#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright 2018-2021 The Matrix.org Foundation C.I.C.
# 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 json
import logging
from typing import cast

from immutabledict import immutabledict

from twisted.internet.testing import MemoryReactor

from synapse.api.constants import EventTypes, Membership
from synapse.api.room_versions import RoomVersions
from synapse.events import EventBase
from synapse.logging.context import LoggingContext
from synapse.server import HomeServer
from synapse.types import JsonDict, RoomID, StateMap, UserID
from synapse.types.state import StateFilter
from synapse.util.clock import Clock
from synapse.util.stringutils import random_string

from tests.unittest import HomeserverTestCase

logger = logging.getLogger(__name__)


class StateStoreTestCase(HomeserverTestCase):
    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
        self.store = hs.get_datastores().main
        self.storage = hs.get_storage_controllers()
        self.state_datastore = self.storage.state.stores.state
        self.event_builder_factory = hs.get_event_builder_factory()
        self.event_creation_handler = hs.get_event_creation_handler()

        self.u_alice = UserID.from_string("@alice:test")
        self.u_bob = UserID.from_string("@bob:test")

        self.room = RoomID.from_string("!abc123:test")

        self.get_success(
            self.store.store_room(
                self.room.to_string(),
                room_creator_user_id="@creator:text",
                is_public=True,
                room_version=RoomVersions.V1,
            )
        )

    def inject_state_event(
        self, room: RoomID, sender: UserID, typ: str, state_key: str, content: JsonDict
    ) -> EventBase:
        builder = self.event_builder_factory.for_room_version(
            RoomVersions.V1,
            {
                "type": typ,
                "sender": sender.to_string(),
                "state_key": state_key,
                "room_id": room.to_string(),
                "content": content,
            },
        )

        event, unpersisted_context = self.get_success(
            self.event_creation_handler.create_new_client_event(builder)
        )

        context = self.get_success(unpersisted_context.persist(event))

        assert self.storage.persistence is not None
        self.get_success(self.storage.persistence.persist_event(event, context))

        return event

    def assertStateMapEqual(
        self, s1: StateMap[EventBase], s2: StateMap[EventBase]
    ) -> None:
        for t in s1:
            # just compare event IDs for simplicity
            self.assertEqual(s1[t].event_id, s2[t].event_id)
        self.assertEqual(len(s1), len(s2))

    def test_get_state_groups_ids(self) -> None:
        e1 = self.inject_state_event(self.room, self.u_alice, EventTypes.Create, "", {})
        e2 = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Name, "", {"name": "test room"}
        )

        state_group_map = self.get_success(
            self.storage.state.get_state_groups_ids(
                self.room.to_string(), [e2.event_id]
            )
        )
        self.assertEqual(len(state_group_map), 1)
        state_map = list(state_group_map.values())[0]
        self.assertDictEqual(
            state_map,
            {(EventTypes.Create, ""): e1.event_id, (EventTypes.Name, ""): e2.event_id},
        )

    def test_get_state_groups(self) -> None:
        e1 = self.inject_state_event(self.room, self.u_alice, EventTypes.Create, "", {})
        e2 = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Name, "", {"name": "test room"}
        )

        state_group_map = self.get_success(
            self.storage.state.get_state_groups(self.room.to_string(), [e2.event_id])
        )
        self.assertEqual(len(state_group_map), 1)
        state_list = list(state_group_map.values())[0]

        self.assertEqual({ev.event_id for ev in state_list}, {e1.event_id, e2.event_id})

    def test_get_state_for_event(self) -> None:
        # this defaults to a linear DAG as each new injection defaults to whatever
        # forward extremities are currently in the DB for this room.
        e1 = self.inject_state_event(self.room, self.u_alice, EventTypes.Create, "", {})
        e2 = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Name, "", {"name": "test room"}
        )
        e3 = self.inject_state_event(
            self.room,
            self.u_alice,
            EventTypes.Member,
            self.u_alice.to_string(),
            {"membership": Membership.JOIN},
        )
        e4 = self.inject_state_event(
            self.room,
            self.u_bob,
            EventTypes.Member,
            self.u_bob.to_string(),
            {"membership": Membership.JOIN},
        )
        e5 = self.inject_state_event(
            self.room,
            self.u_bob,
            EventTypes.Member,
            self.u_bob.to_string(),
            {"membership": Membership.LEAVE},
        )

