# Copyright 2014-2016 OpenMarket 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
import os
from datetime import datetime
from typing import List, Optional, Pattern

from OpenSSL import SSL, crypto
from twisted.internet._sslverify import Certificate, trustRootFromCertificates

from synapse.config._base import Config, ConfigError
from synapse.util import glob_to_regex

logger = logging.getLogger(__name__)


class TlsConfig(Config):
    section = "tls"

    def read_config(self, config: dict, config_dir_path: str, **kwargs):

        self.tls_certificate_file = self.abspath(config.get("tls_certificate_path"))
        self.tls_private_key_file = self.abspath(config.get("tls_private_key_path"))

        if self.root.server.has_tls_listener():
            if not self.tls_certificate_file:
                raise ConfigError(
                    "tls_certificate_path must be specified if TLS-enabled listeners are "
                    "configured."
                )
            if not self.tls_private_key_file:
                raise ConfigError(
                    "tls_private_key_path must be specified if TLS-enabled listeners are "
                    "configured."
                )

        # Whether to verify certificates on outbound federation traffic
        self.federation_verify_certificates = config.get(
            "federation_verify_certificates", True
        )

        # Minimum TLS version to use for outbound federation traffic
        self.federation_client_minimum_tls_version = str(
            config.get("federation_client_minimum_tls_version", 1)
        )

        if self.federation_client_minimum_tls_version not in ["1", "1.1", "1.2", "1.3"]:
            raise ConfigError(
                "federation_client_minimum_tls_version must be one of: 1, 1.1, 1.2, 1.3"
            )

        # Prevent people shooting themselves in the foot here by setting it to
        # the biggest number blindly
        if self.federation_client_minimum_tls_version == "1.3":
            if getattr(SSL, "OP_NO_TLSv1_3", None) is None:
                raise ConfigError(
                    "federation_client_minimum_tls_version cannot be 1.3, "
                    "your OpenSSL does not support it"
                )

        # Whitelist of domains to not verify certificates for
        fed_whitelist_entries = config.get(
            "federation_certificate_verification_whitelist", []
        )
        if fed_whitelist_entries is None:
            fed_whitelist_entries = []

        # Support globs (*) in whitelist values
        self.federation_certificate_verification_whitelist: List[Pattern] = []
        for entry in fed_whitelist_entries:
            try:
                entry_regex = glob_to_regex(entry.encode("ascii").decode("ascii"))
            except UnicodeEncodeError:
                raise ConfigError(
                    "IDNA domain names are not allowed in the "
                    "federation_certificate_verification_whitelist: %s" % (entry,)
                )

            # Convert globs to regex
            self.federation_certificate_verification_whitelist.append(entry_regex)

        # List of custom certificate authorities for federation traffic validation
        custom_ca_list = config.get("federation_custom_ca_list", None)

        # Read in and parse custom CA certificates
        self.federation_ca_trust_root = None
        if custom_ca_list is not None:
            if len(custom_ca_list) == 0:
                # A trustroot cannot be generated without any CA certificates.
                # Raise an error if this option has been specified without any
                # corresponding certificates.
                raise ConfigError(
                    "federation_custom_ca_list specified without "
                    "any certificate files"
                )

            certs = []
            for ca_file in custom_ca_list:
                logger.debug("Reading custom CA certificate file: %s", ca_file)
                content = self.read_file(ca_file, "federation_custom_ca_list")

                # Parse the CA certificates
                try:
                    cert_base = Certificate.loadPEM(content)
                    certs.append(cert_base)
                except Exception as e:
                    raise ConfigError(
                        "Error parsing custom CA certificate file %s: %s" % (ca_file, e)
                    )

            self.federation_ca_trust_root = trustRootFromCertificates(certs)

        # This config option applies to non-federation HTTP clients
        # (e.g. for talking to recaptcha, identity servers, and such)
        # It should never be used in production, and is intended for
        # use only when running tests.
        self.use_insecure_ssl_client_just_for_testing_do_not_use = config.get(
            "use_insecure_ssl_client_just_for_testing_do_not_use"
        )

        self.tls_certificate: Optional[crypto.X509] = None
        self.tls_private_key: Optional[crypto.PKey] = None

    def is_disk_cert_valid(self, allow_self_signed=True):
        """
        Is the certificate we have on disk valid, and if so, for how long?

        Args:
            allow_self_signed (bool): Should we allow the certificate we
                read to be self signed?

