import type { Args, Fn } from "../HKT";

/**
 * Convert a union type to an intersection type.
 *
 * Sig: `<T>(u: UnionOf<T>) => IntersectOf<T>`
 */
export type ToIntersection<U> =
  (U extends unknown ? (_: U) => void : never) extends (mergedIntersection: infer I) => void ?
    I & U // The `& U` is to allow indexing by the resulting type
  : never;

/**
 * [Fn] Convert a union type to an intersection type.
 *
 * Sig: `<T>(u: UnionOf<T>) => IntersectOf<T>`
 */
export default interface ToIntersectionFn extends Fn<[unknown], unknown> {
  def: ([u]: Args<this>) => ToIntersection<typeof u>;
}