"""Background scheduler that scans alerts and dispatches reminder emails."""
import logging
from datetime import date, timezone
from apscheduler.schedulers.background import BackgroundScheduler
from .models import Alert, User, db
from .mailer import send_mail

logger = logging.getLogger(__name__)
_scheduler: BackgroundScheduler | None = None


def _check_and_send(app):
    """Iterate active alerts; for each reminder threshold reached, email all users."""
    with app.app_context():
        today = date.today()
        active_alerts = Alert.query.filter_by(is_active=True).all()
        recipients = [u.email for u in User.query.filter_by(is_active=True).all() if u.email]
        if not recipients:
            logger.info("Scheduler tick: no recipients.")
            return

        for alert in active_alerts:
            days_left = (alert.expiration_date - today).days
            already_sent = set(alert.reminders_sent)
            newly_sent = []
            for threshold in alert.reminder_days:
                if days_left <= threshold and threshold not in already_sent:
                    subject = f"[AlertHub] Reminder: {alert.title} expires in {days_left} day(s)"
                    body_text = (
                        f"Alert: {alert.title}\n"
                        f"Category: {alert.category or '—'}\n"
                        f"Expiration date: {alert.expiration_date.isoformat()}\n"
                        f"Days remaining: {days_left}\n\n"
                        f"{alert.description or ''}\n"
                    )
                    body_html = f"""
                    <div style="font-family: -apple-system, sans-serif; max-width: 600px;">
                      <h2 style="color: #00d4aa;">⏰ AlertHub Reminder</h2>
                      <h3>{alert.title}</h3>
                      <p><strong>Category:</strong> {alert.category or '—'}<br>
                         <strong>Expiration date:</strong> {alert.expiration_date.isoformat()}<br>
                         <strong>Days remaining:</strong> <span style="color:#ff6b6b;font-size:1.2em;">{days_left}</span></p>
                      <p>{alert.description or ''}</p>
                    </div>
                    """
                    ok, info = send_mail(recipients, subject, body_text, body_html,
                                         kind="reminder", triggered_by="system")
                    logger.info("Alert %s threshold %d: send=%s (%s)", alert.id, threshold, ok, info)
                    if ok:
                        newly_sent.append(threshold)
            if newly_sent:
                alert.reminders_sent = list(already_sent.union(newly_sent))
                db.session.commit()


def init_scheduler(app):
    """Start the scheduler if not already running. Called once at app startup."""
    global _scheduler
    if _scheduler is not None and _scheduler.running:
        return _scheduler
    interval = max(1, int(app.config.get("SCHEDULER_INTERVAL_MINUTES", 60)))
    _scheduler = BackgroundScheduler(timezone="UTC")
    _scheduler.add_job(
        _check_and_send,
        "interval",
        minutes=interval,
        args=[app],
        id="alert_reminder_job",
        replace_existing=True,
        next_run_time=None,  # don't run immediately on boot
    )
    _scheduler.start()
    logger.info("Scheduler started; reminder check every %d minute(s).", interval)
    return _scheduler


def trigger_now(app):
    """Manual trigger (for the 'Run check now' button)."""
    _check_and_send(app)