Process manager

rails_application/app/services/send_email.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+class SendEmail
+  def call(event)
+    event_store.link(event.event_id, stream_name: "Sales$#{order_id(event)}")
+
+    state = {}
+
+    event_store.read.stream("Sales$#{order_id(event)}").each do |event_in_stream|
+      case event_in_stream
+      when Ordering::OrderPaid
+        state[:order_paid] = true
+      when Invoicing::InvoiceGenerated
+        state[:invoice_generated] = true
+      end
+    end
+
+    if state[:order_paid] && state[:invoice_generated]
+      Rails.configuration.email_client.send_email(order_id(event))
+    end
+  end
+
+  private
+
+  def order_id(event)
+    case event
+    when Ordering::OrderPaid
+      event.data[:id]
+    when Invoicing::InvoiceGenerated
+      event.data[:order_id]
+    end
+  end
+
+  def event_store
+    Rails.configuration.event_store
+  end
+end

rails_application/lib/configuration.rb

@@ -21,6 +21,11 @@ def call(event_store, command_bus)
       Inventory::UpdateProductCatalog,
       to: [Inventory::StockLevelIncreased, Inventory::StockLevelDecreased]
     )
+
+    event_store.subscribe(
+      SendEmail,
+      to: [Ordering::OrderPaid, Invoicing::InvoiceGenerated]
+    )
   end
 
   def self.available_vat_rates