"""Automatic event registration notifications."""

import logging
from datetime import timedelta

from celery import shared_task
from django.db import transaction
from django.db.models import Q
from django.utils import timezone

from apps.events.models import Registration, RegistrationNotification
from apps.events.checkout import expire_stale_registration_checkouts
from apps.notifications.services import notify_user
from apps.users.tasks import send_critical_sms

logger = logging.getLogger(__name__)


@shared_task(name="apps.events.expire_stale_registration_checkouts")
def expire_stale_registration_checkouts_task():
    """Release seats held by new checkout attempts that reached their deadline."""
    return expire_stale_registration_checkouts()


@shared_task(bind=True, max_retries=3)
def send_registration_confirmation_notification(self, registration_pk: str, notification_id: str | None = None):
    try:
        result = _send_confirmation(registration_pk, notification_id)
        _mark_notification_delivered(notification_id)
        return result
    except Exception as exc:
        logger.error("Failed to notify registration confirmation: %s", exc)
        raise self.retry(exc=exc, countdown=60)


@shared_task(bind=True, max_retries=3)
def send_registration_cancellation_notification(self, registration_pk: str, notification_id: str | None = None):
    try:
        result = _send_cancellation(registration_pk, notification_id)
        _mark_notification_delivered(notification_id)
        return result
    except Exception as exc:
        logger.error("Failed to notify registration cancellation: %s", exc)
        raise self.retry(exc=exc, countdown=60)


def _send_confirmation(registration_pk, notification_id=None):
    registration = Registration.objects.select_related("event", "user").get(pk=registration_pk)
    notify_user(registration.user_id, {
        **({"id": notification_id} if notification_id else {}),
        "type": "event_registration",
        "title": f"ثبت‌نام شما برای «{registration.event.title}» تأیید شد",
        "message": "ثبت‌نام شما در این رویداد تأیید شده است.",
        "level": "success",
        "action_url": f"/events/{registration.event.slug}",
        "entity_type": "event",
        "entity_id": registration.event_id,
        "meta": {"ticket_id": str(registration.ticket_id)},
    })
    return {"sent": True}


def _send_cancellation(registration_pk, notification_id=None):
    registration = Registration.objects.select_related("event", "user").get(pk=registration_pk)
    notify_user(registration.user_id, {
        **({"id": notification_id} if notification_id else {}),
        "type": "event_cancellation",
        "title": f"ثبت‌نام شما برای «{registration.event.title}» لغو شد",
        "message": "ثبت‌نام شما در این رویداد لغو شد.",
        "level": "warning",
        "action_url": f"/events/{registration.event.slug}",
        "entity_type": "event",
        "entity_id": registration.event_id,
    })
    if registration.user.mobile and registration.user.is_mobile_verified:
        send_critical_sms.delay(registration.user.mobile, "event_cancellation", registration.event.title)
    return {"sent": True}


def _mark_notification_delivered(notification_id):
    if not notification_id or not notification_id.startswith("registration-"):
        return
    try:
        entry_id = int(notification_id.split("-", 2)[1])
    except (IndexError, ValueError):
        return
    delivered_at = timezone.now()
    entry = RegistrationNotification.objects.filter(pk=entry_id, delivered_at__isnull=True).first()
    if entry is None:
        return
    entry.delivered_at = delivered_at
    entry.lease_until = None
    entry.save(update_fields=["delivered_at", "lease_until"])
    field = (
        "confirmation_notification_sent_at"
        if entry.kind == RegistrationNotification.Kind.CONFIRMED
        else "cancellation_notification_sent_at"
    )
    Registration.objects.filter(pk=entry.registration_id, **{f"{field}__isnull": True}).update(
        **{field: delivered_at}
    )


@shared_task(name="apps.events.deliver_pending_registration_notifications")
def deliver_pending_registration_notifications():
    """Recover notification delivery without involving registration write requests."""
    now = timezone.now()
    entry_ids = list(
        RegistrationNotification.objects.filter(delivered_at__isnull=True)
        .filter(Q(lease_until__isnull=True) | Q(lease_until__lte=now))
        .order_by("created_at", "pk")
        .values_list("pk", flat=True)[:100]
    )
    delivered = 0
    for entry_id in entry_ids:
        with transaction.atomic():
            entry = RegistrationNotification.objects.select_for_update(skip_locked=True).filter(pk=entry_id).first()
            if entry is None or entry.delivered_at or (entry.lease_until and entry.lease_until > now):
                continue
            entry.lease_until = now + timedelta(minutes=2)
            entry.save(update_fields=["lease_until"])
        try:
            notification_id = f"registration-{entry.pk}-{entry.kind}"
            if entry.kind == RegistrationNotification.Kind.CONFIRMED:
                _send_confirmation(str(entry.registration_id), notification_id)
                sent_field = "confirmation_notification_sent_at"
            else:
                _send_cancellation(str(entry.registration_id), notification_id)
                sent_field = "cancellation_notification_sent_at"
        except Exception:
            logger.exception("Unable to deliver registration notification %s", entry_id)
            RegistrationNotification.objects.filter(pk=entry_id, delivered_at__isnull=True).update(lease_until=None)
            continue
        delivered_at = timezone.now()
        with transaction.atomic():
            RegistrationNotification.objects.filter(pk=entry_id, delivered_at__isnull=True).update(
                delivered_at=delivered_at, lease_until=None,
            )
            Registration.objects.filter(pk=entry.registration_id, **{f"{sent_field}__isnull": True}).update(
                **{sent_field: delivered_at},
            )
        delivered += 1
    return delivered