import _parallel from './internal/parallel';
import eachOfSeries from './eachOfSeries';

/**
 * Run the functions in the `tasks` collection in series, each one running once
 * the previous function has completed. If any functions in the series pass an
 * error to its callback, no more functions are run, and `callback` is
 * immediately called with the value of the error. Otherwise, `callback`
 * receives an array of results when `tasks` have completed.
 *
 * It is also possible to use an object instead of an array. Each property will
 * be run as a function, and the results will be passed to the final `callback`
 * as an object instead of an array. This can be a more readable way of handling
 *  results from {@link async.series}.
 *
 * **Note** that while many implementations preserve the order of object
 * properties, the [ECMAScript Language Specification](http://www.ecma-international.org/ecma-262/5.1/#sec-8.6)
 * explicitly states that
 *
 * > The mechanics and order of enumerating the properties is not specified.
 *
 * So if you rely on the order in which your series of functions are executed,
 * and want this to work on all platforms, consider using an array.
 *
 * @name series
 * @static
 * @memberOf module:ControlFlow
 * @method
 * @category Control Flow
 * @param {Array|Iterable|AsyncIterable|Object} tasks - A collection containing
 * [async functions]{@link AsyncFunction} to run in series.
 * Each function can complete with any number of optional `result` values.
 * @param {Function} [callback] - An optional callback to run once all the
 * functions have completed. This function gets a results array (or object)
 * containing all the result arguments passed to the `task` callbacks. Invoked
 * with (err, result).
 * @return {Promise} a promise, if no callback is passed
 * @example
 * async.series([
 *     function(callback) {
 *         // do some stuff ...
 *         callback(null, 'one');
 *     },
 *     function(callback) {
 *         // do some more stuff ...
 *         callback(null, 'two');
 *     }
 * ],
 * // optional callback
 * function(err, results) {
 *     // results is now equal to ['one', 'two']
 * });
 *
 * async.series({
 *     one: function(callback) {
 *         setTimeout(function() {
 *             callback(null, 1);
 *         }, 200);
 *     },
 *     two: function(callback){
 *         setTimeout(function() {
 *             callback(null, 2);
 *         }, 100);
 *     }
 * }, function(err, results) {
 *     // results is now equal to: {one: 1, two: 2}
 * });
 */
export default function series(tasks, callback) {
    return _parallel(eachOfSeries, tasks, callback);
}