import type { Monad, Monad$GetTypeClassW } from ".";
import type {
  Args,
  Call1W,
  Call2W,
  Fn1,
  GenericFn,
  GenericResolver,
  GenericReturn1W,
  Param0,
  Return,
} from "../../HKT";
import type { Functor$GetTypeClassW } from "../Functor";
import type { HKT$Extract, HKT$GetConstruct, HKT$Mutate } from "../HKT";

/**
 * Map a function over a {@link Monad} and flatten the result.
 *
 * Sig: `<F<~>, T, U>(f: (x: T) => F<U>, fa: F<T>) => F<U>`
 */
export type Chain<F extends Fn1<HKT$Extract<FA>, HKT$GetConstruct<FA>>, FA extends Monad> = Call1W<
  Monad$GetTypeClassW<FA>["Flatten"],
  Call2W<Functor$GetTypeClassW<FA>["Map"], F, FA>
>;

interface Resolver extends GenericResolver<[Fn1<never, Monad>, Monad], Monad> {
  on1_: ([f]: Args<this>) => [[HKT$Mutate<Return<typeof f>, Param0<typeof f>>], Return<typeof f>];
  on_1: ([, fa]: Args<this>) => [
    [Fn1<HKT$Extract<typeof fa>, HKT$GetConstruct<typeof fa>>],
    HKT$GetConstruct<typeof fa>,
  ];
  on11: ([f, fa]: Args<this>) => [[], GenericReturn1W<typeof f, HKT$Extract<typeof fa>>];
}

/**
 * [Fn] Map a function over a {@link Monad} and flatten the result.
 *
 * Sig: `<F<~>, T, U>(f: (x: T) => F<U>, fa: F<T>) => F<U>`
 */
export default interface ChainFn extends GenericFn<Resolver> {
  def: ([f, fa]: Args<this>) => typeof f extends (
    Fn1<HKT$Extract<typeof fa>, HKT$GetConstruct<typeof fa>>
  ) ?
    Chain<typeof f, typeof fa>
  : never;
}