polygerrit-ui/app/elements/plugins/gr-dom-hooks/gr-dom-hooks.ts

/**
 * @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';

type HookCallback = (el: Element) => void;
interface HookApi {
  onAttached(callback: HookCallback): void;
}
interface PluginAPI {
  hook(hookname: string): HookApi;
  getPluginName(): string;
}

/** @constructor */
export class GrDomHooksManager {
  private _hooks: Record<string, GrDomHook>;

  // TODO(TS): Convert type to GrPlugin.
  private _plugin: PluginAPI;

  // TODO(TS): Convert type to GrPlugin.
  constructor(plugin: PluginAPI) {
    this._plugin = plugin;
    this._hooks = {};
  }

  _getHookName(endpointName: string, moduleName?: string) {
    if (moduleName) {
      return endpointName + ' ' + 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: string =
        this._plugin.getPluginName() || 'unknown_plugin';
      return pluginName.toLowerCase() + '-autogenerated-' + endpointName;
    }
  }

  getDomHook(endpointName: string, moduleName?: string) {
    const hookName = this._getHookName(endpointName, moduleName);
    if (!this._hooks[hookName]) {
      this._hooks[hookName] = new GrDomHook(hookName, moduleName);
    }
    return this._hooks[hookName];
  }
}

interface PublicApi {
  onAttached(callback: HookCallback): PublicApi;
  onDetached(callback: HookCallback): PublicApi;
  getAllAttached(): any;
  getLastAttached(): any;
  getModuleName(): string;
}

/** @constructor */
export class GrDomHook {
  // TODO(TS): specify type for this
  private _instances: unknown[] = [];

  private _attachCallbacks: HookCallback[] = [];

  private _detachCallbacks: HookCallback[] = [];

  private _moduleName: string;

  private _lastAttachedPromise: Promise<HookCallback> | null = null;

  constructor(hookName: string, moduleName?: string) {
    if (moduleName) {
      this._moduleName = moduleName;
    } else {
      this._moduleName = hookName;
      this._createPlaceholder(hookName);
    }
  }

  _createPlaceholder(hookName: string) {
    class HookPlaceholder extends PolymerElement {
      static get is() {
        return hookName;
      }

      static get properties() {
        return {
          plugin: Object,
          content: Object,
        };
      }
    }

    customElements.define(HookPlaceholder.is, HookPlaceholder);
  }

  handleInstanceDetached(instance: Element) {
    const index = this._instances.indexOf(instance);
    if (index !== -1) {
      this._instances.splice(index, 1);
    }
    this._detachCallbacks.forEach(callback => callback(instance));
  }

  handleInstanceAttached(instance: Element) {
    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
   */
  getLastAttached() {
    if (this._instances.length) {
      return Promise.resolve(this._instances.slice(-1)[0]);
    }
    if (!this._lastAttachedPromise) {
      let resolve: HookCallback;
      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;
      }) as Promise<HookCallback>;
    }
    return this._lastAttachedPromise;
  }

  /**
   * Get all DOM hook elements.
   */
  getAllAttached() {
    return this._instances;
  }

  /**
   * Install a new callback to invoke when a new instance of DOM hook element
   * is attached.
   */
  onAttached(callback: HookCallback) {
    this._attachCallbacks.push(callback);
    return this;
  }

  /**
   * Install a new callback to invoke when an instance of DOM hook element
   * is detached.
   *
   */
  onDetached(callback: HookCallback) {
    this._detachCallbacks.push(callback);
    return this;
  }

  /**
   * Name of DOM hook element that will be installed into the endpoint.
   */
  getModuleName() {
    return this._moduleName;
  }

  getPublicAPI(): PublicApi {
    return {
      onAttached: this.onAttached.bind(this),
      onDetached: this.onDetached.bind(this),
      getAllAttached: this.getAllAttached.bind(this),
      getLastAttached: this.getLastAttached.bind(this),
      getModuleName: this.getModuleName.bind(this),
    };
  }
}