/**
 * Copyright 2013 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 ReactContext
 */

"use strict";

var merge = require('merge');

/**
 * Keeps track of the current context.
 *
 * The context is automatically passed down the component ownership hierarchy
 * and is accessible via `this.context` on ReactCompositeComponents.
 */
var ReactContext = {

  /**
   * @internal
   * @type {object}
   */
  current: {},

  /**
   * Temporarily extends the current context while executing scopedCallback.
   *
   * A typical use case might look like
   *
   *  render: function() {
   *    var children = ReactContext.withContext({foo: 'foo'} () => (
   *
   *    ));
   *    return <div>{children}</div>;
   *  }
   *
   * @param {object} newContext New context to merge into the existing context
   * @param {function} scopedCallback Callback to run with the new context
   * @return {ReactComponent|array<ReactComponent>}
   */
  withContext: function(newContext, scopedCallback) {
    var result;
    var previousContext = ReactContext.current;
    ReactContext.current = merge(previousContext, newContext);
    try {
      result = scopedCallback();
    } catch (error) {
      // IE8 requires `catch` in order to use `finally`.
      throw error;
    } finally {
      ReactContext.current = previousContext;
    }
    return result;
  }

};

module.exports = ReactContext;
