'use strict';

/**
 * Expose `arrayFlatten`.
 */
module.exports = arrayFlatten;

/**
 * Recursive flatten function with depth.
 *
 * @param  {Array}  array
 * @param  {Array}  result
 * @param  {Number} depth
 * @return {Array}
 */
function flattenWithDepth(array, result, depth) {
  for (var i = 0; i < array.length; i++) {
    var value = array[i];

    if (depth > 0 && Array.isArray(value)) {
      flattenWithDepth(value, result, depth - 1);
    } else {
      result.push(value);
    }
  }

  return result;
}

/**
 * Recursive flatten function. Omitting depth is slightly faster.
 *
 * @param  {Array} array
 * @param  {Array} result
 * @return {Array}
 */
function flattenForever(array, result) {
  for (var i = 0; i < array.length; i++) {
    var value = array[i];

    if (Array.isArray(value)) {
      flattenForever(value, result);
    } else {
      result.push(value);
    }
  }

  return result;
}

/**
 * Flatten an array, with the ability to define a depth.
 *
 * @param  {Array}  array
 * @param  {Number} depth
 * @return {Array}
 */
function arrayFlatten(array, depth) {
  if (depth == null) {
    return flattenForever(array, []);
  }

  return flattenWithDepth(array, [], depth);
}