"""SQLAlchemy 2.x 同步引擎 + 会话管理（MVP: SQLite）。

切换 PostgreSQL 时（扩展接口 1）：
1. DATABASE_URL 改为 postgresql+asyncpg://...
2. 引擎换 create_async_engine + async_sessionmaker
3. get_session 改 async generator + yield
4. 业务层 Repository 调用加 await
"""

from collections.abc import Generator

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

from app.core.config import get_settings

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


def get_engine():
    global _engine
    if _engine is None:
        settings = get_settings()
        _engine = create_engine(
            settings.database_url,
            pool_pre_ping=True,
            echo=False,
            # SQLite 专属：启用 WAL 模式（并发读 + 写串行化）
            connect_args={"check_same_thread": False} if "sqlite" in settings.database_url else {},
        )
        # SQLite: 启用 WAL 模式与外键约束
        if "sqlite" in settings.database_url:
            from sqlalchemy import event, text

            @event.listens_for(_engine, "connect")
            def _set_sqlite_pragma(dbapi_conn, _):  # type: ignore[no-untyped-def]
                cursor = dbapi_conn.cursor()
                cursor.execute("PRAGMA journal_mode=WAL")
                cursor.execute("PRAGMA foreign_keys=ON")
                cursor.close()

    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