"""a_bogus 签名器。

两种后端，接口相同、可互换：

  NodeSigner    调本地 node_signer（真实 webmssdk 跑在伪造浏览器环境里）。
                当前唯一可用的实现，已实测能被抖音接受。
  ABogusSigner  纯 Python 实现。底层 SM3/RC4/自定义 Base64 已在 crypto.py
                验证通过，剩字节拼装顺序待从 ab.js 逆出来。

签名器同时决定 User-Agent：a_bogus 把 UA 编进签名，服务端会交叉校验，
所以请求头的 UA 必须与签名时用的完全一致。
"""

from __future__ import annotations

import json
import subprocess
from dataclasses import dataclass, field
from pathlib import Path
from typing import Dict, List, Protocol, Sequence


class SignError(RuntimeError):
    pass


class SignerNotConfigured(SignError):
    pass


class Signer(Protocol):
    """client 只依赖这两个成员。"""

    @property
    def user_agent(self) -> str:
        """签名时使用的 UA，请求头必须用同一个。"""
        ...

    def sign_url(self, url: str, fp: str = "") -> str:
        """给一条裸 URL，返回带 a_bogus 的完整 URL。"""
        ...


# --------------------------------------------------------------------------- #
# Node 后端
# --------------------------------------------------------------------------- #

class NodeSigner:
    """通过 node_signer/sign.js 签名。

    node 启动 + 加载 347KB 的 SDK 大约 0.7s，所以支持 batch 一次签多条，
    把这份固定开销摊掉。
    """

    def __init__(self, signer_dir: str | Path, node: str = "node",
                 timeout: float = 120.0) -> None:
        self.dir = Path(signer_dir)
        self.node = node
        self.timeout = timeout
        self._ua: str | None = None

        script = self.dir / "sign.js"
        if not script.exists():
            raise SignerNotConfigured(f"找不到签名脚本: {script}")

    def _run(self, args: Sequence[str], stdin: str | None = None) -> dict:
        try:
            proc = subprocess.run(
                [self.node, "sign.js", *args], cwd=self.dir, input=stdin,
                capture_output=True, text=True, encoding="utf-8",
                timeout=self.timeout,
            )
        except FileNotFoundError as exc:
            raise SignerNotConfigured(f"找不到 node 可执行文件: {self.node}") from exc
        except subprocess.TimeoutExpired as exc:
            raise SignError(f"签名超时（>{self.timeout}s）") from exc

        out = (proc.stdout or "").strip()
        if not out:
            raise SignError(f"签名器无输出，rc={proc.returncode}，stderr={proc.stderr[:400]}")
        try:
            # sign.js 只在最后一行吐 JSON，前面可能有 SDK 自己的噪声
            return json.loads(out.splitlines()[-1])
        except ValueError as exc:
            raise SignError(f"签名器输出不是 JSON: {out[:300]!r}") from exc

    @property
    def user_agent(self) -> str:
        if self._ua is None:
            probe = self._run(["https://www.douyin.com/aweme/v1/web/aweme/detail/?aweme_id=1", ""])
            self._ua = probe.get("userAgent") or ""
            if not self._ua:
                raise SignError("签名器没有返回 userAgent")
        return self._ua

    def sign_url(self, url: str, fp: str = "") -> str:
        res = self._run([url, fp])
        if not res.get("ok"):
            raise SignError(f"签名失败: {res.get('error')}")
        self._ua = res.get("userAgent") or self._ua
        return res["signedUrl"]

    def sign_many(self, urls: List[str], fp: str = "") -> List[str]:
        """一次 node 启动签完多条。"""
        if not urls:
            return []
        res = self._run(["--batch", fp], stdin=json.dumps(urls))
        if not res.get("ok"):
            raise SignError(f"批量签名失败: {res.get('error')}")
        self._ua = res.get("userAgent") or self._ua
        signed = []
        for item in res["results"]:
            if not item.get("ok"):
                raise SignError(f"某条签名失败: {item.get('error')} url={item.get('rawUrl')}")
            signed.append(item["signedUrl"])
        return signed


# --------------------------------------------------------------------------- #
# 纯 Python 后端（待补）
# --------------------------------------------------------------------------- #

@dataclass
class ABogusConfig:
    """a_bogus 算法常量。必须与线上 webmssdk.js 当前版本一致。"""

    alphabets: Dict[str, str] = field(default_factory=dict)
    ua_key: bytes = b""
    arguments: List[int] = field(default_factory=list)
    browser_fp: str = ""
    end_string: str = ""
    user_agent: str = ""

    def validate(self) -> None:
        missing = [n for n in ("alphabets", "ua_key", "arguments",
                               "browser_fp", "end_string", "user_agent")
                   if not getattr(self, n)]
        if missing:
            raise SignerNotConfigured("a_bogus 常量未配置，缺少: " + ", ".join(missing))


class ABogusSigner:
    """纯 Python a_bogus。crypto.py 里的 SM3/RC4/Base64 已验证可用。"""

    def __init__(self, config: ABogusConfig) -> None:
        config.validate()
        self.config = config

    @property
    def user_agent(self) -> str:
        return self.config.user_agent

    def sign_url(self, url: str, fp: str = "") -> str:
        raise NotImplementedError(
            "a_bogus 字节拼装顺序待从 ab.js 逆出。目前请用 NodeSigner。"
        )