"""
Celery tasks for notifications.
"""

import logging
from celery import shared_task
from django.utils import timezone
from datetime import timedelta

logger = logging.getLogger(__name__)


@shared_task
def send_due_reminders():
    """
    Check for tasks due soon and send reminders.
    Runs every 5 minutes via Celery Beat.
    """
    from tasks.models import Task
    from users.models import DeviceToken
    from .models import Notification, ScheduledReminder

    now = timezone.now()

    # Find scheduled reminders that need to be sent
    reminders = ScheduledReminder.objects.filter(
        remind_at__lte=now,
        is_sent=False,
        task__status__in=['pending', 'in_progress']
    ).select_related('task', 'task__user')

    for reminder in reminders:
        task = reminder.task
        user = task.user

        # Create notification
        Notification.objects.create(
            user=user,
            notification_type='reminder',
            title=f'Reminder: {task.title}',
            message=f'Task "{task.title}" is due soon.',
            task=task,
        )

        # Send push notifications
        send_push_to_user.delay(
            user_id=str(user.id),
            title=f'Reminder: {task.title}',
            body=f'Task is due soon.',
            data={'task_id': str(task.id)}
        )

        # Mark as sent
        reminder.is_sent = True
        reminder.sent_at = now
        reminder.save()


@shared_task
def check_overdue_tasks():
    """
    Check for overdue tasks and notify users.
    Runs daily.
    """
    from tasks.models import Task
    from .models import Notification

    today = timezone.now().date()

    # Find overdue tasks that haven't been notified today
    overdue_tasks = Task.objects.filter(
        due_date__lt=today,
        status__in=['pending', 'in_progress']
    ).select_related('user')

    for task in overdue_tasks:
        # Check if we already sent an overdue notification today
        existing = Notification.objects.filter(
            user=task.user,
            task=task,
            notification_type='overdue',
            created_at__date=today
        ).exists()

        if not existing:
            Notification.objects.create(
                user=task.user,
                notification_type='overdue',
                title=f'Overdue: {task.title}',
                message=f'Task "{task.title}" is overdue.',
                task=task,
            )

            send_push_to_user.delay(
                user_id=str(task.user.id),
                title=f'Overdue: {task.title}',
                body='This task is overdue.',
                data={'task_id': str(task.id)}
            )


@shared_task
def send_push_to_user(user_id, title, body, data=None):
    """
    Send push notification to all user devices.
    """
    from django.contrib.auth import get_user_model
    from users.models import DeviceToken

    User = get_user_model()

    try:
        user = User.objects.get(id=user_id)
    except User.DoesNotExist:
        return

    if not user.push_notifications:
        return

    tokens = DeviceToken.objects.filter(user=user, is_active=True)

    for token in tokens:
        if token.platform == 'android':
            send_fcm_notification.delay(token.token, title, body, data)
        elif token.platform == 'web':
            send_web_push_notification.delay(token.token, title, body, data)
        elif token.platform == 'desktop':
            # Desktop notifications are handled via WebSocket
            pass


@shared_task
def send_fcm_notification(token, title, body, data=None):
    """Send FCM notification to Android device."""
    from django.conf import settings

    # Only send if FCM is configured
    if not getattr(settings, 'FCM_CREDENTIALS_PATH', None):
        return

    try:
        import firebase_admin
        from firebase_admin import credentials, messaging

        # Initialize Firebase if not already done
        if not firebase_admin._apps:
            cred = credentials.Certificate(settings.FCM_CREDENTIALS_PATH)
            firebase_admin.initialize_app(cred)

        message = messaging.Message(
            notification=messaging.Notification(
                title=title,
                body=body,
            ),
            data=data or {},
            token=token,
        )

        messaging.send(message)

    except Exception as e:
        # Log error but don't fail
        logger.error(f"FCM notification failed: {e}")


@shared_task
def send_web_push_notification(subscription_info, title, body, data=None):
    """Send Web Push notification."""
    from django.conf import settings

    vapid_private_key = getattr(settings, 'VAPID_PRIVATE_KEY', None)
    vapid_email = getattr(settings, 'VAPID_ADMIN_EMAIL', None)

    if not vapid_private_key or not vapid_email:
        return

    try:
        from pywebpush import webpush, WebPushException
        import json

        webpush(
            subscription_info=json.loads(subscription_info),
            data=json.dumps({
                'title': title,
                'body': body,
                'data': data or {}
            }),
            vapid_private_key=vapid_private_key,
            vapid_claims={'sub': f'mailto:{vapid_email}'}
        )

    except Exception as e:
        logger.error(f"Web push notification failed: {e}")


@shared_task
def schedule_task_reminder(task_id):
    """
    Schedule a reminder for a task based on its due date and user preferences.
    Called when a task is created or updated.
    """
    from tasks.models import Task
    from .models import ScheduledReminder

    try:
        task = Task.objects.get(id=task_id)
    except Task.DoesNotExist:
        return

    # Remove existing scheduled reminders for this task
    ScheduledReminder.objects.filter(task=task, is_sent=False).delete()

    # Only schedule if task has a reminder time or due date
    if task.reminder_at:
        ScheduledReminder.objects.create(
            task=task,
            remind_at=task.reminder_at
        )
    elif task.due_date:
        # Default reminder based on user preference
        reminder_minutes = task.user.default_reminder_minutes
        if task.due_time:
            from datetime import datetime
            due_datetime = datetime.combine(task.due_date, task.due_time)
            due_datetime = timezone.make_aware(due_datetime)
        else:
            # Default to 9 AM on due date
            due_datetime = timezone.make_aware(
                datetime.combine(task.due_date, datetime.min.time())
            ).replace(hour=9)

        remind_at = due_datetime - timedelta(minutes=reminder_minutes)

        if remind_at > timezone.now():
            ScheduledReminder.objects.create(
                task=task,
                remind_at=remind_at
            )


@shared_task
def process_recurring_tasks():
    """
    Process completed recurring tasks and create next instances.
    This runs periodically as a safety net to catch any tasks that weren't
    automatically handled when marked as completed.
    Runs every hour via Celery Beat.
    """
    from tasks.models import Task

    # Find completed recurring tasks that don't have a next instance created yet
    # We look for tasks completed in the last 24 hours to avoid reprocessing old tasks
    yesterday = timezone.now() - timedelta(days=1)

    completed_recurring_tasks = Task.objects.filter(
        status='completed',
        recurrence__in=['daily', 'weekly', 'biweekly', 'monthly', 'yearly', 'custom'],
        completed_at__gte=yesterday
    ).exclude(recurrence='none')

    tasks_created = 0
    for task in completed_recurring_tasks:
        # Check if a next recurrence already exists
        # Look for pending tasks with the same title, user, and recurrence pattern
        next_due_date = task.calculate_next_due_date()
        if next_due_date:
            # Check if we already created this recurrence
            existing = Task.objects.filter(
                user=task.user,
                title=task.title,
                due_date=next_due_date,
                recurrence=task.recurrence,
                status='pending'
            ).exists()

            if not existing:
                # Create the next recurrence
                new_task = task.create_next_recurrence()
                if new_task:
                    tasks_created += 1
                    logger.info(f"Created recurring task: {new_task.title} (due: {new_task.due_date})")

    if tasks_created > 0:
        logger.info(f"Created {tasks_created} recurring task instances")

    return tasks_created