change offer calculations

ecommerce/pricing/lib/pricing/commands.rb

@@ -3,6 +3,7 @@ class AddPriceItem < Infra::Command
     attribute :order_id, Infra::Types::UUID
     attribute :product_id, Infra::Types::UUID
     attribute :price, Infra::Types::Price
+    attribute :promotion, Infra::Types::Strict::Bool.default(false)
 
     alias aggregate_id order_id
   end

ecommerce/pricing/lib/pricing/discounts.rb

@@ -60,5 +60,15 @@ def add(other_discount)
       def exists?
       end
     end
+
+    class ThreePlusOneGratis
+      def apply(product_quantities, product_id, base_price)
+        product = product_quantities.find { |product_quantity| product_quantity.fetch(:product_id) == product_id }
+        return [false, base_price] if product.nil?
+        quantity = product.fetch(:quantity) + 1
+        return [false, base_price] if !quantity.%(4).eql?(0)
+        [true, 0]
+      end
+    end
   end
 end

ecommerce/pricing/lib/pricing/events.rb

@@ -36,18 +36,27 @@ class PercentageDiscountSet < Infra::Event
     attribute :order_id, Infra::Types::UUID
     attribute :type, Infra::Types::String
     attribute :amount, Infra::Types::PercentageDiscount
+    attribute :base_total_value, Infra::Types::Price
+    attribute :total_value, Infra::Types::Price
   end
 
   class PriceItemAdded < Infra::Event
     attribute :order_id, Infra::Types::UUID
     attribute :product_id, Infra::Types::UUID
+    attribute :base_price, Infra::Types::Price
     attribute :price, Infra::Types::Price
+    attribute :base_total_value, Infra::Types::Price
+    attribute :total_value, Infra::Types::Price
+    attribute? :applied_promotion, Infra::Types::String
   end
 
   class PriceItemRemoved < Infra::Event
     attribute :order_id, Infra::Types::UUID
     attribute :product_id, Infra::Types::UUID
+    attribute :base_price, Infra::Types::Price
     attribute :price, Infra::Types::Price
+    attribute :base_total_value, Infra::Types::Price
+    attribute :total_value, Infra::Types::Price
   end
 
   class PercentageDiscountRemoved < Infra::Event

ecommerce/pricing/lib/pricing/offer.rb

@@ -12,23 +12,39 @@ def initialize(id)
       @state = :draft
     end
 
-    def add_item(product_id, price)
-      apply PriceItemAdded.new(
-        data: {
-          order_id: @id,
-          product_id: product_id,
-          price: price,
-        }
-      )
+    def add_item(product_id, base_price, promotion)
+      if promotion
+        promotion_applies, price = promotion.apply(@list.quantities, product_id, base_price)
+      end
+
+      unless promotion_applies
+        price = @discounts.inject(Discounts::NoPercentageDiscount.new, :add).apply(base_price)
+      end
+
+      data = {
+        order_id: @id,
+        product_id: product_id,
+        base_price: base_price,
+        price: price,
+        base_total_value: @list.base_sum + base_price,
+        total_value: @list.actual_sum + price,
+      }
+
+      data[:applied_promotion] = promotion.class.name if promotion_applies
+
+      apply PriceItemAdded.new(data:)
     end
 
     def remove_item(product_id)
-      price = @list.lowest_price(product_id)
+      item = @list.lowest_price_item(product_id)
       apply PriceItemRemoved.new(
         data: {
           order_id: @id,
           product_id: product_id,
-          price: price
+          base_price: item.base_price,
+          price: item.price,
+          base_total_value: @list.base_sum - item.base_price,
+          total_value: @list.actual_sum - item.price
         }
       )
     end
@@ -39,7 +55,9 @@ def apply_discount(discount)
         data: {
           order_id: @id,
           type: discount.type,
-          amount: discount.value
+          amount: discount.value,
+          base_total_value: @list.base_sum,
+          total_value: @list.actual_sum - @list.actual_sum * (discount.value / 100)
         }
       )
     end
@@ -87,7 +105,7 @@ def remove_free_product(order_id, product_id)
 
     def calculate_total_value
       total_value = @list.base_sum
-      discounted_value = @discounts.inject(Discounts::NoPercentageDiscount.new, :add).apply(total_value)
+      discounted_value = @list.actual_sum
 
