zulip/zerver/actions/streams.py

import hashlib
from collections import defaultdict
from dataclasses import dataclass
from typing import (
    TYPE_CHECKING,
    Any,
    Collection,
    Dict,
    Iterable,
    List,
    Mapping,
    Optional,
    Set,
    Tuple,
)

import orjson
from django.conf import settings
from django.db import transaction
from django.utils.timezone import now as timezone_now
from django.utils.translation import gettext as _
from django.utils.translation import override as override_language

from zerver.actions.default_streams import (
    do_remove_default_stream,
    do_remove_streams_from_default_stream_group,
)
from zerver.actions.message_send import internal_send_stream_message
from zerver.lib.cache import (
    cache_delete,
    cache_delete_many,
    cache_set,
    display_recipient_cache_key,
    get_stream_cache_key,
    to_dict_cache_key_id,
)
from zerver.lib.email_mirror_helpers import encode_email_address
from zerver.lib.mention import silent_mention_syntax_for_user
from zerver.lib.message import get_last_message_id
from zerver.lib.queue import queue_json_publish
from zerver.lib.stream_color import pick_colors
from zerver.lib.stream_subscription import (
    SubInfo,
    bulk_get_private_peers,
    bulk_get_subscriber_peer_info,
    get_active_subscriptions_for_stream_id,
    get_bulk_stream_subscriber_info,
    get_used_colors_for_user_ids,
)
from zerver.lib.stream_traffic import get_average_weekly_stream_traffic, get_streams_traffic
from zerver.lib.streams import (
    can_access_stream_user_ids,
    get_default_value_for_history_public_to_subscribers,
    get_occupied_streams,
    get_stream_permission_policy_name,
    render_stream_description,
    send_stream_creation_event,
)
from zerver.lib.subscription_info import get_subscribers_query
from zerver.lib.types import APISubscriptionDict
from zerver.models import (
    ArchivedAttachment,
    Attachment,
    DefaultStream,
    DefaultStreamGroup,
    Message,
    Realm,
    RealmAuditLog,
    Recipient,
    Stream,
    Subscription,
    UserProfile,
    active_non_guest_user_ids,
    get_system_bot,
)
from zerver.tornado.django_api import send_event

if TYPE_CHECKING:
    from django.db.models.query import _QuerySet as ValuesQuerySet


@transaction.atomic(savepoint=False)
def do_deactivate_stream(
    stream: Stream, log: bool = True, *, acting_user: Optional[UserProfile]
) -> None:
    # We want to mark all messages in the to-be-deactivated stream as
    # read for all users; otherwise they will pollute queries like
    # "Get the user's first unread message".  Since this can be an
    # expensive operation, we do it via the deferred_work queue
    # processor.
    deferred_work_event = {
        "type": "mark_stream_messages_as_read_for_everyone",
        "stream_recipient_id": stream.recipient_id,
    }
    transaction.on_commit(lambda: queue_json_publish("deferred_work", deferred_work_event))

    # Get the affected user ids *before* we deactivate everybody.
    affected_user_ids = can_access_stream_user_ids(stream)

    get_active_subscriptions_for_stream_id(stream.id, include_deactivated_users=True).update(
        active=False
    )

    was_invite_only = stream.invite_only
    stream.deactivated = True
    stream.invite_only = True
    # Preserve as much as possible the original stream name while giving it a
    # special prefix that both indicates that the stream is deactivated and
    # frees up the original name for reuse.
    old_name = stream.name

    # Prepend a substring of the hashed stream ID to the new stream name
    streamID = str(stream.id)
    stream_id_hash_object = hashlib.sha512(streamID.encode())
    hashed_stream_id = stream_id_hash_object.hexdigest()[0:7]

    new_name = (hashed_stream_id + "!DEACTIVATED:" + old_name)[: Stream.MAX_NAME_LENGTH]

    stream.name = new_name[: Stream.MAX_NAME_LENGTH]
    stream.save(update_fields=["name", "deactivated", "invite_only"])

    # If this is a default stream, remove it, properly sending a
    # notification to browser clients.
    if DefaultStream.objects.filter(realm_id=stream.realm_id, stream_id=stream.id).exists():
        do_remove_default_stream(stream)

    default_stream_groups_for_stream = DefaultStreamGroup.objects.filter(streams__id=stream.id)
    for group in default_stream_groups_for_stream:
        do_remove_streams_from_default_stream_group(stream.realm, group, [stream])

    # Remove the old stream information from remote cache.
    old_cache_key = get_stream_cache_key(old_name, stream.realm_id)
    cache_delete(old_cache_key)

    stream_dict = stream.to_dict()
    stream_dict.update(dict(name=old_name, invite_only=was_invite_only))
    event = dict(type="stream", op="delete", streams=[stream_dict])
    transaction.on_commit(lambda: send_event(stream.realm, event, affected_user_ids))

    event_time = timezone_now()
    RealmAuditLog.objects.create(
        realm=stream.realm,
        acting_user=acting_user,
        modified_stream=stream,
        event_type=RealmAuditLog.STREAM_DEACTIVATED,
        event_time=event_time,
    )


def bulk_delete_cache_keys(message_ids_to_clear: List[int]) -> None:
    while len(message_ids_to_clear) > 0:
        batch = message_ids_to_clear[0:5000]

        keys_to_delete = [to_dict_cache_key_id(message_id) for message_id in batch]
        cache_delete_many(keys_to_delete)

        message_ids_to_clear = message_ids_to_clear[5000:]


def merge_streams(
    realm: Realm, stream_to_keep: Stream, stream_to_destroy: Stream
) -> Tuple[int, int, int]:
    recipient_to_destroy = stream_to_destroy.recipient
    recipient_to_keep = stream_to_keep.recipient
    if recipient_to_destroy.id == recipient_to_keep.id:
        return (0, 0, 0)

    # The high-level approach here is to move all the messages to
    # the surviving stream, deactivate all the subscriptions on
    # the stream to be removed and deactivate the stream, and add
    # new subscriptions to the stream to keep for any users who
    # were only on the now-deactivated stream.

