React Native Flatlist/Flashlist Reverse Page counter based on scroll position

FlastlistScroll.tsx

const PER_PAGE = 30;
const [current_page,setPage] = useState(0);
const ITEM_HEIGHT = 55;  //each item height including vertical padding/margin

const calculatePage = (e: NativeSyntheticEvent<NativeScrollEvent>) => {
    const cPage = Math.floor(e.nativeEvent.contentOffset.y / (ITEM_HEIGHT * (current_page + 1 * PER_PAGE)));
    console.log(cPage);
    return cPage;
  };
  
  <FlashList
      keyExtractor={keyExtractor}
      removeClippedSubviews
      estimatedItemSize={55}
      data={data}
      renderItem={_renderItem}
      onEndReached={setPage}
      onEndReachedThreshold={0.5}
      scrollEventThrottle={200}
      onScroll={calculatePage}
    />