zulip/zerver/actions/streams.py

import hashlib
from collections import defaultdict
from dataclasses import dataclass
from typing import 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.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


@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 get_subscriber_ids(stream: Stream, requesting_user: Optional[UserProfile] = None) -> List[str]:
    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 = []
        for sub_info in sub_infos:
            stream = sub_info.stream
            stream_info = stream_info_dict[stream.id]
            subscription = sub_info.sub
            sub_dict = stream.to_dict()
            for field_name in Subscription.API_FIELDS:
                sub_dict[field_name] = getattr(subscription, field_name)

            sub_dict["in_home_view"] = not subscription.is_muted
            sub_dict["email_address"] = stream_info.email_address
            sub_dict["stream_weekly_traffic"] = stream_info.stream_weekly_traffic
            sub_dict["subscribers"] = stream_info.subscribers
            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 = {}
    for stream in streams:
        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] = {stream.recipient_id for stream in streams}

        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)

    # We do all the database changes in a transaction to ensure
    # RealmAuditLog entries are atomically created when making changes.
    with transaction.atomic():
        occupied_streams_before = list(get_occupied_streams(realm))
        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],
        }
        queue_json_publish("deferred_work", event)

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

    new_vacant_streams = set(occupied_streams_before) - 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.
            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.
            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(),
    )

    recipient_id = 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,
    )