completed backend for paytm

backend/config.js

@@ -0,0 +1,3 @@
+module.exports = {
+    JWT_SECRETS: "paytm@prince"    
+}

backend/db.js

@@ -0,0 +1,49 @@
+const mongoose = require("mongoose");
+
+mongoose.connect("mongodb+srv://prince981620:Hello%[email protected]/paytm");
+
+const userSchema = new mongoose.Schema({
+    username: {
+        type: String,
+        required: true,
+        unique: true,
+        trim: true, // trim spaces from begininig and ends
+        lowercase: true,
+        minLength: 3,
+        maxLength: 30
+    },
+    password: {
+        type: String,
+        required: true,
+        minLength: 6
+    },
+    firstName: {
+        type: String,
+        required: true,
+        trim: true,
+        maxLength: 50
+    },
+    lastName: {
+        type: String,
+        required: true,
+        maxLength: 50
+    }
+})
+const accountSchema = new mongoose.Schema({
+    userId: {
+        type: mongoose.Schema.Types.ObjectId,
+        ref: 'User',
+        required: true
+    },
+    balance: {
+        type: Number,
+        required: true
+    }
+})
+const Account = mongoose.model("account",accountSchema);
+const User = mongoose.model("User",userSchema);
+
+module.exports = {
+    User,
+    Account
+}

backend/index.js

@@ -1,3 +1,14 @@
 const express = require("express");
+const mainRouter = require("./routes/index");
+const cors = require("cors");
 
+const app = express();
 
+app.use(cors());
+app.use(express.json());
+// all the req for /api/v1 goes to mainRouter i.e /routes/index.js
+app.use("/api/v1",mainRouter);
+
+app.listen(3000,()=>{
+    console.log("listening on port 3000");
+})

backend/middileware.js

@@ -0,0 +1,26 @@
+const jwt = require("jsonwebtoken");
+const { JWT_SECRETS } = require("./config");
+
+
+const authMiddleware = (req,res,next)=>{
+    const authHeader = req.headers.authorization;
+    if(!authHeader || !authHeader.startsWith('Bearer ')){
+        return res.status(411).json({});
+    }
+    const token = authHeader.split(" ")[1];
+
+    try{
+        const decoded = jwt.verify(token,JWT_SECRETS);
+        if(decoded.userId){
+            req.userId = decoded.userId;
+            next();
+        }else{
+            return res.status(403).json({});
+        }
+    }catch(err){
+        return res.status(403),json({});
+    }
+}
+module.exports = {
+    authMiddleware
+}

backend/package.json

@@ -10,7 +10,9 @@
   "author": "",
   "license": "ISC",
   "dependencies": {
+    "cors": "^2.8.5",
     "express": "^4.18.2",
+    "jsonwebtoken": "^9.0.2",
     "mongoose": "^8.1.0",
     "zod": "^3.22.4"
   }

backend/routes/account.js

@@ -0,0 +1,56 @@
+const express = require("express");
+const { authMiddleware } = require("../middileware");
+const { Account } = require("../db");
+const { default: mongoose } = require("mongoose");
+
+const router = express.Router();
+
+router.get("/balance",authMiddleware, async (req,res)=>{
+    const account = await Account.findOne({
+        userId: req.userId
+    })
+    if(account){
+        res.status(200).json({
+            balance: account.balance
+        })
+    }
+})
+
+router.post("/transfer",authMiddleware,async (req,res)=>{
+    const session = await mongoose.startSession();
+
+    session.startTransaction();
+    const { amount, to } = req.body;
+    // fetch the account details initiating trtansaction
+    const account = await Account.findOne({userId: req.userId}).session(session);
+
+    if(!account || account.balance < amount){
+        await session.abortTransaction();
+        return res.status(400).json({
+            msg: "Insufficient balance"
+        })
+    }
+    // fetch the account details of the user receivnig money
+
+    const toAccount = await Account.findOne({userId: to}).session(session);
+
+    if(!toAccount){
+        await session.abortTransaction();
+        return res.status(400).json({
+            message: "Invalid Account"
+        })
+    }
+
+    // perform the transfer
+    await Account.updateOne({userId: req.userId},{$inc: {balance: -amount}}).session(session);
+    await Account.updateOne({userId: to},{$inc: {balance: amount}}).session(session);
+
+    // now commit the transaction
+     await session.commitTransaction();
+     res.json({
+        msg: "transfer Successfull"
+     })
+
+})
+
+module.exports = router;

backend/routes/index.js

@@ -0,0 +1,12 @@
+const express = require("express");
+const userRouter = require("./user");
+const accountRouter = require("./account"); 
+const router = express.Router();
+// all the req for /api/v1 comes to this router i.e /routes/index.js
+
+// and from here all the req goes to /api/v1/user goes to
+router.use("/user",userRouter);
+// and from here all the req goes to /api/v1/account goes to
+router.use("/account",accountRouter);
+
+module.exports = router;