    # Move the messages, and delete the old copies from caches.
    message_ids_to_clear = list(
        Message.objects.filter(recipient=recipient_to_destroy).values_list("id", flat=True)
    )
    count = Message.objects.filter(recipient=recipient_to_destroy).update(
        recipient=recipient_to_keep
    )
    bulk_delete_cache_keys(message_ids_to_clear)

    # Move the Subscription objects.  This algorithm doesn't
    # preserve any stream settings/colors/etc. from the stream
    # being destroyed, but it's convenient.
    existing_subs = Subscription.objects.filter(recipient=recipient_to_keep)
    users_already_subscribed = {sub.user_profile_id: sub.active for sub in existing_subs}

    subs_to_deactivate = Subscription.objects.filter(recipient=recipient_to_destroy, active=True)
    users_to_activate = [
        sub.user_profile
        for sub in subs_to_deactivate
        if not users_already_subscribed.get(sub.user_profile_id, False)
    ]

    if len(subs_to_deactivate) > 0:
        bulk_remove_subscriptions(
            realm,
            [sub.user_profile for sub in subs_to_deactivate],
            [stream_to_destroy],
            acting_user=None,
        )
    do_deactivate_stream(stream_to_destroy, acting_user=None)
    if len(users_to_activate) > 0:
        bulk_add_subscriptions(realm, [stream_to_keep], users_to_activate, acting_user=None)
    return (len(users_to_activate), count, len(subs_to_deactivate))


def get_subscriber_ids(
    stream: Stream, requesting_user: Optional[UserProfile] = None
) -> "ValuesQuerySet[Subscription, int]":
    subscriptions_query = get_subscribers_query(stream, requesting_user)
    return subscriptions_query.values_list("user_profile_id", flat=True)


@dataclass
class StreamInfo:
    email_address: str
    stream_weekly_traffic: Optional[int]
    subscribers: List[int]


def send_subscription_add_events(
    realm: Realm,
    sub_info_list: List[SubInfo],
    subscriber_dict: Dict[int, Set[int]],
) -> None:
    info_by_user: Dict[int, List[SubInfo]] = defaultdict(list)
    for sub_info in sub_info_list:
        info_by_user[sub_info.user.id].append(sub_info)

    stream_ids = {sub_info.stream.id for sub_info in sub_info_list}
    recent_traffic = get_streams_traffic(stream_ids=stream_ids)

    # We generally only have a few streams, so we compute stream
    # data in its own loop.
    stream_info_dict: Dict[int, StreamInfo] = {}
    for sub_info in sub_info_list:
        stream = sub_info.stream
        if stream.id not in stream_info_dict:
            email_address = encode_email_address(stream, show_sender=True)
            stream_weekly_traffic = get_average_weekly_stream_traffic(
                stream.id, stream.date_created, recent_traffic
            )
            if stream.is_in_zephyr_realm and not stream.invite_only:
                subscribers = []
            else:
                subscribers = list(subscriber_dict[stream.id])
            stream_info_dict[stream.id] = StreamInfo(
                email_address=email_address,
                stream_weekly_traffic=stream_weekly_traffic,
                subscribers=subscribers,
            )

    for user_id, sub_infos in info_by_user.items():
        sub_dicts: List[APISubscriptionDict] = []
        for sub_info in sub_infos:
            stream = sub_info.stream
            stream_info = stream_info_dict[stream.id]
            subscription = sub_info.sub
            stream_dict = stream.to_dict()
            # This is verbose as we cannot unpack existing TypedDict
            # to initialize another TypedDict while making mypy happy.
            # https://github.com/python/mypy/issues/5382
            sub_dict = APISubscriptionDict(
                # Fields from Subscription.API_FIELDS
                audible_notifications=subscription.audible_notifications,
                color=subscription.color,
                desktop_notifications=subscription.desktop_notifications,
                email_notifications=subscription.email_notifications,
                is_muted=subscription.is_muted,
                pin_to_top=subscription.pin_to_top,
                push_notifications=subscription.push_notifications,
                role=subscription.role,
                wildcard_mentions_notify=subscription.wildcard_mentions_notify,
                # Computed fields not present in Subscription.API_FIELDS
                email_address=stream_info.email_address,
                in_home_view=not subscription.is_muted,
                stream_weekly_traffic=stream_info.stream_weekly_traffic,
                subscribers=stream_info.subscribers,
                # Fields from Stream.API_FIELDS
                date_created=stream_dict["date_created"],
                description=stream_dict["description"],
                first_message_id=stream_dict["first_message_id"],
                history_public_to_subscribers=stream_dict["history_public_to_subscribers"],
                invite_only=stream_dict["invite_only"],
                is_web_public=stream_dict["is_web_public"],
                message_retention_days=stream_dict["message_retention_days"],
                name=stream_dict["name"],
                rendered_description=stream_dict["rendered_description"],
                stream_id=stream_dict["stream_id"],
                stream_post_policy=stream_dict["stream_post_policy"],
                # Computed fields not present in Stream.API_FIELDS
                is_announcement_only=stream_dict["is_announcement_only"],
            )

            sub_dicts.append(sub_dict)

