zulip/zerver/lib/narrow.py

import re
from collections.abc import Callable, Iterable, Sequence
from dataclasses import dataclass
from typing import Any, Generic, TypeAlias, TypeVar

from django.conf import settings
from django.contrib.auth.models import AnonymousUser
from django.core.exceptions import ValidationError
from django.db import connection
from django.utils.translation import gettext as _
from pydantic import BaseModel, model_validator
from sqlalchemy.dialects import postgresql
from sqlalchemy.engine import Connection, Row
from sqlalchemy.sql import (
    ClauseElement,
    ColumnElement,
    Select,
    and_,
    column,
    false,
    func,
    join,
    literal,
    literal_column,
    not_,
    or_,
    select,
    table,
    union_all,
)
from sqlalchemy.sql.selectable import SelectBase
from sqlalchemy.types import ARRAY, Boolean, Integer, Text
from typing_extensions import override

from zerver.lib.addressee import get_user_profiles, get_user_profiles_by_ids
from zerver.lib.exceptions import ErrorCode, JsonableError, MissingAuthenticationError
from zerver.lib.message import (
    access_message,
    access_web_public_message,
    get_first_visible_message_id,
)
from zerver.lib.narrow_predicate import channel_operators, channels_operators
from zerver.lib.recipient_users import recipient_for_user_profiles
from zerver.lib.sqlalchemy_utils import get_sqlalchemy_connection
from zerver.lib.streams import (
    can_access_stream_history_by_id,
    can_access_stream_history_by_name,
    get_public_streams_queryset,
    get_stream_by_narrow_operand_access_unchecked,
    get_web_public_streams_queryset,
)
from zerver.lib.topic_sqlalchemy import (
    get_followed_topic_condition_sa,
    get_resolved_topic_condition_sa,
    topic_column_sa,
    topic_match_sa,
)
from zerver.lib.types import Validator
from zerver.lib.user_topics import exclude_topic_mutes
from zerver.lib.validator import (
    check_bool,
    check_required_string,
    check_string,
    check_string_or_int,
    check_string_or_int_list,
)
from zerver.models import (
    DirectMessageGroup,
    Message,
    Realm,
    Recipient,
    Stream,
    Subscription,
    UserMessage,
    UserProfile,
)
from zerver.models.recipients import get_direct_message_group_user_ids
from zerver.models.streams import get_active_streams
from zerver.models.users import (
    get_user_by_id_in_realm_including_cross_realm,
    get_user_including_cross_realm,
)


class NarrowParameter(BaseModel):
    operator: str
    operand: Any
    negated: bool = False

    @model_validator(mode="before")
    @classmethod
    def convert_term(cls, elem: dict[str, Any] | list[str]) -> dict[str, Any]:
        # We have to support a legacy tuple format.
        if isinstance(elem, list):
            if len(elem) != 2 or any(not isinstance(x, str) for x in elem):
                raise ValueError("element is not a string pair")
            return dict(operator=elem[0], operand=elem[1])

        elif isinstance(elem, dict):
            if "operand" not in elem or elem["operand"] is None:
                raise ValueError("operand is missing")

            if "operator" not in elem or elem["operator"] is None:
                raise ValueError("operator is missing")
            return elem
        else:
            raise ValueError("dict or list required")

    @model_validator(mode="after")
    def validate_terms(self) -> "NarrowParameter":
        # Make sure to sync this list to frontend also when adding a new operator that
        # supports integer IDs. Relevant code is located in web/src/message_fetch.ts
        # in handle_operators_supporting_id_based_api function where you will need to
        # update operators_supporting_id, or operators_supporting_ids array.
        operators_supporting_id = [
            *channel_operators,
            "id",
            "sender",
            "group-pm-with",
            "dm-including",
            "with",
        ]
        operators_supporting_ids = ["pm-with", "dm"]
        operators_non_empty_operand = {"search"}

        operator = self.operator
        if operator in operators_supporting_id:
            operand_validator: Validator[object] = check_string_or_int
        elif operator in operators_supporting_ids:
            operand_validator = check_string_or_int_list
        elif operator in operators_non_empty_operand:
            operand_validator = check_required_string
        else:
            operand_validator = check_string

        try:
            self.operand = operand_validator("operand", self.operand)
            self.operator = check_string("operator", self.operator)
            if self.negated is not None:
                self.negated = check_bool("negated", self.negated)
        except ValidationError as error:
            raise JsonableError(error.message)

        # whitelist the fields we care about for now
        return self


def is_spectator_compatible(narrow: Iterable[NarrowParameter]) -> bool:
    # This implementation should agree with is_spectator_compatible in hash_parser.ts.
    supported_operators = [
        *channel_operators,
        *channels_operators,
        "topic",
        "sender",
        "has",
        "search",
        "near",
        "id",
        "with",
    ]
    for element in narrow:
        operator = element.operator
        if operator not in supported_operators:
            return False
    return True


def is_web_public_narrow(narrow: Iterable[NarrowParameter] | None) -> bool:
    if narrow is None:
        return False

    return any(
        # Web-public queries are only allowed for limited types of narrows.
        # term == {'operator': 'channels', 'operand': 'web-public', 'negated': False}
        # or term == {'operator': 'streams', 'operand': 'web-public', 'negated': False}
        term.operator in channels_operators
        and term.operand == "web-public"
        and term.negated is False
        for term in narrow
    )


LARGER_THAN_MAX_MESSAGE_ID = 10000000000000000


class BadNarrowOperatorError(JsonableError):
    code = ErrorCode.BAD_NARROW
    data_fields = ["desc"]

    def __init__(self, desc: str) -> None:
        self.desc: str = desc

    @staticmethod
    @override
    def msg_format() -> str:
        return _("Invalid narrow operator: {desc}")


class InvalidOperatorCombinationError(JsonableError):
    code = ErrorCode.BAD_NARROW
    data_fields = ["desc"]

    def __init__(self, desc: str) -> None:
        self.desc: str = desc

    @staticmethod
    @override
    def msg_format() -> str:
        return _("Invalid narrow operator combination: {desc}")


ConditionTransform: TypeAlias = Callable[[ClauseElement], ClauseElement]

