#!/usr/bin/env python3
from __future__ import annotations
import json
import os
import re
import socket
import subprocess
import time
import urllib.parse
import urllib.request
import threading
from pathlib import Path
from typing import Any

ROOT_DIR = Path(__file__).resolve().parent
DATA_DIR = Path(os.environ["VPNGATE_DATA_DIR"]).resolve() if os.environ.get("VPNGATE_DATA_DIR") else ROOT_DIR / "vpngate_data"
IP_CACHE_FILE = DATA_DIR / "ip_cache.json"

ip_cache_lock = threading.RLock()
physical_interface_lock = threading.Lock()
physical_interface_cache: tuple[str | None, float] = (None, 0.0)

COUNTRY_TRANSLATIONS = {
    "Japan": "日本",
    "Korea Republic of": "韩国",
    "Korea": "韩国",
    "Republic of Korea": "韩国",
    "Thailand": "泰国",
    "United States": "美国",
    "United Kingdom": "英国",
    "Russian Federation": "俄罗斯",
    "Russian": "俄罗斯",
    "Viet Nam": "越南",
    "Vietnam": "越南",
    "China": "中国",
    "Taiwan": "台湾",
    "Taiwan Province of China": "台湾",
    "Hong Kong": "香港",
    "Singapore": "新加坡",
    "Malaysia": "马来西亚",
    "Indonesia": "印度尼西亚",
    "India": "印度",
    "Philippines": "菲律宾",
    "Australia": "澳大利亚",
    "New Zealand": "新西兰",
    "Canada": "加拿大",
    "Ukraine": "乌克兰",
    "France": "法国",
    "Germany": "德国",
    "Netherlands": "荷兰",
    "Sweden": "瑞典",
    "Norway": "挪威",
    "Spain": "西班牙",
    "Turkey": "土耳其",
    "South Africa": "南非",
    "Brazil": "巴西",
    "Argentina": "阿根廷",
    "Chile": "智利",
    "Mexico": "墨西哥",
    "Egypt": "埃及",
    "Romania": "罗马尼亚",
    "Poland": "波兰",
    "Kazakhstan": "哈萨克斯坦",
    "Georgia": "格鲁吉亚",
    "Mongolia": "蒙古",
    "Saudi Arabia": "沙特阿拉伯",
    "Iran": "伊朗",
    "Iraq": "伊拉克",
    "Colombia": "哥伦比亚",
    "Cambodia": "柬埔寨",
    "Ireland": "爱尔兰",
    "Italy": "意大利",
    "Switzerland": "瑞士",
    "Belgium": "比利时",
    "Austria": "奥地利",
    "Denmark": "丹麦",
    "Finland": "芬兰",
    "Portugal": "葡萄牙",
    "Greece": "希腊",
    "Czech Republic": "捷克",
    "Hungary": "匈牙利",
    "Israel": "以色列",
    "United Arab Emirates": "阿联酋",
    "UAE": "阿联酋",
    "Macao": "澳门",
    "Macau": "澳门",
    "Iceland": "冰岛",
    "Luxembourg": "卢森堡",
}

def _safe_int(val: Any, default: int = 0) -> int:
    try:
        return int(val)
    except (ValueError, TypeError):
        return default

def parse_proxy_endpoint(value: str, default_port: int) -> tuple[str | None, int | None]:
    value = value.strip()
    if not value:
        return None, None
    if "://" in value:
        parsed = urllib.parse.urlsplit(value)
        if parsed.hostname:
            return parsed.hostname, parsed.port or default_port
        return None, None
    if value.startswith("["):
        host_part, sep, rest = value.partition("]")
        host = host_part.lstrip("[")
        port = default_port
        if sep and rest.startswith(":"):
            port = _safe_int(rest[1:], default_port)
        return host or None, port
    if value.count(":") == 1:
        host, _, port_text = value.rpartition(":")
        return host or None, _safe_int(port_text, default_port)
    return value, default_port

