"""虎牙证书 nonce(rnd) 本地生成器。

基于 XXTEA 算法与 uid + k1 派生密钥。
"""
from __future__ import annotations

import hashlib
import struct
import time

K1_DEFAULT = "865a4924a40897ac1fcfe6b4c2cbb0e3"


def _xxtea_encrypt_words(v: list[int], k: list[int]) -> list[int]:
    """标准 XXTEA (delta=0x9e3779b9, rounds=6+52/n)。"""
    n = len(v)
    if n < 2:
        return v
    z = v[n - 1]
    y = v[0]
    s = 0
    delta = 0x9E3779B9
    q = 6 + 52 // n
    while q > 0:
        s = (s + delta) & 0xFFFFFFFF
        e = (s >> 2) & 3
        p = 0
        while p < n - 1:
            y = v[p + 1]
            z = (v[p] + ((((z >> 5) ^ (y << 2)) + ((y >> 3) ^ (z << 4)))
                         ^ ((s ^ y) + (k[(p & 3) ^ e] ^ z)))) & 0xFFFFFFFF
            v[p] = z
            p += 1
        y = v[0]
        z = (v[n - 1] + ((((z >> 5) ^ (y << 2)) + ((y >> 3) ^ (z << 4)))
                         ^ ((s ^ y) + (k[((n - 1) & 3) ^ e] ^ z)))) & 0xFFFFFFFF
        v[n - 1] = z
        q -= 1
    return v


def xxtea_encrypt(data: bytes, key16: bytes) -> bytes:
    """虎牙专用 XXTEA: 输出 words = ceil(len/4)+1, 末尾 word 存原始长度。"""
    n = len(data)
    nwords = (n // 4) + 1
    v = [0] * nwords
    for i in range(n // 4):
        v[i] = struct.unpack("<I", data[i * 4:i * 4 + 4])[0]
    v[nwords - 1] = n
    k = [struct.unpack("<I", key16[i * 4:i * 4 + 4])[0] for i in range(4)]
    _xxtea_encrypt_words(v, k)
    return b"".join(struct.pack("<I", w & 0xFFFFFFFF) for w in v)


def pack_u64(v: int) -> bytes:
    """8字节小端裸值。"""
    return struct.pack("<Q", v & 0xFFFFFFFFFFFFFFFF)


def gen_nonce(
    uid: int,
    k1: str = K1_DEFAULT,
    service_time_ms: int | None = None,
    counter: int = 0,
) -> bytes:
    """按设备算法生成 20B nonce(rnd)。

    - uid: 虎牙 uid 数字（如 1199666914671）
    - k1: 设备常量 32hex
    - service_time_ms: 缺省为当前毫秒时间戳
    - counter: 计数器（通常为 0）
    """
    st = service_time_ms if service_time_ms is not None else int(time.time() * 1000)
    st &= 0x7FFFFFFFFFFF
    nonce_val = (counter & 0xFFFF) | (st << 16)
    data = pack_u64(st) + pack_u64(nonce_val)
    key = hashlib.md5((str(uid) + k1).encode()).hexdigest()[:16].encode()
    return xxtea_encrypt(data, key)