/**
 * 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>
 */

/**
 * 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.
 */

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

/**
 * The base implementation of `_.at` without support for strings and individual
 * key arguments.
 *
 * @private
 * @param {Array|Object} collection The collection to iterate over.
 * @param {number[]|string[]} [props] The property names or indexes of elements to pick.
 * @returns {Array} Returns the new array of picked elements.
 */
function baseAt(collection, props) {
  var index = -1,
      length = collection.length,
      isArr = isLength(length),
      propsLength = props.length,
      result = Array(propsLength);

  while(++index < propsLength) {
    var key = props[index];
    if (isArr) {
      key = parseFloat(key);
      result[index] = isIndex(key, length) ? collection[key] : undefined;
    } else {
      result[index] = collection[key];
    }
  }
  return result;
}

/**
 * Checks if `value` is a valid array-like index.
 *
 * @private
 * @param {*} value The value to check.
 * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
 * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
 */
function isIndex(value, length) {
  value = +value;
  length = length == null ? MAX_SAFE_INTEGER : length;
  return value > -1 && value % 1 == 0 && value < length;
}

/**
 * Checks if `value` is a valid array-like length.
 *
 * **Note:** This function is based on [`ToLength`](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-tolength).
 *
 * @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;
}

module.exports = baseAt;