pdf-quiz-generator/backend/app/routers/flashcards.py

"""Flashcard decks and cards — generate, browse, edit, delete, and schedule."""
from datetime import datetime
from typing import Literal

from fastapi import APIRouter, Depends, HTTPException, Query
from pydantic import BaseModel
from sqlalchemy import or_, text as sa_text
from sqlalchemy.orm import Session

from app.database import get_db
from app.models.article import Article
from app.models.flashcard import (
    FlashcardDeck, Flashcard, FlashcardDeckRating,
    FlashcardQuestionLink, FlashcardArticleLink,
)
from app.models.question import Question
from app.models.section import Section
from app.models.question_category import QuestionCategory
from app.models.user import User
from app.services import card_review
from app.services.quiz_builder import category_descendants
from app.services.search_service import hybrid_ids
from app.services.quiz_builder import bank_question_predicate
from app.utils.auth import get_current_user, require_moderator

router = APIRouter()


# ── Schemas ──────────────────────────────────────────────────────────

class FlashcardDeckUpdate(BaseModel):
    title: str | None = None
    category_id: int | None = None


class FlashcardDeckResponse(BaseModel):
    id: int
    title: str
    section_id: int | None = None
    # Where the deck is filed. It was set on every deck written from an
    # article — and left out of this schema, so the list drew every one of
    # them as "Uncategorized" and an educator refiled a deck the system had
    # already filed correctly.
    category_id: int | None = None
    # Nullable: bank content has no owner, and a schema that promises an
    # int where the column says NULL is a 500 on serialisation.
    user_id: int | None = None
    card_count: int
    is_shared: int = 0
    created_at: object
    deleted_at: object | None = None

    class Config:
        from_attributes = True


class RatingRequest(BaseModel):
    rating: int  # 1-5


class FlashcardCardResponse(BaseModel):
    id: int
    deck_id: int
    front: str
    back: str
    page_reference: int | None = None
    image_path: str | None = None
    created_at: object

    class Config:
        from_attributes = True


class FlashcardDeckDetail(BaseModel):
    id: int
    title: str
    section_id: int | None = None
    # Nullable: bank content has no owner, and a schema that promises an
    # int where the column says NULL is a 500 on serialisation.
    user_id: int | None = None
    card_count: int
    created_at: object
    cards: list[FlashcardCardResponse]

    class Config:
        from_attributes = True


class CardEdit(BaseModel):
    front: str | None = None
    back: str | None = None
    #: A picture on the card. Empty string clears it, which is why this is
    #: `| None` for "not mentioned" rather than for "remove".
    image_path: str | None = None


def _deck_or_404(deck_id: int, current_user: User, db: Session) -> FlashcardDeck:
    """A deck, for somebody who works on decks.

    A deck used to be its creator's, and access turned on that. Decks are
    study material the whole site reads, so they belong to the bank: an
    educator or an admin reaches any of them, and nobody else reaches one
    this way. Studying a shared deck goes through the shared routes.
    """
    deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == deck_id).first()
    if not deck:
        raise HTTPException(status_code=404, detail="Deck not found")
    if not current_user.is_moderator:
        raise HTTPException(status_code=404, detail="Deck not found")
    return deck


def _own_deck_to_edit(deck_id: int, current_user: User, db: Session) -> FlashcardDeck:
    """Yours to change, and you are somebody who writes decks.

    Cards are written by educators. Ownership alone is not enough: if a learner
    ever comes to own a deck — inherited, imported, granted — that must not by
    itself make them an author of study material other people may end up
    seeing.
    """
    if not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Writing cards needs educator access")
    return _deck_or_404(deck_id, current_user, db)


# ── Deck endpoints ───────────────────────────────────────────────────

class ManualDeckCreate(BaseModel):
    title: str
    category_id: int | None = None


# No deck from a PDF section. Cards are written from an article — the text a
# person has already read, edited and published — rather than from whatever
# happened to be on pages 40-58 of a source document. The article path is
# POST /articles/{id}/ai-cards; a deck by hand is POST /flashcards/manual.


