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

/**
 * Append an element to a tuple.
 *
 * Sig: `<TS extends readonly unknown[], U>(y: U, xs: TS) => [...TS, U]`
 */
export type Append<U, TS extends readonly unknown[]> =
  TS extends unknown[] ? [...TS, U] : readonly [...TS, U];

interface Resolver extends GenericResolver<[unknown, readonly unknown[]], readonly unknown[]> {
  on1_: ([y]: Args<this>) => [[readonly unknown[]], readonly unknown[]];
  on_1: ([, xs]: Args<this>) => [
    [unknown],
    typeof xs extends unknown[] ? [...typeof xs, unknown] : readonly [...typeof xs, unknown],
  ];
  on11: ([y, xs]: Args<this>) => [
    [],
    typeof xs extends unknown[] ? [...typeof xs, typeof y] : readonly [...typeof xs, typeof y],
  ];
}

/**
 * [Fn] Append an element to a tuple.
 *
 * Sig: `<TS extends readonly unknown[], U>(y: U, xs: TS) => [...TS, U]`
 */
export default interface AppendFn extends GenericFn<Resolver> {
  def: ([y, xs]: Args<this>) => Append<typeof y, typeof xs>;
}