# Copyright 2016 OpenMarket Ltd
# Copyright 2021 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 typing import (
    TYPE_CHECKING,
    Collection,
    Dict,
    Iterable,
    List,
    Optional,
    Set,
    Tuple,
    cast,
)

from synapse.logging import issue9533_logger
from synapse.logging.opentracing import log_kv, set_tag, trace
from synapse.replication.tcp.streams import ToDeviceStream
from synapse.storage._base import SQLBaseStore, db_to_json
from synapse.storage.database import (
    DatabasePool,
    LoggingDatabaseConnection,
    LoggingTransaction,
    make_in_list_sql_clause,
)
from synapse.storage.engines import PostgresEngine
from synapse.storage.util.id_generators import (
    AbstractStreamIdGenerator,
    MultiWriterIdGenerator,
    StreamIdGenerator,
)
from synapse.types import JsonDict
from synapse.util import json_encoder
from synapse.util.caches.expiringcache import ExpiringCache
from synapse.util.caches.stream_change_cache import StreamChangeCache

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)


class DeviceInboxWorkerStore(SQLBaseStore):
    def __init__(
        self,
        database: DatabasePool,
        db_conn: LoggingDatabaseConnection,
        hs: "HomeServer",
    ):
        super().__init__(database, db_conn, hs)

        self._instance_name = hs.get_instance_name()

        # Map of (user_id, device_id) to the last stream_id that has been
        # deleted up to. This is so that we can no op deletions.
        self._last_device_delete_cache: ExpiringCache[
            Tuple[str, Optional[str]], int
        ] = ExpiringCache(
            cache_name="last_device_delete_cache",
            clock=self._clock,
            max_len=10000,
            expiry_ms=30 * 60 * 1000,
        )

        if isinstance(database.engine, PostgresEngine):
            self._can_write_to_device = (
                self._instance_name in hs.config.worker.writers.to_device
            )

            self._device_inbox_id_gen: AbstractStreamIdGenerator = (
                MultiWriterIdGenerator(
                    db_conn=db_conn,
                    db=database,
                    stream_name="to_device",
                    instance_name=self._instance_name,
                    tables=[("device_inbox", "instance_name", "stream_id")],
                    sequence_name="device_inbox_sequence",
                    writers=hs.config.worker.writers.to_device,
                )
            )
        else:
            self._can_write_to_device = True
            self._device_inbox_id_gen = StreamIdGenerator(
                db_conn, "device_inbox", "stream_id"
            )

        max_device_inbox_id = self._device_inbox_id_gen.get_current_token()
        device_inbox_prefill, min_device_inbox_id = self.db_pool.get_cache_dict(
            db_conn,
            "device_inbox",
            entity_column="user_id",
            stream_column="stream_id",
            max_value=max_device_inbox_id,
            limit=1000,
        )
        self._device_inbox_stream_cache = StreamChangeCache(
            "DeviceInboxStreamChangeCache",
            min_device_inbox_id,
            prefilled_cache=device_inbox_prefill,
        )

        # The federation outbox and the local device inbox uses the same
        # stream_id generator.
        device_outbox_prefill, min_device_outbox_id = self.db_pool.get_cache_dict(
            db_conn,
            "device_federation_outbox",
            entity_column="destination",
            stream_column="stream_id",
            max_value=max_device_inbox_id,
            limit=1000,
        )
        self._device_federation_outbox_stream_cache = StreamChangeCache(
            "DeviceFederationOutboxStreamChangeCache",
            min_device_outbox_id,
            prefilled_cache=device_outbox_prefill,
        )

    def process_replication_rows(
        self,
        stream_name: str,
        instance_name: str,
        token: int,
        rows: Iterable[ToDeviceStream.ToDeviceStreamRow],
    ) -> None:
        if stream_name == ToDeviceStream.NAME:
            # If replication is happening than postgres must be being used.
            assert isinstance(self._device_inbox_id_gen, MultiWriterIdGenerator)
            self._device_inbox_id_gen.advance(instance_name, token)
            for row in rows:
                if row.entity.startswith("@"):
                    self._device_inbox_stream_cache.entity_has_changed(
                        row.entity, token
                    )
                else:
                    self._device_federation_outbox_stream_cache.entity_has_changed(
                        row.entity, token
                    )
        return super().process_replication_rows(stream_name, instance_name, token, rows)

    def get_to_device_stream_token(self) -> int:
        return self._device_inbox_id_gen.get_current_token()

    async def get_messages_for_user_devices(
        self,
        user_ids: Collection[str],
        from_stream_id: int,
        to_stream_id: int,
    ) -> Dict[Tuple[str, str], List[JsonDict]]:
        """
        Retrieve to-device messages for a given set of users.

