Create BaseService for Auto Merge architecture

It abstracts some codes for common methods in AutoMerge::*Services.

2 files changed, 57 insertions, 29 deletions

diff --git a/app/services/auto_merge/base_service.rb b/app/services/auto_merge/base_service.rb
new file mode 100644
index 00000000000..058105db3a4
--- /dev/null
+++ b/app/services/auto_merge/base_service.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module AutoMerge
+  class BaseService < ::BaseService
+    include Gitlab::Utils::StrongMemoize
+
+    def execute(merge_request)
+      merge_request.merge_params.merge!(params)
+      merge_request.auto_merge_enabled = true
+      merge_request.merge_user = current_user
+      merge_request.auto_merge_strategy = strategy
+
+      return :failed unless merge_request.save
+
+      yield if block_given?
+
+      strategy.to_sym
+    end
+
+    def cancel(merge_request)
+      if cancel_auto_merge(merge_request)
+        yield if block_given?
+
+        success
+      else
+        error("Can't cancel the automatic merge", 406)
+      end
+    end
+
+    private
+
+    def strategy
+      strong_memoize(:strategy) do
+        self.class.name.demodulize.remove('Service').underscore
+      end
+    end
+
+    def cancel_auto_merge(merge_request)
+      merge_request.auto_merge_enabled = false
+      merge_request.merge_user = nil
+
+      merge_request.merge_params&.except!(
+        'should_remove_source_branch',
+        'commit_message',
+        'squash_commit_message',
+        'auto_merge_strategy'
+      )
+
+      merge_request.save
+    end
+  end
+end
diff --git a/app/services/auto_merge/merge_when_pipeline_succeeds_service.rb b/app/services/auto_merge/merge_when_pipeline_succeeds_service.rb
index d0586468859..c41073a73e9 100644
--- a/app/services/auto_merge/merge_when_pipeline_succeeds_service.rb
+++ b/app/services/auto_merge/merge_when_pipeline_succeeds_service.rb
@@ -1,32 +1,12 @@
 # frozen_string_literal: true
 
 module AutoMerge
-  class MergeWhenPipelineSucceedsService < BaseService
+  class MergeWhenPipelineSucceedsService < AutoMerge::BaseService
     def execute(merge_request)
-      return :failed unless merge_request.actual_head_pipeline
-
-      if merge_request.actual_head_pipeline.active?
-        merge_request.merge_params.merge!(params)
-
-        unless merge_request.auto_merge_enabled?
-          merge_request.auto_merge_enabled = true
-          merge_request.merge_user = @current_user
-          merge_request.auto_merge_strategy = AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS
-
-          SystemNoteService.merge_when_pipeline_succeeds(merge_request, @project, @current_user, merge_request.diff_head_commit)
+      super do
+        if merge_request.saved_change_to_auto_merge_enabled?
+          SystemNoteService.merge_when_pipeline_succeeds(merge_request, project, current_user, merge_request.diff_head_commit)
         end
-
-        return :failed unless merge_request.save
-
-        :merge_when_pipeline_succeeds
-      elsif merge_request.actual_head_pipeline.success?
-        # This can be triggered when a user clicks the auto merge button while
-        # the tests finish at about the same time
-        merge_request.merge_async(current_user.id, merge_params)
-
-        :success
-      else
-        :failed
       end
     end
 
@@ -38,12 +18,8 @@ module AutoMerge
     end
 
     def cancel(merge_request)
-      if merge_request.reset_auto_merge
+      super do
         SystemNoteService.cancel_merge_when_pipeline_succeeds(merge_request, @project, @current_user)
-
-        success
-      else
-        error("Can't cancel the automatic merge", 406)
       end
     end