# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# 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 re
from typing import TYPE_CHECKING, Awaitable, Callable, Dict, Optional, Set, Tuple

import attr
import saml2
import saml2.response
from saml2.client import Saml2Client

from synapse.api.errors import RedirectException
from synapse.config import ConfigError
from synapse.config.saml2 import DEFAULT_USER_MAPPING_PROVIDER
from synapse.handlers._base import BaseHandler
from synapse.handlers.sso import MappingException, UserAttributes
from synapse.http.servlet import parse_string
from synapse.http.site import SynapseRequest
from synapse.module_api import ModuleApi
from synapse.types import (
    UserID,
    map_username_to_mxid_localpart,
    mxid_localpart_allowed_characters,
)
from synapse.util import dict_merge
from synapse.util.async_helpers import maybe_awaitable
from synapse.util.iterutils import chunk_seq

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)


@attr.s(slots=True)
class Saml2SessionData:
    """Data we track about SAML2 sessions"""

    # time the session was created, in milliseconds
    creation_time = attr.ib()
    # The user interactive authentication session ID associated with this SAML
    # session (or None if this SAML session is for an initial login).
    ui_auth_session_id = attr.ib(type=Optional[str], default=None)


class SamlHandler(BaseHandler):
    def __init__(self, hs: "HomeServer"):
        super().__init__(hs)

        # If support for legacy saml2_mapping_providers is dropped then this
        # is where the DefaultSamlMappingProvider should be loaded

        self._user_mapping_provider = hs.get_saml2_user_mapping_provider()

        # At this point either a module will have registered user mapping provider
        # callbacks or the default will have been registered.
        assert self._user_mapping_provider.module_has_registered

        # Merge the required and optional saml_attributes registered by the mapping
        # provider with the base sp config. NOTE: If there are conflicts then the
        # module's expected attributes are overwritten by the base sp_config. This is
        # how it worked with legacy modules.
        (
            required_attributes,
            optional_attributes,
        ) = self._user_mapping_provider.get_saml_attributes()

        # Required for backwards compatability
        if hs.config.saml2_grandfathered_mxid_source_attribute:
            optional_attributes.add(hs.config.saml2_grandfathered_mxid_source_attribute)

        optional_attributes -= required_attributes

        sp_config_dict = {
            "service": {
                "sp": {
                    "required_attributes": list(required_attributes),
                    "optional_attributes": list(optional_attributes),
                }
            },
        }

        # Merged this way around for backwards compatability
        dict_merge(
            merge_dict=hs.config.saml2.base_sp_config,
            into_dict=sp_config_dict,
        )

        self.saml2_sp_config = saml2.config.SPConfig()
        self.saml2_sp_config.load(sp_config_dict)

        self._saml_client = Saml2Client(self.saml2_sp_config)
        self._saml_idp_entityid = hs.config.saml2_idp_entityid

        self._saml2_session_lifetime = hs.config.saml2_session_lifetime
        self._grandfathered_mxid_source_attribute = (
            hs.config.saml2_grandfathered_mxid_source_attribute
        )
        self._saml2_attribute_requirements = hs.config.saml2.attribute_requirements
        self._error_template = hs.config.sso_error_template

        # identifier for the external_ids table
        self.idp_id = "saml"

        # user-facing name of this auth provider
        self.idp_name = "SAML"

        # we do not currently support icons/brands for SAML auth, but this is required by
        # the SsoIdentityProvider protocol type.
        self.idp_icon = None
        self.idp_brand = None
        self.unstable_idp_brand = None

        # a map from saml session id to Saml2SessionData object
        self._outstanding_requests_dict: Dict[str, Saml2SessionData] = {}

        self._sso_handler = hs.get_sso_handler()
        self._sso_handler.register_identity_provider(self)

    async def handle_redirect_request(
        self,
        request: SynapseRequest,
        client_redirect_url: Optional[bytes],
        ui_auth_session_id: Optional[str] = None,
    ) -> str:
        """Handle an incoming request to /login/sso/redirect

        Args:
            request: the incoming HTTP request
            client_redirect_url: the URL that we should redirect the
                client to after login (or None for UI Auth).
            ui_auth_session_id: The session ID of the ongoing UI Auth (or
                None if this is a login).

