Server-Side Aggregation of Multiple External APIs

const express = require('express');
const fetch = require('node-fetch'); // For Node.js, install with `npm install node-fetch@2` for CommonJS or @3 for ES Modules

const app = express();
app.use(express.json());

// External API configurations
const API_CONFIGS = {
  products: {
    url: 'https://api.externalproducts.com/v1/products',
    token: 'PRODUCT_API_KEY' // Replace with actual API key/token
  },
  reviews: {
    url: 'https://api.externalreviews.com/v1/reviews',
    token: 'REVIEW_API_KEY'
  },
  shipping: {
    url: 'https://api.externalshipping.com/v1/shipping-costs',
    token: 'SHIPPING_API_KEY'
  }
};

/**
 * Aggregates data from multiple external APIs for a single product ID.
 * This endpoint fetches product details, reviews, and shipping costs concurrently.
 */
app.get('/api/product-details/:productId', async (req, res) => {
  const productId = req.params.productId;

  try {
    // Make concurrent requests to external APIs
    const [productRes, reviewsRes, shippingRes] = await Promise.all([
      fetch(`${API_CONFIGS.products.url}/${productId}`, {
        headers: { 'Authorization': `Bearer ${API_CONFIGS.products.token}` }
      }),
      fetch(`${API_CONFIGS.reviews.url}?productId=${productId}`, {
        headers: { 'Authorization': `Bearer ${API_CONFIGS.reviews.token}` }
      }),
      fetch(`${API_CONFIGS.shipping.url}?region=US&productId=${productId}`, {
        headers: { 'Authorization': `Bearer ${API_CONFIGS.shipping.token}` }
      })
    ]);

    // Check responses and parse JSON
    if (!productRes.ok) throw new Error(`Product API error: ${productRes.statusText}`);
    if (!reviewsRes.ok) throw new Error(`Reviews API error: ${reviewsRes.statusText}`);
    if (!shippingRes.ok) throw new Error(`Shipping API error: ${shippingRes.statusText}`);

    const productData = await productRes.json();
    const reviewsData = await reviewsRes.json();
    const shippingData = await shippingRes.json();

    // Aggregate the data into a single response object
    const aggregatedData = {
      product: productData,
      reviews: reviewsData.results || [], // Assuming reviews API returns { results: [...] }
      shipping: shippingData.cost || null, // Assuming shipping API returns { cost: X }
      lastUpdated: new Date().toISOString()
    };

    res.json(aggregatedData);

  } catch (error) {
    console.error('Error during API aggregation:', error.message);
    res.status(500).json({ error: 'Failed to aggregate data from external services.', details: error.message });
  }
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Aggregation service running on port ${PORT}`);
});