# Copyright 2014-2016 OpenMarket Ltd
# Copyright 2019 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import logging

from zope.interface import implementer

from OpenSSL import SSL, crypto
from twisted.internet._sslverify import ClientTLSOptions, _defaultCurveName
from twisted.internet.abstract import isIPAddress, isIPv6Address
from twisted.internet.interfaces import IOpenSSLClientConnectionCreator
from twisted.internet.ssl import CertificateOptions, ContextFactory, platformTrust
from twisted.python.failure import Failure

logger = logging.getLogger(__name__)


class ServerContextFactory(ContextFactory):
    """Factory for PyOpenSSL SSL contexts that are used to handle incoming
    connections."""

    def __init__(self, config):
        self._context = SSL.Context(SSL.SSLv23_METHOD)
        self.configure_context(self._context, config)

    @staticmethod
    def configure_context(context, config):
        try:
            _ecCurve = crypto.get_elliptic_curve(_defaultCurveName)
            context.set_tmp_ecdh(_ecCurve)

        except Exception:
            logger.exception("Failed to enable elliptic curve for TLS")
        context.set_options(SSL.OP_NO_SSLv2 | SSL.OP_NO_SSLv3)
        context.use_certificate_chain_file(config.tls_certificate_file)
        context.use_privatekey(config.tls_private_key)

        # https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/
        context.set_cipher_list(
            "ECDH+AESGCM:ECDH+CHACHA20:ECDH+AES256:ECDH+AES128:!aNULL:!SHA1"
        )

    def getContext(self):
        return self._context


def _idnaBytes(text):
    """
    Convert some text typed by a human into some ASCII bytes. This is a
    copy of twisted.internet._idna._idnaBytes. For documentation, see the
    twisted documentation.
    """
    try:
        import idna
    except ImportError:
        return text.encode("idna")
    else:
        return idna.encode(text)


def _tolerateErrors(wrapped):
    """
    Wrap up an info_callback for pyOpenSSL so that if something goes wrong
    the error is immediately logged and the connection is dropped if possible.
    This is a copy of twisted.internet._sslverify._tolerateErrors. For
    documentation, see the twisted documentation.
    """

    def infoCallback(connection, where, ret):
        try:
            return wrapped(connection, where, ret)
        except:  # noqa: E722, taken from the twisted implementation
            f = Failure()
            logger.exception("Error during info_callback")
            connection.get_app_data().failVerification(f)

    return infoCallback


@implementer(IOpenSSLClientConnectionCreator)
class ClientTLSOptionsNoVerify(object):
    """
    Client creator for TLS without certificate identity verification. This is a
    copy of twisted.internet._sslverify.ClientTLSOptions with the identity
    verification left out. For documentation, see the twisted documentation.
    """

    def __init__(self, hostname, ctx):
        self._ctx = ctx

        if isIPAddress(hostname) or isIPv6Address(hostname):
            self._hostnameBytes = hostname.encode('ascii')
            self._sendSNI = False
        else:
            self._hostnameBytes = _idnaBytes(hostname)
            self._sendSNI = True

        ctx.set_info_callback(_tolerateErrors(self._identityVerifyingInfoCallback))

    def clientConnectionForTLS(self, tlsProtocol):
        context = self._ctx
        connection = SSL.Connection(context, None)
        connection.set_app_data(tlsProtocol)
        return connection

    def _identityVerifyingInfoCallback(self, connection, where, ret):
        # Literal IPv4 and IPv6 addresses are not permitted
        # as host names according to the RFCs
        if where & SSL.SSL_CB_HANDSHAKE_START and self._sendSNI:
            connection.set_tlsext_host_name(self._hostnameBytes)


class ClientTLSOptionsFactory(object):
    """Factory for Twisted ClientTLSOptions that are used to make connections
    to remote servers for federation."""

    def __init__(self, config):
        self._config = config
        self._options_noverify = CertificateOptions()

        # Check if we're using a custom list of a CA certificates
        trust_root = config.federation_ca_trust_root
        if trust_root is None:
            # Use CA root certs provided by OpenSSL
            trust_root = platformTrust()

        self._options_verify = CertificateOptions(trustRoot=trust_root)

    def get_options(self, host):
        # Use _makeContext so that we get a fresh OpenSSL CTX each time.

        # Check if certificate verification has been enabled
        should_verify = self._config.federation_verify_certificates

        # Check if we've disabled certificate verification for this host
        if should_verify:
            for regex in self._config.federation_certificate_verification_whitelist:
                if regex.match(host):
                    should_verify = False
                    break

        if should_verify:
            return ClientTLSOptions(host, self._options_verify._makeContext())
        return ClientTLSOptionsNoVerify(host, self._options_noverify._makeContext())