import type { List } from ".";
import type { Args, GenericFn, GenericResolver } from "../HKT";
import type { None, Option, Some } from "../Option";

/**
 * Get all elements in a {@link List} except the first one.
 *
 * Sig: `<T>(xs: List<T>) => Option<List<T>>`
 */
export type Tail<TS extends List> =
  TS extends readonly [unknown, ...infer Tail] ? Some<Tail> : None;

interface Resolver extends GenericResolver<[List], Option<List<unknown>>> {
  on1: ([xs]: Args<this>) => [
    [],
    Option<typeof xs extends unknown[] ? (typeof xs)[number][] : List<(typeof xs)[number]>>,
  ];
}

/**
 * [Fn] Get all elements in a {@link List} except the first one.
 *
 * Sig: `<T>(xs: List<T>) => Option<List<T>>`
 */
export default interface TailFn extends GenericFn<Resolver> {
  def: ([xs]: Args<this>) => Tail<typeof xs>;
}