"""
Watchdog: APScheduler BackgroundScheduler，每 3 分鐘掃描 schedules 表。
防重複執行：原子 UPDATE status='Going'，影響 0 筆則跳過。
"""
import logging
from datetime import datetime
from apscheduler.schedulers.background import BackgroundScheduler
from croniter import croniter
from sqlalchemy import update
from sqlalchemy.orm import Session

from app.core.database import SessionLocal
from app.models.schedule import Schedule, ScheduleLog

logger = logging.getLogger(__name__)

_scheduler = BackgroundScheduler(timezone="Asia/Taipei")


def _watchdog_tick():
    db: Session = SessionLocal()
    try:
        due = (
            db.query(Schedule)
            .filter(
                Schedule.status == "Waiting",
                Schedule.next_run_at <= datetime.utcnow(),
            )
            .all()
        )
        for schedule in due:
            # Atomic lock: only one process wins
            affected = db.execute(
                update(Schedule)
                .where(Schedule.id == schedule.id, Schedule.status == "Waiting")
                .values(status="Going")
            ).rowcount
            db.commit()

            if affected == 0:
                # Another process already grabbed it
                continue

            log = ScheduleLog(
                schedule_id=schedule.id,
                schedule_name=schedule.name,
                started_at=datetime.utcnow(),
                status="running",
            )
            db.add(log)
            db.commit()
            db.refresh(log)

            try:
                from app.services.scheduler.runner import dispatch_schedule
                dispatch_schedule(schedule.id, log.id, db)
                final_status = "ok"
            except Exception as e:
                logger.exception(f"Schedule {schedule.name} failed: {e}")
                final_status = "error"

            # Update log
            log.ended_at = datetime.utcnow()
            log.status = final_status

            # Recalculate next_run_at
            try:
                cron = croniter(schedule.cron_timer, datetime.utcnow())
                next_run = cron.get_next(datetime)
            except Exception:
                next_run = None

            # Reset schedule
            db.execute(
                update(Schedule)
                .where(Schedule.id == schedule.id)
                .values(
                    status="Waiting",
                    last_run_at=datetime.utcnow(),
                    next_run_at=next_run,
                    last_status=final_status,
                )
            )
            db.commit()

    except Exception as e:
        logger.exception(f"Watchdog tick error: {e}")
        db.rollback()
    finally:
        db.close()


def start_watchdog():
    _scheduler.add_job(
        _watchdog_tick,
        trigger="interval",
        minutes=3,
        id="watchdog",
        replace_existing=True,
    )
    _scheduler.start()
    logger.info("Watchdog scheduler started")


def stop_watchdog():
    _scheduler.shutdown(wait=False)
    logger.info("Watchdog scheduler stopped")