/**
 * lodash 3.1.0 (Custom Build) <https://lodash.com/>
 * Build: `lodash modern modularize exports="npm" -o ./`
 * Copyright 2012-2015 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2015 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <https://lodash.com/license>
 */
var baseAssign = require('lodash._baseassign'),
    createAssigner = require('lodash._createassigner'),
    isNative = require('lodash.isnative'),
    keys = require('lodash.keys');

/** Used for native method references. */
var arrayProto = Array.prototype;

/** Native method references. */
var getOwnPropertySymbols = isNative(getOwnPropertySymbols = Object.getOwnPropertySymbols) && getOwnPropertySymbols,
    push = arrayProto.push;

/**
 * A specialized version of `_.assign` for customizing assigned values without
 * support for argument juggling, multiple sources, and `this` binding `customizer`
 * functions.
 *
 * @private
 * @param {Object} object The destination object.
 * @param {Object} source The source object.
 * @param {Function} customizer The function to customize assigned values.
 * @returns {Object} Returns `object`.
 */
function assignWith(object, source, customizer) {
  var props = keys(source);
  push.apply(props, getSymbols(source));

  var index = -1,
      length = props.length;

  while (++index < length) {
    var key = props[index],
        value = object[key],
        result = customizer(value, source[key], key, object, source);

    if ((result === result ? (result !== value) : (value === value)) ||
        (value === undefined && !(key in object))) {
      object[key] = result;
    }
  }
  return object;
}

/**
 * Creates an array of the own symbols of `object`.
 *
 * @private
 * @param {Object} object The object to query.
 * @returns {Array} Returns the array of symbols.
 */
var getSymbols = !getOwnPropertySymbols ? constant([]) : function(object) {
  return getOwnPropertySymbols(toObject(object));
};

/**
 * Converts `value` to an object if it is not one.
 *
 * @private
 * @param {*} value The value to process.
 * @returns {Object} Returns the object.
 */
function toObject(value) {
  return isObject(value) ? value : Object(value);
}

/**
 * Checks if `value` is the [language type](https://es5.github.io/#x8) of `Object`.
 * (e.g. arrays, functions, objects, regexes, `new Number(0)`, and `new String('')`)
 *
 * @static
 * @memberOf _
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is an object, else `false`.
 * @example
 *
 * _.isObject({});
 * // => true
 *
 * _.isObject([1, 2, 3]);
 * // => true
 *
 * _.isObject(1);
 * // => false
 */
function isObject(value) {
  // Avoid a V8 JIT bug in Chrome 19-20.
  // See https://code.google.com/p/v8/issues/detail?id=2291 for more details.
  var type = typeof value;
  return type == 'function' || (!!value && type == 'object');
}

/**
 * Assigns own enumerable properties of source object(s) to the destination
 * object. Subsequent sources overwrite property assignments of previous sources.
 * If `customizer` is provided it is invoked to produce the assigned values.
 * The `customizer` is bound to `thisArg` and invoked with five arguments:
 * (objectValue, sourceValue, key, object, source).
 *
 * **Note:** This method mutates `object` and is based on
 * [`Object.assign`](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.assign).
 *
 * @static
 * @memberOf _
 * @alias extend
 * @category Object
 * @param {Object} object The destination object.
 * @param {...Object} [sources] The source objects.
 * @param {Function} [customizer] The function to customize assigned values.
 * @param {*} [thisArg] The `this` binding of `customizer`.
 * @returns {Object} Returns `object`.
 * @example
 *
 * _.assign({ 'user': 'barney' }, { 'age': 40 }, { 'user': 'fred' });
 * // => { 'user': 'fred', 'age': 40 }
 *
 * // using a customizer callback
 * var defaults = _.partialRight(_.assign, function(value, other) {
 *   return _.isUndefined(value) ? other : value;
 * });
 *
 * defaults({ 'user': 'barney' }, { 'age': 36 }, { 'user': 'fred' });
 * // => { 'user': 'barney', 'age': 36 }
 */
var assign = createAssigner(function(object, source, customizer) {
  return customizer
    ? assignWith(object, source, customizer)
    : baseAssign(object, source);
});

/**
 * Creates a function that returns `value`.
 *
 * @static
 * @memberOf _
 * @category Utility
 * @param {*} value The value to return from the new function.
 * @returns {Function} Returns the new function.
 * @example
 *
 * var object = { 'user': 'fred' };
 * var getter = _.constant(object);
 *
 * getter() === object;
 * // => true
 */
function constant(value) {
  return function() {
    return value;
  };
}

module.exports = assign;