"""数据库引擎与会话管理。"""

from __future__ import annotations

from collections.abc import Iterator

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

from app.config import get_settings


class Base(DeclarativeBase):
    """所有 ORM 模型的基类。"""


_engine = None
_SessionLocal: 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, future=True)
    return _engine


def get_sessionmaker() -> sessionmaker[Session]:
    global _SessionLocal
    if _SessionLocal is None:
        _SessionLocal = sessionmaker(bind=get_engine(), expire_on_commit=False)
    return _SessionLocal


def get_session() -> Iterator[Session]:
    """FastAPI 依赖注入用的会话生成器。"""
    sm = get_sessionmaker()
    with sm() as session:
        yield session