def _proxy_config_from_env(env_name: str, forced_type: str | None = None) -> tuple[str, str, int, str | None, str | None] | None:
    val = os.environ.get(env_name)
    if not val:
        return None
    if "://" in val:
        try:
            parsed = urllib.parse.urlsplit(val)
        except Exception:
            return None
        if not parsed.hostname:
            return None
        ptype = forced_type or ("socks" if parsed.scheme.startswith("socks") else "http")
        username = urllib.parse.unquote(parsed.username) if parsed.username is not None else None
        password = urllib.parse.unquote(parsed.password or "") if parsed.username is not None else None
        return ptype, parsed.hostname, parsed.port or 10808, username, password
    host, port = parse_proxy_endpoint(val, 10808)
    if host and port:
        return forced_type or "http", host, port, None, None
    return None

def get_upstream_proxy_config() -> tuple[str | None, str | None, int | None, str | None, str | None]:
    for env_name, forced_type in [
        ("OPENVPN_UPSTREAM_SOCKS", "socks"),
        ("OPENVPN_UPSTREAM_HTTP", "http"),
        ("http_proxy", None),
        ("HTTP_PROXY", None),
        ("https_proxy", None),
        ("HTTPS_PROXY", None),
    ]:
        cfg = _proxy_config_from_env(env_name, forced_type)
        if cfg:
            ptype, host, port, username, password = cfg
            return ptype, host, port, username, password
    return None, None, None, None, None

def get_upstream_proxy() -> tuple[str | None, str | None, int | None]:
    """
    Returns (proxy_type, host, port) from environment variables.
    proxy_type is 'socks' or 'http'.
    """
    ptype, host, port, _, _ = get_upstream_proxy_config()
    return ptype, host, port

def get_upstream_proxy_auth() -> tuple[str | None, str | None]:
    """
    Returns optional (username, password) for the configured upstream proxy.
    Supports credentials embedded in proxy URLs and explicit env vars.
    """
    _, _, _, username, password = get_upstream_proxy_config()
    if username is not None:
        return username, password or ""

    user = os.environ.get("OPENVPN_UPSTREAM_USER") or os.environ.get("OPENVPN_UPSTREAM_USERNAME")
    password = os.environ.get("OPENVPN_UPSTREAM_PASS") or os.environ.get("OPENVPN_UPSTREAM_PASSWORD")
    if user is not None:
        return user, password or ""
    return None, None

def is_config_tcp(config_text: str) -> bool:
    try:
        for line in config_text.splitlines():
            line = line.strip()
            if not line or line.startswith(("#", ";")):
                continue
            parts = line.split()
            if parts[0].lower() == "proto" and len(parts) >= 2:
                if "tcp" in parts[1].lower():
                    return True
            elif parts[0].lower() == "remote" and len(parts) >= 4:
                if "tcp" in parts[3].lower():
                    return True
    except Exception:
        pass
    return False

def parse_remote(config_text: str, fallback_ip: str = "") -> tuple[str, int, str]:
    remote_host = fallback_ip
    remote_port = 0
    proto = "unknown"
    for raw_line in config_text.splitlines():
        line = raw_line.strip()
        if not line or line.startswith(("#", ";")):
            continue
        parts = line.split()
        if parts[0].lower() == "proto" and len(parts) >= 2:
            proto = parts[1].lower()
        elif parts[0].lower() == "remote" and len(parts) >= 3:
            remote_host = parts[1]
            remote_port = int(parts[2]) if parts[2].isdigit() else 0
            if len(parts) >= 4:
                proto = parts[3].lower()
    return remote_host, remote_port, proto

def _detect_physical_interface() -> str | None:
    try:
        res = subprocess.run(["ip", "route"], capture_output=True, text=True, timeout=2)
        if res.returncode == 0:
            routes = []
            for line in res.stdout.splitlines():
                if line.startswith("default"):
                    parts = line.split()
                    try:
                        dev = parts[parts.index("dev") + 1]
                        metric = 0
                        if "metric" in parts:
                            metric = int(parts[parts.index("metric") + 1])
                        gw = parts[parts.index("via") + 1] if "via" in parts else ""
                        routes.append((gw, dev, metric))
                    except (ValueError, IndexError):
                        continue
            if routes:
                routes.sort(key=lambda x: x[2])
                for gw, dev, metric in routes:
                    if not dev.startswith(("tun", "tap", "wg", "ppp")):
                        return dev
                return routes[0][1]
    except Exception:
        pass
    return None

