mathe-app/backend/src/routes/topics.js

import { Router } from 'express';
import { requireAuth } from '../middleware/auth.js';
import pool from '../db/index.js';

const router = Router();

// GET /api/topics — alle Kategorien mit Topics
router.get('/', requireAuth, async (req, res) => {
  try {
    const cats = await pool.query(
      'SELECT id, slug, title, icon FROM categories ORDER BY sort_order'
    );
    const topics = await pool.query(
      `SELECT t.id, t.category_id, t.slug, t.title, t.description, t.difficulty, t.is_premium,
              COUNT(tk.id) AS task_count
       FROM topics t
       LEFT JOIN tasks tk ON tk.topic_id = t.id
       GROUP BY t.id
       ORDER BY t.sort_order`
    );

    const result = cats.rows.map(cat => ({
      ...cat,
      topics: topics.rows.filter(t => t.category_id === cat.id),
    }));

    res.json(result);
  } catch (err) {
    console.error(err);
    res.status(500).json({ message: 'Serverfehler' });
  }
});

// GET /api/topics/:slug/tasks — Aufgaben eines Topics (mit Fortschritt)
router.get('/:slug/tasks', requireAuth, async (req, res) => {
  try {
    const topic = await pool.query(
      'SELECT * FROM topics WHERE slug = $1', [req.params.slug]
    );
    if (!topic.rows[0]) return res.status(404).json({ message: 'Topic nicht gefunden' });

    const tasks = await pool.query(
      `SELECT tk.id, tk.title, tk.question, tk.answer_type, tk.choices,
              tk.unit, tk.xp_reward, tk.difficulty,
              up.correct AS solved, up.solved_at
       FROM tasks tk
       LEFT JOIN user_progress up ON up.task_id = tk.id AND up.user_id = $1
       WHERE tk.topic_id = $2
       ORDER BY tk.difficulty, tk.id`,
      [req.user.id, topic.rows[0].id]
    );

    res.json({ topic: topic.rows[0], tasks: tasks.rows });
  } catch (err) {
    console.error(err);
    res.status(500).json({ message: 'Serverfehler' });
  }
});

export default router;