import { describe, expect, it } from '@jest/globals';
import { toNumber as $, Num, Succ, Zero, fromNumber as _, ifz, mul, pred, sub, succ, sum } from '../src/num';

describe('Num', () => {
  describe('toNumber', () => {
    it('converts 0', () => {
      expect($(Zero)).toBe(0);
    });

    it('converts 1', () => {
      expect($(Succ._(Zero))).toBe(1);
    });

    it('converts 2', () => {
      expect($(Succ._(Succ._(Zero)))).toBe(2);
    });
  });

  describe('fromNumber', () => {
    it('converts 0', () => {
      expect($(_(0))).toBe(0);
    });

    it('converts 1', () => {
      expect($(_(1))).toBe(1);
    });

    it('converts 2', () => {
      expect($(_(2))).toBe(2);
    });
  });

  describe('ifz', () => {
    it('returns zero branch', () => {
      expect(ifz).toDeferEvaluationOf(_(0), true, false);
      expect($(ifz._(_(0))._(_(0))._(_(1)))).toBe(0);
    });

    it('returns non-zero branch', () => {
      expect(ifz).toDeferEvaluationOf(_(1), true, false);
      expect($(ifz._(_(1))._(_(0))._(_(1)))).toBe(1);
    });

    it('returns non-zero branch', () => {
      expect(ifz).toDeferEvaluationOf(_(100), true, false);
      expect($(ifz._(_(10))._(_(0))._(_(1)))).toBe(1);
    });

    it('deeply lazy', () => {
      const alot: Num = _(1000000);
      expect($(ifz._(Succ._(alot))._(_(0))._(_(1)))).toBe(1);
      expect(alot.evaluated).toBe(false);
    });
  });

  describe('succ', () => {
    it('succ 0 is 1', () => {
      expect(succ).toDeferEvaluationOf(_(0));
      expect($(succ._(_(0)))).toBe(1);
    });

    it('succ 1 is 2', () => {
      expect(succ).toDeferEvaluationOf(_(0));
      expect($(succ._(_(1)))).toBe(2);
    });

    it('succ 10 is 11', () => {
      expect(succ).toDeferEvaluationOf(_(10));
      expect($(succ._(_(10)))).toBe(11);
    });
  });

  describe('pred', () => {
    it('pred 0 is 0', () => {
      expect(pred).toDeferEvaluationOf(_(0));
      expect($(pred._(_(0)))).toBe(0);
    });

    it('pred 1 is 0', () => {
      expect(pred).toDeferEvaluationOf(_(0));
      expect($(pred._(_(1)))).toBe(0);
    });

    it('pred 10 is 9', () => {
      expect(pred).toDeferEvaluationOf(_(10));
      expect($(pred._(_(10)))).toBe(9);
    });
  });

  describe('sum', () => {
    it('0 sum 0 is 0', () => {
      expect(sum).toDeferEvaluationOf(_(0), _(0));
      expect($(sum._(_(0))._(_(0)))).toBe(0);
    });

    it('0 sum 1 is 1', () => {
      expect(sum).toDeferEvaluationOf(_(0), _(1));
      expect($(sum._(_(0))._(_(1)))).toBe(1);
    });

    it('1 sum 0 is 1', () => {
      expect(sum).toDeferEvaluationOf(_(1), _(0));
      expect($(sum._(_(1))._(_(0)))).toBe(1);
    });

    it('3 sum 4 is 7', () => {
      expect(sum).toDeferEvaluationOf(_(3), _(4));
      expect($(sum._(_(3))._(_(4)))).toBe(7);
    });
  });

  describe('sub', () => {
    it('0 sub 0 is 0', () => {
      expect(sub).toDeferEvaluationOf(_(0), _(0));
      expect($(sub._(_(0))._(_(0)))).toBe(0);
    });

    it('0 sub 1 is 0', () => {
      expect(sub).toDeferEvaluationOf(_(0), _(1));
      expect($(sub._(_(0))._(_(1)))).toBe(0);
    });

    it('1 sub 0 is 1', () => {
      expect(sub).toDeferEvaluationOf(_(1), _(0));
      expect($(sub._(_(1))._(_(0)))).toBe(1);
    });

    it('7 sub 4 is 3', () => {
      expect(sub).toDeferEvaluationOf(_(7), _(4));
      expect($(sub._(_(7))._(_(4)))).toBe(3);
    });
  });

  describe('mul', () => {
    it('0 mul 0 is 0', () => {
      expect(mul).toDeferEvaluationOf(_(0), _(0));
      expect($(mul._(_(0))._(_(0)))).toBe(0);
    });

    it('0 mul 10 is 0', () => {
      expect(mul).toDeferEvaluationOf(_(0), expect.skipped(_(10)));
      expect($(mul._(_(0))._(_(10)))).toBe(0);
    });

    it('10 mul 0 is 0', () => {
      expect(mul).toDeferEvaluationOf(_(10), _(0));
      expect($(mul._(_(1))._(_(0)))).toBe(0);
    });

    it('1 mul 10 is 10', () => {
      expect(mul).toDeferEvaluationOf(_(1), _(10));
      expect($(mul._(_(1))._(_(10)))).toBe(10);
    });

    it('10 mul 1 is 10', () => {
      expect(mul).toDeferEvaluationOf(_(10), _(1));
      expect($(mul._(_(10))._(_(1)))).toBe(10);
    });

    it('3 mul 4 is 12', () => {
      expect(mul).toDeferEvaluationOf(_(3), _(4));
      expect($(mul._(_(3))._(_(4)))).toBe(12);
    });
  });
});