MDL-40992 quiz: let students to redo questions within an attempt

question/engine/questionusage.php

@@ -822,6 +822,22 @@ class question_usage_by_activity {
         $this->observer->notify_attempt_modified($newqa);
     }
 
+    /**
+     * Replace a question in this usage.
+     * @param int $slot the number used to identify this question within this usage.*
+     */
+    public function replace_question($slot) {
+        global $OUTPUT;
+        $oldqa = $this->get_question_attempt($slot);
+        $newqa = new question_attempt($oldqa->get_question(), $oldqa->get_usage_id(), $this->observer);
+        $newqa->set_database_id($oldqa->get_database_id());
+        $newqa->set_slot($oldqa->get_slot());
+        $this->questionattempts[$slot] = $newqa;
+        $this->observer->notify_attempt_deleted($oldqa);
+        $this->observer->notify_attempt_added($newqa);
+        $this->start_question($slot);
+    }
+
     /**
      * Regrade all the questions in this usage (without changing their max mark).
      * @param bool $finished whether each question should be forced to be finished
@@ -979,6 +995,12 @@ interface question_usage_observer {
      */
     public function notify_attempt_added(question_attempt $qa);
 
+    /**
+     * Called when the fields of a question attempt in this usage are deleted.
+     * @param question_attempt $qa
+     */
+    public function notify_attempt_deleted(question_attempt $qa);
+
     /**
      * Called when a new step is added to a question attempt in this usage.
      * @param question_attempt_step $step the new step.
@@ -1017,6 +1039,8 @@ class question_usage_null_observer implements question_usage_observer {
     }
     public function notify_attempt_modified(question_attempt $qa) {
     }
+    public function notify_attempt_deleted(question_attempt $qa) {
+    }
     public function notify_attempt_added(question_attempt $qa) {
     }
     public function notify_step_added(question_attempt_step $step, question_attempt $qa, $seq) {