"""
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 app.core.utils import now_tw
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 <= now_tw(),
            )
            .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=now_tw(),
                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 = now_tw()
            log.status = final_status

            # Recalculate next_run_at (5-field cron: 分 時 日 月 週)
            try:
                cron = croniter(schedule.cron_timer, now_tw())
                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=now_tw(),
                    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")