class Fugit::Cron

def determine_weekdays(arr)
  @weekdays = []
  arr.each do |a, z, sl, ha, mo| # a to z, slash, hash, and mod
    if ha || mo
      @weekdays << [ a, ha || mo ]
    elsif sl
      ((a || 0)..(z || (a ? a : 6))).step(sl < 1 ? 1 : sl)
        .each { |i| @weekdays << [ i ] }
    elsif z
      z = z + 7 if a > z
      (a..z).each { |i| @weekdays << [ (i > 6) ? i - 7 : i ] }
    elsif a
      @weekdays << [ a ]
    #else
    end
  end
  @weekdays.each { |wd| wd[0] = 0 if wd[0] == 7 } # turn sun7 into sun0
  @weekdays.uniq!
  @weekdays.sort!
  @weekdays = nil if @weekdays.empty?
  true
end