class Fugit::Cron

def brute_frequency(year=2017)


Nota bene: cron with seconds are not supported.

a leap second on 2016-12-31)
2017 is a non leap year (though it is preceded by

Avoid for "business" use, it's slow.
Mostly used as a #next_time sanity check. 
def brute_frequency(year=2017)
  FREQUENCY_CACHE["#{to_cron_s}|#{year}"] ||=
    begin
      deltas = []
      t = EtOrbi.make_time("#{year}-01-01") - 1
      t0 = nil
      t1 = nil
      loop do
        t1 = next_time(t)
        deltas << (t1 - t).to_i if t0
        t0 ||= t1
        break if deltas.any? && t1.year > year
        break if t1.year - t0.year > 7
        t = t1
      end
      Frequency.new(deltas, t1 - t0)
    end
end