        Returns:
            URL to redirect to
        """
        if not client_redirect_url:
            # Some SAML identity providers (e.g. Google) require a
            # RelayState parameter on requests, so pass in a dummy redirect URL
            # (which will never get used).
            client_redirect_url = b"unused"

        reqid, info = self._saml_client.prepare_for_authenticate(
            entityid=self._saml_idp_entityid, relay_state=client_redirect_url
        )

        # Since SAML sessions timeout it is useful to log when they were created.
        logger.info("Initiating a new SAML session: %s" % (reqid,))

        now = self.clock.time_msec()
        self._outstanding_requests_dict[reqid] = Saml2SessionData(
            creation_time=now,
            ui_auth_session_id=ui_auth_session_id,
        )

        for key, value in info["headers"]:
            if key == "Location":
                return value

        # this shouldn't happen!
        raise Exception("prepare_for_authenticate didn't return a Location header")

    async def handle_saml_response(self, request: SynapseRequest) -> None:
        """Handle an incoming request to /_synapse/client/saml2/authn_response

        Args:
            request: the incoming request from the browser. We'll
                respond to it with a redirect.

        Returns:
            Completes once we have handled the request.
        """
        resp_bytes = parse_string(request, "SAMLResponse", required=True)
        relay_state = parse_string(request, "RelayState", required=True)

        # expire outstanding sessions before parse_authn_request_response checks
        # the dict.
        self.expire_sessions()

        try:
            saml2_auth = self._saml_client.parse_authn_request_response(
                resp_bytes,
                saml2.BINDING_HTTP_POST,
                outstanding=self._outstanding_requests_dict,
            )
        except saml2.response.UnsolicitedResponse as e:
            # the pysaml2 library helpfully logs an ERROR here, but neglects to log
            # the session ID. I don't really want to put the full text of the exception
            # in the (user-visible) exception message, so let's log the exception here
            # so we can track down the session IDs later.
            logger.warning(str(e))
            self._sso_handler.render_error(
                request, "unsolicited_response", "Unexpected SAML2 login."
            )
            return
        except Exception as e:
            self._sso_handler.render_error(
                request,
                "invalid_response",
                "Unable to parse SAML2 response: %s." % (e,),
            )
            return

        if saml2_auth.not_signed:
            self._sso_handler.render_error(
                request, "unsigned_respond", "SAML2 response was not signed."
            )
            return

        logger.debug("SAML2 response: %s", saml2_auth.origxml)

        await self._handle_authn_response(request, saml2_auth, relay_state)

    async def _handle_authn_response(
        self,
        request: SynapseRequest,
        saml2_auth: saml2.response.AuthnResponse,
        relay_state: str,
    ) -> None:
        """Handle an AuthnResponse, having parsed it from the request params

        Assumes that the signature on the response object has been checked. Maps
        the user onto an MXID, registering them if necessary, and returns a response
        to the browser.

        Args:
            request: the incoming request from the browser. We'll respond to it with an
                HTML page or a redirect
            saml2_auth: the parsed AuthnResponse object
            relay_state: the RelayState query param, which encodes the URI to rediret
               back to
        """

        for assertion in saml2_auth.assertions:
            # kibana limits the length of a log field, whereas this is all rather
            # useful, so split it up.
            count = 0
            for part in chunk_seq(str(assertion), 10000):
                logger.info(
                    "SAML2 assertion: %s%s", "(%i)..." % (count,) if count else "", part
                )
                count += 1

        logger.info("SAML2 mapped attributes: %s", saml2_auth.ava)

        current_session = self._outstanding_requests_dict.pop(
            saml2_auth.in_response_to, None
        )

