% Express.js REST API

\section{Express.js REST API}

\begin{frame}{Mi az Express.js?}
  \begin{block}{Express}
    Gyors, minimalista web framework Node.js-hez.
  \end{block}
  
  \begin{exampleblock}{Jellemzők}
    \begin{itemize}
      \item Egyszerű API
      \item Middleware-alapú
      \item Routing támogatás
      \item Template engine-ek
      \item Nagy közösség és sok plugin
    \end{itemize}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{Express telepítése}
  \begin{exampleblock}{NPM inicializálás és telepítés}
    \tiny
    \begin{verbatim}
npm init -y
npm install express
    \end{verbatim}
  \end{exampleblock}
  
  \begin{exampleblock}{package.json}
    \tiny
    \begin{verbatim}
{
  "name": "my-api",
  "version": "1.0.0",
  "main": "server.js",
  "scripts": {
    "start": "node server.js",
    "dev": "nodemon server.js"
  },
  "dependencies": {
    "express": "^4.18.2"
  }
}
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{Első Express szerver}
  \begin{exampleblock}{server.js}
    \tiny
    \begin{verbatim}
const express = require('express');
const app = express();
const PORT = 3000;

// Middleware
app.use(express.json());

// Egyszerű route
app.get('/', (req, res) => {
  res.json({ message: 'Hello, Express!' });
});

// Szerver indítása
app.listen(PORT, () => {
  console.log(`Server running on http://localhost:${PORT}`);
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{GET végpont}
  \begin{exampleblock}{Összes elem lekérdezése}
    \tiny
    \begin{verbatim}
let users = [
  {id: 1, name: 'Alice', email: 'alice@example.com'},
  {id: 2, name: 'Bob', email: 'bob@example.com'}
];

app.get('/api/users', (req, res) => {
  res.json(users);
});
    \end{verbatim}
  \end{exampleblock}
  
  \begin{exampleblock}{Egy elem lekérdezése}
    \tiny
    \begin{verbatim}
app.get('/api/users/:id', (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));
  if (!user) {
    return res.status(404).json({ error: 'User not found' });
  }
  res.json(user);
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{POST végpont}
  \begin{exampleblock}{Új elem létrehozása}
    \tiny
    \begin{verbatim}
app.post('/api/users', (req, res) => {
  const { name, email } = req.body;
  
  if (!name || !email) {
    return res.status(400).json({ error: 'Name and email required' });
  }
  
  const newUser = {
    id: users.length + 1,
    name,
    email
  };
  
  users.push(newUser);
  res.status(201).json(newUser);
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{PUT és PATCH végpontok}
  \begin{exampleblock}{PUT - Teljes frissítés}
    \tiny
    \begin{verbatim}
app.put('/api/users/:id', (req, res) => {
  const idx = users.findIndex(u => u.id === parseInt(req.params.id));
  if (idx === -1) return res.status(404).json({ error: 'Not found' });
  
  users[idx] = { id: parseInt(req.params.id), ...req.body };
  res.json(users[idx]);
});
    \end{verbatim}
  \end{exampleblock}
  
  \begin{exampleblock}{PATCH - Részleges frissítés}
    \tiny
    \begin{verbatim}
app.patch('/api/users/:id', (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));
  if (!user) return res.status(404).json({ error: 'Not found' });
  
  Object.assign(user, req.body);
  res.json(user);
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{DELETE végpont}
  \begin{exampleblock}{Elem törlése}
    \tiny
    \begin{verbatim}
app.delete('/api/users/:id', (req, res) => {
  const idx = users.findIndex(u => u.id === parseInt(req.params.id));
  
  if (idx === -1) {
    return res.status(404).json({ error: 'User not found' });
  }
  
  users.splice(idx, 1);
  res.status(204).send();
});
    \end{verbatim}
  \end{exampleblock}
  
