@router.post("/import")
async def import_subjects(file: UploadFile = File(...), user: User = Depends(get_current_user),
                          db: AsyncSession = Depends(get_db)):
    fname = (file.filename or "").lower()
    if fname.endswith(".json"):
        raise HTTPException(400, "Only CSV/TXT subject imports are supported")
    content = (await file.read()).decode("utf-8", errors="replace")
    subjects = []
    if fname.endswith(".csv"):
        for row in csv.reader(io.StringIO(content)):
            if row and row[0].strip() and not row[0].lower().startswith(("subject", "subject line")):
                subjects.append(row[0].strip())
    else:
        for line in content.splitlines():
            line = line.strip()
            if line and not line.startswith("#") and not line.lower().startswith("subject"):
                subjects.append(line)
    subjects = subjects[:settings.MAX_SUBJECTS]
    existing = set((await db.execute(select(SubjectLine.subject).where(
        SubjectLine.user_id == user.id))).scalars().all())
    added = 0
    for s in subjects:
        if s not in existing:
            db.add(SubjectLine(user_id=user.id, subject=s[:500]))
            added += 1
    await db.commit()
    return {"ok": True, "seen": len(subjects), "added": added}


@router.get("/export")
async def export_subjects(user: User = Depends(get_current_user), db: AsyncSession = Depends(get_db)):
    rows = (await db.execute(select(SubjectLine).where(SubjectLine.user_id == user.id)
                             .order_by(SubjectLine.id))).scalars().all()
    buf = io.StringIO()
    w = csv.writer(buf)
    w.writerow(["subject", "use_count"])
    for s in rows:
        w.writerow([s.subject, s.use_count])
    buf.seek(0)
    return StreamingResponse(iter([buf.getvalue()]), media_type="text/csv",
                             headers={"Content-Disposition": "attachment; filename=subjects.csv"})


@router.put("/{subject_id}")
async def edit_subject(subject_id: int, payload: SubjectIn,
                       user: User = Depends(get_current_user), db: AsyncSession = Depends(get_db)):
    row = await db.get(SubjectLine, subject_id)
    if not row or row.user_id != user.id:
        raise HTTPException(404, "Not found")
    row.subject = payload.subject.strip()[:500]
    await db.commit()
    return {"ok": True}


@router.delete("/{subject_id}")
async def delete_subject(subject_id: int, user: User = Depends(get_current_user),
                         db: AsyncSession = Depends(get_db)):
    row = await db.get(SubjectLine, subject_id)
    if not row or row.user_id != user.id:
        raise HTTPException(404, "Not found")
    await db.delete(row)
    await db.commit()
    return {"ok": True}


@router.post("/clear-all")
async def clear_all(user: User = Depends(get_current_user), db: AsyncSession = Depends(get_db)):
    await db.execute(sa_delete(SubjectLine).where(SubjectLine.user_id == user.id))