        Only to-device messages with stream ids between the given boundaries
        (from < X <= to) are returned.

        Args:
            user_ids: The users to retrieve to-device messages for.
            from_stream_id: The lower boundary of stream id to filter with (exclusive).
            to_stream_id: The upper boundary of stream id to filter with (inclusive).

        Returns:
            A dictionary of (user id, device id) -> list of to-device messages.
        """
        # We expect the stream ID returned by _get_device_messages to always
        # be to_stream_id. So, no need to return it from this function.
        (
            user_id_device_id_to_messages,
            last_processed_stream_id,
        ) = await self._get_device_messages(
            user_ids=user_ids,
            from_stream_id=from_stream_id,
            to_stream_id=to_stream_id,
        )

        assert (
            last_processed_stream_id == to_stream_id
        ), "Expected _get_device_messages to process all to-device messages up to `to_stream_id`"

        return user_id_device_id_to_messages

    async def get_messages_for_device(
        self,
        user_id: str,
        device_id: str,
        from_stream_id: int,
        to_stream_id: int,
        limit: int = 100,
    ) -> Tuple[List[JsonDict], int]:
        """
        Retrieve to-device messages for a single user device.

        Only to-device messages with stream ids between the given boundaries
        (from < X <= to) are returned.

        Args:
            user_id: The ID of the user to retrieve messages for.
            device_id: The ID of the device to retrieve to-device messages for.
            from_stream_id: The lower boundary of stream id to filter with (exclusive).
            to_stream_id: The upper boundary of stream id to filter with (inclusive).
            limit: A limit on the number of to-device messages returned.

        Returns:
            A tuple containing:
                * A list of to-device messages within the given stream id range intended for
                  the given user / device combo.
                * The last-processed stream ID. Subsequent calls of this function with the
                  same device should pass this value as 'from_stream_id'.
        """
        (
            user_id_device_id_to_messages,
            last_processed_stream_id,
        ) = await self._get_device_messages(
            user_ids=[user_id],
            device_id=device_id,
            from_stream_id=from_stream_id,
            to_stream_id=to_stream_id,
            limit=limit,
        )

        if not user_id_device_id_to_messages:
            # There were no messages!
            return [], to_stream_id

        # Extract the messages, no need to return the user and device ID again
        to_device_messages = user_id_device_id_to_messages.get((user_id, device_id), [])

        return to_device_messages, last_processed_stream_id

    async def _get_device_messages(
        self,
        user_ids: Collection[str],
        from_stream_id: int,
        to_stream_id: int,
        device_id: Optional[str] = None,
        limit: Optional[int] = None,
    ) -> Tuple[Dict[Tuple[str, str], List[JsonDict]], int]:
        """
        Retrieve pending to-device messages for a collection of user devices.

        Only to-device messages with stream ids between the given boundaries
        (from < X <= to) are returned.

        Note that a stream ID can be shared by multiple copies of the same message with
        different recipient devices. Stream IDs are only unique in the context of a single
        user ID / device ID pair. Thus, applying a limit (of messages to return) when working
        with a sliding window of stream IDs is only possible when querying messages of a
        single user device.

        Finally, note that device IDs are not unique across users.

        Args:
            user_ids: The user IDs to filter device messages by.
            from_stream_id: The lower boundary of stream id to filter with (exclusive).
            to_stream_id: The upper boundary of stream id to filter with (inclusive).
            device_id: A device ID to query to-device messages for. If not provided, to-device
                messages from all device IDs for the given user IDs will be queried. May not be
                provided if `user_ids` contains more than one entry.
            limit: The maximum number of to-device messages to return. Can only be used when
                passing a single user ID / device ID tuple.