def get_physical_interface() -> str | None:
    global physical_interface_cache
    now = time.monotonic()
    with physical_interface_lock:
        cached_interface, cached_at = physical_interface_cache
        if cached_at > 0 and now - cached_at < 30:
            return cached_interface
        detected = _detect_physical_interface()
        physical_interface_cache = (detected, now)
        return detected

def tcp_latency_ms(host: str, port: int, dev: str | None = None) -> int:
    started = time.time()
    # Auto-detect address family based on host address
    af = socket.AF_INET6 if ":" in host else socket.AF_INET
    s = None
    try:
        s = socket.socket(af, socket.SOCK_STREAM)
        s.settimeout(5)
        if dev:
            try:
                s.setsockopt(socket.SOL_SOCKET, socket.SO_BINDTODEVICE, dev.encode("utf-8"))
            except OSError:
                pass
        s.connect((host, port))
        return max(1, int((time.time() - started) * 1000))
    except OSError:
        return 0
    finally:
        if s is not None:
            try:
                s.close()
            except Exception:
                pass

def ping_latency_ms(host: str, port: int, fallback_ping: int = 0) -> int:
    dev = get_physical_interface()
    # 1. Try ping with interface binding
    if dev:
        try:
            cmd = ["ping", "-c", "1", "-W", "2", "-I", dev, host]
            res = subprocess.run(
                cmd,
                stdout=subprocess.PIPE,
                stderr=subprocess.PIPE,
                text=True,
                timeout=2
            )
            if res.returncode == 0:
                match = re.search(r"time=([\d.]+)\s*ms", res.stdout)
                if match:
                    val = int(float(match.group(1)))
                    if val > 0:
                        return val
        except Exception:
            pass

    # 2. Try ping without interface binding
    try:
        cmd = ["ping", "-c", "1", "-W", "2", host]
        res = subprocess.run(
            cmd,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True,
            timeout=2
        )
        if res.returncode == 0:
            match = re.search(r"time=([\d.]+)\s*ms", res.stdout)
            if match:
                val = int(float(match.group(1)))
                if val > 0:
                    return val
    except Exception:
        pass

    # 3. Try TCP latency check
    tcp_val = tcp_latency_ms(host, port, dev)
    if tcp_val > 0:
        return tcp_val

    # 4. Fallback
    if fallback_ping > 0:
        return fallback_ping
    return 0

def check_and_fix_dns() -> None:
    """
    Checks if DNS resolution is broken.
    If names fail but direct IP connections work, appends public DNS nameservers to /etc/resolv.conf.
    Supports both IPv4 and IPv6 network environments.
    """
    try:
        socket.getaddrinfo("www.vpngate.net", 443)
        return
    except (socket.gaierror, OSError):
        pass

    network_ok = False
    # Test IPv4 DNS servers first, then IPv6
    dns_targets = [
        ("8.8.8.8", 53, socket.AF_INET),
        ("1.1.1.1", 53, socket.AF_INET),
        ("2001:4860:4860::8888", 53, socket.AF_INET6),
        ("2606:4700:4700::1111", 53, socket.AF_INET6),
    ]
    for ip, port, af in dns_targets:
        s = None
        try:
            s = socket.socket(af, socket.SOCK_DGRAM)
            s.settimeout(2)
            s.connect((ip, port))
            network_ok = True
            break
        except Exception:
            pass
        finally:
            if s is not None:
                try:
                    s.close()
                except Exception:
                    pass

    if not network_ok:
        return

    resolv_file = Path("/etc/resolv.conf")
    if resolv_file.exists():
        try:
            content = resolv_file.read_text(encoding="utf-8", errors="replace")
            if "nameserver 1.1.1.1" not in content and "nameserver 8.8.8.8" not in content:
                print("[dns_heal] Resolving names failed, but IP network is OK. Appending public DNS to /etc/resolv.conf...", flush=True)
                with open("/etc/resolv.conf", "a", encoding="utf-8") as f:
                    f.write("\nnameserver 1.1.1.1\nnameserver 8.8.8.8\n")
        except Exception as e:
            print(f"[dns_heal] Failed to write DNS fallback: {e}", flush=True)

