import datetime
import itertools
import time
from collections import defaultdict
from typing import Any, Dict, Mapping, Sequence, Set

from django.utils.timezone import now as timezone_now

from zerver.lib.timestamp import datetime_to_timestamp
from zerver.models import PushDeviceToken, Realm, UserPresence, UserProfile, query_for_ids


def get_status_dicts_for_rows(
    all_rows: Sequence[Mapping[str, Any]], mobile_user_ids: Set[int], slim_presence: bool
) -> Dict[str, Dict[str, Any]]:

    # Note that datetime values have sub-second granularity, which is
    # mostly important for avoiding test flakes, but it's also technically
    # more precise for real users.
    # We could technically do this sort with the database, but doing it
    # here prevents us from having to assume the caller is playing nice.
    all_rows = sorted(
        all_rows,
        key=lambda row: (row["user_profile_id"], row["timestamp"]),
    )

    if slim_presence:
        # Stringify user_id here, since it's gonna be turned
        # into a string anyway by JSON, and it keeps mypy happy.
        get_user_key = lambda row: str(row["user_profile_id"])
        get_user_info = get_modern_user_info
    else:
        get_user_key = lambda row: row["user_profile__email"]
        get_user_info = get_legacy_user_info

    user_statuses: Dict[str, Dict[str, Any]] = {}

    for user_key, presence_rows in itertools.groupby(all_rows, get_user_key):
        info = get_user_info(
            list(presence_rows),
            mobile_user_ids=mobile_user_ids,
        )
        user_statuses[user_key] = info

    return user_statuses


def get_modern_user_info(
    presence_rows: Sequence[Mapping[str, Any]], mobile_user_ids: Set[int]
) -> Dict[str, Any]:

    active_timestamp = None
    for row in reversed(presence_rows):
        if row["status"] == UserPresence.ACTIVE:
            active_timestamp = datetime_to_timestamp(row["timestamp"])
            break

    idle_timestamp = None
    for row in reversed(presence_rows):
        if row["status"] == UserPresence.IDLE:
            idle_timestamp = datetime_to_timestamp(row["timestamp"])
            break

    # Be stingy about bandwidth, and don't even include
    # keys for entities that have None values.  JS
    # code should just do a falsy check here.
    result = {}

    if active_timestamp is not None:
        result["active_timestamp"] = active_timestamp

    if idle_timestamp is not None:
        result["idle_timestamp"] = idle_timestamp

    return result


def get_legacy_user_info(
    presence_rows: Sequence[Mapping[str, Any]], mobile_user_ids: Set[int]
) -> Dict[str, Any]:

    # The format of data here is for legacy users of our API,
    # including old versions of the mobile app.
    info_rows = []
    for row in presence_rows:
        client_name = row["client__name"]
        status = UserPresence.status_to_string(row["status"])
        dt = row["timestamp"]
        timestamp = datetime_to_timestamp(dt)
        push_enabled = row["user_profile__enable_offline_push_notifications"]
        has_push_devices = row["user_profile_id"] in mobile_user_ids
        pushable = push_enabled and has_push_devices

        info = dict(
            client=client_name,
            status=status,
            timestamp=timestamp,
            pushable=pushable,
        )

        info_rows.append(info)

    most_recent_info = info_rows[-1]

    result = {}

    # The word "aggregated" here is possibly misleading.
    # It's really just the most recent client's info.
    result["aggregated"] = dict(
        client=most_recent_info["client"],
        status=most_recent_info["status"],
        timestamp=most_recent_info["timestamp"],
    )

    # Build a dictionary of client -> info.  There should
    # only be one row per client, but to be on the safe side,
    # we always overwrite with rows that are later in our list.
    for info in info_rows:
        result[info["client"]] = info

    return result


def get_presence_for_user(
    user_profile_id: int, slim_presence: bool = False
) -> Dict[str, Dict[str, Any]]:
    query = UserPresence.objects.filter(user_profile_id=user_profile_id).values(
        "client__name",
        "status",
        "timestamp",
        "user_profile__email",
        "user_profile_id",
        "user_profile__enable_offline_push_notifications",
    )
    presence_rows = list(query)

    mobile_user_ids: Set[int] = set()
    if PushDeviceToken.objects.filter(user_id=user_profile_id).exists():  # nocoverage
        # TODO: Add a test, though this is low priority, since we don't use mobile_user_ids yet.
        mobile_user_ids.add(user_profile_id)

    return get_status_dicts_for_rows(presence_rows, mobile_user_ids, slim_presence)


def get_status_dict_by_realm(
    realm_id: int, slim_presence: bool = False
) -> Dict[str, Dict[str, Any]]:
    two_weeks_ago = timezone_now() - datetime.timedelta(weeks=2)
    query = UserPresence.objects.filter(
        realm_id=realm_id,
        timestamp__gte=two_weeks_ago,
        user_profile__is_active=True,
        user_profile__is_bot=False,
    ).values(
        "client__name",
        "status",
        "timestamp",
        "user_profile__email",
        "user_profile_id",
        "user_profile__enable_offline_push_notifications",
    )

    presence_rows = list(query)

    mobile_query = PushDeviceToken.objects.distinct("user_id").values_list(
        "user_id",
        flat=True,
    )

    user_profile_ids = [presence_row["user_profile_id"] for presence_row in presence_rows]
    if len(user_profile_ids) == 0:
        # This conditional is necessary because query_for_ids
        # throws an exception if passed an empty list.
        #
        # It's not clear this condition is actually possible,
        # though, because it shouldn't be possible to end up with
        # a realm with 0 active users.
        return {}

    mobile_query = query_for_ids(
        query=mobile_query,
        user_ids=user_profile_ids,
        field="user_id",
    )
    mobile_user_ids = set(mobile_query)

    return get_status_dicts_for_rows(presence_rows, mobile_user_ids, slim_presence)


def get_presences_for_realm(
    realm: Realm, slim_presence: bool
) -> Dict[str, Dict[str, Dict[str, Any]]]:

    if realm.presence_disabled:
        # Return an empty dict if presence is disabled in this realm
        return defaultdict(dict)

    return get_status_dict_by_realm(realm.id, slim_presence)


def get_presence_response(
    requesting_user_profile: UserProfile, slim_presence: bool
) -> Dict[str, Any]:
    realm = requesting_user_profile.realm
    server_timestamp = time.time()
    presences = get_presences_for_realm(realm, slim_presence)
    return dict(presences=presences, server_timestamp=server_timestamp)
