zulip/zerver/lib/message.py

import datetime
import ujson
import zlib

from django.utils.translation import ugettext as _
from django.utils.timezone import now as timezone_now
from django.db.models import Sum

from analytics.lib.counts import COUNT_STATS, RealmCount

from zerver.lib.avatar import get_avatar_field
import zerver.lib.bugdown as bugdown
from zerver.lib.cache import (
    cache_with_key,
    generic_bulk_cached_fetch,
    to_dict_cache_key,
    to_dict_cache_key_id,
    realm_first_visible_message_id_cache_key,
    cache_get, cache_set,
)
from zerver.lib.request import JsonableError
from zerver.lib.stream_subscription import (
    get_stream_subscriptions_for_user,
)
from zerver.lib.timestamp import datetime_to_timestamp
from zerver.lib.topic_mutes import (
    build_topic_mute_checker,
    topic_is_muted,
)

from zerver.models import (
    get_display_recipient_by_id,
    get_user_profile_by_id,
    query_for_ids,
    Message,
    Realm,
    Recipient,
    Stream,
    SubMessage,
    Subscription,
    UserProfile,
    UserMessage,
    Reaction,
    get_usermessage_by_message_id,
)

from typing import Any, Dict, List, Optional, Set, Tuple, Union, Sequence
from mypy_extensions import TypedDict

RealmAlertWords = Dict[int, List[str]]

RawUnreadMessagesResult = TypedDict('RawUnreadMessagesResult', {
    'pm_dict': Dict[int, Any],
    'stream_dict': Dict[int, Any],
    'huddle_dict': Dict[int, Any],
    'mentions': Set[int],
    'muted_stream_ids': List[int],
    'unmuted_stream_msgs': Set[int],
})

UnreadMessagesResult = TypedDict('UnreadMessagesResult', {
    'pms': List[Dict[str, Any]],
    'streams': List[Dict[str, Any]],
    'huddles': List[Dict[str, Any]],
    'mentions': List[int],
    'count': int,
})

# We won't try to fetch more unread message IDs from the database than
# this limit.  The limit is super high, in large part because it means
# client-side code mostly doesn't need to think about the case that a
# user has more older unread messages that were cut off.
MAX_UNREAD_MESSAGES = 50000

def messages_for_ids(message_ids: List[int],
                     user_message_flags: Dict[int, List[str]],
                     search_fields: Dict[int, Dict[str, str]],
                     apply_markdown: bool,
                     client_gravatar: bool,
                     allow_edit_history: bool) -> List[Dict[str, Any]]:

    cache_transformer = MessageDict.build_dict_from_raw_db_row
    id_fetcher = lambda row: row['id']

    message_dicts = generic_bulk_cached_fetch(to_dict_cache_key_id,
                                              MessageDict.get_raw_db_rows,
                                              message_ids,
                                              id_fetcher=id_fetcher,
                                              cache_transformer=cache_transformer,
                                              extractor=extract_message_dict,
                                              setter=stringify_message_dict)

    message_list = []  # type: List[Dict[str, Any]]

    for message_id in message_ids:
        msg_dict = message_dicts[message_id]
        msg_dict.update({"flags": user_message_flags[message_id]})
        if message_id in search_fields:
            msg_dict.update(search_fields[message_id])
        # Make sure that we never send message edit history to clients
        # in realms with allow_edit_history disabled.
        if "edit_history" in msg_dict and not allow_edit_history:
            del msg_dict["edit_history"]
        message_list.append(msg_dict)

    MessageDict.post_process_dicts(message_list, apply_markdown, client_gravatar)

    return message_list

def sew_messages_and_reactions(messages: List[Dict[str, Any]],
                               reactions: List[Dict[str, Any]]) -> List[Dict[str, Any]]:
    """Given a iterable of messages and reactions stitch reactions
    into messages.
    """
    # Add all messages with empty reaction item
    for message in messages:
        message['reactions'] = []

