import { describe, expect, it } from 'vitest';

import {
  addCivilDays,
  civilDayOfWeek,
  compareCivil,
  minutesOfTime,
  toCivilDate,
  toCivilTime,
} from './civil';

const ZURICH = 'Europe/Zurich';

describe('toCivilDate / toCivilTime', () => {
  it('converts an instant to the wall clock of the shop', () => {
    // 2026-09-20T08:15:00Z is 10:15 in Zurich (CEST, UTC+2).
    const instant = new Date('2026-09-20T08:15:00Z');
    expect(toCivilDate(instant, ZURICH)).toBe('2026-09-20');
    expect(toCivilTime(instant, ZURICH)).toBe('10:15');
  });

  it('keeps the local day when UTC has already rolled over', () => {
    // 22:30 UTC is 00:30 the next day in Zurich: the civil date must follow
    // the shop, not the server.
    const instant = new Date('2026-09-20T22:30:00Z');
    expect(toCivilDate(instant, ZURICH)).toBe('2026-09-21');
    expect(toCivilTime(instant, ZURICH)).toBe('00:30');
  });

  it('reads the same instant differently in winter and in summer', () => {
    // CET (UTC+1) in January, CEST (UTC+2) in July.
    expect(toCivilTime(new Date('2026-01-15T12:00:00Z'), ZURICH)).toBe('13:00');
    expect(toCivilTime(new Date('2026-07-15T12:00:00Z'), ZURICH)).toBe('14:00');
  });
});

describe('addCivilDays', () => {
  it('walks forward across a month boundary', () => {
    expect(addCivilDays('2026-09-30', 1)).toBe('2026-10-01');
  });

  it('walks forward across a year boundary', () => {
    expect(addCivilDays('2026-12-31', 1)).toBe('2027-01-01');
  });

  it('handles a leap day', () => {
    expect(addCivilDays('2028-02-28', 1)).toBe('2028-02-29');
    expect(addCivilDays('2028-02-29', 1)).toBe('2028-03-01');
  });

  it('is unaffected by the spring daylight-saving switch', () => {
    // 2026-03-29 is the last Sunday of March: Zurich loses an hour that night.
    // Civil dates must still advance by exactly one day.
    expect(addCivilDays('2026-03-28', 1)).toBe('2026-03-29');
    expect(addCivilDays('2026-03-29', 1)).toBe('2026-03-30');
  });

  it('is unaffected by the autumn daylight-saving switch', () => {
    // 2026-10-25 is the last Sunday of October: that day has 25 hours.
    expect(addCivilDays('2026-10-24', 1)).toBe('2026-10-25');
    expect(addCivilDays('2026-10-25', 1)).toBe('2026-10-26');
  });

  it('walks backwards', () => {
    expect(addCivilDays('2026-01-01', -1)).toBe('2025-12-31');
  });
});

describe('civilDayOfWeek', () => {
  it('matches JS getDay(), Sunday first', () => {
    expect(civilDayOfWeek('2026-09-20')).toBe(0); // Sunday
    expect(civilDayOfWeek('2026-09-21')).toBe(1); // Monday
    expect(civilDayOfWeek('2026-09-26')).toBe(6); // Saturday
  });

  it('is stable across the daylight-saving switches', () => {
    expect(civilDayOfWeek('2026-03-29')).toBe(0);
    expect(civilDayOfWeek('2026-10-25')).toBe(0);
  });
});

describe('compareCivil', () => {
  it('orders dates chronologically', () => {
    expect(compareCivil('2026-09-20', '2026-09-21')).toBeLessThan(0);
    expect(compareCivil('2026-09-21', '2026-09-20')).toBeGreaterThan(0);
    expect(compareCivil('2026-09-20', '2026-09-20')).toBe(0);
  });

  it('orders across year boundaries', () => {
    expect(compareCivil('2026-12-31', '2027-01-01')).toBeLessThan(0);
  });
});

describe('minutesOfTime', () => {
  it('converts a wall-clock time to minutes since midnight', () => {
    expect(minutesOfTime('00:00')).toBe(0);
    expect(minutesOfTime('10:00')).toBe(600);
    expect(minutesOfTime('18:30')).toBe(1110);
    expect(minutesOfTime('23:59')).toBe(1439);
  });
});