/**
 * lodash 4.3.1 (Custom Build) <https://lodash.com/>
 * Build: `lodash modularize exports="npm" -o ./`
 * Copyright 2012-2016 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2016 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <https://lodash.com/license>
 */
var baseFor = require('lodash._basefor'),
    baseIteratee = require('lodash._baseiteratee'),
    keys = require('lodash.keys');

/** Used for built-in method references. */
var objectProto = Object.prototype;

/** Used to check objects for own properties. */
var hasOwnProperty = objectProto.hasOwnProperty;

/**
 * The base implementation of `_.forOwn` without support for iteratee shorthands.
 *
 * @private
 * @param {Object} object The object to iterate over.
 * @param {Function} iteratee The function invoked per iteration.
 * @returns {Object} Returns `object`.
 */
function baseForOwn(object, iteratee) {
  return object && baseFor(object, iteratee, keys);
}

/**
 * The base implementation of `_.invert` and `_.invertBy` which inverts
 * `object` with values transformed by `iteratee` and set by `setter`.
 *
 * @private
 * @param {Object} object The object to iterate over.
 * @param {Function} setter The function to set `accumulator` values.
 * @param {Function} iteratee The iteratee to transform values.
 * @param {Object} accumulator The initial inverted object.
 * @returns {Function} Returns `accumulator`.
 */
function baseInverter(object, setter, iteratee, accumulator) {
  baseForOwn(object, function(value, key, object) {
    setter(accumulator, iteratee(value), key, object);
  });
  return accumulator;
}

/**
 * Creates a function like `_.invertBy`.
 *
 * @private
 * @param {Function} setter The function to set accumulator values.
 * @param {Function} toIteratee The function to resolve iteratees.
 * @returns {Function} Returns the new inverter function.
 */
function createInverter(setter, toIteratee) {
  return function(object, iteratee) {
    return baseInverter(object, setter, toIteratee(iteratee), {});
  };
}

/**
 * This method is like `_.invert` except that the inverted object is generated
 * from the results of running each element of `object` through `iteratee`.
 * The corresponding inverted value of each inverted key is an array of keys
 * responsible for generating the inverted value. The iteratee is invoked
 * with one argument: (value).
 *
 * @static
 * @memberOf _
 * @category Object
 * @param {Object} object The object to invert.
 * @param {Function|Object|string} [iteratee=_.identity] The iteratee invoked per element.
 * @returns {Object} Returns the new inverted object.
 * @example
 *
 * var object = { 'a': 1, 'b': 2, 'c': 1 };
 *
 * _.invertBy(object);
 * // => { '1': ['a', 'c'], '2': ['b'] }
 *
 * _.invertBy(object, function(value) {
 *   return 'group' + value;
 * });
 * // => { 'group1': ['a', 'c'], 'group2': ['b'] }
 */
var invertBy = createInverter(function(result, value, key) {
  if (hasOwnProperty.call(result, value)) {
    result[value].push(key);
  } else {
    result[value] = [key];
  }
}, baseIteratee);

module.exports = invertBy;