from sqlalchemy.orm import Session
from sqlalchemy import select, delete
from model.wl_score_model import Score
from model.wl_student_model import Student


def get_student_by_no(db: Session, stu_no: str):
    """按学号查学生。
    新增成绩前先确认学生真实存在：wl_score.stu_no 是指向学生表的外键，
    给一个不存在的学号会在 commit 时抛外键异常，那样报出来就是 500 了。
    """
    return db.scalar(select(Student).where(Student.stu_no == stu_no))


def get_student_by_id(db: Session, stu_id: int):
    """检测学生是否存在：通过学生id查学生表"""
    return db.scalar(select(Student).where(Student.stu_id == stu_id))


def get_student_by_name(db: Session, stu_name: str):
    """通过学生姓名查询学生"""
    return db.scalar(select(Student).where(Student.stu_name == stu_name))


def get_score(db: Session, stu_no: str, exam_order: int):
    """根据学号+考试批次查询单条成绩"""
    stmt = select(Score).where(
        Score.stu_no == stu_no,
        Score.exam_order == exam_order
    )
    return db.scalar(stmt)


def list_score_by_stu_no(db: Session, stu_no: str):
    """查询一个学生全部成绩。
    学号不存在时自然就是空列表，不用单独去查一次学生。
    """
    stmt = select(Score).where(Score.stu_no == stu_no)
    return db.scalars(stmt).all()


def create_score(db: Session, stu_no: str, exam_order: int, score: float):
    """
    新增成绩
    返回：成功返回Score对象；检测不通过返回None
    """
    # 1.检测：学生是否真实存在学生表
    if not get_student_by_no(db, stu_no):
        print("[检测] 学生表无此学生,stu_no=", stu_no)
        return None

    # 2.检测：该学生该批次成绩是否已经存在（重复新增）
    if get_score(db, stu_no, exam_order):
        print("[检测] 成绩已存在 stu_no=", stu_no, "exam_order=", exam_order)
        return None

    # 3.构建ORM对象插入数据库
    new_score = Score(
        stu_no=stu_no,
        exam_order=exam_order,
        score=score
    )
    db.add(new_score)
    db.commit()
    db.refresh(new_score)
    return new_score


def update_score(db: Session, stu_no: str, exam_order: int, new_score: float):
    """
    更新指定学生指定考试批次的分数
    """
    # 检测这条成绩记录是否存在（记录在，学生就一定在，外键保证的）
    score_obj = get_score(db, stu_no, exam_order)
    if not score_obj:
        print("[检测] 更新失败：该学生该批次成绩记录不存在")
        return None

    # 直接修改对象属性
    score_obj.score = new_score
    db.commit()
    db.refresh(score_obj)
    return score_obj


def delete_score(db: Session, stu_no: str, exam_order: int):
    """删除某个学生某一次考核成绩"""
    # 检测记录是否存在
    score_obj = get_score(db, stu_no, exam_order)
    if not score_obj:
        print("[检测] 删除失败，记录不存在")
        return False

    stmt = delete(Score).where(
        Score.stu_no == stu_no,
        Score.exam_order == exam_order
    )
    db.execute(stmt)
    db.commit()
    return True