Refactoring digital shipping calculation and display

* removed the deface override that modified the checkout/_delivery partial
* created custom digital delivery calculator
* removed digital_shipping_method from Spree::Order. Moved logic to available_shipping_methods monkey patch

The main goal was to eliminate the shipping method detection logic from the _delivery partial.
This was a bit of a hack all along and didn't really present the correct information to the underlying
order logic (i.e. rate_hash.blank? would return true when there was no shipping options available).
This should be more future proof and make overriding another aspect of the delivery process easier.

app/models/spree/calculator/digital_delivery.rb

@@ -0,0 +1,18 @@
+# https://github.com/spree/spree/issues/1439
+require_dependency 'spree/calculator'
+
+module Spree
+  class Calculator::DigitalDelivery < Calculator::FlatRate
+    def self.description
+      I18n.t(:digital_delivery)
+    end
+
+    def compute(object=nil)
+      self.preferred_amount
+    end
+
+    def available?(order)
+      order.digital?
+    end
+  end
+end

app/models/spree/order_decorator.rb

@@ -1,26 +1,25 @@
 Spree::Order.class_eval do
-  
-  # Are all products/variants of this Order to be downloaded by the customer?
+  # all products are digital
   def digital?
     line_items.map { |item| return false unless item.digital? }
     true
   end
   
-  # Is at least one product/variant digital?
   def some_digital?
     line_items.map { |item| return true if item.digital? }
     false
   end
-  
-  # Determine which method to use for shipping of digital products.
-  def digital_shipping_method
-    rates = rate_hash
-    # If there is a shipping method has "Download" in its name then we take that one.
-    rates.each { |rate| return rate if rate[:name].downcase.include?('download') }
-    # Other than that, we take the first one that we find that doesn't cost anything.
-    rates.each { |rate| return rate if rate[:cost] == 0 }
-    # Well, at this point we have a problem. No shipping method is cost-free or called "download".
-    nil
-  end
 
+  # TODO this works as of spree 1.1.1; make sure to check the original function on upgrade
+
+  def available_shipping_methods(display_on = nil)
+    return [] unless ship_address
+    all_methods = Spree::ShippingMethod.all_available(self, display_on)
+
+    if self.digital?
+      all_methods.detect { |m| m.calculator.class == Spree::Calculator::DigitalDelivery }.try { |d| [d] } || all_methods
+    else
+      all_methods
+    end
+  end
 end

app/models/spree/product_decorator.rb

@@ -1,4 +1,3 @@
-
 Spree::Product.class_eval do
   has_many :digitals, :through => :variants_including_master
 end

app/overrides/modify_shipping_options_display.rb

@@ -1,39 +0,0 @@
-Deface::Override.new(:virtual_path => "spree/checkout/_delivery",
-                     :name => "modify_shipping_options_display",
-                     :replace_contents => "#shipping_method #methods p.radios",
-                     :original => %q{
- <% @order.rate_hash.each do |shipping_method| %>
-   <label>
-     <%= radio_button(:order, :shipping_method_id, shipping_method[:id]) %>
-     <% if Spree::Config[:shipment_inc_vat] %>
-       <%= shipping_method[:name] %> <%= format_price (1 + Spree::TaxRate.default) * shipping_method[:cost] %>
-     <% else %>
-     <%= shipping_method[:name] %> <%= number_to_currency shipping_method[:cost] %>
-     <% end %>
-   </label>
- <% end %>
- },
-                     :text => %q{
-<% if @order.digital? && @order.digital_shipping_method.present? %>
-<label>
-  <%= radio_button :order, :shipping_method_id, @order.digital_shipping_method[:id] %>
-  <%== t 'digital_shipping', :email => @order.email %> (<%= number_to_currency @order.digital_shipping_method[:cost] %>)
-</label>
-<% else %>
-<% filtered_rate_hash = @order.rate_hash.select { |m| !(@order.digital_shipping_method && m[:id] == @order.digital_shipping_method[:id]) } %>
-<% if filtered_rate_hash.count > 0 %>
-<% filtered_rate_hash.each do |shipping_method| %>
-  <label>
-    <%= radio_button(:order, :shipping_method_id, shipping_method[:id]) %>
-    <% if Spree::Config[:shipment_inc_vat] %>
-      <%= shipping_method[:name] %> <%= format_price (1 + Spree::TaxRate.default) * shipping_method[:cost] %>
-    <% else %>
-    <%= shipping_method[:name] %> <%= number_to_currency shipping_method[:cost] %>
-    <% end %>
-  </label>
-<% end %>
-<% else %>
-<%= t :no_shipping_methods %>
-<% end %>
-<% end %>
-})