Add template builder service

app/services/template_builder.rb

@@ -0,0 +1,40 @@
+# frozen_string_literaL: true
+
+class TemplateBuilder
+  class << self
+    def create!(name:, from:, game_system:)
+      Template.create!(
+        name:,
+        klass: from.class.name,
+        game_system:,
+        content: serialize_character_sheet_section(from),
+      )
+    end
+
+    private
+
+      def serialize_character_sheet_section(section)
+        always_except = [ :id, :created_at, :updated_at ]
+        subsection_except = [ :character_id, :parent_section_id ]
+        always_include = {
+          stats: { except: always_except + [ :value ] },
+          text_fields: { except: always_except },
+        }
+
+        section.to_json(
+          except: always_except + subsection_except,
+          include: {
+            character_sheet_subsections: {
+              except: always_except + subsection_except,
+              include: always_include.merge(
+                character_sheet_subsections: {
+                  except: always_except + subsection_except,
+                  include: always_include,
+                },
+              ),
+            },
+          }.merge(always_include),
+        )
+      end
+  end
+end