Вот полный код `app.js` без комментариев:

```javascript const express = require('express'); const fs = require('fs'); const jwt = require('jsonwebtoken'); const mysql = require('mysql2'); const app = express();

app.use(express.json());

const SECRET_KEY = 'your_secret_key';

const db = mysql.createConnection({ host: 'localhost', user: 'your_username', password: 'your_password', database: 'survey_db' });

db.connect(err => { if (err) throw err; console.log('Connected to MySQL database'); });

const authenticateToken = (req, res, next) => { const token = req.headers['authorization']; if (!token) return res.sendStatus(401);

  jwt.verify(token, SECRET_KEY, (err, user) => {
    if (err) return res.sendStatus(403);
    req.user = user;
    next();
  });

};

app.post('/login', (req, res) => { const { username, password } = req.body; if (username === 'admin' && password === 'password') { const token = jwt.sign({ username }, SECRET_KEY, { expiresIn: '1h' }); res.json({ token }); } else { res.status(401).json({ error: 'Invalid credentials' }); } });

app.post('/surveys', authenticateToken, (req, res) => { const { title } = req.body; db.query('INSERT INTO surveys (title) VALUES (?)', [title], (err, result) => { if (err) throw err; res.status(201).json({ id: result.insertId, title, editable: true }); }); });

app.get('/surveys', authenticateToken, (req, res) => { db.query('SELECT * FROM surveys', (err, results) => { if (err) throw err; res.json(results); }); });

app.put('/surveys/:id', authenticateToken, (req, res) => { const { title } = req.body; const surveyId = req.params.id; db.query('SELECT editable FROM surveys WHERE id = ?', [surveyId], (err, results) => { if (err) throw err; if (!results[0].editable) { return res.status(403).json({ error: 'Survey cannot be edited' }); } db.query('UPDATE surveys SET title = ?, editable = FALSE WHERE id = ?', [title, surveyId], (err) => { if (err) throw err; res.json({ id: surveyId, title, editable: false }); }); }); });

app.delete('/surveys/:id', authenticateToken, (req, res) => { const surveyId = req.params.id; db.query('DELETE FROM surveys WHERE id = ?', [surveyId], (err, result) => { if (err) throw err; res.status(204).send(); }); });

app.get('/surveys/:id/statistics', authenticateToken, (req, res) => { const surveyId = req.params.id; db.query('SELECT COUNT(*) AS response_count FROM responses WHERE survey_id = ?', [surveyId], (err, results) => { if (err) throw err; res.json({ surveyId, response_count: results[0].response_count }); }); });

const PORT = 3000; app.listen(PORT, () => { console.log(`Server is running on http://localhost:${PORT}`); }); ```

Замените `your_username`, `your_password`, и `survey_db` на ваши данные.