    # Convert list of messages into dictionary to make reaction stitching easy
    converted_messages = {message['id']: message for message in messages}

    for reaction in reactions:
        converted_messages[reaction['message_id']]['reactions'].append(
            reaction)

    return list(converted_messages.values())


def sew_messages_and_submessages(messages: List[Dict[str, Any]],
                                 submessages: List[Dict[str, Any]]) -> None:
    # This is super similar to sew_messages_and_reactions.
    for message in messages:
        message['submessages'] = []

    message_dict = {message['id']: message for message in messages}

    for submessage in submessages:
        message_id = submessage['message_id']
        if message_id in message_dict:
            message = message_dict[message_id]
            message['submessages'].append(submessage)

def extract_message_dict(message_bytes: bytes) -> Dict[str, Any]:
    return ujson.loads(zlib.decompress(message_bytes).decode("utf-8"))

def stringify_message_dict(message_dict: Dict[str, Any]) -> bytes:
    return zlib.compress(ujson.dumps(message_dict).encode())

@cache_with_key(to_dict_cache_key, timeout=3600*24)
def message_to_dict_json(message: Message) -> bytes:
    return MessageDict.to_dict_uncached(message)

def save_message_rendered_content(message: Message, content: str) -> str:
    rendered_content = render_markdown(message, content, realm=message.get_realm())
    message.rendered_content = rendered_content
    message.rendered_content_version = bugdown.version
    message.save_rendered_content()
    return rendered_content

class MessageDict:
    @staticmethod
    def wide_dict(message: Message) -> Dict[str, Any]:
        '''
        The next two lines get the cachable field related
        to our message object, with the side effect of
        populating the cache.
        '''
        json = message_to_dict_json(message)
        obj = extract_message_dict(json)

        '''
        The steps below are similar to what we do in
        post_process_dicts(), except we don't call finalize_payload(),
        since that step happens later in the queue
        processor.
        '''
        MessageDict.bulk_hydrate_sender_info([obj])
        MessageDict.hydrate_recipient_info(obj)

        return obj

    @staticmethod
    def post_process_dicts(objs: List[Dict[str, Any]], apply_markdown: bool, client_gravatar: bool) -> None:
        MessageDict.bulk_hydrate_sender_info(objs)

        for obj in objs:
            MessageDict.hydrate_recipient_info(obj)
            MessageDict.finalize_payload(obj, apply_markdown, client_gravatar)

    @staticmethod
    def finalize_payload(obj: Dict[str, Any],
                         apply_markdown: bool,
                         client_gravatar: bool) -> None:
        MessageDict.set_sender_avatar(obj, client_gravatar)
        if apply_markdown:
            obj['content_type'] = 'text/html'
            obj['content'] = obj['rendered_content']
        else:
            obj['content_type'] = 'text/x-markdown'

        del obj['rendered_content']
        del obj['sender_realm_id']
        del obj['sender_avatar_source']
        del obj['sender_avatar_version']

        del obj['raw_display_recipient']
        del obj['recipient_type']
        del obj['recipient_type_id']
        del obj['sender_is_mirror_dummy']

    @staticmethod
    def to_dict_uncached(message: Message) -> bytes:
        dct = MessageDict.to_dict_uncached_helper(message)
        return stringify_message_dict(dct)

    @staticmethod
    def to_dict_uncached_helper(message: Message) -> Dict[str, Any]:
        return MessageDict.build_message_dict(
            message = message,
            message_id = message.id,
            last_edit_time = message.last_edit_time,
            edit_history = message.edit_history,
            content = message.content,
            subject = message.subject,
            pub_date = message.pub_date,
            rendered_content = message.rendered_content,
            rendered_content_version = message.rendered_content_version,
            sender_id = message.sender.id,
            sender_realm_id = message.sender.realm_id,
            sending_client_name = message.sending_client.name,
            recipient_id = message.recipient.id,
            recipient_type = message.recipient.type,
            recipient_type_id = message.recipient.type_id,
            reactions = Reaction.get_raw_db_rows([message.id]),
            submessages = SubMessage.get_raw_db_rows([message.id]),
        )

