Move option value naming logic into separate lib class

lib/open_food_network/option_value_namer.rb

@@ -0,0 +1,59 @@
+module OpenFoodNetwork
+  class OptionValueNamer < Struct.new(:variant)
+    def name
+      value, unit = self.option_value_value_unit
+      separator = self.value_scaled? ? '' : ' '
+
+      name_fields = []
+      name_fields << "#{value}#{separator}#{unit}" if value.present? && unit.present?
+      name_fields << variant.unit_description   if variant.unit_description.present?
+      name_fields.join ' '
+    end
+
+    def value_scaled?
+      variant.product.variant_unit_scale.present?
+    end
+
+    def option_value_value_unit
+      if variant.unit_value.present?
+        if %w(weight volume).include? variant.product.variant_unit
+          value, unit_name = self.option_value_value_unit_scaled
+
+        else
+          value = variant.unit_value
+          unit_name = variant.product.variant_unit_name
+          unit_name = unit_name.pluralize if value > 1
+        end
+
+        value = value.to_i if value == value.to_i
+
+      else
+        value = unit_name = nil
+      end
+
+      [value, unit_name]
+    end
+
+    def option_value_value_unit_scaled
+      unit_scale, unit_name = self.scale_for_unit_value
+
+      value = variant.unit_value / unit_scale
+
+      [value, unit_name]
+    end
+
+    def scale_for_unit_value
+      units = {'weight' => {1.0 => 'g', 1000.0 => 'kg', 1000000.0 => 'T'},
+               'volume' => {0.001 => 'mL', 1.0 => 'L',  1000000.0 => 'ML'}}
+
+      # Find the largest available unit where unit_value comes to >= 1 when expressed in it.
+      # If there is none available where this is true, use the smallest available unit.
+      unit = units[variant.product.variant_unit].select { |scale, unit_name|
+        variant.unit_value / scale >= 1
+      }.to_a.last
+      unit = units[variant.product.variant_unit].first if unit.nil?
+
+      unit
+    end
+  end
+end