Introduce JSON response in controller

app/assets/javascripts/moirai_translation_controller.js

@@ -27,6 +27,15 @@ export default class MoiraiTranslationController extends Controller {
           value: event.target.innerText
         }
       })
+    })
+    .then(response => response.json())
+    .then(data => {
+      if (data?.fallback_translation) {
+        event.target.innerText = data.fallback_translation
+      }
+    })
+    .catch(error => {
+      console.error('Error:', error);
     });
   }
 }

app/controllers/moirai/translation_files_controller.rb

@@ -40,7 +40,17 @@ def handle_update(translation)
       if translation_params[:value].blank? || translation_same_as_current?
         translation.destroy
         flash.notice = "Translation #{translation.key} was successfully deleted."
-        redirect_to_translation_file(translation.file_path)
+        respond_to do |format|
+          format.json do
+            flash.discard
+            render json: {
+              fallback_translation: get_fallback_translation
+            }
+          end
+          format.html do
+            redirect_to_translation_file(translation.file_path)
+          end
+        end
         return
       end
 
@@ -60,6 +70,15 @@ def handle_create
         return
       end
 
+      if translation_params[:value].blank? && request.format.json?
+        respond_to do |format|
+          format.json do
+            render json: {fallback_translation: get_fallback_translation}
+          end
+        end
+        return
+      end
+
       translation = Translation.new(translation_params)
 
       if translation.save
@@ -115,5 +134,14 @@ def translation_same_as_current?
 
       translation_params[:value] == @file_handler.parse_file(file_paths.first)[translation_params[:key]]
     end
+
+    def get_fallback_translation
+      file_paths = KeyFinder.new.file_paths_for(translation_params[:key], locale: translation_params[:locale])
+
+      return "" if file_paths.empty?
+      return "" unless file_paths.all? { |file_path| File.exist?(file_path) }
+
+      @file_handler.parse_file(file_paths.first)[translation_params[:key]]
+    end
   end
 end

test/controllers/moirai/translation_files_controller_test.rb

@@ -63,6 +63,12 @@ class TranslationFilesControllerTest < ActionDispatch::IntegrationTest
     assert_equal translation_count_before, Moirai::Translation.count
   end
 
+  test "create translation empty json" do
+    post translation_files_url, params: {translation: {key: "locales.german", locale: "de", value: ""}}, as: :json
+    assert_response :ok
+    assert_equal "Deutsch", JSON.parse(response.body)["fallback_translation"]
+  end
+
   # Update action tests
   test "update translation with blank value" do
     count_before = Moirai::Translation.count
@@ -74,6 +80,12 @@ class TranslationFilesControllerTest < ActionDispatch::IntegrationTest
     assert_equal count_before - 1, Moirai::Translation.count
   end
 
+  test "update translation with blank value json" do
+    post translation_files_url, params: {translation: {key: "locales.german", locale: "de", value: ""}}, as: :json
+    assert_response :ok
+    assert_equal "Deutsch", JSON.parse(response.body)["fallback_translation"]
+  end
+
   test "update translation with non-blank new value" do
     post translation_files_url, params: {translation: {key: "locales.german", locale: "de", value: "Hochdeutsch"}}