import mysql from 'mysql'
import util from 'util'

const MySQL = 'MySQL'

const sqlQueryExecutor = {
	/**
	 * Asynchronous function that handles queries for MySQL datasources and returns data from the database.
	 *
	 * @param {object} query This query is created by the user upon creation of the original dataset.
	 * @param {string} includedFields The projection fields used by the current visualization. Only these fields are pulled from the database. Maps to 'SELECT' in MySQL
	 * @param {int} limit Limits number of responses.
	 * @param {string} match Matches values. Maps to 'WHERE' in MySQL
	 */
	async executeQuery(query, {includedFields, limit, match}) {
		const primaryKey = query.key
		const connection = mysql.createConnection({
			host: `${query.dataSource.host}`,
			user: `${query.dataSource.user}`,
			password: `${query.dataSource.password}`,
			database: `${query.dataSource.db}`
		})
		//Map projection fields into a MySQL SELECT function
		if (includedFields !== undefined) {
			if (includedFields.length > 1 && query.query !== '') {
				includedFields.concat('_id')
				_.uniq(includedFields)
				const fieldIndex = includedFields.indexOf('_id')
				if (fieldIndex !== -1)
					includedFields[fieldIndex] = primaryKey
				const projection = 'SELECT ' + includedFields + ' FROM (' + query.query + ') as RESULT'
				query.query = projection
			}
		}
		//map match to MySQL WHERE function
		if (match !== undefined) {
			for (const matchKey in match) {
				query.query = query.query + ' WHERE ' + primaryKey + ' IN (' + match[matchKey] + ')'
			}

		}
		//Map limit to MySQL LIMIT function
		if (limit !== undefined) {
			query.query = query.query + ' LIMIT ' + limit
		}
		//connection.query needs to be promisified in order to work with async/await
		connection.query = util.promisify(connection.query)
		if (query.query !== '' && query.key !== 'Primary Key') {
			try {
				const queryResult = await connection.query(query.query)
				for (let i=0; i<queryResult.length; i++) {

					//Match user-defined primary key to _id
					queryResult[i]._id = queryResult[i][primaryKey]
				}
				return queryResult
			} catch (err) {
				throw `An error occurred while connecting to MySQL database: "${err.name}: ${err.message}"\n`
			}
		} else {
			return []
		}
	},
	queryType: MySQL
}

export default sqlQueryExecutor