import eachOfLimit from './internal/eachOfLimit.js'
import awaitify from './internal/awaitify.js'
import once from './internal/once.js'
import wrapAsync from './internal/wrapAsync.js'

/**
 * The same as [`mapValues`]{@link module:Collections.mapValues} but runs a maximum of `limit` async operations at a
 * time.
 *
 * @name mapValuesLimit
 * @static
 * @memberOf module:Collections
 * @method
 * @see [async.mapValues]{@link module:Collections.mapValues}
 * @category Collection
 * @param {Object} obj - A collection to iterate over.
 * @param {number} limit - The maximum number of async operations at a time.
 * @param {AsyncFunction} iteratee - A function to apply to each value and key
 * in `coll`.
 * The iteratee should complete with the transformed value as its result.
 * Invoked with (value, key, callback).
 * @param {Function} [callback] - A callback which is called when all `iteratee`
 * functions have finished, or an error occurs. `result` is a new object consisting
 * of each key from `obj`, with each transformed value on the right-hand side.
 * Invoked with (err, result).
 * @returns {Promise} a promise, if no callback is passed
 */
function mapValuesLimit(obj, limit, iteratee, callback) {
    callback = once(callback);
    var newObj = {};
    var _iteratee = wrapAsync(iteratee)
    return eachOfLimit(limit)(obj, (val, key, next) => {
        _iteratee(val, key, (err, result) => {
            if (err) return next(err);
            newObj[key] = result;
            next(err);
        });
    }, err => callback(err, newObj));
}

export default awaitify(mapValuesLimit, 4)