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

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

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

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

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

    it('converts 1', () => {
      expect(toNumber(fromNumber(1))).toBe(1);
    });

    it('converts 2', () => {
      expect(toNumber(fromNumber(2))).toBe(2);
    });
  });

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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