docs: private File prepareBackupFile(final long timeForSuffix) {
      final String timeSuffix = this.backupSuffixHelper
          .backupTimeAsString(timeForSuffix);
      final BackupFile backupFile = new BackupFile(
          this.getAppender().getIoFile(), timeSuffix);
      // read in a sorted list of log files (most recent first), filtered on
      // the suffix pattern
      final LogFileList logFileList = this.logFileListFilteredOn(backupFile);
      String backupCountSuffix = this.backupSuffixHelper
          .defaultBackupCountAsString();
      if (!logFileList.isEmpty()) {
        // file list not empty: numbering to be added to suffix.
        final File lastLogFile = logFileList.lastFile();
        // extract number appended to filename of last file in list
        backupCountSuffix = this.backupSuffixHelper.nextBackupCountAsString(
            lastLogFile.getName(), backupFile.getBaseFile());
      }
      backupFile.setBackupCountSuffix(backupCountSuffix);
      return backupFile.getBackupFile();
    }