"""Scheduler jobs for background maintenance tasks.

- Reminder notifications: checks every 5 minutes for due event reminders and
  delivers them to the in-app notification feed.
- CalDAV pull sync: runs every hour for all users with CalDAV configured.
- Recurring-task spawn: every 15 minutes, creates the next occurrence of any
  recurring task whose spawn time has arrived.

Uses the BackgroundScheduler pattern shared with the other *_scheduler modules.
"""
from __future__ import annotations

import asyncio
import logging
from datetime import datetime, timedelta, timezone

from apscheduler.schedulers.background import BackgroundScheduler
from apscheduler.triggers.interval import IntervalTrigger
from dateutil.rrule import rrulestr
from sqlalchemy import and_, or_, select

from fabledassistant.models import async_session
from fabledassistant.models.event import Event

logger = logging.getLogger(__name__)

_scheduler: BackgroundScheduler | None = None
_loop: asyncio.AbstractEventLoop | None = None


# ---------------------------------------------------------------------------
# Reminder job
# ---------------------------------------------------------------------------

async def _fire_reminders() -> None:
    """Fire in-app reminders for events whose reminder time has arrived.

    One-shot events fire once (gated on reminder_sent_at IS NULL). Recurring
    events fire once PER OCCURRENCE: reminder_sent_at stores the start of the
    occurrence we last reminded about, so each new occurrence re-arms the
    reminder instead of the whole series firing only once.
    """
    now = datetime.now(timezone.utc)
    window_end = now + timedelta(minutes=5)

    async with async_session() as session:
        result = await session.execute(
            select(Event).where(
                Event.reminder_minutes.isnot(None),
                Event.deleted_at.is_(None),
                or_(
                    # Recurring events are evaluated every sweep against their
                    # next occurrence (the base start_dt is long past).
                    Event.recurrence.isnot(None),
                    # One-shot events: classic gate.
                    and_(Event.reminder_sent_at.is_(None), Event.start_dt > now),
                ),
            )
        )
        candidates = list(result.scalars().all())

    # (event_id, occurrence_start) — occurrence_start is also the dedup marker
    # written to reminder_sent_at, so a given occurrence reminds exactly once.
    to_notify: list[tuple[int, datetime]] = []
    for event in candidates:
        if event.recurrence:
            try:
                rule = rrulestr(event.recurrence, dtstart=event.start_dt, ignoretz=False)
                occ = rule.after(now, inc=True)
            except Exception:
                logger.warning("Failed to expand RRULE for event %d reminder", event.id, exc_info=True)
                continue
            if occ is None:
                continue
            reminder_dt = occ - timedelta(minutes=event.reminder_minutes)
            if reminder_dt <= window_end and event.reminder_sent_at != occ:
                to_notify.append((event.id, occ))
        else:
            reminder_dt = event.start_dt - timedelta(minutes=event.reminder_minutes)
            if reminder_dt <= window_end:
                to_notify.append((event.id, event.start_dt))

    if not to_notify:
        return

    # Deliver via the in-app notification feed (push was removed in Phase 8).
    from fabledassistant.services.notifications import create_in_app_notification

    async with async_session() as session:
        for event_id, occurrence_start in to_notify:
            ev = (await session.execute(
                select(Event).where(Event.id == event_id)
            )).scalar_one_or_none()
            # Skip if this exact occurrence was already reminded (covers a
            # concurrent sweep and the one-shot already-sent case).
            if ev is None or ev.reminder_sent_at == occurrence_start:
                continue
            await create_in_app_notification(ev.user_id, "event_reminder", {
                "event_id": ev.id,
                "title": ev.title,
                "start_dt": occurrence_start.isoformat(),
                "url": "/calendar",
            })
            # Stamp the occurrence marker only after the notification is
            # created, so a delivery failure leaves it eligible to retry.
            ev.reminder_sent_at = occurrence_start
        await session.commit()


def _run_reminders(loop: asyncio.AbstractEventLoop) -> None:
    asyncio.run_coroutine_threadsafe(_fire_reminders(), loop)


# ---------------------------------------------------------------------------
# CalDAV pull sync job
# ---------------------------------------------------------------------------

async def _run_caldav_sync() -> None:
    from fabledassistant.services.caldav_sync import sync_all_users  # noqa: PLC0415
    try:
        await sync_all_users()
    except Exception:
        logger.warning("CalDAV pull sync job failed", exc_info=True)


def _run_caldav_sync_threadsafe(loop: asyncio.AbstractEventLoop) -> None:
    asyncio.run_coroutine_threadsafe(_run_caldav_sync(), loop)


# ---------------------------------------------------------------------------
# Recurring-task spawn job
# ---------------------------------------------------------------------------

async def _run_recurrence_spawn() -> None:
    from fabledassistant.services.recurrence import spawn_recurring_tasks  # noqa: PLC0415
    try:
        await spawn_recurring_tasks()
    except Exception:
        logger.warning("Recurring-task spawn job failed", exc_info=True)


def _run_recurrence_spawn_threadsafe(loop: asyncio.AbstractEventLoop) -> None:
    asyncio.run_coroutine_threadsafe(_run_recurrence_spawn(), loop)


# ---------------------------------------------------------------------------
# Lifecycle
# ---------------------------------------------------------------------------

def start_event_scheduler(loop: asyncio.AbstractEventLoop) -> None:
    global _scheduler, _loop
    if _scheduler is not None:
        return
    _loop = loop
    _scheduler = BackgroundScheduler()

    # Check reminders every 5 minutes
    _scheduler.add_job(
        _run_reminders,
        trigger=IntervalTrigger(minutes=5),
        args=[loop],
        id="event_reminders",
        replace_existing=True,
    )

    # CalDAV pull sync every hour
    _scheduler.add_job(
        _run_caldav_sync_threadsafe,
        trigger=IntervalTrigger(hours=1),
        args=[loop],
        id="caldav_pull_sync",
        replace_existing=True,
    )

    # Spawn the next occurrence of due recurring tasks every 15 minutes.
    # Without this job, recurrence_next_spawn_at is armed on completion but
    # never drained, so recurring tasks never recur.
    _scheduler.add_job(
        _run_recurrence_spawn_threadsafe,
        trigger=IntervalTrigger(minutes=15),
        args=[loop],
        id="recurrence_spawn",
        replace_existing=True,
    )

    _scheduler.start()
    logger.info(
        "Event scheduler started (reminders every 5m, CalDAV sync every 1h, "
        "recurring-task spawn every 15m)"
    )


def stop_event_scheduler() -> None:
    global _scheduler
    if _scheduler is not None:
        _scheduler.shutdown(wait=False)
        _scheduler = None
        logger.info("Event scheduler stopped")