"""
worker.py — PragatiVeer Celery Background Tasks
Active Tasks:
  - generate_daily_study_plans: Runs daily at 5:00 AM IST via Celery Beat

Deferred (Phase 2 — AI LLM):
  - process_pdf_test: Automated PDF → LLM → Questions pipeline
"""
import os
from datetime import datetime
from celery import Celery
from celery.schedules import crontab
from sqlmodel import Session, select

from database import engine
import models

REDIS_URL = os.getenv("REDIS_URL", "redis://redis:6379/0")

# Initialize Celery connected to our Redis broker
celery_app = Celery(
    "pragativeer_tasks",
    broker=REDIS_URL,
    backend=REDIS_URL
)

# Configure timezone to IST for accurate 5:00 AM scheduling
celery_app.conf.update(
    timezone='Asia/Kolkata',
    enable_utc=True,
)

@celery_app.task(name="generate_daily_study_plans", bind=True, default_retry_delay=60, max_retries=3)
def generate_daily_study_plans(self):
    """
    Runs daily to evaluate students' weak areas and generate
    a personalized study plan for the day.
    """
    try:
        with Session(engine) as session:
            # Fetch all active users on the AI Coach tier
            ai_students = session.exec(
                select(models.User).where(models.User.tier == models.TierEnum.AI_COACH)
            ).all()

            today = datetime.utcnow().date()
            plans_created = 0

            for student in ai_students:
                # 1. Fetch pending spaced repetition mistakes for today
                pending_mistakes = session.exec(
                    select(models.Mistake)
                    .where(models.Mistake.user_id == student.id)
                    .where(models.Mistake.is_mastered == False)
                    .where(models.Mistake.next_review <= datetime.utcnow())
                ).all()

                # 2. Extract weak topics (for revision recommendation)
                topics = [m.topic for m in pending_mistakes]
                most_weak_topic = max(set(topics), key=topics.count) if topics else "Mixed Syllabus"

                # 3. Construct the time-budgeted dynamic task list
                tasks = [
                    {"type": "Revision", "description": f"Revise {most_weak_topic}", "duration_minutes": 15, "status": "Pending"},
                    {"type": "Mistake_Review", "description": "Daily Mistake Review Session", "duration_minutes": 10, "status": "Pending"},
                    {"type": "DPS", "description": f"Attempt {most_weak_topic} Practice Sheet", "duration_minutes": 20, "status": "Pending"}
                ]

                # 4. Save to Database
                new_plan = models.StudyPlan(
                    user_id=student.id,
                    date=today,
                    tasks=tasks,
                    is_completed=False
                )
                session.add(new_plan)
                plans_created += 1

            session.commit()
            return f"Successfully generated {plans_created} daily study plans."
    except Exception as exc:
        print(f"Database error during study plan generation: {exc}")
        raise self.retry(exc=exc)


# Schedule: 5:00 AM IST every day
celery_app.conf.beat_schedule = {
    'generate-study-plans-every-morning': {
        'task': 'generate_daily_study_plans',
        'schedule': crontab(hour=5, minute=0),
    },
}