1 files changed, 56 insertions, 0 deletions
diff --git a/lib/sidebars/concerns/positionable_list.rb b/lib/sidebars/concerns/positionable_list.rb
new file mode 100644
index 00000000000..0bbe1d918e5
--- /dev/null
+++ b/lib/sidebars/concerns/positionable_list.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+# This module handles element positions in a list.
+module Sidebars
+  module Concerns
+    module PositionableList
+      def add_element(list, element)
+        return unless element
+
+        list << element
+      end
+
+      def insert_element_before(list, before_element, new_element)
+        return unless new_element
+
+        index = index_of(list, before_element)
+
+        if index
+          list.insert(index, new_element)
+        else
+          list.unshift(new_element)
+        end
+      end
+
+      def insert_element_after(list, after_element, new_element)
+        return unless new_element
+
+        index = index_of(list, after_element)
+
+        if index
+          list.insert(index + 1, new_element)
+        else
+          add_element(list, new_element)
+        end
+      end
+
+      def replace_element(list, element_to_replace, new_element)
+        return unless new_element
+
+        index = index_of(list, element_to_replace)
+
+        return unless index
+
+        list[index] = new_element
+      end
+
+      private
+
+      # Classes including this method will have to define
+      # the way to identify elements through this method
+      def index_of(list, element)
+        raise NotImplementedError
+      end
+    end
+  end
+end