# These delimiters will not appear in rendered messages or HTML-escaped topics.
TS_START = "<ts-match>"
TS_STOP = "</ts-match>"


def ts_locs_array(
    config: ColumnElement[Text],
    text: ColumnElement[Text],
    tsquery: ColumnElement[Any],
) -> ColumnElement[ARRAY[Integer]]:
    options = f"HighlightAll = TRUE, StartSel = {TS_START}, StopSel = {TS_STOP}"
    delimited = func.ts_headline(config, text, tsquery, options, type_=Text)
    part = func.unnest(
        func.string_to_array(delimited, TS_START, type_=ARRAY(Text)), type_=Text
    ).column_valued()
    part_len = func.length(part, type_=Integer) - len(TS_STOP)
    match_pos = func.sum(part_len, type_=Integer).over(rows=(None, -1)) + len(TS_STOP)
    match_len = func.strpos(part, TS_STOP, type_=Integer) - 1
    return func.array(
        select(postgresql.array([match_pos, match_len])).offset(1).scalar_subquery(),
        type_=ARRAY(Integer),
    )


class NarrowBuilder:
    """
    Build up a SQLAlchemy query to find messages matching a narrow.
    """

    # This class has an important security invariant:
    #
    #   None of these methods ever *add* messages to a query's result.
    #
    # That is, the `add_term` method, and its helpers the `by_*` methods,
    # are passed a Select object representing a query for messages; they may
    # call some methods on it, and then they return a resulting Select
    # object.  Things these methods may do to the queries they handle
    # include
    #  * add conditions to filter out rows (i.e., messages), with `query.where`
    #  * add columns for more information on the same message, with `query.column`
    #  * add a join for more information on the same message
    #
    # Things they may not do include
    #  * anything that would pull in additional rows, or information on
    #    other messages.

    def __init__(
        self,
        user_profile: UserProfile | None,
        msg_id_column: ColumnElement[Integer],
        realm: Realm,
        is_web_public_query: bool = False,
    ) -> None:
        self.user_profile = user_profile
        self.msg_id_column = msg_id_column
        self.realm = realm
        self.is_web_public_query = is_web_public_query
        self.by_method_map = {
            "has": self.by_has,
            "in": self.by_in,
            "is": self.by_is,
            "channel": self.by_channel,
            # "stream" is a legacy alias for "channel"
            "stream": self.by_channel,
            "channels": self.by_channels,
            # "streams" is a legacy alias for "channels"
            "streams": self.by_channels,
            "topic": self.by_topic,
            "sender": self.by_sender,
            "near": self.by_near,
            "id": self.by_id,
            "search": self.by_search,
            "dm": self.by_dm,
            # "pm-with:" is a legacy alias for "dm:"
            "pm-with": self.by_dm,
            "dm-including": self.by_dm_including,
            # "group-pm-with:" was deprecated by the addition of "dm-including:"
            "group-pm-with": self.by_group_pm_with,
            # TODO/compatibility: Prior to commit a9b3a9c, the server implementation
            # for documented search operators with dashes, also implicitly supported
            # clients sending those same operators with underscores. We can remove
            # support for the below operators when support for the associated dashed
            # operator is removed.
            "pm_with": self.by_dm,
            "group_pm_with": self.by_group_pm_with,
        }
        self.is_channel_narrow = False
        self.is_dm_narrow = False

    def check_not_both_channel_and_dm_narrow(
        self, is_dm_narrow: bool = False, is_channel_narrow: bool = False
    ) -> None:
        if is_dm_narrow:
            self.is_dm_narrow = True
        if is_channel_narrow:
            self.is_channel_narrow = True
        if self.is_channel_narrow and self.is_dm_narrow:
            raise BadNarrowOperatorError(
                "No message can be both a channel message and direct message"
            )

    def add_term(self, query: Select, term: NarrowParameter) -> Select:
        """
        Extend the given query to one narrowed by the given term, and return the result.

        This method satisfies an important security property: the returned
        query never includes a message that the given query didn't.  In
        particular, if the given query will only find messages that a given
        user can legitimately see, then so will the returned query.
        """
        # To maintain the security property, we hold all the `by_*`
        # methods to the same criterion.  See the class's block comment
        # for details.

        operator = term.operator
        operand = term.operand

        negated = term.negated

        if operator in self.by_method_map:
            method = self.by_method_map[operator]
        else:
            raise BadNarrowOperatorError("unknown operator " + operator)

        if negated:
            maybe_negate: ConditionTransform = not_
        else:
            maybe_negate = lambda cond: cond

        return method(query, operand, maybe_negate)

    def by_has(self, query: Select, operand: str, maybe_negate: ConditionTransform) -> Select:
        if operand not in ["attachment", "image", "link", "reaction"]:
            raise BadNarrowOperatorError("unknown 'has' operand " + operand)

        if operand == "reaction":
            if self.msg_id_column.name == "message_id":
                # If the initial query uses `zerver_usermessage`
                check_col = literal_column("zerver_usermessage.message_id", Integer)
            else:
                # If the initial query doesn't use `zerver_usermessage`
                check_col = literal_column("zerver_message.id", Integer)
            exists_cond = (
                select(1)
                .select_from(table("zerver_reaction"))
                .where(check_col == literal_column("zerver_reaction.message_id", Integer))
                .exists()
            )
            return query.where(maybe_negate(exists_cond))

        col_name = "has_" + operand
        cond = column(col_name, Boolean)
        return query.where(maybe_negate(cond))

    def by_in(self, query: Select, operand: str, maybe_negate: ConditionTransform) -> Select:
        # This operator does not support is_web_public_query.
        assert not self.is_web_public_query
        assert self.user_profile is not None

        if operand == "home":
            conditions = exclude_muting_conditions(self.user_profile, [])
            return query.where(and_(*conditions))
        elif operand == "all":
            return query

        raise BadNarrowOperatorError("unknown 'in' operand " + operand)

    def by_is(self, query: Select, operand: str, maybe_negate: ConditionTransform) -> Select:
        # This operator class does not support is_web_public_query.
        assert not self.is_web_public_query
        assert self.user_profile is not None

