# Copyright 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 contextlib
import logging
import time
from typing import Optional, Type, Union

import attr
from zope.interface import implementer

from twisted.internet.interfaces import IAddress
from twisted.python.failure import Failure
from twisted.web.server import Request, Site

from synapse.config.server import ListenerConfig
from synapse.http import get_request_user_agent, redact_uri
from synapse.http.request_metrics import RequestMetrics, requests_counter
from synapse.logging.context import LoggingContext, PreserveLoggingContext
from synapse.types import Requester

logger = logging.getLogger(__name__)

_next_request_seq = 0


class SynapseRequest(Request):
    """Class which encapsulates an HTTP request to synapse.

    All of the requests processed in synapse are of this type.

    It extends twisted's twisted.web.server.Request, and adds:
     * Unique request ID
     * A log context associated with the request
     * Redaction of access_token query-params in __repr__
     * Logging at start and end
     * Metrics to record CPU, wallclock and DB time by endpoint.

    It also provides a method `processing`, which returns a context manager. If this
    method is called, the request won't be logged until the context manager is closed;
    this is useful for asynchronous request handlers which may go on processing the
    request even after the client has disconnected.

    Attributes:
        logcontext: the log context for this request
    """

    def __init__(self, channel, *args, **kw):
        Request.__init__(self, channel, *args, **kw)
        self.site = channel.site  # type: SynapseSite
        self._channel = channel  # this is used by the tests
        self.start_time = 0.0

        # The requester, if authenticated. For federation requests this is the
        # server name, for client requests this is the Requester object.
        self.requester = None  # type: Optional[Union[Requester, str]]

        # we can't yet create the logcontext, as we don't know the method.
        self.logcontext = None  # type: Optional[LoggingContext]

        global _next_request_seq
        self.request_seq = _next_request_seq
        _next_request_seq += 1

        # whether an asynchronous request handler has called processing()
        self._is_processing = False

        # the time when the asynchronous request handler completed its processing
        self._processing_finished_time = None

        # what time we finished sending the response to the client (or the connection
        # dropped)
        self.finish_time = None

    def __repr__(self):
        # We overwrite this so that we don't log ``access_token``
        return "<%s at 0x%x method=%r uri=%r clientproto=%r site=%r>" % (
            self.__class__.__name__,
            id(self),
            self.get_method(),
            self.get_redacted_uri(),
            self.clientproto.decode("ascii", errors="replace"),
            self.site.site_tag,
        )

    def get_request_id(self):
        return "%s-%i" % (self.get_method(), self.request_seq)

    def get_redacted_uri(self) -> str:
        """Gets the redacted URI associated with the request (or placeholder if the URI
        has not yet been received).

        Note: This is necessary as the placeholder value in twisted is str
        rather than bytes, so we need to sanitise `self.uri`.

        Returns:
            The redacted URI as a string.
        """
        uri = self.uri  # type: Union[bytes, str]
        if isinstance(uri, bytes):
            uri = uri.decode("ascii", errors="replace")
        return redact_uri(uri)

    def get_method(self) -> str:
        """Gets the method associated with the request (or placeholder if method
        has not yet been received).

        Note: This is necessary as the placeholder value in twisted is str
        rather than bytes, so we need to sanitise `self.method`.

        Returns:
            The request method as a string.
        """
        method = self.method  # type: Union[bytes, str]
        if isinstance(method, bytes):
            return self.method.decode("ascii")
        return method

    def render(self, resrc):
        # this is called once a Resource has been found to serve the request; in our
        # case the Resource in question will normally be a JsonResource.

        # create a LogContext for this request
        request_id = self.get_request_id()
        self.logcontext = LoggingContext(request_id, request=request_id)

        # override the Server header which is set by twisted
        self.setHeader("Server", self.site.server_version_string)

        with PreserveLoggingContext(self.logcontext):
            # we start the request metrics timer here with an initial stab
            # at the servlet name. For most requests that name will be
            # JsonResource (or a subclass), and JsonResource._async_render
            # will update it once it picks a servlet.
            servlet_name = resrc.__class__.__name__
            self._started_processing(servlet_name)

            Request.render(self, resrc)

            # record the arrival of the request *after*
            # dispatching to the handler, so that the handler
            # can update the servlet name in the request
            # metrics
            requests_counter.labels(self.get_method(), self.request_metrics.name).inc()

    @contextlib.contextmanager
    def processing(self):
        """Record the fact that we are processing this request.

