import datetime
from functools import partial

from celery.utils.log import get_task_logger
from django.conf import settings
from django.db import transaction
from django.db.models import DateTimeField, DurationField, ExpressionWrapper, F
from django.db.models.functions import Cast
from django.utils import timezone

from apps.heartbeat.models import IntegrationHeartBeat
from apps.integrations.tasks import create_alert
from common.custom_celery_tasks import shared_dedicated_queue_retry_task
from settings.base import DatabaseTypes

logger = get_task_logger(__name__)


@shared_dedicated_queue_retry_task()
def check_heartbeats() -> str:
    """
    Periodic task to check heartbeats status change and create alerts (or auto-resolve alerts) if needed
    """
    # Heartbeat is considered enabled if it
    # * has timeout_seconds set to non-zero (non-default) value,
    # * received at least one checkup (last_heartbeat_time set to non-null value)\

    def _get_timeout_expression() -> ExpressionWrapper:
        if settings.DATABASES["default"]["ENGINE"] == f"django.db.backends.{DatabaseTypes.POSTGRESQL}":
            # DurationField: When used on PostgreSQL, the data type used is an interval
            # https://docs.djangoproject.com/en/3.2/ref/models/fields/#durationfield
            return ExpressionWrapper(datetime.timedelta(seconds=1) * F("timeout_seconds"), output_field=DurationField())
        else:
            # DurationField: ...Otherwise a bigint of microseconds is used...
            # microseconds = seconds * 10**6
            # https://docs.djangoproject.com/en/3.2/ref/models/fields/#durationfield
            return ExpressionWrapper(F("timeout_seconds") * 10**6, output_field=DurationField())

    enabled_heartbeats = (
        IntegrationHeartBeat.objects.filter(last_heartbeat_time__isnull=False)
        .exclude(timeout_seconds=0)
        .annotate(period_start=(Cast(timezone.now() - _get_timeout_expression(), DateTimeField())))
    )
    with transaction.atomic():
        # Heartbeat is considered expired if it
        # * is enabled,
        # * is not already expired,
        # * last check in was before the timeout period start
        expired_heartbeats = (
            enabled_heartbeats.select_for_update()
            .filter(
                last_heartbeat_time__lte=F("period_start"),
                previous_alerted_state_was_life=True,
                alert_receive_channel__organization__deleted_at__isnull=True,
            )
            .select_related("alert_receive_channel")
        )
        # Schedule alert creation for each expired heartbeat after transaction commit
        timestamp = timezone.now().isoformat()
        for heartbeat in expired_heartbeats:
            transaction.on_commit(
                partial(
                    create_alert.apply_async,
                    kwargs={
                        "title": heartbeat.alert_receive_channel.heartbeat_expired_title,
                        "message": heartbeat.alert_receive_channel.heartbeat_expired_message,
                        "image_url": None,
                        "link_to_upstream_details": None,
                        "alert_receive_channel_pk": heartbeat.alert_receive_channel.pk,
                        "integration_unique_data": {},
                        "raw_request_data": heartbeat.alert_receive_channel.heartbeat_expired_payload,
                        "received_at": timestamp,
                    },
                )
            )
        # Update previous_alerted_state_was_life to False
        expired_count = expired_heartbeats.update(previous_alerted_state_was_life=False)
    with transaction.atomic():
        # Heartbeat is considered restored if it
        # * is enabled,
        # * last check in was after the timeout period start,
        # * was is alerted state (previous_alerted_state_was_life is False), i.e. was expired
        restored_heartbeats = enabled_heartbeats.select_for_update().filter(
            last_heartbeat_time__gte=F("period_start"), previous_alerted_state_was_life=False
        )
        # Schedule auto-resolve alert creation for each expired heartbeat after transaction commit
        timestamp = timezone.now().isoformat()
        for heartbeat in restored_heartbeats:
            transaction.on_commit(
                partial(
                    create_alert.apply_async,
                    kwargs={
                        "title": heartbeat.alert_receive_channel.heartbeat_restored_title,
                        "message": heartbeat.alert_receive_channel.heartbeat_restored_message,
                        "image_url": None,
                        "link_to_upstream_details": None,
                        "alert_receive_channel_pk": heartbeat.alert_receive_channel.pk,
                        "integration_unique_data": {},
                        "raw_request_data": heartbeat.alert_receive_channel.heartbeat_restored_payload,
                        "received_at": timestamp,
                    },
                )
            )
        restored_count = restored_heartbeats.update(previous_alerted_state_was_life=True)
    return f"Found {expired_count} expired and {restored_count} restored heartbeats"


@shared_dedicated_queue_retry_task()
def process_heartbeat_task(alert_receive_channel_pk):
    IntegrationHeartBeat.objects.filter(
        alert_receive_channel__pk=alert_receive_channel_pk,
    ).update(last_heartbeat_time=timezone.now())