"""同账套任务串行锁；独立持有 MySQL 连接，跨分页 commit 仍保持有效。"""

import hashlib
from contextlib import contextmanager

from sqlalchemy import text
from sqlalchemy.orm import Session


class TPlusBusyError(RuntimeError):
    """已有任务持有执行锁。"""


def lock_name(session: Session) -> str:
    """生成不含地址、账号或密码的固定长度锁名。"""
    database = session.get_bind().url.database or "default"
    return "ys:tplus:read:" + hashlib.sha256(database.encode()).hexdigest()[:24]


@contextmanager
def sync_lock(session: Session):
    """只在取得锁后执行；释放失败时使连接失效，防止带锁回池。"""
    engine = session.get_bind()
    if engine.dialect.name != "mysql":
        raise RuntimeError("T+ 执行协调需要 MySQL 命名锁")
    connection = engine.connect()
    acquired = False
    try:
        acquired = (
            connection.execute(
                text("SELECT GET_LOCK(:name, 0)"), {"name": lock_name(session)}
            ).scalar_one()
            == 1
        )
        if not acquired:
            raise TPlusBusyError("已有 T+ 任务正在执行，请稍后重试")
        yield
    finally:
        if acquired:
            try:
                released = connection.execute(
                    text("SELECT RELEASE_LOCK(:name)"), {"name": lock_name(session)}
                ).scalar_one()
                if released != 1:
                    connection.invalidate()
            except Exception:
                connection.invalidate()
        connection.close()