Custom sorting rules and presenters

loads_presenter.rb

class LoadsPresenter
  extend ActiveSupport::Memoizable

  def loads; raise "Implement #loads in subclass"; end
  memoize :loads

  def each(&block)
    loads.each(&block)
  end

  def class
    Load
  end
end

scheduled_loads_presenter.rb

class ScheduledLoadsPresenter < LoadsPresenter
  def loads
    Load.scheduled.eager.map{ |l| LoadPresenter.new(l) }.sort{|x, y|
      sort_with_custom_rules(comparators, x, y)
    }
  end

  def comparators
    [SortByDeliverOn, SortByLoadTypeName, SortByCustomerName, SortByDestinationName, SortBySupplierName]
  end

  class SortByDeliverOn
    def self.compare(x, y)
      x.deliver_on <=> y.deliver_on
    end
  end

  class SortByLoadTypeName
    def self.compare(x, y)
      load_type_order = %w(Hauling Wholesale Home Vacation)
      x_index = load_type_order.index(x.load_type_name)
      y_index = load_type_order.index(y.load_type_name)
      x_index <=> y_index
    end
  end

  class SortByCustomerName
    def self.compare(x, y)
      x.customer_name <=> y.customer_name
    end
  end

  class SortByDestinationName
    def self.compare(x, y)
      x.destination_name <=> y.destination_name
    end
  end

  class SortBySupplierName
    def self.compare(x, y)
      x.supplier_name <=> y.supplier_name
    end
  end

  private
    def sort_with_custom_rules(comparators, x, y)
      comparators.each{|c| result = c.compare(x, y); return result unless result.zero? }
    end
end