    @staticmethod
    def get_raw_db_rows(needed_ids: List[int]) -> List[Dict[str, Any]]:
        # This is a special purpose function optimized for
        # callers like get_messages_backend().
        fields = [
            'id',
            'subject',
            'pub_date',
            'last_edit_time',
            'edit_history',
            'content',
            'rendered_content',
            'rendered_content_version',
            'recipient_id',
            'recipient__type',
            'recipient__type_id',
            'sender_id',
            'sending_client__name',
            'sender__realm_id',
        ]
        messages = Message.objects.filter(id__in=needed_ids).values(*fields)

        submessages = SubMessage.get_raw_db_rows(needed_ids)
        sew_messages_and_submessages(messages, submessages)

        reactions = Reaction.get_raw_db_rows(needed_ids)
        return sew_messages_and_reactions(messages, reactions)

    @staticmethod
    def build_dict_from_raw_db_row(row: Dict[str, Any]) -> Dict[str, Any]:
        '''
        row is a row from a .values() call, and it needs to have
        all the relevant fields populated
        '''
        return MessageDict.build_message_dict(
            message = None,
            message_id = row['id'],
            last_edit_time = row['last_edit_time'],
            edit_history = row['edit_history'],
            content = row['content'],
            subject = row['subject'],
            pub_date = row['pub_date'],
            rendered_content = row['rendered_content'],
            rendered_content_version = row['rendered_content_version'],
            sender_id = row['sender_id'],
            sender_realm_id = row['sender__realm_id'],
            sending_client_name = row['sending_client__name'],
            recipient_id = row['recipient_id'],
            recipient_type = row['recipient__type'],
            recipient_type_id = row['recipient__type_id'],
            reactions=row['reactions'],
            submessages=row['submessages'],
        )

    @staticmethod
    def build_message_dict(
            message: Optional[Message],
            message_id: int,
            last_edit_time: Optional[datetime.datetime],
            edit_history: Optional[str],
            content: str,
            subject: str,
            pub_date: datetime.datetime,
            rendered_content: Optional[str],
            rendered_content_version: Optional[int],
            sender_id: int,
            sender_realm_id: int,
            sending_client_name: str,
            recipient_id: int,
            recipient_type: int,
            recipient_type_id: int,
            reactions: List[Dict[str, Any]],
            submessages: List[Dict[str, Any]]
    ) -> Dict[str, Any]:

        obj = dict(
            id                = message_id,
            sender_id         = sender_id,
            content           = content,
            recipient_type_id = recipient_type_id,
            recipient_type    = recipient_type,
            recipient_id      = recipient_id,
            subject           = subject,
            timestamp         = datetime_to_timestamp(pub_date),
            client            = sending_client_name)

        obj['sender_realm_id'] = sender_realm_id

        obj['raw_display_recipient'] = get_display_recipient_by_id(
            recipient_id,
            recipient_type,
            recipient_type_id
        )

        obj['subject_links'] = bugdown.subject_links(sender_realm_id, subject)

        if last_edit_time is not None:
            obj['last_edit_timestamp'] = datetime_to_timestamp(last_edit_time)
            assert edit_history is not None
            obj['edit_history'] = ujson.loads(edit_history)

        if Message.need_to_render_content(rendered_content, rendered_content_version, bugdown.version):
            if message is None:
                # We really shouldn't be rendering objects in this method, but there is
                # a scenario where we upgrade the version of bugdown and fail to run
                # management commands to re-render historical messages, and then we
                # need to have side effects.  This method is optimized to not need full
                # blown ORM objects, but the bugdown renderer is unfortunately highly
                # coupled to Message, and we also need to persist the new rendered content.
                # If we don't have a message object passed in, we get one here.  The cost
                # of going to the DB here should be overshadowed by the cost of rendering
                # and updating the row.
                # TODO: see #1379 to eliminate bugdown dependencies
                message = Message.objects.select_related().get(id=message_id)

