def prefetch_and_select_related(query_set, info):
    if info.parent_type.name != 'Query':
        return query_set

    select_list, prefetch_list = [], []

    for ffield in info.field_asts:
        s, p = _prefetch_and_select_related(
            selections=ffield.selection_set.selections,
            prefix='',
            select_list=[],
            prefetch_list=[],
        )
        select_list += s
        prefetch_list += p
    print('Select', select_list)
    print('Prefetch', prefetch_list)
    if len(select_list) > 0:
        query_set = query_set.select_related(*select_list)
    if len(prefetch_list) > 0:
        query_set = query_set.prefetch_related(*prefetch_list)
    return query_set


def _prefetch_and_select_related(selections, prefix, select_list, prefetch_list):
    for field in selections:
        if field.selection_set is not None:
            name = camelToSnake(field.name.value)
            if '_set' in name:
                select_list, prefetch_list = _prefetch_and_select_related(
                    selections=field.selection_set.selections,
                    prefix=concat(prefix, name),
                    select_list=select_list,
                    prefetch_list=prefetch_list + [concat(prefix, name)],
                )
            else:
                select_list, prefetch_list = _prefetch_and_select_related(
                    selections=field.selection_set.selections,
                    prefix=concat(prefix, name),
                    select_list=select_list + [concat(prefix, name)],
                    prefetch_list=prefetch_list,
                )

    return select_list, prefetch_list


def concat(prefix, name):
    return '__'.join(filter(lambda str: len(str) > 0, [prefix, name]))


class PrefetchMiddleware(object):
    def resolve(self, next, root, info, **args):
        if info.parent_type.name != 'Query':
            return next(root, info, **args)
        else:
            return Promise.resolve(prefetch_and_select_related(next(root, info, **args).value, info))