import type { List } from ".";
import type { Args, GenericFn, GenericResolver } from "../HKT";

/**
 * Reverse a {@link List}.
 *
 * Sig: `<T>(xs: List<T>) => List<T>`
 */
export type Reverse<TS extends List> =
  TS extends unknown[] ? ReverseWritable<TS, []> : ReverseReadonly<TS, readonly []>;
type ReverseReadonly<TS extends List, Result extends List> =
  TS extends readonly [infer Head, ...infer Tail] ?
    ReverseReadonly<Tail, readonly [Head, ...Result]>
  : Result;
type ReverseWritable<TS extends List, Result extends List> =
  TS extends readonly [infer Head, ...infer Tail] ? ReverseWritable<Tail, [Head, ...Result]>
  : Result;

interface Resolver extends GenericResolver<[List<unknown>], List<unknown>> {
  on1: ([xs]: Args<this>) => [
    [],
    typeof xs extends (infer T)[] ? T[]
    : typeof xs extends readonly (infer T)[] ? readonly T[]
    : never,
  ];
}

/**
 * [Fn] Reverse a {@link List}.
 *
 * Sig: `<T>(xs: List<T>) => List<T>`
 */
export default interface ReverseFn extends GenericFn<Resolver> {
  def: ([xs]: Args<this>) => Reverse<typeof xs>;
}