/**
 * lodash 3.0.0 (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 1.7.0 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2015 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <https://lodash.com/license>
 */
var arrayCopy = require('lodash._arraycopy'),
    arrayEach = require('lodash._arrayeach'),
    baseFor = require('lodash._basefor'),
    createAssigner = require('lodash._createassigner'),
    isArguments = require('lodash.isarguments'),
    isArray = require('lodash.isarray'),
    isPlainObject = require('lodash.isplainobject'),
    isTypedArray = require('lodash.istypedarray'),
    keys = require('lodash.keys'),
    toPlainObject = require('lodash.toplainobject');

/**
 * Checks if `value` is object-like.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is object-like, else `false`.
 */
function isObjectLike(value) {
  return (value && typeof value == 'object') || false;
}

/**
 * Used as the maximum length of an array-like value.
 * See the [ES spec](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-number.max_safe_integer)
 * for more details.
 */
var MAX_SAFE_INTEGER = Math.pow(2, 53) - 1;

/**
 * The base implementation of `_.forOwn` without support for callback
 * shorthands and `this` binding.
 *
 * @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 baseFor(object, iteratee, keys);
}

/**
 * The base implementation of `_.merge` 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 merging properties.
 * @param {Array} [stackA=[]] Tracks traversed source objects.
 * @param {Array} [stackB=[]] Associates values with source counterparts.
 * @returns {Object} Returns the destination object.
 */
function baseMerge(object, source, customizer, stackA, stackB) {
  var isSrcArr = isLength(source.length) && (isArray(source) || isTypedArray(source));

  (isSrcArr ? arrayEach : baseForOwn)(source, function(srcValue, key, source) {
    if (isObjectLike(srcValue)) {
      stackA || (stackA = []);
      stackB || (stackB = []);
      return baseMergeDeep(object, source, key, baseMerge, customizer, stackA, stackB);
    }
    var value = object[key],
        result = customizer ? customizer(value, srcValue, key, object, source) : undefined,
        isCommon = typeof result == 'undefined';

    if (isCommon) {
      result = srcValue;
    }
    if ((isSrcArr || typeof result != 'undefined') &&
        (isCommon || (result === result ? result !== value : value === value))) {
      object[key] = result;
    }
  });
  return object;
}

/**
 * A specialized version of `baseMerge` for arrays and objects which performs
 * deep merges and tracks traversed objects enabling objects with circular
 * references to be merged.
 *
 * @private
 * @param {Object} object The destination object.
 * @param {Object} source The source object.
 * @param {string} key The key of the value to merge.
 * @param {Function} mergeFunc The function to merge values.
 * @param {Function} [customizer] The function to customize merging properties.
 * @param {Array} [stackA=[]] Tracks traversed source objects.
 * @param {Array} [stackB=[]] Associates values with source counterparts.
 * @returns {boolean} Returns `true` if the objects are equivalent, else `false`.
 */
function baseMergeDeep(object, source, key, mergeFunc, customizer, stackA, stackB) {
  var length = stackA.length,
      srcValue = source[key];

  while (length--) {
    if (stackA[length] == srcValue) {
      object[key] = stackB[length];
      return;
    }
  }
  var value = object[key],
      result = customizer ? customizer(value, srcValue, key, object, source) : undefined,
      isCommon = typeof result == 'undefined';

  if (isCommon) {
    result = srcValue;
    if (isLength(srcValue.length) && (isArray(srcValue) || isTypedArray(srcValue))) {
      result = isArray(value)
        ? value
        : (value ? arrayCopy(value) : []);
    }
    else if (isPlainObject(srcValue) || isArguments(srcValue)) {
      result = isArguments(value)
        ? toPlainObject(value)
        : (isPlainObject(value) ? value : {});
    }
  }
  // Add the source value to the stack of traversed objects and associate
  // it with its merged value.
  stackA.push(srcValue);
  stackB.push(result);

  if (isCommon) {
    // Recursively merge objects and arrays (susceptible to call stack limits).
    object[key] = mergeFunc(result, srcValue, customizer, stackA, stackB);
  } else if (result === result ? result !== value : value === value) {
    object[key] = result;
  }
}

/**
 * Checks if `value` is a valid array-like length.
 *
 * **Note:** This function is based on ES `ToLength`. See the
 * [ES spec](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-tolength)
 * for more details.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a valid length, else `false`.
 */
function isLength(value) {
  return typeof value == 'number' && value > -1 && value % 1 == 0 && value <= MAX_SAFE_INTEGER;
}

/**
 * Recursively merges own enumerable properties of the source object(s), that
 * don't resolve to `undefined` into the destination object. Subsequent sources
 * overwrite property assignments of previous sources. If `customizer` is
 * provided it is invoked to produce the merged values of the destination and
 * source properties. If `customizer` returns `undefined` merging is handled
 * by the method instead. The `customizer` is bound to `thisArg` and invoked
 * with five arguments; (objectValue, sourceValue, key, object, source).
 *
 * @static
 * @memberOf _
 * @category Object
 * @param {Object} object The destination object.
 * @param {...Object} [sources] The source objects.
 * @param {Function} [customizer] The function to customize merging properties.
 * @param {*} [thisArg] The `this` binding of `customizer`.
 * @returns {Object} Returns `object`.
 * @example
 *
 * var users = {
 *   'data': [{ 'user': 'barney' }, { 'user': 'fred' }]
 * };
 *
 * var ages = {
 *   'data': [{ 'age': 36 }, { 'age': 40 }]
 * };
 *
 * _.merge(users, ages);
 * // => { 'data': [{ 'user': 'barney', 'age': 36 }, { 'user': 'fred', 'age': 40 }] }
 *
 * // using a customizer callback
 * var object = {
 *   'fruits': ['apple'],
 *   'vegetables': ['beet']
 * };
 *
 * var other = {
 *   'fruits': ['banana'],
 *   'vegetables': ['carrot']
 * };
 *
 * _.merge(object, other, function(a, b) {
 *   return _.isArray(a) ? a.concat(b) : undefined;
 * });
 * // => { 'fruits': ['apple', 'banana'], 'vegetables': ['beet', 'carrot'] }
 */
var merge = createAssigner(baseMerge);

module.exports = merge;