moser/foxtrot_mike

module ValidityCheck
  module ClassMethods
    def valid_at(time)
      where("(valid_from <= ? OR valid_from IS NULL) AND (valid_to >= ? OR valid_to IS NULL)", time, time)
    end

    def not_valid_anymore_at(time)
      where("(valid_to < ? AND valid_to IS NOT NULL)", time)
    end

    def not_yet_valid_at(time)
      where("(valid_from > ? AND valid_from IS NOT NULL)", time)
    end
  end

  # valid_from == nil <=> valid_from = -infinity
  # valid_to == nil <=> valid_to = infinity
  def valid_at?(time = Time.zone.now)
    time = time.to_date
    (valid_from.nil? || valid_from <= time) && (valid_to.nil? || time <= valid_to)
  end

  def not_valid_anymore_at?(time = Time.zone.now)
    time = time.to_date
    !valid_to.nil? && time > valid_to
  end

  def not_yet_valid_at?(time = Time.zone.now)
    time = time.to_date
    !valid_from.nil? && valid_from > time
  end

  # The rule could be in use and thus must not be changed anymore
  # The only change allowed is to set the valid_to date (must be after
  # AccountingSession.latest_finished_session_end).
  def in_effect?
    valid_at?(AccountingSession.latest_finished_session_end)
  end

  # The rule cannot be edited anymore, because it's validity ended before
  # AccountingSession.latest_finished_session_end.
  def outdated?
    not_valid_anymore_at?(AccountingSession.latest_finished_session_end)
  end

  def not_yet_in_effect?
    not_yet_valid_at?(AccountingSession.latest_finished_session_end)
  end

  def self.included(base)
    base.extend ClassMethods
    base.validates_presence_of :valid_from
    base.validates_each :valid_to do |record, attr, value|
      unless record.valid_from.nil? || record.valid_to.nil? || record.valid_from < record.valid_to
        record.errors.add(attr, :greater_than, { :count => (I18n.l(record.valid_from, :format => :short) rescue '') } )
      end
    end
  end
end