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

/**
 * Pick properties from an object.
 *
 * Sig: `<K extends keyof O, O>(k: K, o: O) => object`
 */
type Pick_<K extends keyof O, O> = Pick<O, K>;
export type { Pick_ as Pick };

interface Resolver extends GenericResolver<[PropertyKey, object], object> {
  on1_: ([k]: Args<this>) => [
    [{ readonly [P in typeof k]: any }],
    { readonly [P in typeof k]: unknown },
  ];
  on_1: ([, o]: Args<this>) => [[keyof typeof o], object];
  on11: ([k, o]: Args<this>) => [
    [],
    IsPropertyKeyLiteral<typeof k> extends true ?
      { [P in keyof typeof o as P extends typeof k ? P : never]: (typeof o)[P] } extends infer R ?
        Eq<R, typeof o> extends true ?
          typeof o
        : R
      : never
    : { readonly [P in typeof k]: (typeof o)[keyof typeof o] } extends infer R ?
      Eq<R, typeof o> extends true ?
        typeof o
      : R
    : never,
  ];
}

/**
 * [Fn] Pick properties from an object.
 *
 * Sig: `<K extends keyof O, O>(k: K, o: O) => object`
 */
export default interface PickFn extends GenericFn<Resolver> {
  def: ([k, o]: Args<this>) => {
    [P in keyof typeof o as P extends typeof k ? P : never]: (typeof o)[P];
  };
}