        Returns:
            A tuple containing:
                * A dict of (user_id, device_id) -> list of to-device messages
                * The last-processed stream ID. If this is less than `to_stream_id`, then
                    there may be more messages to retrieve. If `limit` is not set, then this
                    is always equal to 'to_stream_id'.
        """
        if not user_ids:
            logger.warning("No users provided upon querying for device IDs")
            return {}, to_stream_id

        # Prevent a query for one user's device also retrieving another user's device with
        # the same device ID (device IDs are not unique across users).
        if len(user_ids) > 1 and device_id is not None:
            raise AssertionError(
                "Programming error: 'device_id' cannot be supplied to "
                "_get_device_messages when >1 user_id has been provided"
            )

        # A limit can only be applied when querying for a single user ID / device ID tuple.
        # See the docstring of this function for more details.
        if limit is not None and device_id is None:
            raise AssertionError(
                "Programming error: _get_device_messages was passed 'limit' "
                "without a specific user_id/device_id"
            )

        user_ids_to_query: Set[str] = set()
        device_ids_to_query: Set[str] = set()

        # Note that a device ID could be an empty str
        if device_id is not None:
            # If a device ID was passed, use it to filter results.
            # Otherwise, device IDs will be derived from the given collection of user IDs.
            device_ids_to_query.add(device_id)

        # Determine which users have devices with pending messages
        for user_id in user_ids:
            if self._device_inbox_stream_cache.has_entity_changed(
                user_id, from_stream_id
            ):
                # This user has new messages sent to them. Query messages for them
                user_ids_to_query.add(user_id)

        if not user_ids_to_query:
            return {}, to_stream_id

        def get_device_messages_txn(
            txn: LoggingTransaction,
        ) -> Tuple[Dict[Tuple[str, str], List[JsonDict]], int]:
            # Build a query to select messages from any of the given devices that
            # are between the given stream id bounds.

            # If a list of device IDs was not provided, retrieve all devices IDs
            # for the given users. We explicitly do not query hidden devices, as
            # hidden devices should not receive to-device messages.
            # Note that this is more efficient than just dropping `device_id` from the query,
            # since device_inbox has an index on `(user_id, device_id, stream_id)`
            if not device_ids_to_query:
                user_device_dicts = self.db_pool.simple_select_many_txn(
                    txn,
                    table="devices",
                    column="user_id",
                    iterable=user_ids_to_query,
                    keyvalues={"user_id": user_id, "hidden": False},
                    retcols=("device_id",),
                )

                device_ids_to_query.update(
                    {row["device_id"] for row in user_device_dicts}
                )

            if not device_ids_to_query:
                # We've ended up with no devices to query.
                return {}, to_stream_id

            # We include both user IDs and device IDs in this query, as we have an index
            # (device_inbox_user_stream_id) for them.
            user_id_many_clause_sql, user_id_many_clause_args = make_in_list_sql_clause(
                self.database_engine, "user_id", user_ids_to_query
            )
            (
                device_id_many_clause_sql,
                device_id_many_clause_args,
            ) = make_in_list_sql_clause(
                self.database_engine, "device_id", device_ids_to_query
            )

            sql = f"""
                SELECT stream_id, user_id, device_id, message_json FROM device_inbox
                WHERE {user_id_many_clause_sql}
                AND {device_id_many_clause_sql}
                AND ? < stream_id AND stream_id <= ?
                ORDER BY stream_id ASC
            """
            sql_args = (
                *user_id_many_clause_args,
                *device_id_many_clause_args,
                from_stream_id,
                to_stream_id,
            )

            # If a limit was provided, limit the data retrieved from the database
            if limit is not None:
                sql += "LIMIT ?"
                sql_args += (limit,)

            txn.execute(sql, sql_args)

            # Create and fill a dictionary of (user ID, device ID) -> list of messages
            # intended for each device.
            last_processed_stream_pos = to_stream_id
            recipient_device_to_messages: Dict[Tuple[str, str], List[JsonDict]] = {}
            rowcount = 0
            for row in txn:
                rowcount += 1

                last_processed_stream_pos = row[0]
                recipient_user_id = row[1]
                recipient_device_id = row[2]
                message_dict = db_to_json(row[3])

                # Store the device details
                recipient_device_to_messages.setdefault(
                    (recipient_user_id, recipient_device_id), []
                ).append(message_dict)

            if limit is not None and rowcount == limit:
                # We ended up bumping up against the message limit. There may be more messages
                # to retrieve. Return what we have, as well as the last stream position that
                # was processed.
                #
                # The caller is expected to set this as the lower (exclusive) bound
                # for the next query of this device.
                return recipient_device_to_messages, last_processed_stream_pos

            # The limit was not reached, thus we know that recipient_device_to_messages
            # contains all to-device messages for the given device and stream id range.
            #
            # We return to_stream_id, which the caller should then provide as the lower
            # (exclusive) bound on the next query of this device.
            return recipient_device_to_messages, to_stream_id

        return await self.db_pool.runInteraction(
            "get_device_messages", get_device_messages_txn
        )

    @trace
    async def delete_messages_for_device(
        self, user_id: str, device_id: Optional[str], up_to_stream_id: int
    ) -> int:
        """
        Args:
            user_id: The recipient user_id.
            device_id: The recipient device_id.
            up_to_stream_id: Where to delete messages up to.