            assert message is not None  # Hint for mypy.
            # It's unfortunate that we need to have side effects on the message
            # in some cases.
            rendered_content = save_message_rendered_content(message, content)

        if rendered_content is not None:
            obj['rendered_content'] = rendered_content
        else:
            obj['rendered_content'] = ('<p>[Zulip note: Sorry, we could not ' +
                                       'understand the formatting of your message]</p>')

        if rendered_content is not None:
            obj['is_me_message'] = Message.is_status_message(content, rendered_content)
        else:
            obj['is_me_message'] = False

        obj['reactions'] = [ReactionDict.build_dict_from_raw_db_row(reaction)
                            for reaction in reactions]
        obj['submessages'] = submessages
        return obj

    @staticmethod
    def bulk_hydrate_sender_info(objs: List[Dict[str, Any]]) -> None:

        sender_ids = list({
            obj['sender_id']
            for obj in objs
        })

        if not sender_ids:
            return

        query = UserProfile.objects.values(
            'id',
            'full_name',
            'short_name',
            'email',
            'realm__string_id',
            'avatar_source',
            'avatar_version',
            'is_mirror_dummy',
        )

        rows = query_for_ids(query, sender_ids, 'zerver_userprofile.id')

        sender_dict = {
            row['id']: row
            for row in rows
        }

        for obj in objs:
            sender_id = obj['sender_id']
            user_row = sender_dict[sender_id]
            obj['sender_full_name'] = user_row['full_name']
            obj['sender_short_name'] = user_row['short_name']
            obj['sender_email'] = user_row['email']
            obj['sender_realm_str'] = user_row['realm__string_id']
            obj['sender_avatar_source'] = user_row['avatar_source']
            obj['sender_avatar_version'] = user_row['avatar_version']
            obj['sender_is_mirror_dummy'] = user_row['is_mirror_dummy']

    @staticmethod
    def hydrate_recipient_info(obj: Dict[str, Any]) -> None:
        '''
        This method hyrdrates recipient info with things
        like full names and emails of senders.  Eventually
        our clients should be able to hyrdrate these fields
        themselves with info they already have on users.
        '''

        display_recipient = obj['raw_display_recipient']
        recipient_type = obj['recipient_type']
        recipient_type_id = obj['recipient_type_id']
        sender_is_mirror_dummy = obj['sender_is_mirror_dummy']
        sender_email = obj['sender_email']
        sender_full_name = obj['sender_full_name']
        sender_short_name = obj['sender_short_name']
        sender_id = obj['sender_id']

        if recipient_type == Recipient.STREAM:
            display_type = "stream"
        elif recipient_type in (Recipient.HUDDLE, Recipient.PERSONAL):
            assert not isinstance(display_recipient, str)
            display_type = "private"
            if len(display_recipient) == 1:
                # add the sender in if this isn't a message between
                # someone and themself, preserving ordering
                recip = {'email': sender_email,
                         'full_name': sender_full_name,
                         'short_name': sender_short_name,
                         'id': sender_id,
                         'is_mirror_dummy': sender_is_mirror_dummy}
                if recip['email'] < display_recipient[0]['email']:
                    display_recipient = [recip, display_recipient[0]]
                elif recip['email'] > display_recipient[0]['email']:
                    display_recipient = [display_recipient[0], recip]
        else:
            raise AssertionError("Invalid recipient type %s" % (recipient_type,))

        obj['display_recipient'] = display_recipient
        obj['type'] = display_type
        if obj['type'] == 'stream':
            obj['stream_id'] = recipient_type_id

