# -*- coding: utf-8 -*-
"""错题变式题映射：base_question -> variant_question（同知识点）"""

from datetime import datetime

from sqlalchemy import Column, DateTime, ForeignKey, Integer, UniqueConstraint

from backend.database import Base


class QuestionVariant(Base):
    __tablename__ = "question_variants"
    __table_args__ = (
        UniqueConstraint("base_question_id", "variant_question_id", name="uk_base_variant"),
    )

    id = Column(Integer, primary_key=True, index=True)

    # base_question_id：用户曾错过的“原题”
    base_question_id = Column(Integer, ForeignKey("questions.id"), nullable=False, index=True)

    # variant_question_id：同知识点变式题（可重复训练）
    variant_question_id = Column(Integer, ForeignKey("questions.id"), nullable=False, index=True)

    # 同知识点标注（可为空；若为空将退回 QuestionVariant 的 base/variant 映射）
    knowledge_point_id = Column(Integer, ForeignKey("knowledge_points.id"), nullable=True, index=True)

    weight = Column(Integer, default=1)
    created_at = Column(DateTime, default=datetime.utcnow)