from datetime import datetime

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

from app.database import Base


class QuestionFolder(Base):
    """A hand-picked set of questions an educator assembles for someone else.

    Deliberately not a `user_collections` row with a flag on it. The two look
    alike — both are a named list of questions — but the access arrow runs the
    other way. A library is a *consequence* of access: you can only save what
    the bank predicate already lets you see, and the API says `private: True`
    about every row. A folder is a *source* of access: a grant points at one,
    and holding that grant is how an educator comes to reach the questions
    inside. Putting both in one table would mean thousands of private rows
    sitting beside a handful that confer permission, told apart by a flag —
    and a mistake reading that flag is either a privacy leak or a privilege
    escalation, in a table where the common case is somebody's private list.

    Membership is the owner's and a moderator's to change, never a grantee's:
    otherwise the holder of a folder grant could add any question to the folder
    and so widen their own grant.
    """

    __tablename__ = "question_folders"

    id = Column(Integer, primary_key=True, index=True)
    name = Column(String(200), nullable=False)
    description = Column(Text, nullable=True)
    # Who assembled it. SET NULL rather than CASCADE: a folder someone was
    # granted must not disappear because the educator who built it left.
    user_id = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True, index=True)
    created_at = Column(DateTime, default=datetime.utcnow)
    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)


class QuestionFolderQuestion(Base):
    __tablename__ = "question_folder_questions"
    __table_args__ = (UniqueConstraint("folder_id", "question_id", name="uq_folder_question"),)

    id = Column(Integer, primary_key=True, index=True)
    folder_id = Column(Integer, ForeignKey("question_folders.id", ondelete="CASCADE"),
                       nullable=False, index=True)
    question_id = Column(Integer, ForeignKey("questions.id", ondelete="CASCADE"),
                         nullable=False, index=True)
    added_by = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True)
    added_at = Column(DateTime, default=datetime.utcnow)