from datetime import datetime
from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, Text, UniqueConstraint
from sqlalchemy.orm import relationship
from app.database import Base


class QuestionCategory(Base):
    __tablename__ = "question_categories"

    id = Column(Integer, primary_key=True, index=True)
    parent_id = Column(Integer, ForeignKey("question_categories.id", ondelete="RESTRICT", name="fk_question_categories_parent"), nullable=True)
    name = Column(String, nullable=False)
    description = Column(Text, nullable=True)
    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
    # The organ system this topic belongs to, said once here rather than
    # inferred from a keyword on each question. A category's discipline is
    # where it sits in the tree; its system is a separate fact about it —
    # conjunctivitis is filed under Infectious Disease and is an eye.
    #
    # No ForeignKey in the model: `question_tags` is a raw-SQL table with no
    # ORM class, so declaring one here leaves every metadata build unable to
    # resolve it. The constraint is real in Postgres; the migration adds it.
    system_id = Column(Integer, nullable=True)
    created_at = Column(DateTime, default=datetime.utcnow)

    questions = relationship("Question", back_populates="question_category",
                             foreign_keys="Question.question_category_id")


class QuestionCategoryLink(Base):
    """Additional (non-primary) category assignments for a question."""

    __tablename__ = "question_category_links"
    __table_args__ = (UniqueConstraint("question_id", "category_id", name="uq_question_category_link"),)

    id = Column(Integer, primary_key=True, index=True)
    question_id = Column(Integer, ForeignKey("questions.id", ondelete="CASCADE"), nullable=False)
    category_id = Column(Integer, ForeignKey("question_categories.id", ondelete="CASCADE"), nullable=False)