var baseMerge = require('../internal/baseMerge'),
    createAssigner = require('../internal/createAssigner');

/**
 * 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;
