# Documented in https://zulip.readthedocs.io/en/latest/subsystems/sending-messages.html#soft-deactivation
import logging
from collections import defaultdict
from typing import Any, DefaultDict, Dict, List, Optional, Union

from django.conf import settings
from django.db import transaction
from django.db.models import Max
from django.utils.timezone import now as timezone_now

from zerver.lib.logging_util import log_to_file
from zerver.models import (
    Message,
    Realm,
    RealmAuditLog,
    Recipient,
    Subscription,
    UserActivity,
    UserMessage,
    UserProfile,
)

logger = logging.getLogger("zulip.soft_deactivation")
log_to_file(logger, settings.SOFT_DEACTIVATION_LOG_PATH)
BULK_CREATE_BATCH_SIZE = 10000

def filter_by_subscription_history(user_profile: UserProfile,
                                   all_stream_messages: DefaultDict[int, List[Message]],
                                   all_stream_subscription_logs: DefaultDict[int, List[RealmAuditLog]],
                                   ) -> List[UserMessage]:
    user_messages_to_insert: List[UserMessage] = []

    def store_user_message_to_insert(message: Message) -> None:
        message = UserMessage(user_profile=user_profile,
                              message_id=message['id'], flags=0)
        user_messages_to_insert.append(message)

    for (stream_id, stream_messages_raw) in all_stream_messages.items():
        stream_subscription_logs = all_stream_subscription_logs[stream_id]
        # Make a copy of the original list of messages, which we will
        # mutate in the loop below.
        stream_messages = list(stream_messages_raw)

        for log_entry in stream_subscription_logs:
            # For each stream, we iterate through all of the changes
            # to the user's subscription to that stream, ordered by
            # event_last_message_id, to determine whether the user was
            # subscribed to the target stream at that time.
            #
            # For each message, we're looking for the first event for
            # the user's subscription to the target stream after the
            # message was sent.
            # * If it's an unsubscribe, we know the user was subscribed
            #   when the message was sent, and create a UserMessage
            # * If it's a subscribe, we know the user was not, and we
            #   skip the message by mutating the stream_messages list
            #   to skip that message.

            if len(stream_messages) == 0:
                # Because stream_messages gets mutated below, this
                # check belongs in this inner loop, not the outer loop.
                break

            if log_entry.event_type == RealmAuditLog.SUBSCRIPTION_DEACTIVATED:
                # If the event shows the user was unsubscribed after
                # event_last_message_id, we know they must have been
                # subscribed immediately before the event.
                for stream_message in stream_messages:
                    if stream_message['id'] <= log_entry.event_last_message_id:
                        store_user_message_to_insert(stream_message)
                    else:
                        break
            elif log_entry.event_type in (RealmAuditLog.SUBSCRIPTION_ACTIVATED,
                                          RealmAuditLog.SUBSCRIPTION_CREATED):
                initial_msg_count = len(stream_messages)
                for i, stream_message in enumerate(stream_messages):
                    if stream_message['id'] > log_entry.event_last_message_id:
                        stream_messages = stream_messages[i:]
                        break
                final_msg_count = len(stream_messages)
                if initial_msg_count == final_msg_count:
                    if stream_messages[-1]['id'] <= log_entry.event_last_message_id:
                        stream_messages = []
            else:
                raise AssertionError(f'{log_entry.event_type} is not a subscription event.')

        if len(stream_messages) > 0:
            # We do this check for last event since if the last subscription
            # event was a subscription_deactivated then we don't want to create
            # UserMessage rows for any of the remaining messages.
            if stream_subscription_logs[-1].event_type in (
                    RealmAuditLog.SUBSCRIPTION_ACTIVATED,
                    RealmAuditLog.SUBSCRIPTION_CREATED):
                for stream_message in stream_messages:
                    store_user_message_to_insert(stream_message)
    return user_messages_to_insert

def add_missing_messages(user_profile: UserProfile) -> None:
    """This function takes a soft-deactivated user, and computes and adds
    to the database any UserMessage rows that were not created while
    the user was soft-deactivated.  The end result is that from the
    perspective of the message database, it should be impossible to
    tell that the user was soft-deactivated at all.

    At a high level, the algorithm is as follows:

    * Find all the streams that the user was at any time a subscriber
      of when or after they were soft-deactivated (`recipient_ids`
      below).

    * Find all the messages sent to those streams since the user was
      soft-deactivated.  This will be a superset of the target
      UserMessages we need to create in two ways: (1) some UserMessage
      rows will have already been created in do_send_messages because
      the user had a nonzero set of flags (the fact that we do so in
      do_send_messages simplifies things considerably, since it means
      we don't need to inspect message content to look for things like
      mentions here), and (2) the user might not have been subscribed
      to all of the streams in recipient_ids for the entire time
      window.