        # Send a notification to the user who subscribed.
        event = dict(type="subscription", op="add", subscriptions=sub_dicts)
        send_event(realm, event, [user_id])


# This function contains all the database changes as part of
# subscribing users to streams; we use a transaction to ensure that
# the RealmAuditLog entries are created atomically with the
# Subscription object creation (and updates).
@transaction.atomic(savepoint=False)
def bulk_add_subs_to_db_with_logging(
    realm: Realm,
    acting_user: Optional[UserProfile],
    subs_to_add: List[SubInfo],
    subs_to_activate: List[SubInfo],
) -> None:

    Subscription.objects.bulk_create(info.sub for info in subs_to_add)
    sub_ids = [info.sub.id for info in subs_to_activate]
    Subscription.objects.filter(id__in=sub_ids).update(active=True)

    # Log subscription activities in RealmAuditLog
    event_time = timezone_now()
    event_last_message_id = get_last_message_id()

    all_subscription_logs: (List[RealmAuditLog]) = []
    for sub_info in subs_to_add:
        all_subscription_logs.append(
            RealmAuditLog(
                realm=realm,
                acting_user=acting_user,
                modified_user=sub_info.user,
                modified_stream=sub_info.stream,
                event_last_message_id=event_last_message_id,
                event_type=RealmAuditLog.SUBSCRIPTION_CREATED,
                event_time=event_time,
            )
        )
    for sub_info in subs_to_activate:
        all_subscription_logs.append(
            RealmAuditLog(
                realm=realm,
                acting_user=acting_user,
                modified_user=sub_info.user,
                modified_stream=sub_info.stream,
                event_last_message_id=event_last_message_id,
                event_type=RealmAuditLog.SUBSCRIPTION_ACTIVATED,
                event_time=event_time,
            )
        )
    # Now since we have all log objects generated we can do a bulk insert
    RealmAuditLog.objects.bulk_create(all_subscription_logs)


def send_stream_creation_events_for_private_streams(
    realm: Realm,
    stream_dict: Dict[int, Stream],
    altered_user_dict: Dict[int, Set[int]],
) -> None:
    for stream_id, stream_users_ids in altered_user_dict.items():
        stream = stream_dict[stream_id]

        if not stream.is_public():
            # Users newly added to invite-only streams
            # need a `create` notification.  The former, because
            # they need the stream to exist before
            # they get the "subscribe" notification, and the latter so
            # they can manage the new stream.
            # Realm admins already have all created private streams.
            realm_admin_ids = {user.id for user in realm.get_admin_users_and_bots()}
            notify_user_ids = list(stream_users_ids - realm_admin_ids)

            if notify_user_ids:
                send_stream_creation_event(stream, notify_user_ids)


def send_peer_subscriber_events(
    op: str,
    realm: Realm,
    stream_dict: Dict[int, Stream],
    altered_user_dict: Dict[int, Set[int]],
    private_peer_dict: Dict[int, Set[int]],
) -> None:
    # Send peer_add/peer_remove events to other users who are tracking the
    # subscribers lists of streams in their browser; everyone for
    # public streams and only existing subscribers for private streams.

    assert op in ["peer_add", "peer_remove"]

    private_stream_ids = [
        stream_id for stream_id in altered_user_dict if stream_dict[stream_id].invite_only
    ]

    for stream_id in private_stream_ids:
        altered_user_ids = altered_user_dict[stream_id]
        peer_user_ids = private_peer_dict[stream_id] - altered_user_ids

        if peer_user_ids and altered_user_ids:
            event = dict(
                type="subscription",
                op=op,
                stream_ids=[stream_id],
                user_ids=sorted(list(altered_user_ids)),
            )
            send_event(realm, event, peer_user_ids)

    public_stream_ids = [
        stream_id
        for stream_id in altered_user_dict
        if not stream_dict[stream_id].invite_only and not stream_dict[stream_id].is_in_zephyr_realm
    ]

    if public_stream_ids:
        user_streams: Dict[int, Set[int]] = defaultdict(set)

        public_peer_ids = set(active_non_guest_user_ids(realm.id))

        for stream_id in public_stream_ids:
            altered_user_ids = altered_user_dict[stream_id]
            peer_user_ids = public_peer_ids - altered_user_ids

            if peer_user_ids and altered_user_ids:
                if len(altered_user_ids) == 1:
                    # If we only have one user, we will try to
                    # find other streams they have (un)subscribed to
                    # (where it's just them).  This optimization
                    # typically works when a single user is subscribed
                    # to multiple default public streams during
                    # new-user registration.
                    #
                    # This optimization depends on all public streams
                    # having the same peers for any single user, which
                    # isn't the case for private streams.
                    altered_user_id = list(altered_user_ids)[0]
                    user_streams[altered_user_id].add(stream_id)
                else:
                    event = dict(
                        type="subscription",
                        op=op,
                        stream_ids=[stream_id],
                        user_ids=sorted(list(altered_user_ids)),
                    )
                    send_event(realm, event, peer_user_ids)

        for user_id, stream_ids in user_streams.items():
            peer_user_ids = public_peer_ids - {user_id}
            event = dict(
                type="subscription",
                op=op,
                stream_ids=sorted(list(stream_ids)),
                user_ids=[user_id],
            )
            send_event(realm, event, peer_user_ids)


