gradebook uploads display error when no file is given

Fixes CNVS-21851

Test Plan:

  1. Go to a Gradebook Uploads page
     (/courses/:id/gradebook_uploads/new)
  2. Click the upload button.
  3. Verify that an error message is displayed
     and the user is redirected to the
     Gradebook Uploads page.

Change-Id: I78cfc149243d4bd169c095807cf36df3a3616ce2
Reviewed-on: https://gerrit.instructure.com/58293
Tested-by: Jenkins
Reviewed-by: Derek Bender <dbender@instructure.com>
QA-Review: Jason Carter <jcarter@instructure.com>
Product-Review: Strand McCutchen <smccutchen@instructure.com>

app/controllers/gradebook_uploads_controller.rb

@@ -22,19 +22,12 @@ class GradebookUploadsController < ApplicationController
 
   before_filter :require_context
 
-  def gradebook_upload
-    GradebookUpload.where(
-      course_id: @context,
-      user_id: @current_user
-    ).first
-  end
-
   def new
     if authorized_action(@context, @current_user, :manage_grades)
-
       # GradebookUpload is a singleton.  If there is
       # already an instance we'll redirect to it or kill it
-      if previous_upload = gradebook_upload
+      previous_upload = gradebook_upload
+      if previous_upload
         if previous_upload.stale?
           previous_upload.destroy
         elsif previous_upload
@@ -48,7 +41,6 @@ class GradebookUploadsController < ApplicationController
 
   def show
     if authorized_action(@context, @current_user, :manage_grades)
-
       upload = gradebook_upload
       unless upload
         redirect_to new_course_gradebook_upload_path(@context)
@@ -62,10 +54,16 @@ class GradebookUploadsController < ApplicationController
 
   def create
     if authorized_action(@context, @current_user, :manage_grades)
-      attachment = params[:gradebook_upload][:uploaded_data]
-      @progress = GradebookUpload.queue_from(@context, @current_user, attachment.read)
-      js_env gradebook_env(@progress)
-      render :show
+      if params[:gradebook_upload]
+        attachment = params[:gradebook_upload][:uploaded_data]
+        @progress = GradebookUpload.queue_from(@context, @current_user, attachment.read)
+        js_env gradebook_env(@progress)
+        render :show
+      else
+        flash[:error] = t(:no_file_attached, "We did not detect a CSV to "\
+          "upload. Please select a CSV to upload and submit again.")
+        redirect_to action: :new
+      end
     end
   end
 
@@ -79,6 +77,7 @@ class GradebookUploadsController < ApplicationController
     end
   end
 
+  private
   def gradebook_env(progress)
     {
       progress: progress_json(progress, @current_user, session),
@@ -89,4 +88,11 @@ class GradebookUploadsController < ApplicationController
       new_gradebook_upload_path: new_course_gradebook_upload_path(@context),
     }
   end
+
+  def gradebook_upload
+    GradebookUpload.where(
+      course_id: @context,
+      user_id: @current_user
+    ).first
+  end
 end