docs: def get_file_type(variant_source):
      """Check what kind of file variant source is
      
          Args:
              variant_source (str): Path to variant source
          
          Returns:
              file_type (str): 'vcf', 'gemini' or 'unknown'
      """
      file_type = 'unknown'
      valid_vcf_suffixes = ('.vcf', '.vcf.gz')
      if variant_source:
          logger.debug("Check file type with file: {0}".format(variant_source))
          if variant_source.endswith('.db'):
              file_type = 'gemini'
              logger.debug("File {0} is a gemini database".format(variant_source))
          elif variant_source.endswith(valid_vcf_suffixes):
              file_type = 'vcf'
              logger.debug("File {0} is a vcf".format(variant_source))
          else:
              logger.debug("File is in a unknown format")
      
      return file_type