tweb-i2p/src/helpers/scrollSaver.ts

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

import Scrollable from "../components/scrollable";
import { IS_SAFARI } from "../environment/userAgent";
import reflowScrollableElement from "./dom/reflowScrollableElement";

export default class ScrollSaver {
  private previousScrollHeight: number;
  private previousScrollHeightMinusTop: number/* , previousScrollHeight: number */;

  /**
   * 
   * @param scrollable to reset scroll position and direction
   * @param reverse true means top
   */
  constructor(
    private scrollable: Scrollable, 
    private reverse: boolean
  ) {

  }

  private get container() {
    return this.scrollable.container;
  }

  public save() {
    const {scrollTop, scrollHeight} = this.container;

    //previousScrollHeight = scrollHeight;
    //previousScrollHeight = scrollHeight + padding;
    this.previousScrollHeight = scrollHeight;
    this.previousScrollHeightMinusTop = this.reverse ? scrollHeight - scrollTop : scrollTop;

    //this.chatInner.style.paddingTop = padding + 'px';
    /* if(reverse) {
      previousScrollHeightMinusTop = this.scrollable.scrollHeight - scrollTop;
    } else {
      previousScrollHeightMinusTop = scrollTop;
    } */

    /* if(DEBUG) {
      this.log('performHistoryResult: messagesQueueOnRender, scrollTop:', scrollTop, scrollHeight, previousScrollHeightMinusTop);
    } */
  }

  public restore(useReflow?: boolean) {
    const {container, previousScrollHeightMinusTop, scrollable} = this;
    if(previousScrollHeightMinusTop !== undefined) {
      const scrollHeight = container.scrollHeight;
      if(scrollHeight === this.previousScrollHeight) {
        return;
      }

      /* const scrollHeight = container.scrollHeight;
      const addedHeight = scrollHeight - previousScrollHeight;
      
      this.chatInner.style.paddingTop = (10000 - addedHeight) + 'px'; */
      /* const scrollHeight = scrollHeight;
      const addedHeight = scrollHeight - previousScrollHeight;
      
      this.chatInner.style.paddingTop = (padding - addedHeight) + 'px';
      
      //const newScrollTop = reverse ? scrollHeight - previousScrollHeightMinusTop : previousScrollHeightMinusTop;
      const newScrollTop = reverse ? scrollHeight - addedHeight - previousScrollHeightMinusTop : previousScrollHeightMinusTop;
      this.log('performHistoryResult: will set scrollTop', 
      previousScrollHeightMinusTop, scrollHeight, 
      newScrollTop, container.container.clientHeight); */
      //const newScrollTop = reverse ? scrollHeight - previousScrollHeightMinusTop : previousScrollHeightMinusTop;
      const newScrollTop = this.reverse ? scrollHeight - previousScrollHeightMinusTop : previousScrollHeightMinusTop;
      
      /* if(DEBUG) {
        this.log('performHistoryResult: will set up scrollTop:', newScrollTop, this.isHeavyAnimationInProgress);
      } */

      // touchSupport for safari iOS
      //isTouchSupported && isApple && (container.container.style.overflow = 'hidden');
      container.scrollTop = newScrollTop;
      //container.scrollTop = scrollHeight;
      //isTouchSupported && isApple && (container.container.style.overflow = '');

      scrollable.lastScrollPosition = newScrollTop;
      // scrollable.lastScrollDirection = 0;

      if(IS_SAFARI && useReflow/*  && !isAppleMobile */) { // * fix blinking and jumping
        reflowScrollableElement(container);
      }

      /* if(DEBUG) {
        this.log('performHistoryResult: have set up scrollTop:', newScrollTop, container.scrollTop, container.scrollHeight, this.isHeavyAnimationInProgress);
      } */
    }
  }
}