const createMiddleware = (fieldNames, middlewareFn, flag) =>
    (...args) => {
        const [resolve,,,, info] = args;

        // applies middleware function to all resolvers if flag is `*`
        if (flag === '*')
            return middlewareFn(...args);

        // middleware only for specific resolvers otherwise calls resolver directly
        return fieldNames.includes(info.fieldName)
            ? middlewareFn(...args)
            : resolve();
};