        # check we get the full state as of the final event
        state = self.get_success(self.storage.state.get_state_for_event(e5.event_id))

        self.assertIsNotNone(e4)

        self.assertStateMapEqual(
            {
                (e1.type, e1.state_key): e1,
                (e2.type, e2.state_key): e2,
                (e3.type, e3.state_key): e3,
                # e4 is overwritten by e5
                (e5.type, e5.state_key): e5,
            },
            state,
        )

        # check we can filter to the m.room.name event (with a '' state key)
        state = self.get_success(
            self.storage.state.get_state_for_event(
                e5.event_id, StateFilter.from_types([(EventTypes.Name, "")])
            )
        )

        self.assertStateMapEqual({(e2.type, e2.state_key): e2}, state)

        # check we can filter to the m.room.name event (with a wildcard None state key)
        state = self.get_success(
            self.storage.state.get_state_for_event(
                e5.event_id, StateFilter.from_types([(EventTypes.Name, None)])
            )
        )

        self.assertStateMapEqual({(e2.type, e2.state_key): e2}, state)

        # check we can grab the m.room.member events (with a wildcard None state key)
        state = self.get_success(
            self.storage.state.get_state_for_event(
                e5.event_id, StateFilter.from_types([(EventTypes.Member, None)])
            )
        )

        self.assertStateMapEqual(
            {(e3.type, e3.state_key): e3, (e5.type, e5.state_key): e5}, state
        )

        # check we can grab a specific room member without filtering out the
        # other event types
        state = self.get_success(
            self.storage.state.get_state_for_event(
                e5.event_id,
                state_filter=StateFilter(
                    types=immutabledict(
                        {EventTypes.Member: frozenset({self.u_alice.to_string()})}
                    ),
                    include_others=True,
                ),
            )
        )

        self.assertStateMapEqual(
            {
                (e1.type, e1.state_key): e1,
                (e2.type, e2.state_key): e2,
                (e3.type, e3.state_key): e3,
            },
            state,
        )

        # check that we can grab everything except members
        state = self.get_success(
            self.storage.state.get_state_for_event(
                e5.event_id,
                state_filter=StateFilter(
                    types=immutabledict({EventTypes.Member: frozenset()}),
                    include_others=True,
                ),
            )
        )

        self.assertStateMapEqual(
            {(e1.type, e1.state_key): e1, (e2.type, e2.state_key): e2}, state
        )

        #######################################################
        # _get_state_for_group_using_cache tests against a full cache
        #######################################################

        room_id = self.room.to_string()
        group_ids = self.get_success(
            self.storage.state.get_state_groups_ids(room_id, [e5.event_id])
        )
        group = list(group_ids.keys())[0]

        # test _get_state_for_group_using_cache correctly filters out members
        # with types=[]
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset()}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual(
            {
                (e1.type, e1.state_key): e1.event_id,
                (e2.type, e2.state_key): e2.event_id,
            },
            state_dict,
        )

        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset()}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual({}, state_dict)

        # test _get_state_for_group_using_cache correctly filters in members
        # with wildcard types
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: None}), include_others=True
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual(
            {
                (e1.type, e1.state_key): e1.event_id,
                (e2.type, e2.state_key): e2.event_id,
            },
            state_dict,
        )

        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: None}), include_others=True
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual(
            {
                (e3.type, e3.state_key): e3.event_id,
                # e4 is overwritten by e5
                (e5.type, e5.state_key): e5.event_id,
            },
            state_dict,
        )

        # test _get_state_for_group_using_cache correctly filters in members
        # with specific types
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset({e5.state_key})}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual(
            {
                (e1.type, e1.state_key): e1.event_id,
                (e2.type, e2.state_key): e2.event_id,
            },
            state_dict,
        )

