Modulo extension weeks change on Wednesday

[hughkelsey]

Issue description

When scheduling a cron to run every other week using the Modulo operator the even/odd week switches between Tuesday and Wednesday rather than Saturday and Sunday. This may in fact be an issue within EtOrbi but I'm seeing it with my cron parsing.

It would be expected that the jobs below would all run every other week on Monday and Wednesday however they actually run one week on Monday and the next week on Wednesday.
0 12 * * 1%2+1,3%2+1
0 12 * * 3%2+1
0 12 * * 1%2+1

In contrast 0 12 * * 3%2+1,4%2+1 runs every other Wed/Thursday in the same week.

How to reproduce

require 'fugit'
Date.today # "2025-09-25"
Fugit.parse_cron("0 12 * * 1%2+1,3%2+1").next.take(6).map(&:to_s).each {puts it}
# 2025-10-01 12:00:00 +0000
# 2025-10-06 12:00:00 +0000
# 2025-10-15 12:00:00 +0000
# 2025-10-20 12:00:00 +0000
# 2025-10-29 12:00:00 +0000
# 2025-11-03 12:00:00 +0000

Expected behaviour

I would expect the Monday and Wednesday to fall within the same week
2025-09-29 12:00:00 +0000
2025-10-01 12:00:00 +0000
2025-10-12 12:00:00 +0000
2025-10-15 12:00:00 +0000

This is possibly from the EtOrbi reference date 2019-01-01 being a Tuesday rather than a Sunday.

Context

Darwin Mac.home.local 24.6.0 Darwin Kernel Version 24.6.0: Mon Jul 14 11:30:51 PDT 2025; root:xnu-11417.140.69~1/RELEASE_ARM64_T8112 arm64
ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [arm64-darwin24]
[:env_tz, nil]
(secs:1758837896.222628,utc~:"2025-09-25 22:04:56.22262811660766602",ltz~:"PDT")
(etz:nil,tnz:"PDT",tziv:"2.0.6",tzidv:"1.2024.2",rv:"3.4.2",rp:"arm64-darwin24",win:false,rorv:nil,astz:nil,chronic:nil,eov:"1.3.0",eotnz:#<TZInfo::TimezoneProxy: America/Ensenada>,eotnfz:"-0700",eotlzn:"America/Ensenada",eotnfZ:"PDT",debian:nil,centos:nil,osx:"zoneinfo/America/Vancouver")
[:et_orbi, "1.3.0"]
[:fugit, "1.11.1"]
[:now, 2025-09-25 15:04:57.115353 -0700, :zone, "PDT"]

[jmettraux]

This is possibly from the EtOrbi reference date 2019-01-01 being a Tuesday rather than a Sunday.

Thanks a lot for reporting that. I have an idea on how to tune that easily so that it matches each person, whether their weeks start on Sunday, Monday, or even Saturday.

[hughkelsey]

@jmettraux - I was going to offer a hand with this but noticed your changes are there already. I pulled in your commits from EtOrbi and I think that has it solved. Thanks!!

[jmettraux]

@hughkelsey thanks a ton for testing. I'll package a new et-orbi and release it, then document the change in fugit.

[jmettraux]

Et-orbi 1.4.0 released, documented in its readme.

[jmettraux]

