Expose migrated legacy carto champs on api

app/serializers/champ_serializer.rb

@@ -6,10 +6,62 @@ class ChampSerializer < ActiveModel::Serializer
   has_one :type_de_champ
 
   def value
-    if object.piece_justificative_file.attached?
-      url_for(object.piece_justificative_file)
+    case object
+    when GeoArea, UserGeometry, Cadastre, QuartierPrioritaire
+      object.geometry
     else
-      object.value
+      if object.piece_justificative_file.attached?
+        url_for(object.piece_justificative_file)
+      else
+        object.value
+      end
+    end
+  end
+
+  def type_de_champ
+    case object
+    when GeoArea, UserGeometry, Cadastre, QuartierPrioritaire
+      legacy_type_de_champ
+    else
+      object.type_de_champ
+    end
+  end
+
+  private
+
+  def legacy_type_de_champ
+    {
+      id: -1,
+      libelle: legacy_carto_libelle,
+      type_champ: legacy_carto_type_champ,
+      order_place: -1,
+      descripton: ''
+    }
+  end
+
+  def legacy_carto_libelle
+    case object
+    when UserGeometry, Cadastre, QuartierPrioritaire
+      object.class.name.underscore.tr('_', ' ')
+    else
+      if object.source == GeoArea.sources.fetch(:selection_utilisateur)
+        'user geometry'
+      else
+        object.source.to_s.tr('_', ' ')
+      end
+    end
+  end
+
+  def legacy_carto_type_champ
+    case object
+    when UserGeometry, Cadastre, QuartierPrioritaire
+      object.class.name.underscore
+    else
+      if object.source == GeoArea.sources.fetch(:selection_utilisateur)
+        'user_geometry'
+      else
+        object.source.to_s
+      end
     end
   end
 end