"""MySQL 会话（懒）：首次访问才创建 AsyncEngine + 连接池，不随应用启动初始化。

引擎/会话工厂都是函数式访问，第一次调用时建出单例；dispose 清理已建对象。
"""
from sqlalchemy import text
from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine

from config.settings import settings

_engine = None
_sessionmaker = None


def get_engine():
    global _engine
    if _engine is None:
        _engine = create_async_engine(
            settings.mysql.url,
            pool_size=settings.mysql.pool_size,
            max_overflow=settings.mysql.max_overflow,
            pool_recycle=settings.mysql.pool_recycle,
            pool_pre_ping=True,  # 取/还连接时探测，自动剔除死连接
            pool_timeout=settings.mysql.pool_timeout,
            connect_args={"connect_timeout": settings.mysql.connect_timeout},
        )
    return _engine


def get_session_factory():
    global _sessionmaker
    if _sessionmaker is None:
        _sessionmaker = async_sessionmaker(bind=get_engine(), expire_on_commit=False)
    return _sessionmaker


async def init_db() -> None:
    """手动预热入口（registry.init_db 逐库调用；不随应用启动自动执行）。"""
    get_engine()


async def dispose() -> None:
    global _engine, _sessionmaker
    if _engine is not None:
        await _engine.dispose()
        _engine = None
        _sessionmaker = None


async def check_health() -> None:
    async with get_engine().connect() as conn:
        await conn.execute(text("SELECT 1"))