database.js

//environment variables
require('dotenv').config();

//libraries
let mysql = require('mysql');

//utilities
let { log } = require('./logging.js');

let connection;

let connectionWrapper = { //use a wrapper that will always point to the correct database object
	query: (sql, args) => new Promise( (resolve, reject) => {
		connection.query(sql, args, (err, rows) => {
			if (err) return reject(err);
			return resolve(rows);
		});
	}),
	close: () => connection.close(),
	unwrap: () => connection
};

const handleDisconnect = () => {
	//use the config
	connection = mysql.createConnection({
		host: process.env.DB_HOST,
		user: process.env.DB_USER,
		password: process.env.DB_PASS,
		database: process.env.DB_NAME,
		port: process.env.DB_PORT
	});

	//connect
	connection.connect((err) => {
		if (err) {
			log('Error connecting to mysql: ', err);
			setTimeout(handleDisconnect, 2000);
		} else {
			log('Connected to mysql');
		}
	});

	//prepare for failure
	connection.on('error', (err) => {
		log('mysql error: ', err);

		if (err.code === 'PROTOCOL_CONNECTION_LOST') {
			handleDisconnect();
		} else {
			throw (err);
		}
	});

	//finally
	return connectionWrapper;
};

module.exports = handleDisconnect;

mysql_mock.js

const mysqlMock = {
	createConnection(config) {
		return {
			//the mock connection
			connected: false,
			lastQuery: '',
			nextResult: null,

			connect(cb) {
				if (this.connected) {
					throw 'mysqlMock already connected';
				}

				this.connected = true;
				if (cb) {
					cb();
				}
			},

			on(msg, cb) {
				//DO NOTHING
			},

			query(query, params, cb) {
				if (!this.connected) {
					throw 'mysqlMock not connected';
				}

				//So much for default arguments in node
				if (!Array.isArray(params)) {
					cb = params;
					params = null;
				}

				//do the mysql substitution
				let counter = 0;
				this.lastQuery = query.replace(/\?/g, () => `${params[counter++]}`);

				//no promises afterall
				if (cb) {
					cb(undefined, this.nextResult);
				}
			},

			close() {
				if (!this.connected) {
					throw 'mysqlMock not connected';
				}
				this.connected = false;
			}
		};
	}
};

module.exports = mysqlMock;