    @staticmethod
    def set_sender_avatar(obj: Dict[str, Any], client_gravatar: bool) -> None:
        sender_id = obj['sender_id']
        sender_realm_id = obj['sender_realm_id']
        sender_email = obj['sender_email']
        sender_avatar_source = obj['sender_avatar_source']
        sender_avatar_version = obj['sender_avatar_version']

        obj['avatar_url'] = get_avatar_field(
            user_id=sender_id,
            realm_id=sender_realm_id,
            email=sender_email,
            avatar_source=sender_avatar_source,
            avatar_version=sender_avatar_version,
            medium=False,
            client_gravatar=client_gravatar,
        )

class ReactionDict:
    @staticmethod
    def build_dict_from_raw_db_row(row: Dict[str, Any]) -> Dict[str, Any]:
        return {'emoji_name': row['emoji_name'],
                'emoji_code': row['emoji_code'],
                'reaction_type': row['reaction_type'],
                'user': {'email': row['user_profile__email'],
                         'id': row['user_profile__id'],
                         'full_name': row['user_profile__full_name']}}


def access_message(user_profile: UserProfile, message_id: int) -> Tuple[Message, Optional[UserMessage]]:
    """You can access a message by ID in our APIs that either:
    (1) You received or have previously accessed via starring
        (aka have a UserMessage row for).
    (2) Was sent to a public stream in your realm.

    We produce consistent, boring error messages to avoid leaking any
    information from a security perspective.
    """
    try:
        message = Message.objects.select_related().get(id=message_id)
    except Message.DoesNotExist:
        raise JsonableError(_("Invalid message(s)"))

    user_message = get_usermessage_by_message_id(user_profile, message_id)

    if has_message_access(user_profile, message, user_message):
        return (message, user_message)
    raise JsonableError(_("Invalid message(s)"))

def has_message_access(user_profile: UserProfile, message: Message,
                       user_message: Optional[UserMessage]) -> bool:
    if user_message is None:
        if message.recipient.type != Recipient.STREAM:
            # You can't access private messages you didn't receive
            return False

        stream = Stream.objects.get(id=message.recipient.type_id)
        if stream.realm != user_profile.realm:
            # You can't access public stream messages in other realms
            return False

        if not stream.is_history_public_to_subscribers():
            # You can't access messages you didn't directly receive
            # unless history is public to subscribers.
            return False

        if not stream.is_public():
            # This stream is an invite-only stream where message
            # history is available to subscribers.  So we check if
            # you're subscribed.
            if not Subscription.objects.filter(user_profile=user_profile, active=True,
                                               recipient=message.recipient).exists():
                return False

            # You are subscribed, so let this fall through to the public stream case.
        elif user_profile.is_guest:
            # Guest users don't get automatic access to public stream messages
            if not Subscription.objects.filter(user_profile=user_profile, active=True,
                                               recipient=message.recipient).exists():
                return False
        else:
            # Otherwise, the message was sent to a public stream in
            # your realm, so return the message, user_message pair
            pass

    return True

def bulk_access_messages(user_profile: UserProfile, messages: Sequence[Message]) -> List[Message]:
    filtered_messages = []

    for message in messages:
        user_message = get_usermessage_by_message_id(user_profile, message.id)
        if has_message_access(user_profile, message, user_message):
            filtered_messages.append(message)
    return filtered_messages

def render_markdown(message: Message,
                    content: str,
                    realm: Optional[Realm]=None,
                    realm_alert_words: Optional[RealmAlertWords]=None,
                    user_ids: Optional[Set[int]]=None,
                    mention_data: Optional[bugdown.MentionData]=None,
                    email_gateway: Optional[bool]=False) -> str:
    """Return HTML for given markdown. Bugdown may add properties to the
    message object such as `mentions_user_ids`, `mentions_user_group_ids`, and
    `mentions_wildcard`.  These are only on this Django object and are not
    saved in the database.
    """