    * Correct the list from the previous state by excluding those with
      existing UserMessage rows.

    * Correct the list from the previous state by excluding those
      where the user wasn't subscribed at the time, using the
      RealmAuditLog data to determine exactly when the user was
      subscribed/unsubscribed.

    * Create the UserMessage rows.

    For further documentation, see:

      https://zulip.readthedocs.io/en/latest/subsystems/sending-messages.html#soft-deactivation

    """
    assert user_profile.last_active_message_id is not None
    all_stream_subs = list(Subscription.objects.filter(
        user_profile=user_profile,
        recipient__type=Recipient.STREAM).values('recipient_id', 'recipient__type_id'))

    # For Stream messages we need to check messages against data from
    # RealmAuditLog for visibility to user. So we fetch the subscription logs.
    stream_ids = [sub['recipient__type_id'] for sub in all_stream_subs]
    events = [RealmAuditLog.SUBSCRIPTION_CREATED, RealmAuditLog.SUBSCRIPTION_DEACTIVATED,
              RealmAuditLog.SUBSCRIPTION_ACTIVATED]

    # Important: We order first by event_last_message_id, which is the
    # official ordering, and then tiebreak by RealmAuditLog event ID.
    # That second tiebreak is important in case a user is subscribed
    # and then unsubscribed without any messages being sent in the
    # meantime.  Without that tiebreak, we could end up incorrectly
    # processing the ordering of those two subscription changes.
    subscription_logs = list(RealmAuditLog.objects.select_related(
        'modified_stream').filter(
        modified_user=user_profile,
        modified_stream__id__in=stream_ids,
        event_type__in=events).order_by('event_last_message_id', 'id'))

    all_stream_subscription_logs: DefaultDict[int, List[RealmAuditLog]] = defaultdict(list)
    for log in subscription_logs:
        all_stream_subscription_logs[log.modified_stream_id].append(log)

    recipient_ids = []
    for sub in all_stream_subs:
        stream_subscription_logs = all_stream_subscription_logs[sub['recipient__type_id']]
        if stream_subscription_logs[-1].event_type == RealmAuditLog.SUBSCRIPTION_DEACTIVATED:
            assert stream_subscription_logs[-1].event_last_message_id is not None
            if stream_subscription_logs[-1].event_last_message_id <= user_profile.last_active_message_id:
                # We are going to short circuit this iteration as its no use
                # iterating since user unsubscribed before soft-deactivation
                continue
        recipient_ids.append(sub['recipient_id'])

    all_stream_msgs = list(Message.objects.filter(
        recipient__id__in=recipient_ids,
        id__gt=user_profile.last_active_message_id).order_by('id').values(
        'id', 'recipient__type_id'))
    already_created_ums = set(UserMessage.objects.filter(
        user_profile=user_profile,
        message__recipient__type=Recipient.STREAM,
        message__id__gt=user_profile.last_active_message_id).values_list('message__id', flat=True))

    # Filter those messages for which UserMessage rows have been already created
    all_stream_msgs = [msg for msg in all_stream_msgs
                       if msg['id'] not in already_created_ums]

    stream_messages: DefaultDict[int, List[Message]] = defaultdict(list)
    for msg in all_stream_msgs:
        stream_messages[msg['recipient__type_id']].append(msg)

    # Calling this function to filter out stream messages based upon
    # subscription logs and then store all UserMessage objects for bulk insert
    # This function does not perform any SQL related task and gets all the data
    # required for its operation in its params.
    user_messages_to_insert = filter_by_subscription_history(
        user_profile, stream_messages, all_stream_subscription_logs)

    # Doing a bulk create for all the UserMessage objects stored for creation.
    while len(user_messages_to_insert) > 0:
        messages, user_messages_to_insert = (
            user_messages_to_insert[0:BULK_CREATE_BATCH_SIZE],
            user_messages_to_insert[BULK_CREATE_BATCH_SIZE:])
        UserMessage.objects.bulk_create(messages)
        user_profile.last_active_message_id = messages[-1].message_id
        user_profile.save(update_fields=['last_active_message_id'])

