"""安全工具 — 文件上传校验和 URL 安全校验。"""
import ipaddress
import io
import logging
import os
import socket

logger = logging.getLogger(__name__)

# PDF 文件头魔数
PDF_MAGIC = b"%PDF"

# 文件大小限制（默认 30MB）
MAX_FILE_SIZE = int(os.environ.get("MAX_UPLOAD_SIZE_MB", "30")) * 1024 * 1024

# PDF 页数限制（默认 200 页）
MAX_PDF_PAGES = int(os.environ.get("MAX_PDF_PAGES", "200"))

# 私网/保留 IP 前缀
_PRIVATE_NETWORKS = [
    ipaddress.ip_network("127.0.0.0/8"),      # loopback
    ipaddress.ip_network("10.0.0.0/8"),        # 私网 A
    ipaddress.ip_network("172.16.0.0/12"),     # 私网 B
    ipaddress.ip_network("192.168.0.0/16"),    # 私网 C
    ipaddress.ip_network("169.254.0.0/16"),    # 链路本地
    ipaddress.ip_network("0.0.0.0/8"),         # 当前网络
    ipaddress.ip_network("::1/128"),           # IPv6 loopback
    ipaddress.ip_network("fc00::/7"),          # IPv6 私网
    ipaddress.ip_network("fe80::/10"),         # IPv6 链路本地
]


def prepare_pdf_upload(file_storage, password: str = "") -> tuple[bool, str, bytes | None]:
    """校验 PDF；加密文件解密后返回可供解析的 PDF 字节。

    密码不会写入数据库或日志。空密码可自动处理仅限制复制/打印的 PDF。
    返回 (is_valid, error_message, pdf_bytes)。
    """
    file_storage.seek(0)
    original_bytes = file_storage.read()
    file_storage.seek(0)

    # 1. 检查文件大小
    size = len(original_bytes)

    if size == 0:
        return False, "文件为空", None
    if size > MAX_FILE_SIZE:
        return False, f"文件大小 {size // (1024*1024)}MB 超过限制 {MAX_FILE_SIZE // (1024*1024)}MB", None

    # 2. 检查 PDF 魔数
    if not original_bytes[:8].startswith(PDF_MAGIC):
        return False, "文件不是有效的 PDF 格式", None

    # 3. 解密并检查页数
    try:
        import pypdf
        reader = pypdf.PdfReader(io.BytesIO(original_bytes))
        pdf_bytes = original_bytes
        if reader.is_encrypted:
            decrypt_result = reader.decrypt(password or "")
            if decrypt_result == 0:
                message = "PDF 密码错误，请重新输入" if password else "该 PDF 需要打开密码，请填写密码后重试"
                return False, message, None

            writer = pypdf.PdfWriter()
            writer.append_pages_from_reader(reader)
            output = io.BytesIO()
            writer.write(output)
            pdf_bytes = output.getvalue()

        # 4. 检查页数
        if len(reader.pages) > MAX_PDF_PAGES:
            return False, f"PDF 页数 {len(reader.pages)} 超过限制 {MAX_PDF_PAGES} 页", None
    except ImportError:
        # pypdf 不可用时跳过加密和页数检查
        pdf_bytes = original_bytes
    except Exception as e:
        logger.warning(f"PDF 解析检查失败: {e}")
        return False, "PDF 文件内容损坏、密码错误或格式无效", None
    finally:
        file_storage.seek(0)

    return True, "", pdf_bytes


def validate_pdf_upload(file_storage, password: str = "") -> tuple[bool, str]:
    """兼容旧调用：只返回 PDF 校验结果。"""
    is_valid, error_message, _ = prepare_pdf_upload(file_storage, password)
    return is_valid, error_message


def is_safe_base_url(url: str) -> tuple[bool, str]:
    """检查 Base URL 是否安全（拒绝私网、环回、元数据地址）。

    返回 (is_safe, error_message)。
    """
    if not url:
        return True, ""

    # 只允许 http/https
    if not url.startswith(("http://", "https://")):
        return False, "仅支持 http/https 协议"

    # 解析主机名
    from urllib.parse import urlparse
    try:
        parsed = urlparse(url)
    except Exception:
        return False, "URL 格式无效"

    hostname = parsed.hostname
    if not hostname:
        return False, "URL 缺少主机名"

    # 拒绝明确的 localhost
    if hostname in ("localhost", "0.0.0.0"):
        return False, f"不允许访问 {hostname}"

    # DNS 解析后检查 IP
    try:
        for info in socket.getaddrinfo(hostname, None, socket.AF_UNSPEC, socket.SOCK_STREAM):
            ip_str = info[4][0]
            ip = ipaddress.ip_address(ip_str)
            for network in _PRIVATE_NETWORKS:
                if ip in network:
                    return False, f"不允许访问私网/保留地址 ({ip_str})"
    except socket.gaierror:
        pass  # DNS 解析失败不阻止，让后续调用报错
    except Exception as e:
        logger.warning(f"URL 安全检查异常: {e}")

    return True, ""


def _is_private_ip(ip_str: str) -> bool:
    """检查 IP 是否属于私网/保留地址。"""
    try:
        ip = ipaddress.ip_address(ip_str)
        for network in _PRIVATE_NETWORKS:
            if ip in network:
                return True
    except ValueError:
        pass
    return False


class _SafeHTTPTransport:
    """httpcore HTTP 传输层，在连接时验证目标 IP 不是私网地址（防止 DNS rebinding SSRF）。"""

    def __init__(self, **kwargs):
        import httpcore
        self._transport = httpcore.HTTPTransport(**kwargs)

    def handle_request(self, request):
        url = request.url
        host = url.host
        port = url.port or (443 if url.scheme == b"https" else 80)
        try:
            for info in socket.getaddrinfo(host, port, socket.AF_UNSPEC, socket.SOCK_STREAM):
                ip_str = info[4][0]
                if _is_private_ip(ip_str):
                    raise ValueError(f"SSRF 阻止: 目标 {host} 解析到私网地址 {ip_str}")
        except socket.gaierror:
            pass  # DNS 失败时让底层处理
        return self._transport.handle_request(request)


class _SafeHTTPAsyncTransport:
    """httpcore 异步 HTTP 传输层，连接时验证 IP。"""

    def __init__(self, **kwargs):
        import httpcore
        self._transport = httpcore.AsyncHTTPTransport(**kwargs)

    async def handle_async_request(self, request):
        url = request.url
        host = url.host
        port = url.port or (443 if url.scheme == b"https" else 80)
        try:
            for info in socket.getaddrinfo(host, port, socket.AF_UNSPEC, socket.SOCK_STREAM):
                ip_str = info[4][0]
                if _is_private_ip(ip_str):
                    raise ValueError(f"SSRF 阻止: 目标 {host} 解析到私网地址 {ip_str}")
        except socket.gaierror:
            pass
        return await self._transport.handle_async_request(request)


def safe_httpx_client(**kwargs):
    """创建带有 SSRF 防护的 httpx.Client（每次连接时重新验证 DNS）。"""
    import httpx
    transport = _SafeHTTPTransport(retries=kwargs.pop("retries", 0))
    return httpx.Client(transport=transport, **kwargs)


def safe_httpx_async_client(**kwargs):
    """创建带有 SSRF 防护的 httpx.AsyncClient。"""
    import httpx
    transport = _SafeHTTPAsyncTransport(retries=kwargs.pop("retries", 0))
    return httpx.AsyncClient(transport=transport, **kwargs)