import { describe, expect, it } from '@jest/globals';
import { undef } from '../src/core';
import { toBoolean as $b, fromBoolean as _b, not } from '../src/bool';
import { toNumber as $n, fromNumber as _n, succ } from '../src/num';
import { Pair, both, first, fst, second, snd } from '../src/pair';

describe('Pair', () => {
  describe('fst', () => {
    it('returns first', () => {
      expect($b(fst._(Pair._(_b(false))._(_n(0))))).toBe(false);
    });

    it('ignores second', () => {
      expect($b(fst._(Pair._(_b(false))._(undef)))).toBe(false);
    });
  });

  describe('snd', () => {
    it('returns second', () => {
      expect($n(snd._(Pair._(_b(false))._(_n(0))))).toBe(0);
    });

    it('ignores first', () => {
      expect($n(snd._(Pair._(undef)._(_n(0))))).toBe(0);
    });
  });

  describe('first', () => {
    it('updates first', () => {
      expect($b(fst._(first._(not)._(Pair._(_b(false))._(_n(0)))))).toBe(true);
    });

    it('ignores second', () => {
      expect($b(fst._(first._(not)._(Pair._(_b(false))._(undef))))).toBe(true);
    });
  });

  describe('second', () => {
    it('updates second', () => {
      expect($n(snd._(second._(succ)._(Pair._(_b(false))._(_n(0)))))).toBe(1);
    });

    it('ignores first', () => {
      expect($n(snd._(second._(succ)._(Pair._(undef)._(_n(0)))))).toBe(1);
    });
  });

  describe('both', () => {
    it('updates both', () => {
      expect($b(fst._(both._(not)._(succ)._(Pair._(_b(false))._(_n(0)))))).toBe(true);
      expect($n(snd._(both._(not)._(succ)._(Pair._(_b(false))._(_n(0)))))).toBe(1);
    });
  });
});