app.js

const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const md5 = require('md5');
const dotenv = require('dotenv');

dotenv.config();
app.set('view engine', 'ejs');
app.use(express.static(__dirname+'/public'))
app.use(
    express.urlencoded({
      extended: true
    })
);

app.use(express.json());

app.get('/',(req,res)=>{
    res.render('index')     
})

var isVerified;    // return value for md5 verification check

app.post('/notify',async(req,res)=>{

      //* Post parameters
        isVerified = false;
        var merchant_id = req.body.merchant_id; // PayHere Merchant ID of the merchant
        var order_id = req.body.order_id;     // Order ID sent by Merchant to Checkout page
        var payment_id = req.body.payment_id;  // Unique Payment ID generated by PayHere for the processed payment
        var payhere_amount = req.body.payhere_amount;  // Total Amount of the payment
        var payhere_currency = req.body.payhere_currency; // Currency code of the payment (LKR/USD/GBP/EUR/AUD)
        var method = req.body.method; // Payment method selected by the customer. (VISA, MASTER, AMEX, EZCASH, MCASH, GENIE, VISHWA, PAYAPP, HNB, FRIMI)
        var status_code = req.body.status_code;
        var status_message = req.body.status_message; // Message received from payment gateway which the customer tried to pay If the customer made the payment by VISA or MASTER credit/debit card, following parameters will also be available.
        
        // ** for card payments
        if(req.body.card_holder_name){
            var card_holder_name = req.body.card_holder_name;// Card Holder Name
            var card_no = req.body.card_no; // Masked card number (Ex: ************4564)
            var card_expiry = req.body.card_expiry; // Card expiry in format MMYY (Ex: 0122) Payment Status Codes
        } 
        //other custom parameters if available....

   // handle transaction status here 
   switch(status_code){
        case "0" :
           console.log('Transaction is Pending');
           break;
        case "2" :
           console.log("Transaction is Successful");

           // *** verification of payment status ***  
           //generate local md5 signature
           var localMd5Sig = (md5(merchant_id+order_id+payhere_amount+payhere_currency+status_code+md5(process.env.PAYHERE_SECRET).toUpperCase())).toUpperCase();
           if(localMd5Sig===req.body.md5sig){
                console.log('Verified')
                isVerified=true;
               // update the database with successfull transation details here
           } else {
                console.log("Unverified")
                isVerified=false;
               // something is wrong
           }
           break;
        case "-1" :
            console.log("Transaction Canceled");
            break;
        case "-2" :
            console.log("Transaction Failed");
            break;
        case "-3":
            console.log("Charged Back");
            break;
        default:
            console.log("Unknown Error");               
   }
   res.end();
})

app.get('/check',(req,res)=>{
    res.send({"Verified":isVerified})
})

app.get('/return',(req,res)=>{    // redirect url after the transaction..(provided in the html form )
    res.send('success');
})

app.get('/cancel',(req,res)=>{
    res.send('cancel');
})
app.listen(3000 || process.env.PORT,()=>{
    console.log("Listening on port 3000");
})