Introduced Sequencer Unit base class Sequencer::Unit::Common::FallbackProvider to handle simple setting fallback values of state attributes if not already present.

lib/sequencer/sequence/import/ldap/users.rb

@@ -9,6 +9,7 @@ class Sequencer
               'Import::Ldap::Users::StaticAttributes',
               'Import::Ldap::Users::DryRun::Flag',
               'Import::Ldap::Users::DryRun::Payload',
+              'Ldap::Config',
               'Ldap::Connection',
               'Import::Ldap::Users::UserRoles',
               'Import::Ldap::Users::Sum',

lib/sequencer/unit/common/fallback_provider.rb

@@ -0,0 +1,29 @@
+class Sequencer
+  class Unit
+    module Common
+      class FallbackProvider < Sequencer::Unit::Base
+
+        def process
+          provides = self.class.provides
+          raise 'Only one provide attribute possible' if provides.size != 1
+
+          attribute = provides.shift
+          return if state.provided?(attribute)
+
+          result = fallback
+
+          # don't store nil values which are default anyway
+          return if result.nil?
+
+          state.provide(attribute, result)
+        end
+
+        private
+
+        def fallback
+          raise 'Missing implementation of fallback method'
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/exchange/connection.rb

@@ -1,27 +1,22 @@
 class Sequencer
   class Unit
     module Exchange
-      class Connection < Sequencer::Unit::Base
+      class Connection < Sequencer::Unit::Common::FallbackProvider
 
         uses :ews_config
         provides :ews_connection
 
-        def process
-          # check if EWS connection is already given (sub sequence)
-          return if state.provided?(:ews_connection)
-
-          state.provide(:ews_connection) do
-            Viewpoint::EWSClient.new(
-              config[:endpoint],
-              config[:user],
-              config[:password],
-              additional_opts
-            )
-          end
-        end
-
         private
 
+        def fallback
+          Viewpoint::EWSClient.new(
+            config[:endpoint],
+            config[:user],
+            config[:password],
+            additional_opts
+          )
+        end
+
         def config
           @config ||= begin
             ews_config || ::Import::Exchange.config

lib/sequencer/unit/import/exchange/folder_contacts/folder_ids.rb

@@ -3,19 +3,14 @@ class Sequencer
     module Import
       module Exchange
         module FolderContacts
-          class FolderIds < Sequencer::Unit::Base
-            include ::Sequencer::Unit::Exchange::Folders::Mixin::Folder
+          class FolderIds < Sequencer::Unit::Common::FallbackProvider
 
             provides :ews_folder_ids
 
-            def process
-              # check if ids are already processed
-              return if state.provided?(:ews_folder_ids)
+            private
 
-              state.provide(:ews_folder_ids) do
-                config = ::Import::Exchange.config
-                config[:folders]
-              end
+            def fallback
+              ::Import::Exchange.config[:folders]
             end
           end
         end

lib/sequencer/unit/ldap/config.rb

@@ -0,0 +1,17 @@
+require 'import/ldap'
+
+class Sequencer
+  class Unit
+    module Ldap
+      class Config < Sequencer::Unit::Common::FallbackProvider
+        provides :ldap_config
+
+        private
+
+        def fallback
+          ::Import::Ldap.config
+        end
+      end
+    end
+  end
+end

lib/sequencer/unit/ldap/connection.rb

@@ -1,22 +1,16 @@
 require 'ldap'
-require 'import/ldap'
 
 class Sequencer
   class Unit
     module Ldap
-      class Connection < Sequencer::Unit::Base
+      class Connection < Sequencer::Unit::Common::FallbackProvider
         uses :ldap_config
         provides :ldap_connection
 
-        def process
-          return if state.provided?(:ldap_connection)
+        private
 
-          state.provide(:ldap_connection) do
-            config   = ldap_config
-            config ||= ::Import::Ldap.config
-
-            ::Ldap.new(config)
-          end
+        def fallback
+          ::Ldap.new(ldap_config)
         end
       end
     end