import asyncio
import ipaddress
import logging
import os
import socket
from enum import StrEnum
from urllib.parse import urlparse

logger = logging.getLogger(__name__)

_LOOPBACK_HOSTS = frozenset(["localhost", "127.0.0.1", "::1"])

_PRIVATE_IP_NETS = [
    ipaddress.ip_network("10.0.0.0/8"),
    ipaddress.ip_network("172.16.0.0/12"),
    ipaddress.ip_network("192.168.0.0/16"),
    ipaddress.ip_network("127.0.0.0/8"),
    ipaddress.ip_network("::1/128"),
    ipaddress.ip_network("fc00::/7"),
    ipaddress.ip_network("fe80::/10"),
]

_TAILNET_IPV4_NET = ipaddress.ip_network("100.64.0.0/10")

_ENV_ALLOW_INSECURE_PRIVATE_WS = "YUXI_ALLOW_INSECURE_PRIVATE_WS"


class GatewayBindMode(StrEnum):
    LOOPBACK = "loopback"
    LAN = "lan"
    TAILNET = "tailnet"
    AUTO = "auto"
    CUSTOM = "custom"


def is_loopback_address(ip: str | None) -> bool:
    if not ip:
        return False
    try:
        return ipaddress.ip_address(ip.strip()).is_loopback
    except ValueError:
        return False


def is_trusted_proxy_address(ip: str | None, trusted_proxies: list[str] | None) -> bool:
    if not ip or not trusted_proxies:
        return False
    try:
        addr = ipaddress.ip_address(ip.strip())
    except ValueError:
        return False
    for proxy in trusted_proxies:
        candidate = proxy.strip()
        if not candidate:
            continue
        try:
            net = ipaddress.ip_network(candidate, strict=False)
        except ValueError:
            continue
        if addr in net:
            return True
    return False


TAILSCALE_TRUSTED_PROXIES = ["127.0.0.1", "::1"]


def _parse_ip_literal(raw: str | None) -> str | None:
    if not raw:
        return None
    trimmed = raw.strip()
    if not trimmed:
        return None
    if trimmed.startswith("[") and "]" in trimmed:
        trimmed = trimmed[1 : trimmed.index("]")]
    if ":" in trimmed and "." in trimmed:
        last_colon = trimmed.rfind(":")
        candidate = trimmed[:last_colon]
        try:
            ipaddress.IPv4Address(candidate)
            trimmed = candidate
        except ValueError:
            pass
    try:
        ipaddress.ip_address(trimmed)
        return trimmed
    except ValueError:
        return None


def resolve_forwarded_client_ip(
    forwarded_for: str | None,
    trusted_proxies: list[str] | None,
) -> str | None:
    if not trusted_proxies:
        return None
    chain: list[str] = []
    for entry in (forwarded_for or "").split(","):
        normalized = _parse_ip_literal(entry)
        if normalized:
            chain.append(normalized)
    if not chain:
        return None
    for hop in reversed(chain):
        if is_loopback_address(hop):
            continue
        if not is_trusted_proxy_address(hop, trusted_proxies):
            return hop
    return None


def resolve_client_ip(
    remote_addr: str | None,
    forwarded_for: str | None = None,
    real_ip: str | None = None,
    trusted_proxies: list[str] | None = None,
    allow_real_ip_fallback: bool = False,
) -> str | None:
    remote = _parse_ip_literal(remote_addr)
    if not remote:
        return None
    if not is_trusted_proxy_address(remote, trusted_proxies):
        return remote
    forwarded = resolve_forwarded_client_ip(forwarded_for, trusted_proxies)
    if forwarded:
        return forwarded
    if allow_real_ip_fallback:
        return _parse_ip_literal(real_ip)
    return None


def has_forwarded_request_headers(headers: dict) -> bool:
    return bool(
        headers.get("forwarded")
        or headers.get("x-forwarded-for")
        or headers.get("x-forwarded-proto")
        or headers.get("x-real-ip")
        or headers.get("x-forwarded-host")
    )


def is_local_direct_request(
    remote_addr: str | None,
    headers: dict | None = None,
) -> bool:
    if not remote_addr:
        return False
    if headers and has_forwarded_request_headers(headers):
        return False
    return is_loopback_address(remote_addr)


def has_tailscale_proxy_headers(headers: dict | None) -> bool:
    if not headers:
        return False
    return bool(headers.get("x-forwarded-for") and headers.get("x-forwarded-proto") and headers.get("x-forwarded-host"))


def is_tailscale_proxy_request(
    remote_addr: str | None,
    headers: dict | None = None,
) -> bool:
    if not remote_addr:
        return False
    return is_loopback_address(remote_addr) and has_tailscale_proxy_headers(headers)


def resolve_tailscale_client_ip(
    remote_addr: str | None,
    headers: dict | None = None,
) -> str | None:
    return resolve_client_ip(
        remote_addr=remote_addr,
        forwarded_for=headers.get("x-forwarded-for") if headers else None,
        trusted_proxies=list(TAILSCALE_TRUSTED_PROXIES),
    )


def is_loopback_host(host: str) -> bool:
    host = host.strip().lower().rstrip(".")
    if not host:
        return False
    if host in _LOOPBACK_HOSTS:
        return True
    try:
        addr = ipaddress.ip_address(host)
    except ValueError:
        return False
    return addr.is_loopback