@router.post("/manual")
def create_deck_manually(
    data: ManualDeckCreate,
    db: Session = Depends(get_db),
    current_user: User = Depends(require_moderator),
):
    """An empty deck, to write cards into by hand.

    Every deck until now came out of a model — generated from a document
    section or from an article — so an educator who simply wanted to write six
    cards had nowhere to put them. The single-card route already existed and
    could only add to a deck that did not exist yet.

    Unshared, like every other new deck: sharing is a second, deliberate act.
    """
    title = (data.title or "").strip()
    if not title:
        raise HTTPException(status_code=400, detail="A deck needs a title")
    deck = FlashcardDeck(title=title[:200], user_id=current_user.id,
                         category_id=data.category_id, card_count=0, is_shared=0)
    db.add(deck)
    db.commit()
    db.refresh(deck)
    return {"id": deck.id, "title": deck.title, "card_count": 0, "is_shared": 0}


@router.get("/", response_model=list[FlashcardDeckResponse])
def list_flashcard_decks(
    include_deleted: bool = Query(False),
    category_id: int | None = Query(None),
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """The bank's decks, optionally by category. Educators only.

    There is no "my decks" any more — a deck is not anybody's. A learner
    studies what has been shared with them, which is the /shared listing.
    """
    if not current_user.is_moderator:
        return []
    q = db.query(FlashcardDeck)
    if not include_deleted:
        q = q.filter(FlashcardDeck.deleted_at.is_(None))
    if category_id is not None:
        # A parent category includes everything filed beneath it.
        wanted = category_descendants(db.query(QuestionCategory).all(), [category_id])
        q = q.filter(FlashcardDeck.category_id.in_(wanted))
    return q.order_by(FlashcardDeck.created_at.desc()).all()


@router.get("/trash", response_model=list[FlashcardDeckResponse])
def list_trashed_decks(
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Decks in the bin. Editors' business, like the decks themselves."""
    if not current_user.is_moderator:
        return []
    return db.query(FlashcardDeck).filter(
        FlashcardDeck.deleted_at.isnot(None),
    ).order_by(FlashcardDeck.deleted_at.desc()).all()


@router.get("/shared")
def list_shared_decks(
    limit: int = Query(20, le=100),
    offset: int = Query(0),
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """List shared decks sorted by average rating (desc), with pagination."""
    from sqlalchemy import func

    avg_rating = db.query(
        FlashcardDeckRating.deck_id,
        func.avg(FlashcardDeckRating.rating).label("avg_rating"),
        func.count(FlashcardDeckRating.id).label("rating_count"),
    ).group_by(FlashcardDeckRating.deck_id).subquery()

    my_ratings = {}
    for r in db.query(FlashcardDeckRating).filter(FlashcardDeckRating.user_id == current_user.id).all():
        my_ratings[r.deck_id] = r.rating

    total = db.query(FlashcardDeck).filter(
        FlashcardDeck.is_shared == 1,
        FlashcardDeck.deleted_at.is_(None),
    ).count()

    decks_with_rating = db.query(
        FlashcardDeck,
        func.coalesce(avg_rating.c.avg_rating, 0).label("avg_rating"),
        func.coalesce(avg_rating.c.rating_count, 0).label("rating_count"),
    ).outerjoin(
        avg_rating, FlashcardDeck.id == avg_rating.c.deck_id
    ).filter(
        FlashcardDeck.is_shared == 1,
        FlashcardDeck.deleted_at.is_(None),
    ).order_by(
        func.coalesce(avg_rating.c.avg_rating, 0).desc(),
        FlashcardDeck.created_at.desc(),
    ).offset(offset).limit(limit).all()

