config.js

require('dotenv').config();
const env = process.env.NODE_ENV || dev;
// 'dev' or 'test' or 'prod'

const dev = {
    name: 'dev',
    app: {
        port: process.env.PORT || 9000
    },
    db: {
        name: 'todo-dev',
        host: process.env.DB_HOST,
        port: process.env.DB_PORT,
        username: process.env.DB_USERNAME,
        password: process.env.DB_PASSWORD
    }
};

const test = {
    name: 'test',
    app: {
        port: process.env.PORT || 9000
    },
    db: {
        name: 'todo-test',
        host: process.env.DB_HOST,
        port: process.env.DB_PORT,
        username: process.env.DB_USERNAME,
        password: process.env.DB_PASSWORD
    }
};

const prod = {
    name: 'prod',
    app: {
        port: process.env.PORT || 9000
    },
    db: {
        name: 'todo',
        host: process.env.DB_HOST,
        port: process.env.DB_PORT,
        username: process.env.DB_USERNAME,
        password: process.env.DB_PASSWORD
    }
};

const config = {
    dev,
    test,
    prod
};

function _checkIfEnvIsValid(env) {
    if (!env || !env.db || !env.db.host || !env.db.name) {
        return false;
    }
    return true;
}

function getConnectionString(env) {

    if (!_checkIfEnvIsValid(env)) {
        throw "Passed invalid environment";
    }

    // for hosts without a port
    // atlas clusters will not provide a port
    // only localhost will have a port
    // mongodb+srv://<username>:<password>@host/db-name
    if (!env.db.port) {
        if (env.db.username === '' || env.db.password === '') {
            return `mongodb+srv://${env.db.host}/${env.db.name}`;
        }
        return `mongodb+srv://${env.db.username}:${env.db.password}@${env.db.host}/${env.db.name}`;
    } else {
        if (env.db.username === '' || env.db.password === '') {
            return `mongodb+srv://${env.db.host}:${env.db.port}/${env.db.name}`;
        }
        return `mongodb+srv://${env.db.username}:${env.db.password}@${env.db.host}:${env.db.port}/${env.db.name}`;
    }
}

module.exports = config[env] || config['dev'];
module.exports.dbConn = getConnectionString;