/**
 * Copyright 2013-2014 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 flattenChildren
 */

"use strict";

var traverseAllChildren = require('traverseAllChildren');
var warning = require('warning');

/**
 * @param {function} traverseContext Context passed through traversal.
 * @param {?ReactComponent} child React child component.
 * @param {!string} name String name of key path to child.
 */
function flattenSingleChildIntoContext(traverseContext, child, name) {
  // We found a component instance.
  var result = traverseContext;
  var keyUnique = !result.hasOwnProperty(name);
  warning(
    keyUnique,
    'flattenChildren(...): Encountered two children with the same key, ' +
    '`%s`. Child keys must be unique; when two children share a key, only ' +
    'the first child will be used.',
    name
  );
  if (keyUnique && child != null) {
    result[name] = child;
  }
}

/**
 * Flattens children that are typically specified as `props.children`. Any null
 * children will not be included in the resulting object.
 * @return {!object} flattened children keyed by name.
 */
function flattenChildren(children) {
  if (children == null) {
    return children;
  }
  var result = {};
  traverseAllChildren(children, flattenSingleChildIntoContext, result);
  return result;
}

module.exports = flattenChildren;