    result = []
    for deck, avg_r, r_count in decks_with_rating:
        result.append({
            "id": deck.id,
            "title": deck.title,
            "card_count": deck.card_count,
            # No owner to name. A shared deck is the library's.
            "user_id": None,
            "owner_name": "PedsHub",
            "is_shared": deck.is_shared,
            "created_at": deck.created_at,
            "avg_rating": round(float(avg_r), 1),
            "rating_count": int(r_count),
            "my_rating": my_ratings.get(deck.id),
        })

    return {"total": total, "decks": result}


@router.get("/{deck_id}", response_model=FlashcardDeckDetail)
def get_flashcard_deck(
    deck_id: int,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Get a deck with all its cards. Accessible if owned or shared."""
    deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == deck_id).first()
    if not deck:
        raise HTTPException(status_code=404, detail="Deck not found")
    if not deck.is_shared and not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Not your deck")
    return deck


class CardVerdict(BaseModel):
    """What a learner said about a card. Two answers, deliberately."""

    outcome: Literal["known", "again"]


@router.get("/{deck_id}/study")
def study_deck(deck_id: int, db: Session = Depends(get_db),
               current_user: User = Depends(get_current_user)):
    """The deck in the order it should be sat, with what is due said out loud.

    Ordering happens here rather than in the page because it needs this
    learner's history, and a page that fetched the whole review log to sort
    twenty cards would be downloading a year of answers to draw one screen.
    """
    deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == deck_id).first()
    if not deck:
        raise HTTPException(status_code=404, detail="Deck not found")
    if not deck.is_shared and not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Not your deck")

    cards = db.query(Flashcard).filter(Flashcard.deck_id == deck_id).order_by(Flashcard.id).all()
    ordered, counts = card_review.study_order(db, current_user.id, cards)
    return {
        "deck": {"id": deck.id, "title": deck.title, "card_count": len(cards)},
        **counts,
        "cards": [{"id": card.id, "front": card.front, "back": card.back,
                   "image_path": card.image_path} for card in ordered],
    }


@router.post("/cards/{card_id}/review")
def review_card(card_id: int, data: CardVerdict, db: Session = Depends(get_db),
                current_user: User = Depends(get_current_user)):
    """Record how a card went, so the deck can come back at the right time."""
    card = db.get(Flashcard, card_id)
    if not card:
        raise HTTPException(status_code=404, detail="Card not found")
    deck = db.get(FlashcardDeck, card.deck_id)
    if deck and not deck.is_shared and not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Not your deck")
    card_review.record(db, current_user.id, card_id, data.outcome)
    return {"card_id": card_id, "outcome": data.outcome}


@router.get("/questions/{question_id}/cards")
def cards_for_question(question_id: int, db: Session = Depends(get_db),
                       current_user: User = Depends(get_current_user)):
    """The cards an educator tied to this question.

    The link is read from the question's end only. A card that listed the
    questions it belongs to would hand a learner revising the deck the shape of
    the exam — and the answer, since a card's back is an answer.
    """
    rows = db.query(Flashcard, FlashcardDeck).join(
        FlashcardQuestionLink, FlashcardQuestionLink.flashcard_id == Flashcard.id).join(
        FlashcardDeck, FlashcardDeck.id == Flashcard.deck_id).filter(
        FlashcardQuestionLink.question_id == question_id,
        FlashcardDeck.deleted_at.is_(None)).all()
    return [{"card_id": card.id, "deck_id": deck.id, "deck_title": deck.title,
             "front": card.front}
            for card, deck in rows
            if deck.is_shared or current_user.is_moderator]


@router.delete("/{deck_id}", status_code=204)
def delete_flashcard_deck(
    deck_id: int,
    permanent: bool = Query(False),
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Soft-delete a deck (moves to trash). Use ?permanent=true to permanently delete."""
    deck = _deck_or_404(deck_id, current_user, db)
    if permanent:
        db.delete(deck)
    else:
        deck.deleted_at = datetime.utcnow()
    db.commit()