        Returns a context manager; the correct way to use this is:

        async def handle_request(request):
            with request.processing("FooServlet"):
                await really_handle_the_request()

        Once the context manager is closed, the completion of the request will be logged,
        and the various metrics will be updated.
        """
        if self._is_processing:
            raise RuntimeError("Request is already processing")
        self._is_processing = True

        try:
            yield
        except Exception:
            # this should already have been caught, and sent back to the client as a 500.
            logger.exception(
                "Asynchronous message handler raised an uncaught exception"
            )
        finally:
            # the request handler has finished its work and either sent the whole response
            # back, or handed over responsibility to a Producer.

            self._processing_finished_time = time.time()
            self._is_processing = False

            # if we've already sent the response, log it now; otherwise, we wait for the
            # response to be sent.
            if self.finish_time is not None:
                self._finished_processing()

    def finish(self):
        """Called when all response data has been written to this Request.

        Overrides twisted.web.server.Request.finish to record the finish time and do
        logging.
        """
        self.finish_time = time.time()
        Request.finish(self)
        if not self._is_processing:
            assert self.logcontext is not None
            with PreserveLoggingContext(self.logcontext):
                self._finished_processing()

    def connectionLost(self, reason):
        """Called when the client connection is closed before the response is written.

        Overrides twisted.web.server.Request.connectionLost to record the finish time and
        do logging.
        """
        # There is a bug in Twisted where reason is not wrapped in a Failure object
        # Detect this and wrap it manually as a workaround
        # More information: https://github.com/matrix-org/synapse/issues/7441
        if not isinstance(reason, Failure):
            reason = Failure(reason)

        self.finish_time = time.time()
        Request.connectionLost(self, reason)

        if self.logcontext is None:
            logger.info(
                "Connection from %s lost before request headers were read", self.client
            )
            return

        # we only get here if the connection to the client drops before we send
        # the response.
        #
        # It's useful to log it here so that we can get an idea of when
        # the client disconnects.
        with PreserveLoggingContext(self.logcontext):
            logger.info("Connection from client lost before response was sent")

            if not self._is_processing:
                self._finished_processing()

    def _started_processing(self, servlet_name):
        """Record the fact that we are processing this request.

        This will log the request's arrival. Once the request completes,
        be sure to call finished_processing.

        Args:
            servlet_name (str): the name of the servlet which will be
                processing this request. This is used in the metrics.

                It is possible to update this afterwards by updating
                self.request_metrics.name.
        """
        self.start_time = time.time()
        self.request_metrics = RequestMetrics()
        self.request_metrics.start(
            self.start_time, name=servlet_name, method=self.get_method()
        )

        self.site.access_logger.debug(
            "%s - %s - Received request: %s %s",
            self.getClientIP(),
            self.site.site_tag,
            self.get_method(),
            self.get_redacted_uri(),
        )

    def _finished_processing(self):
        """Log the completion of this request and update the metrics"""
        assert self.logcontext is not None
        usage = self.logcontext.get_resource_usage()

        if self._processing_finished_time is None:
            # we completed the request without anything calling processing()
            self._processing_finished_time = time.time()

        # the time between receiving the request and the request handler finishing
        processing_time = self._processing_finished_time - self.start_time

        # the time between the request handler finishing and the response being sent
        # to the client (nb may be negative)
        response_send_time = self.finish_time - self._processing_finished_time

        # Convert the requester into a string that we can log
        authenticated_entity = None
        if isinstance(self.requester, str):
            authenticated_entity = self.requester
        elif isinstance(self.requester, Requester):
            authenticated_entity = self.requester.authenticated_entity

            # If this is a request where the target user doesn't match the user who
            # authenticated (e.g. and admin is puppetting a user) then we log both.
            if self.requester.user.to_string() != authenticated_entity:
                authenticated_entity = "{},{}".format(
                    authenticated_entity,
                    self.requester.user.to_string(),
                )
        elif self.requester is not None:
            # This shouldn't happen, but we log it so we don't lose information
            # and can see that we're doing something wrong.
            authenticated_entity = repr(self.requester)  # type: ignore[unreachable]

        user_agent = get_request_user_agent(self, "-")

        code = str(self.code)
        if not self.finished:
            # we didn't send the full response before we gave up (presumably because
            # the connection dropped)
            code += "!"

