nth.ts

// Copyright (c) 2020 Jozty. All rights reserved. MIT license.

import type { FunctorWithArLk, PH } from './utils/types.ts';
import { isArrayLike, isIterable, isIterator, isString } from './utils/is.ts';
import { getIterable } from './utils/get.ts';
import { throwFunctorError } from './utils/throw.ts';
import type { InferElementType } from './utils/types.ts';
import curryN from './utils/curry_n.ts';

// @types
type Nth_2 = <F extends FunctorWithArLk | string>(
  functor: F,
) => InferElementType<F>;

type Nth_1<F extends FunctorWithArLk | string> = (
  index: number,
) => InferElementType<F>;

type Nth =
  & ((index: number) => Nth_2)
  & (<F extends FunctorWithArLk | string>(index: PH, functor: F) => Nth_1<F>)
  & (<F extends FunctorWithArLk | string>(
    index: number,
    functor: F,
  ) => InferElementType<F>);

function _nth<F extends FunctorWithArLk<T> | string, T>(
  index: number,
  functor: F,
) {
  let f: ArrayLike<T> | string = '';

  if (isArrayLike(functor)) f = functor;
  else if (isIterable(functor)) f = [...functor] as T[];
  else if (isIterator(functor)) f = [...getIterable(functor)] as T[];
  else if (isString(functor)) f = functor;
  else throwFunctorError();

  index = index < 0 ? index + f.length : index;
  return f[index] ? f[index] : isString(functor) ? '' : f[index];
}

/**
 * Returns `index`th element of `functor`.
 * Returns element counting from right end if `index` is -ve.
 * Works in array-like/string/iterable/iterator
 */
export const nth = curryN(2, _nth) as Nth;