Introduce stock level commands

rails_application/app/controllers/orders_controller.rb

@@ -77,7 +77,7 @@ def add_item
 
     @order = Order.find(params[:id])
     @order.add_item(product)
-    Inventory::ProductService.new.decrement_stock_level(product.id)
+    Inventory::ProductService.new.decrement_stock_level(Inventory::DecreaseStockLevel.new(product_id: product.id))
     @order.save!
 
     redirect_to edit_order_path(params[:id])
@@ -87,7 +87,7 @@ def remove_item
     product = Product.find(params[:product_id])
     @order = Order.find(params[:id])
     @order.remove_item(product)
-    Inventory::ProductService.new.increment_stock_level(product.id)
+    Inventory::ProductService.new.increment_stock_level(Inventory::IncreaseStockLevel.new(product_id: product.id))
     @order.save!
 
     redirect_to edit_order_path(params[:id])
@@ -113,7 +113,7 @@ def expire
       .where(status: "Draft")
       .find_each do |order|
       order.order_items.each do |item|
-        Inventory::ProductService.new.increment_stock_level(item.product.id)
+        Inventory::ProductService.new.increment_stock_level(Inventory::IncreaseStockLevel.new(product_id: item.product_id))
       end
       order.status = "Expired"
       order.save!

rails_application/app/models/inventory/decrease_stock_level.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module Inventory
+  DecreaseStockLevel = Struct.new(:product_id)
+end
+

rails_application/app/models/inventory/increase_stock_level.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+module Inventory
+  IncreaseStockLevel = Struct.new(:product_id)
+end

rails_application/app/models/inventory/product_service.rb

@@ -7,7 +7,8 @@ def initialize
       @repository = Infra::AggregateRootRepository.new(event_store)
     end
 
-    def decrement_stock_level(product_id)
+    def decrement_stock_level(command)
+      product_id = command.product_id
       ApplicationRecord.with_advisory_lock("change_stock_level_for_#{product_id}") do
         product = ::Product.find(product_id)
         product_stream = event_store.read.stream("Inventory::Product$#{product_id}").to_a
@@ -26,7 +27,8 @@ def decrement_stock_level(product_id)
       end
     end
 
-    def increment_stock_level(product_id)
+    def increment_stock_level(command)
+      product_id = command.product_id
       ApplicationRecord.with_advisory_lock("change_stock_level_for_#{product_id}") do
         product = ::Product.find(product_id)
         product_stream = event_store.read.stream("Inventory::Product$#{product_id}").to_a