@router.post("/{deck_id}/restore", status_code=200)
def restore_flashcard_deck(
    deck_id: int,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Restore a soft-deleted deck from trash."""
    deck = _deck_or_404(deck_id, current_user, db)
    if not deck.deleted_at:
        raise HTTPException(status_code=400, detail="Deck is not in trash")
    deck.deleted_at = None
    db.commit()
    return {"id": deck.id, "title": deck.title, "restored": True}


# ── Sharing & rating ────────────────────────────────────────────────

@router.patch("/{deck_id}")
def update_deck(
    deck_id: int,
    data: FlashcardDeckUpdate,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Update deck metadata (title, category). Owner or admin only."""
    deck = _own_deck_to_edit(deck_id, current_user, db)
    if data.title is not None:
        title = data.title.strip()
        if not title:
            raise HTTPException(status_code=400, detail="Title cannot be empty")
        deck.title = title[:300]
    if "category_id" in data.model_fields_set:
        # Same tree as questions and articles, so the id must exist in it.
        if data.category_id is not None and not db.get(QuestionCategory, data.category_id):
            raise HTTPException(status_code=404, detail="Category not found")
        deck.category_id = data.category_id
    db.commit()
    db.refresh(deck)
    return {"id": deck.id, "title": deck.title, "category_id": deck.category_id}


@router.put("/{deck_id}/share")
def toggle_share_deck(
    deck_id: int,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Toggle sharing on a deck. Owner or admin."""
    deck = _deck_or_404(deck_id, current_user, db)
    deck.is_shared = 0 if deck.is_shared else 1
    db.commit()
    return {"id": deck.id, "is_shared": deck.is_shared}


@router.delete("/{deck_id}/share", status_code=204)
def admin_unshare_deck(
    deck_id: int,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Admin: force-unshare any deck."""
    if not current_user.is_admin:
        raise HTTPException(status_code=403, detail="Admin only")
    deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == deck_id).first()
    if not deck:
        raise HTTPException(status_code=404, detail="Deck not found")
    deck.is_shared = 0
    db.commit()


@router.post("/{deck_id}/rate")
def rate_deck(
    deck_id: int,
    data: RatingRequest,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Rate a shared deck (1-5). Updates if already rated."""
    if data.rating < 1 or data.rating > 5:
        raise HTTPException(status_code=400, detail="Rating must be 1-5")

    deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == deck_id).first()
    if not deck:
        raise HTTPException(status_code=404, detail="Deck not found")
    if not deck.is_shared:
        raise HTTPException(status_code=400, detail="Deck is not shared")

    existing = db.query(FlashcardDeckRating).filter(
        FlashcardDeckRating.deck_id == deck_id,
        FlashcardDeckRating.user_id == current_user.id,
    ).first()

    if existing:
        existing.rating = data.rating
    else:
        db.add(FlashcardDeckRating(
            deck_id=deck_id,
            user_id=current_user.id,
            rating=data.rating,
        ))
    db.commit()

    # Return updated average
    from sqlalchemy import func
    avg = db.query(func.avg(FlashcardDeckRating.rating)).filter(
        FlashcardDeckRating.deck_id == deck_id
    ).scalar()
    count = db.query(FlashcardDeckRating).filter(FlashcardDeckRating.deck_id == deck_id).count()

    return {"deck_id": deck_id, "my_rating": data.rating, "avg_rating": round(float(avg), 1), "rating_count": count}


