/**
 * Lo-Dash 2.4.1 (Custom Build) <http://lodash.com/>
 * Build: `lodash modularize modern exports="npm" -o ./npm/`
 * Copyright 2012-2013 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.5.2 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2013 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <http://lodash.com/license>
 */
var baseFlatten = require('lodash._baseflatten'),
    map = require('lodash.map');

/**
 * Flattens a nested array (the nesting can be to any depth). If `isShallow`
 * is truey, the array will only be flattened a single level. If a callback
 * is provided each element of the array is passed through the callback before
 * flattening. The callback is bound to `thisArg` and invoked with three
 * arguments; (value, index, array).
 *
 * If a property name is provided for `callback` the created "_.pluck" style
 * callback will return the property value of the given element.
 *
 * If an object is provided for `callback` the created "_.where" style callback
 * will return `true` for elements that have the properties of the given object,
 * else `false`.
 *
 * @static
 * @memberOf _
 * @category Arrays
 * @param {Array} array The array to flatten.
 * @param {boolean} [isShallow=false] A flag to restrict flattening to a single level.
 * @param {Function|Object|string} [callback=identity] The function called
 *  per iteration. If a property name or object is provided it will be used
 *  to create a "_.pluck" or "_.where" style callback, respectively.
 * @param {*} [thisArg] The `this` binding of `callback`.
 * @returns {Array} Returns a new flattened array.
 * @example
 *
 * _.flatten([1, [2], [3, [[4]]]]);
 * // => [1, 2, 3, 4];
 *
 * _.flatten([1, [2], [3, [[4]]]], true);
 * // => [1, 2, 3, [[4]]];
 *
 * var characters = [
 *   { 'name': 'barney', 'age': 30, 'pets': ['hoppy'] },
 *   { 'name': 'fred',   'age': 40, 'pets': ['baby puss', 'dino'] }
 * ];
 *
 * // using "_.pluck" callback shorthand
 * _.flatten(characters, 'pets');
 * // => ['hoppy', 'baby puss', 'dino']
 */
function flatten(array, isShallow, callback, thisArg) {
  // juggle arguments
  if (typeof isShallow != 'boolean' && isShallow != null) {
    thisArg = callback;
    callback = (typeof isShallow != 'function' && thisArg && thisArg[isShallow] === array) ? null : isShallow;
    isShallow = false;
  }
  if (callback != null) {
    array = map(array, callback, thisArg);
  }
  return baseFlatten(array, isShallow);
}

module.exports = flatten;
