gestionnaire: move commentaire creation into a service

app/services/commentaire_service.rb

@@ -0,0 +1,17 @@
+class CommentaireService
+  class << self
+    def create(sender, dossier, params)
+      attributes = params.merge(email: sender.email, dossier: dossier)
+
+      # If the user submits a empty message, simple_format will replace '' by '<p></p>',
+      # and thus bypass the not-empty constraint on commentaire's body.
+      #
+      # To avoid this, format the message only if a body is present in the first place.
+      if attributes[:body].present?
+        attributes[:body] = ActionController::Base.helpers.simple_format(attributes[:body])
+      end
+
+      Commentaire.new(attributes)
+    end
+  end
+end