"""
Celery tasks for event management and cleanup.
"""
from datetime import timedelta
from django.utils import timezone
from celery import shared_task

from core.models.events import Event
from core.services.events import MISSION_CRITICAL_EVENTS


@shared_task
def cleanup_old_events():
    """
    Periodic task to clean up old non-critical events.

    Retention policy:
    - Mission-critical events: Kept forever (audit trail, compliance)
    - Non-critical events: Deleted after 90 days

    This task should be scheduled to run daily or weekly via Celery Beat.
    """
    # Calculate cutoff date (90 days ago)
    cutoff_date = timezone.now() - timedelta(days=90)

    # Delete non-critical events older than 90 days
    deleted_count, _ = Event.objects.filter(
        created_at__lt=cutoff_date
    ).exclude(
        event_type__in=MISSION_CRITICAL_EVENTS
    ).delete()

    return {
        'deleted_count': deleted_count,
        'cutoff_date': cutoff_date.isoformat(),
        'retention_days': 90
    }


@shared_task
def get_event_statistics():
    """
    Generate statistics about event storage and distribution.
    Useful for monitoring and capacity planning.
    """
    from django.db.models import Count

    total_events = Event.objects.count()

    # Count by event type
    events_by_type = Event.objects.values('event_type').annotate(
        count=Count('event_type')
    ).order_by('-count')[:20]  # Top 20 event types

    # Count mission-critical vs non-critical
    critical_count = Event.objects.filter(
        event_type__in=MISSION_CRITICAL_EVENTS
    ).count()
    non_critical_count = total_events - critical_count

    # Events in last 24 hours
    last_24h = timezone.now() - timedelta(hours=24)
    recent_count = Event.objects.filter(created_at__gte=last_24h).count()

    # Events in last 7 days
    last_7d = timezone.now() - timedelta(days=7)
    weekly_count = Event.objects.filter(created_at__gte=last_7d).count()

    return {
        'total_events': total_events,
        'critical_events': critical_count,
        'non_critical_events': non_critical_count,
        'events_last_24h': recent_count,
        'events_last_7d': weekly_count,
        'top_event_types': list(events_by_type),
        'mission_critical_types_count': len(MISSION_CRITICAL_EVENTS),
    }