import type { Applicative, Applicative$GetTypeClassW } from ".";
import type {
  Args,
  Call2W,
  Fn1,
  GenericFn,
  GenericResolver,
  GenericReturn1W,
  Param0W,
  ReturnW,
} from "../../HKT";
import type { HKT$Extract, HKT$GetConstruct, HKT$Mutate } from "../HKT";

/**
 * Apply an {@link Applicative} of a function to an {@link Applicative} of a value.
 *
 * Sig: `<F<~>, T, U>(fab: F<(x: T) => U>, f: F<T>) => F<U>`
 */
export type Ap<
  FAB extends HKT$Mutate<F, Fn1<HKT$Extract<F>, unknown>>,
  F extends Applicative,
> = Call2W<Applicative$GetTypeClassW<F>["Ap"], FAB, F>;

interface Resolver extends GenericResolver<[Applicative<Fn1>, Applicative], Applicative> {
  on1_: ([fab]: Args<this>) => [
    [HKT$Mutate<typeof fab, Param0W<HKT$Extract<typeof fab>>>],
    HKT$Mutate<typeof fab, ReturnW<HKT$Extract<typeof fab>>>,
  ];
  on_1: ([, f]: Args<this>) => [
    [HKT$Mutate<typeof f, Fn1<HKT$Extract<typeof f>, unknown>>],
    HKT$GetConstruct<typeof f>,
  ];
  on11: ([fab, f]: Args<this>) => [
    [],
    HKT$Mutate<typeof fab, GenericReturn1W<HKT$Extract<typeof fab>, HKT$Extract<typeof f>>>,
  ];
}

/**
 * [Fn] Apply an {@link Applicative} of a function to an {@link Applicative} of a value.
 *
 * Sig: `<F<~>, T, U>(fab: F<(x: T) => U>, f: F<T>) => F<U>`
 */
export default interface ApFn extends GenericFn<Resolver> {
  def: ([fab, f]: Args<this>) => typeof fab extends (
    HKT$Mutate<typeof f, Fn1<HKT$Extract<typeof f>, unknown>>
  ) ?
    Ap<typeof fab, typeof f>
  : never;
}