"""路由、白名单和转发器共用的网络基础函数。"""

import functools
import ipaddress
import socket
import threading
import time


def ttl_cache(seconds: int, maxsize: int = 16384):
    """带 TTL 的小型线程安全缓存，并保留 ``cache_clear`` 兼容接口。"""
    def decorator(function):
        store = {}
        lock = threading.Lock()

        @functools.wraps(function)
        def wrapper(*args, **kwargs):
            key = (args, tuple(sorted(kwargs.items())))
            now = time.time()
            with lock:
                hit = store.get(key)
            if hit and now - hit[0] < seconds:
                return hit[1]
            value = function(*args, **kwargs)
            with lock:
                store[key] = (now, value)
                if len(store) > maxsize:
                    cutoff = now - seconds
                    for cached_key, (timestamp, _) in list(store.items()):
                        if timestamp < cutoff:
                            del store[cached_key]
                    if len(store) > maxsize:
                        store.clear()
            return value

        def cache_clear():
            with lock:
                store.clear()

        wrapper.cache_clear = cache_clear
        return wrapper
    return decorator


def is_private_ipv4_int(value: int) -> bool:
    """整数形式 IPv4 是否属于常见私网、回环或链路本地段。"""
    return (
        (value & 0xFF000000) == 0x0A000000
        or (value & 0xFFF00000) == 0xAC100000
        or (value & 0xFFFF0000) == 0xC0A80000
        or (value & 0xFF000000) == 0x7F000000
        or (value & 0xFFFF0000) == 0xA9FE0000
    )


def resolve_host_ips(host: str):
    """解析主机名的 IPv4/IPv6 集合；字面量 IP 返回自身，失败返回空集合。"""
    try:
        return {ipaddress.ip_address(host)}
    except ValueError:
        pass
    try:
        return {
            ipaddress.ip_address(address[4][0])
            for address in socket.getaddrinfo(host, None, socket.AF_UNSPEC, socket.SOCK_STREAM)
        }
    except Exception:
        return set()


def is_private_host(host: str) -> bool:
    """目标是否命中私网、回环或 IPv6 ULA/链路本地地址。"""
    for address in resolve_host_ips(host):
        if address.version == 4 and is_private_ipv4_int(int(address)):
            return True
        if address.version == 6 and (
            address.is_loopback
            or address.is_link_local
            or address in ipaddress.ip_network("fc00::/7")
        ):
            return True
    return False