    if user_ids is None:
        message_user_ids = set()  # type: Set[int]
    else:
        message_user_ids = user_ids

    message.mentions_wildcard = False
    message.mentions_user_ids = set()
    message.mentions_user_group_ids = set()
    message.alert_words = set()
    message.links_for_preview = set()

    if realm is None:
        realm = message.get_realm()

    possible_words = set()  # type: Set[str]
    if realm_alert_words is not None:
        for user_id, words in realm_alert_words.items():
            if user_id in message_user_ids:
                possible_words.update(set(words))

    sent_by_bot = get_user_profile_by_id(message.sender_id).is_bot

    # DO MAIN WORK HERE -- call bugdown to convert
    rendered_content = bugdown.convert(
        content,
        message=message,
        message_realm=realm,
        possible_words=possible_words,
        sent_by_bot=sent_by_bot,
        mention_data=mention_data,
        email_gateway=email_gateway
    )

    if message is not None:
        message.user_ids_with_alert_words = set()

        if realm_alert_words is not None:
            for user_id, words in realm_alert_words.items():
                if user_id in message_user_ids:
                    if set(words).intersection(message.alert_words):
                        message.user_ids_with_alert_words.add(user_id)

    return rendered_content

def huddle_users(recipient_id: int) -> str:
    display_recipient = get_display_recipient_by_id(recipient_id,
                                                    Recipient.HUDDLE,
                                                    None)  # type: Union[str, List[Dict[str, Any]]]

    # str is for streams.
    assert not isinstance(display_recipient, str)

    user_ids = [obj['id'] for obj in display_recipient]  # type: List[int]
    user_ids = sorted(user_ids)
    return ','.join(str(uid) for uid in user_ids)

def aggregate_message_dict(input_dict: Dict[int, Dict[str, Any]],
                           lookup_fields: List[str],
                           collect_senders: bool) -> List[Dict[str, Any]]:
    lookup_dict = dict()  # type: Dict[Tuple[Any, ...], Dict[str, Any]]

    '''
    A concrete example might help explain the inputs here:

    input_dict = {
        1002: dict(stream_id=5, topic='foo', sender_id=40),
        1003: dict(stream_id=5, topic='foo', sender_id=41),
        1004: dict(stream_id=6, topic='baz', sender_id=99),
    }

    lookup_fields = ['stream_id', 'topic']

    The first time through the loop:
        attribute_dict = dict(stream_id=5, topic='foo', sender_id=40)
        lookup_dict = (5, 'foo')

    lookup_dict = {
        (5, 'foo'): dict(stream_id=5, topic='foo',
                         unread_message_ids=[1002, 1003],
                         sender_ids=[40, 41],
                        ),
        ...
    }

    result = [
        dict(stream_id=5, topic='foo',
             unread_message_ids=[1002, 1003],
             sender_ids=[40, 41],
            ),
        ...
    ]
    '''

    for message_id, attribute_dict in input_dict.items():
        lookup_key = tuple([attribute_dict[f] for f in lookup_fields])
        if lookup_key not in lookup_dict:
            obj = {}
            for f in lookup_fields:
                obj[f] = attribute_dict[f]
            obj['unread_message_ids'] = []
            if collect_senders:
                obj['sender_ids'] = set()
            lookup_dict[lookup_key] = obj

        bucket = lookup_dict[lookup_key]
        bucket['unread_message_ids'].append(message_id)
        if collect_senders:
            bucket['sender_ids'].add(attribute_dict['sender_id'])

    for dct in lookup_dict.values():
        dct['unread_message_ids'].sort()
        if collect_senders:
            dct['sender_ids'] = sorted(list(dct['sender_ids']))

    sorted_keys = sorted(lookup_dict.keys())

    return [lookup_dict[k] for k in sorted_keys]

