type MapFunction<In, Out> = (input: In) => Promise<[In, Out] | null>;

export async function map_parallel<In, Out>(
  inputs: Iterable<In>,
  map_fn: MapFunction<In, Out>,
): Promise<Map<In, Out>> {
  const queue = [...inputs].map((input) => map_fn(input));

  return new Map<In, Out>(
    (await Promise.all(queue)).filter((job): job is [In, Out] => job !== null),
  );
}