@hughkelsey do the specs below capture the issue? Thanks in advance

fugit/spec/cron_spec.rb

Lines 1773 to 1821 in 6b01fdf

	describe 'the module % extension' do
	# mostly about 2025-09-26 gh-114
	context 'EtOrbi.rweek_ref = :iso / :monday' do
	it 'runs "0 12 * * sun%2+1,wed%3+1" as Wed+Sun then 1w pause' do
	EtOrbi.rweek_ref = :monday # just to be sure
	expect(EtOrbi.rweek_ref).to eq('2018-12-31')
	r = Fugit.parse_cron("0 12 * * 0%2+1,3%2+1")
	.next('2025-09-25')
	.take(7)
	.map { |t| "#{t.strftime('%F %a')} #{t.rweek}" }
	expect(r).to eq([
	'2025-09-28 Sun 351', # week 351
	'2025-10-08 Wed 353', '2025-10-12 Sun 353', # week 353
	'2025-10-22 Wed 355', '2025-10-26 Sun 355', # week 355
	'2025-11-05 Wed 357', '2025-11-09 Sun 357' ]) # week 357
	end
	end
	context 'EtOrbi.rweek_ref = :us / :sunday' do
	it 'runs "0 12 * * sun%2+1,wed%3+1" as Sun+Wed then 1w pause' do
	EtOrbi.rweek_ref = :sunday
	expect(EtOrbi.rweek_ref).to eq('2018-12-30')
	r = Fugit.parse_cron("0 12 * * 0%2+1,3%2+1")
	.next('2025-09-25')
	.take(7)
	.map { |t| "#{t.strftime('%F %a')} #{t.rweek}" }
	expect(r).to eq([
	'2025-10-05 Sun 353', '2025-10-08 Wed 353', # week 353
	'2025-10-19 Sun 355', '2025-10-22 Wed 355', # week 355
	'2025-11-02 Sun 357', '2025-11-05 Wed 357', # week 357
	'2025-11-16 Sun 359' ]) # week 359
	ensure
	EtOrbi.rweek_ref = :iso # :monday
	end
	end

[hughkelsey]

@jmettraux - Looks like it yes. Quick question, is there any way to do every 4 weeks? wed%4, wed%4+1? I tried this and it appears to still just run every other week. Thx.

[jmettraux]

Quick question, is there any way to do every 4 weeks?

it 'runs every fourth week on tuesday' do

  ts = Fugit.parse_cron('20 0 * * 2%4')
    .next('2025-09-25')
    .take(14)

  tts = ts
    .each_with_index
    .map { |t, i|
      tt = i > 0 ? ts[i - 1] : nil
      d = tt ? (t.rday - tt.rday) : 0
      "#{t.strftime('%F %a')} #{t.rweek} +#{d}" }

  expect(tts).to eq([
    '2025-09-30 Tue 352 +0',
    '2025-10-28 Tue 356 +28',
    '2025-11-25 Tue 360 +28',
    '2025-12-23 Tue 364 +28',
    '2026-01-20 Tue 368 +28',
    '2026-02-17 Tue 372 +28',
    '2026-03-17 Tue 376 +28',
    '2026-04-14 Tue 380 +28',
    '2026-05-12 Tue 384 +28',
    '2026-06-09 Tue 388 +28',
    '2026-07-07 Tue 392 +28',
    '2026-08-04 Tue 396 +28',
    '2026-09-01 Tue 400 +28',
    '2026-09-29 Tue 404 +28' ])
end

wed%4, wed%4+1? I tried this and it appears to still just run every other week

I don't see it "just run every other week", I see it running every fourth week, the wed%4 seeming to push out the wed%4+1.

Is that what you are seeing?

#ts = Fugit.parse_cron('12 0 * * wed%4,wed%4+1')
ts = Fugit.parse_cron('12 0 * * wed%4+1,wed%4')
  .next('2025-09-25')
  .take(14)

tts = ts
  .each_with_index
  .map { |t, i|
    tt = i > 0 ? ts[i - 1] : nil
    d = tt ? (t.rday - tt.rday) : 0
    "#{t.strftime('%F %a')} #{t.rweek} +#{d}" }

pp tts

[ "2025-10-01 Wed 352 +0",
  "2025-10-29 Wed 356 +28",
  "2025-11-26 Wed 360 +28",
  "2025-12-24 Wed 364 +28",
  "2026-01-21 Wed 368 +28",
  "2026-02-18 Wed 372 +28",
  "2026-03-18 Wed 376 +28",
  "2026-04-15 Wed 380 +28",
  "2026-05-13 Wed 384 +28",
  "2026-06-10 Wed 388 +28",
  "2026-07-08 Wed 392 +28",
  "2026-08-05 Wed 396 +28",
  "2026-09-02 Wed 400 +28",
  "2026-09-30 Wed 404 +28" ] # :-( only `wed%4` seems to appear, I want `wed%4+1` to appear as well...