Correct calculation of tax on EnterpriseFees with TaxRates where included_in_price=false

app/models/spree/calculator/default_tax_decorator.rb

@@ -0,0 +1,39 @@
+require 'open_food_network/enterprise_fee_calculator'
+
+Spree::Calculator::DefaultTax.class_eval do
+
+  private
+
+  # Override this method to enable calculation of tax for
+  # enterprise fees with tax rates where included_in_price = false
+  def compute_order(order)
+    matched_line_items = order.line_items.select do |line_item|
+      line_item.product.tax_category == rate.tax_category
+    end
+
+    line_items_total = matched_line_items.sum(&:total)
+
+    # Added this line
+    calculator = OpenFoodNetwork::EnterpriseFeeCalculator.new(order.distributor, order.order_cycle)
+
+    # Added this block, finds relevant fees for each line_item, calculates the tax on them, and returns the total tax
+    per_item_fees_total = order.line_items.sum do |line_item|
+      calculator.send(:per_item_enterprise_fee_applicators_for, line_item.variant)
+      .select { |applicator| applicator.enterprise_fee.tax_category == rate.tax_category }
+      .sum { |applicator| applicator.enterprise_fee.compute_amount(line_item) }
+    end
+
+    # Added this block, finds relevant fees for whole order, calculates the tax on them, and returns the total tax
+    per_order_fees_total = calculator.send(:per_order_enterprise_fee_applicators_for, order)
+      .select { |applicator| applicator.enterprise_fee.tax_category == rate.tax_category }
+      .sum { |applicator| applicator.enterprise_fee.compute_amount(order) }
+
+    # round_to_two_places(line_items_total * rate.amount) # Removed this line
+
+    # Added this block
+    [line_items_total, per_item_fees_total, per_order_fees_total].sum do |total|
+      round_to_two_places(total * rate.amount)
+    end
+  end
+
+end

lib/open_food_network/enterprise_fee_applicator.rb

@@ -34,7 +34,7 @@ module OpenFoodNetwork
     def adjustment_tax(order, adjustment)
       tax_rates = enterprise_fee.tax_category ? enterprise_fee.tax_category.tax_rates.match(order) : []
 
-      tax_rates.sum do |rate|
+      tax_rates.select(&:included_in_price).sum do |rate|
         rate.compute_tax adjustment.amount
       end
     end

spec/models/spree/adjustment_spec.rb

@@ -137,21 +137,25 @@ module Spree
         context "when enterprise fees are taxed per-order" do
           let(:enterprise_fee) { create(:enterprise_fee, enterprise: coordinator, tax_category: tax_category, calculator: Calculator::FlatRate.new(preferred_amount: 50.0)) }
 
-          it "records the tax on the enterprise fee adjustments" do
-            # The fee is $50, tax is 10%, and the fee is inclusive of tax
-            # Therefore, the included tax should be 0.1/1.1 * 50 = $4.55
+          describe "when the tax rate includes the tax in the price" do
+            it "records the tax on the enterprise fee adjustments" do
+              # The fee is $50, tax is 10%, and the fee is inclusive of tax
+              # Therefore, the included tax should be 0.1/1.1 * 50 = $4.55
 
-            adjustment.included_tax.should == 4.55
+              adjustment.included_tax.should == 4.55
+            end
           end
 
           describe "when the tax rate does not include the tax in the price" do
             before do
               tax_rate.update_attribute :included_in_price, false
+              order.create_tax_charge! # Updating line_item or order has the same effect
               order.update_distribution_charge!
             end
 
-            it "treats it as inclusive anyway" do
-              adjustment.included_tax.should == 4.55
+            it "records the tax on TaxRate adjustment on the order" do
+              adjustment.included_tax.should == 0
+              order.adjustments.tax.first.amount.should == 5.0
             end
           end
 
@@ -172,8 +176,23 @@ module Spree
         context "when enterprise fees are taxed per-item" do
           let(:enterprise_fee) { create(:enterprise_fee, enterprise: coordinator, tax_category: tax_category, calculator: Calculator::PerItem.new(preferred_amount: 50.0)) }
 
-          it "records the tax on the enterprise fee adjustments" do
-            adjustment.included_tax.should == 4.55
+          describe "when the tax rate includes the tax in the price" do
+            it "records the tax on the enterprise fee adjustments" do
+              adjustment.included_tax.should == 4.55
+            end
+          end
+
+          describe "when the tax rate does not include the tax in the price" do
+            before do
+              tax_rate.update_attribute :included_in_price, false
+              order.create_tax_charge!  # Updating line_item or order has the same effect
+              order.update_distribution_charge!
+            end
+
+            it "records the tax on TaxRate adjustment on the order" do
+              adjustment.included_tax.should == 0
+              order.adjustments.tax.first.amount.should == 5.0
+            end
           end
         end
       end