i18next HTTP Middleware

import express from 'express';
import i18next from 'i18next';
import { LanguageDetector, handle } from 'i18next-http-middleware';

const app = express();
const PORT = process.env.PORT || 3000;

// Initialize i18next with the language detector and some translations
i18next.use(LanguageDetector).init({
  preload: ['en', 'de', 'fr'],
  fallbackLng: 'en',
  debug: true,
  resources: {
    en: {
      translation: {
        welcome: 'Hello world!',
        greeting: 'Welcome to our internationalized app!',
        howAreYou: 'How are you?'
      }
    },
    de: {
      translation: {
        welcome: 'Hallo Welt!',
        greeting: 'Willkommen in unserer internationalisierten App!',
        howAreYou: 'Wie geht es dir?'
      }
    },
    fr: {
      translation: {
        welcome: 'Bonjour le monde!',
        greeting: 'Bienvenue dans notre application internationalisée!',
        howAreYou: 'Comment allez-vous?'
      }
    }
  }
});

// Apply the i18next-http-middleware
app.use(handle(i18next, {
  ignoreRoutes: ['/health'], // Example: ignore specific routes from i18n processing
  removeLngFromUrl: false // Set to true if language is part of the URL path (e.g., /en/home)
}));

// Example route demonstrating i18n usage
app.get('/', (req, res) => {
  // Access i18n properties from the request object
  const language = req.language || 'en';
  const translatedGreeting = req.t('greeting');
  const translatedWelcome = req.t('welcome');

  res.send(`
    <h1>${translatedWelcome}</h1>
    <p>${translatedGreeting}</p>
    <p>Current language: <strong>${language}</strong></p>
    <p>Detected languages: ${req.languages?.join(', ') || 'N/A'}</p>
    <p>Try going to <a href="/de">/de</a> or <a href="/fr">/fr</a></p>
  `);
});

// Example route for a specific language path segment (if LanguageDetector is configured for path)
app.get('/:lng', (req, res, next) => {
  // The middleware would have already set req.language based on the path if configured
  // For this example, we just render the root path again with the detected language
  if (['en', 'de', 'fr'].includes(req.params.lng)) {
      return res.redirect('/');
  }
  next(); // Pass to next handler if not a language code
});

// Health check route, ignored by i18n middleware
app.get('/health', (req, res) => {
  res.send('OK');
});

app.listen(PORT, () => {
  console.log(`Server listening on http://localhost:${PORT}`);
  console.log('Test with:');
  console.log(`- http://localhost:${PORT}/en`);
  console.log(`- http://localhost:${PORT}/de`);
  console.log(`- http://localhost:${PORT}/fr`);
  console.log(`- http://localhost:${PORT}?lng=fr`);
  console.log(`- curl -H "Accept-Language: de" http://localhost:${PORT}`);
});