SubT = Tuple[List[SubInfo], List[SubInfo]]


def bulk_add_subscriptions(
    realm: Realm,
    streams: Collection[Stream],
    users: Iterable[UserProfile],
    color_map: Mapping[str, str] = {},
    from_user_creation: bool = False,
    *,
    acting_user: Optional[UserProfile],
) -> SubT:
    users = list(users)
    user_ids = [user.id for user in users]

    # Sanity check out callers
    for stream in streams:
        assert stream.realm_id == realm.id

    for user in users:
        assert user.realm_id == realm.id

    recipient_ids = [stream.recipient_id for stream in streams]
    recipient_id_to_stream = {stream.recipient_id: stream for stream in streams}

    recipient_color_map = {}
    recipient_ids_set: Set[int] = set()
    for stream in streams:
        assert stream.recipient_id is not None
        recipient_ids_set.add(stream.recipient_id)
        color: Optional[str] = color_map.get(stream.name, None)
        if color is not None:
            recipient_color_map[stream.recipient_id] = color

    used_colors_for_user_ids: Dict[int, Set[str]] = get_used_colors_for_user_ids(user_ids)

    existing_subs = Subscription.objects.filter(
        user_profile_id__in=user_ids,
        recipient__type=Recipient.STREAM,
        recipient_id__in=recipient_ids,
    )

    subs_by_user: Dict[int, List[Subscription]] = defaultdict(list)
    for sub in existing_subs:
        subs_by_user[sub.user_profile_id].append(sub)

    already_subscribed: List[SubInfo] = []
    subs_to_activate: List[SubInfo] = []
    subs_to_add: List[SubInfo] = []
    for user_profile in users:
        my_subs = subs_by_user[user_profile.id]

        # Make a fresh set of all new recipient ids, and then we will
        # remove any for which our user already has a subscription
        # (and we'll re-activate any subscriptions as needed).
        new_recipient_ids: Set[int] = recipient_ids_set.copy()

        for sub in my_subs:
            if sub.recipient_id in new_recipient_ids:
                new_recipient_ids.remove(sub.recipient_id)
                stream = recipient_id_to_stream[sub.recipient_id]
                sub_info = SubInfo(user_profile, sub, stream)
                if sub.active:
                    already_subscribed.append(sub_info)
                else:
                    subs_to_activate.append(sub_info)

        used_colors = used_colors_for_user_ids.get(user_profile.id, set())
        user_color_map = pick_colors(used_colors, recipient_color_map, list(new_recipient_ids))

        for recipient_id in new_recipient_ids:
            stream = recipient_id_to_stream[recipient_id]
            color = user_color_map[recipient_id]

            sub = Subscription(
                user_profile=user_profile,
                is_user_active=user_profile.is_active,
                active=True,
                color=color,
                recipient_id=recipient_id,
            )
            sub_info = SubInfo(user_profile, sub, stream)
            subs_to_add.append(sub_info)

    bulk_add_subs_to_db_with_logging(
        realm=realm,
        acting_user=acting_user,
        subs_to_add=subs_to_add,
        subs_to_activate=subs_to_activate,
    )

    altered_user_dict: Dict[int, Set[int]] = defaultdict(set)
    for sub_info in subs_to_add + subs_to_activate:
        altered_user_dict[sub_info.stream.id].add(sub_info.user.id)

    stream_dict = {stream.id: stream for stream in streams}

    new_streams = [stream_dict[stream_id] for stream_id in altered_user_dict]

    subscriber_peer_info = bulk_get_subscriber_peer_info(
        realm=realm,
        streams=new_streams,
    )

    # We now send several types of events to notify browsers.  The
    # first batches of notifications are sent only to the user(s)
    # being subscribed; we can skip these notifications when this is
    # being called from the new user creation flow.
    if not from_user_creation:
        send_stream_creation_events_for_private_streams(
            realm=realm,
            stream_dict=stream_dict,
            altered_user_dict=altered_user_dict,
        )

        send_subscription_add_events(
            realm=realm,
            sub_info_list=subs_to_add + subs_to_activate,
            subscriber_dict=subscriber_peer_info.subscribed_ids,
        )

    send_peer_subscriber_events(
        op="peer_add",
        realm=realm,
        altered_user_dict=altered_user_dict,
        stream_dict=stream_dict,
        private_peer_dict=subscriber_peer_info.private_peer_dict,
    )

    return (
        subs_to_add + subs_to_activate,
        already_subscribed,
    )


def send_peer_remove_events(
    realm: Realm,
    streams: List[Stream],
    altered_user_dict: Dict[int, Set[int]],
) -> None:
    private_streams = [stream for stream in streams if stream.invite_only]

    private_peer_dict = bulk_get_private_peers(
        realm=realm,
        private_streams=private_streams,
    )
    stream_dict = {stream.id: stream for stream in streams}

    send_peer_subscriber_events(
        op="peer_remove",
        realm=realm,
        stream_dict=stream_dict,
        altered_user_dict=altered_user_dict,
        private_peer_dict=private_peer_dict,
    )


def notify_subscriptions_removed(
    realm: Realm, user_profile: UserProfile, streams: Iterable[Stream]
) -> None:

    payload = [dict(name=stream.name, stream_id=stream.id) for stream in streams]
    event = dict(type="subscription", op="remove", subscriptions=payload)
    send_event(realm, event, [user_profile.id])


