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interface SchedulerOptions {  deferEvents: boolean;}
const defaultOptions: SchedulerOptions = {  deferEvents: false};
export class Scheduler {  private processingEvent: boolean = false;  private queue: Array<() => void> = [];  private initialized = false;
  // deferred feature  private options: SchedulerOptions;
  constructor(options?: Partial<SchedulerOptions>) {    this.options = { ...defaultOptions, ...options };  }
  public initialize(callback?: () => void): void {    this.initialized = true;
    if (callback) {      if (!this.options.deferEvents) {        this.schedule(callback);        return;      }
      this.process(callback);    }
    this.flushEvents();  }
  public schedule(task: () => void): void {    if (!this.initialized || this.processingEvent) {      this.queue.push(task);      return;    }
    if (this.queue.length !== 0) {      throw new Error(        'Event queue should be empty when it is not processing events'      );    }
    this.process(task);    this.flushEvents();  }
  public clear(): void {    this.queue = [];  }
  private flushEvents() {    let nextCallback: (() => void) | undefined = this.queue.shift();    while (nextCallback) {      this.process(nextCallback);      nextCallback = this.queue.shift();    }  }
  private process(callback: () => void) {    this.processingEvent = true;    try {      callback();    } catch (e) {      // there is no use to keep the future events      // as the situation is not anymore the same      this.clear();      throw e;    } finally {      this.processingEvent = false;    }  }}