        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset({e5.state_key})}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual({(e5.type, e5.state_key): e5.event_id}, state_dict)

        # test _get_state_for_group_using_cache correctly filters in members
        # with specific types
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset({e5.state_key})}),
                include_others=False,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual({(e5.type, e5.state_key): e5.event_id}, state_dict)

        #######################################################
        # deliberately remove e2 (room name) from the _state_group_cache

        cache_entry = self.state_datastore._state_group_cache.get(group)
        state_dict_ids = cache_entry.value

        self.assertEqual(cache_entry.full, True)
        self.assertEqual(cache_entry.known_absent, set())
        self.assertDictEqual(
            state_dict_ids,
            {
                (e1.type, e1.state_key): e1.event_id,
                (e2.type, e2.state_key): e2.event_id,
            },
        )

        state_dict_ids.pop((e2.type, e2.state_key))
        self.state_datastore._state_group_cache.invalidate(group)
        self.state_datastore._state_group_cache.update(
            sequence=self.state_datastore._state_group_cache.sequence,
            key=group,
            value=state_dict_ids,
            # list fetched keys so it knows it's partial
            fetched_keys=((e1.type, e1.state_key),),
        )

        cache_entry = self.state_datastore._state_group_cache.get(group)
        state_dict_ids = cache_entry.value

        self.assertEqual(cache_entry.full, False)
        self.assertEqual(cache_entry.known_absent, set())
        self.assertDictEqual(state_dict_ids, {})

        ############################################
        # test that things work with a partial cache

        # test _get_state_for_group_using_cache correctly filters out members
        # with types=[]
        room_id = self.room.to_string()
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset()}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, False)
        self.assertDictEqual({}, state_dict)

        room_id = self.room.to_string()
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset()}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual({}, state_dict)

        # test _get_state_for_group_using_cache correctly filters in members
        # wildcard types
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: None}), include_others=True
            ),
        )

        self.assertEqual(is_all, False)
        self.assertDictEqual({}, state_dict)

        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: None}), include_others=True
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual(
            {
                (e3.type, e3.state_key): e3.event_id,
                (e5.type, e5.state_key): e5.event_id,
            },
            state_dict,
        )

        # test _get_state_for_group_using_cache correctly filters in members
        # with specific types
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset({e5.state_key})}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, False)
        self.assertDictEqual({}, state_dict)

        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset({e5.state_key})}),
                include_others=True,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual({(e5.type, e5.state_key): e5.event_id}, state_dict)

        # test _get_state_for_group_using_cache correctly filters in members
        # with specific types
        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset({e5.state_key})}),
                include_others=False,
            ),
        )

        self.assertEqual(is_all, False)
        self.assertDictEqual({}, state_dict)

        state_dict, is_all = self.state_datastore._get_state_for_group_using_cache(
            self.state_datastore._state_group_members_cache,
            group,
            state_filter=StateFilter(
                types=immutabledict({EventTypes.Member: frozenset({e5.state_key})}),
                include_others=False,
            ),
        )

        self.assertEqual(is_all, True)
        self.assertDictEqual({(e5.type, e5.state_key): e5.event_id}, state_dict)

    def test_batched_state_group_storing(self) -> None:
        creation_event = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Create, "", {}
        )
        state_to_event = self.get_success(
            self.storage.state.get_state_groups(
                self.room.to_string(), [creation_event.event_id]
            )
        )
        current_state_group = list(state_to_event.keys())[0]