  \begin{alertblock}{204 No Content}
    Sikeres törlés esetén nem kell response body.
  \end{alertblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{Middleware-ek}
  \begin{block}{Mi a Middleware?}
    Függvények, amelyek hozzáférnek a request és response objektumokhoz, és a \texttt{next()} függvényhez.
  \end{block}
  
  \begin{exampleblock}{Logger middleware}
    \tiny
    \begin{verbatim}
app.use((req, res, next) => {
  console.log(`${req.method} ${req.url}`);
  next();
});
    \end{verbatim}
  \end{exampleblock}
  
  \begin{exampleblock}{Auth middleware}
    \tiny
    \begin{verbatim}
const authMiddleware = (req, res, next) => {
  const token = req.headers.authorization;
  if (!token) return res.status(401).json({ error: 'Unauthorized' });
  next();
};

app.get('/api/protected', authMiddleware, (req, res) => {
  res.json({ data: 'Protected data' });
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{Error Handling}
  \begin{exampleblock}{Error handling middleware}
    \tiny
    \begin{verbatim}
app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).json({
    error: {
      message: err.message,
      code: 'INTERNAL_ERROR'
    }
  });
});
    \end{verbatim}
  \end{exampleblock}
  
  \begin{exampleblock}{Try-catch async}
    \tiny
    \begin{verbatim}
app.get('/api/users/:id', async (req, res, next) => {
  try {
    const user = await getUserById(req.params.id);
    if (!user) throw new Error('User not found');
    res.json(user);
  } catch (error) {
    next(error);
  }
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{Validáció Joi-val (1/2)}
  \begin{exampleblock}{Joi telepítése}
    \tiny
    \begin{verbatim}
npm install joi
    \end{verbatim}
  \end{exampleblock}
  
  \begin{exampleblock}{Schema definiálás}
    \tiny
    \begin{verbatim}
const Joi = require('joi');

const userSchema = Joi.object({
  name: Joi.string().min(3).max(50).required(),
  email: Joi.string().email().required(),
  age: Joi.number().integer().min(0).max(120)
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{Validáció Joi-val (2/2)}
  \begin{exampleblock}{Validáció használata}
    \tiny
    \begin{verbatim}
app.post('/api/users', (req, res) => {
  const { error, value } = userSchema.validate(req.body);
  
  if (error) {
    return res.status(400).json({
      error: error.details[0].message
    });
  }
  
  // value a validált adat
  const newUser = { id: users.length + 1, ...value };
  users.push(newUser);
  res.status(201).json(newUser);
});
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=15]{Express Router - Moduláris routing (1/2)}
  \begin{exampleblock}{routes/users.js}
    \tiny
    \begin{verbatim}
const express = require('express');
const router = express.Router();

router.get('/', (req, res) => {
  res.json({ message: 'Get all users' });
});

router.get('/:id', (req, res) => {
  res.json({ message: `Get user ${req.params.id}` });
});

router.post('/', (req, res) => {
  res.json({ message: 'Create user' });
});

module.exports = router;
    \end{verbatim}
  \end{exampleblock}
\end{frame}

\begin{frame}[fragile,shrink=10]{Express Router - Moduláris routing (2/2)}
  \begin{exampleblock}{app.js - Router használata}
    \tiny
    \begin{verbatim}
const express = require('express');
const app = express();
const userRoutes = require('./routes/users');

app.use(express.json());
app.use('/api/users', userRoutes);

app.listen(3000);
    \end{verbatim}
  \end{exampleblock}
  
  \begin{alertblock}{Prefix}
    Az \texttt{app.use('/api/users', userRoutes)} prefix-szel látja el az összes route-ot.
  \end{alertblock}
\end{frame}

\begin{frame}{Összefoglalás - Express}
  \begin{itemize}
    \item Express = minimalista web framework
    \item Routing: GET, POST, PUT, PATCH, DELETE
    \item Middleware-ek: kérések feldolgozása
    \item Error handling: hibakezelő middleware
    \item Validáció: Joi vagy más library
    \item Router: moduláris útvonalkezelés
  \end{itemize}
  
  \vspace{0.5cm}
  
\end{frame}