        # first check if we're doing a UIA
        if current_session and current_session.ui_auth_session_id:
            try:
                remote_user_id = await self._user_mapping_provider.get_remote_user_id(
                    saml2_auth, None
                )
            except MappingException as e:
                logger.exception("Failed to extract remote user id from SAML response")
                self._sso_handler.render_error(request, "mapping_error", str(e))
                return

            return await self._sso_handler.complete_sso_ui_auth_request(
                self.idp_id,
                remote_user_id,
                current_session.ui_auth_session_id,
                request,
            )

        # otherwise, we're handling a login request.

        # Ensure that the attributes of the logged in user meet the required
        # attributes.
        if not self._sso_handler.check_required_attributes(
            request, saml2_auth.ava, self._saml2_attribute_requirements
        ):
            return

        # Call the mapper to register/login the user
        try:
            await self._complete_saml_login(saml2_auth, request, relay_state)
        except MappingException as e:
            logger.exception("Could not map user")
            self._sso_handler.render_error(request, "mapping_error", str(e))

    async def _complete_saml_login(
        self,
        saml2_auth: saml2.response.AuthnResponse,
        request: SynapseRequest,
        client_redirect_url: str,
    ) -> None:
        """
        Given a SAML response, complete the login flow

        Retrieves the remote user ID, registers the user if necessary, and serves
        a redirect back to the client with a login-token.

        Args:
            saml2_auth: The parsed SAML2 response.
            request: The request to respond to
            client_redirect_url: The redirect URL passed in by the client.

        Raises:
            MappingException if there was a problem mapping the response to a user.
            RedirectException: some mapping providers may raise this if they need
                to redirect to an interstitial page.
        """
        remote_user_id = await self._user_mapping_provider.get_remote_user_id(
            saml2_auth, client_redirect_url
        )

        async def saml_response_to_remapped_user_attributes(
            failures: int,
        ) -> UserAttributes:
            """
            Call the mapping provider to map a SAML response to user attributes and coerce the result into the standard form.

            This is backwards compatibility for abstraction for the SSO handler.
            """
            # Call the mapping provider.
            result = await self._user_mapping_provider.saml_response_to_user_attributes(
                saml2_auth, failures, client_redirect_url
            )
            # Remap some of the results.
            return UserAttributes(
                localpart=result.get("mxid_localpart"),
                display_name=result.get("displayname"),
                emails=result.get("emails", []),
            )

        async def grandfather_existing_users() -> Optional[str]:
            # backwards-compatibility hack: see if there is an existing user with a
            # suitable mapping from the uid
            if (
                self._grandfathered_mxid_source_attribute
                and self._grandfathered_mxid_source_attribute in saml2_auth.ava
            ):
                attrval = saml2_auth.ava[self._grandfathered_mxid_source_attribute][0]
                user_id = UserID(
                    map_username_to_mxid_localpart(attrval), self.server_name
                ).to_string()

                logger.debug(
                    "Looking for existing account based on mapped %s %s",
                    self._grandfathered_mxid_source_attribute,
                    user_id,
                )

                users = await self.store.get_users_by_id_case_insensitive(user_id)
                if users:
                    registered_user_id = list(users.keys())[0]
                    logger.info("Grandfathering mapping to %s", registered_user_id)
                    return registered_user_id

            return None

        await self._sso_handler.complete_sso_login_request(
            self.idp_id,
            remote_user_id,
            request,
            client_redirect_url,
            saml_response_to_remapped_user_attributes,
            grandfather_existing_users,
        )

    def expire_sessions(self):
        expire_before = self.clock.time_msec() - self._saml2_session_lifetime
        to_expire = set()
        for reqid, data in self._outstanding_requests_dict.items():
            if data.creation_time < expire_before:
                to_expire.add(reqid)
        for reqid in to_expire:
            logger.debug("Expiring session id %s", reqid)
            del self._outstanding_requests_dict[reqid]


DOT_REPLACE_PATTERN = re.compile(
    "[^%s]" % (re.escape("".join(mxid_localpart_allowed_characters)),)
)


def dot_replace_for_mxid(username: str) -> str:
    """Replace any characters which are not allowed in Matrix IDs with a dot."""
    username = username.lower()
    username = DOT_REPLACE_PATTERN.sub(".", username)

