A different way to move ProcessState definition to the bottom of a process class.

This way include is on the very top of the class definition, ProcessState is passed in a block that is called later. The ProcessState definition can be moved to the very bottom of the class.
- pass a block to the with_state method
- the block is stored in the module ivar and then in the host class ivar
- the block is called during initial_state method execution, ProcssState has to be defined at this point

Author: dysk

ecommerce/processes/lib/processes/determine_vat_rates_on_order_placed.rb

@@ -1,15 +1,7 @@
 module Processes
   class DetermineVatRatesOnOrderPlaced
+    include Infra::ProcessManager.with_state { ProcessState }
 
-    ProcessState = Data.define(:offer_accepted, :order_placed, :order_id, :order_lines) do
-      def initialize(offer_accepted: false, order_placed: false, order_id: nil, order_lines: [])
-        super
-      end
-
-      def placed? = offer_accepted && order_placed
-    end
-
-    include Infra::ProcessManager.with_state(ProcessState)
     subscribes_to(
       Pricing::OfferAccepted,
       Fulfillment::OrderRegistered
@@ -46,5 +38,12 @@ def fetch_id(event)
       event.data.fetch(:order_id)
     end
 
+    ProcessState = Data.define(:offer_accepted, :order_placed, :order_id, :order_lines) do
+      def initialize(offer_accepted: false, order_placed: false, order_id: nil, order_lines: [])
+        super
+      end
+
+      def placed? = offer_accepted && order_placed
+    end
   end
 end

ecommerce/processes/lib/processes/order_item_invoicing_process.rb

@@ -1,17 +1,6 @@
 module Processes
   class OrderItemInvoicingProcess
-
-    ProcessState = Data.define(:order_id, :product_id, :quantity, :vat_rate, :discounted_amount) do
-      def initialize(order_id: nil, product_id: nil, quantity: nil, vat_rate: nil, discounted_amount: nil)
-        super
-      end
-
-      def can_create_invoice_item?
-        order_id && product_id && quantity && vat_rate && discounted_amount
-      end
-    end
-
-    include Infra::ProcessManager.with_state(ProcessState)
+    include Infra::ProcessManager.with_state { ProcessState }
 
     subscribes_to(
       Pricing::PriceItemValueCalculated,
@@ -56,6 +45,16 @@ def apply(event)
     def fetch_id(event)
       "#{event.data.fetch(:order_id)}$#{event.data.fetch(:product_id)}"
     end
+
+    ProcessState = Data.define(:order_id, :product_id, :quantity, :vat_rate, :discounted_amount) do
+      def initialize(order_id: nil, product_id: nil, quantity: nil, vat_rate: nil, discounted_amount: nil)
+        super
+      end
+
+      def can_create_invoice_item?
+        order_id && product_id && quantity && vat_rate && discounted_amount
+      end
+    end
   end
 
   class MoneySplitter

ecommerce/processes/lib/processes/release_payment_process.rb

@@ -1,17 +1,6 @@
 module Processes
   class ReleasePaymentProcess
-
-    ProcessState = Data.define(:order, :payment, :order_id) do
-      def initialize(order: :draft, payment: :none, order_id: nil)
-        super
-      end
-
-      def release?
-        payment.eql?(:authorized) && order.eql?(:expired)
-      end
-    end
-
-    include Infra::ProcessManager.with_state(ProcessState)
+    include Infra::ProcessManager.with_state { ProcessState }
 
     subscribes_to(
       Payments::PaymentAuthorized,
@@ -52,5 +41,15 @@ def release_payment
     def fetch_id(event)
       event.data.fetch(:order_id)
     end
+
+    ProcessState = Data.define(:order, :payment, :order_id) do
+      def initialize(order: :draft, payment: :none, order_id: nil)
+        super
+      end
+
+      def release?
+        payment.eql?(:authorized) && order.eql?(:expired)
+      end
+    end
   end
 end

ecommerce/processes/lib/processes/reservation_process.rb

@@ -1,14 +1,6 @@
 module Processes
   class ReservationProcess
-    ProcessState = Data.define(:order, :order_lines) do
-      def initialize(order: nil, order_lines: [])
-        super(order:, order_lines: order_lines.freeze)
-      end
-
-      def reserved_product_ids = order_lines.keys
-    end
-
-    include Infra::ProcessManager.with_state(ProcessState)
+    include Infra::ProcessManager.with_state { ProcessState }
 
     subscribes_to(
       Pricing::OfferAccepted,
@@ -92,6 +84,14 @@ def fetch_id(event)
       event.data.fetch(:order_id)
     end
 
