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

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

/**
 * Type class constraints for type class {@link Applicative}.
 */
export interface TypeClass$$Applicative<F extends Functor> {
  /**
   * Apply an {@link Applicative} of a function to an {@link Applicative} of a value.
   *
   * **⚠️ Warning:** Correctness of the method is not fully checked, so be careful when implementing
   * this method.
   *
   * Sig: `<F<~>, T, U>(fab: F<(x: T) => U>, f: F<T>) => F<U>`
   */
  Ap: Fn2<Kind<F, Fn1>, F, F>;

  /**
   * Build an {@link Applicative} from a value.
   *
   * **⚠️ Warning:** Correctness of the method is not fully checked, so be careful when implementing
   * this method.
   *
   * Sig: `<F<~>, T>(x: T) => F<T>`
   */
  Of: Fn1<unknown, F>;
}

/**
 * Implementations for type class {@link Applicative}.
 */
export interface ApplicativeImpl {}

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

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

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

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

/***********
 * Methods *
 ***********/
/**
 * Methods for `Applicative`.
 */
export namespace Applicative {
  /**
   * [Fn] Apply an {@link Applicative} of a function to an {@link Applicative} of a value.
   *
   * Sig: `<F<~>, T, U>[f: F<T>](fab: F<(x: T) => U>) => F<U>`
   */
  export type Ap<F extends Applicative> = PartialApply<ApFn, [F], "_1">;
}