/**
 * Copyright 2014 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @providesModule toArray
 * @typechecks
 */

var invariant = require('invariant');

/**
 * Convert array-like objects to arrays.
 *
 * This API assumes the caller knows the contents of the data type. For less
 * well defined inputs use createArrayFrom.
 *
 * @param {object|function|filelist} obj
 * @return {array}
 */
function toArray(obj) {
  var length = obj.length;

  // Some browse builtin objects can report typeof 'function' (e.g. NodeList in
  // old versions of Safari).
  invariant(
    !Array.isArray(obj) &&
    (typeof obj === 'object' || typeof obj === 'function'),
    'toArray: Array-like object expected'
  );

  invariant(
    typeof length === 'number',
    'toArray: Object needs a length property'
  );

  invariant(
    length === 0 ||
    (length - 1) in obj,
    'toArray: Object should have keys for indices'
  );

  // Old IE doesn't give collections access to hasOwnProperty. Assume inputs
  // without method will throw during the slice call and skip straight to the
  // fallback.
  if (obj.hasOwnProperty) {
    try {
      return Array.prototype.slice.call(obj);
    } catch (e) {
      // IE < 9 does not support Array#slice on collections objects
    }
  }

  // Fall back to copying key by key. This assumes all keys have a value,
  // so will not preserve sparsely populated inputs.
  var ret = Array(length);
  for (var ii = 0; ii < length; ii++) {
    ret[ii] = obj[ii];
  }
  return ret;
}

module.exports = toArray;
