either.ts

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

import curryN from './utils/curry_n.ts';
import type { Func, PH } from './utils/types.ts';
import { isFunction } from './utils/is.ts';
import { lift } from './lift.ts';
import { or } from './or.ts';

// @types
type Either_2<A extends unknown[]> = (g: Func<A>) => Func<A, boolean>;

type Either_1<A extends unknown[]> = (f: Func<A>) => Func<A, boolean>;

type Either =
  & (<A extends unknown[]>(f: Func<A>) => Either_2<A>)
  & (<A extends unknown[]>(f: PH, g: Func<A>) => Either_1<A>)
  & (<A extends unknown[]>(f: Func<A>, g: Func<A>) => Func<A, boolean>);

function _either<T extends Func>(f: T, g: T): T {
  if (isFunction(f)) {
    const __either = function (this: unknown, ...args: unknown[]) {
      return f.apply(this, args) || g.apply(this, args);
    };
    return __either as T;
  } else {
    // @ts-ignore: will remove this in future
    return lift(or)(f, g);
  }
}

/**
 * A function wrapping calls to the two functions in an `||` operation,
 * returning the result of the first function if it is true and the result
 * of the second function otherwise. Second function will not be invoked if the first returns a
 * true value.
 *
 *      const gt10 = x => x > 10
 *      const even = x => (x & 1) === 0
 *      const f = Fae.either(gt10, even)
 *      f(101) //=> true
 *      f(8) //=> true
 */
export const either = curryN(2, _either) as Either;