class Pagy::Calendar::Helper

def init(conf, period, params)
  new.send(:init, conf, period, params)
end

def init(conf, period, params)
  @units = Calendar::UNITS & conf.keys # get the units in time length desc order
  raise ArgumentError, 'no calendar unit found in pagy_calendar @configuration' if @units.empty?
  @period     = period
  @params     = params
  @page_param = conf[:pagy][:page_param] || DEFAULT[:page_param]
  @conf       = Marshal.load(Marshal.dump(conf))  # store a copy
  @units.each do |unit|  # set all the :page_param vars for later deletion
    unit_page_param         = :"#{unit}_#{@page_param}"
    conf[unit][:page_param] = unit_page_param
    conf[unit][:page]       = @params[unit_page_param]
  end
  calendar = {}
  object   = nil
  @units.each_with_index do |unit, index|
    params_to_delete    = @units[(index + 1), @units.size].map { |sub| conf[sub][:page_param] } + [@page_param]
    conf[unit][:params] = lambda do |unit_params|  # delete page_param from the sub-units
                            # Hash#except missing from ruby 2.5 baseline
                            params_to_delete.each { |p| unit_params.delete(p.to_s) }
                            unit_params
                          end
    conf[unit][:period] = object&.send(:active_period) || @period
    calendar[unit]      = object = Calendar.send(:create, unit, conf[unit])
  end
  [replace(calendar), object.from, object.to]
end

def last_object_at(time)
  conf        = Marshal.load(Marshal.dump(@conf))
  page_params = {}
  @units.inject(nil) do |object, unit|
    conf[unit][:period] = object&.send(:active_period) || @period
    conf[unit][:page]   = page_params[:"#{unit}_#{@page_param}"] \
                        = Calendar.send(:create, unit, conf[unit]).send(:page_at, time)
    conf[unit][:params] ||= {}
    conf[unit][:params].merge!(page_params)
    Calendar.send(:create, unit, conf[unit])
  end
end