       apply(
         OrderTotalValueCalculated.new(
@@ -110,8 +128,8 @@ def calculate_sub_amounts
               order_id: @id,
               product_id: product_id,
               quantity: h.fetch(:quantity),
-              amount: h.fetch(:amount),
-              discounted_amount: @discounts.inject(Discounts::NoPercentageDiscount.new, :add).apply(h.fetch(:amount))
+              amount: h.fetch(:base_amount),
+              discounted_amount: h.fetch(:amount),
             }
           )
         )
@@ -156,7 +174,7 @@ def expire
     private
 
     on PriceItemAdded do |event|
-      @list.add_item(event.data.fetch(:product_id), event.data.fetch(:price))
+      @list.add_item(event.data.fetch(:product_id), event.data.fetch(:base_price), event.data.fetch(:price))
     end
 
     on PriceItemRemoved do |event|
@@ -171,15 +189,18 @@ def expire
 
     on PercentageDiscountSet do |event|
       @discounts << Discounts::PercentageDiscount.new(event.data.fetch(:type), event.data.fetch(:amount))
+      @list.apply_discounts(@discounts)
     end
 
     on PercentageDiscountChanged do |event|
       @discounts.delete_if { |discount| discount.type == event.data.fetch(:type) }
       @discounts << Discounts::PercentageDiscount.new(event.data.fetch(:type), event.data.fetch(:amount))
+      @list.apply_discounts(@discounts)
     end
 
     on PercentageDiscountRemoved do |event|
       @discounts.delete_if { |discount| discount.type == event.data.fetch(:type) }
+      @list.apply_discounts(@discounts)
     end
 
     on ProductMadeFreeForOrder do |event|
@@ -210,34 +231,49 @@ def discount_exists?(type)
     end
 
     class List
-      Item = Data.define(:product_id, :quantity, :price, :catalog_price) do
-        def initialize(product_id:, quantity:, price:, catalog_price: price) = super
-      end
+      Item = Data.define(:product_id, :quantity, :base_price, :price)
 
       def initialize
         @items = []
       end
 
-      def add_item(product_id, price)
-        @items << Item.new(product_id:, price:, quantity: 1)
+      def add_item(product_id, base_price, price)
+        @items << Item.new(product_id:, base_price:, price:, quantity: 1)
       end
 
       def remove_item(product_id, price)
         index_of_item_to_remove = @items.index { |item| item.product_id == product_id && item.price == price }
         @items.delete_at(index_of_item_to_remove)
       end
 
+      def apply_discounts(discounts)
+        @items = @items.map do |item|
+          next item if is_free?(item)
+          price = discounts.inject(Discounts::NoPercentageDiscount.new, :add).apply(item.base_price)
+          item.with(price:)
+        end
+      end
+
+      def is_free?(item)
+        item.price == 0
+      end
+
       def contains_free_products?
         @items.any? { |item| item.price == 0 }
       end
 
       def base_sum
+        @items.sum(&:base_price)
+      end
+
+      def actual_sum
         @items.sum(&:price)
       end
 
       def sub_amounts_total
         @items.each_with_object({}) do |item, memo|
-          memo[item.product_id] ||= { amount: 0, quantity: 0 }
+          memo[item.product_id] ||= { base_amount: 0, amount: 0, quantity: 0 }
+          memo[item.product_id][:base_amount] += item.base_price * item.quantity
           memo[item.product_id][:amount] += item.price * item.quantity
           memo[item.product_id][:quantity] += item.quantity
         end
@@ -253,15 +289,14 @@ def restore_nonfree(product_id)
         idx = @items.index { |item| item.product_id == product_id && item.price == 0 }
         return unless idx
         old_item = @items.delete_at(idx)
-        @items << old_item.with(price: old_item.catalog_price)
+        @items << old_item.with(price: old_item.base_price)
       end
 
