import {
    AsyncErrorCallback,
    SimpleFunction,
    ParallelCallback,
    NumericDictionary
} from "../interfaces";

import {
    once
} from "../common";

/**
 * This method executes a series of functions at once, and wait for the results
 * thereof.
 */
export function parallel<E>(
    fns: SimpleFunction<E>[],
    final?: ParallelCallback<E>
): void {

    fns = fns.slice();

    let errorNum: number = 0, completed: number = 0;

    let errors: NumericDictionary<E> = {};

    for (let i = 0; i < fns.length; i++) {

        fns[i](once(function(err?: E): void {

            completed++;

            if (err) {

                errors[i] = err;
                errorNum++;
            }

            if (completed === fns.length) {

                final(errorNum ? errors : null);
            }
        }));
    }
}