        if operand in ["dm", "private"]:
            # "is:private" is a legacy alias for "is:dm"
            self.check_not_both_channel_and_dm_narrow(is_dm_narrow=True)
            cond = column("flags", Integer).op("&")(UserMessage.flags.is_private.mask) != 0
            return query.where(maybe_negate(cond))
        elif operand == "starred":
            cond = column("flags", Integer).op("&")(UserMessage.flags.starred.mask) != 0
            return query.where(maybe_negate(cond))
        elif operand == "unread":
            cond = column("flags", Integer).op("&")(UserMessage.flags.read.mask) == 0
            return query.where(maybe_negate(cond))
        elif operand == "mentioned":
            mention_flags_mask = (
                UserMessage.flags.mentioned.mask
                | UserMessage.flags.stream_wildcard_mentioned.mask
                | UserMessage.flags.topic_wildcard_mentioned.mask
                | UserMessage.flags.group_mentioned.mask
            )
            cond = column("flags", Integer).op("&")(mention_flags_mask) != 0
            return query.where(maybe_negate(cond))
        elif operand == "alerted":
            cond = column("flags", Integer).op("&")(UserMessage.flags.has_alert_word.mask) != 0
            return query.where(maybe_negate(cond))
        elif operand == "resolved":
            cond = get_resolved_topic_condition_sa()
            return query.where(maybe_negate(cond))
        elif operand == "followed":
            cond = get_followed_topic_condition_sa(self.user_profile.id)
            return query.where(maybe_negate(cond))
        raise BadNarrowOperatorError("unknown 'is' operand " + operand)

    _alphanum = frozenset("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")

    def _pg_re_escape(self, pattern: str) -> str:
        """
        Escape user input to place in a regex

        Python's re.escape escapes Unicode characters in a way which PostgreSQL
        fails on, '\u03bb' to '\\\u03bb'. This function will correctly escape
        them for PostgreSQL, '\u03bb' to '\\u03bb'.
        """
        s = list(pattern)
        for i, c in enumerate(s):
            if c not in self._alphanum:
                if ord(c) >= 128:
                    # convert the character to hex PostgreSQL regex will take
                    # \uXXXX
                    s[i] = f"\\u{ord(c):0>4x}"
                else:
                    s[i] = "\\" + c
        return "".join(s)

    def by_channel(
        self, query: Select, operand: str | int, maybe_negate: ConditionTransform
    ) -> Select:
        self.check_not_both_channel_and_dm_narrow(is_channel_narrow=True)

        try:
            # Because you can see your own message history for
            # private channels you are no longer subscribed to, we
            # need get_stream_by_narrow_operand_access_unchecked here.
            channel = get_stream_by_narrow_operand_access_unchecked(operand, self.realm)

            if self.is_web_public_query and not channel.is_web_public:
                raise BadNarrowOperatorError("unknown web-public channel " + str(operand))
        except Stream.DoesNotExist:
            raise BadNarrowOperatorError("unknown channel " + str(operand))

        if self.realm.is_zephyr_mirror_realm:
            # MIT users expect narrowing to "social" to also show messages to
            # /^(un)*social(.d)*$/ (unsocial, ununsocial, social.d, ...).

            # In `ok_to_include_history`, we assume that a non-negated
            # `channel` term for a public channel will limit the query to
            # that specific channel. So it would be a bug to hit this
            # codepath after relying on this term there. But all channels in
            # a Zephyr realm are private, so that doesn't happen.
            assert not channel.is_public()

            m = re.search(r"^(?:un)*(.+?)(?:\.d)*$", channel.name, re.IGNORECASE)
            # Since the regex has a `.+` in it and "" is invalid as a
            # channel name, this will always match
            assert m is not None
            base_channel_name = m.group(1)

            matching_channels = get_active_streams(self.realm).filter(
                name__iregex=rf"^(un)*{self._pg_re_escape(base_channel_name)}(\.d)*$"
            )
            recipient_ids = [
                matching_channel.recipient_id for matching_channel in matching_channels
            ]
            cond = column("recipient_id", Integer).in_(recipient_ids)
            return query.where(maybe_negate(cond))

        recipient_id = channel.recipient_id
        assert recipient_id is not None
        cond = column("recipient_id", Integer) == recipient_id
        return query.where(maybe_negate(cond))

    def by_channels(self, query: Select, operand: str, maybe_negate: ConditionTransform) -> Select:
        self.check_not_both_channel_and_dm_narrow(is_channel_narrow=True)

        if operand == "public":
            # Get all both subscribed and non-subscribed public channels
            # but exclude any private subscribed channels.
            recipient_queryset = get_public_streams_queryset(self.realm)
        elif operand == "web-public":
            recipient_queryset = get_web_public_streams_queryset(self.realm)
        else:
            raise BadNarrowOperatorError("unknown channels operand " + operand)

        recipient_ids = recipient_queryset.values_list("recipient_id", flat=True).order_by("id")
        cond = column("recipient_id", Integer).in_(recipient_ids)
        return query.where(maybe_negate(cond))

    def by_topic(self, query: Select, operand: str, maybe_negate: ConditionTransform) -> Select:
        self.check_not_both_channel_and_dm_narrow(is_channel_narrow=True)

        if self.realm.is_zephyr_mirror_realm:
            # MIT users expect narrowing to topic "foo" to also show messages to /^foo(.d)*$/
            # (foo, foo.d, foo.d.d, etc)
            m = re.search(r"^(.*?)(?:\.d)*$", operand, re.IGNORECASE)
            # Since the regex has a `.*` in it, this will always match
            assert m is not None
            base_topic = m.group(1)