SubAndRemovedT = Tuple[List[Tuple[UserProfile, Stream]], List[Tuple[UserProfile, Stream]]]


def bulk_remove_subscriptions(
    realm: Realm,
    users: Iterable[UserProfile],
    streams: Iterable[Stream],
    *,
    acting_user: Optional[UserProfile],
) -> SubAndRemovedT:

    users = list(users)
    streams = list(streams)

    # Sanity check our callers
    for stream in streams:
        assert stream.realm_id == realm.id

    for user in users:
        assert user.realm_id == realm.id

    stream_dict = {stream.id: stream for stream in streams}

    existing_subs_by_user = get_bulk_stream_subscriber_info(users, streams)

    def get_non_subscribed_subs() -> List[Tuple[UserProfile, Stream]]:
        stream_ids = {stream.id for stream in streams}

        not_subscribed: List[Tuple[UserProfile, Stream]] = []

        for user_profile in users:
            user_sub_stream_info = existing_subs_by_user[user_profile.id]

            subscribed_stream_ids = {sub_info.stream.id for sub_info in user_sub_stream_info}
            not_subscribed_stream_ids = stream_ids - subscribed_stream_ids

            for stream_id in not_subscribed_stream_ids:
                stream = stream_dict[stream_id]
                not_subscribed.append((user_profile, stream))

        return not_subscribed

    not_subscribed = get_non_subscribed_subs()

    subs_to_deactivate: List[SubInfo] = []
    sub_ids_to_deactivate: List[int] = []

    # This loop just flattens out our data into big lists for
    # bulk operations.
    for sub_infos in existing_subs_by_user.values():
        for sub_info in sub_infos:
            subs_to_deactivate.append(sub_info)
            sub_ids_to_deactivate.append(sub_info.sub.id)

    streams_to_unsubscribe = [sub_info.stream for sub_info in subs_to_deactivate]
    # We do all the database changes in a transaction to ensure
    # RealmAuditLog entries are atomically created when making changes.
    with transaction.atomic():
        Subscription.objects.filter(
            id__in=sub_ids_to_deactivate,
        ).update(active=False)
        occupied_streams_after = list(get_occupied_streams(realm))

        # Log subscription activities in RealmAuditLog
        event_time = timezone_now()
        event_last_message_id = get_last_message_id()
        all_subscription_logs = [
            RealmAuditLog(
                realm=sub_info.user.realm,
                acting_user=acting_user,
                modified_user=sub_info.user,
                modified_stream=sub_info.stream,
                event_last_message_id=event_last_message_id,
                event_type=RealmAuditLog.SUBSCRIPTION_DEACTIVATED,
                event_time=event_time,
            )
            for sub_info in subs_to_deactivate
        ]

        # Now since we have all log objects generated we can do a bulk insert
        RealmAuditLog.objects.bulk_create(all_subscription_logs)

    altered_user_dict: Dict[int, Set[int]] = defaultdict(set)
    streams_by_user: Dict[int, List[Stream]] = defaultdict(list)
    for sub_info in subs_to_deactivate:
        stream = sub_info.stream
        streams_by_user[sub_info.user.id].append(stream)
        altered_user_dict[stream.id].add(sub_info.user.id)

    for user_profile in users:
        if len(streams_by_user[user_profile.id]) == 0:
            continue
        notify_subscriptions_removed(realm, user_profile, streams_by_user[user_profile.id])

        event = {
            "type": "mark_stream_messages_as_read",
            "user_profile_id": user_profile.id,
            "stream_recipient_ids": [
                stream.recipient_id for stream in streams_by_user[user_profile.id]
            ],
        }
        queue_json_publish("deferred_work", event)

    send_peer_remove_events(
        realm=realm,
        streams=streams,
        altered_user_dict=altered_user_dict,
    )

    new_vacant_streams = set(streams_to_unsubscribe) - set(occupied_streams_after)
    new_vacant_private_streams = [stream for stream in new_vacant_streams if stream.invite_only]

    if new_vacant_private_streams:
        # Deactivate any newly-vacant private streams
        for stream in new_vacant_private_streams:
            do_deactivate_stream(stream, acting_user=acting_user)

    return (
        [(sub_info.user, sub_info.stream) for sub_info in subs_to_deactivate],
        not_subscribed,
    )


def do_change_subscription_property(
    user_profile: UserProfile,
    sub: Subscription,
    stream: Stream,
    property_name: str,
    value: Any,
    *,
    acting_user: Optional[UserProfile],
) -> None:
    database_property_name = property_name
    event_property_name = property_name
    database_value = value
    event_value = value

    # For this property, is_muted is used in the database, but
    # in_home_view in the API, since we haven't migrated the events
    # API to the new name yet.
    if property_name == "in_home_view":
        database_property_name = "is_muted"
        database_value = not value
    if property_name == "is_muted":
        event_property_name = "in_home_view"
        event_value = not value

    old_value = getattr(sub, database_property_name)
    setattr(sub, database_property_name, database_value)
    sub.save(update_fields=[database_property_name])
    event_time = timezone_now()
    RealmAuditLog.objects.create(
        realm=user_profile.realm,
        event_type=RealmAuditLog.SUBSCRIPTION_PROPERTY_CHANGED,
        event_time=event_time,
        modified_user=user_profile,
        acting_user=acting_user,
        modified_stream=stream,
        extra_data=orjson.dumps(
            {
                RealmAuditLog.OLD_VALUE: old_value,
                RealmAuditLog.NEW_VALUE: database_value,
                "property": database_property_name,
            }
        ).decode(),
    )

