"""Scheduled (recurring) stack backups to a destination.

A background loop wakes every minute, runs any schedules whose ``next_run`` has
passed, uploads the backup to the destination, prunes old backups per the
retention setting, and records status + the next run time.

Times are stored as naive UTC to match SQLite's datetime handling.
"""
from __future__ import annotations

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

from sqlmodel import Session, select

from database import engine
from models.backup_destination import BackupDestination
from models.backup_schedule import BackupSchedule
from models.setting import EVENT_BACKUP_FAILED
from models.stack import Stack
from services import (
    backup_destination_service as dest_service,
    backup_service,
    compose_service,
    notify_service,
)

logger = logging.getLogger("stackpilot.schedule")


def _now() -> datetime:
    return datetime.now(timezone.utc).replace(tzinfo=None)


def compute_next_run(
    frequency: str, hour: int, minute: int, weekday: int, after: datetime
) -> datetime:
    """Next run strictly after ``after`` (naive UTC)."""
    if frequency == "hourly":
        nxt = after.replace(minute=minute % 60, second=0, microsecond=0)
        if nxt <= after:
            nxt += timedelta(hours=1)
        return nxt

    base = after.replace(hour=hour % 24, minute=minute % 60, second=0, microsecond=0)
    if frequency == "weekly":
        days_ahead = (weekday - base.weekday()) % 7
        cand = base + timedelta(days=days_ahead)
        if cand <= after:
            cand += timedelta(days=7)
        return cand

    # daily (default)
    if base <= after:
        base += timedelta(days=1)
    return base


def _backup_filename(stack_id: str, include_volumes: bool) -> str:
    date = compose_service.now().strftime("%Y%m%d-%H%M%S")
    suffix = "full" if include_volumes else "config"
    return f"backup-{stack_id}-{suffix}-{date}.tar.gz"


def _prune(dest: BackupDestination, stack_id: str, keep: int) -> int:
    if keep <= 0:
        return 0
    items = dest_service.list_backups(dest)
    mine = [i for i in items if i["name"].startswith(f"backup-{stack_id}-")]
    mine.sort(key=lambda x: x.get("modified") or 0, reverse=True)
    removed = 0
    for old in mine[keep:]:
        try:
            dest_service.delete(dest, old["name"])
            removed += 1
        except dest_service.DestinationError as exc:
            logger.warning("retention delete failed for %s: %s", old["name"], exc)
    return removed


async def run_schedule(session: Session, schedule: BackupSchedule) -> dict:
    """Execute one schedule now. Updates status + next_run. Returns a summary."""
    now = _now()
    stack = session.get(Stack, schedule.stack_id)
    dest = session.get(BackupDestination, schedule.destination_id)
    result: dict = {"ok": False}
    path = None
    try:
        if not stack:
            raise RuntimeError(f"stack '{schedule.stack_id}' not found")
        if not dest:
            raise RuntimeError(f"destination {schedule.destination_id} not found")
        path = await backup_service.create_backup(
            schedule.stack_id, stack.name,
            include_volumes=schedule.include_volumes, stop_first=schedule.stop_first,
        )
        filename = _backup_filename(schedule.stack_id, schedule.include_volumes)
        await asyncio.to_thread(dest_service.upload, dest, path, filename)
        pruned = await asyncio.to_thread(_prune, dest, schedule.stack_id, schedule.keep)
        schedule.last_status = "ok"
        result = {"ok": True, "name": filename, "destination": dest.name, "pruned": pruned}
        logger.info("Scheduled backup %s → %s ok (pruned %d)", schedule.stack_id, dest.name, pruned)
    except Exception as exc:  # noqa: BLE001
        schedule.last_status = f"error: {exc}"[:300]
        result = {"ok": False, "error": str(exc)}
        logger.warning("Scheduled backup %s failed: %s", schedule.stack_id, exc)
        try:
            await notify_service.notify(
                EVENT_BACKUP_FAILED,
                f"Scheduled backup of '{schedule.stack_id}' failed",
                str(exc),
                session,
            )
        except Exception:  # noqa: BLE001
            pass
    finally:
        if path and os.path.exists(path):
            os.unlink(path)
        schedule.last_run = now
        schedule.next_run = compute_next_run(
            schedule.frequency, schedule.hour, schedule.minute, schedule.weekday, now
        )
        session.add(schedule)
        session.commit()
        session.refresh(schedule)
    return result


async def run_due() -> None:
    now = _now()
    with Session(engine) as session:
        schedules = session.exec(
            select(BackupSchedule).where(BackupSchedule.enabled == True)  # noqa: E712
        ).all()
        due = []
        for s in schedules:
            if s.next_run is None:
                s.next_run = compute_next_run(s.frequency, s.hour, s.minute, s.weekday, now)
                session.add(s)
            elif s.next_run <= now:
                due.append(s)
        session.commit()
        for s in due:
            await run_schedule(session, s)


async def scheduler_loop() -> None:
    await asyncio.sleep(20)  # let startup settle
    while True:
        try:
            await run_due()
        except Exception as exc:  # noqa: BLE001
            logger.warning("scheduler tick failed: %s", exc)
        await asyncio.sleep(60)