1 files changed, 54 insertions, 0 deletions
diff --git a/app/services/merge_requests/mergeability_check_service.rb b/app/services/merge_requests/mergeability_check_service.rb
new file mode 100644
index 00000000000..d277d38127c
--- /dev/null
+++ b/app/services/merge_requests/mergeability_check_service.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+module MergeRequests
+  class MergeabilityCheckService < ::BaseService
+    delegate :project, to: :@merge_request
+    delegate :repository, to: :project
+
+    def initialize(merge_request)
+      @merge_request = merge_request
+    end
+
+    # Updates the MR merge_status. Whenever it switches to a can_be_merged state,
+    # the merge-ref is refreshed.
+    #
+    # Returns a ServiceResponse indicating merge_status is/became can_be_merged
+    # and the merge-ref is synced. Success in case of being/becoming mergeable,
+    # error otherwise.
+    def execute
+      return ServiceResponse.error('Invalid argument') unless merge_request
+      return ServiceResponse.error('Unsupported operation') if Gitlab::Database.read_only?
+
+      update_merge_status
+
+      unless merge_request.can_be_merged?
+        return ServiceResponse.error(message: 'Merge request is not mergeable')
+      end
+
+      ServiceResponse.success
+    end
+
+    private
+
+    attr_reader :merge_request
+
+    def update_merge_status
+      return unless merge_request.recheck_merge_status?
+
+      if can_git_merge?
+        merge_to_ref && merge_request.mark_as_mergeable
+      else
+        merge_request.mark_as_unmergeable
+      end
+    end
+
+    def can_git_merge?
+      !merge_request.broken? && repository.can_be_merged?(merge_request.diff_head_sha, merge_request.target_branch)
+    end
+
+    def merge_to_ref
+      result = MergeRequests::MergeToRefService.new(project, merge_request.author).execute(merge_request)
+      result[:status] == :success
+    end
+  end
+end