import type { Ary } from ".";
import type { Args, GenericFn, GenericResolver } from "../HKT";

/**
 * Mutate the element type of an {@link Ary} (i.e., `Array` or `ReadonlyArray`).
 *
 * Sig: `<T, U>(y: U, a: Ary<T>) => Ary<U>`
 *
 * @example
 * ```typescript
 * type R1 = Mutate<number, string[]>;
 * //   ^?: number[]
 * type R2 = Mutate<"foo", readonly number[]>;
 * //   ^?: readonly "foo"[]
 * ```
 */
export type Mutate<U, A extends Ary> = A extends unknown[] ? U[] : readonly U[];

interface Resolver extends GenericResolver<[unknown, Ary<unknown>], Ary<unknown>> {
  on1_: ([y]: Args<this>) => [[Ary<unknown>], Ary<unknown>];
  on_1: ([, a]: Args<this>) => [[unknown], Ary<unknown>];
  on11: ([y, a]: Args<this>) => [[], Mutate<typeof y, typeof a>];
}

/**
 * [Fn] Mutate the element type of an {@link Ary} (i.e., `Array` or `ReadonlyArray`).
 *
 * Sig: `<T, U>(y: U, a: Ary<T>) => Ary<U>`
 */
export default interface MutateFn extends GenericFn<Resolver> {
  def: ([y, a]: Args<this>) => Mutate<typeof y, typeof a>;
}