        Returns:
            The number of messages deleted.
        """
        # If we have cached the last stream id we've deleted up to, we can
        # check if there is likely to be anything that needs deleting
        last_deleted_stream_id = self._last_device_delete_cache.get(
            (user_id, device_id), None
        )

        set_tag("last_deleted_stream_id", last_deleted_stream_id)

        if last_deleted_stream_id:
            has_changed = self._device_inbox_stream_cache.has_entity_changed(
                user_id, last_deleted_stream_id
            )
            if not has_changed:
                log_kv({"message": "No changes in cache since last check"})
                return 0

        def delete_messages_for_device_txn(txn: LoggingTransaction) -> int:
            sql = (
                "DELETE FROM device_inbox"
                " WHERE user_id = ? AND device_id = ?"
                " AND stream_id <= ?"
            )
            txn.execute(sql, (user_id, device_id, up_to_stream_id))
            return txn.rowcount

        count = await self.db_pool.runInteraction(
            "delete_messages_for_device", delete_messages_for_device_txn
        )

        log_kv({"message": f"deleted {count} messages for device", "count": count})

        # Update the cache, ensuring that we only ever increase the value
        updated_last_deleted_stream_id = self._last_device_delete_cache.get(
            (user_id, device_id), 0
        )
        self._last_device_delete_cache[(user_id, device_id)] = max(
            updated_last_deleted_stream_id, up_to_stream_id
        )

        return count

    @trace
    async def get_new_device_msgs_for_remote(
        self, destination: str, last_stream_id: int, current_stream_id: int, limit: int
    ) -> Tuple[List[JsonDict], int]:
        """
        Args:
            destination: The name of the remote server.
            last_stream_id: The last position of the device message stream
                that the server sent up to.
            current_stream_id: The current position of the device message stream.
        Returns:
            A list of messages for the device and where in the stream the messages got to.
        """

        set_tag("destination", destination)
        set_tag("last_stream_id", last_stream_id)
        set_tag("current_stream_id", current_stream_id)
        set_tag("limit", limit)

        has_changed = self._device_federation_outbox_stream_cache.has_entity_changed(
            destination, last_stream_id
        )
        if not has_changed or last_stream_id == current_stream_id:
            log_kv({"message": "No new messages in stream"})
            return [], current_stream_id

        if limit <= 0:
            # This can happen if we run out of room for EDUs in the transaction.
            return [], last_stream_id

        @trace
        def get_new_messages_for_remote_destination_txn(
            txn: LoggingTransaction,
        ) -> Tuple[List[JsonDict], int]:
            sql = (
                "SELECT stream_id, messages_json FROM device_federation_outbox"
                " WHERE destination = ?"
                " AND ? < stream_id AND stream_id <= ?"
                " ORDER BY stream_id ASC"
                " LIMIT ?"
            )
            txn.execute(sql, (destination, last_stream_id, current_stream_id, limit))

            messages = []
            stream_pos = current_stream_id

            for row in txn:
                stream_pos = row[0]
                messages.append(db_to_json(row[1]))

            # If the limit was not reached we know that there's no more data for this
            # user/device pair up to current_stream_id.
            if len(messages) < limit:
                log_kv({"message": "Set stream position to current position"})
                stream_pos = current_stream_id

            return messages, stream_pos

        return await self.db_pool.runInteraction(
            "get_new_device_msgs_for_remote",
            get_new_messages_for_remote_destination_txn,
        )

    @trace
    async def delete_device_msgs_for_remote(
        self, destination: str, up_to_stream_id: int
    ) -> None:
        """Used to delete messages when the remote destination acknowledges
        their receipt.