def load_ip_cache() -> dict[str, dict[str, Any]]:
    with ip_cache_lock:
        try:
            if IP_CACHE_FILE.exists():
                return json.loads(IP_CACHE_FILE.read_text(encoding="utf-8"))
        except Exception:
            pass
        return {}

def save_ip_cache(cache: dict[str, dict[str, Any]]) -> None:
    with ip_cache_lock:
        try:
            DATA_DIR.mkdir(exist_ok=True, parents=True)
            IP_CACHE_FILE.write_text(json.dumps(cache, ensure_ascii=False, indent=2), encoding="utf-8")
        except Exception:
            pass

def enrich_ip_info(nodes: list[dict[str, Any]]) -> None:
    # 1. Read cache thread-safely
    with ip_cache_lock:
        cache = load_ip_cache()

    ips_to_query = []
    now = time.time()

    for node in nodes:
        ip = node.get("ip") or node.get("remote_host")
        if not ip:
            continue
        if ip in cache and now - cache[ip].get("cached_at", 0) < 7 * 24 * 3600:
            cached = cache[ip]
            node["owner"] = cached.get("owner", "")
            node["asn"] = cached.get("asn", "")
            node["as_name"] = cached.get("as_name", "")
            node["location"] = cached.get("location", "")
            node["ip_type"] = cached.get("ip_type", "")
            node["quality"] = cached.get("quality", "")
        else:
            if ip not in ips_to_query:
                ips_to_query.append(ip)

    if not ips_to_query:
        return

    # 2. Perform HTTP query outside lock
    new_entries = {}
    chunk_size = 100
    for i in range(0, len(ips_to_query), chunk_size):
        chunk = ips_to_query[i : i + chunk_size]
        payload = json.dumps(chunk).encode("utf-8")
        request = urllib.request.Request(
            "http://ip-api.com/batch?lang=zh-CN&fields=status,message,query,country,regionName,city,isp,org,as,asname,proxy,hosting,mobile",
            data=payload,
            headers={"Content-Type": "application/json", "User-Agent": "vpngate-manager/2.2"},
            method="POST",
        )
        try:
            with urllib.request.urlopen(request, timeout=15) as response:
                data = json.loads(response.read().decode("utf-8", errors="replace"))
                if not isinstance(data, list):
                    continue
                for item in data:
                    if not isinstance(item, dict):
                        continue
                    if item.get("status") != "success":
                        continue
                    query_ip = item.get("query")
                    if not query_ip:
                        continue

                    ip_type = "residential"
                    if item.get("mobile"):
                        ip_type = "mobile"
                    elif item.get("hosting") or item.get("proxy"):
                        ip_type = "hosting"

                    quality = "normal"
                    if item.get("proxy"):
                        quality = "proxy"
                    elif item.get("hosting"):
                        quality = "datacenter"
                    elif item.get("mobile"):
                        quality = "mobile"

                    loc = " ".join(part for part in [item.get("country"), item.get("regionName"), item.get("city")] if part)

                    new_entries[query_ip] = {
                        "owner": item.get("org") or item.get("isp") or "",
                        "asn": item.get("as") or "",
                        "as_name": item.get("asname") or "",
                        "location": loc,
                        "ip_type": ip_type,
                        "quality": quality,
                        "cached_at": now,
                    }
        except Exception as e:
            print(f"[enrich_ip_info] Query failed: {e}", flush=True)

    if not new_entries:
        return

    # 3. Save cache thread-safely (reload & update to avoid overwrite of concurrent queries)
    with ip_cache_lock:
        cache = load_ip_cache()
        cache.update(new_entries)
        save_ip_cache(cache)

    # 4. Enrich nodes with newly queried info
    for node in nodes:
        ip = node.get("ip") or node.get("remote_host")
        if ip in new_entries:
            cached = new_entries[ip]
            node["owner"] = cached.get("owner", "")
            node["asn"] = cached.get("asn", "")
            node["as_name"] = cached.get("as_name", "")
            node["location"] = cached.get("location", "")
            node["ip_type"] = cached.get("ip_type", "")
            node["quality"] = cached.get("quality", "")


def diagnose_api_failure(api_url: str = "https://www.vpngate.net/api/iphone/") -> tuple[int, str]:
    try:
        parsed = urllib.parse.urlsplit(api_url)
        domain = parsed.hostname or "www.vpngate.net"
        port = parsed.port or (443 if parsed.scheme == "https" else 80)
    except Exception:
        domain = "www.vpngate.net"
        port = 443

