/**

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 *

 * This source code is licensed under the MIT license found in the

 * LICENSE file in the root directory of this source tree.

 *

 * @flow

 */

import type {Rect} from '../geometry';

import type {ScrollState} from '../utils/scrollState';

import type {Surface} from '../Surface';

import type {ViewState} from '../../types';

import {VerticalScrollBarView} from './VerticalScrollBarView';

import {withVerticalScrollbarLayout} from './withVerticalScrollbarLayout';

import {View} from '../View';

import {VerticalScrollView} from '../VerticalScrollView';

export class VerticalScrollOverflowView extends View {

  _contentView: View;

  _isProcessingOnChange: boolean = false;

  _isScrolling: boolean = false;

  _scrollOffset: number = 0;

  _scrollBarView: VerticalScrollBarView;

  _verticalScrollView: VerticalScrollView;

  constructor(

    surface: Surface,

    frame: Rect,

    contentView: View,

    viewState: ViewState,

  ) {

    super(surface, frame, withVerticalScrollbarLayout);

    this._contentView = contentView;

    this._verticalScrollView = new VerticalScrollView(

      surface,

      frame,

      contentView,

      viewState,

      'VerticalScrollOverflowView',

    );

    this._verticalScrollView.onChange(this._onVerticalScrollViewChange);

    this._scrollBarView = new VerticalScrollBarView(surface, frame, this);

    this.addSubview(this._verticalScrollView);

    this.addSubview(this._scrollBarView);

  }

  layoutSubviews() {

    super.layoutSubviews();

    const contentSize = this._contentView.desiredSize();

    // This should be done after calling super.layoutSubviews() – calling it

    // before somehow causes _contentView to need display on every mousemove

    // event when the scroll bar is shown.

    this._scrollBarView.setContentHeight(contentSize.height);

  }

  setScrollOffset(newScrollOffset: number, maxScrollOffset: number) {

    const deltaY = newScrollOffset - this._scrollOffset;

    if (!this._isProcessingOnChange) {

      this._verticalScrollView.scrollBy(-deltaY);

    }

    this._scrollOffset = newScrollOffset;

    this.setNeedsDisplay();

  }

  _onVerticalScrollViewChange: (

    scrollState: ScrollState,

    containerLength: number,

  ) => void = (scrollState: ScrollState, containerLength: number) => {

    const maxOffset = scrollState.length - containerLength;

    if (maxOffset === 0) {

      return;

    }

    const percentage = Math.abs(scrollState.offset) / maxOffset;

    const maxScrollThumbY = this._scrollBarView.getMaxScrollThumbY();

    this._isProcessingOnChange = true;

    this._scrollBarView.setScrollThumbY(percentage * maxScrollThumbY);

    this._isProcessingOnChange = false;

  };

}