import re
import socket
from django.conf import settings
from django.http import HttpResponse


def is_valid_ipv6(ip_address):
    try:
        socket.inet_pton(socket.AF_INET6, ip_address)
        return True
    except socket.error:
        return False


def is_ipv6_exempt(path):
    return any(re.match(m, path) for m in settings.IPV6_EXEMPT_URLS)


def block_ipv4(get_response):
    ''' block IPv4 requests except if the url is in IPV6_EXEMPT_URLS'''

    def middleware(request):
        if getattr(settings, 'DISABLE_IPV4_BLOCK', False):
            return get_response(request)

        path = request.path_info.lstrip('/')

        real_ip_headers = ['HTTP_X_REAL_IP', 'REMOTE_ADDR', 'HTTP_X_FORWARDED_FOR']
        client_ip = None

        for header in real_ip_headers:
            client_ip = request.META.get(header)

            if client_ip:
                break

        if is_valid_ipv6(client_ip) or is_ipv6_exempt(path):
            return get_response(request)
        else:
            return HttpResponse('Sorry, only reachable by IPv6')

    return middleware