/**
 * The direction a stream is ordered in. Tracked covariantly in the type: a
 * stream of a known direction is also a stream of `"asc" | "desc"`, the class
 * default, so annotations that omit the direction accept every stream.
 * Combining streams of different known directions—`merge`, or a `flatMap` whose
 * inner streams run the other way—is a type error; a direction chosen at
 * runtime types as the union, and the runtime check catches what the types
 * can't see (`merge` throws when the streams are combined, `flatMap` fails when
 * the join runs).
 *
 * @experimental
 */
export type QueryStreamOrderDirection = "asc" | "desc";

/**
 * The opposite of a direction; a runtime-chosen direction stays the union.
 *
 * @experimental
 */
export type Flip<OrderDirection extends QueryStreamOrderDirection> =
  OrderDirection extends "asc" ? "desc" : "asc";

/**
 * @experimental
 */
export const flip = <OrderDirection extends QueryStreamOrderDirection>(
  orderDirection: OrderDirection,
): Flip<OrderDirection> =>
  (orderDirection === "asc" ? "desc" : "asc") as Flip<OrderDirection>;