def is_private_host(host: str) -> bool:
    host = host.strip().lower().rstrip(".")
    if not host:
        return False
    try:
        addr = ipaddress.ip_address(host)
    except ValueError:
        return False
    return addr.is_private


def is_private_or_loopback_host(host: str) -> bool:
    host = host.strip().lower().rstrip(".")
    if not host:
        return False
    try:
        addr = ipaddress.ip_address(host)
    except ValueError:
        return False
    return addr.is_private or addr.is_loopback or addr.is_link_local


def is_localish_host(host: str | None) -> bool:
    if not host:
        return False
    host = host.strip().lower().rstrip(".")
    return is_loopback_host(host) or host.endswith(".ts.net")


def is_secure_ws_url(url: str, allow_private_ws: bool = False) -> bool:
    try:
        parsed = urlparse(url)
    except ValueError:
        return False

    protocol = parsed.scheme.lower()
    if protocol == "wss":
        return True
    if protocol not in ("ws", "http"):
        return False

    hostname = _extract_ws_hostname(parsed)
    if not hostname:
        return False

    if is_loopback_host(hostname):
        return True

    if allow_private_ws and is_private_or_loopback_host(hostname):
        return True

    return False


def _extract_ws_hostname(parsed) -> str:
    netloc = parsed.netloc or parsed.hostname or ""
    if "@" in netloc:
        netloc = netloc.rsplit("@", 1)[-1]
    if "[" in netloc and "]" in netloc:
        start = netloc.index("[") + 1
        end = netloc.index("]")
        return netloc[start:end]
    if ":" in netloc:
        return netloc.rsplit(":", 1)[0]
    return netloc


async def can_bind_to_host(host: str) -> bool:
    loop = asyncio.get_running_loop()
    return await loop.run_in_executor(None, _sync_can_bind_to_host, host)


def _sync_can_bind_to_host(host: str) -> bool:
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    try:
        sock.bind((host, 0))
        return True
    except OSError:
        return False
    finally:
        sock.close()


_can_bind_cache: dict[str, bool] = {}


async def can_bind_to_host_cached(host: str) -> bool:
    cached = _can_bind_cache.get(host)
    if cached is not None:
        return cached
    result = await can_bind_to_host(host)
    _can_bind_cache[host] = result
    return result


def _is_container_environment() -> bool:
    if os.path.exists("/.dockerenv"):
        return True
    try:
        with open("/proc/1/cgroup") as f:
            content = f.read()
            if "docker" in content or "kubepods" in content:
                return True
    except OSError:
        pass
    return False


def _pick_primary_tailnet_ipv4() -> str | None:
    try:
        for info in socket.getaddrinfo(socket.gethostname(), None, socket.AF_INET):
            ip = info[4][0]
            try:
                addr = ipaddress.ip_address(ip)
            except ValueError:
                continue
            if addr in _TAILNET_IPV4_NET:
                return ip
    except OSError:
        pass
    return None


async def resolve_gateway_bind_host(
    mode: GatewayBindMode | None = None,
    custom_host: str | None = None,
) -> str:
    mode = mode or GatewayBindMode.LOOPBACK

    if mode == GatewayBindMode.LOOPBACK:
        if await can_bind_to_host("127.0.0.1"):
            return "127.0.0.1"
        return "0.0.0.0"

    if mode == GatewayBindMode.TAILNET:
        tailnet_ip = _pick_primary_tailnet_ipv4()
        if tailnet_ip and await can_bind_to_host(tailnet_ip):
            return tailnet_ip
        if await can_bind_to_host("127.0.0.1"):
            return "127.0.0.1"
        return "0.0.0.0"

    if mode == GatewayBindMode.LAN:
        return "0.0.0.0"

    if mode == GatewayBindMode.CUSTOM:
        host = (custom_host or "").strip()
        if not host:
            return "0.0.0.0"
        try:
            ipaddress.ip_address(host)
        except ValueError:
            logger.warning("gateway bind=custom: invalid IP '%s', falling back to 0.0.0.0", host)
            return "0.0.0.0"
        if await can_bind_to_host(host):
            return host
        logger.warning("gateway bind=custom: cannot bind '%s', falling back to 0.0.0.0", host)
        return "0.0.0.0"

    if mode == GatewayBindMode.AUTO:
        if _is_container_environment():
            return "0.0.0.0"
        if await can_bind_to_host("127.0.0.1"):
            return "127.0.0.1"
        return "0.0.0.0"

    return "0.0.0.0"


def build_ws_security_error(display_host: str) -> str:
    allow_private = os.environ.get(_ENV_ALLOW_INSECURE_PRIVATE_WS) == "1"
    msg = (
        f'SECURITY ERROR: Cannot connect to "{display_host}" over plaintext ws://. '
        "Both credentials and chat data would be exposed to network interception. "
        "Use wss:// for remote URLs. Safe defaults: keep gateway.bind=loopback and "
        "connect via SSH tunnel "
        "(ssh -N -L 18789:127.0.0.1:18789 user@gateway-host), or use Tailscale Serve/Funnel."
    )
    if not allow_private:
        msg += f" Break-glass (trusted private networks only): set {_ENV_ALLOW_INSECURE_PRIVATE_WS}=1."
    return msg