    # 1. 检查本地 DNS 解析是否完全失效
    dns_ok = False
    for test_domain in ["api.ipify.org", "dns.google", "one.one.one.one"]:
        try:
            socket.getaddrinfo(test_domain, 443)
            dns_ok = True
            break
        except Exception:
            pass

    # 2. 检查是否能解析 API 域名
    api_dns_ok = False
    api_addr = None  # (af, ip) tuple
    try:
        results = socket.getaddrinfo(domain, port, 0, socket.SOCK_STREAM)
        if results:
            api_dns_ok = True
            api_addr = (results[0][0], results[0][4][0])  # (address_family, ip)
    except Exception:
        pass

    if not api_dns_ok:
        if not dns_ok:
            return 1006, "[ERR_LOCAL_DNS_BROKEN] 本地 DNS 解析器完全失效。原因: 无法解析任何外部域名，请检查系统 DNS 配置(如 /etc/resolv.conf)及外网连接。"
        else:
            return 1007, f"[ERR_API_DOMAIN_BLOCKED] 解析 API 域名 {domain} 失败。原因: 其他外部域名解析正常，确认该官方 API 域名遭 DNS 污染或本地防火墙拦截。"

    # 3. 检查 TCP 连接 API 域名
    api_conn_ok = False
    api_af, api_ip = api_addr
    s = None
    try:
        s = socket.socket(api_af, socket.SOCK_STREAM)
        s.settimeout(4)
        s.connect((api_ip, port))
        api_conn_ok = True
    except Exception:
        pass
    finally:
        if s is not None:
            try:
                s.close()
            except Exception:
                pass

    if not api_conn_ok:
        ext_conn_ok = False
        # Test both IPv4 and IPv6 external connectivity
        ext_targets = [
            ("8.8.8.8", 53, socket.AF_INET),
            ("1.1.1.1", 53, socket.AF_INET),
            ("2001:4860:4860::8888", 53, socket.AF_INET6),
            ("2606:4700:4700::1111", 53, socket.AF_INET6),
        ]
        for test_ip, test_port, af in ext_targets:
            s = None
            try:
                s = socket.socket(af, socket.SOCK_STREAM)
                s.settimeout(3)
                s.connect((test_ip, test_port))
                ext_conn_ok = True
                break
            except Exception:
                pass
            finally:
                if s is not None:
                    try:
                        s.close()
                    except Exception:
                        pass
        if ext_conn_ok:
            return 1008, f"[ERR_API_IP_BLOCKED_OR_DOWN] 连接 API 服务器失败。原因: 外部网络连接通畅，但无法建立到 {domain} ({api_ip}:{port}) 的连接，可能是由于官方 IP 遭 GFW/防火墙 IP 阻断封锁或官方服务器宕机。"
        else:
            return 1009, "[ERR_VPS_OUTBOUND_BLOCKED] VPS 完全断网。原因: 任何外部测试连接均失败（IPv4 和 IPv6 均不可达），请检查 VPS 网卡和宿主机连接。"

    return 1010, f"[ERR_API_TLS_INTERFERENCE] HTTPS/TLS 握手被干扰。原因: 可以建立 TCP 连接但请求超时，通常是由于防火墙通过 SNI 阻断了 TLS 握手流。"


def diagnose_openvpn_failure(log_tail: list[str]) -> tuple[int, str]:
    joined_log = "\n".join(log_tail).lower()
    
    if "command not found" in joined_log or "no such file or directory" in joined_log:
        return 2001, "[ERR_OVPN_CMD_NOT_FOUND] 未找到 openvpn 命令。原因: 系统中未安装 OpenVPN 软件，或环境变量 PATH 不正确。"
    
