import re


PATH_REGEX = re.compile(r'^[a-zA-Z_-][a-zA-Z0-9_-]*$')
FQDN_REGEX = re.compile(r'^([a-zA-Z0-9.-]+\.)+[a-zA-Z]{2,}$')


def validate_fqdn(fqdn: str) -> bool:
    """
    Validates a string against the FQDN regex pattern.

    Args:
        fqdn: The fully qualified domain name to validate (e.g., "example.com")

    Returns:
        True if the input matches the FQDN pattern, False otherwise
    """
    return re.match(FQDN_REGEX, fqdn) is not None


def split_and_validate_path(path: str) -> list[str] | None:
    """
        Splits a path string by slashes, filters out empty fragments, and validates each label.

        Args:
            path: Input path string in format like "a/b/c" or "/a/b/c"

        Returns:
            List of validated path labels, or None if validation fails (empty input or invalid characters)
        """
    # Split by slashes and filter out empty fragments
    labels = list(filter(lambda x: x != "", path.strip().split("/")))

    # Return None for empty paths
    if len(labels) == 0:
        return None

    # Validate each label against the PATH_REGEX pattern
    for label in labels:
        if not re.match(PATH_REGEX, label):
            return None

    return labels