"""Validators to determine the current webserver configuration"""
import logging
import socket
import requests
import zope.interface

import six
from six.moves import xrange  # pylint: disable=import-error,redefined-builtin

from acme import crypto_util
from acme import errors as acme_errors
from certbot import interfaces


logger = logging.getLogger(__name__)


@zope.interface.implementer(interfaces.IValidator)
class Validator(object):
    # pylint: disable=no-self-use
    """Collection of functions to test a live webserver's configuration"""

    def certificate(self, cert, name, alt_host=None, port=443):
        """Verifies the certificate presented at name is cert"""
        if alt_host is None:
            host = socket.gethostbyname(name)
        elif isinstance(alt_host, six.binary_type):
            host = alt_host
        else:
            host = alt_host.encode()
        name = name if isinstance(name, six.binary_type) else name.encode()

        try:
            presented_cert = crypto_util.probe_sni(name, host, port)
        except acme_errors.Error as error:
            logger.exception(error)
            return False

        return presented_cert.digest("sha256") == cert.digest("sha256")

    def redirect(self, name, port=80, headers=None):
        """Test whether webserver redirects to secure connection."""
        url = "http://{0}:{1}".format(name, port)
        if headers:
            response = requests.get(url, headers=headers, allow_redirects=False)
        else:
            response = requests.get(url, allow_redirects=False)

        redirect_location = response.headers.get("location", "")
        # We're checking that the redirect we added behaves correctly.
        # It's okay for some server configuration to redirect to an
        # http URL, as long as it's on some other domain.
        if not redirect_location.startswith("https://"):
            return False

        if response.status_code != 301:
            logger.error("Server did not redirect with permanent code")
            return False

        return True

    def any_redirect(self, name, port=80, headers=None):
        """Test whether webserver redirects."""
        url = "http://{0}:{1}".format(name, port)
        if headers:
            response = requests.get(url, headers=headers, allow_redirects=False)
        else:
            response = requests.get(url, allow_redirects=False)

        return response.status_code in xrange(300, 309)

    def hsts(self, name):
        """Test for HTTP Strict Transport Security header"""
        headers = requests.get("https://" + name).headers
        hsts_header = headers.get("strict-transport-security")

        if not hsts_header:
            return False

        # Split directives following RFC6797, section 6.1
        directives = [d.split("=") for d in hsts_header.split(";")]
        max_age = [d for d in directives if d[0] == "max-age"]

        if not max_age:
            logger.error("Server responded with invalid HSTS header field")
            return False

        try:
            _, max_age_value = max_age[0]
            max_age_value = int(max_age_value)
        except ValueError:
            logger.error("Server responded with invalid HSTS header field")
            return False

        # Test whether HSTS does not expire for at least two weeks.
        if max_age_value <= (2 * 7 * 24 * 3600):
            logger.error("HSTS should not expire in less than two weeks")
            return False

        return True

    def ocsp_stapling(self, name):
        """Verify ocsp stapling for domain."""
        raise NotImplementedError()
