index.js

const express = require('express');
const Redis = require('ioredis');
const amqp = require('amqplib');


const app = express();
const redis = new Redis();

app.use(express.json());

// Global variables for RabbitMQ
let channel, connection;

async function connectQueue(){
   try { connection = await amqp.connect('amqp://localhost');
    channel = await connection.createChannel();

    // Create a specific box named 'orders' to store our messages
    await channel.assertQueue('orders');
    console.log('✅ Connected to RabbitMQ');}
    catch (err) { 
        console.log('Queue Error:', error);
    }
}

// Start the connection immediately
connectQueue();

// 1. Initialize the Sale (Resets the stock)
app.post('/init',async (req,res)=>{
    await redis.set('iphone_stock',100);
    res.send('flash sale initialized! Stock: 100');
});

// 2. The "Buy" Endpoint (CONTAINS A CRITICAL BUG)

// The "Note" (Lua Script)
// It says: Check stock. If > 0, decrease it. All in one go.
const buyScript = `
    local stock = tonumber(redis.call('get', KEYS[1]))
    if stock > 0 then
        redis.call('decr', KEYS[1])
        return 1
    else
        return 0
    end
`;

app.post('/buy',async (req,res)=>{
    try {
        const result = await redis.eval(buyScript,1,'iphone_stock');
        if(result === 1){
            const orderData = { 
                userId: 'user_' + Math.floor(Math.random() * 1000), // Random user
                item: 'iPhone 15',
                price: 1000,
                quantity: 1,
                timeStamp: new Date()
             };

            // Send the message to the 'orders' queue
            channel.sendToQueue('orders', Buffer.from(JSON.stringify(orderData)));
            
            console.log('🎉 Sent to Queue:', orderData.userId);
            res.json({ message: 'Order Placed! Confirmation sent.' });
        } else {
            console.log('Sold Out!');
            res.status(400).json({ message: 'Sold Out!' });
        }
    } catch (error) {
        console.error(err);
        res.status(500).send('Server Error');
    }
});

app.listen(3000, () => console.log('Server running on http://localhost:3000'));