MDL-59311 course: duplicate module rebuilds cache twice

slightly refactor duplicate_module() code so it does not rebuild course cache
twice and also we do not need to move module if it is already the last module in a section

course/lib.php

@@ -3329,15 +3329,23 @@ function duplicate_module($course, $cm) {
         }
     }
 
+    $rc->destroy();
+
+    if (empty($CFG->keeptempdirectoriesonbackup)) {
+        fulldelete($backupbasepath);
+    }
+
     // If we know the cmid of the new course module, let us move it
     // right below the original one. otherwise it will stay at the
     // end of the section.
     if ($newcmid) {
-        $info = get_fast_modinfo($course);
-        $newcm = $info->get_cm($newcmid);
         $section = $DB->get_record('course_sections', array('id' => $cm->section, 'course' => $cm->course));
-        moveto_module($newcm, $section, $cm);
-        moveto_module($cm, $section, $newcm);
+        $modarray = explode(",", trim($section->sequence));
+        $cmindex = array_search($cm->id, $modarray);
+        if ($cmindex !== false && $cmindex < count($modarray) - 1) {
+            $newcm = get_coursemodule_from_id($cm->modname, $newcmid, $cm->course);
+            moveto_module($newcm, $section, $modarray[$cmindex + 1]);
+        }
 
         // Update calendar events with the duplicated module.
         $refresheventsfunction = $newcm->modname . '_refresh_events';
@@ -3346,16 +3354,10 @@ function duplicate_module($course, $cm) {
         }
 
         // Trigger course module created event. We can trigger the event only if we know the newcmid.
+        $newcm = get_fast_modinfo($cm->course)->get_cm($newcmid);
         $event = \core\event\course_module_created::create_from_cm($newcm);
         $event->trigger();
     }
-    rebuild_course_cache($cm->course);
-
-    $rc->destroy();
-
-    if (empty($CFG->keeptempdirectoriesonbackup)) {
-        fulldelete($backupbasepath);
-    }
 
     return isset($newcm) ? $newcm : null;
 }