"""客户评级数据访问（每客户一行）。

本层只 flush 不 commit —— 事务边界由 services 层控制。
"""

from sqlalchemy import select
from sqlalchemy.orm import Session

from app.models import CustomerRating

# ==================== 读取 ====================


def get_by_customer_id(session: Session, customer_id: int) -> CustomerRating | None:
    """查某客户的当前评级（uk_customer_ratings_customer_id 保证至多一行）。"""
    stmt = select(CustomerRating).where(CustomerRating.customer_id == customer_id)
    return session.execute(stmt).scalar_one_or_none()


# ==================== 写入 ====================


def create(session: Session, rating: CustomerRating) -> CustomerRating:
    """新增评级行。只 flush 以取得自增 id。"""
    session.add(rating)
    session.flush()
    return rating


def delete(session: Session, rating: CustomerRating) -> None:
    """删除评级行（客户物理删除前的联动清理，调用方先校验业务引用）。"""
    session.delete(rating)
    session.flush()