            # Additionally, MIT users expect the empty instance and
            # instance "personal" to be the same.
            if base_topic in ("", "personal", '(instance "")'):
                cond: ClauseElement = or_(
                    topic_match_sa(""),
                    topic_match_sa(".d"),
                    topic_match_sa(".d.d"),
                    topic_match_sa(".d.d.d"),
                    topic_match_sa(".d.d.d.d"),
                    topic_match_sa("personal"),
                    topic_match_sa("personal.d"),
                    topic_match_sa("personal.d.d"),
                    topic_match_sa("personal.d.d.d"),
                    topic_match_sa("personal.d.d.d.d"),
                    topic_match_sa('(instance "")'),
                    topic_match_sa('(instance "").d'),
                    topic_match_sa('(instance "").d.d'),
                    topic_match_sa('(instance "").d.d.d'),
                    topic_match_sa('(instance "").d.d.d.d'),
                )
            else:
                # We limit `.d` counts, since PostgreSQL has much better
                # query planning for this than they do for a regular
                # expression (which would sometimes table scan).
                cond = or_(
                    topic_match_sa(base_topic),
                    topic_match_sa(base_topic + ".d"),
                    topic_match_sa(base_topic + ".d.d"),
                    topic_match_sa(base_topic + ".d.d.d"),
                    topic_match_sa(base_topic + ".d.d.d.d"),
                )
            return query.where(maybe_negate(cond))

        cond = topic_match_sa(operand)
        return query.where(maybe_negate(cond))

    def by_sender(
        self, query: Select, operand: str | int, maybe_negate: ConditionTransform
    ) -> Select:
        try:
            if isinstance(operand, str):
                sender = get_user_including_cross_realm(operand, self.realm)
            else:
                sender = get_user_by_id_in_realm_including_cross_realm(operand, self.realm)
        except UserProfile.DoesNotExist:
            raise BadNarrowOperatorError("unknown user " + str(operand))

        cond = column("sender_id", Integer) == literal(sender.id)
        return query.where(maybe_negate(cond))

    def by_near(self, query: Select, operand: str, maybe_negate: ConditionTransform) -> Select:
        return query

    def by_id(self, query: Select, operand: int | str, maybe_negate: ConditionTransform) -> Select:
        if not str(operand).isdigit() or int(operand) > Message.MAX_POSSIBLE_MESSAGE_ID:
            raise BadNarrowOperatorError("Invalid message ID")
        cond = self.msg_id_column == literal(operand)
        return query.where(maybe_negate(cond))

    def by_dm(
        self, query: Select, operand: str | Iterable[int], maybe_negate: ConditionTransform
    ) -> Select:
        # This operator does not support is_web_public_query.
        assert not self.is_web_public_query
        assert self.user_profile is not None

        self.check_not_both_channel_and_dm_narrow(is_dm_narrow=True)

        try:
            if isinstance(operand, str):
                email_list = operand.split(",")
                user_profiles = get_user_profiles(
                    emails=email_list,
                    realm=self.realm,
                )
            else:
                """
                This is where we handle passing a list of user IDs for the narrow, which is the
                preferred/cleaner API.
                """
                user_profiles = get_user_profiles_by_ids(
                    user_ids=operand,
                    realm=self.realm,
                )

            if user_profiles == []:
                return query.where(maybe_negate(false()))

            recipient = recipient_for_user_profiles(
                user_profiles=user_profiles,
                forwarded_mirror_message=False,
                forwarder_user_profile=None,
                sender=self.user_profile,
                allow_deactivated=True,
                create=False,
            )
        except (JsonableError, ValidationError):
            raise BadNarrowOperatorError("unknown user in " + str(operand))
        except DirectMessageGroup.DoesNotExist:
            # Group DM where direct message group doesn't exist
            return query.where(maybe_negate(false()))

        # Group direct message
        if recipient.type == Recipient.DIRECT_MESSAGE_GROUP:
            cond = column("recipient_id", Integer) == recipient.id
            return query.where(maybe_negate(cond))

        # 1:1 direct message
        other_participant = None

        # Find if another person is in direct message
        for user in user_profiles:
            if user.id != self.user_profile.id:
                other_participant = user

        # Direct message with another person
        if other_participant:
            # We need bidirectional direct messages with another person.
            # But Recipient.PERSONAL objects only encode the person who
            # received the message, and not the other participant in
            # the thread (the sender), we need to do a somewhat
            # complex query to get messages between these two users
            # with either of them as the sender.
            self_recipient_id = self.user_profile.recipient_id
            cond = and_(
                column("flags", Integer).op("&")(UserMessage.flags.is_private.mask) != 0,
                column("realm_id", Integer) == self.realm.id,
                or_(
                    and_(
                        column("sender_id", Integer) == other_participant.id,
                        column("recipient_id", Integer) == self_recipient_id,
                    ),
                    and_(
                        column("sender_id", Integer) == self.user_profile.id,
                        column("recipient_id", Integer) == recipient.id,
                    ),
                ),
            )
            return query.where(maybe_negate(cond))

        # Direct message with self
        cond = and_(
            column("flags", Integer).op("&")(UserMessage.flags.is_private.mask) != 0,
            column("realm_id", Integer) == self.realm.id,
            column("sender_id", Integer) == self.user_profile.id,
            column("recipient_id", Integer) == recipient.id,
        )
        return query.where(maybe_negate(cond))

    def _get_direct_message_group_recipients(self, other_user: UserProfile) -> set[int]:
        self_recipient_ids = [
            recipient_tuple["recipient_id"]
            for recipient_tuple in Subscription.objects.filter(
                user_profile=self.user_profile,
                recipient__type=Recipient.DIRECT_MESSAGE_GROUP,
            ).values("recipient_id")
        ]
        narrow_recipient_ids = [
            recipient_tuple["recipient_id"]
            for recipient_tuple in Subscription.objects.filter(
                user_profile=other_user,
                recipient__type=Recipient.DIRECT_MESSAGE_GROUP,
            ).values("recipient_id")
        ]

        return set(self_recipient_ids) & set(narrow_recipient_ids)

    def by_dm_including(
        self, query: Select, operand: str | int, maybe_negate: ConditionTransform
    ) -> Select:
        # This operator does not support is_web_public_query.
        assert not self.is_web_public_query
        assert self.user_profile is not None

        self.check_not_both_channel_and_dm_narrow(is_dm_narrow=True)

        try:
            if isinstance(operand, str):
                narrow_user_profile = get_user_including_cross_realm(operand, self.realm)
            else:
                narrow_user_profile = get_user_by_id_in_realm_including_cross_realm(
                    operand, self.realm
                )
        except UserProfile.DoesNotExist:
            raise BadNarrowOperatorError("unknown user " + str(operand))

        # "dm-including" when combined with the user's own ID/email as the operand
        # should return all group and 1:1 direct messages (including direct messages
        # with self), so the simplest query to get these messages is the same as "is:dm".
        if narrow_user_profile.id == self.user_profile.id:
            cond = column("flags", Integer).op("&")(UserMessage.flags.is_private.mask) != 0
            return query.where(maybe_negate(cond))

