// @flow strict
import * as React from 'react';


type InfiniteScrollOptions = {
  itemSize: number | ((index: number) => number),
  threshold: number,
  itemsLength: number,
  hasNextPage: boolean,
  loadMoreItems: () => Promise<void>,
  containerHeight: number,
  isVariableSizeList?: boolean,
};

export function useInfiniteScroll({
  itemSize,
  threshold,
  itemsLength,
  hasNextPage,
  loadMoreItems,
  containerHeight,
  isVariableSizeList,
}: InfiniteScrollOptions): (scrollData: {
  scrollOffset: number,
  scrollDirection: 'forward' | 'backward',
}) => void {
  const [isLoading, setIsLoading] = React.useState(false);
  const loadingRef = React.useRef(false);

  const handleLoadMore = React.useCallback(async () => {
    if (!hasNextPage || isLoading || loadingRef.current) {
      return;
    }

    loadingRef.current = true;
    setIsLoading(true);

    try {
      await loadMoreItems();
    } catch (err) {
      console.error('Error loading more items:', err);
    } finally {
      loadingRef.current = false;
      setIsLoading(false);
    }
  }, [hasNextPage, isLoading, loadMoreItems]);

  return React.useCallback(
    ({scrollOffset, scrollDirection}) => {
      if (scrollDirection !== 'forward') {
        return;
      }

      let totalSize = 0;
      if (isVariableSizeList && typeof itemSize === 'function') {
        for (let i = 0; i < itemsLength; i++) {
          totalSize += itemSize(i);
        }
      } else if (typeof itemSize === 'number') {
        totalSize = itemsLength * itemSize;
      }

      if (
        scrollOffset > totalSize - containerHeight - threshold &&
        hasNextPage &&
        !isLoading
      ) {
        handleLoadMore();
      }
    },
    [
      itemSize,
      threshold,
      isLoading,
      itemsLength,
      hasNextPage,
      handleLoadMore,
      containerHeight,
      isVariableSizeList,
    ],
  );
}