Disallow creating or updating scheduler if invalid

app/controllers/schedulers_controller.rb

@@ -23,9 +23,25 @@ def new; end
   action_auth_level :create, :instructor
   def create
     @scheduler = @course.scheduler.new(scheduler_params)
+    # Check if the action file exists and is readable
+    action_path = Rails.root.join(scheduler_params[:action]).to_path
+    unless File.exist?(action_path) && File.readable?(action_path)
+      flash[:error] = "Scheduler create failed. Action file does not exist or is
+        not readable at #{action_path}."
+      redirect_to(new_course_scheduler_path(@course)) and return
+    end
+
     if @scheduler.save
-      flash[:success] = "Scheduler created!"
-      redirect_to(course_schedulers_path(@course))
+      # Ensure visual run is successful
+      begin
+        test_run_visual_scheduler(@scheduler)
+        flash[:success] = "Scheduler created and executed successfully!"
+        redirect_to(course_schedulers_path(@course))
+      rescue StandardError => e
+        @scheduler.destroy # Destroy the created scheduler if visual run fails
+        flash[:error] = "Scheduler creation failed. Error: #{e.message}"
+        redirect_to(new_course_scheduler_path(@course))
+      end
     else
       flash[:error] = "Scheduler create failed. Please check all fields."
       redirect_to(new_course_scheduler_path(@course))
@@ -87,9 +103,29 @@ def visual_run
   action_auth_level :update, :instructor
   def update
     @scheduler = Scheduler.find_by(id: params[:id])
-    if @scheduler&.update(scheduler_params)
-      flash[:success] = "Scheduler updated."
-      redirect_to(course_schedulers_path(@course))
+    # Check if the action file exists and is readable
+    action_path = Rails.root.join(scheduler_params[:action]).to_path
+    unless File.exist?(action_path) && File.readable?(action_path)
+      flash[:error] = "Scheduler update failed. Action file does not exist or is
+        not readable at #{action_path}."
+      redirect_to(edit_course_scheduler_path(@course)) and return
+    end
+
+    # Save the current state of the scheduler in case we need to revert
+    previous_scheduler_state = @scheduler.attributes
+
+    if @scheduler.update(scheduler_params)
+      begin
+        # Run the visual scheduler to ensure the new update works
+        test_run_visual_scheduler(@scheduler)
+        flash[:success] = "Scheduler updated and executed successfully!"
+        redirect_to(course_schedulers_path(@course))
+      rescue StandardError => e
+        @scheduler.update(previous_scheduler_state) # If error, revert to previous state.
+        flash[:error] = "Scheduler update failed. Reverting to previous state.
+          Error: #{e.message}"
+        redirect_to(edit_course_scheduler_path(@course, @scheduler))
+      end
     else
       flash[:error] = "Scheduler update failed! Please check your fields."
       redirect_to(edit_course_scheduler_path(@course, @scheduler))
@@ -119,4 +155,40 @@ def set_manage_scheduler_breadcrumb
 
     @breadcrumbs << (view_context.link_to "Manage Schedulers", course_schedulers_path(@course))
   end
+
+  def test_run_visual_scheduler(scheduler)
+    # Do a test visual run to check if created/updated info valid
+    action = scheduler
+    read, write = IO.pipe
+
+    pid = fork do
+      read.close
+      mod_name = Rails.root.join(action.action).to_path
+      fork_log = ""
+      begin
+        require mod_name
+        output = Updater.update(action.course)
+        if output.respond_to?(:to_str)
+          fork_log << "----- Script Output -----\n"
+          fork_log << output
+          fork_log << "\n----- End Script Output -----"
+        end
+      rescue ScriptError, StandardError => e
+        fork_log << "----- Script Error Output -----\n"
+        fork_log << "Error in '#{action.course.name}' updater: #{e.message}\n"
+        fork_log << e.backtrace.join("\n\t")
+        fork_log << "\n---- End Script Error Output -----"
+      end
+      write.print fork_log
+    end
+
+    write.close
+    result = read.read
+    Process.wait2(pid)
+
+    # Raise an exception if something goes wrong
+    return unless result.is_a?(String) && result.include?("Error")
+
+    raise "Scheduler execution failed."
+  end
 end