import { describe, it, expect } from 'vitest';
import { getISOWeek, getWeekYearLabel, getWeekBounds } from '@/lib/date-utils';

// ── getISOWeek ─────────────────────────────────────────────────────────────

describe('getISOWeek', () => {
  it('returns week 1 for January 4 (always in ISO week 1)', () => {
    expect(getISOWeek(new Date(2026, 0, 4))).toBe(1);
    expect(getISOWeek(new Date(2024, 0, 4))).toBe(1);
  });

  it('returns week 1 for Jan 1 when Jan 1 is Thursday (2026)', () => {
    // Jan 1, 2026 is a Thursday → week 1
    expect(getISOWeek(new Date(2026, 0, 1))).toBe(1);
  });

  it('returns week 53 for Dec 31 when it falls in last ISO week', () => {
    // Dec 31, 2020 is a Thursday → week 53 of 2020
    expect(getISOWeek(new Date(2020, 11, 31))).toBe(53);
  });

  it('returns correct week for a known mid-year date', () => {
    // Mar 10, 2026 is in week 11
    expect(getISOWeek(new Date(2026, 2, 10))).toBe(11);
  });

  it('returns week 52 for Dec 28 (always in ISO week 52 or 53)', () => {
    // Dec 28 is always in the last week of the year per ISO
    const week = getISOWeek(new Date(2026, 11, 28));
    expect(week).toBeGreaterThanOrEqual(52);
  });

  it('week advances by 1 between consecutive Mondays', () => {
    const w1 = getISOWeek(new Date(2026, 2, 9));  // Monday March 9
    const w2 = getISOWeek(new Date(2026, 2, 16)); // Monday March 16
    expect(w2 - w1).toBe(1);
  });

  it('same week for all days Monday through Saturday of a given week', () => {
    // Week of March 9–15, 2026
    const week = getISOWeek(new Date(2026, 2, 9)); // Monday
    expect(getISOWeek(new Date(2026, 2, 10))).toBe(week); // Tuesday
    expect(getISOWeek(new Date(2026, 2, 11))).toBe(week); // Wednesday
    expect(getISOWeek(new Date(2026, 2, 14))).toBe(week); // Saturday
  });
});

// ── getWeekYearLabel ──────────────────────────────────────────────────────

describe('getWeekYearLabel', () => {
  it('formats as "S{NN}-{YYYY}"', () => {
    const label = getWeekYearLabel(new Date(2026, 2, 10));
    expect(label).toMatch(/^S\d{2}-\d{4}$/);
  });

  it('returns "S11-2026" for March 10 2026', () => {
    expect(getWeekYearLabel(new Date(2026, 2, 10))).toBe('S11-2026');
  });

  it('zero-pads single-digit week numbers', () => {
    // Jan 4, 2026 is week 1
    expect(getWeekYearLabel(new Date(2026, 0, 4))).toBe('S01-2026');
  });
});

// ── getWeekBounds ─────────────────────────────────────────────────────────

describe('getWeekBounds', () => {
  it('returns Monday as start for a Wednesday', () => {
    const { start } = getWeekBounds(new Date(2026, 2, 11)); // Wednesday March 11
    expect(start.getDate()).toBe(9);
    expect(start.getMonth()).toBe(2); // March
    expect(start.getFullYear()).toBe(2026);
  });

  it('returns Sunday as end for a Wednesday', () => {
    const { end } = getWeekBounds(new Date(2026, 2, 11));
    expect(end.getDate()).toBe(15);
    expect(end.getMonth()).toBe(2); // March
  });

  it('start is at 00:00:00.000', () => {
    const { start } = getWeekBounds(new Date(2026, 2, 10));
    expect(start.getHours()).toBe(0);
    expect(start.getMinutes()).toBe(0);
    expect(start.getSeconds()).toBe(0);
    expect(start.getMilliseconds()).toBe(0);
  });

  it('end is at 23:59:59.999', () => {
    const { end } = getWeekBounds(new Date(2026, 2, 10));
    expect(end.getHours()).toBe(23);
    expect(end.getMinutes()).toBe(59);
    expect(end.getSeconds()).toBe(59);
    expect(end.getMilliseconds()).toBe(999);
  });

  it('start and end are 6 days apart', () => {
    const { start, end } = getWeekBounds(new Date(2026, 2, 10));
    const diffDays = (end.getTime() - start.getTime()) / (1000 * 60 * 60 * 24);
    expect(Math.floor(diffDays)).toBe(6);
  });

  it('returns same bounds for any day within the same week', () => {
    const monday = getWeekBounds(new Date(2026, 2, 9));
    const wednesday = getWeekBounds(new Date(2026, 2, 11));
    const saturday = getWeekBounds(new Date(2026, 2, 14));
    expect(monday.start.getTime()).toBe(wednesday.start.getTime());
    expect(monday.start.getTime()).toBe(saturday.start.getTime());
    expect(monday.end.getTime()).toBe(wednesday.end.getTime());
  });

  it('returns Monday as start when given a Monday', () => {
    const { start } = getWeekBounds(new Date(2026, 2, 9)); // Monday March 9
    expect(start.getDate()).toBe(9);
  });
});