1 files changed, 71 insertions, 0 deletions
diff --git a/app/services/boards/lists/base_create_service.rb b/app/services/boards/lists/base_create_service.rb
new file mode 100644
index 00000000000..8399b1cc149
--- /dev/null
+++ b/app/services/boards/lists/base_create_service.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+module Boards
+  module Lists
+    # This class is used by issue and epic board lists
+    # for creating new list
+    class BaseCreateService < Boards::BaseService
+      include Gitlab::Utils::StrongMemoize
+
+      def execute(board)
+        list = case type
+               when :backlog
+                 create_backlog(board)
+               else
+                 target = target(board)
+                 position = next_position(board)
+
+                 return ServiceResponse.error(message: _('%{board_target} not found') % { board_target: type.to_s.capitalize }) if target.blank?
+
+                 create_list(board, type, target, position)
+               end
+
+        return ServiceResponse.error(message: list.errors.full_messages) unless list.persisted?
+
+        ServiceResponse.success(payload: { list: list })
+      end
+
+      private
+
+      def type
+        # We don't ever expect to have more than one list
+        # type param at once.
+        if params.key?('backlog')
+          :backlog
+        else
+          :label
+        end
+      end
+
+      def target(board)
+        strong_memoize(:target) do
+          available_labels.find_by(id: params[:label_id]) # rubocop: disable CodeReuse/ActiveRecord
+        end
+      end
+
+      def available_labels
+        ::Labels::AvailableLabelsService.new(current_user, parent, {})
+          .available_labels
+      end
+
+      def next_position(board)
+        max_position = board.lists.movable.maximum(:position)
+        max_position.nil? ? 0 : max_position.succ
+      end
+
+      def create_list(board, type, target, position)
+        board.lists.create(create_list_attributes(type, target, position))
+      end
+
+      def create_list_attributes(type, target, position)
+        { type => target, list_type: type, position: position }
+      end
+
+      def create_backlog(board)
+        return board.lists.backlog.first if board.lists.backlog.exists?
+
+        board.lists.create(list_type: :backlog, position: nil)
+      end
+    end
+  end
+end