"""SQLAlchemy 2.x 同步引擎 + 会话管理。

支持 MySQL / SQLite，通过 DATABASE_URL 自动切换。
"""

from collections.abc import Generator

from sqlalchemy import create_engine, event, text
from sqlalchemy.orm import Session, sessionmaker

from app.core.config import get_settings
from app.core.logging import get_logger

logger = get_logger(__name__)

_engine = None
_session_factory: sessionmaker[Session] | None = None


def get_engine():
    global _engine
    if _engine is None:
        settings = get_settings()

        engine_kwargs = {
            "pool_pre_ping": True,
            "echo": False,
        }

        if settings.is_mysql:
            # MySQL 配置
            engine_kwargs.update({
                "pool_size": 10,
                "max_overflow": 20,
                "pool_recycle": 3600,  # 1 小时回收连接，防止 MySQL 超时断开
                "connect_args": {
                    "charset": "utf8mb4",
                },
            })
        elif settings.is_sqlite:
            # SQLite 配置
            engine_kwargs["connect_args"] = {"check_same_thread": False}

        _engine = create_engine(settings.database_url, **engine_kwargs)

        # SQLite: 启用 WAL 模式 + 外键约束
        if settings.is_sqlite:
            @event.listens_for(_engine, "connect")
            def _set_sqlite_pragma(dbapi_conn, _):
                cursor = dbapi_conn.cursor()
                cursor.execute("PRAGMA journal_mode=WAL")
                cursor.execute("PRAGMA foreign_keys=ON")
                cursor.close()

        # MySQL: 设置字符集和 SQL 模式
        if settings.is_mysql:
            @event.listens_for(_engine, "connect")
            def _set_mysql_session(dbapi_conn, _):
                cursor = dbapi_conn.cursor()
                cursor.execute("SET NAMES utf8mb4")
                cursor.execute("SET SESSION sql_mode='STRICT_TRANS_TABLES,NO_ZERO_DATE,NO_ZERO_IN_DATE,ERROR_FOR_DIVISION_BY_ZERO'")
                cursor.close()

        logger.info("Database engine created: %s", "MySQL" if settings.is_mysql else "SQLite")

    return _engine


def get_session_factory() -> sessionmaker[Session]:
    global _session_factory
    if _session_factory is None:
        _session_factory = sessionmaker(
            get_engine(),
            class_=Session,
            expire_on_commit=False,
        )
    return _session_factory


def get_session() -> Generator[Session, None, None]:
    """FastAPI 依赖：请求级会话。"""
    factory = get_session_factory()
    session = factory()
    try:
        yield session
        session.commit()
    except Exception:
        session.rollback()
        raise
    finally:
        session.close()


def dispose_engine() -> None:
    global _engine, _session_factory
    if _engine is not None:
        _engine.dispose()
    _engine = None
    _session_factory = None