celery_app.py

"""
Celery Application Factory

Creates Celery instance compatible with Flask app factory pattern.
Use this for background task processing (iCal sync, OAuth refresh, email notifications).
"""

from celery import Celery
from celery.schedules import crontab
import os


def make_celery(app=None):
    """
    Create Celery instance with Flask app context.

    Usage:
        from celery_app import celery

        @celery.task
        def my_background_task(arg):
            # Task runs with Flask app context
            from models import User
            user = User.query.get(arg)

    Args:
        app: Flask application instance (optional, set later via init_app)

    Returns:
        Celery instance configured for Flask
    """
    celery = Celery(
        'bos_checklist',
        broker=os.getenv('CELERY_BROKER_URL', 'redis://localhost:6379/0'),
        backend=os.getenv('CELERY_RESULT_BACKEND', 'redis://localhost:6379/0'),
        include=['tasks.ical_sync', 'tasks.oauth_refresh']  # Task modules
    )

    # Celery configuration
    celery.conf.update(
        # Task result settings
        result_expires=3600,  # Results expire after 1 hour

        # Task execution settings
        task_serializer='json',
        result_serializer='json',
        accept_content=['json'],
        timezone='UTC',
        enable_utc=True,

        # Worker settings
        worker_prefetch_multiplier=1,  # One task at a time per worker
        worker_max_tasks_per_child=1000,  # Restart worker after 1000 tasks (prevent memory leaks)

        # Task routing (optional: separate queues for different task types)
        task_routes={
            'tasks.ical_sync.*': {'queue': 'ical'},
            'tasks.oauth_refresh.*': {'queue': 'oauth'},
        },

        # Periodic task schedule (Celery Beat)
        beat_schedule={
            'sync-ical-calendars': {
                'task': 'tasks.ical_sync.sync_all_ical_calendars',
                'schedule': crontab(minute='*/30'),  # Every 30 minutes
            },
            'refresh-oauth-tokens': {
                'task': 'tasks.oauth_refresh.refresh_expiring_tokens',
                'schedule': crontab(minute='0', hour='*/6'),  # Every 6 hours
            },
        },
    )

    if app:
        init_celery(celery, app)

    return celery


def init_celery(celery, app):
    """
    Initialize Celery with Flask app context.

    Ensures all Celery tasks run within Flask application context,
    allowing database access, config variables, etc.

    Args:
        celery: Celery instance
        app: Flask application instance
    """
    class ContextTask(celery.Task):
        """Celery Task that runs within Flask app context"""
        def __call__(self, *args, **kwargs):
            with app.app_context():
                return self.run(*args, **kwargs)

    celery.Task = ContextTask
    celery.conf.update(app.config)


# Create default Celery instance (app context set later in app.py)
celery = make_celery()