    event = dict(
        type="subscription",
        op="update",
        property=event_property_name,
        value=event_value,
        stream_id=stream.id,
    )
    send_event(user_profile.realm, event, [user_profile.id])


def send_change_stream_permission_notification(
    stream: Stream,
    *,
    old_policy_name: str,
    new_policy_name: str,
    acting_user: UserProfile,
) -> None:
    sender = get_system_bot(settings.NOTIFICATION_BOT, acting_user.realm_id)
    user_mention = silent_mention_syntax_for_user(acting_user)

    with override_language(stream.realm.default_language):
        notification_string = _(
            "{user} changed the [access permissions](/help/stream-permissions) "
            "for this stream from **{old_policy}** to **{new_policy}**."
        )
        notification_string = notification_string.format(
            user=user_mention,
            old_policy=old_policy_name,
            new_policy=new_policy_name,
        )
        internal_send_stream_message(
            sender, stream, Realm.STREAM_EVENTS_NOTIFICATION_TOPIC, notification_string
        )


def do_change_stream_permission(
    stream: Stream,
    *,
    invite_only: Optional[bool] = None,
    history_public_to_subscribers: Optional[bool] = None,
    is_web_public: Optional[bool] = None,
    acting_user: UserProfile,
) -> None:
    old_invite_only_value = stream.invite_only
    old_history_public_to_subscribers_value = stream.history_public_to_subscribers
    old_is_web_public_value = stream.is_web_public

    # A note on these assertions: It's possible we'd be better off
    # making all callers of this function pass the full set of
    # parameters, rather than having default values.  Doing so would
    # allow us to remove the messy logic below, where we sometimes
    # ignore the passed parameters.
    #
    # But absent such a refactoring, it's important to assert that
    # we're not requesting an unsupported configurations.
    if is_web_public:
        assert history_public_to_subscribers is not False
        assert invite_only is not True
        stream.is_web_public = True
        stream.invite_only = False
        stream.history_public_to_subscribers = True
    else:
        assert invite_only is not None
        # is_web_public is falsey
        history_public_to_subscribers = get_default_value_for_history_public_to_subscribers(
            stream.realm,
            invite_only,
            history_public_to_subscribers,
        )
        stream.invite_only = invite_only
        stream.history_public_to_subscribers = history_public_to_subscribers
        stream.is_web_public = False

    with transaction.atomic():
        stream.save(update_fields=["invite_only", "history_public_to_subscribers", "is_web_public"])

        event_time = timezone_now()
        if old_invite_only_value != stream.invite_only:
            # Reset the Attachment.is_realm_public cache for all
            # messages in the stream whose permissions were changed.
            assert stream.recipient_id is not None
            Attachment.objects.filter(messages__recipient_id=stream.recipient_id).update(
                is_realm_public=None
            )
            # We need to do the same for ArchivedAttachment to avoid
            # bugs if deleted attachments are later restored.
            ArchivedAttachment.objects.filter(messages__recipient_id=stream.recipient_id).update(
                is_realm_public=None
            )

            RealmAuditLog.objects.create(
                realm=stream.realm,
                acting_user=acting_user,
                modified_stream=stream,
                event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
                event_time=event_time,
                extra_data=orjson.dumps(
                    {
                        RealmAuditLog.OLD_VALUE: old_invite_only_value,
                        RealmAuditLog.NEW_VALUE: stream.invite_only,
                        "property": "invite_only",
                    }
                ).decode(),
            )

        if old_history_public_to_subscribers_value != stream.history_public_to_subscribers:
            RealmAuditLog.objects.create(
                realm=stream.realm,
                acting_user=acting_user,
                modified_stream=stream,
                event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
                event_time=event_time,
                extra_data=orjson.dumps(
                    {
                        RealmAuditLog.OLD_VALUE: old_history_public_to_subscribers_value,
                        RealmAuditLog.NEW_VALUE: stream.history_public_to_subscribers,
                        "property": "history_public_to_subscribers",
                    }
                ).decode(),
            )

        if old_is_web_public_value != stream.is_web_public:
            # Reset the Attachment.is_realm_public cache for all
            # messages in the stream whose permissions were changed.
            assert stream.recipient_id is not None
            Attachment.objects.filter(messages__recipient_id=stream.recipient_id).update(
                is_web_public=None
            )
            # We need to do the same for ArchivedAttachment to avoid
            # bugs if deleted attachments are later restored.
            ArchivedAttachment.objects.filter(messages__recipient_id=stream.recipient_id).update(
                is_web_public=None
            )

            RealmAuditLog.objects.create(
                realm=stream.realm,
                acting_user=acting_user,
                modified_stream=stream,
                event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
                event_time=event_time,
                extra_data=orjson.dumps(
                    {
                        RealmAuditLog.OLD_VALUE: old_is_web_public_value,
                        RealmAuditLog.NEW_VALUE: stream.is_web_public,
                        "property": "is_web_public",
                    }
                ).decode(),
            )

    event = dict(
        op="update",
        type="stream",
        property="invite_only",
        value=stream.invite_only,
        history_public_to_subscribers=stream.history_public_to_subscribers,
        is_web_public=stream.is_web_public,
        stream_id=stream.id,
        name=stream.name,
    )
    send_event(stream.realm, event, can_access_stream_user_ids(stream))

    old_policy_name = get_stream_permission_policy_name(
        invite_only=old_invite_only_value,
        history_public_to_subscribers=old_history_public_to_subscribers_value,
        is_web_public=old_is_web_public_value,
    )
    new_policy_name = get_stream_permission_policy_name(
        invite_only=stream.invite_only,
        history_public_to_subscribers=stream.history_public_to_subscribers,
        is_web_public=stream.is_web_public,
    )
    send_change_stream_permission_notification(
        stream,
        old_policy_name=old_policy_name,
        new_policy_name=new_policy_name,
        acting_user=acting_user,
    )


