adding function to check if a backup exists

wled00/cfg.cpp

@@ -777,6 +777,10 @@ bool verifyConfig() {
   return validateJsonFile(s_cfg_json);
 }
 
+bool configBackupExists() {
+  return checkBackupExists(s_cfg_json);
+}
+
 // rename config file and reboot
 // if the cfg file doesn't exist, such as after a reset, do nothing
 void resetConfig() {

wled00/fcn_declare.h

@@ -27,6 +27,7 @@ void IRAM_ATTR touchButtonISR();
 bool backupConfig();
 bool restoreConfig();
 bool verifyConfig();
+bool configBackupExists();
 void resetConfig();
 bool deserializeConfig(JsonObject doc, bool fromFS = false);
 bool deserializeConfigFromFS();
@@ -103,6 +104,7 @@ inline bool readObjectFromFile(const String &file, const char* key, JsonDocument
 bool copyFile(const char* src_path, const char* dst_path);
 bool backupFile(const char* filename);
 bool restoreFile(const char* filename);
+bool checkBackupExists(const char* filename);
 bool validateJsonFile(const char* filename);
 void dumpFilesToSerial();
 

wled00/file.cpp

@@ -557,6 +557,12 @@ bool restoreFile(const char* filename) {
   return false;
 }
 
+bool checkBackupExists(const char* filename) {
+  char backupname[32];
+  snprintf_P(backupname, sizeof(backupname), s_backup_fmt, filename + 1); // skip leading '/' in filename
+  return WLED_FS.exists(backupname);
+}
+
 bool validateJsonFile(const char* filename) {
   if (!WLED_FS.exists(filename)) return false;
   File file = WLED_FS.open(filename, "r");