# ── Card browse endpoints ────────────────────────────────────────────

@router.get("/cards/browse")
def browse_flashcards(
    q: str | None = Query(None),
    deck_id: int | None = Query(None),
    tag_ids: str | None = Query(None, description="Comma-separated tag IDs (AND filter)"),
    limit: int = Query(50, le=200),
    offset: int = Query(0),
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Browse the cards in the bank's decks. Educators; learners study shared."""
    if not current_user.is_moderator:
        return {"total": 0, "cards": []}
    own_deck_ids = [d.id for d in db.query(FlashcardDeck.id).filter(
        FlashcardDeck.deleted_at.is_(None),
    ).all()]
    if not own_deck_ids:
        return {"total": 0, "cards": []}

    query = db.query(Flashcard).filter(Flashcard.deck_id.in_(own_deck_ids))

    if deck_id:
        query = query.filter(Flashcard.deck_id == deck_id)

    if q and q.strip():
        # Hybrid retrieval, same as questions and articles.
        ranked, _ = hybrid_ids(db, q.strip(), "flashcard", limit=500)
        if not ranked:
            return {"total": 0, "cards": []}
        query = query.filter(Flashcard.id.in_(ranked))

    # Tag filter
    if tag_ids:
        tag_id_list = [int(t.strip()) for t in tag_ids.split(",") if t.strip().isdigit()]
        if tag_id_list:
            matching_ids = list(db.execute(sa_text("""
                SELECT flashcard_id FROM flashcard_tag_links
                WHERE tag_id = ANY(:tag_ids)
                GROUP BY flashcard_id
                HAVING COUNT(DISTINCT tag_id) = :cnt
            """), {"tag_ids": tag_id_list, "cnt": len(tag_id_list)}).scalars())
            if matching_ids:
                query = query.filter(Flashcard.id.in_(matching_ids))
            else:
                return {"total": 0, "cards": []}

    total = query.count()
    cards = query.order_by(Flashcard.deck_id, Flashcard.id).offset(offset).limit(limit).all()

    deck_cache: dict[int, str] = {}
    result = []
    for card in cards:
        if card.deck_id not in deck_cache:
            deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == card.deck_id).first()
            deck_cache[card.deck_id] = deck.title if deck else f"Deck {card.deck_id}"
        result.append({
            "id": card.id,
            "deck_id": card.deck_id,
            "deck_title": deck_cache[card.deck_id],
            "front": card.front,
            "back": card.back,
            "page_reference": card.page_reference,
            "image_path": card.image_path,
            "created_at": card.created_at,
        })

    return {"total": total, "cards": result}


@router.get("/cards/browse/ids")
def browse_flashcard_ids(
    q: str | None = Query(None),
    deck_id: int | None = Query(None),
    tag_ids: str | None = Query(None),
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Return just IDs for matching cards (for select-all)."""
    if not current_user.is_moderator:
        return []
    own_deck_ids = [d.id for d in db.query(FlashcardDeck.id).filter(
        FlashcardDeck.deleted_at.is_(None),
    ).all()]
    if not own_deck_ids:
        return []

    query = db.query(Flashcard.id).filter(Flashcard.deck_id.in_(own_deck_ids))

    if deck_id:
        query = query.filter(Flashcard.deck_id == deck_id)
    if q and q.strip():
        phrase = q.strip()
        query = query.filter(or_(
            Flashcard.front.ilike(f"%{phrase}%"),
            Flashcard.back.ilike(f"%{phrase}%"),
        ))
    if tag_ids:
        tag_id_list = [int(t.strip()) for t in tag_ids.split(",") if t.strip().isdigit()]
        if tag_id_list:
            matching_ids = list(db.execute(sa_text("""
                SELECT flashcard_id FROM flashcard_tag_links
                WHERE tag_id = ANY(:tag_ids)
                GROUP BY flashcard_id
                HAVING COUNT(DISTINCT tag_id) = :cnt
            """), {"tag_ids": tag_id_list, "cnt": len(tag_id_list)}).scalars())
            if matching_ids:
                query = query.filter(Flashcard.id.in_(matching_ids))
            else:
                return []

    return [row[0] for row in query.all()]