        log_level = logging.INFO if self._should_log_request() else logging.DEBUG
        self.site.access_logger.log(
            log_level,
            "%s - %s - {%s}"
            " Processed request: %.3fsec/%.3fsec (%.3fsec, %.3fsec) (%.3fsec/%.3fsec/%d)"
            ' %sB %s "%s %s %s" "%s" [%d dbevts]',
            self.getClientIP(),
            self.site.site_tag,
            authenticated_entity,
            processing_time,
            response_send_time,
            usage.ru_utime,
            usage.ru_stime,
            usage.db_sched_duration_sec,
            usage.db_txn_duration_sec,
            int(usage.db_txn_count),
            self.sentLength,
            code,
            self.get_method(),
            self.get_redacted_uri(),
            self.clientproto.decode("ascii", errors="replace"),
            user_agent,
            usage.evt_db_fetch_count,
        )

        try:
            self.request_metrics.stop(self.finish_time, self.code, self.sentLength)
        except Exception as e:
            logger.warning("Failed to stop metrics: %r", e)

    def _should_log_request(self) -> bool:
        """Whether we should log at INFO that we processed the request."""
        if self.path == b"/health":
            return False

        if self.method == b"OPTIONS":
            return False

        return True


class XForwardedForRequest(SynapseRequest):
    """Request object which honours proxy headers

    Extends SynapseRequest to replace getClientIP, getClientAddress, and isSecure with
    information from request headers.
    """

    # the client IP and ssl flag, as extracted from the headers.
    _forwarded_for = None  # type: Optional[_XForwardedForAddress]
    _forwarded_https = False  # type: bool

    def requestReceived(self, command, path, version):
        # this method is called by the Channel once the full request has been
        # received, to dispatch the request to a resource.
        # We can use it to set the IP address and protocol according to the
        # headers.
        self._process_forwarded_headers()
        return super().requestReceived(command, path, version)

    def _process_forwarded_headers(self):
        headers = self.requestHeaders.getRawHeaders(b"x-forwarded-for")
        if not headers:
            return

        # for now, we just use the first x-forwarded-for header. Really, we ought
        # to start from the client IP address, and check whether it is trusted; if it
        # is, work backwards through the headers until we find an untrusted address.
        # see https://github.com/matrix-org/synapse/issues/9471
        self._forwarded_for = _XForwardedForAddress(
            headers[0].split(b",")[0].strip().decode("ascii")
        )

        # if we got an x-forwarded-for header, also look for an x-forwarded-proto header
        header = self.getHeader(b"x-forwarded-proto")
        if header is not None:
            self._forwarded_https = header.lower() == b"https"
        else:
            # this is done largely for backwards-compatibility so that people that
            # haven't set an x-forwarded-proto header don't get a redirect loop.
            logger.warning(
                "forwarded request lacks an x-forwarded-proto header: assuming https"
            )
            self._forwarded_https = True

    def isSecure(self):
        if self._forwarded_https:
            return True
        return super().isSecure()

    def getClientIP(self) -> str:
        """
        Return the IP address of the client who submitted this request.

        This method is deprecated.  Use getClientAddress() instead.
        """
        if self._forwarded_for is not None:
            return self._forwarded_for.host
        return super().getClientIP()

    def getClientAddress(self) -> IAddress:
        """
        Return the address of the client who submitted this request.
        """
        if self._forwarded_for is not None:
            return self._forwarded_for
        return super().getClientAddress()


@implementer(IAddress)
@attr.s(frozen=True, slots=True)
class _XForwardedForAddress:
    host = attr.ib(type=str)


class SynapseSite(Site):
    """
    Subclass of a twisted http Site that does access logging with python's
    standard logging
    """

    def __init__(
        self,
        logger_name,
        site_tag,
        config: ListenerConfig,
        resource,
        server_version_string,
        *args,
        **kwargs
    ):
        Site.__init__(self, resource, *args, **kwargs)

        self.site_tag = site_tag

        assert config.http_options is not None
        proxied = config.http_options.x_forwarded
        self.requestFactory = (
            XForwardedForRequest if proxied else SynapseRequest
        )  # type: Type[Request]
        self.access_logger = logging.getLogger(logger_name)
        self.server_version_string = server_version_string.encode("ascii")

    def log(self, request):
        pass