        # all direct messages including another person (group and 1:1)
        direct_message_group_recipient_ids = self._get_direct_message_group_recipients(
            narrow_user_profile
        )

        self_recipient_id = self.user_profile.recipient_id
        # See note above in `by_dm` about needing bidirectional messages
        # for direct messages with another person.
        cond = and_(
            column("flags", Integer).op("&")(UserMessage.flags.is_private.mask) != 0,
            column("realm_id", Integer) == self.realm.id,
            or_(
                and_(
                    column("sender_id", Integer) == narrow_user_profile.id,
                    column("recipient_id", Integer) == self_recipient_id,
                ),
                and_(
                    column("sender_id", Integer) == self.user_profile.id,
                    column("recipient_id", Integer) == narrow_user_profile.recipient_id,
                ),
                and_(
                    column("recipient_id", Integer).in_(direct_message_group_recipient_ids),
                ),
            ),
        )
        return query.where(maybe_negate(cond))

    def by_group_pm_with(
        self, query: Select, operand: str | int, maybe_negate: ConditionTransform
    ) -> Select:
        # This operator does not support is_web_public_query.
        assert not self.is_web_public_query
        assert self.user_profile is not None

        self.check_not_both_channel_and_dm_narrow(is_dm_narrow=True)

        try:
            if isinstance(operand, str):
                narrow_profile = get_user_including_cross_realm(operand, self.realm)
            else:
                narrow_profile = get_user_by_id_in_realm_including_cross_realm(operand, self.realm)
        except UserProfile.DoesNotExist:
            raise BadNarrowOperatorError("unknown user " + str(operand))

        recipient_ids = self._get_direct_message_group_recipients(narrow_profile)
        cond = and_(
            column("flags", Integer).op("&")(UserMessage.flags.is_private.mask) != 0,
            column("realm_id", Integer) == self.realm.id,
            column("recipient_id", Integer).in_(recipient_ids),
        )
        return query.where(maybe_negate(cond))

    def by_search(self, query: Select, operand: str, maybe_negate: ConditionTransform) -> Select:
        if settings.USING_PGROONGA:
            return self._by_search_pgroonga(query, operand, maybe_negate)
        else:
            return self._by_search_tsearch(query, operand, maybe_negate)

    def _by_search_pgroonga(
        self, query: Select, operand: str, maybe_negate: ConditionTransform
    ) -> Select:
        match_positions_character = func.pgroonga_match_positions_character
        query_extract_keywords = func.pgroonga_query_extract_keywords
        operand_escaped = func.escape_html(operand, type_=Text)
        keywords = query_extract_keywords(operand_escaped)
        query = query.add_columns(
            match_positions_character(column("rendered_content", Text), keywords).label(
                "content_matches"
            ),
            match_positions_character(
                func.escape_html(topic_column_sa(), type_=Text), keywords
            ).label("topic_matches"),
        )
        condition = column("search_pgroonga", Text).op("&@~")(operand_escaped)
        return query.where(maybe_negate(condition))

    def _by_search_tsearch(
        self, query: Select, operand: str, maybe_negate: ConditionTransform
    ) -> Select:
        tsquery = func.plainto_tsquery(literal("zulip.english_us_search"), literal(operand))
        query = query.add_columns(
            ts_locs_array(
                literal("zulip.english_us_search", Text), column("rendered_content", Text), tsquery
            ).label("content_matches"),
            # We HTML-escape the topic in PostgreSQL to avoid doing a server round-trip
            ts_locs_array(
                literal("zulip.english_us_search", Text),
                func.escape_html(topic_column_sa(), type_=Text),
                tsquery,
            ).label("topic_matches"),
        )

        # Do quoted string matching.  We really want phrase
        # search here so we can ignore punctuation and do
        # stemming, but there isn't a standard phrase search
        # mechanism in PostgreSQL
        for term in re.findall(r'"[^"]+"|\S+', operand):
            if term[0] == '"' and term[-1] == '"':
                term = term[1:-1]
                term = "%" + connection.ops.prep_for_like_query(term) + "%"
                cond: ClauseElement = or_(
                    column("content", Text).ilike(term), topic_column_sa().ilike(term)
                )
                query = query.where(maybe_negate(cond))

        cond = column("search_tsvector", postgresql.TSVECTOR).op("@@")(tsquery)
        return query.where(maybe_negate(cond))


def ok_to_include_history(
    narrow: list[NarrowParameter] | None,
    user_profile: UserProfile | None,
    is_web_public_query: bool,
) -> bool:
    # There are occasions where we need to find Message rows that
    # have no corresponding UserMessage row, because the user is
    # reading a public channel that might include messages that
    # were sent while the user was not subscribed, but which they are
    # allowed to see.  We have to be very careful about constructing
    # queries in those situations, so this function should return True
    # only if we are 100% sure that we're gonna add a clause to the
    # query that narrows to a particular public channel on the user's realm.
    # If we screw this up, then we can get into a nasty situation of
    # polluting our narrow results with messages from other realms.

    # For web-public queries, we are always returning history.  The
    # analogues of the below channel access checks for whether channels
    # have is_web_public set and banning is operators in this code
    # path are done directly in NarrowBuilder.
    if is_web_public_query:
        assert user_profile is None
        return True

    assert user_profile is not None

    include_history = False
    if narrow is not None:
        for term in narrow:
            if term.operator in channel_operators and not term.negated:
                operand: str | int = term.operand
                if isinstance(operand, str):
                    include_history = can_access_stream_history_by_name(user_profile, operand)
                else:
                    include_history = can_access_stream_history_by_id(user_profile, operand)
            elif (
                term.operator in channels_operators
                and term.operand == "public"
                and not term.negated
                and user_profile.can_access_public_streams()
            ):
                include_history = True
        # Disable historical messages if the user is narrowing on anything
        # that's a property on the UserMessage table.  There cannot be
        # historical messages in these cases anyway.
        for term in narrow:
            if term.operator == "is" and term.operand not in {"resolved", "followed"}:
                include_history = False

    return include_history


def get_channel_from_narrow_access_unchecked(
    narrow: list[NarrowParameter] | None, realm: Realm
) -> Stream | None:
    if narrow is not None:
        for term in narrow:
            if term.operator in channel_operators:
                return get_stream_by_narrow_operand_access_unchecked(term.operand, realm)
    return None


