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

    [sort_by_val_proc(:deliver_on),
     Proc.new{|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
     }, 
     sort_by_val_proc(:customer_name), 
     sort_by_val_proc(:destination_name),
     sort_by_val_proc(:supplier_name)]
  end


  private
    def sort_by_val_proc(field_name)
      Proc.new{|x,y|x.send(field_name) <=> y.send(field_name)}
    end
    def sort_with_custom_rules(comparators, x, y)
      comparators.each{|c| result = c.call(x, y); return result unless result.zero? }
    end
end