import type * as P from "@principia/prelude";
import * as HKT from "@principia/prelude/HKT";

import { zipWith_ } from "./apply";
import { Functor } from "./functor";
import type { URI, V } from "./model";
import { unit } from "./unit";

/*
 * -------------------------------------------
 * Applicative Array
 * -------------------------------------------
 */

export const zip_ = <A, B>(fa: ReadonlyArray<A>, fb: ReadonlyArray<B>): ReadonlyArray<readonly [A, B]> =>
   zipWith_(fa, fb, (a, b) => [a, b]);

export const zip = <B>(fb: ReadonlyArray<B>) => <A>(fa: ReadonlyArray<A>): ReadonlyArray<readonly [A, B]> =>
   zip_(fa, fb);

export const both_ = zip_;

export const both = zip;

/**
 * ```haskell
 * pure :: a -> Array a
 * ```
 *
 * Lifts a value into an Array
 *
 * @category Applicative
 * @since 1.0.0
 */
export const pure = <A>(a: A): ReadonlyArray<A> => [a];

export const Applicative: P.Applicative<[URI], V> = HKT.instance({
   ...Functor,
   both_: zip_,
   both: zip,
   unit
});