"""多实例定时任务互斥。锁有过期时间，持有进程异常退出后其他实例仍能继续。"""

from __future__ import annotations

import os
import socket
from datetime import timedelta

from sqlalchemy import update
from sqlalchemy.exc import IntegrityError

from app.clock import utcnow
from app.database import session_scope
from app.models import SchedulerLock

OWNER = f"{socket.gethostname()}:{os.getpid()}"


def acquire_lock(name: str, ttl: timedelta) -> bool:
    now = utcnow()
    until = now + ttl
    try:
        with session_scope() as session:
            lock = session.get(SchedulerLock, name)
            if lock is None:
                session.add(SchedulerLock(name=name, locked_until=until, owner=OWNER))
                try:
                    session.flush()
                except IntegrityError:
                    session.rollback()
                    return False
                return True
            updated = session.execute(
                update(SchedulerLock)
                .where(SchedulerLock.name == name)
                .where(SchedulerLock.locked_until <= now)
                .values(locked_until=until, owner=OWNER)
            )
            return updated.rowcount == 1
    except IntegrityError:
        return False