    if "cannot allocate tun" in joined_log or "cannot open tun/tap dev" in joined_log or "cannot ioctl" in joined_log or "cannot allocate tun/tap dev" in joined_log or "dev/net/tun" in joined_log or "operation not permitted" in joined_log:
        return 2009, "[ERR_OVPN_TUN_NOT_AVAILABLE] 无法创建或访问虚拟网卡 (TUN 设备)。原因: ① 缺少 tun 内核模块；② 当前运行在容器(如 LXC/OpenVZ/Docker)中且宿主机未授予网卡创建权限/未启用 CAP_NET_ADMIN 权限；③ `/dev/net/tun` 文件权限不足；④ 未使用 root 用户运行。如果是 Docker，请添加 `--cap-add=NET_ADMIN` 和 `--device=/dev/net/tun` 参数重新运行。"
        
    if "auth_failed" in joined_log or "authentication failed" in joined_log:
        return 2005, "[ERR_OVPN_AUTH_FAILED] OpenVPN 身份验证失败。原因: 节点配置的用户名密码不正确，或者该免费节点已失效/限制连接。"
        
    if "cannot resolve host address" in joined_log or "resolve: host name" in joined_log:
        return 2003, "[ERR_OVPN_DNS_RESOLVE] 节点服务器域名解析失败。原因: 本地 DNS 解析异常，或者节点域名已失效。"
        
    if "tls error: tls key negotiation failed" in joined_log or "tls error: tls handshake failed" in joined_log:
        return 2006, "[ERR_OVPN_TLS_BLOCKED] TLS 握手超时/失败。原因: 可能是由于物理链路极差导致握手包丢失，或者受 VPS 防火墙规则/网络监管(如 GFW)深度包检测拦截了 OpenVPN 协议流量。"
        
    if "connection timed out" in joined_log or "timeout" in joined_log:
        return 2004, "[ERR_OVPN_NODE_UNREACHABLE] 节点连接超时。原因: 远程节点已关机、VPS 本身出站流量被本地防火墙拦截，或者目的 IP:端口遭 ISP/GFW 屏蔽拦截。"
    if "connection refused" in joined_log:
        return 2004, "[ERR_OVPN_NODE_UNREACHABLE] 节点连接被拒绝。原因: 目的服务器未在指定端口监听，或者主动拒绝了连接。"
        
    if "permission denied" in joined_log or "root privileges" in joined_log or "need root" in joined_log:
        return 2002, "[ERR_OVPN_PERMISSION_DENIED] 权限不足。原因: 运行 OpenVPN 需要 root 权限，请确保以 root 用户身份或使用 sudo 运行本系统。"

    if "options error" in joined_log:
        return 2007, "[ERR_OVPN_ROUTE_NOPULL] 获取/解析 PUSH 配置参数冲突。原因: 某些推送选项在当前版本的客户端或配置环境中不可用。"
        
    return 2010, "[ERR_OVPN_UNKNOWN] OpenVPN 其他运行时异常。原因: 连接握手期间发生其他协议错误，详细信息请查看日志尾部。"


def diagnose_local_obstructions(proxy_port: int = 7928, host: str = "127.0.0.1") -> tuple[int, str] | None:
    import sys
    # 1. 检查端口是否被占用
    is_ipv6 = ":" in host or host == ""
    af = socket.AF_INET6 if is_ipv6 else socket.AF_INET
    s = None
    try:
        s = socket.socket(af, socket.SOCK_STREAM)
        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        s.bind((host, proxy_port))
    except OSError as e:
        if e.errno == 98 or e.errno == 10048 or "already in use" in str(e).lower() or "not supported" in str(e).lower():
            if e.errno in (98, 10048) or "already in use" in str(e).lower():
                return 3005, f"[ERR_PORT_IN_USE] 本地代理端口 {proxy_port} 被占用。原因: 其他进程已抢占该端口，导致本系统代理网关启动失败。请运行 'lsof -i :{proxy_port}' 检查占用进程。"
    finally:
        if s is not None:
            try:
                s.close()
            except Exception:
                pass

