"""站点预览签名 URL：HMAC 短时效令牌，密钥首次使用时生成并持久化。

令牌只授予「该站点 dist/ 目录静态文件读」这一项能力，不携带任何其他 API 权限。
"""

from __future__ import annotations

import base64
import hashlib
import hmac
import secrets
import time
from pathlib import Path

from deerflow.config.runtime_paths import runtime_home

SECRET_FILE_NAME = ".web-app-secret"
_DEFAULT_TTL_SECONDS = 7200

_secret_cache: bytes | None = None


def _secret_path() -> Path:
    return runtime_home() / SECRET_FILE_NAME


def get_preview_secret() -> bytes:
    """加载或生成实例级 HMAC 密钥（0600 权限持久化在 .deer-flow 下）。"""
    global _secret_cache
    if _secret_cache is not None:
        return _secret_cache
    path = _secret_path()
    try:
        if path.is_file():
            data = path.read_bytes().strip()
            if len(data) >= 32:
                _secret_cache = data
                return _secret_cache
        path.parent.mkdir(parents=True, exist_ok=True)
        data = secrets.token_hex(32).encode("ascii")
        path.write_bytes(data)
        try:
            path.chmod(0o600)
        except OSError:  # Windows 无 POSIX 权限，忽略
            pass
        _secret_cache = data
        return _secret_cache
    except OSError:
        # 持久化失败时退化为进程内随机密钥（重启后旧令牌失效，可接受）
        _secret_cache = secrets.token_hex(32).encode("ascii")
        return _secret_cache


def mint_preview_token(thread_id: str, site_name: str, ttl_seconds: int = _DEFAULT_TTL_SECONDS) -> tuple[str, int]:
    """签发预览令牌，返回 (token, expires_at_epoch)。"""
    expires_at = int(time.time()) + max(60, ttl_seconds)
    payload = f"{thread_id}|{site_name}|{expires_at}"
    encoded = base64.urlsafe_b64encode(payload.encode("utf-8")).decode("ascii").rstrip("=")
    signature = hmac.new(get_preview_secret(), payload.encode("utf-8"), hashlib.sha256).hexdigest()
    return f"{encoded}.{signature}", expires_at


def verify_preview_token(token: str) -> tuple[str, str]:
    """校验令牌，返回 (thread_id, site_name)。

    Raises:
        ValueError: 令牌格式非法、签名不符或已过期。
    """
    if not token or token.count(".") != 1:
        raise ValueError("malformed token")
    encoded, signature = token.split(".", 1)
    if not encoded or not signature:
        raise ValueError("malformed token")
    padding = "=" * (-len(encoded) % 4)
    try:
        payload = base64.urlsafe_b64decode(encoded + padding).decode("utf-8")
    except (ValueError, UnicodeDecodeError) as exc:
        raise ValueError("malformed token") from exc
    parts = payload.split("|")
    if len(parts) != 3:
        raise ValueError("malformed token")
    thread_id, site_name, exp_raw = parts
    expected = hmac.new(get_preview_secret(), payload.encode("utf-8"), hashlib.sha256).hexdigest()
    if not hmac.compare_digest(expected, signature):
        raise ValueError("bad signature")
    try:
        expires_at = int(exp_raw)
    except ValueError as exc:
        raise ValueError("malformed token") from exc
    if time.time() > expires_at:
        raise ValueError("token expired")
    if not thread_id or not site_name:
        raise ValueError("malformed token")
    return thread_id, site_name