Add a per-pound calculator and a spec for it

app/controllers/spree/admin/shipping_methods_controller.rb

@@ -88,7 +88,8 @@ module Spree
           :require_ship_address, :tag_list, :calculator_type,
           distributor_ids: [],
           calculator_attributes: [
-            :id, :preferred_currency, :preferred_amount, :preferred_per_kg, :preferred_flat_percent,
+            :id, :preferred_currency, :preferred_amount, :preferred_per_kg,
+            :preferred_per_lb, :preferred_flat_percent,
             :preferred_first_item, :preferred_additional_item, :preferred_max_items,
             :preferred_minimal_amount, :preferred_normal_amount, :preferred_discount_amount
           ]

app/models/calculator/weight_lb.rb

@@ -0,0 +1,75 @@
+require 'spree/localized_number'
+
+module Calculator
+  class WeightLb < Spree::Calculator
+    extend Spree::LocalizedNumber
+    preference :per_lb, :decimal, default: 0.0
+    localize_number :preferred_per_lb
+
+    def self.description
+      I18n.t('spree.weight_lb')
+    end
+
+    def compute(object)
+      line_items = line_items_for object
+      (total_weight(line_items) * preferred_per_lb).round(2)
+    end
+
+    private
+
+    def total_weight(line_items)
+      line_items.sum do |line_item|
+        line_item_weight(line_item)
+      end
+    end
+
+    def line_item_weight(line_item)
+      if final_weight_volume_present?(line_item)
+        weight_per_final_weight_volume(line_item)
+      else
+        weight_per_variant(line_item) * line_item.quantity
+      end
+    end
+
+    def weight_per_variant(line_item)
+      if variant_unit(line_item) == 'weight'
+        # The calculator price is per_lb so we need to convert unit_value to lb
+        convert_g_to_lb(line_item.variant.andand.unit_value)
+      else
+        line_item.variant.andand.weight || 0
+      end
+    end
+
+    def weight_per_final_weight_volume(line_item)
+      if variant_unit(line_item) == 'weight'
+        # The calculator price is per_lb so we need to convert final_weight_volume to lb
+        convert_g_to_lb(line_item.final_weight_volume)
+      else
+        weight_per_variant(line_item) * quantity_implied_in_final_weight_volume(line_item)
+      end
+    end
+
+    #  Example: 2 (line_item.quantity) wine glasses of 125mL (line_item.variant.unit_value)
+    #    Customer ends up getting 350mL (line_item.final_weight_volume) of wine
+    #      that represent 2.8 (quantity_implied_in_final_weight_volume) glasses of wine
+    def quantity_implied_in_final_weight_volume(line_item)
+      return line_item.quantity if line_item.variant.unit_value.to_f.zero?
+
+      (1.0 * line_item.final_weight_volume / line_item.variant.unit_value).round(3)
+    end
+
+    def final_weight_volume_present?(line_item)
+      line_item.respond_to?(:final_weight_volume) && line_item.final_weight_volume.present?
+    end
+
+    def variant_unit(line_item)
+      line_item.variant.product.andand.variant_unit
+    end
+
+    def convert_g_to_lb(value)
+      return 0 unless value
+
+      value / 453.6
+    end
+  end
+end

config/application.rb

@@ -54,7 +54,8 @@ module Openfoodnetwork
         Calculator::FlexiRate,
         Calculator::PerItem,
         Calculator::PriceSack,
-        Calculator::Weight
+        Calculator::Weight,
+        Calculator::WeightLb
       ]
 
       app.config.spree.calculators.add_class('enterprise_fees')
@@ -64,7 +65,8 @@ module Openfoodnetwork
         Calculator::FlexiRate,
         Calculator::PerItem,
         Calculator::PriceSack,
-        Calculator::Weight
+        Calculator::Weight,
+        Calculator::WeightLb
       ]
 
       app.config.spree.calculators.add_class('payment_methods')

config/locales/en.yml

@@ -3127,6 +3127,7 @@ See the %{link} to find out more about %{sitename}'s features and to start using
     inventory: Inventory
     zipcode: Postcode
     weight: Weight (per kg)
+    weight_lb: Weight (per lb)
     error_user_destroy_with_orders: "Users with completed orders may not be deleted"
     cannot_create_payment_without_payment_methods: "You cannot create a payment for an order without any payment methods defined."
     please_define_payment_methods: "Please define some payment methods first."

spec/controllers/spree/admin/shipping_methods_controller_spec.rb

@@ -38,6 +38,15 @@ describe Spree::Admin::ShippingMethodsController, type: :controller do
       expect(shipping_method.reload.calculator.preferred_per_kg).to eq 10
     end
 
+    it "updates preferred_per_lb of a Weight (Lb) calculator" do
+      shipping_method.calculator = create(:weight_lb_calculator, calculable: shipping_method)
+      params[:shipping_method][:calculator_attributes][:preferred_per_lb] = 10
+
+      spree_post :update, params
+
+      expect(shipping_method.reload.calculator.preferred_per_lb).to eq 10
+    end
+
     it "updates preferred_flat_percent of a FlatPercentPerItem calculator" do
       shipping_method.calculator = Calculator::FlatPercentPerItem.new(preferred_flat_percent: 20,
 

spec/factories/calculator_factory.rb

@@ -16,4 +16,9 @@ FactoryBot.define do
     after(:build)  { |c| c.set_preference(:per_kg, 0.5) }
     after(:create) { |c| c.set_preference(:per_kg, 0.5); c.save! }
   end
+
+  factory :weight_lb_calculator, class: Calculator::WeightLb do
+    after(:build)  { |c| c.set_preference(:per_lb, 0.5) }
+    after(:create) { |c| c.set_preference(:per_lb, 0.5); c.save! }
+  end
 end