    # regular mxids aren't allowed to start with an underscore either
    username = re.sub("^_", "", username)
    return username


MXID_MAPPER_MAP: Dict[str, Callable[[str], str]] = {
    "hexencode": map_username_to_mxid_localpart,
    "dotreplace": dot_replace_for_mxid,
}


@attr.s
class SamlConfig:
    mxid_source_attribute = attr.ib()
    mxid_mapper = attr.ib()


# The type definition for the user mapping provider callbacks
GET_REMOTE_USER_ID_CALLBACK = Callable[
    [saml2.response.AuthnResponse, Optional[str]], Awaitable[str]
]
SAML_RESPONSE_TO_USER_ATTRIBUTES_CALLBACK = Callable[
    [saml2.response.AuthnResponse, int, str], Awaitable[Dict]
]


class DefaultSamlMappingProvider:
    __version__ = "0.0.1"

    def __init__(self, parsed_config: SamlConfig, module_api: ModuleApi):
        """The default SAML user mapping provider

        Args:
            parsed_config: Module configuration
            module_api: module api proxy
        """
        self._mxid_source_attribute = parsed_config.mxid_source_attribute
        self._mxid_mapper = parsed_config.mxid_mapper

        module_api.register_saml2_user_mapping_provider_callbacks(
            get_remote_user_id=self.get_remote_user_id,
            saml_response_to_user_attributes=self.saml_response_to_user_attributes,
            saml_attributes=(
                {"uid", self._mxid_source_attribute},
                {"displayName", "email"},
            ),
        )

    async def get_remote_user_id(
        self,
        saml_response: saml2.response.AuthnResponse,
        client_redirect_url: Optional[str],
    ) -> str:
        """Extracts the remote user id from the SAML response"""
        try:
            return saml_response.ava["uid"][0]
        except KeyError:
            logger.warning("SAML2 response lacks a 'uid' attestation")
            raise MappingException("'uid' not in SAML2 response")

    async def saml_response_to_user_attributes(
        self,
        saml_response: saml2.response.AuthnResponse,
        failures: int,
        client_redirect_url: str,
    ) -> dict:
        """Maps some text from a SAML response to attributes of a new user

        Args:
            saml_response: A SAML auth response object

            failures: How many times a call to this function with this
                saml_response has resulted in a failure

            client_redirect_url: where the client wants to redirect to

        Returns:
            dict: A dict containing new user attributes. Possible keys:
                * mxid_localpart (str): Required. The localpart of the user's mxid
                * displayname (str): The displayname of the user
                * emails (list[str]): Any emails for the user
        """
        try:
            mxid_source = saml_response.ava[self._mxid_source_attribute][0]
        except KeyError:
            logger.warning(
                "SAML2 response lacks a '%s' attestation",
                self._mxid_source_attribute,
            )
            raise MappingException(
                "%s not in SAML2 response" % (self._mxid_source_attribute,)
            )

        # Use the configured mapper for this mxid_source
        localpart = self._mxid_mapper(mxid_source)

        # Append suffix integer if last call to this function failed to produce
        # a usable mxid.
        localpart += str(failures) if failures else ""

        # Retrieve the display name from the saml response
        # If displayname is None, the mxid_localpart will be used instead
        displayname = saml_response.ava.get("displayName", [None])[0]

        # Retrieve any emails present in the saml response
        emails = saml_response.ava.get("email", [])

        return {
            "mxid_localpart": localpart,
            "displayname": displayname,
            "emails": emails,
        }

    @staticmethod
    def parse_config(config: dict) -> SamlConfig:
        """Parse the dict provided by the homeserver's config
        Args:
            config: A dictionary containing configuration options for this provider
        Returns:
            SamlConfig: A custom config object for this module
        """
        # Parse config options and use defaults where necessary
        mxid_source_attribute = config.get("mxid_source_attribute", "uid")
        mapping_type = config.get("mxid_mapping", "hexencode")

