const express = require('express');
const { exec } = require('child_process');
const xml2js = require('xml2js');
const cors = require('cors');
const os = require('os');
const { promisify } = require('util');

const execAsync = promisify(exec);

const app = express();
const port = 3001;

// Use CORS to allow requests from the frontend
app.use(cors());
app.use(express.json());

// Basic validation for CIDR notation
const isValidCIDR = (cidr) => {
    const cidrRegex = /^([0-9]{1,3}\.){3}[0-9]{1,3}(\/([0-9]|[1-2][0-9]|3[0-2]))$/;
    return cidrRegex.test(cidr);
};

app.post('/api/scan', async (req, res) => {
    const { network } = req.body;

    if (!network || !isValidCIDR(network)) {
        return res.status(400).json({ error: 'Invalid or missing network address in CIDR format (e.g., 192.168.1.0/24).' });
    }

    // Sanitize input to prevent command injection
    // The regex validation is the primary defense here.
    const sanitizedNetwork = network;

    console.log(`[SCAN STARTED] for network: ${sanitizedNetwork}`);

    // Command to find hosts with a wide range of common web ports open and output as XML.
    // This is more efficient than scanning all 65535 ports.
    const command = `nmap -p 80,443,3000,5000,7878,8080,8443,9000,9090,9091,9443,10000,32400,8000-8999 --open ${sanitizedNetwork} -oX -`;

    try {
        const { stdout, stderr } = await execAsync(command, { timeout: 300000 }); // 5 minute timeout

        if (stderr) {
            console.error(`[NMAP STDERR] ${stderr}`);
        }

        const parser = new xml2js.Parser();
        const result = await parser.parseStringPromise(stdout);
        const services = [];

        if (result.nmaprun && result.nmaprun.host) {
            result.nmaprun.host.forEach(host => {
                const address = host.address[0].$.addr;
                if (host.ports && host.ports[0].port) {
                    host.ports[0].port.forEach(portInfo => {
                        const port = portInfo.$.portid;
                        
                        let url;
                        if (port === '443') {
                            url = `https://${address}`;
                        } else if (port === '80') {
                            url = `http://${address}`;
                        } else {
                            url = `http://${address}:${port}`;
                        }
                        
                        const serviceName = portInfo.service && portInfo.service[0].$.name 
                            ? portInfo.service[0].$.name.replace(/-http$/, '') // Clean up names like 'http-proxy'
                            : `Web Service @ ${address}`;

                        services.push({
                            name: `${serviceName.charAt(0).toUpperCase() + serviceName.slice(1)} (${port})`,
                            url: url,
                            description: `Discovered service on port ${port}.`
                        });
                    });
                }
            });
        }
        
        console.log(`[SCAN COMPLETE] Found ${services.length} services on ${sanitizedNetwork}.`);
        res.json(services);

    } catch (error) {
        console.error(`[SCAN FAILED] Error executing nmap:`, error);
        res.status(500).json({ error: 'Failed to execute nmap scan. Is nmap installed and in your system PATH?' });
    }
});

app.listen(port, () => {
    console.log(`Backend server running on http://localhost:${port}`);
});