def send_change_stream_post_policy_notification(
    stream: Stream, *, old_post_policy: int, new_post_policy: int, acting_user: UserProfile
) -> None:
    sender = get_system_bot(settings.NOTIFICATION_BOT, acting_user.realm_id)
    user_mention = silent_mention_syntax_for_user(acting_user)

    with override_language(stream.realm.default_language):
        notification_string = _(
            "{user} changed the [posting permissions](/help/stream-sending-policy) "
            "for this stream:\n\n"
            "* **Old permissions**: {old_policy}.\n"
            "* **New permissions**: {new_policy}.\n"
        )
        notification_string = notification_string.format(
            user=user_mention,
            old_policy=Stream.POST_POLICIES[old_post_policy],
            new_policy=Stream.POST_POLICIES[new_post_policy],
        )
        internal_send_stream_message(
            sender, stream, Realm.STREAM_EVENTS_NOTIFICATION_TOPIC, notification_string
        )


def do_change_stream_post_policy(
    stream: Stream, stream_post_policy: int, *, acting_user: UserProfile
) -> None:
    old_post_policy = stream.stream_post_policy
    with transaction.atomic():
        stream.stream_post_policy = stream_post_policy
        stream.save(update_fields=["stream_post_policy"])
        RealmAuditLog.objects.create(
            realm=stream.realm,
            acting_user=acting_user,
            modified_stream=stream,
            event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
            event_time=timezone_now(),
            extra_data=orjson.dumps(
                {
                    RealmAuditLog.OLD_VALUE: old_post_policy,
                    RealmAuditLog.NEW_VALUE: stream_post_policy,
                    "property": "stream_post_policy",
                }
            ).decode(),
        )

    event = dict(
        op="update",
        type="stream",
        property="stream_post_policy",
        value=stream_post_policy,
        stream_id=stream.id,
        name=stream.name,
    )
    send_event(stream.realm, event, can_access_stream_user_ids(stream))

    # Backwards-compatibility code: We removed the
    # is_announcement_only property in early 2020, but we send a
    # duplicate event for legacy mobile clients that might want the
    # data.
    event = dict(
        op="update",
        type="stream",
        property="is_announcement_only",
        value=stream.stream_post_policy == Stream.STREAM_POST_POLICY_ADMINS,
        stream_id=stream.id,
        name=stream.name,
    )
    send_event(stream.realm, event, can_access_stream_user_ids(stream))

    send_change_stream_post_policy_notification(
        stream,
        old_post_policy=old_post_policy,
        new_post_policy=stream_post_policy,
        acting_user=acting_user,
    )


def do_rename_stream(stream: Stream, new_name: str, user_profile: UserProfile) -> Dict[str, str]:
    old_name = stream.name
    stream.name = new_name
    stream.save(update_fields=["name"])

    RealmAuditLog.objects.create(
        realm=stream.realm,
        acting_user=user_profile,
        modified_stream=stream,
        event_type=RealmAuditLog.STREAM_NAME_CHANGED,
        event_time=timezone_now(),
        extra_data=orjson.dumps(
            {
                RealmAuditLog.OLD_VALUE: old_name,
                RealmAuditLog.NEW_VALUE: new_name,
            }
        ).decode(),
    )

    assert stream.recipient_id is not None
    recipient_id: int = stream.recipient_id
    messages = Message.objects.filter(recipient_id=recipient_id).only("id")

    # Update the display recipient and stream, which are easy single
    # items to set.
    old_cache_key = get_stream_cache_key(old_name, stream.realm_id)
    new_cache_key = get_stream_cache_key(stream.name, stream.realm_id)
    if old_cache_key != new_cache_key:
        cache_delete(old_cache_key)
        cache_set(new_cache_key, stream)
    cache_set(display_recipient_cache_key(recipient_id), stream.name)

    # Delete cache entries for everything else, which is cheaper and
    # clearer than trying to set them. display_recipient is the out of
    # date field in all cases.
    cache_delete_many(to_dict_cache_key_id(message.id) for message in messages)
    new_email = encode_email_address(stream, show_sender=True)

    # We will tell our users to essentially
    # update stream.name = new_name where name = old_name
    # and update stream.email = new_email where name = old_name.
    # We could optimize this by trying to send one message, but the
    # client code really wants one property update at a time, and
    # updating stream names is a pretty infrequent operation.
    # More importantly, we want to key these updates by id, not name,
    # since id is the immutable primary key, and obviously name is not.
    data_updates = [
        ["email_address", new_email],
        ["name", new_name],
    ]
    for property, value in data_updates:
        event = dict(
            op="update",
            type="stream",
            property=property,
            value=value,
            stream_id=stream.id,
            name=old_name,
        )
        send_event(stream.realm, event, can_access_stream_user_ids(stream))
    sender = get_system_bot(settings.NOTIFICATION_BOT, stream.realm_id)
    with override_language(stream.realm.default_language):
        internal_send_stream_message(
            sender,
            stream,
            Realm.STREAM_EVENTS_NOTIFICATION_TOPIC,
            _("{user_name} renamed stream {old_stream_name} to {new_stream_name}.").format(
                user_name=silent_mention_syntax_for_user(user_profile),
                old_stream_name=f"**{old_name}**",
                new_stream_name=f"**{new_name}**",
            ),
        )
    # Even though the token doesn't change, the web client needs to update the
    # email forwarding address to display the correctly-escaped new name.
    return {"email_address": new_email}


