Helper util for pulling union GQL types into named objects based on their __typename

dataByTypename.ts

/* based on https://github.com/artsy/artsy.github.io/issues/495#issuecomment-509697859 as https://artsy.github.io/blog/2018/10/19/where-art-thou-my-error/ */

type OfUnion<T extends { __typename: string }> = {
  [P in T['__typename']]: Extract<T, { __typename: P }>;
};

const dataByTypename = <T extends { __typename: string }>(data?: T): OfUnion<T> => {
  const typedData = data
    ? {
        [data.__typename]: data,
      }
    : {};
  return typedData as OfUnion<T>;
};

export default dataByTypename;