"""Database session management and engine configuration.

统一使用 app.config 中的数据库配置，移除重复的 DatabaseSettings。
"""
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, Session
from contextlib import contextmanager
from typing import Generator

from app.config import settings


engine = create_engine(
    settings.database_url,
    pool_size=settings.DATABASE_POOL_SIZE,
    max_overflow=settings.DATABASE_MAX_OVERFLOW,
    pool_timeout=settings.DATABASE_POOL_TIMEOUT,
    pool_recycle=settings.DATABASE_POOL_RECYCLE,
)

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


def get_db() -> Generator[Session, None, None]:
    """Dependency for getting database sessions."""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


@contextmanager
def get_db_context() -> Generator[Session, None, None]:
    """Context manager for database sessions.
    
    Usage:
        with get_db_context() as db:
            db.query(Model).all()
    """
    db = SessionLocal()
    try:
        yield db
        db.commit()
    except Exception:
        db.rollback()
        raise
    finally:
        db.close()