Make stuff sortable

app/models/element.rb

@@ -8,7 +8,8 @@ class Element < ApplicationRecord
 
   delegate :report, to: :page
 
-  after_validation :set_position
+  before_validation :set_position
+  before_update :update_positions, if: :position_changed?
 
   # Calculate actual conformity level:
   # - if a success_criterion has result :failed -> the confirmity_level
@@ -33,12 +34,20 @@ class Element < ApplicationRecord
     @max_level ||= success_criteria.reject(&:not_applicable?).max(&:level)
   end
 
+  def number
+    "#{page.position}.#{position}"
+  end
+
+  private
   def set_position
     Rails.logger.debug("element: position #{position}")
     self.position ||= (page.elements.pluck(:position).max || 0) + 1
   end
 
-  def number
-    "#{page.position}.#{position}"
+  def update_positions
+    if position_was
+      page.elements.where("position > ?", position_was).update_all("position = position - 1")
+    end
+    page.elements.where(position: position..).update_all("position = position + 1")
   end
 end