# -*- coding: utf-8 -*-
# Copyright 2014, 2015 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.

from twisted.internet import defer

from synapse.api.urls import FEDERATION_PREFIX as PREFIX
from synapse.api.errors import Codes, SynapseError, LimitExceededError
from synapse.util.async import sleep
from synapse.util.logutils import log_function

import collections
import logging
import simplejson as json
import re


logger = logging.getLogger(__name__)


class FederationRateLimiter(object):
    def __init__(self, clock, window_size, sleep_limit, sleep_msec,
                 reject_limit, concurrent_requests):
        """
        Args:
            clock (Clock)
            window_size (int): The window size in milliseconds.
            sleep_limit (int): The number of requests received in the last
                `window_size` milliseconds before we artificially start
                delaying processing of requests.
            sleep_msec (int): The number of milliseconds to delay processing
                of incoming requests by.
            reject_limit (int): The maximum number of requests that are can be
                queued for processing before we start rejecting requests with
                a 429 Too Many Requests response.
            concurrent_requests (int): The number of concurrent requests to
                process.
        """
        self.clock = clock

        self.window_size = window_size
        self.sleep_limit = sleep_limit
        self.sleep_msec = sleep_msec
        self.reject_limit = reject_limit
        self.concurrent_requests = concurrent_requests

        self.ratelimiters = {}

    def ratelimit(self, host):
        """Used to ratelimit an incoming request from given host

        Example usage:

            with rate_limiter.ratelimit(origin) as wait_deferred:
                yield wait_deferred
                # Handle request ...

        Args:
            host (str): Origin of incoming request.

        Returns:
            _PerHostRatelimiter
        """
        return self.ratelimiters.setdefault(
            host,
            _PerHostRatelimiter(
                clock=self.clock,
                window_size=self.window_size,
                sleep_limit=self.sleep_limit,
                sleep_msec=self.sleep_msec,
                reject_limit=self.reject_limit,
                concurrent_requests=self.concurrent_requests,
            )
        ).ratelimit()


class _PerHostRatelimiter(object):
    def __init__(self, clock, window_size, sleep_limit, sleep_msec,
                 reject_limit, concurrent_requests):
        self.clock = clock

        self.window_size = window_size
        self.sleep_limit = sleep_limit
        self.sleep_msec = sleep_msec
        self.reject_limit = reject_limit
        self.concurrent_requests = concurrent_requests

        self.sleeping_requests = set()
        self.ready_request_queue = collections.OrderedDict()
        self.current_processing = set()
        self.request_times = []

    def is_empty(self):
        time_now = self.clock.time_msec()
        self.request_times[:] = [
            r for r in self.request_times
            if time_now - r < self.window_size
        ]

        return not (
            self.ready_request_queue
            or self.sleeping_requests
            or self.current_processing
            or self.request_times
        )

    def ratelimit(self):
        request_id = object()

        def on_enter():
            return self._on_enter(request_id)

        def on_exit(exc_type, exc_val, exc_tb):
            return self._on_exit(request_id)

        return ContextManagerFunction(on_enter, on_exit)

    def _on_enter(self, request_id):
        time_now = self.clock.time_msec()
        self.request_times[:] = [
            r for r in self.request_times
            if time_now - r < self.window_size
        ]

        queue_size = len(self.ready_request_queue) + len(self.sleeping_requests)
        if queue_size > self.reject_limit:
            raise LimitExceededError(
                retry_after_ms=int(
                    self.window_size / self.sleep_limit
                ),
            )

        self.request_times.append(time_now)

        def queue_request():
            if len(self.current_processing) > self.concurrent_requests:
                logger.debug("Ratelimit [%s]: Queue req", id(request_id))
                queue_defer = defer.Deferred()
                self.ready_request_queue[request_id] = queue_defer
                return queue_defer
            else:
                return defer.succeed(None)

        logger.debug(
            "Ratelimit [%s]: len(self.request_times)=%d",
            id(request_id), len(self.request_times),
        )

        if len(self.request_times) > self.sleep_limit:
            logger.debug(
                "Ratelimit [%s]: sleeping req",
                id(request_id),
            )
            ret_defer = sleep(self.sleep_msec/1000.0)

            self.sleeping_requests.add(request_id)

            def on_wait_finished(_):
                logger.debug(
                    "Ratelimit [%s]: Finished sleeping",
                    id(request_id),
                )
                self.sleeping_requests.discard(request_id)
                queue_defer = queue_request()
                return queue_defer

            ret_defer.addBoth(on_wait_finished)
        else:
            ret_defer = queue_request()

        def on_start(r):
            logger.debug(
                "Ratelimit [%s]: Processing req",
                id(request_id),
            )
            self.current_processing.add(request_id)
            return r

        def on_err(r):
            self.current_processing.discard(request_id)
            return r

