import type { Option, Some } from ".";
import type { Args, GenericFn, GenericResolver } from "../HKT";
import type { AssertUnknown, Broaden } from "../helpers";

/**
 * Get the inner value of an {@link Option} if it is {@link Some}, otherwise return `Default`.
 *
 * Sig: `<T>(default: T, o: Option<T>) => T`
 */
export type UnwrapOr<Default, O extends Option<unknown>> = AssertUnknown<
  O extends Some<infer T> ? T : Default
>;

interface Resolver extends GenericResolver<[unknown, Option<unknown>], unknown> {
  on1_: ([d]: Args<this>) => [[Option<Broaden<typeof d>>], Broaden<typeof d>];
  on_1: ([, o]: Args<this>) => [
    [Option<typeof o extends Option<infer T> ? T : never>],
    typeof o extends Option<infer T> ? T : never,
  ];
  on11: ([d, o]: Args<this>) => [[], (typeof o extends Option<infer T> ? T : never) | typeof d];
}

/**
 * [Fn] Get the inner value of an {@link Option} if it is {@link Some}, otherwise return `default`.
 *
 * Sig: `<T>(default: T, o: Option<T>) => T`
 */
export default interface UnwrapOrFn extends GenericFn<Resolver> {
  def: ([d, o]: Args<this>) => UnwrapOr<typeof d, typeof o>;
}