        Args:
            destination: The destination server_name
            up_to_stream_id: Where to delete messages up to.
        """

        def delete_messages_for_remote_destination_txn(txn: LoggingTransaction) -> None:
            sql = (
                "DELETE FROM device_federation_outbox"
                " WHERE destination = ?"
                " AND stream_id <= ?"
            )
            txn.execute(sql, (destination, up_to_stream_id))

        await self.db_pool.runInteraction(
            "delete_device_msgs_for_remote", delete_messages_for_remote_destination_txn
        )

    async def get_all_new_device_messages(
        self, instance_name: str, last_id: int, current_id: int, limit: int
    ) -> Tuple[List[Tuple[int, tuple]], int, bool]:
        """Get updates for to device replication stream.

        Args:
            instance_name: The writer we want to fetch updates from. Unused
                here since there is only ever one writer.
            last_id: The token to fetch updates from. Exclusive.
            current_id: The token to fetch updates up to. Inclusive.
            limit: The requested limit for the number of rows to return. The
                function may return more or fewer rows.

        Returns:
            A tuple consisting of: the updates, a token to use to fetch
            subsequent updates, and whether we returned fewer rows than exists
            between the requested tokens due to the limit.

            The token returned can be used in a subsequent call to this
            function to get further updatees.

            The updates are a list of 2-tuples of stream ID and the row data
        """

        if last_id == current_id:
            return [], current_id, False

        def get_all_new_device_messages_txn(
            txn: LoggingTransaction,
        ) -> Tuple[List[Tuple[int, tuple]], int, bool]:
            # We limit like this as we might have multiple rows per stream_id, and
            # we want to make sure we always get all entries for any stream_id
            # we return.
            upper_pos = min(current_id, last_id + limit)
            sql = (
                "SELECT max(stream_id), user_id"
                " FROM device_inbox"
                " WHERE ? < stream_id AND stream_id <= ?"
                " GROUP BY user_id"
            )
            txn.execute(sql, (last_id, upper_pos))
            updates = [(row[0], row[1:]) for row in txn]

            sql = (
                "SELECT max(stream_id), destination"
                " FROM device_federation_outbox"
                " WHERE ? < stream_id AND stream_id <= ?"
                " GROUP BY destination"
            )
            txn.execute(sql, (last_id, upper_pos))
            updates.extend((row[0], row[1:]) for row in txn)

            # Order by ascending stream ordering
            updates.sort()

            limited = False
            upto_token = current_id
            if len(updates) >= limit:
                upto_token = updates[-1][0]
                limited = True

            return updates, upto_token, limited

        return await self.db_pool.runInteraction(
            "get_all_new_device_messages", get_all_new_device_messages_txn
        )

    @trace
    async def add_messages_to_device_inbox(
        self,
        local_messages_by_user_then_device: Dict[str, Dict[str, JsonDict]],
        remote_messages_by_destination: Dict[str, JsonDict],
    ) -> int:
        """Used to send messages from this server.

        Args:
            local_messages_by_user_then_device:
                Dictionary of recipient user_id to recipient device_id to message.
            remote_messages_by_destination:
                Dictionary of destination server_name to the EDU JSON to send.

        Returns:
            The new stream_id.
        """

        assert self._can_write_to_device

        def add_messages_txn(
            txn: LoggingTransaction, now_ms: int, stream_id: int
        ) -> None:
            # Add the local messages directly to the local inbox.
            self._add_messages_to_local_device_inbox_txn(
                txn, stream_id, local_messages_by_user_then_device
            )

            # Add the remote messages to the federation outbox.
            # We'll send them to a remote server when we next send a
            # federation transaction to that destination.
            self.db_pool.simple_insert_many_txn(
                txn,
                table="device_federation_outbox",
                keys=(
                    "destination",
                    "stream_id",
                    "queued_ts",
                    "messages_json",
                    "instance_name",
                ),
                values=[
                    (
                        destination,
                        stream_id,
                        now_ms,
                        json_encoder.encode(edu),
                        self._instance_name,
                    )
                    for destination, edu in remote_messages_by_destination.items()
                ],
            )

            if remote_messages_by_destination:
                issue9533_logger.debug(
                    "Queued outgoing to-device messages with stream_id %i for %s",
                    stream_id,
                    list(remote_messages_by_destination.keys()),
                )

