code: func (f *FileLogger) isMustSplit() bool {
  
  	switch f.splitType {
  	case SplitType_Size:
  		logFile := joinFilePath(f.fileDir, f.fileName)
  		if f.fileCount > 1 {
  			if fileSize(logFile) >= f.fileSize {
  				return true
  			}
  		}
  	case SplitType_Daily:
  		t, _ := time.Parse(DATEFORMAT, time.Now().Format(DATEFORMAT))
  		if t.After(*f.date) {
  			return true
  		}
  	}
  
  	return false
  }
docs: // used for determine the fileLogger f is time to split.
  // size: once the current fileLogger's fileSize >= config.fileSize need to split
  // daily: once the current fileLogger stands for yesterday need to split