server.js

const express = require('C:/Users/User/AppData/Roaming/npm/node_modules/express');
const path = require('C:/Users/User/AppData/Roaming/npm/node_modules/path');
const {PythonShell} = require('C:/Users/User/AppData/Roaming/npm/node_modules/python-shell');
const app = express();
const router = express.Router();
const port = process.env.PORT || 3000;//port to which the server start listening
const createCsvWriter = require('C:/Users/User/AppData/Roaming/npm/node_modules/csv-writer').createObjectCsvWriter;

router.get('/', function (req, res) {
    res.sendFile(path.join(__dirname + '/index.html'));
});

//the express server hosts the html file
app.use('/', router);
app.use(express.json());//indispensabile sennò il body della request è undefinied

const mode = 'all';

const N = 20

if (mode == 'system') {

    const csvWriter = createCsvWriter({
        path: 'Data.csv',
        header: [
            { id: 'E', title: 'Energy' },
            { id: 'T', title: 'Temp' },
            { id: 'P', title: 'Press' },
            { id: 'V', title: 'Volume' },
            { id: 'N', title: 'Num' },
        ],
        append: true // to append to the file, without clearing
    });

    csvWriter.writeRecords([{ E: 'Energy', V: 'Volume', N: 'Num', T: 'Temp', P: 'Press' }])       // returns a promise
        .then(() => {
            console.log('Data.csv created');
        });

    PythonShell.run('system.py', {}, (err, res) => {
        if (err) console.log(err);
        if(res) console.log(res);
    }) //to run the python script

    let data_counter = 0;
    app.post('/system', (req, res) => {
        const data = req.body;

        res.json({
            status: 'success',
        })

        csvWriter.writeRecords([data])       // returns a promise
            .then(() => {
                console.log(data);
            });
        data_counter += 1;
    })
}

else if (mode == 'all') {

    const csvWriter = createCsvWriter({
        path: 'distribution.csv',
        header: [
            { id: 'vx', title: 'vx' },
            { id: 'vy', title: 'vy' },
        ],
        append : false
    });

    const experimental_data = [];

    PythonShell.run('distribution.py', {}, (err, res) => {
        if (err) console.log(err);
        if (res) console.log(res);
    }) //to run the python script

    app.post('/all', (req, res) => {
        const data = req.body.data;

        for (let item of data) {
            experimental_data.push(item);
        }

        csvWriter.writeRecords(experimental_data)       // returns a promise
            .then(() => {
                console.log('...Done');
            });

        res.json({
            status: 'success',
        })
    })

}

app.listen(port, () => console.log('listening to port ' + port));
//TO REMOVE ELEMENTS FROM THE DATABASE
// db.remove({ name: 'leo' }, { multi: true }, (err, numRemoved) => {
//     console.log(numRemoved);
// });