def get_inactive_recipient_ids(user_profile: UserProfile) -> List[int]:
    rows = get_stream_subscriptions_for_user(user_profile).filter(
        active=False,
    ).values(
        'recipient_id'
    )
    inactive_recipient_ids = [
        row['recipient_id']
        for row in rows]
    return inactive_recipient_ids

def get_muted_stream_ids(user_profile: UserProfile) -> List[int]:
    rows = get_stream_subscriptions_for_user(user_profile).filter(
        active=True,
        in_home_view=False,
    ).values(
        'recipient__type_id'
    )
    muted_stream_ids = [
        row['recipient__type_id']
        for row in rows]
    return muted_stream_ids

def get_raw_unread_data(user_profile: UserProfile) -> RawUnreadMessagesResult:

    excluded_recipient_ids = get_inactive_recipient_ids(user_profile)

    user_msgs = UserMessage.objects.filter(
        user_profile=user_profile
    ).exclude(
        message__recipient_id__in=excluded_recipient_ids
    ).extra(
        where=[UserMessage.where_unread()]
    ).values(
        'message_id',
        'message__sender_id',
        'message__subject',
        'message__recipient_id',
        'message__recipient__type',
        'message__recipient__type_id',
        'flags',
    ).order_by("-message_id")

    # Limit unread messages for performance reasons.
    user_msgs = list(user_msgs[:MAX_UNREAD_MESSAGES])

    rows = list(reversed(user_msgs))

    muted_stream_ids = get_muted_stream_ids(user_profile)

    topic_mute_checker = build_topic_mute_checker(user_profile)

    def is_row_muted(stream_id: int, recipient_id: int, topic: str) -> bool:
        if stream_id in muted_stream_ids:
            return True

        if topic_mute_checker(recipient_id, topic):
            return True

        return False

    huddle_cache = {}  # type: Dict[int, str]

    def get_huddle_users(recipient_id: int) -> str:
        if recipient_id in huddle_cache:
            return huddle_cache[recipient_id]

        user_ids_string = huddle_users(recipient_id)
        huddle_cache[recipient_id] = user_ids_string
        return user_ids_string

    pm_dict = {}
    stream_dict = {}
    unmuted_stream_msgs = set()
    huddle_dict = {}
    mentions = set()

    for row in rows:
        message_id = row['message_id']
        msg_type = row['message__recipient__type']
        recipient_id = row['message__recipient_id']
        sender_id = row['message__sender_id']

        if msg_type == Recipient.STREAM:
            stream_id = row['message__recipient__type_id']
            topic = row['message__subject']
            stream_dict[message_id] = dict(
                stream_id=stream_id,
                topic=topic,
                sender_id=sender_id,
            )
            if not is_row_muted(stream_id, recipient_id, topic):
                unmuted_stream_msgs.add(message_id)

        elif msg_type == Recipient.PERSONAL:
            pm_dict[message_id] = dict(
                sender_id=sender_id,
            )

        elif msg_type == Recipient.HUDDLE:
            user_ids_string = get_huddle_users(recipient_id)
            huddle_dict[message_id] = dict(
                user_ids_string=user_ids_string,
            )

        is_mentioned = (row['flags'] & UserMessage.flags.mentioned) != 0
        if is_mentioned:
            mentions.add(message_id)

    return dict(
        pm_dict=pm_dict,
        stream_dict=stream_dict,
        muted_stream_ids=muted_stream_ids,
        unmuted_stream_msgs=unmuted_stream_msgs,
        huddle_dict=huddle_dict,
        mentions=mentions,
    )

def aggregate_unread_data(raw_data: RawUnreadMessagesResult) -> UnreadMessagesResult:

    pm_dict = raw_data['pm_dict']
    stream_dict = raw_data['stream_dict']
    unmuted_stream_msgs = raw_data['unmuted_stream_msgs']
    huddle_dict = raw_data['huddle_dict']
    mentions = list(raw_data['mentions'])

