Yearly rules not completing

[sarge]

Hello, firstly thanks for the library! Elixir is missing a complete implementation.

I wish to help improve the rrule coverage. In testing a range of icalendar rules I have found a few gaps that I wish to help with. I am by no means a RRULE expert it has an extremely broad set rules.

These will be known to you, BYSETPOS BYMONTHDAY etc.

This is intended to capture an RRULE like FREQ=YEARLY;BYDAY=5MO

   test "yearly with days" do
      rule = Rule.new(:yearly, days: [{5, :monday}])
      |> IO.inspect(label: "state")
        |> Rule.init(~U[2025-02-01 07:00:00Z])
      assert rule.state.next == ~N[2025-02-03T07:00:00]

      rule = Rule.next(rule)
      assert rule.state.next == ~N[2026-02-02T07:00:00]

      rule = Rule.next(rule)
      assert rule.state.next == ~N[2027-02-01T07:00:00]
    end

In my investigation my thoughts are that the frequency needs to be passed down into the days.ex validation, I also suspect all of the BY... rules might need to be added to the days.ex? What are your thoughts on this? It might be a significant refactor.

Let me know if you open to PRs to support these features.

[Matsa59]

Effectively this is an interesting problem.
I don't think adding that will be a big problem.

The lock for month is a mistake and should be removed. Every others locks are good.
We should create a new validation for month. By adding yearly we should add special behaviour for the month validation.

1. The days validation is present.

• We have a days_by_week not empty, so skip it
• Otherwise add a new Month validation that will force the same month it not present

2. days is not present, and month is not present add the Month validation for every month

This will also add a new support of RRULE BYMONTH

[Matsa59]

That's really intense (as always for RRULE)

First, we miss MonthOfYear validation (this one is really important)

Once validations are build, we should put_new days with current day number and have the same behaviour for month. So we could remove lock for month and day.

Then on the next we should provide the frequency. Because 5MO means the 5th monday depending of the frequency. Also just monday should generate every monday of the year (52 results). Currently FREQ=yearly;BYDAY=MO will returns 1 result instead of 52.

In general, I wonder if we should not simply remove the lock system in favor of default validation.