import type { List } from ".";
import type { Concat } from "./Concat";
// @ts-ignore - Only used in doc comments
import type ConcatFn from "./Concat";
// @ts-ignore - Only used in doc comments
import type { Extend } from "./Extend";
// @ts-ignore - Only used in doc comments
import type ExtendFn from "./Extend";
import type { Args, GenericFn, GenericResolver } from "../HKT";
import type { Broaden } from "../helpers";

/**
 * Extend a {@link List} by concatenating another {@link List} on the **left**.
 *
 * It is actually an alias of {@link Concat}.
 *
 * Sig: `<T>(ys: List<T>, xs: List<T>) => List<T>`
 *
 * @see {@link Extend} for the opposite.
 */
export type ExtendLeft<US extends List, TS extends List> = Concat<US, TS>;

interface Resolver extends GenericResolver<[List, List], List> {
  on1_: ([ys]: Args<this>) => [
    [List<Broaden<(typeof ys)[number]>>],
    List<Broaden<(typeof ys)[number]>>,
  ];
  on_1: ([, xs]: Args<this>) => [
    [List<Broaden<(typeof xs)[number]>>],
    List<Broaden<(typeof xs)[number]>>,
  ];
  on11: ([ys, xs]: Args<this>) => [[], List<(typeof xs)[number] | (typeof ys)[number]>];
}

/**
 * [Fn] Extend a {@link List} by concatenating another {@link List} on the **left**.
 *
 * It is actually an alias of {@link ConcatFn}.
 *
 * Sig: `<T>(ys: List<T>, xs: List<T>) => List<T>`
 *
 * @see {@link ExtendFn} for the opposite.
 */
export default interface ExtendLeftFn extends GenericFn<Resolver> {
  def: ([ys, xs]: Args<this>) => Concat<typeof ys, typeof xs>;
}