        # create some unpersisted events and event contexts to store against room
        events_and_context = []
        builder = self.event_builder_factory.for_room_version(
            RoomVersions.V1,
            {
                "type": EventTypes.Name,
                "sender": self.u_alice.to_string(),
                "state_key": "",
                "room_id": self.room.to_string(),
                "content": {"name": "first rename of room"},
            },
        )

        event1, unpersisted_context1 = self.get_success(
            self.event_creation_handler.create_new_client_event(builder)
        )
        events_and_context.append((event1, unpersisted_context1))

        builder2 = self.event_builder_factory.for_room_version(
            RoomVersions.V1,
            {
                "type": EventTypes.JoinRules,
                "sender": self.u_alice.to_string(),
                "state_key": "",
                "room_id": self.room.to_string(),
                "content": {"join_rule": "private"},
            },
        )

        event2, unpersisted_context2 = self.get_success(
            self.event_creation_handler.create_new_client_event(builder2)
        )
        events_and_context.append((event2, unpersisted_context2))

        builder3 = self.event_builder_factory.for_room_version(
            RoomVersions.V1,
            {
                "type": EventTypes.Message,
                "sender": self.u_alice.to_string(),
                "room_id": self.room.to_string(),
                "content": {"body": "hello from event 3", "msgtype": "m.text"},
            },
        )

        event3, unpersisted_context3 = self.get_success(
            self.event_creation_handler.create_new_client_event(builder3)
        )
        events_and_context.append((event3, unpersisted_context3))

        builder4 = self.event_builder_factory.for_room_version(
            RoomVersions.V1,
            {
                "type": EventTypes.JoinRules,
                "sender": self.u_alice.to_string(),
                "state_key": "",
                "room_id": self.room.to_string(),
                "content": {"join_rule": "public"},
            },
        )

        event4, unpersisted_context4 = self.get_success(
            self.event_creation_handler.create_new_client_event(builder4)
        )
        events_and_context.append((event4, unpersisted_context4))

        processed_events_and_context = self.get_success(
            self.hs.get_datastores().state.store_state_deltas_for_batched(
                events_and_context, self.room.to_string(), current_state_group
            )
        )

        # check that only state events are in state_groups, and all state events are in state_groups
        res = cast(
            list[tuple[str]],
            self.get_success(
                self.store.db_pool.simple_select_list(
                    table="state_groups",
                    keyvalues=None,
                    retcols=("event_id",),
                )
            ),
        )

        events = []
        for result in res:
            self.assertNotIn(event3.event_id, result)  # XXX
            events.append(result[0])

        for event, _ in processed_events_and_context:
            if event.is_state():
                self.assertIn(event.event_id, events)

        # check that each unique state has state group in state_groups_state and that the
        # type/state key is correct, and check that each state event's state group
        # has an entry and prev event in state_group_edges
        for event, context in processed_events_and_context:
            if event.is_state():
                state = cast(
                    list[tuple[str, str]],
                    self.get_success(
                        self.store.db_pool.simple_select_list(
                            table="state_groups_state",
                            keyvalues={"state_group": context.state_group_after_event},
                            retcols=("type", "state_key"),
                        )
                    ),
                )
                self.assertEqual(event.type, state[0][0])
                self.assertEqual(event.state_key, state[0][1])

                groups = cast(
                    list[tuple[str]],
                    self.get_success(
                        self.store.db_pool.simple_select_list(
                            table="state_group_edges",
                            keyvalues={"state_group": context.state_group_after_event},
                            retcols=("prev_state_group",),
                        )
                    ),
                )
                self.assertEqual(context.state_group_before_event, groups[0][0])

    def test_get_partial_filtered_current_state_ids_concrete(self) -> None:
        """A filter with no wildcards is served from the per-key cache, and the
        absence of a key is cached too."""
        room_id = self.room.to_string()

        create = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Create, "", {}
        )
        name = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Name, "", {"name": "test room"}
        )

        state_filter = StateFilter.from_types(
            [(EventTypes.Create, ""), (EventTypes.Name, ""), (EventTypes.Topic, "")]
        )

        state = self.get_success(
            self.store.get_partial_filtered_current_state_ids(room_id, state_filter)
        )

        self.assertEqual(
            dict(state),
            {
                (EventTypes.Create, ""): create.event_id,
                (EventTypes.Name, ""): name.event_id,
            },
        )

