import re


def normalize_irc_target(target: str) -> str:
    target = target.strip()
    target = re.sub(r"^irc:", "", target)
    target = re.sub(r"^(channel|user):", "", target)
    if not re.match(r"^[^\s:@!]+$", target) and not target.startswith(("#", "&")):
        target = target.split("!")[0]
    return target


def is_channel_target(target: str) -> bool:
    return target.startswith("#") or target.startswith("&")


def build_irc_allowlist_candidates(
    nick: str,
    user: str | None,
    host: str | None,
    allow_name_matching: bool = False,
) -> list[str]:
    candidates = []
    nick_lower = nick.lower()
    if user and host:
        candidates.append(f"{nick_lower}!{user.lower()}@{host.lower()}")
    if user:
        candidates.append(f"{nick_lower}!{user.lower()}")
    if host:
        candidates.append(f"{nick_lower}@{host.lower()}")
    if allow_name_matching:
        candidates.append(nick_lower)
    return candidates