    if sys.platform.startswith("linux"):
        # 1.5 检查 /dev/net/tun 虚拟网卡接口是否可用与具备权限
        tun_path = Path("/dev/net/tun")
        if not tun_path.exists():
            return 3009, "[ERR_TUN_DEV_NOT_FOUND] 系统中不存在虚拟网卡设备节点 `/dev/net/tun`。原因: 内核未加载 tun 模块，或宿主机禁用了 TUN 设备创建权限。请尝试运行 `modprobe tun` 加载模块，或在 VPS 控制面板中开启 TUN 支持。"
        try:
            with open(tun_path, "r+b") as f:
                pass
        except PermissionError:
            return 3010, "[ERR_TUN_PERMISSION_DENIED] 无权访问虚拟网卡设备节点 `/dev/net/tun`。原因: 当前用户对该节点没有读写权限。请确保使用 root 权限运行，或者运行 `chmod 666 /dev/net/tun` 赋予读写权限。"
        except Exception:
            pass

        # 2. 检查 IPv4 转发是否开启
        ip_forward_path = Path("/proc/sys/net/ipv4/ip_forward")
        if ip_forward_path.exists():
            try:
                val = ip_forward_path.read_text(encoding="utf-8").strip()
                if val == "0":
                    return 3001, "[ERR_ROUTE_FORWARD_DISABLED] 系统未开启 IPv4 流量转发。原因: /proc/sys/net/ipv4/ip_forward 值为 0，会导致 VPN 隧道内的流量无法进行正常的网络转发。"
            except Exception:
                pass

        # 3. 检查本机防火墙策略
        # 检查 UFW
        try:
            res = subprocess.run(["ufw", "status"], capture_output=True, text=True, timeout=2)
            if res.returncode == 0 and "Status: active" in res.stdout:
                if str(proxy_port) not in res.stdout:
                    return 3007, f"[ERR_FIREWALL_BLOCKING_FORWARD] 本机 UFW 防火墙处于激活状态，但未在规则中允许代理端口 {proxy_port}。这可能会阻断客户端的连接。"
        except Exception:
            pass

        # 检查 Firewalld
        try:
            res = subprocess.run(["systemctl", "is-active", "firewalld"], capture_output=True, text=True, timeout=2)
            if res.returncode == 0 and res.stdout.strip() == "active":
                return 3007, "[ERR_FIREWALL_BLOCKING_FORWARD] 本机 Firewalld 防火墙正在运行。请确保您已将代理端口及 VPN 网卡(tun0)加入信任区域以避免流量被拦截。"
        except Exception:
            pass

        # 检查 iptables 默认策略
        try:
            res = subprocess.run(["iptables", "-S"], capture_output=True, text=True, timeout=2)
            if res.returncode == 0:
                lines = res.stdout.splitlines()
                has_output_drop = False
                has_forward_drop = False
                for line in lines:
                    if line.startswith("-P OUTPUT DROP"):
                        has_output_drop = True
                    elif line.startswith("-P FORWARD DROP"):
                        has_forward_drop = True
                
                if has_output_drop:
                    return 3007, "[ERR_FIREWALL_BLOCKING_FORWARD] 本机 iptables OUTPUT 默认策略被设为 DROP。这会导致 VPS 出站数据包被静默丢弃，从而彻底阻碍网关运行。"
                if has_forward_drop:
                    return 3007, "[ERR_FIREWALL_BLOCKING_FORWARD] 本机 iptables FORWARD 默认策略被设为 DROP。且未配置相应的转发规则，这通常会拦截 VPN 网卡的流量穿透。"
        except Exception:
            pass

        # 4. 检查系统反向路径过滤 (rp_filter) 设置
        rp_all_path = Path("/proc/sys/net/ipv4/conf/all/rp_filter")
        if rp_all_path.exists():
            try:
                val = rp_all_path.read_text(encoding="utf-8").strip()
                if val == "1":
                    return 3008, "[ERR_ROUTE_RP_FILTER_STRICT] 系统启用了严格的反向路径过滤(rp_filter=1)。原因: 在启用策略路由时，严格的路径过滤会导致通过虚拟网卡 tun0 的回包被内核静默丢弃，导致连接超时。请将 net.ipv4.conf.all.rp_filter 设置为 2 或 0。"
            except Exception:
                pass

    return None