import type MapFn from "./Map";
import type { Fn1, Fn2, PartialApply } from "../../HKT";
import type { ValueOf } from "../../Obj/ValueOf";
import type { Eq, Lazied, Lazied$Get } from "../../helpers";
import type { HKT, Kind } from "../HKT";

/**
 * A type class for types that can be converted to a string.
 */
export type Functor<T = unknown> = Lazied$Get<FunctorL<T>>;
/**
 * {@link Lazied} version of {@link Functor}.
 */
export type FunctorL<T = unknown> = Lazied<Kind<FunctorImpl[keyof FunctorImpl][0], T>>;

/**
 * Type class constraints for type class {@link Functor}.
 */
export interface TypeClass$$Functor<F extends HKT> {
  /**
   * Map a {@link Functor} through a function.
   *
   * **⚠️ Warning:** Correctness of the method is not fully checked, so be careful when implementing
   * this method.
   *
   * Sig: `<F<~>, T, U>(f: (x: T) => U, fa: F<T>) => F<U>`
   */
  Map: Fn2<Fn1<never, any>, F, F>;
}

/**
 * Implementations for type class {@link Functor}.
 */
export interface FunctorImpl {}

/**
 * Helper type for implementing type class {@link Functor}.
 */
export type ImplFunctorFor<F extends HKT, TypeClass extends TypeClass$$Functor<F>> = [F, TypeClass];

/**
 * Get the matching entry of {@link FunctorImpl} for `F`.
 * @private
 */
type _Functor$GetMatch<F extends Functor> = ValueOf<{
  [P in keyof FunctorImpl as F extends FunctorImpl[P][0] ? P : never]: FunctorImpl[P];
}>;

/**
 * Get the constructor of `F` from {@link FunctorImpl}.
 */
export type Functor$GetConstruct<F extends Functor> =
  Eq<F, Functor> extends true ? Functor
  : _Functor$GetMatch<F> extends [infer F extends HKT, unknown] ? F
  : never;
/**
 * The **unsafe** version of {@link Functor$GetConstruct} (i.e. no type checking with `F`).
 */
export type Functor$GetConstructW<F> = F extends Functor ? Functor$GetConstruct<F> : never;

/**
 * Get the type class of `F` from {@link FunctorImpl}.
 */
export type Functor$GetTypeClass<F extends Functor> =
  _Functor$GetMatch<F> extends [unknown, infer TypeClass] ? TypeClass : never;
/**
 * The **unsafe** version of {@link Functor$GetTypeClass} (i.e. no type checking with `F`).
 */
export type Functor$GetTypeClassW<F> = F extends Functor ? Functor$GetTypeClass<F> : never;

/***********
 * Methods *
 ***********/
/**
 * Methods for `Functor`.
 */
export namespace Functor {
  /**
   * [Fn] Map a {@link Functor} through a function.
   *
   * Sig: `<F<~>, T, U>[f: (x: T) => U](fa: F<T>) => F<U>`
   */
  export type Map<F extends Fn1> = PartialApply<MapFn, [F]>;
}