        async with self._device_inbox_id_gen.get_next() as stream_id:
            now_ms = self._clock.time_msec()
            await self.db_pool.runInteraction(
                "add_messages_to_device_inbox", add_messages_txn, now_ms, stream_id
            )
            for user_id in local_messages_by_user_then_device.keys():
                self._device_inbox_stream_cache.entity_has_changed(user_id, stream_id)
            for destination in remote_messages_by_destination.keys():
                self._device_federation_outbox_stream_cache.entity_has_changed(
                    destination, stream_id
                )

        return self._device_inbox_id_gen.get_current_token()

    async def add_messages_from_remote_to_device_inbox(
        self,
        origin: str,
        message_id: str,
        local_messages_by_user_then_device: Dict[str, Dict[str, JsonDict]],
    ) -> int:
        assert self._can_write_to_device

        def add_messages_txn(
            txn: LoggingTransaction, now_ms: int, stream_id: int
        ) -> None:
            # Check if we've already inserted a matching message_id for that
            # origin. This can happen if the origin doesn't receive our
            # acknowledgement from the first time we received the message.
            already_inserted = self.db_pool.simple_select_one_txn(
                txn,
                table="device_federation_inbox",
                keyvalues={"origin": origin, "message_id": message_id},
                retcols=("message_id",),
                allow_none=True,
            )
            if already_inserted is not None:
                return

            # Add an entry for this message_id so that we know we've processed
            # it.
            self.db_pool.simple_insert_txn(
                txn,
                table="device_federation_inbox",
                values={
                    "origin": origin,
                    "message_id": message_id,
                    "received_ts": now_ms,
                },
            )

            # Add the messages to the appropriate local device inboxes so that
            # they'll be sent to the devices when they next sync.
            self._add_messages_to_local_device_inbox_txn(
                txn, stream_id, local_messages_by_user_then_device
            )

        async with self._device_inbox_id_gen.get_next() as stream_id:
            now_ms = self._clock.time_msec()
            await self.db_pool.runInteraction(
                "add_messages_from_remote_to_device_inbox",
                add_messages_txn,
                now_ms,
                stream_id,
            )
            for user_id in local_messages_by_user_then_device.keys():
                self._device_inbox_stream_cache.entity_has_changed(user_id, stream_id)

        return stream_id

    def _add_messages_to_local_device_inbox_txn(
        self,
        txn: LoggingTransaction,
        stream_id: int,
        messages_by_user_then_device: Dict[str, Dict[str, JsonDict]],
    ) -> None:
        assert self._can_write_to_device

        local_by_user_then_device = {}
        for user_id, messages_by_device in messages_by_user_then_device.items():
            messages_json_for_user = {}
            devices = list(messages_by_device.keys())
            if len(devices) == 1 and devices[0] == "*":
                # Handle wildcard device_ids.
                # We exclude hidden devices (such as cross-signing keys) here as they are
                # not expected to receive to-device messages.
                devices = self.db_pool.simple_select_onecol_txn(
                    txn,
                    table="devices",
                    keyvalues={"user_id": user_id, "hidden": False},
                    retcol="device_id",
                )

                message_json = json_encoder.encode(messages_by_device["*"])
                for device_id in devices:
                    # Add the message for all devices for this user on this
                    # server.
                    messages_json_for_user[device_id] = message_json
            else:
                if not devices:
                    continue

                # We exclude hidden devices (such as cross-signing keys) here as they are
                # not expected to receive to-device messages.
                rows = self.db_pool.simple_select_many_txn(
                    txn,
                    table="devices",
                    keyvalues={"user_id": user_id, "hidden": False},
                    column="device_id",
                    iterable=devices,
                    retcols=("device_id",),
                )

                for row in rows:
                    # Only insert into the local inbox if the device exists on
                    # this server
                    device_id = row["device_id"]
                    message_json = json_encoder.encode(messages_by_device[device_id])
                    messages_json_for_user[device_id] = message_json

            if messages_json_for_user:
                local_by_user_then_device[user_id] = messages_json_for_user

        if not local_by_user_then_device:
            return

        self.db_pool.simple_insert_many_txn(
            txn,
            table="device_inbox",
            keys=("user_id", "device_id", "stream_id", "message_json", "instance_name"),
            values=[
                (user_id, device_id, stream_id, message_json, self._instance_name)
                for user_id, messages_by_device in local_by_user_then_device.items()
                for device_id, message_json in messages_by_device.items()
            ],
        )

        issue9533_logger.debug(
            "Stored to-device messages with stream_id %i for %s",
            stream_id,
            [
                (user_id, device_id)
                for (user_id, messages_by_device) in local_by_user_then_device.items()
                for device_id in messages_by_device.keys()
            ],
        )


class DeviceInboxBackgroundUpdateStore(SQLBaseStore):
    DEVICE_INBOX_STREAM_ID = "device_inbox_stream_drop"
    REMOVE_DELETED_DEVICES = "remove_deleted_devices_from_device_inbox"
    REMOVE_HIDDEN_DEVICES = "remove_hidden_devices_from_device_inbox"
    REMOVE_DEAD_DEVICES_FROM_INBOX = "remove_dead_devices_from_device_inbox"