    count = len(pm_dict) + len(unmuted_stream_msgs) + len(huddle_dict)

    pm_objects = aggregate_message_dict(
        input_dict=pm_dict,
        lookup_fields=[
            'sender_id',
        ],
        collect_senders=False,
    )

    stream_objects = aggregate_message_dict(
        input_dict=stream_dict,
        lookup_fields=[
            'stream_id',
            'topic',
        ],
        collect_senders=True,
    )

    huddle_objects = aggregate_message_dict(
        input_dict=huddle_dict,
        lookup_fields=[
            'user_ids_string',
        ],
        collect_senders=False,
    )

    result = dict(
        pms=pm_objects,
        streams=stream_objects,
        huddles=huddle_objects,
        mentions=mentions,
        count=count)  # type: UnreadMessagesResult

    return result

def apply_unread_message_event(user_profile: UserProfile,
                               state: Dict[str, Any],
                               message: Dict[str, Any],
                               flags: List[str]) -> None:
    message_id = message['id']
    if message['type'] == 'stream':
        message_type = 'stream'
    elif message['type'] == 'private':
        others = [
            recip for recip in message['display_recipient']
            if recip['id'] != message['sender_id']
        ]
        if len(others) <= 1:
            message_type = 'private'
        else:
            message_type = 'huddle'
    else:
        raise AssertionError("Invalid message type %s" % (message['type'],))

    sender_id = message['sender_id']

    if message_type == 'stream':
        stream_id = message['stream_id']
        topic = message['subject']
        new_row = dict(
            stream_id=stream_id,
            topic=topic,
            sender_id=sender_id,
        )
        state['stream_dict'][message_id] = new_row

        if stream_id not in state['muted_stream_ids']:
            # This next check hits the database.
            if not topic_is_muted(user_profile, stream_id, topic):
                state['unmuted_stream_msgs'].add(message_id)

    elif message_type == 'private':
        sender_id = message['sender_id']
        new_row = dict(
            sender_id=sender_id,
        )
        state['pm_dict'][message_id] = new_row

    else:
        display_recipient = message['display_recipient']
        user_ids = [obj['id'] for obj in display_recipient]
        user_ids = sorted(user_ids)
        user_ids_string = ','.join(str(uid) for uid in user_ids)
        new_row = dict(
            user_ids_string=user_ids_string,
        )
        state['huddle_dict'][message_id] = new_row

    if 'mentioned' in flags:
        state['mentions'].add(message_id)

def estimate_recent_messages(realm: Realm, hours: int) -> int:
    stat = COUNT_STATS['messages_sent:is_bot:hour']
    d = timezone_now() - datetime.timedelta(hours=hours)
    return RealmCount.objects.filter(property=stat.property, end_time__gt=d,
                                     realm=realm).aggregate(Sum('value'))['value__sum'] or 0

def get_first_visible_message_id(realm: Realm) -> int:
    val = cache_get(realm_first_visible_message_id_cache_key(realm))
    if val is not None:
        return val[0]
    return 0

def maybe_update_first_visible_message_id(realm: Realm, lookback_hours: int) -> None:
    cache_empty = cache_get(realm_first_visible_message_id_cache_key(realm)) is None
    recent_messages_count = estimate_recent_messages(realm, lookback_hours)
    if realm.message_visibility_limit is not None and (recent_messages_count > 0 or cache_empty):
        update_first_visible_message_id(realm)

def update_first_visible_message_id(realm: Realm) -> None:
    try:
        # We have verified that the limit is not none before calling this function.
        assert realm.message_visibility_limit is not None
        first_visible_message_id = Message.objects.filter(sender__realm=realm).values('id').\
            order_by('-id')[realm.message_visibility_limit - 1]["id"]
    except IndexError:
        first_visible_message_id = 0
    cache_set(realm_first_visible_message_id_cache_key(realm), first_visible_message_id)