# ── Single card endpoints ────────────────────────────────────────────

@router.put("/cards/{card_id}")
def update_flashcard(
    card_id: int,
    data: CardEdit,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Edit a single flashcard (front, back). Owner or admin."""
    card = db.query(Flashcard).filter(Flashcard.id == card_id).first()
    if not card:
        raise HTTPException(status_code=404, detail="Card not found")
    deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == card.deck_id).first()
    if deck and not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Not your card")
    if data.front is not None:
        card.front = data.front
    if data.back is not None:
        card.back = data.back
    if data.image_path is not None:
        card.image_path = data.image_path.strip() or None
    db.commit()
    db.refresh(card)
    return {"id": card.id, "deck_id": card.deck_id, "front": card.front,
            "back": card.back, "image_path": card.image_path}


@router.delete("/cards/{card_id}", status_code=204)
def delete_flashcard(
    card_id: int,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Delete a single flashcard. Owner or admin."""
    card = db.query(Flashcard).filter(Flashcard.id == card_id).first()
    if not card:
        raise HTTPException(status_code=404, detail="Card not found")
    deck = db.query(FlashcardDeck).filter(FlashcardDeck.id == card.deck_id).first()
    if deck and not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Not your card")
    db.delete(card)
    if deck and deck.card_count > 0:
        deck.card_count -= 1
    db.commit()


# ── Manual cards and question/article associations ────────────────────

class CardCreate(BaseModel):
    front: str
    back: str
    image_path: str | None = None


class CardQuestionLinkIn(BaseModel):
    question_id: int


class CardArticleLinkIn(BaseModel):
    article_id: int
    article_section_id: str | None = None


@router.post("/decks/{deck_id}/cards")
def create_flashcard_manually(
    deck_id: int,
    data: CardCreate,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Add a single card to an existing deck. Owner or admin."""
    deck = _own_deck_to_edit(deck_id, current_user, db)
    if not data.front.strip() or not data.back.strip():
        raise HTTPException(status_code=400, detail="Both sides are required")
    card = Flashcard(deck_id=deck.id, front=data.front.strip(), back=data.back.strip(),
                     image_path=(data.image_path or None) or None)
    db.add(card)
    deck.card_count = (deck.card_count or 0) + 1
    db.commit()
    db.refresh(card)
    return {"id": card.id, "deck_id": deck.id, "front": card.front, "back": card.back, "image_path": card.image_path}


def _own_card_or_404(card_id: int, current_user: User, db: Session) -> Flashcard:
    card = db.get(Flashcard, card_id)
    if not card:
        raise HTTPException(status_code=404, detail="Card not found")
    deck = db.get(FlashcardDeck, card.deck_id)
    if deck and not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Not your card")
    return card


@router.get("/cards/{card_id}/links")
def list_card_links(
    card_id: int,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Questions and articles associated with a card (access follows the deck)."""
    card = db.get(Flashcard, card_id)
    if not card:
        raise HTTPException(status_code=404, detail="Card not found")
    deck = db.get(FlashcardDeck, card.deck_id)
    if deck and not deck.is_shared and not current_user.is_moderator:
        raise HTTPException(status_code=403, detail="Not your card")
    questions = db.query(Question.id, Question.question_text)
    if not current_user.is_moderator:
        questions = questions.filter(bank_question_predicate(current_user))
    questions = questions.join(
        FlashcardQuestionLink, FlashcardQuestionLink.question_id == Question.id,
    ).filter(FlashcardQuestionLink.flashcard_id == card_id).all()
    articles = db.query(Article.id, Article.title, Article.status, FlashcardArticleLink.article_section_id)
    if not current_user.is_moderator:
        articles = articles.filter(Article.status == 'published')
    articles = articles.join(
        FlashcardArticleLink, FlashcardArticleLink.article_id == Article.id,
    ).filter(FlashcardArticleLink.flashcard_id == card_id).all()
    return {
        "questions": [{"id": qid, "question_text": text} for qid, text in questions],
        "articles": [{"id": aid, "title": title, "status": status, "article_section_id": sid}
                     for aid, title, status, sid in articles],
    }


