text: /**
   * @license
   * Copyright (C) 2017 The Android Open Source Project
   *
   * 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.
   */
  import {PolymerElement} from '@polymer/polymer/polymer-element.js';
  
  /** @constructor */
  export function GrDomHooksManager(plugin) {
    this._plugin = plugin;
    this._hooks = {};
  }
  
  GrDomHooksManager.prototype._getHookName = function(endpointName,
      opt_moduleName) {
    if (opt_moduleName) {
      return endpointName + ' ' + opt_moduleName;
    } else {
      // lowercase in case plugin's name contains uppercase letters
      // TODO: this still can not prevent if plugin has invalid char
      // other than uppercase, but is the first step
      // https://html.spec.whatwg.org/multipage/custom-elements.html#valid-custom-element-name
      const pluginName = this._plugin.getPluginName() || 'unknown_plugin';
      return pluginName.toLowerCase() + '-autogenerated-' + endpointName;
    }
  };
  
  GrDomHooksManager.prototype.getDomHook = function(endpointName,
      opt_moduleName) {
    const hookName = this._getHookName(endpointName, opt_moduleName);
    if (!this._hooks[hookName]) {
      this._hooks[hookName] = new GrDomHook(hookName, opt_moduleName);
    }
    return this._hooks[hookName];
  };
  
  /** @constructor */
  export function GrDomHook(hookName, opt_moduleName) {
    this._instances = [];
    this._attachCallbacks = [];
    this._detachCallbacks = [];
    if (opt_moduleName) {
      this._moduleName = opt_moduleName;
    } else {
      this._moduleName = hookName;
      this._createPlaceholder(hookName);
    }
  }
  
  GrDomHook.prototype._createPlaceholder = function(hookName) {
    class HookPlaceholder extends PolymerElement {
      static get is() { return hookName; }
  
      static get properties() {
        return {
          plugin: Object,
          content: Object,
        };
      }
    }
  
    customElements.define(HookPlaceholder.is, HookPlaceholder);
  };
  
  GrDomHook.prototype.handleInstanceDetached = function(instance) {
    const index = this._instances.indexOf(instance);
    if (index !== -1) {
      this._instances.splice(index, 1);
    }
    this._detachCallbacks.forEach(callback => callback(instance));
  };
  
  GrDomHook.prototype.handleInstanceAttached = function(instance) {
    this._instances.push(instance);
    this._attachCallbacks.forEach(callback => callback(instance));
  };
  
  /**
   * Get instance of last DOM hook element attached into the endpoint.
   * Returns a Promise, that's resolved when attachment is done.
   *
   * @return {!Promise<!Element>}
   */
  GrDomHook.prototype.getLastAttached = function() {
    if (this._instances.length) {
      return Promise.resolve(this._instances.slice(-1)[0]);
    }
    if (!this._lastAttachedPromise) {
      let resolve;
      const promise = new Promise(r => resolve = r);
      this._attachCallbacks.push(resolve);
      this._lastAttachedPromise = promise.then(element => {
        this._lastAttachedPromise = null;
        const index = this._attachCallbacks.indexOf(resolve);
        if (index !== -1) {
          this._attachCallbacks.splice(index, 1);
        }
        return element;
      });
    }
    return this._lastAttachedPromise;
  };
  
  /**
   * Get all DOM hook elements.
   */
  GrDomHook.prototype.getAllAttached = function() {
    return this._instances;
  };
  
  /**
   * Install a new callback to invoke when a new instance of DOM hook element
   * is attached.
   *
   * @param {function(Element)} callback
   */
  GrDomHook.prototype.onAttached = function(callback) {
    this._attachCallbacks.push(callback);
    return this;
  };
  
  /**
   * Install a new callback to invoke when an instance of DOM hook element
   * is detached.
   *
   * @param {function(Element)} callback
   */
  GrDomHook.prototype.onDetached = function(callback) {
    this._detachCallbacks.push(callback);
    return this;
  };
  
  /**
   * Name of DOM hook element that will be installed into the endpoint.
   */
  GrDomHook.prototype.getModuleName = function() {
    return this._moduleName;
  };
  
  GrDomHook.prototype.getPublicAPI = function() {
    const result = {};
    const exposedMethods = [
      'onAttached',
      'onDetached',
      'getLastAttached',
      'getAllAttached',
      'getModuleName',
    ];
    for (const p of exposedMethods) {
      result[p] = this[p].bind(this);
    }
    return result;
  };
  