+    ProcessState = Data.define(:order, :order_lines) do
+      def initialize(order: nil, order_lines: [])
+        super(order:, order_lines: order_lines.freeze)
+      end
+
+      def reserved_product_ids = order_lines.keys
+    end
+
     class SomeInventoryNotAvailable < StandardError
       attr_reader :unavailable_products
 

ecommerce/processes/lib/processes/shipment_process.rb

@@ -1,10 +1,6 @@
 module Processes
   class ShipmentProcess
-    ProcessState = Data.define(:order, :shipment) do
-      def initialize(order: nil, shipment: nil) = super
-    end
-
-    include Infra::ProcessManager.with_state(ProcessState)
+    include Infra::ProcessManager.with_state { ProcessState }
 
     subscribes_to(
       Shipping::ShippingAddressAddedToShipment,
@@ -47,5 +43,9 @@ def authorize_shipment
     def fetch_id(event)
       event.data.fetch(:order_id)
     end
+
+    ProcessState = Data.define(:order, :shipment) do
+      def initialize(order: nil, shipment: nil) = super
+    end
   end
 end

ecommerce/processes/lib/processes/three_plus_one_free.rb

@@ -1,21 +1,6 @@
 module Processes
   class ThreePlusOneFree
-
-    ProcessState = Data.define(:lines, :free_product) do
-      def initialize(lines: [], free_product: nil)
-        super(lines: lines.freeze, free_product:)
-      end
-
-      MIN_ORDER_LINES_QUANTITY = 4
-
-      def eligible_free_product
-        if lines.size >= MIN_ORDER_LINES_QUANTITY
-          lines.sort_by { _1.fetch(:price) }.first.fetch(:product_id)
-        end
-      end
-    end
-
-    include Infra::ProcessManager.with_state(ProcessState)
+    include Infra::ProcessManager.with_state { ProcessState }
 
     subscribes_to(
       Pricing::PriceItemAdded,
@@ -66,5 +51,19 @@ def make_new_product_for_free(product_id)
     def fetch_id(event)
       event.data.fetch(:order_id)
     end
+
+    ProcessState = Data.define(:lines, :free_product) do
+      def initialize(lines: [], free_product: nil)
+        super(lines: lines.freeze, free_product:)
+      end
+
+      MIN_ORDER_LINES_QUANTITY = 4
+
+      def eligible_free_product
+        if lines.size >= MIN_ORDER_LINES_QUANTITY
+          lines.sort_by { _1.fetch(:price) }.first.fetch(:product_id)
+        end
+      end
+    end
   end
 end

infra/lib/infra/process_manager.rb

@@ -43,18 +43,31 @@ def subscribes_to(*events)
       attr_reader :subscribed_events
     end
 
-    def self.with_state(state_class)
+    def self.with_state(&state_class_block)
+      unless block_given?
+        raise ArgumentError, "A block returning the state class is required."
+      end
 
       Module.new do
-        define_method :initial_state do
+        @state_definition_block = state_class_block
+
+        define_method(:initial_state) do
+          block = self.class.instance_variable_get(:@state_definition_block)
+          raise "State definition block not found on #{self.class}" unless block
+
+          state_class = block.call
+          raise "State definition block did not return a Class" unless state_class.is_a?(Class)
+
           state_class.new
         end
 
-        def state
+        define_method(:state) do
           @state ||= initial_state
         end
 
         def self.included(host_class)
+          host_class.instance_variable_set(:@state_definition_block, @state_definition_block)
+
           host_class.include(ProcessMethods)
           host_class.include(Infra::Retry)
           host_class.extend(Subscriptions)