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

        self.db_pool.updates.register_background_index_update(
            "device_inbox_stream_index",
            index_name="device_inbox_stream_id_user_id",
            table="device_inbox",
            columns=["stream_id", "user_id"],
        )

        self.db_pool.updates.register_background_update_handler(
            self.DEVICE_INBOX_STREAM_ID, self._background_drop_index_device_inbox
        )

        # Used to be a background update that deletes all device_inboxes for deleted
        # devices.
        self.db_pool.updates.register_noop_background_update(
            self.REMOVE_DELETED_DEVICES
        )
        # Used to be a background update that deletes all device_inboxes for hidden
        # devices.
        self.db_pool.updates.register_noop_background_update(self.REMOVE_HIDDEN_DEVICES)

        self.db_pool.updates.register_background_update_handler(
            self.REMOVE_DEAD_DEVICES_FROM_INBOX,
            self._remove_dead_devices_from_device_inbox,
        )

    async def _background_drop_index_device_inbox(
        self, progress: JsonDict, batch_size: int
    ) -> int:
        def reindex_txn(conn: LoggingDatabaseConnection) -> None:
            txn = conn.cursor()
            txn.execute("DROP INDEX IF EXISTS device_inbox_stream_id")
            txn.close()

        await self.db_pool.runWithConnection(reindex_txn)

        await self.db_pool.updates._end_background_update(self.DEVICE_INBOX_STREAM_ID)

        return 1

    async def _remove_dead_devices_from_device_inbox(
        self,
        progress: JsonDict,
        batch_size: int,
    ) -> int:
        """A background update to remove devices that were either deleted or hidden from
        the device_inbox table.

        Args:
            progress: The update's progress dict.
            batch_size: The batch size for this update.

        Returns:
            The number of rows deleted.
        """

        def _remove_dead_devices_from_device_inbox_txn(
            txn: LoggingTransaction,
        ) -> Tuple[int, bool]:

            if "max_stream_id" in progress:
                max_stream_id = progress["max_stream_id"]
            else:
                txn.execute("SELECT max(stream_id) FROM device_inbox")
                # There's a type mismatch here between how we want to type the row and
                # what fetchone says it returns, but we silence it because we know that
                # res can't be None.
                res = cast(Tuple[Optional[int]], txn.fetchone())
                if res[0] is None:
                    # this can only happen if the `device_inbox` table is empty, in which
                    # case we have no work to do.
                    return 0, True
                else:
                    max_stream_id = res[0]

            start = progress.get("stream_id", 0)
            stop = start + batch_size

            # delete rows in `device_inbox` which do *not* correspond to a known,
            # unhidden device.
            sql = """
                DELETE FROM device_inbox
                WHERE
                    stream_id >= ? AND stream_id < ?
                    AND NOT EXISTS (
                        SELECT * FROM devices d
                        WHERE
                            d.device_id=device_inbox.device_id
                            AND d.user_id=device_inbox.user_id
                            AND NOT hidden
                    )
                """

            txn.execute(sql, (start, stop))

            self.db_pool.updates._background_update_progress_txn(
                txn,
                self.REMOVE_DEAD_DEVICES_FROM_INBOX,
                {
                    "stream_id": stop,
                    "max_stream_id": max_stream_id,
                },
            )

            return stop > max_stream_id

        finished = await self.db_pool.runInteraction(
            "_remove_devices_from_device_inbox_txn",
            _remove_dead_devices_from_device_inbox_txn,
        )

        if finished:
            await self.db_pool.updates._end_background_update(
                self.REMOVE_DEAD_DEVICES_FROM_INBOX,
            )

        return batch_size


class DeviceInboxStore(DeviceInboxWorkerStore, DeviceInboxBackgroundUpdateStore):
    pass
