filter.ts

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

import type { FunctorWithArLk, Obj, PH, Predicate1 } from './utils/types.ts';
import {
  isArray,
  isArrayLike,
  isIterable,
  isIterator,
  isObject,
} from './utils/is.ts';
import { reduce } from './reduce.ts';
import { throwFunctorError } from './utils/throw.ts';
import { dispatch } from './utils/dispatch.ts';
import FilterTransformer from './utils/Transformers/filter.ts';
import curryN from './utils/curry_n.ts';

// @types
type Filter_1<T> = (predicate: Predicate1<T>) => T[] | Partial<Obj<T>>;

type Filter_2<T> = (
  functor: FunctorWithArLk<T> | Obj<T>,
) => T[] | Partial<Obj<T>>;

type Filter =
  & (<T>(predicate: Predicate1<T>) => Filter_2<T>)
  & (<T>(predicate: PH, functor: FunctorWithArLk<T> | Obj<T>) => Filter_1<T>)
  & (<T>(
    predicate: Predicate1<T>,
    functor: FunctorWithArLk<T> | Obj<T>,
  ) => T[] | Partial<Obj<T>>);

function _objectFilter<T>(predicate: Predicate1<T>, functor: Obj<T>) {
  return reduce(
    (acc: Obj<T>, key: string) => {
      if (predicate(functor[key])) acc[key] = functor[key];
      return acc;
    },
    {},
    Object.keys(functor),
  );
}

function _functorFilter<T>(
  predicate: Predicate1<T>,
  functor: FunctorWithArLk<T>,
): T[] {
  return reduce(
    (acc: T[], value: T) => {
      if (predicate(value)) acc.push(value);
      return acc;
    },
    [],
    functor,
  );
}

function _filter<T = unknown>(
  predicate: Predicate1<T>,
  functor: FunctorWithArLk<T> | Obj<T>,
): T[] | Partial<Obj<T>> {
  if (isArray(functor)) return (functor as T[]).filter(predicate) as T[];

  if (
    isArrayLike(functor) ||
    isIterable(functor) ||
    isIterator(functor)
  ) {
    return _functorFilter(predicate, functor);
  }

  if (isObject(functor)) return _objectFilter(predicate, functor);
  throw throwFunctorError();
}

const dispatchedFilter = dispatch(FilterTransformer, _filter);

/**
 * Filters the those elements from `functor` that satisfies `predicate`.
 * The `functor` may be an array/object/iterable/iterator.
 *
 * Acts as a transducer if a transformer is passed in place of `functor`
 */
export const filter: Filter = curryN(2, dispatchedFilter);