/*
 * https://github.com/morethanwords/tweb
 * Copyright (C) 2019-2021 Eduard Kuzmenko
 * https://github.com/morethanwords/tweb/blob/master/LICENSE
 */

import { fastRaf } from "./schedulers";
import { CancellablePromise, deferredPromise } from "./cancellablePromise";
import { MOUNT_CLASS_TO } from "../config/debug";
import isInDOM from "./dom/isInDOM";

class SequentialDom {
  private promises: Partial<{
    read: CancellablePromise<void>,
    write: CancellablePromise<void>
  }> = {};
  private raf = fastRaf.bind(null);
  private scheduled = false;

  private do(kind: keyof SequentialDom['promises'], callback?: VoidFunction) {
    let promise = this.promises[kind];
    if(!promise) {
      this.scheduleFlush();
      promise = this.promises[kind] = deferredPromise<void>();
    }

    if(callback !== undefined) {
      promise.then(() => callback());
    }
    
    return promise;
  }

  public measure(callback?: VoidFunction) {
    return this.do('read', callback);
  }

  public mutate(callback?: VoidFunction) {
    return this.do('write', callback);
  }

  /**
   * Will fire instantly if element is not connected
   * @param element 
   * @param callback 
   */
  public mutateElement(element: HTMLElement, callback?: VoidFunction) {
    const promise = isInDOM(element) ? this.mutate() : Promise.resolve();

    if(callback !== undefined) {
      promise.then(() => callback());
    }

    return promise;
  }

  private scheduleFlush() {
    if(!this.scheduled) {
      this.scheduled = true;

      this.raf(() => {
        this.promises.read && this.promises.read.resolve();
        this.promises.write && this.promises.write.resolve();

        this.scheduled = false;
        this.promises = {};
      });
    }
  }
}

const sequentialDom = new SequentialDom();
MOUNT_CLASS_TO && (MOUNT_CLASS_TO.sequentialDom = sequentialDom);
export default sequentialDom;