Cron: CSV import: Add validation for the existence of template mail welcome message - refs BT#20405

main/cron/import_csv.php

@@ -1611,7 +1611,7 @@ class ImportCsv
 
                         $tpl->assign('teachers', $teachersToString);
 
-                        $templateName = $tpl->get_template('mail/custom_calendar_welcome.tpl');
+                        $templateName = $this->getCustomMailTemplate();
                         $emailBody = $tpl->fetch($templateName);
 
                         $coaches = SessionManager::getCoachesByCourseSession(
@@ -3606,6 +3606,28 @@ class ImportCsv
             fwrite($f, '";');
         }*/
     }
+    /**
+     * Get custom tpl for mail welcome
+     */
+    private function getCustomMailTemplate(): string
+    {
+        $name = 'mail/custom_calendar_welcome.tpl';
+        $sysTemplatePath = api_get_path(SYS_TEMPLATE_PATH);
+        if (is_readable($sysTemplatePath.'overrides/'.$name)) {
+            return 'overrides/'.$name;
+        }
+        $customThemeFolder = api_get_configuration_value('default_template');
+        if (is_readable($sysTemplatePath.$customThemeFolder.'/'.$name)) {
+            return $customThemeFolder.'/'.$name;
+        }
+        if (is_readable($sysTemplatePath.'default/'.$name)) {
+            return 'default/'.$name;
+        }
+        // If none has been found, it means we don't have a custom mail
+        // welcome message, so use the .dist version
+        $alternateName = 'mail/custom_calendar_welcome.dist.tpl';
+        return 'default/'.$alternateName;
+    }
 }
 
 $logger = new Logger('cron');