def do_soft_deactivate_user(user_profile: UserProfile) -> None:
    try:
        user_profile.last_active_message_id = UserMessage.objects.filter(
            user_profile=user_profile).order_by(
                '-message__id')[0].message_id
    except IndexError:  # nocoverage
        # In the unlikely event that a user somehow has never received
        # a message, we just use the overall max message ID.
        user_profile.last_active_message_id = Message.objects.last().id
    user_profile.long_term_idle = True
    user_profile.save(update_fields=[
        'long_term_idle',
        'last_active_message_id'])
    logger.info('Soft deactivated user %s', user_profile.id)

def do_soft_deactivate_users(users: List[UserProfile]) -> List[UserProfile]:
    BATCH_SIZE = 100
    users_soft_deactivated = []
    while True:
        (user_batch, users) = (users[0:BATCH_SIZE], users[BATCH_SIZE:])
        if len(user_batch) == 0:
            break
        with transaction.atomic():
            realm_logs = []
            for user in user_batch:
                do_soft_deactivate_user(user)
                event_time = timezone_now()
                log = RealmAuditLog(
                    realm=user.realm,
                    modified_user=user,
                    event_type=RealmAuditLog.USER_SOFT_DEACTIVATED,
                    event_time=event_time,
                )
                realm_logs.append(log)
                users_soft_deactivated.append(user)
            RealmAuditLog.objects.bulk_create(realm_logs)

        logger.info("Soft-deactivated batch of %s users; %s remain to process", len(user_batch), len(users))

    return users_soft_deactivated

def do_auto_soft_deactivate_users(inactive_for_days: int, realm: Optional[Realm]) -> List[UserProfile]:
    filter_kwargs: Dict[str, Realm] = {}
    if realm is not None:
        filter_kwargs = dict(user_profile__realm=realm)
    users_to_deactivate = get_users_for_soft_deactivation(inactive_for_days, filter_kwargs)
    users_deactivated = do_soft_deactivate_users(users_to_deactivate)

    if not settings.AUTO_CATCH_UP_SOFT_DEACTIVATED_USERS:
        logger.info('Not catching up users since AUTO_CATCH_UP_SOFT_DEACTIVATED_USERS is off')
        return users_deactivated

    if realm is not None:
        filter_kwargs = dict(realm=realm)
    users_to_catch_up = get_soft_deactivated_users_for_catch_up(filter_kwargs)
    do_catch_up_soft_deactivated_users(users_to_catch_up)
    return users_deactivated

def reactivate_user_if_soft_deactivated(user_profile: UserProfile) -> Union[UserProfile, None]:
    if user_profile.long_term_idle:
        add_missing_messages(user_profile)
        user_profile.long_term_idle = False
        user_profile.save(update_fields=['long_term_idle'])
        RealmAuditLog.objects.create(
            realm=user_profile.realm,
            modified_user=user_profile,
            event_type=RealmAuditLog.USER_SOFT_ACTIVATED,
            event_time=timezone_now(),
        )
        logger.info('Soft Reactivated user %s', user_profile.id)
        return user_profile
    return None

def get_users_for_soft_deactivation(inactive_for_days: int, filter_kwargs: Any) -> List[UserProfile]:
    users_activity = list(UserActivity.objects.filter(
        user_profile__is_active=True,
        user_profile__is_bot=False,
        user_profile__long_term_idle=False,
        **filter_kwargs).values('user_profile_id').annotate(
        last_visit=Max('last_visit')))
    user_ids_to_deactivate = []
    today = timezone_now()
    for user_activity in users_activity:
        if (today - user_activity['last_visit']).days > inactive_for_days:
            user_ids_to_deactivate.append(user_activity['user_profile_id'])
    users_to_deactivate = list(UserProfile.objects.filter(
        id__in=user_ids_to_deactivate))
    return users_to_deactivate

def do_soft_activate_users(users: List[UserProfile]) -> List[UserProfile]:
    users_soft_activated = []
    for user_profile in users:
        user_activated = reactivate_user_if_soft_deactivated(user_profile)
        if user_activated:
            users_soft_activated.append(user_activated)
    return users_soft_activated

def do_catch_up_soft_deactivated_users(users: List[UserProfile]) -> List[UserProfile]:
    users_caught_up = []
    for user_profile in users:
        if user_profile.long_term_idle:
            add_missing_messages(user_profile)
            users_caught_up.append(user_profile)
    logger.info("Caught up %d soft-deactivated users", len(users_caught_up))
    return users_caught_up

def get_soft_deactivated_users_for_catch_up(filter_kwargs: Any) -> List[UserProfile]:
    users_to_catch_up = UserProfile.objects.select_related().filter(
        long_term_idle=True,
        is_active=True,
        is_bot=False,
        **filter_kwargs,
    )
    return users_to_catch_up