/**
 * 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 ReactOwner
 */

"use strict";

var emptyObject = require('emptyObject');
var invariant = require('invariant');

/**
 * ReactOwners are capable of storing references to owned components.
 *
 * All components are capable of //being// referenced by owner components, but
 * only ReactOwner components are capable of //referencing// owned components.
 * The named reference is known as a "ref".
 *
 * Refs are available when mounted and updated during reconciliation.
 *
 *   var MyComponent = React.createClass({
 *     render: function() {
 *       return (
 *         <div onClick={this.handleClick}>
 *           <CustomComponent ref="custom" />
 *         </div>
 *       );
 *     },
 *     handleClick: function() {
 *       this.refs.custom.handleClick();
 *     },
 *     componentDidMount: function() {
 *       this.refs.custom.initialize();
 *     }
 *   });
 *
 * Refs should rarely be used. When refs are used, they should only be done to
 * control data that is not handled by React's data flow.
 *
 * @class ReactOwner
 */
var ReactOwner = {

  /**
   * @param {?object} object
   * @return {boolean} True if `object` is a valid owner.
   * @final
   */
  isValidOwner: function(object) {
    return !!(
      object &&
      typeof object.attachRef === 'function' &&
      typeof object.detachRef === 'function'
    );
  },

  /**
   * Adds a component by ref to an owner component.
   *
   * @param {ReactComponent} component Component to reference.
   * @param {string} ref Name by which to refer to the component.
   * @param {ReactOwner} owner Component on which to record the ref.
   * @final
   * @internal
   */
  addComponentAsRefTo: function(component, ref, owner) {
    invariant(
      ReactOwner.isValidOwner(owner),
      'addComponentAsRefTo(...): Only a ReactOwner can have refs. This ' +
      'usually means that you\'re trying to add a ref to a component that ' +
      'doesn\'t have an owner (that is, was not created inside of another ' +
      'component\'s `render` method). Try rendering this component inside of ' +
      'a new top-level component which will hold the ref.'
    );
    owner.attachRef(ref, component);
  },

  /**
   * Removes a component by ref from an owner component.
   *
   * @param {ReactComponent} component Component to dereference.
   * @param {string} ref Name of the ref to remove.
   * @param {ReactOwner} owner Component on which the ref is recorded.
   * @final
   * @internal
   */
  removeComponentAsRefFrom: function(component, ref, owner) {
    invariant(
      ReactOwner.isValidOwner(owner),
      'removeComponentAsRefFrom(...): Only a ReactOwner can have refs. This ' +
      'usually means that you\'re trying to remove a ref to a component that ' +
      'doesn\'t have an owner (that is, was not created inside of another ' +
      'component\'s `render` method). Try rendering this component inside of ' +
      'a new top-level component which will hold the ref.'
    );
    // Check that `component` is still the current ref because we do not want to
    // detach the ref if another component stole it.
    if (owner.refs[ref] === component) {
      owner.detachRef(ref);
    }
  },

  /**
   * A ReactComponent must mix this in to have refs.
   *
   * @lends {ReactOwner.prototype}
   */
  Mixin: {

    construct: function() {
      this.refs = emptyObject;
    },

    /**
     * Lazily allocates the refs object and stores `component` as `ref`.
     *
     * @param {string} ref Reference name.
     * @param {component} component Component to store as `ref`.
     * @final
     * @private
     */
    attachRef: function(ref, component) {
      invariant(
        component.isOwnedBy(this),
        'attachRef(%s, ...): Only a component\'s owner can store a ref to it.',
        ref
      );
      var refs = this.refs === emptyObject ? (this.refs = {}) : this.refs;
      refs[ref] = component;
    },

    /**
     * Detaches a reference name.
     *
     * @param {string} ref Name to dereference.
     * @final
     * @private
     */
    detachRef: function(ref) {
      delete this.refs[ref];
    }

  }

};

module.exports = ReactOwner;
