numolus/src/engine/__tests__/dates.spec.ts

import { describe, it, expect } from 'vitest';
import {
  dateToSerial,
  timeSerial,
  serialToUtcDate,
  todaySerial,
  parseDateTimeLiteral,
} from '../dates';

describe('dateToSerial / serialToUtcDate', () => {
  it('epoch is 1899-12-30: serial 1 = 1899-12-31, serial 2 = 1900-01-01', () => {
    expect(dateToSerial(1899, 12, 31)).toBe(1);
    expect(dateToSerial(1900, 1, 1)).toBe(2);
  });

  it('round-trips through serialToUtcDate', () => {
    const s = dateToSerial(2026, 9, 2);
    const d = serialToUtcDate(s);
    expect(d.getUTCFullYear()).toBe(2026);
    expect(d.getUTCMonth()).toBe(8); // 0-based
    expect(d.getUTCDate()).toBe(2);
  });

  it('allows overflow, like Excel DATE() (month 13 -> next January)', () => {
    const s = dateToSerial(2026, 13, 1);
    const d = serialToUtcDate(s);
    expect(d.getUTCFullYear()).toBe(2027);
    expect(d.getUTCMonth()).toBe(0);
    expect(d.getUTCDate()).toBe(1);
  });

  it('carries a fractional part for a time-of-day component', () => {
    const s = dateToSerial(2026, 9, 2, 12, 0, 0);
    expect(s % 1).toBeCloseTo(0.5, 10);
  });
});

describe('timeSerial', () => {
  it('noon = 0.5, midnight = 0', () => {
    expect(timeSerial(12, 0, 0)).toBeCloseTo(0.5, 10);
    expect(timeSerial(0, 0, 0)).toBe(0);
  });

  it('wraps past 24h like Excel TIME()', () => {
    expect(timeSerial(25, 0, 0)).toBeCloseTo(1 / 24, 10);
  });
});

describe('todaySerial', () => {
  it('matches the local calendar date', () => {
    const n = new Date();
    expect(todaySerial()).toBe(Math.trunc(dateToSerial(n.getFullYear(), n.getMonth() + 1, n.getDate())));
  });
});

describe('parseDateTimeLiteral', () => {
  it('recognizes ISO dates', () => {
    const r = parseDateTimeLiteral('2026-09-02');
    expect(r).toEqual({ kind: 'date', serial: dateToSerial(2026, 9, 2) });
  });

  it('recognizes ISO datetimes (space or T separator, optional seconds)', () => {
    expect(parseDateTimeLiteral('2026-09-02 14:30')).toEqual({
      kind: 'datetime',
      serial: dateToSerial(2026, 9, 2, 14, 30, 0),
    });
    expect(parseDateTimeLiteral('2026-09-02T14:30:15')).toEqual({
      kind: 'datetime',
      serial: dateToSerial(2026, 9, 2, 14, 30, 15),
    });
  });

  it('recognizes dot dates, 4- and 2-digit years', () => {
    expect(parseDateTimeLiteral('02.09.2026')).toEqual({
      kind: 'date',
      serial: dateToSerial(2026, 9, 2),
    });
    expect(parseDateTimeLiteral('02.09.26')).toEqual({
      kind: 'date',
      serial: dateToSerial(2026, 9, 2),
    });
    expect(parseDateTimeLiteral('02.09.99')).toEqual({
      kind: 'date',
      serial: dateToSerial(1999, 9, 2),
    });
  });

  it('recognizes dot datetimes', () => {
    expect(parseDateTimeLiteral('02.09.2026 14:30')).toEqual({
      kind: 'datetime',
      serial: dateToSerial(2026, 9, 2, 14, 30, 0),
    });
  });

  it('recognizes plain times', () => {
    expect(parseDateTimeLiteral('14:30')).toEqual({ kind: 'time', serial: timeSerial(14, 30, 0) });
    expect(parseDateTimeLiteral('14:30:15')).toEqual({ kind: 'time', serial: timeSerial(14, 30, 15) });
  });

  it('does NOT recognize slash-separated dates (day-first/month-first ambiguity)', () => {
    expect(parseDateTimeLiteral('02/09/2026')).toBeNull();
  });

  it('rejects an out-of-range or rolled-over date instead of silently guessing', () => {
    expect(parseDateTimeLiteral('31.04.2026')).toBeNull(); // April has 30 days
    expect(parseDateTimeLiteral('30.02.2026')).toBeNull(); // no Feb 30
    expect(parseDateTimeLiteral('2026-13-01')).toBeNull(); // month 13
  });

  it('rejects an out-of-range time', () => {
    expect(parseDateTimeLiteral('25:00')).toBeNull();
    expect(parseDateTimeLiteral('12:60')).toBeNull();
  });

  it('does not misfire on plain numbers or arbitrary text', () => {
    expect(parseDateTimeLiteral('1234.5')).toBeNull();
    expect(parseDateTimeLiteral('hello')).toBeNull();
    expect(parseDateTimeLiteral('')).toBeNull();
  });
});