        Returns:
            int: Days remaining of certificate validity.
            None: No certificate exists.
        """
        if not os.path.exists(self.tls_certificate_file):
            return None

        try:
            with open(self.tls_certificate_file, "rb") as f:
                cert_pem = f.read()
        except Exception as e:
            raise ConfigError(
                "Failed to read existing certificate file %s: %s"
                % (self.tls_certificate_file, e)
            )

        try:
            tls_certificate = crypto.load_certificate(crypto.FILETYPE_PEM, cert_pem)
        except Exception as e:
            raise ConfigError(
                "Failed to parse existing certificate file %s: %s"
                % (self.tls_certificate_file, e)
            )

        if not allow_self_signed:
            if tls_certificate.get_subject() == tls_certificate.get_issuer():
                raise ValueError(
                    "TLS Certificate is self signed, and this is not permitted"
                )

        # YYYYMMDDhhmmssZ -- in UTC
        expires_on = datetime.strptime(
            tls_certificate.get_notAfter().decode("ascii"), "%Y%m%d%H%M%SZ"
        )
        now = datetime.utcnow()
        days_remaining = (expires_on - now).days
        return days_remaining

    def read_certificate_from_disk(self):
        """
        Read the certificates and private key from disk.
        """
        self.tls_private_key = self.read_tls_private_key()
        self.tls_certificate = self.read_tls_certificate()

    def generate_config_section(
        self,
        config_dir_path,
        server_name,
        data_dir_path,
        tls_certificate_path,
        tls_private_key_path,
        **kwargs,
    ):
        """If the TLS paths are not specified the default will be certs in the
        config directory"""

        base_key_name = os.path.join(config_dir_path, server_name)

        if bool(tls_certificate_path) != bool(tls_private_key_path):
            raise ConfigError(
                "Please specify both a cert path and a key path or neither."
            )

        tls_enabled = "" if tls_certificate_path and tls_private_key_path else "#"

        if not tls_certificate_path:
            tls_certificate_path = base_key_name + ".tls.crt"
        if not tls_private_key_path:
            tls_private_key_path = base_key_name + ".tls.key"

        # flake8 doesn't recognise that variables are used in the below string
        _ = tls_enabled

        return (
            """\
        ## TLS ##

        # PEM-encoded X509 certificate for TLS.
        # This certificate, as of Synapse 1.0, will need to be a valid and verifiable
        # certificate, signed by a recognised Certificate Authority.
        #
        # Be sure to use a `.pem` file that includes the full certificate chain including
        # any intermediate certificates (for instance, if using certbot, use
        # `fullchain.pem` as your certificate, not `cert.pem`).
        #
        %(tls_enabled)stls_certificate_path: "%(tls_certificate_path)s"

        # PEM-encoded private key for TLS
        #
        %(tls_enabled)stls_private_key_path: "%(tls_private_key_path)s"

        # Whether to verify TLS server certificates for outbound federation requests.
        #
        # Defaults to `true`. To disable certificate verification, uncomment the
        # following line.
        #
        #federation_verify_certificates: false

        # The minimum TLS version that will be used for outbound federation requests.
        #
        # Defaults to `1`. Configurable to `1`, `1.1`, `1.2`, or `1.3`. Note
        # that setting this value higher than `1.2` will prevent federation to most
        # of the public Matrix network: only configure it to `1.3` if you have an
        # entirely private federation setup and you can ensure TLS 1.3 support.
        #
        #federation_client_minimum_tls_version: 1.2

        # Skip federation certificate verification on the following whitelist
        # of domains.
        #
        # This setting should only be used in very specific cases, such as
        # federation over Tor hidden services and similar. For private networks
        # of homeservers, you likely want to use a private CA instead.
        #
        # Only effective if federation_verify_certicates is `true`.
        #
        #federation_certificate_verification_whitelist:
        #  - lon.example.com
        #  - *.domain.com
        #  - *.onion

        # List of custom certificate authorities for federation traffic.
        #
        # This setting should only normally be used within a private network of
        # homeservers.
        #
        # Note that this list will replace those that are provided by your
        # operating environment. Certificates must be in PEM format.
        #
        #federation_custom_ca_list:
        #  - myCA1.pem
        #  - myCA2.pem
        #  - myCA3.pem
        """
            # Lowercase the string representation of boolean values
            % {
                x[0]: str(x[1]).lower() if isinstance(x[1], bool) else x[1]
                for x in locals().items()
            }
        )

    def read_tls_certificate(self) -> crypto.X509:
        """Reads the TLS certificate from the configured file, and returns it

        Returns:
            The certificate
        """
        cert_path = self.tls_certificate_file
        logger.info("Loading TLS certificate from %s", cert_path)
        cert_pem = self.read_file(cert_path, "tls_certificate_path")
        cert = crypto.load_certificate(crypto.FILETYPE_PEM, cert_pem)

        return cert

    def read_tls_private_key(self) -> crypto.PKey:
        """Reads the TLS private key from the configured file, and returns it

        Returns:
            The private key
        """
        private_key_path = self.tls_private_key_file
        logger.info("Loading TLS key from %s", private_key_path)
        private_key_pem = self.read_file(private_key_path, "tls_private_key_path")
        return crypto.load_privatekey(crypto.FILETYPE_PEM, private_key_pem)