# This function implements the core logic of the `with` operator,
# which is designed to support permanent links to a topic that
# robustly function if the topic is moved.
#
# The with operator accepts a message ID as an operand. If the
# message ID does not exist or is otherwise not accessible to the
# current user, then it has no effect.
#
# Otherwise, the narrow terms are mutated to remove any
# channel/topic/dm operators, replacing them with the appropriate
# operators for the conversation view containing the targeted message.
def update_narrow_terms_containing_with_operator(
    realm: Realm,
    maybe_user_profile: UserProfile | AnonymousUser,
    narrow: list[NarrowParameter] | None,
) -> list[NarrowParameter] | None:
    if narrow is None:
        return narrow

    with_operator_terms = list(filter(lambda term: term.operator == "with", narrow))

    if len(with_operator_terms) > 1:
        raise InvalidOperatorCombinationError(_("Duplicate 'with' operators."))
    elif len(with_operator_terms) == 0:
        return narrow

    with_term = with_operator_terms[0]
    narrow.remove(with_term)
    try:
        message_id = int(with_term.operand)
    except ValueError:
        # TODO: This probably should be handled earlier.
        raise BadNarrowOperatorError(_("Invalid 'with' operator"))

    if maybe_user_profile.is_authenticated:
        try:
            message = access_message(maybe_user_profile, message_id)
        except JsonableError:
            return narrow
    else:
        try:
            message = access_web_public_message(realm, message_id)
        except MissingAuthenticationError:
            return narrow

    # TODO: It would be better if the legacy names here are canonicalized
    # while building a NarrowParameter.
    filtered_terms = [
        term
        for term in narrow
        if term.operator not in ["stream", "channel", "topic", "dm", "pm-with"]
    ]

    if message.recipient.type == Recipient.STREAM:
        channel_id = message.recipient.type_id
        topic = message.topic_name()
        channel_conversation_terms = [
            NarrowParameter(operator="channel", operand=channel_id),
            NarrowParameter(operator="topic", operand=topic),
        ]
        return channel_conversation_terms + filtered_terms

    elif message.recipient.type == Recipient.PERSONAL:
        dm_conversation_terms = [
            NarrowParameter(operator="dm", operand=[message.recipient.type_id])
        ]
        return dm_conversation_terms + filtered_terms

    elif message.recipient.type == Recipient.DIRECT_MESSAGE_GROUP:
        huddle_user_ids = list(get_direct_message_group_user_ids(message.recipient))
        dm_conversation_terms = [NarrowParameter(operator="dm", operand=huddle_user_ids)]
        return dm_conversation_terms + filtered_terms

    raise AssertionError("Invalid recipient type")


def exclude_muting_conditions(
    user_profile: UserProfile, narrow: list[NarrowParameter] | None
) -> list[ClauseElement]:
    conditions: list[ClauseElement] = []
    channel_id = None
    try:
        # Note: It is okay here to not check access to channel
        # because we are only using the channel ID to exclude data,
        # not to include results.
        channel = get_channel_from_narrow_access_unchecked(narrow, user_profile.realm)
        if channel is not None:
            channel_id = channel.id
    except Stream.DoesNotExist:
        pass

    # Channel-level muting only applies when looking at views that
    # include multiple channels, since we do want users to be able to
    # browser messages within a muted channel.
    if channel_id is None:
        rows = Subscription.objects.filter(
            user_profile=user_profile,
            active=True,
            is_muted=True,
            recipient__type=Recipient.STREAM,
        ).values("recipient_id")
        muted_recipient_ids = [row["recipient_id"] for row in rows]
        if len(muted_recipient_ids) > 0:
            # Only add the condition if we have muted channels to simplify/avoid warnings.
            condition = not_(column("recipient_id", Integer).in_(muted_recipient_ids))
            conditions.append(condition)

    conditions = exclude_topic_mutes(conditions, user_profile, channel_id)

    # Muted user logic for hiding messages is implemented entirely
    # client-side. This is by design, as it allows UI to hint that
    # muted messages exist where their absence might make conversation
    # difficult to understand. As a result, we do not need to consider
    # muted users in this server-side logic for returning messages to
    # clients. (We could in theory exclude direct messages from muted
    # users, but they're likely to be sufficiently rare to not be worth
    # extra logic/testing here).

    return conditions


def get_base_query_for_search(
    realm_id: int, user_profile: UserProfile | None, need_message: bool, need_user_message: bool
) -> tuple[Select, ColumnElement[Integer]]:
    # Handle the simple case where user_message isn't involved first.
    if not need_user_message:
        assert need_message
        query = (
            select(column("id", Integer).label("message_id"))
            .select_from(table("zerver_message"))
            .where(column("realm_id", Integer) == literal(realm_id))
        )

        inner_msg_id_col = literal_column("zerver_message.id", Integer)
        return (query, inner_msg_id_col)

    assert user_profile is not None
    if need_message:
        query = (
            select(column("message_id", Integer), column("flags", Integer))
            # We don't limit by realm_id despite the join to
            # zerver_messages, since the user_profile_id limit in
            # usermessage is more selective, and the query planner
            # can't know about that cross-table correlation.
            .where(column("user_profile_id", Integer) == literal(user_profile.id))
            .select_from(
                join(
                    table("zerver_usermessage"),
                    table("zerver_message"),
                    literal_column("zerver_usermessage.message_id", Integer)
                    == literal_column("zerver_message.id", Integer),
                )
            )
        )
        inner_msg_id_col = column("message_id", Integer)
        return (query, inner_msg_id_col)

    query = (
        select(column("message_id", Integer), column("flags", Integer))
        .where(column("user_profile_id", Integer) == literal(user_profile.id))
        .select_from(table("zerver_usermessage"))
    )
    inner_msg_id_col = column("message_id", Integer)
    return (query, inner_msg_id_col)


def add_narrow_conditions(
    user_profile: UserProfile | None,
    inner_msg_id_col: ColumnElement[Integer],
    query: Select,
    narrow: list[NarrowParameter] | None,
    is_web_public_query: bool,
    realm: Realm,
) -> tuple[Select, bool]:
    is_search = False  # for now

    if narrow is None:
        return (query, is_search)

    # Build the query for the narrow
    builder = NarrowBuilder(user_profile, inner_msg_id_col, realm, is_web_public_query)
    search_operands = []

