doc: add express, cors, and stripe along with middleware and routes to index.js

functions/index.js

@@ -1,9 +1,26 @@
 const functions = require("firebase-functions");
+const express = require("express");
+const cors = require("cors");
+const stripe = require("stripe")(process.env.STRIPE_SECRET_KEY);
 
-// // Create and Deploy Your First Cloud Functions
-// // https://firebase.google.com/docs/functions/write-firebase-functions
-//
-// exports.helloWorld = functions.https.onRequest((request, response) => {
-//   functions.logger.info("Hello logs!", {structuredData: true});
-//   response.send("Hello from Firebase!");
-// });
+// App Config
+const app = express();
+
+// Middleware
+app.use(cors({ origin: true }));
+app.use(express.json());
+
+// API Routes
+app.post("/paymens/create", async (req, res) => {
+  const total = request.query.total;
+  const paymentIntent = await stripe.paymentIntents.create({
+    amount: total, // subunits of the currency
+    currency: "usd",
+  });
+  res.status(201).send({
+    clientSecret: paymentIntent.client_secret,
+  });
+});
+
+// Listen command
+exports.api = functions.https.onRequest(app);