"""虎牙 udb 登录证书 (biz_token) 铸造与解析工具。

证书格式：base64( [0x0c][key_idx][AES-128-ECB(key16, zeropad(P1))] )
"""

from __future__ import annotations

import os
import struct

from .udb_aes import udb_decrypt, udb_encrypt

KEY_TABLE_RAW = [
    "4VYcPdvKKqjBHZtCmbroRXHk",
    "xXEDWqiKLGwEZ6HubEiswCqK",
    "3FMHubdKosFrhmXNLHTNHZwe",
]
DEFAULT_KEY16 = KEY_TABLE_RAW[0][:16].encode()


def build_p1(
    app_id: bytes,
    fingerprint: bytes,
    cred: bytes,
    rnd: bytes | None = None,
) -> bytes:
    """按样本结构组装 P1 明文。

    - app_id: b'5008' 等 4 字节
    - fingerprint: 40 字节 ASCII hex
    - cred: 114 字节 hyCred
    - rnd: 20 字节 nonce，缺省用 os.urandom(20)
    """
    assert len(fingerprint) == 40, f"指纹应为40B, 实际为 {len(fingerprint)}"
    assert len(cred) == 114, f"cred应为114B, 实际为 {len(cred)}"
    r = os.urandom(20) if rnd is None else rnd
    p1 = b"\x01\x04\x00" + app_id
    p1 += struct.pack("<H", len(r)) + r
    p1 += struct.pack("<H", len(fingerprint)) + fingerprint
    p1 += struct.pack("<H", len(cred)) + cred
    assert len(p1) == 187, f"P1长度应为187，实际为 {len(p1)}"
    return p1


def parse_p1(data: bytes) -> dict:
    """解析 P1 结构。"""
    o = 0

    def tk(n: int) -> bytes:
        nonlocal o
        b = data[o : o + n]
        o += n
        return b

    out = {
        "head": tk(3).hex(),
        "app_id": tk(4),
    }
    n = struct.unpack("<H", tk(2))[0]
    out["rnd"] = tk(n)
    n = struct.unpack("<H", tk(2))[0]
    out["fingerprint"] = tk(n)
    n = struct.unpack("<H", tk(2))[0]
    out["cred"] = tk(n)
    out["trailing"] = data[o:]
    return out


def forge_cert(
    p1: bytes,
    key16: bytes = DEFAULT_KEY16,
    key_idx: int = 0x20,
    type_byte: int = 0x0C,
) -> bytes:
    """P1 -> 二进制证书 [type][key_idx][192B AES 密文]。"""
    ct = udb_encrypt(key16, p1)
    assert len(ct) == 192, len(ct)
    return bytes([type_byte, key_idx]) + ct


def parse_cert(blob: bytes) -> tuple[int, int, bytes]:
    """[0x0c][idx][192B] -> (type, idx, ct)。"""
    assert blob[0] == 0x0C and len(blob) >= 194, "非证书结构"
    return blob[0], blob[1], blob[2:194]


def decrypt_cert(blob: bytes, key16: bytes = DEFAULT_KEY16) -> bytes:
    """解密二进制证书为 P1 明文。"""
    _, _, ct = parse_cert(blob)
    return udb_decrypt(key16, ct)