Function useDropIndicator

packages/react-aria/src/dnd/useDropIndicator.ts:45–127

(
  props: DropIndicatorProps,
  state: DroppableCollectionState,
  ref: RefObject<HTMLElement | null>
)

 * Handles drop interactions for a target within a droppable collection.
 */
export function useDropIndicator(
  props: DropIndicatorProps,
  state: DroppableCollectionState,
  ref: RefObject<HTMLElement | null>
): DropIndicatorAria {
  let {target} = props;
  let {collection} = state;

  let stringFormatter = useLocalizedStringFormatter(intlMessages, '@react-aria/dnd');
  let dragSession = DragManager.useDragSession();
  let {dropProps} = useDroppableItem(props, state, ref);
  let id = useId();
  let getText = (key: Key | null) => {
    if (key == null) {
      return '';
    } else {
      return collection.getTextValue?.(key) ?? collection.getItem(key)?.textValue ?? '';
    }
  };

  let label = '';
  let labelledBy: string | undefined;
  if (target.type === 'root') {
    label = stringFormatter.format('dropOnRoot');
    labelledBy = `${id} ${getDroppableCollectionId(state)}`;
  } else if (target.dropPosition === 'on') {
    label = stringFormatter.format('dropOnItem', {
      itemText: getText(target.key)
    });
  } else {
    let before: Key | null | undefined;
    let after: Key | null | undefined;
    if (target.dropPosition === 'before') {
      let prevKey = collection.getItem(target.key)?.prevKey;
      let prevNode = prevKey != null ? collection.getItem(prevKey) : null;
      before = prevNode?.type === 'item' ? prevNode.key : null;
    } else {
      before = target.key;
    }

    if (target.dropPosition === 'after') {
      let nextKey = collection.getItem(target.key)?.nextKey;
      let nextNode = nextKey != null ? collection.getItem(nextKey) : null;
      after = nextNode?.type === 'item' ? nextNode.key : null;
    } else {
      after = target.key;
    }

    if (before != null && after != null) {
      label = stringFormatter.format('insertBetween', {
        beforeItemText: getText(before),
        afterItemText: getText(after)
      });
    } else if (before != null) {
      label = stringFormatter.format('insertAfter', {
        itemText: getText(before)
      });
    } else if (after != null) {