        def on_both(r):
            # Ensure that we've properly cleaned up.
            self.sleeping_requests.discard(request_id)
            self.ready_request_queue.pop(request_id, None)
            return r

        ret_defer.addCallbacks(on_start, on_err)
        ret_defer.addBoth(on_both)
        return ret_defer

    def _on_exit(self, request_id):
        logger.debug(
            "Ratelimit [%s]: Processed req",
            id(request_id),
        )
        self.current_processing.discard(request_id)
        try:
            request_id, deferred = self.ready_request_queue.popitem()
            self.current_processing.add(request_id)
            deferred.callback(None)
        except KeyError:
            pass


class ContextManagerFunction(object):
    def __init__(self, on_enter, on_exit):
        self.on_enter = on_enter
        self.on_exit = on_exit

    def __enter__(self):
        if self.on_enter:
            return self.on_enter()

    def __exit__(self, exc_type, exc_val, exc_tb):
        if self.on_exit:
            return self.on_exit(exc_type, exc_val, exc_tb)


class TransportLayerServer(object):
    """Handles incoming federation HTTP requests"""

    @defer.inlineCallbacks
    def _authenticate_request(self, request):
        json_request = {
            "method": request.method,
            "uri": request.uri,
            "destination": self.server_name,
            "signatures": {},
        }

        content = None
        origin = None

        if request.method in ["PUT", "POST"]:
            # TODO: Handle other method types? other content types?
            try:
                content_bytes = request.content.read()
                content = json.loads(content_bytes)
                json_request["content"] = content
            except:
                raise SynapseError(400, "Unable to parse JSON", Codes.BAD_JSON)

        def parse_auth_header(header_str):
            try:
                params = auth.split(" ")[1].split(",")
                param_dict = dict(kv.split("=") for kv in params)

                def strip_quotes(value):
                    if value.startswith("\""):
                        return value[1:-1]
                    else:
                        return value

                origin = strip_quotes(param_dict["origin"])
                key = strip_quotes(param_dict["key"])
                sig = strip_quotes(param_dict["sig"])
                return (origin, key, sig)
            except:
                raise SynapseError(
                    400, "Malformed Authorization header", Codes.UNAUTHORIZED
                )

        auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")

        if not auth_headers:
            raise SynapseError(
                401, "Missing Authorization headers", Codes.UNAUTHORIZED,
            )

        for auth in auth_headers:
            if auth.startswith("X-Matrix"):
                (origin, key, sig) = parse_auth_header(auth)
                json_request["origin"] = origin
                json_request["signatures"].setdefault(origin, {})[key] = sig

        if not json_request["signatures"]:
            raise SynapseError(
                401, "Missing Authorization headers", Codes.UNAUTHORIZED,
            )

        yield self.keyring.verify_json_for_server(origin, json_request)

        defer.returnValue((origin, content))

    def _with_authentication(self, handler):
        @defer.inlineCallbacks
        def new_handler(request, *args, **kwargs):
            try:
                (origin, content) = yield self._authenticate_request(request)
                with self.ratelimiter.ratelimit(origin) as d:
                    yield d
                    response = yield handler(
                        origin, content, request.args, *args, **kwargs
                    )
            except:
                logger.exception("_authenticate_request failed")
                raise
            defer.returnValue(response)
        return new_handler

    def rate_limit_origin(self, handler):
        def new_handler(origin, *args, **kwargs):
            response = yield handler(origin, *args, **kwargs)
            defer.returnValue(response)
        return new_handler()

    @log_function
    def register_received_handler(self, handler):
        """ Register a handler that will be fired when we receive data.

        Args:
            handler (TransportReceivedHandler)
        """
        self.received_handler = handler

        # This is when someone is trying to send us a bunch of data.
        self.server.register_path(
            "PUT",
            re.compile("^" + PREFIX + "/send/([^/]*)/$"),
            self._with_authentication(self._on_send_request)
        )

    @log_function
    def register_request_handler(self, handler):
        """ Register a handler that will be fired when we get asked for data.

        Args:
            handler (TransportRequestHandler)
        """
        self.request_handler = handler

        # This is for when someone asks us for everything since version X
        self.server.register_path(
            "GET",
            re.compile("^" + PREFIX + "/pull/$"),
            self._with_authentication(
                lambda origin, content, query:
                handler.on_pull_request(query["origin"][0], query["v"])
            )
        )

        # This is when someone asks for a data item for a given server
        # data_id pair.
        self.server.register_path(
            "GET",
            re.compile("^" + PREFIX + "/event/([^/]*)/$"),
            self._with_authentication(
                lambda origin, content, query, event_id:
                handler.on_pdu_request(origin, event_id)
            )
        )