    # As we loop through terms, builder does most of the work to extend
    # our query, but we need to collect the search operands and handle
    # them after the loop.
    for term in narrow:
        if term.operator == "search":
            search_operands.append(term.operand)
        else:
            query = builder.add_term(query, term)

    if search_operands:
        is_search = True
        query = query.add_columns(topic_column_sa(), column("rendered_content", Text))
        search_term = NarrowParameter(
            operator="search",
            operand=" ".join(search_operands),
        )
        query = builder.add_term(query, search_term)

    return (query, is_search)


def find_first_unread_anchor(
    sa_conn: Connection,
    user_profile: UserProfile | None,
    narrow: list[NarrowParameter] | None,
) -> int:
    # For anonymous web users, all messages are treated as read, and so
    # always return LARGER_THAN_MAX_MESSAGE_ID.
    if user_profile is None:
        return LARGER_THAN_MAX_MESSAGE_ID

    # We always need UserMessage in our query, because it has the unread
    # flag for the user.
    need_user_message = True

    # Because we will need to call exclude_muting_conditions, unless
    # the user hasn't muted anything, we will need to include Message
    # in our query.  It may be worth eventually adding an optimization
    # for the case of a user who hasn't muted anything to avoid the
    # join in that case, but it's low priority.
    need_message = True

    query, inner_msg_id_col = get_base_query_for_search(
        realm_id=user_profile.realm_id,
        user_profile=user_profile,
        need_message=need_message,
        need_user_message=need_user_message,
    )

    query, is_search = add_narrow_conditions(
        user_profile=user_profile,
        inner_msg_id_col=inner_msg_id_col,
        query=query,
        narrow=narrow,
        is_web_public_query=False,
        realm=user_profile.realm,
    )

    condition = column("flags", Integer).op("&")(UserMessage.flags.read.mask) == 0

    # We exclude messages on muted topics when finding the first unread
    # message in this narrow
    muting_conditions = exclude_muting_conditions(user_profile, narrow)
    if muting_conditions:
        condition = and_(condition, *muting_conditions)

    first_unread_query = query.where(condition)
    first_unread_query = first_unread_query.order_by(inner_msg_id_col.asc()).limit(1)
    first_unread_result = list(sa_conn.execute(first_unread_query).fetchall())
    if len(first_unread_result) > 0:
        anchor = first_unread_result[0][0]
    else:
        anchor = LARGER_THAN_MAX_MESSAGE_ID

    return anchor


def parse_anchor_value(anchor_val: str | None, use_first_unread_anchor: bool) -> int | None:
    """Given the anchor and use_first_unread_anchor parameters passed by
    the client, computes what anchor value the client requested,
    handling backwards-compatibility and the various string-valued
    fields.  We encode use_first_unread_anchor as anchor=None.
    """
    if use_first_unread_anchor:
        # Backwards-compatibility: Before we added support for the
        # special string-typed anchor values, clients would pass
        # anchor=None and use_first_unread_anchor=True to indicate
        # what is now expressed as anchor="first_unread".
        return None
    if anchor_val is None:
        # Throw an exception if neither an anchor argument not
        # use_first_unread_anchor was specified.
        raise JsonableError(_("Missing 'anchor' argument."))
    if anchor_val == "oldest":
        return 0
    if anchor_val == "newest":
        return LARGER_THAN_MAX_MESSAGE_ID
    if anchor_val == "first_unread":
        return None
    try:
        # We don't use `.isnumeric()` to support negative numbers for
        # anchor.  We don't recommend it in the API (if you want the
        # very first message, use 0 or 1), but it used to be supported
        # and was used by the web app, so we need to continue
        # supporting it for backwards-compatibility
        anchor = int(anchor_val)
        if anchor < 0:
            return 0
        elif anchor > LARGER_THAN_MAX_MESSAGE_ID:
            return LARGER_THAN_MAX_MESSAGE_ID
        return anchor
    except ValueError:
        raise JsonableError(_("Invalid anchor"))


def limit_query_to_range(
    query: Select,
    num_before: int,
    num_after: int,
    anchor: int,
    include_anchor: bool,
    anchored_to_left: bool,
    anchored_to_right: bool,
    id_col: ColumnElement[Integer],
    first_visible_message_id: int,
) -> SelectBase:
    """
    This code is actually generic enough that we could move it to a
    library, but our only caller for now is message search.
    """
    need_before_query = (not anchored_to_left) and (num_before > 0)
    need_after_query = (not anchored_to_right) and (num_after > 0)

    need_both_sides = need_before_query and need_after_query

    # The semantics of our flags are as follows:
    #
    # num_before = number of rows < anchor
    # num_after = number of rows > anchor
    #
    # But we may also want the row where id == anchor (if it exists),
    # and we don't want to union up to 3 queries.  So in some cases
    # we do things like `after_limit = num_after + 1` to grab the
    # anchor row in the "after" query.
    #
    # Note that in some cases, if the anchor row isn't found, we
    # actually may fetch an extra row at one of the extremes.
    if need_both_sides:
        before_anchor = anchor - 1
        after_anchor = max(anchor, first_visible_message_id)
        before_limit = num_before
        after_limit = num_after + 1
    elif need_before_query:
        before_anchor = anchor - (not include_anchor)
        before_limit = num_before
        if not anchored_to_right:
            before_limit += include_anchor
    elif need_after_query:
        after_anchor = max(anchor + (not include_anchor), first_visible_message_id)
        after_limit = num_after + include_anchor

    if need_before_query:
        before_query = query

        if not anchored_to_right:
            before_query = before_query.where(id_col <= before_anchor)

        before_query = before_query.order_by(id_col.desc())
        before_query = before_query.limit(before_limit)

    if need_after_query:
        after_query = query

        if not anchored_to_left:
            after_query = after_query.where(id_col >= after_anchor)

        after_query = after_query.order_by(id_col.asc())
        after_query = after_query.limit(after_limit)

    if need_both_sides:
        return union_all(before_query.self_group(), after_query.self_group())
    elif need_before_query:
        return before_query
    elif need_after_query:
        return after_query
    else:
        # If we don't have either a before_query or after_query, it's because
        # some combination of num_before/num_after/anchor are zero or
        # use_first_unread_anchor logic found no unread messages.
        #
        # The most likely reason is somebody is doing an id search, so searching
        # for something like `message_id = 42` is exactly what we want.  In other
        # cases, which could possibly be buggy API clients, at least we will
        # return at most one row here.
        return query.where(id_col == anchor)


