Move our customisations of FlatPercentItemTotal calculator to a new calc: FlatPercentPerItem

app/models/calculator/flat_percent_per_item.rb

@@ -1,9 +1,19 @@
-Spree::Calculator::FlatPercentItemTotal.class_eval do
-  # Spree's calculator sums all amounts, and then calculates a percentage on them.
+require_dependency 'spree/calculator'
+
+class Calculator::FlatPercentPerItem < Spree::Calculator
+  # Spree's FlatPercentItemTotal calculator sums all amounts, and then calculates a percentage
+  # on them.
   # In the cart, we display line item individual amounts rounded, so to have consistent
   # calculations we do the same internally. Here, we round adjustments at the individual
   # item level first, then multiply by the item quantity.
 
+  preference :flat_percent, :decimal, :default => 0
+
+  attr_accessible :preferred_flat_percent
+
+  def self.description
+    I18n.t(:flat_percent_per_item)
+  end
 
   def compute(object)
     line_items_for(object).sum do |li|

config/application.rb

@@ -29,12 +29,14 @@ module Openfoodnetwork
       app.config.spree.calculators.shipping_methods << OpenFoodNetwork::Calculator::Weight
 
       app.config.spree.calculators.enterprise_fees = [Spree::Calculator::FlatPercentItemTotal,
+                                                      Calculator::FlatPercentPerItem,
                                                       Spree::Calculator::FlatRate,
                                                       Spree::Calculator::FlexiRate,
                                                       Spree::Calculator::PerItem,
                                                       Spree::Calculator::PriceSack,
                                                       OpenFoodNetwork::Calculator::Weight]
       app.config.spree.calculators.payment_methods = [Spree::Calculator::FlatPercentItemTotal,
+                                                      Calculator::FlatPercentPerItem,
                                                       Spree::Calculator::FlatRate,
                                                       Spree::Calculator::FlexiRate,
                                                       Spree::Calculator::PerItem,

config/locales/en.yml

@@ -911,6 +911,7 @@ Please follow the instructions there to make your enterprise visible on the Open
   tax_category: "Tax Category"
   calculator: "Calculator"
   calculator_values: "Calculator values"
+  flat_percent_per_item: "Flat Percent (per item)"
   new_order_cycles: "New Order Cycles"
   select_a_coordinator_for_your_order_cycle: "Select a coordinator for your order cycle"
   edit_order_cycle: "Edit Order Cycle"

spec/features/consumer/shopping/cart_spec.rb

@@ -21,7 +21,7 @@ feature "full-page cart", js: true do
     end
 
     describe "fees" do
-      let(:percentage_fee) { create(:enterprise_fee, calculator: Spree::Calculator::FlatPercentItemTotal.new(preferred_flat_percent: 20)) }
+      let(:percentage_fee) { create(:enterprise_fee, calculator: Calculator::FlatPercentPerItem.new(preferred_flat_percent: 20)) }
 
       before do
         add_enterprise_fee percentage_fee

spec/models/calculator/flat_percent_per_item_spec.rb

@@ -0,0 +1,13 @@
+describe Calculator::FlatPercentPerItem do
+  let(:calculator) { Calculator::FlatPercentPerItem.new preferred_flat_percent: 20 }
+
+  it "calculates for a simple line item" do
+    line_item = Spree::LineItem.new price: 50, quantity: 2
+    expect(calculator.compute(line_item)).to eq 20
+  end
+
+  it "rounds fractional cents before summing" do
+    line_item = Spree::LineItem.new price: 0.86, quantity: 8
+    expect(calculator.compute(line_item)).to eq 1.36
+  end
+end

spec/models/spree/calculator/flat_percent_item_total_spec.rb

@@ -1,15 +0,0 @@
-module Spree
-  describe Calculator::FlatPercentItemTotal do
-    let(:calculator) { Calculator::FlatPercentItemTotal.new preferred_flat_percent: 20 }
-
-    it "calculates for a simple line item" do
-      line_item = LineItem.new price: 50, quantity: 2
-      expect(calculator.compute(line_item)).to eq 20
-    end
-
-    it "rounds fractional cents before summing" do
-      line_item = LineItem.new price: 0.86, quantity: 8
-      expect(calculator.compute(line_item)).to eq 1.36
-    end
-  end
-end