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

/**
 * Get the element at index 1 of a tuple.
 *
 * Sig: `<TS extends readonly [unknown, unknown, ...unknown[]]>(xs: TS) => TS[1]`
 */
export type _1<TS extends readonly unknown[]> = TS[1];

interface Resolver extends GenericResolver<[readonly [unknown, unknown, ...unknown[]]], unknown> {
  on1: ([xs]: Args<this>) => [[], (typeof xs)[1]];
}

/**
 * [Fn] Get the element at index 1 of a tuple.
 *
 * Sig: `<TS extends readonly [unknown, unknown, ...unknown[]]>(xs: TS) => TS[1]`
 */
export default interface _1Fn extends GenericFn<Resolver> {
  def: ([xs]: Args<this>) => _1<typeof xs>;
}