        # This is when someone asks for all data for a given context.
        self.server.register_path(
            "GET",
            re.compile("^" + PREFIX + "/state/([^/]*)/$"),
            self._with_authentication(
                lambda origin, content, query, context:
                handler.on_context_state_request(
                    origin,
                    context,
                    query.get("event_id", [None])[0],
                )
            )
        )

        self.server.register_path(
            "GET",
            re.compile("^" + PREFIX + "/backfill/([^/]*)/$"),
            self._with_authentication(
                lambda origin, content, query, context:
                self._on_backfill_request(
                    origin, context, query["v"], query["limit"]
                )
            )
        )

        # This is when we receive a server-server Query
        self.server.register_path(
            "GET",
            re.compile("^" + PREFIX + "/query/([^/]*)$"),
            self._with_authentication(
                lambda origin, content, query, query_type:
                handler.on_query_request(
                    query_type,
                    {k: v[0].decode("utf-8") for k, v in query.items()}
                )
            )
        )

        self.server.register_path(
            "GET",
            re.compile("^" + PREFIX + "/make_join/([^/]*)/([^/]*)$"),
            self._with_authentication(
                lambda origin, content, query, context, user_id:
                self._on_make_join_request(
                    origin, content, query, context, user_id
                )
            )
        )

        self.server.register_path(
            "GET",
            re.compile("^" + PREFIX + "/event_auth/([^/]*)/([^/]*)$"),
            self._with_authentication(
                lambda origin, content, query, context, event_id:
                handler.on_event_auth(
                    origin, context, event_id,
                )
            )
        )

        self.server.register_path(
            "PUT",
            re.compile("^" + PREFIX + "/send_join/([^/]*)/([^/]*)$"),
            self._with_authentication(
                lambda origin, content, query, context, event_id:
                self._on_send_join_request(
                    origin, content, query,
                )
            )
        )

        self.server.register_path(
            "PUT",
            re.compile("^" + PREFIX + "/invite/([^/]*)/([^/]*)$"),
            self._with_authentication(
                lambda origin, content, query, context, event_id:
                self._on_invite_request(
                    origin, content, query,
                )
            )
        )
        self.server.register_path(
            "POST",
            re.compile("^" + PREFIX + "/query_auth/([^/]*)/([^/]*)$"),
            self._with_authentication(
                lambda origin, content, query, context, event_id:
                self._on_query_auth_request(
                    origin, content, event_id,
                )
            )
        )

    @defer.inlineCallbacks
    @log_function
    def _on_send_request(self, origin, content, query, transaction_id):
        """ Called on PUT /send/<transaction_id>/

        Args:
            request (twisted.web.http.Request): The HTTP request.
            transaction_id (str): The transaction_id associated with this
                request. This is *not* None.

        Returns:
            Deferred: Results in a tuple of `(code, response)`, where
            `response` is a python dict to be converted into JSON that is
            used as the response body.
        """
        # Parse the request
        try:
            transaction_data = content

            logger.debug(
                "Decoded %s: %s",
                transaction_id, str(transaction_data)
            )

            # We should ideally be getting this from the security layer.
            # origin = body["origin"]

            # Add some extra data to the transaction dict that isn't included
            # in the request body.
            transaction_data.update(
                transaction_id=transaction_id,
                destination=self.server_name
            )

        except Exception as e:
            logger.exception(e)
            defer.returnValue((400, {"error": "Invalid transaction"}))
            return

        try:
            handler = self.received_handler
            code, response = yield handler.on_incoming_transaction(
                transaction_data
            )
        except:
            logger.exception("on_incoming_transaction failed")
            raise

        defer.returnValue((code, response))

    @log_function
    def _on_backfill_request(self, origin, context, v_list, limits):
        if not limits:
            return defer.succeed(
                (400, {"error": "Did not include limit param"})
            )

        limit = int(limits[-1])

        versions = v_list

        return self.request_handler.on_backfill_request(
            origin, context, versions, limit
        )

    @defer.inlineCallbacks
    @log_function
    def _on_make_join_request(self, origin, content, query, context, user_id):
        content = yield self.request_handler.on_make_join_request(
            context, user_id,
        )
        defer.returnValue((200, content))

    @defer.inlineCallbacks
    @log_function
    def _on_send_join_request(self, origin, content, query):
        content = yield self.request_handler.on_send_join_request(
            origin, content,
        )

        defer.returnValue((200, content))

    @defer.inlineCallbacks
    @log_function
    def _on_invite_request(self, origin, content, query):
        content = yield self.request_handler.on_invite_request(
            origin, content,
        )

        defer.returnValue((200, content))

    @defer.inlineCallbacks
    @log_function
    def _on_query_auth_request(self, origin, content, event_id):
        new_content = yield self.request_handler.on_query_auth_request(
            origin, content, event_id
        )

        defer.returnValue((200, new_content))