@router.put("/cards/{card_id}/links/question")
def link_card_question(
    card_id: int,
    data: CardQuestionLinkIn,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    _own_card_or_404(card_id, current_user, db)
    if not db.query(Question.id).filter(Question.id == data.question_id, bank_question_predicate(current_user)).first():
        raise HTTPException(status_code=404, detail="Question not found")
    if db.query(FlashcardQuestionLink.id).filter_by(flashcard_id=card_id, question_id=data.question_id).first():
        return {"linked": False}
    db.add(FlashcardQuestionLink(flashcard_id=card_id, question_id=data.question_id))
    db.commit()
    return {"linked": True}


@router.delete("/cards/{card_id}/links/question/{question_id}", status_code=204)
def unlink_card_question(
    card_id: int,
    question_id: int,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    _own_card_or_404(card_id, current_user, db)
    db.query(FlashcardQuestionLink).filter_by(flashcard_id=card_id, question_id=question_id).delete(synchronize_session=False)
    db.commit()


@router.put("/cards/{card_id}/links/article")
def link_card_article(
    card_id: int,
    data: CardArticleLinkIn,
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    _own_card_or_404(card_id, current_user, db)
    article = db.get(Article, data.article_id)
    if not article:
        raise HTTPException(status_code=404, detail="Article not found")
    if data.article_section_id is not None and data.article_section_id not in {
            section["id"] for section in (article.sections or [])}:
        raise HTTPException(status_code=400, detail="Section not found in this article")
    if db.query(FlashcardArticleLink.id).filter_by(
            flashcard_id=card_id, article_id=data.article_id, article_section_id=data.article_section_id).first():
        return {"linked": False}
    db.add(FlashcardArticleLink(flashcard_id=card_id, article_id=data.article_id,
                                article_section_id=data.article_section_id))
    db.commit()
    return {"linked": True}


@router.delete("/cards/{card_id}/links/article/{article_id}", status_code=204)
def unlink_card_article(
    card_id: int,
    article_id: int,
    article_section_id: str | None = Query(None),
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    _own_card_or_404(card_id, current_user, db)
    db.query(FlashcardArticleLink).filter_by(
        flashcard_id=card_id, article_id=article_id, article_section_id=article_section_id,
    ).delete(synchronize_session=False)
    db.commit()


@router.get("/cards/linked")
def cards_for_target(
    question_id: int | None = Query(None),
    article_id: int | None = Query(None),
    db: Session = Depends(get_db),
    current_user: User = Depends(get_current_user),
):
    """Cards linked to a question or article; results follow deck sharing/ownership."""
    if (question_id is None) == (article_id is None):
        raise HTTPException(400, "Provide exactly one of question_id or article_id")
    if question_id is not None and not db.query(Question.id).filter(
            Question.id == question_id, bank_question_predicate(current_user)).first():
        raise HTTPException(404, "Question not found")
    query = db.query(Flashcard, FlashcardDeck).join(
        FlashcardDeck, FlashcardDeck.id == Flashcard.deck_id,
    ).filter(FlashcardDeck.deleted_at.is_(None))
    if question_id is not None:
        query = query.join(FlashcardQuestionLink, FlashcardQuestionLink.flashcard_id == Flashcard.id).filter(
            FlashcardQuestionLink.question_id == question_id)
    else:
        article = db.get(Article, article_id)
        if not article:
            raise HTTPException(404, "Article not found")
        if article.status != "published" and not current_user.is_moderator:
            raise HTTPException(404, "Article not found")
        query = query.join(FlashcardArticleLink, FlashcardArticleLink.flashcard_id == Flashcard.id).filter(
            FlashcardArticleLink.article_id == article_id)
    cards = []
    for card, deck in query.all():
        if not current_user.is_moderator and not deck.is_shared:
            continue
        cards.append({"id": card.id, "deck_id": deck.id, "deck_title": deck.title,
                      "front": card.front, "back": card.back, "image_path": card.image_path})
    return cards