let MongoClient = require('mongodb').MongoClient;

module.exports = function (uri) {
	if (typeof uri !== 'string') {
		throw new TypeError('Expected uri to be a string');
	}

	let connection = null;

	return function expressMongoDb(req, res, next) {
		if (!connection) {
			connection = MongoClient.connect(uri, { useUnifiedTopology: true });
		}

		connection
			.then(function (client) {
				req['db'] = client.db('autocat');
				next();
			})
			.catch(function (err) {
				connection = undefined;
				next(err);
			});
	};
};