-      def lowest_price(product_id)
+      def lowest_price_item(product_id)
         @items
           .select { |item| item.product_id == product_id }
           .sort_by(&:price)
           .first
-          &.price
       end
 
       def quantities

ecommerce/pricing/lib/pricing/services.rb

@@ -120,7 +120,8 @@ def initialize(event_store)
 
     def call(command)
       @repository.with_aggregate(Offer, command.aggregate_id) do |order|
-        order.add_item(command.product_id, command.price)
+        promotion = Discounts::ThreePlusOneGratis.new  if command.promotion
+        order.add_item(command.product_id, command.price, promotion)
       end
     end
   end

ecommerce/pricing/test/apply_time_promotion_test.rb

@@ -5,6 +5,7 @@ class ApplyTimePromotionTest < Test
     cover "Pricing*"
 
     def test_applies_biggest_time_promotion_discount
+
       order_id = SecureRandom.uuid
       product_id = SecureRandom.uuid
       create_inactive_time_promotion(60)
@@ -57,13 +58,18 @@ def create_active_time_promotion(discount)
     end
 
     def item_added_to_basket_event(order_id, product_id)
-      Pricing::PriceItemAdded.new(
+      price_item_added = Pricing::PriceItemAdded.new(
         data: {
           product_id: product_id,
           order_id: order_id,
-          price: 1111,
+          base_price: 1000,
+          price: 1000,
+          base_total_value: 1000,
+          total_value: 1000
           }
         )
+      event_store.append(price_item_added, stream_name: stream_name(order_id))
+      price_item_added
     end
 
     def set_time_promotion_discount(order_id, discount)
@@ -75,7 +81,9 @@ def percentage_discount_set_event(order_id, amount)
         data: {
           order_id: order_id,
           type: Pricing::Discounts::TIME_PROMOTION_DISCOUNT,
-          amount: amount
+          amount: amount,
+          base_total_value: 1000,
+          total_value: 500
         }
       )
     end

ecommerce/pricing/test/discounts_test.rb

@@ -64,5 +64,55 @@ def test_doesnt_change_total
         assert_equal(100, NoPercentageDiscount.new.apply(100))
       end
     end
+
+    class ThreePlusOneGratisTest < Test
+      cover "Pricing::Discounts*"
+      def setup
+        @three_plus_one_gratis = ThreePlusOneGratis.new
+        @product_id = SecureRandom.uuid
+      end
+
+      def test_returns_full_price_when_product_not_found
+        result = @three_plus_one_gratis.apply([], @product_id, 20)
+        assert_equal [false, 20], result
+      end
+
+      def test_returns_full_price_when_quantity_plus_one_is_less_than_4
+        quantities = [{ product_id: @product_id, quantity: 2 }]
+        result = @three_plus_one_gratis.apply(quantities, @product_id, 20)
+        assert_equal [false, 20], result
+      end
+
+      def test_returns_free_when_quantity_plus_one_is_4
+        quantities = [{ product_id: @product_id, quantity: 3 }]
+        result = @three_plus_one_gratis.apply(quantities, @product_id, 20)
+        assert_equal [true, 0], result
+      end
+
+      def test_returns_full_price_when_quantity_plus_one_is_5
+        quantities = [{ product_id: @product_id, quantity: 4 }]
+        result = @three_plus_one_gratis.apply(quantities, @product_id, 20)
+        assert_equal [false, 20], result
+      end
+
+      def test_returns_free_when_quantity_plus_one_is_8
+        quantities = [{ product_id: @product_id, quantity: 7 }]
+        result = @three_plus_one_gratis.apply(quantities, @product_id, 20)
+        assert_equal [true, 0], result
+      end
+
+      def test_returns_full_price_when_quantity_plus_one_is_9
+        quantities = [{ product_id: @product_id, quantity: 8 }]
+        result = @three_plus_one_gratis.apply(quantities, @product_id, 20)
+        assert_equal [false, 20], result
+      end
+
+      def test_does_not_confuse_other_product_ids
+        other_product_id = SecureRandom.uuid
+        quantities = [{ product_id: other_product_id, quantity: 3 }]
+        result = @three_plus_one_gratis.apply(quantities, @product_id, 20)
+        assert_equal [false, 20], result
+      end
+    end
   end
 end

ecommerce/pricing/test/free_products_test.rb

@@ -25,7 +25,7 @@ def test_making_product_free_possible_when_order_is_eligible
           data: {
             order_id: order_id,
             discounted_amount: 60,
-            total_amount: 60
+            total_amount: 80
           }
         )
       ) do
@@ -58,7 +58,7 @@ def test_making_only_the_cheapest_product_free
           data: {
             order_id: order_id,
             discounted_amount: 60,
-            total_amount: 60
+            total_amount: 70
           }
         ),
       ) do
@@ -125,7 +125,7 @@ def test_making_product_free_possible_after_previous_free_product_was_removed
           data: {
             order_id: order_id,
             discounted_amount: 60,
-            total_amount: 60
+            total_amount: 80
           }
         )
       ) do