"""Conversation id helpers for Douyin IM."""


def parse_conversation_parts(conversation_id: str) -> tuple[int, int] | None:
    parts = (conversation_id or "").split(":")
    if len(parts) >= 4 and parts[0] == "0" and parts[1] == "1":
        try:
            return int(parts[2]), int(parts[3])
        except (TypeError, ValueError):
            return None
    return None


def resolve_peer_uid(conversation_id: str, my_uid: int) -> int | None:
    """Resolve peer user id from conversation id or bare numeric id."""
    raw = (conversation_id or "").strip()
    if not raw:
        return None

    parts = parse_conversation_parts(raw)
    if parts:
        uid1, uid2 = parts
        if my_uid and uid1 == my_uid:
            return uid2
        if my_uid and uid2 == my_uid:
            return uid1
        # 0:1:{my}:{peer} — 若 my_uid 与首段不一致，仍取末段为对方
        return uid2

    if raw.isdigit():
        peer = int(raw)
        if my_uid and peer == my_uid:
            return None
        return peer
    return None


def build_conversation_id(my_uid: int, peer_uid: int) -> str:
    return f"0:1:{int(my_uid)}:{int(peer_uid)}"


def normalize_conversation_id(conversation_id: str, my_uid: int) -> str:
    """Ensure conversation id uses current account uid as first participant."""
    peer_uid = resolve_peer_uid(conversation_id, my_uid)
    if peer_uid and my_uid:
        return build_conversation_id(my_uid, peer_uid)
    return (conversation_id or "").strip()


def conversation_belongs_to(conversation_id: str, my_uid: int) -> bool:
    """判断单聊会话是否属于 my_uid 本人。

    托管多个账号时，一条属于别的账号的会话（例如 frontier 长连接按设备号寻址
    造成的跨账号推送）一旦流进本账号的处理链路，resolve_peer_uid 会把末段当成
    「对方」、normalize_conversation_id 再拼成 0:1:{本账号}:{别人的好友}，于是
    本账号就把消息发给了另一个账号的好友。这里给出唯一的归属判据。

    无法判定时一律返回 True（保守放行）：缺 my_uid、群聊、裸 UID 等形态本来就
    不带参与方信息。只有两个参与方都已知、且都不是本账号时才判定为不属于本账号。
    """
    try:
        uid = int(my_uid or 0)
    except (TypeError, ValueError):
        return True
    if not uid:
        return True
    parts = parse_conversation_parts(conversation_id)
    if not parts:
        return True
    return uid in parts