        # The room has no topic, and that fact is cached, so asking again does
        # not go back to the database.
        sentinel = object()
        cache = self.store._get_current_state_event_id.cache
        self.assertIsNone(
            cache.get_immediate((room_id, (EventTypes.Topic, "")), sentinel)
        )
        self.assertEqual(
            cache.get_immediate((room_id, (EventTypes.Name, "")), sentinel),
            name.event_id,
        )

    def test_get_partial_filtered_current_state_ids_invalidation(self) -> None:
        """Persisting a new state event invalidates the cached entries for the
        room."""
        room_id = self.room.to_string()

        self.inject_state_event(self.room, self.u_alice, EventTypes.Create, "", {})

        state_filter = StateFilter.from_types([(EventTypes.Name, "")])

        state = self.get_success(
            self.store.get_partial_filtered_current_state_ids(room_id, state_filter)
        )
        self.assertEqual(dict(state), {})

        name = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Name, "", {"name": "test room"}
        )

        state = self.get_success(
            self.store.get_partial_filtered_current_state_ids(room_id, state_filter)
        )
        self.assertEqual(dict(state), {(EventTypes.Name, ""): name.event_id})

        name2 = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Name, "", {"name": "renamed"}
        )

        state = self.get_success(
            self.store.get_partial_filtered_current_state_ids(room_id, state_filter)
        )
        self.assertEqual(dict(state), {(EventTypes.Name, ""): name2.event_id})

    def test_get_partial_filtered_current_state_ids_uses_full_cache(self) -> None:
        """Test that fetching a single state key from a room with a full cache
        hits the full cache and does not go to the database."""

        room_id = self.room.to_string()

        create = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Create, "", {}
        )
        name = self.inject_state_event(
            self.room, self.u_alice, EventTypes.Name, "", {"name": "test room"}
        )

        # prime the full cache
        state_filter = StateFilter.all()
        state = self.get_success(
            self.store.get_partial_filtered_current_state_ids(room_id, state_filter)
        )
        self.assertEqual(
            dict(state),
            {
                (EventTypes.Create, ""): create.event_id,
                (EventTypes.Name, ""): name.event_id,
            },
        )

        # now fetch a single key and check that it hits the full cache
        with LoggingContext(name="test", server_name=self.hs.hostname) as ctx:
            state_filter = StateFilter.from_types([(EventTypes.Name, "")])
            state = self.get_success(
                self.store.get_partial_filtered_current_state_ids(room_id, state_filter)
            )
            self.assertEqual(dict(state), {(EventTypes.Name, ""): name.event_id})
            self.assertEqual(ctx.get_resource_usage().db_txn_count, 0)


class CurrentStateDeltaStreamTestCase(HomeserverTestCase):
    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
        super().prepare(reactor, clock, hs)
        self.store = hs.get_datastores().main
        self.storage = hs.get_storage_controllers()
        self.state_datastore = self.storage.state.stores.state
        self.event_creation_handler = hs.get_event_creation_handler()
        self.event_builder_factory = hs.get_event_builder_factory()

        # Create a made-up room and a user.
        self.alice_user_id = UserID.from_string("@alice:test")
        self.room = RoomID.from_string("!abc1234:test")

        self.get_success(
            self.store.store_room(
                self.room.to_string(),
                room_creator_user_id="@creator:text",
                is_public=True,
                room_version=RoomVersions.V1,
            )
        )

    def inject_state_event(
        self, room: RoomID, sender: UserID, typ: str, state_key: str, content: JsonDict
    ) -> EventBase:
        builder = self.event_builder_factory.for_room_version(
            RoomVersions.V1,
            {
                "type": typ,
                "sender": sender.to_string(),
                "state_key": state_key,
                "room_id": room.to_string(),
                "content": content,
            },
        )

        event, unpersisted_context = self.get_success(
            self.event_creation_handler.create_new_client_event(builder)
        )

        context = self.get_success(unpersisted_context.persist(event))

        assert self.storage.persistence is not None
        self.get_success(self.storage.persistence.persist_event(event, context))

        return event

    def test_get_partial_current_state_deltas_limit(self) -> None:
        """
        Tests that `get_partial_current_state_deltas` actually returns `limit` rows.

