Load more items when the end scrolls into view

import 'react-horizontal-scrolling-menu/dist/styles.css';

import styled from '@emotion/styled';
import React from 'react';
import {
  type publicApiType,
  ScrollMenu,
  VisibilityContext,
} from 'react-horizontal-scrolling-menu';

export function AddItemsExample() {
  const [items, setItems] = React.useState(() => getItems());
  const [selected, setSelected] = React.useState<string[]>([]);

  const isItemSelected = (id: string): boolean =>
    !!selected.find((el) => el === id);

  const handleItemClick = (itemId: string) => {
    const itemSelected = isItemSelected(itemId);

    setSelected((currentSelected: string[]) =>
      itemSelected
        ? currentSelected.filter((el) => el !== itemId)
        : currentSelected.concat(itemId),
    );
  };

  const newItemsLimit = 24;
  const [loading, setLoading] = React.useState(false);
  const pushNewItems = () => {
    if (loading || items.length > newItemsLimit) {
      return false;
    }

    setLoading(true);
    const newItems = items.concat(
      Array(5)
        .fill(0)
        .map((_, ind) => ({ id: getId(items.length + ind) })),
    );
    new Promise((res) => {
      setTimeout(() => res(setItems(newItems)), 1000);
    }).finally(() => setLoading(false));
  };

  return (
    <div>
      <div>
        <NoScrollbar>
          <ScrollMenu
            LeftArrow={LeftArrow}
            RightArrow={<RightArrow disabled={items.length >= newItemsLimit} />}
            onWheel={onWheel}
            onUpdate={(api) => {
              const lastVisible = api?.items?.last?.()?.visible;
              if (lastVisible && !loading) {
                pushNewItems();
              }
            }}
          >
            {items.map(({ id }) => (
              <Card
                title={id}
                itemId={id} // NOTE: itemId is required for track items
                key={id}
                onClick={() => handleItemClick(id)}
                selected={isItemSelected(id)}
              />
            ))}
            {loading && <Loader itemId="loader" key="loader" />}
          </ScrollMenu>
        </NoScrollbar>
      </div>
    </div>
  );
}

function Loader({ itemId }: { itemId: string }) {
  const ref = React.useRef<HTMLDivElement>(null);

  React.useEffect(() => {
    ref.current?.scrollIntoView();
  }, [ref]);
  return <div ref={ref}>Loading...</div>;
}

export default AddItemsExample;

const NoScrollbar = styled('div')({
  '& .react-horizontal-scrolling-menu--scroll-container::-webkit-scrollbar': {
    display: 'none',
  },
  '& .react-horizontal-scrolling-menu--scroll-container': {
    scrollbarWidth: 'none',
    '-ms-overflow-style': 'none',
  },
});

function LeftArrow() {
  const visibility = React.useContext<publicApiType>(VisibilityContext);

  const disabled = visibility.useLeftArrowVisible();

  return (
    <Arrow
      disabled={disabled}
      onClick={() => visibility.scrollPrev()}
      testId="left-arrow"
    >
      Left
    </Arrow>
  );
}

function RightArrow({ disabled }: { disabled: boolean }) {
  const visibility = React.useContext<publicApiType>(VisibilityContext);
  const isLastItemVisible = visibility.useIsVisible('last', false);

  return (
    <Arrow
      disabled={disabled && isLastItemVisible}
      onClick={() => visibility.scrollNext()}
      testId="right-arrow"
    >
      Right
    </Arrow>
  );
}

function Arrow({
  children,
  disabled,
  onClick,
  className,
  testId,
}: {
  children: React.ReactNode;
  disabled: boolean;
  onClick: VoidFunction;
  className?: string;
  testId: string;
}) {
  return (
    <ArrowButton
      disabled={disabled}
      onClick={onClick}
      className={'arrow' + `-${className}`}
      data-testid={testId}
    >
      {children}
    </ArrowButton>
  );
}
const ArrowButton = styled('button')((props) => ({
  cursor: 'pointer',
  display: 'flex',
  flexDirection: 'column',
  justifyContent: 'center',
  marginBottom: '2px',
  opacity: props.disabled ? '0' : '1',
  userSelect: 'none',
  borderRadius: '6px',
  borderWidth: '1px',
}));

function Card({
  onClick,
  selected,
  title,
  itemId,
}: {
  onClick: (context: publicApiType) => void;
  selected: boolean;
  title: string;
  itemId: string;
}) {
  const visibility = React.useContext<publicApiType>(VisibilityContext);
  const isVisible = visibility.useIsVisible(itemId, true);

  return (
    <CardBody
      data-cy={itemId}
      onClick={() => onClick(visibility)}
      onKeyDown={(ev: React.KeyboardEvent) => {
        ev.code === 'Enter' && onClick(visibility);
      }}
      data-testid="card"
      role="button"
      tabIndex={0}
      className="card"
      visible={isVisible}
      selected={selected}
    >
      <div className="header">
        <div>{title}</div>
        <div className="visible">visible: {JSON.stringify(isVisible)}</div>
        <div className="selected">selected: {JSON.stringify(!!selected)}</div>
      </div>
      <div className="background" />
    </CardBody>
  );
}
const CardBody = styled('div')<{ selected?: boolean; visible?: boolean }>(
  (props) => ({
    border: '1px solid',
    display: 'inline-block',
    margin: '0 10px',
    width: '160px',
    userSelect: 'none',
    borderRadius: '8px',
    overflow: 'hidden',

    '& .header': {
      backgroundColor: 'white',
    },

    '& .visible': {
      backgroundColor: props.visible ? 'transparent' : 'gray',
    },

    '& .background': {
      backgroundColor: props.selected ? 'green' : 'bisque',
      height: '200px',
    },
  }),
);

const getId = (index: number) => `${'test'}${index}`;

const getItems = () =>
  Array(10)
    .fill(0)
    .map((_, ind) => ({ id: getId(ind) }));

const onWheel = (apiObj: publicApiType, ev: React.WheelEvent) => {
  // NOTE: no good standart way to distinguish touchpad scrolling gestures
  // but can assume that gesture will affect X axis, mouse scroll only Y axis
  // of if deltaY too small probably is it touchpad
  const isThouchpad = Math.abs(ev.deltaX) !== 0 || Math.abs(ev.deltaY) < 15;

  if (isThouchpad) {
    ev.stopPropagation();
    return;
  }

  if (ev.deltaY < 0) {
    apiObj.scrollNext();
  } else {
    apiObj.scrollPrev();
  }
};