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