        Regression test for https://github.com/element-hq/synapse/pull/18960.
        """
        # Inject a create event which other events can auth with.
        self.inject_state_event(
            self.room, self.alice_user_id, EventTypes.Create, "", {}
        )

        limit = 2

        # Make N*2 state changes in the room, resulting in 2N+1 total state
        # events (including the create event) in the room.
        for i in range(limit * 2):
            self.inject_state_event(
                self.room,
                self.alice_user_id,
                EventTypes.Name,
                "",
                {"name": f"rename #{i}"},
            )

        # Call the function under test. This must return <= `limit` rows.
        max_stream_id = self.store.get_room_max_stream_ordering()
        clipped_stream_id, deltas = self.get_success(
            self.store.get_partial_current_state_deltas(
                prev_stream_id=0,
                max_stream_id=max_stream_id,
                limit=limit,
            )
        )

        self.assertLessEqual(
            len(deltas), limit, f"Returned {len(deltas)} rows, expected at most {limit}"
        )

        # Advancing from the clipped point should eventually drain the remainder.
        # Make sure we make progress and don’t get stuck.
        if deltas:
            next_prev = clipped_stream_id
            next_clipped, next_deltas = self.get_success(
                self.store.get_partial_current_state_deltas(
                    prev_stream_id=next_prev, max_stream_id=max_stream_id, limit=limit
                )
            )
            self.assertNotEqual(
                next_clipped, clipped_stream_id, "Did not advance clipped_stream_id"
            )
            # Still should respect the limit.
            self.assertLessEqual(len(next_deltas), limit)

    def test_non_unique_stream_ids_in_current_state_delta_stream(self) -> None:
        """
        Tests that `get_partial_current_state_deltas` always returns entire
        groups of state deltas (grouped by `stream_id`), and never part of one.

        We check by passing a `limit` that to the function that, if followed
        blindly, would split a group of state deltas that share a `stream_id`.
        The test passes if that group is not returned at all (because doing so
        would overshoot the limit of returned state deltas).

        Regression test for https://github.com/element-hq/synapse/pull/18960.
        """
        # Inject a create event to start with.
        self.inject_state_event(
            self.room, self.alice_user_id, EventTypes.Create, "", {}
        )

        # Then inject one "real" m.room.name event. This will give us a stream_id that
        # we can create some more (fake) events with.
        self.inject_state_event(
            self.room,
            self.alice_user_id,
            EventTypes.Name,
            "",
            {"name": "rename #1"},
        )

        # Get the stream_id of the last-inserted event.
        max_stream_id = self.store.get_room_max_stream_ordering()

        # Make 3 more state changes in the room, resulting in 5 total state
        # events (including the create event, and the first name update) in
        # the room.
        #
        # All of these state deltas have the same `stream_id` as the original name event.
        # Do so by editing the table directly as that's the simplest way to have
        # all share the same `stream_id`.
        self.get_success(
            self.store.db_pool.simple_insert_many(
                "current_state_delta_stream",
                keys=(
                    "stream_id",
                    "room_id",
                    "type",
                    "state_key",
                    "event_id",
                    "prev_event_id",
                    "instance_name",
                ),
                values=[
                    (
                        max_stream_id,
                        self.room.to_string(),
                        EventTypes.Name,
                        "",
                        f"${random_string(5)}:test",
                        json.dumps({"name": f"rename #{i}"}),
                        "master",
                    )
                    for i in range(3)
                ],
                desc="inject_room_name_state_events",
            )
        )

        # Call the function under test with a limit of 4. Without the limit, we
        # would return 5 state deltas:
        #
        # C N N N N
        # 1 2 3 4 5
        #
        # C = m.room.create
        # N = m.room.name
        #
        # With the limit, we should return only the create event, as returning 4
        # state deltas would result in splitting a group:
        #
        # 2 3 3 3 3 - state IDs/groups
        # C N N N N
        # 1 2 3 4 X

        clipped_stream_id, deltas = self.get_success(
            self.store.get_partial_current_state_deltas(
                prev_stream_id=0,
                max_stream_id=max_stream_id,
                limit=4,
            )
        )

