when.ts

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

import type { FuncArr1, PH, Predicate1 } from './utils/types.ts';
import curryN from './utils/curry_n.ts';

// @types
type When_1<T, R> = (predicate: Predicate1<T>) => T | R;

type When_2<T> = <R>(func: FuncArr1<T, R>) => T | R;

type When_3<T, R> = (value: T) => T | R;

type When_2_3<T> =
  & (<R>(func: FuncArr1<T, R>) => When_3<T, R>)
  & ((func: PH, value: T) => When_2<T>)
  & (<R>(func: FuncArr1<T, R>, value: T) => T | R);

type When_1_3<T, R> =
  & ((predicate: Predicate1<T>) => When_3<T, R>)
  & ((predicate: PH, value: T) => When_1<T, R>)
  & ((predicate: Predicate1<T>, value: T) => T | R);

type When_1_2<T> =
  & ((predicate: Predicate1<T>) => When_2<T>)
  & (<R>(predicate: PH, func: FuncArr1<T, R>) => When_1<T, R>)
  & (<R>(predicate: Predicate1<T>, func: FuncArr1<T, R>) => T | R);

type When =
  & (<T>(predicate: Predicate1<T>) => When_2_3<T>)
  & (<T, R>(predicate: PH, func: FuncArr1<T, R>) => When_1_3<T, R>)
  & (<T>(predicate: PH, func: PH, value: T) => When_1_2<T>)
  & (<T, R>(predicate: Predicate1<T>, func: FuncArr1<T, R>) => When_3<T, R>)
  & (<T>(predicate: Predicate1<T>, func: PH, value: T) => When_2<T>)
  & (<T, R>(predicate: PH, func: FuncArr1<T, R>, value: T) => When_1<T, R>)
  & (<T, R>(predicate: Predicate1<T>, func: FuncArr1<T, R>, value: T) => T | R);

function _when<T, R>(
  predicate: Predicate1<T>,
  func: FuncArr1<T, R>,
  value: T,
): T | R {
  return predicate(value) ? func(value) : value;
}

/**
 * Applies `func` on `value` if the test `predicate` is true and returns it;
 * returns `value` otherwise.
 *
 *      const truncate = Fae.when(
 *        Fae.propSatisfies(Fae.gt(Fae._, 10), 'length'),
 *        Fae.pipe(Fae.take(10), Fae.append('…'), Fae.join(''))
 *      );
 *      truncate('12345');         //=> '12345'
 *      truncate('0123456789ABC'); //=> '0123456789…'
 */
export const when = curryN(3, _when) as When;