def send_change_stream_description_notification(
    stream: Stream, *, old_description: str, new_description: str, acting_user: UserProfile
) -> None:
    sender = get_system_bot(settings.NOTIFICATION_BOT, acting_user.realm_id)
    user_mention = silent_mention_syntax_for_user(acting_user)

    with override_language(stream.realm.default_language):
        if new_description == "":
            new_description = "*" + _("No description.") + "*"
        if old_description == "":
            old_description = "*" + _("No description.") + "*"

        notification_string = (
            _("{user} changed the description for this stream.").format(user=user_mention)
            + "\n\n* **"
            + _("Old description")
            + ":**"
            + f"\n```` quote\n{old_description}\n````\n"
            + "* **"
            + _("New description")
            + ":**"
            + f"\n```` quote\n{new_description}\n````"
        )

        internal_send_stream_message(
            sender, stream, Realm.STREAM_EVENTS_NOTIFICATION_TOPIC, notification_string
        )


def do_change_stream_description(
    stream: Stream, new_description: str, *, acting_user: UserProfile
) -> None:
    old_description = stream.description

    with transaction.atomic():
        stream.description = new_description
        stream.rendered_description = render_stream_description(new_description)
        stream.save(update_fields=["description", "rendered_description"])
        RealmAuditLog.objects.create(
            realm=stream.realm,
            acting_user=acting_user,
            modified_stream=stream,
            event_type=RealmAuditLog.STREAM_PROPERTY_CHANGED,
            event_time=timezone_now(),
            extra_data=orjson.dumps(
                {
                    RealmAuditLog.OLD_VALUE: old_description,
                    RealmAuditLog.NEW_VALUE: new_description,
                    "property": "description",
                }
            ).decode(),
        )

    event = dict(
        type="stream",
        op="update",
        property="description",
        name=stream.name,
        stream_id=stream.id,
        value=new_description,
        rendered_description=stream.rendered_description,
    )
    send_event(stream.realm, event, can_access_stream_user_ids(stream))

    send_change_stream_description_notification(
        stream,
        old_description=old_description,
        new_description=new_description,
        acting_user=acting_user,
    )


def send_change_stream_message_retention_days_notification(
    user_profile: UserProfile, stream: Stream, old_value: Optional[int], new_value: Optional[int]
) -> None:
    sender = get_system_bot(settings.NOTIFICATION_BOT, user_profile.realm_id)
    user_mention = silent_mention_syntax_for_user(user_profile)

    # If switching from or to the organization's default retention policy,
    # we want to take the realm's default into account.
    if old_value is None:
        old_value = stream.realm.message_retention_days
    if new_value is None:
        new_value = stream.realm.message_retention_days

    with override_language(stream.realm.default_language):
        if old_value == Stream.MESSAGE_RETENTION_SPECIAL_VALUES_MAP["unlimited"]:
            old_retention_period = _("Forever")
            new_retention_period = f"{new_value} days"
            summary_line = f"Messages in this stream will now be automatically deleted {new_value} days after they are sent."
        elif new_value == Stream.MESSAGE_RETENTION_SPECIAL_VALUES_MAP["unlimited"]:
            old_retention_period = f"{old_value} days"
            new_retention_period = _("Forever")
            summary_line = _("Messages in this stream will now be retained forever.")
        else:
            old_retention_period = f"{old_value} days"
            new_retention_period = f"{new_value} days"
            summary_line = f"Messages in this stream will now be automatically deleted {new_value} days after they are sent."
        notification_string = _(
            "{user} has changed the [message retention period](/help/message-retention-policy) for this stream:\n"
            "* **Old retention period**: {old_retention_period}\n"
            "* **New retention period**: {new_retention_period}\n\n"
            "{summary_line}"
        )
        notification_string = notification_string.format(
            user=user_mention,
            old_retention_period=old_retention_period,
            new_retention_period=new_retention_period,
            summary_line=summary_line,
        )
        internal_send_stream_message(
            sender, stream, Realm.STREAM_EVENTS_NOTIFICATION_TOPIC, notification_string
        )


def do_change_stream_message_retention_days(
    stream: Stream, acting_user: UserProfile, message_retention_days: Optional[int] = None
) -> None:
    old_message_retention_days_value = stream.message_retention_days

    with transaction.atomic():
        stream.message_retention_days = message_retention_days
        stream.save(update_fields=["message_retention_days"])
        RealmAuditLog.objects.create(
            realm=stream.realm,
            acting_user=acting_user,
            modified_stream=stream,
            event_type=RealmAuditLog.STREAM_MESSAGE_RETENTION_DAYS_CHANGED,
            event_time=timezone_now(),
            extra_data=orjson.dumps(
                {
                    RealmAuditLog.OLD_VALUE: old_message_retention_days_value,
                    RealmAuditLog.NEW_VALUE: message_retention_days,
                }
            ).decode(),
        )

    event = dict(
        op="update",
        type="stream",
        property="message_retention_days",
        value=message_retention_days,
        stream_id=stream.id,
        name=stream.name,
    )
    send_event(stream.realm, event, can_access_stream_user_ids(stream))
    send_change_stream_message_retention_days_notification(
        user_profile=acting_user,
        stream=stream,
        old_value=old_message_retention_days_value,
        new_value=message_retention_days,
    )