"""数据库引擎、Session 与 Declarative Base。"""

from __future__ import annotations

from collections.abc import Generator

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

from .config import get_settings

_settings = get_settings()

engine = create_engine(
    _settings.db_url(),
    pool_pre_ping=True,
    pool_size=_settings.database.pool_size,
    pool_recycle=_settings.database.pool_recycle,
    future=True,
)

SessionLocal = sessionmaker(bind=engine, autoflush=False, autocommit=False, future=True)


class Base(DeclarativeBase):
    pass


def get_db() -> Generator[Session, None, None]:
    """FastAPI 依赖：为每个请求产出一个 Session。"""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def init_db_schema() -> None:
    """按需建表（幂等）。先导入 models 以注册映射。"""
    from . import models  # noqa: F401
    Base.metadata.create_all(bind=engine)