from urllib.parse import ParseResult, urlparse, urlsplit


def parse(domain: str, scheme: str = 'http') -> str:
    """
    Convert domain name to 'http://www.domain.com' format
    """
    # https://stackoverflow.com/questions/21659044/how-can-i-prepend-http-to-a-url-if-it-doesnt-begin-with-http
    p = urlparse(domain, 'http')
    netloc = p.netloc or p.path
    path = p.path if p.netloc else ''
    p = ParseResult(p.scheme, netloc, path, *p[3:])
    return p.geturl()


def hostname_only(value: str) -> str:
    """
    Reduce a domain or a URL to its bare, lowercased hostname.

    The canonical host-comparison helper: report.py matches
    ScrapeResult.website against the domain list with it, and
    ConfigManager.is_domain_ignored() normalises with it before applying
    ignore_list patterns. Both receive a mix of shapes -- get_domains() runs
    every domain through parse(), so it yields 'http://host', while
    ScrapeResult.website holds the post-redirect URL (scheme + trailing slash
    + path, sometimes a port).

    Implemented on urlsplit() of a '//'-prefixed value rather than
    urlparse(value, 'http'): for a scheme-less 'host:port' the RFC 3986
    scheme grammar permits dots, so urlparse reads 'sub.example.com' as the
    scheme and '8080' as the path. Forcing netloc parsing also gets port,
    credential and IPv6-bracket stripping from .hostname for free.

    Never raises. Returns '' for input with no host, and for input urlsplit()
    rejects -- notably a bracketed fnmatch character class such as
    '*.test[0-9].example.com', which it reads as a malformed IPv6 literal.
    ignore_list entries may legitimately contain those, and a caller treats ''
    as "not a hostname", falling back to verbatim matching. An exception here
    would instead escape is_domain_ignored() and abort the whole scanner
    iteration plus every report path.
    """
    value = (value or '').strip()
    if '://' not in value and not value.startswith('//'):
        value = f'//{value}'
    try:
        return urlsplit(value).hostname or ''
    except ValueError:
        return ''