MessageRowT = TypeVar("MessageRowT", bound=Sequence[Any])


@dataclass
class LimitedMessages(Generic[MessageRowT]):
    rows: list[MessageRowT]
    found_anchor: bool
    found_newest: bool
    found_oldest: bool
    history_limited: bool


def post_process_limited_query(
    rows: Sequence[MessageRowT],
    num_before: int,
    num_after: int,
    anchor: int,
    anchored_to_left: bool,
    anchored_to_right: bool,
    first_visible_message_id: int,
) -> LimitedMessages[MessageRowT]:
    # Our queries may have fetched extra rows if they added
    # "headroom" to the limits, but we want to truncate those
    # rows.
    #
    # Also, in cases where we had non-zero values of num_before or
    # num_after, we want to know found_oldest and found_newest, so
    # that the clients will know that they got complete results.

    if first_visible_message_id > 0:
        visible_rows: Sequence[MessageRowT] = [r for r in rows if r[0] >= first_visible_message_id]
    else:
        visible_rows = rows

    rows_limited = len(visible_rows) != len(rows)

    if anchored_to_right:
        num_after = 0
        before_rows = visible_rows[:]
        anchor_rows = []
        after_rows = []
    else:
        before_rows = [r for r in visible_rows if r[0] < anchor]
        anchor_rows = [r for r in visible_rows if r[0] == anchor]
        after_rows = [r for r in visible_rows if r[0] > anchor]

    if num_before:
        before_rows = before_rows[-1 * num_before :]

    if num_after:
        after_rows = after_rows[:num_after]

    limited_rows = [*before_rows, *anchor_rows, *after_rows]

    found_anchor = len(anchor_rows) == 1
    found_oldest = anchored_to_left or (len(before_rows) < num_before)
    found_newest = anchored_to_right or (len(after_rows) < num_after)
    # BUG: history_limited is incorrect False in the event that we had
    # to bump `anchor` up due to first_visible_message_id, and there
    # were actually older messages.  This may be a rare event in the
    # context where history_limited is relevant, because it can only
    # happen in one-sided queries with no num_before (see tests tagged
    # BUG in PostProcessTest for examples), and we don't generally do
    # those from the UI, so this might be OK for now.
    #
    # The correct fix for this probably involves e.g. making a
    # `before_query` when we increase `anchor` just to confirm whether
    # messages were hidden.
    history_limited = rows_limited and found_oldest

    return LimitedMessages(
        rows=limited_rows,
        found_anchor=found_anchor,
        found_newest=found_newest,
        found_oldest=found_oldest,
        history_limited=history_limited,
    )


@dataclass
class FetchedMessages(LimitedMessages[Row]):
    anchor: int
    include_history: bool
    is_search: bool


def fetch_messages(
    *,
    narrow: list[NarrowParameter] | None,
    user_profile: UserProfile | None,
    realm: Realm,
    is_web_public_query: bool,
    anchor: int | None,
    include_anchor: bool,
    num_before: int,
    num_after: int,
) -> FetchedMessages:
    include_history = ok_to_include_history(narrow, user_profile, is_web_public_query)
    if include_history:
        # The initial query in this case doesn't use `zerver_usermessage`,
        # and isn't yet limited to messages the user is entitled to see!
        #
        # This is OK only because we've made sure this is a narrow that
        # will cause us to limit the query appropriately elsewhere.
        # See `ok_to_include_history` for details.
        #
        # Note that is_web_public_query=True goes here, since
        # include_history is semantically correct for is_web_public_query.
        need_message = True
        need_user_message = False
    elif narrow is None:
        # We need to limit to messages the user has received, but we don't actually
        # need any fields from Message
        need_message = False
        need_user_message = True
    else:
        need_message = True
        need_user_message = True

    query: SelectBase
    query, inner_msg_id_col = get_base_query_for_search(
        realm_id=realm.id,
        user_profile=user_profile,
        need_message=need_message,
        need_user_message=need_user_message,
    )

    query, is_search = add_narrow_conditions(
        user_profile=user_profile,
        inner_msg_id_col=inner_msg_id_col,
        query=query,
        narrow=narrow,
        realm=realm,
        is_web_public_query=is_web_public_query,
    )

    with get_sqlalchemy_connection() as sa_conn:
        if anchor is None:
            # `anchor=None` corresponds to the anchor="first_unread" parameter.
            anchor = find_first_unread_anchor(
                sa_conn,
                user_profile,
                narrow,
            )

        anchored_to_left = anchor == 0

        # Set value that will be used to short circuit the after_query
        # altogether and avoid needless conditions in the before_query.
        anchored_to_right = anchor >= LARGER_THAN_MAX_MESSAGE_ID
        if anchored_to_right:
            num_after = 0

        first_visible_message_id = get_first_visible_message_id(realm)

        query = limit_query_to_range(
            query=query,
            num_before=num_before,
            num_after=num_after,
            anchor=anchor,
            include_anchor=include_anchor,
            anchored_to_left=anchored_to_left,
            anchored_to_right=anchored_to_right,
            id_col=inner_msg_id_col,
            first_visible_message_id=first_visible_message_id,
        )

        main_query = query.subquery()
        query = (
            select(*main_query.c)
            .select_from(main_query)
            .order_by(column("message_id", Integer).asc())
        )
        # This is a hack to tag the query we use for testing
        query = query.prefix_with("/* get_messages */")
        rows = list(sa_conn.execute(query).fetchall())

    query_info = post_process_limited_query(
        rows=rows,
        num_before=num_before,
        num_after=num_after,
        anchor=anchor,
        anchored_to_left=anchored_to_left,
        anchored_to_right=anchored_to_right,
        first_visible_message_id=first_visible_message_id,
    )

    return FetchedMessages(
        rows=query_info.rows,
        found_anchor=query_info.found_anchor,
        found_newest=query_info.found_newest,
        found_oldest=query_info.found_oldest,
        history_limited=query_info.history_limited,
        anchor=anchor,
        include_history=include_history,
        is_search=is_search,
    )