        # Retrieve the associating mapping function
        try:
            mxid_mapper = MXID_MAPPER_MAP[mapping_type]
        except KeyError:
            raise ConfigError(
                "saml2_config.user_mapping_provider.config: '%s' is not a valid "
                "mxid_mapping value" % (mapping_type,)
            )

        return SamlConfig(mxid_source_attribute, mxid_mapper)


def load_default_or_legacy_saml2_mapping_provider(hs: "HomeServer"):
    """Wrapper that loads a saml2 mapping provider either from the default module or
    configured using the legacy configuration. Legacy modules then have their callbacks
    registered
    """

    if hs.config.saml2.saml2_user_mapping_provider_class is None:
        # This should be an impossible position to be in
        raise RuntimeError("No default saml2 user mapping provider is set")

    module = hs.config.saml2.saml2_user_mapping_provider_class
    config = hs.config.saml2.saml2_user_mapping_provider_config
    api = hs.get_module_api()

    mapping_provider = module(config, api)

    # if we were loading the default provider, then it has already registered its callbacks!
    # so we can stop here
    if module == DEFAULT_USER_MAPPING_PROVIDER:
        return

    # The required hooks. If a custom module doesn't implement all of these then raise an error
    required_mapping_provider_methods = {
        "get_saml_attributes",
        "saml_response_to_user_attributes",
        "get_remote_user_id",
    }
    missing_methods = [
        method
        for method in required_mapping_provider_methods
        if not hasattr(module, method)
    ]
    if missing_methods:
        raise RuntimeError(
            "Class specified by saml2_config."
            " user_mapping_provider.module is missing required"
            " methods: %s" % (", ".join(missing_methods),)
        )

    # New modules have to proactively register this instead of just the callback
    saml_attributes = mapping_provider.get_saml_attributes(config)

    mapping_provider_methods = {
        "saml_response_to_user_attributes",
        "get_remote_user_id",
    }

    # Methods that the module provides should be async, but this wasn't the case
    # in the old module system, so we wrap them if needed
    def async_wrapper(f: Callable) -> Callable[..., Awaitable]:
        def run(*args, **kwargs):
            return maybe_awaitable(f(*args, **kwargs))

        return run

    # Register the hooks through the module API.
    hooks = {
        hook: async_wrapper(getattr(mapping_provider, hook, None))
        for hook in mapping_provider_methods
    }

    api.register_saml2_user_mapping_provider_callbacks(
        saml_attributes=saml_attributes, **hooks
    )


class Saml2UserMappingProvider:
    def __init__(self, hs: "HomeServer"):
        """The SAML user mapping provider

        Args:
            parsed_config: Module configuration
            module_api: module api proxy
        """
        # self._mxid_source_attribute = parsed_config.mxid_source_attribute
        # self._mxid_mapper = parsed_config.mxid_mapper
        self.get_remote_user_id_callback: Optional[GET_REMOTE_USER_ID_CALLBACK] = None
        self.saml_response_to_user_attributes_callback: Optional[
            SAML_RESPONSE_TO_USER_ATTRIBUTES_CALLBACK
        ] = None
        self.saml_attributes: Tuple[Set[str], Set[str]] = set(), set()
        self.module_has_registered = False

    def register_saml2_user_mapping_provider_callbacks(
        self,
        get_remote_user_id: GET_REMOTE_USER_ID_CALLBACK,
        saml_response_to_user_attributes: SAML_RESPONSE_TO_USER_ATTRIBUTES_CALLBACK,
        saml_attributes: Tuple[Set[str], Set[str]],
    ):
        """Called by modules to register callbacks and saml_attributes"""

        # Only one module can register callbacks
        if self.module_has_registered:
            raise RuntimeError(
                "Multiple modules have attempted to register as saml mapping providers"
            )
        self.module_has_registered = True

        self.get_remote_user_id_callback = get_remote_user_id
        self.saml_response_to_user_attributes_callback = (
            saml_response_to_user_attributes
        )
        self.saml_attributes = saml_attributes

    async def get_remote_user_id(
        self,
        saml_response: saml2.response.AuthnResponse,
        client_redirect_url: Optional[str],
    ) -> str:
        """Extracts the remote user id from the SAML response