        # 2 is the stream ID of the m.room.create event.
        self.assertEqual(clipped_stream_id, 2)
        self.assertEqual(
            len(deltas),
            1,
            f"Returned {len(deltas)} rows, expected only one (the create event): {deltas}",
        )

        # Advance once more with our limit of 4. We should now get all 4
        # `m.room.name` state deltas as they can fit under the limit.
        clipped_stream_id, next_deltas = self.get_success(
            self.store.get_partial_current_state_deltas(
                prev_stream_id=clipped_stream_id, max_stream_id=max_stream_id, limit=4
            )
        )
        self.assertEqual(
            clipped_stream_id, 3
        )  # The stream ID of the 4 m.room.name events.

        self.assertEqual(
            len(next_deltas),
            4,
            f"Returned {len(next_deltas)} rows, expected all 4 m.room.name events: {next_deltas}",
        )

    def test_get_partial_current_state_deltas_does_not_enter_infinite_loop(
        self,
    ) -> None:
        """
        Tests that `get_partial_current_state_deltas` does not repeatedly return
        zero entries due to the passed `limit` parameter being less than the
        size of the next group of state deltas from the given `prev_stream_id`.
        """
        # Inject a create event to start with.
        self.inject_state_event(
            self.room, self.alice_user_id, EventTypes.Create, "", {}
        )

        # Then inject one "real" m.room.name event. This will give us a stream_id that
        # we can create some more (fake) events with.
        self.inject_state_event(
            self.room,
            self.alice_user_id,
            EventTypes.Name,
            "",
            {"name": "rename #1"},
        )

        # Get the stream_id of the last-inserted event.
        max_stream_id = self.store.get_room_max_stream_ordering()

        # Make 3 more state changes in the room, resulting in 5 total state
        # events (including the create event, and the first name update) in
        # the room.
        #
        # All of these state deltas have the same `stream_id` as the original name event.
        # Do so by editing the table directly as that's the simplest way to have
        # all share the same `stream_id`.
        self.get_success(
            self.store.db_pool.simple_insert_many(
                "current_state_delta_stream",
                keys=(
                    "stream_id",
                    "room_id",
                    "type",
                    "state_key",
                    "event_id",
                    "prev_event_id",
                    "instance_name",
                ),
                values=[
                    (
                        max_stream_id,
                        self.room.to_string(),
                        EventTypes.Name,
                        "",
                        f"${random_string(5)}:test",
                        json.dumps({"name": f"rename #{i}"}),
                        "master",
                    )
                    for i in range(3)
                ],
                desc="inject_room_name_state_events",
            )
        )

        # Call the function under test with a limit of 4. Without the limit, we would return
        # 5 state deltas:
        #
        # C N N N N
        # 1 2 3 4 5
        #
        # C = m.room.create
        # N = m.room.name
        #
        # With the limit, we should return only the create event, as returning 4
        # state deltas would result in splitting a group:
        #
        # 2 3 3 3 3 - state IDs/groups
        # C N N N N
        # 1 2 3 4 X

        clipped_stream_id, deltas = self.get_success(
            self.store.get_partial_current_state_deltas(
                prev_stream_id=2,  # Start after the create event (which has stream_id 2).
                max_stream_id=max_stream_id,
                limit=2,  # Less than the size of the next group (which is 4).
            )
        )

        self.assertEqual(
            clipped_stream_id, 3
        )  # The stream ID of the 4 m.room.name events.

        # We should get all 4 `m.room.name` state deltas, instead of 0, which
        # would result in the caller entering an infinite loop.
        self.assertEqual(
            len(deltas),
            4,
            f"Returned {len(deltas)} rows, expected 4 even though it broke our limit: {deltas}",
        )