import { describe, it, expect } from 'vitest'
import { fiscalWeek, fiscalWeekYear } from './fiscalWeek'

/**
 * The number has to match what the classic ASP site shows, because people will
 * have both open. The awkward cases are all at the year boundary, which is
 * exactly where a naive "day of year / 7" gets it wrong.
 */
describe('fiscalWeek', () => {
  it('counts the week containing 4 January as week 1', () => {
    expect(fiscalWeek(new Date(2026, 0, 4))).toBe(1)
  })

  it('puts a late-December date in week 1 of the NEXT year', () => {
    // 2025-12-29 is a Monday; its Thursday falls in 2026, so it is 2026 week 1.
    expect(fiscalWeek(new Date(2025, 11, 29))).toBe(1)
    expect(fiscalWeekYear(new Date(2025, 11, 29))).toBe(2026)
  })

  it('puts an early-January date in the LAST week of the previous year', () => {
    // 2027-01-01 is a Friday; its Thursday is 2026-12-31, so it is 2026 week 53.
    expect(fiscalWeek(new Date(2027, 0, 1))).toBe(53)
    expect(fiscalWeekYear(new Date(2027, 0, 1))).toBe(2026)
  })

  it('holds the same number all week, Monday through Sunday', () => {
    const monday = new Date(2026, 7, 10)
    const week = fiscalWeek(monday)
    for (let i = 0; i < 7; i++) {
      const day = new Date(2026, 7, 10 + i)
      expect(fiscalWeek(day)).toBe(week)
    }
  })

  it('increments the following Monday', () => {
    expect(fiscalWeek(new Date(2026, 7, 17))).toBe(fiscalWeek(new Date(2026, 7, 10)) + 1)
  })

  it('gives a 53-week year its 53rd week', () => {
    // 2026 starts on a Thursday, so it runs to 53 weeks.
    expect(fiscalWeek(new Date(2026, 11, 31))).toBe(53)
  })

  it('is not fooled by a time of day', () => {
    const morning = new Date(2026, 7, 12, 6, 0, 0)
    const nearMidnight = new Date(2026, 7, 12, 23, 59, 0)
    expect(fiscalWeek(morning)).toBe(fiscalWeek(nearMidnight))
  })
})