        Args:
            saml2_auth: The parsed SAML2 response.
            client_redirect_url: The redirect URL passed in by the client. This may
                be None.
        Returns:
            remote user id

        Raises:
            MappingException: if there was an error extracting the user id
            Any other exception: for backwards compatability
        """

        # If no module has registered callbacks then raise an error
        if not self.module_has_registered:
            raise RuntimeError("No Saml2 mapping provider has been registered")

        assert self.get_remote_user_id_callback is not None

        try:
            result = await self.get_remote_user_id_callback(
                saml_response, client_redirect_url
            )
        except MappingException:
            # Mapping providers are allowed to issue a mapping exception
            # if a remote user id cannot be generated.
            raise
        except Exception as e:
            logger.warning(
                f"Something went wrong when calling custom module callback for get_remote_user_id: {e}"
            )
            # for compatablity with legacy modules, need to raise this exception as is:
            raise e

            # # If the module raises some other sort of exception then don't display that to the user
            # raise MappingException(
            #     "Failed to extract remote user id from SAML response"
            # )

        if not isinstance(result, str):
            logger.warning(  # type: ignore[unreachable]
                f"Wrong type returned by module callback for get_remote_user_id: {result}, expected str"
            )
            # Don't overshare to the user, as something has clearly gone wrong
            raise MappingException(
                "Failed to extract remote user id from SAML response"
            )

        return result

    async def saml_response_to_user_attributes(
        self,
        saml_response: saml2.response.AuthnResponse,
        failures: int,
        client_redirect_url: str,
    ) -> dict:
        """Maps some text from a SAML response to attributes of a new user

        Args:
            saml_response: A SAML auth response object

            failures: How many times a call to this function with this
                saml_response has resulted in a failure

            client_redirect_url: where the client wants to redirect to

        Returns:
            dict: A dict containing new user attributes. Possible keys:
                * mxid_localpart (str): Required. The localpart of the user's mxid
                * displayname (str): The displayname of the user
                * emails (list[str]): Any emails for the user

        Raises:
            MappingException: if something goes wrong while processing the response
            RedirectException: some mapping providers may raise this if they need
                to redirect to an interstitial page.
            Any other exception: for backwards compatability
        """

        # If no module has registered callbacks then raise an error
        if not self.module_has_registered:
            raise RuntimeError("No Saml2 mapping provider has been registered")

        assert self.saml_response_to_user_attributes_callback is not None

        try:
            result = await self.saml_response_to_user_attributes_callback(
                saml_response, failures, client_redirect_url
            )
        except (RedirectException, MappingException):
            # Mapping providers are allowed to issue a redirect (e.g. to ask
            # the user for more information) and can issue a mapping exception
            # if a name cannot be generated.
            raise
        except Exception as e:
            logger.warning(
                f"Something went wrong when calling custom module callback for saml_response_to_user_attributes: {e}"
            )
            # for compatablity with legacy modules, need to raise this exception as is:
            raise e

            # # If the module raises some other sort of exception then don't display that to the user
            # raise MappingException(
            #     "Unable to map from SAML2 response to user attributes"
            # )

        if not isinstance(result, dict):
            logger.warning(  # type: ignore[unreachable]
                f"Wrong type returned by module callback for get_remote_user_id: {result}, expected dict"
            )
            # Don't overshare to the user, as something has clearly gone wrong
            raise MappingException(
                "Unable to map from SAML2 response to user attributes"
            )

        return result

    def get_saml_attributes(self) -> Tuple[Set[str], Set[str]]:
        """Returns the required attributes of a SAML

        Args:
            config: A SamlConfig object containing configuration params for this provider

        Returns:
            The first set equates to the saml auth response
                attributes that are required for the module to function, whereas the
                second set consists of those attributes which can be used if
                available, but are not necessary
        """
        return self.saml_attributes