"""Regexes used in the DNS protocol"""


def grpm(regex):
    """Make a matching group"""
    return grp(regex, matching=True)


def grp(regex, matching=False):
    """Make a group"""
    return r'(' + (r'' if matching else r'?:') + regex + r')'


def opt(regex):
    """Make an optional group"""
    return grp(grp(regex) + r'?')


def regex_opt_r(*regexes):
    """Make a group that matches one of the given regexes"""
    return grp(r'|'.join(regexes))


DIGIT = r'\d'
LETTER = r'[a-zA-Z]'
LETDIG = grp(regex_opt_r(DIGIT, LETTER))
LETDIGHYP = grp(regex_opt_r(LETDIG, r'-'))
LDHSTR = grp(LETDIGHYP + r'+')
LABEL = grp(LETTER + opt(opt(LDHSTR) + LETDIG))
SUBDOMAIN = grp(grpm(grp(LABEL + r'\.') + r'*') + grpm(LABEL))
DOMAIN = regex_opt_r(SUBDOMAIN, r' ')

IP = r'(?:(?:\d{1,3}\.){3}\d{1,3})'