ibm-streams/src/webviews/message.ts

IBM Streams Support for Visual Studio Code

/**
 * Message object to send to the extension
 */
interface IRequestMessage<T> {
  req: string;
  command: string;
  args: T;
}

/**
 * Message object sent from the extension
 */
interface IReplyMessage {
  seq: string;
  err: any;
  res: any;
}

// To access the VS Code API object. Can only be invoked once per session.
declare let acquireVsCodeApi: any;
const vscode = acquireVsCodeApi();

/**
 * Handle messages between the extension and the webview
 */
export default class MessageHandler {
  private _commandHandler: ((message: any) => void) | null;
  private _lastSentReq: number;
  private _pendingReplies: any;

  constructor(commandHandler: any) {
    this._commandHandler = commandHandler;
    this._lastSentReq = 0;
    this._pendingReplies = Object.create(null);
    window.addEventListener('message', this.handleMessage.bind(this));
  }

  /**
   * Send a message to the extension
   * @param message the JSON message to send
   */
  public async postMessage(message: any): Promise<any> {
    const req = String(++this._lastSentReq);
    return new Promise<any>((resolve, reject) => {
      this._pendingReplies[req] = { resolve, reject };
      message = Object.assign(message, { req });
      vscode.postMessage(message as IRequestMessage<any>);
    });
  }

  /**
   * Handle messages from the extension
   * @param event the message event
   */
  private handleMessage(event: any): void {
    const message: IReplyMessage = event.data;
    if (message.seq) {
      const pendingReply = this._pendingReplies[message.seq];
      if (pendingReply) {
        if (message.err) {
          pendingReply.reject(message.err);
        } else {
          pendingReply.resolve(message.res);
        }
      }
    }

    if (this._commandHandler) {
      this._commandHandler(message.res);
    }
  }
}