Set option type on product when variant unit changed

app/models/spree/product_decorator.rb

@@ -17,6 +17,7 @@ Spree::Product.class_eval do
                         if: -> p { p.variant_unit == 'items' }
 
   after_initialize :set_available_on_to_now, :if => :new_record?
+  after_save :update_units
 
 
   # -- Joins
@@ -106,4 +107,25 @@ Spree::Product.class_eval do
   def set_available_on_to_now
     self.available_on ||= Time.now
   end
+
+
+  def update_units
+    if variant_unit_changed?
+      option_types.delete self.class.all_variant_unit_option_types
+      option_types << option_type_for_variant_unit if variant_unit.present?
+    end
+  end
+
+  def option_type_for_variant_unit
+    option_type_name = "unit_#{variant_unit}"
+    option_type_presentation = variant_unit.capitalize
+
+    Spree::OptionType.find_by_name(option_type_name) ||
+      Spree::OptionType.create!(name: option_type_name, presentation: option_type_presentation)
+  end
+
+  def self.all_variant_unit_option_types
+    Spree::OptionType.where('name LIKE ?', 'unit_%%')
+  end
+
 end

spec/models/spree/product_spec.rb

@@ -302,5 +302,96 @@ module Spree
         p1.should_not be_in_order_cycle oc2
       end
     end
+
+    describe "variant units" do
+      context "when the product initially has no variant unit" do
+        let!(:p) { create(:simple_product,
+                          variant_unit: nil,
+                          variant_unit_scale: nil,
+                          variant_unit_name: nil) }
+
+        context "when the required option type does not exist" do
+          it "creates the option type and assigns it to the product" do
+            expect {
+              p.update_attributes!(variant_unit: 'weight', variant_unit_scale: 1000)
+            }.to change(Spree::OptionType, :count).by(1)
+
+            ot = Spree::OptionType.last
+            ot.name.should == 'unit_weight'
+            ot.presentation.should == 'Weight'
+
+            p.option_types.should == [ot]
+          end
+
+          it "does the same with volume" do
+            expect {
+              p.update_attributes!(variant_unit: 'volume', variant_unit_scale: 1000)
+            }.to change(Spree::OptionType, :count).by(1)
+
+            ot = Spree::OptionType.last
+            ot.name.should == 'unit_volume'
+            ot.presentation.should == 'Volume'
+
+            p.option_types.should == [ot]
+          end
+
+          it "does the same with items" do
+            expect {
+              p.update_attributes!(variant_unit: 'items', variant_unit_name: 'packet')
+            }.to change(Spree::OptionType, :count).by(1)
+
+            ot = Spree::OptionType.last
+            ot.name.should == 'unit_items'
+            ot.presentation.should == 'Items'
+
+            p.option_types.should == [ot]
+          end
+        end
+
+        context "when the required option type already exists" do
+          let!(:ot) { create(:option_type, name: 'unit_weight', presentation: 'Weight') }
+
+          it "looks up the option type and assigns it to the product" do
+            expect {
+              p.update_attributes!(variant_unit: 'weight', variant_unit_scale: 1000)
+            }.to change(Spree::OptionType, :count).by(0)
+
+            p.option_types.should == [ot]
+          end
+        end
+      end
+
+      context "when the product already has a variant unit set (and all required option types exist)" do
+        let!(:p) { create(:simple_product,
+                          variant_unit: 'weight',
+                          variant_unit_scale: 1,
+                          variant_unit_name: nil) }
+
+        let!(:ot_volume) { create(:option_type, name: 'unit_volume', presentation: 'Volume') }
+
+        it "removes the old option type and assigns the new one" do
+          p.update_attributes!(variant_unit: 'volume', variant_unit_scale: 0.001)
+          p.option_types.should == [ot_volume]
+        end
+
+        it "removes the related option values from all its variants"
+
+        it "leaves option type unassigned if none is provided"
+
+        it "does not remove and re-add the option type if it is not changed" do
+          p.option_types.should_receive(:delete).never
+          p.update_attributes!(name: 'foo')
+        end
+      end
+
+      it "finds all variant unit option types" do
+        ot1 = create(:option_type, name: 'unit_weight', presentation: 'Weight')
+        ot2 = create(:option_type, name: 'unit_volume', presentation: 'Volume')
+        ot3 = create(:option_type, name: 'unit_items', presentation: 'Items')
+        ot4 = create(:option_type, name: 'foo_unit_bar', presentation: 'Foo')
+
+        Spree::Product.all_variant_unit_option_types.sort.should == [ot1, ot2, ot3].sort
+      end
+    end
   end
 end