GetMessagesResult(
            messages_chunk=filtered_events,
            bundled_aggregations=aggregations,
            state=state,
            start_token=from_token,
            end_token=next_token,
        )

    async def _shutdown_and_purge_room(
        self,
        task: ScheduledTask,
    ) -> tuple[TaskStatus, JsonMapping | None, str | None]:
        """
        Scheduler action to shutdown and purge a room.
        """
        if task.resource_id is None or task.params is None:
            raise Exception(
                "No room id and/or no parameters passed to shutdown_and_purge_room task"
            )

        room_id = task.resource_id

        async def update_result(result: JsonMapping | None) -> None:
            await self._task_scheduler.update_task(task.id, result=result)

        shutdown_result = (
            cast(ShutdownRoomResponse, task.result) if task.result else None
        )

        shutdown_result = await self._room_shutdown_handler.shutdown_room(
            room_id,
            cast(ShutdownRoomParams, task.params),
            shutdown_result,
            update_result,
        )

        if task.params.get("purge", False):
            await self.purge_room(
                room_id,
                task.params.get("force_purge", False),
            )

        return (TaskStatus.COMPLETE, shutdown_result, None)

    async def start_shutdown_and_purge_room(
        self,
        room_id: str,
        shutdown_params: ShutdownRoomParams,
    ) -> str:
        """Start off shut down and purge on a room.

        Args:
            room_id: The ID of the room to shut down.
            shutdown_params: parameters for the shutdown

        Returns:
            unique ID for this delete transaction.
        """
        if len(await self.get_delete_tasks_by_room(room_id, only_active=True)) > 0:
            raise SynapseError(400, "Purge already in progress for %s" % (room_id,))

        # This check is double to `RoomShutdownHandler.shutdown_room`
        # But here the requester get a direct response / error with HTTP request
        # and do not have to check the purge status
        new_room_user_id = shutdown_params["new_room_user_id"]
        if new_room_user_id is not None:
            if not self.hs.is_mine_id(new_room_user_id):
                raise SynapseError(
                    400, "User must be our own: %s" % (new_room_user_id,)
                )

        delete_id = await self._task_scheduler.schedule_task(
            SHUTDOWN_AND_PURGE_ROOM_ACTION_NAME,
            resource_id=room_id,
            params=shutdown_params,
        )

        # we log the delete_id here so that it can be tied back to the
        # request id in the log lines.
        logger.info(
            "starting shutdown room_id %s with delete_id %s",
            room_id,
            delete_id,
        )

        return delete_id
