# -*- coding: utf-8 -*-
# Copyright 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 .federation_base import FederationBase
from .units import Edu

from synapse.api.errors import (
    CodeMessageException, HttpResponseException, SynapseError,
)
from synapse.util import unwrapFirstError
from synapse.util.expiringcache import ExpiringCache
from synapse.util.logutils import log_function
from synapse.events import FrozenEvent
import synapse.metrics

from synapse.util.retryutils import get_retry_limiter, NotRetryingDestination

import itertools
import logging
import random


logger = logging.getLogger(__name__)


# synapse.federation.federation_client is a silly name
metrics = synapse.metrics.get_metrics_for("synapse.federation.client")

sent_pdus_destination_dist = metrics.register_distribution("sent_pdu_destinations")

sent_edus_counter = metrics.register_counter("sent_edus")

sent_queries_counter = metrics.register_counter("sent_queries", labels=["type"])


class FederationClient(FederationBase):

    def start_get_pdu_cache(self):
        self._get_pdu_cache = ExpiringCache(
            cache_name="get_pdu_cache",
            clock=self._clock,
            max_len=1000,
            expiry_ms=120*1000,
            reset_expiry_on_get=False,
        )

        self._get_pdu_cache.start()

    @log_function
    def send_pdu(self, pdu, destinations):
        """Informs the replication layer about a new PDU generated within the
        home server that should be transmitted to others.

        TODO: Figure out when we should actually resolve the deferred.

        Args:
            pdu (Pdu): The new Pdu.

        Returns:
            Deferred: Completes when we have successfully processed the PDU
            and replicated it to any interested remote home servers.
        """
        order = self._order
        self._order += 1

        sent_pdus_destination_dist.inc_by(len(destinations))

        logger.debug("[%s] transaction_layer.enqueue_pdu... ", pdu.event_id)

        # TODO, add errback, etc.
        self._transaction_queue.enqueue_pdu(pdu, destinations, order)

        logger.debug(
            "[%s] transaction_layer.enqueue_pdu... done",
            pdu.event_id
        )

    @log_function
    def send_edu(self, destination, edu_type, content):
        edu = Edu(
            origin=self.server_name,
            destination=destination,
            edu_type=edu_type,
            content=content,
        )

        sent_edus_counter.inc()

        # TODO, add errback, etc.
        self._transaction_queue.enqueue_edu(edu)
        return defer.succeed(None)

    @log_function
    def send_failure(self, failure, destination):
        self._transaction_queue.enqueue_failure(failure, destination)
        return defer.succeed(None)

    @log_function
    def make_query(self, destination, query_type, args,
                   retry_on_dns_fail=True):
        """Sends a federation Query to a remote homeserver of the given type
        and arguments.

        Args:
            destination (str): Domain name of the remote homeserver
            query_type (str): Category of the query type; should match the
                handler name used in register_query_handler().
            args (dict): Mapping of strings to strings containing the details
                of the query request.

        Returns:
            a Deferred which will eventually yield a JSON object from the
            response
        """
        sent_queries_counter.inc(query_type)

        return self.transport_layer.make_query(
            destination, query_type, args, retry_on_dns_fail=retry_on_dns_fail
        )

    @defer.inlineCallbacks
    @log_function
    def backfill(self, dest, context, limit, extremities):
        """Requests some more historic PDUs for the given context from the
        given destination server.

        Args:
            dest (str): The remote home server to ask.
            context (str): The context to backfill.
            limit (int): The maximum number of PDUs to return.
            extremities (list): List of PDU id and origins of the first pdus
                we have seen from the context

        Returns:
            Deferred: Results in the received PDUs.
        """
        logger.debug("backfill extrem=%s", extremities)

        # If there are no extremeties then we've (probably) reached the start.
        if not extremities:
            return

        transaction_data = yield self.transport_layer.backfill(
            dest, context, extremities, limit)

        logger.debug("backfill transaction_data=%s", repr(transaction_data))

        pdus = [
            self.event_from_pdu_json(p, outlier=False)
            for p in transaction_data["pdus"]
        ]

        # FIXME: We should handle signature failures more gracefully.
        pdus[:] = yield self._check_sigs_and_hashes(pdus)

        defer.returnValue(pdus)

    @defer.inlineCallbacks
    @log_function
    def get_pdu(self, destinations, event_id, outlier=False, timeout=None):
        """Requests the PDU with given origin and ID from the remote home
        servers.

        Will attempt to get the PDU from each destination in the list until
        one succeeds.

        This will persist the PDU locally upon receipt.

        Args:
            destinations (list): Which home servers to query
            pdu_origin (str): The home server that originally sent the pdu.
            event_id (str)
            outlier (bool): Indicates whether the PDU is an `outlier`, i.e. if
                it's from an arbitary point in the context as opposed to part
                of the current block of PDUs. Defaults to `False`
            timeout (int): How long to try (in ms) each destination for before
                moving to the next destination. None indicates no timeout.

        Returns:
            Deferred: Results in the requested PDU.
        """

        # TODO: Rate limit the number of times we try and get the same event.

        if self._get_pdu_cache:
            e = self._get_pdu_cache.get(event_id)
            if e:
                defer.returnValue(e)

        pdu = None
        for destination in destinations:
            try:
                limiter = yield get_retry_limiter(
                    destination,
                    self._clock,
                    self.store,
                )

                with limiter:
                    transaction_data = yield self.transport_layer.get_event(
                        destination, event_id, timeout=timeout,
                    )

                    logger.debug("transaction_data %r", transaction_data)

                    pdu_list = [
                        self.event_from_pdu_json(p, outlier=outlier)
                        for p in transaction_data["pdus"]
                    ]

                    if pdu_list and pdu_list[0]:
                        pdu = pdu_list[0]

                        # Check signatures are correct.
                        pdu = yield self._check_sigs_and_hashes([pdu])[0]

                        break

            except SynapseError:
                logger.info(
                    "Failed to get PDU %s from %s because %s",
                    event_id, destination, e,
                )
                continue
            except CodeMessageException as e:
                if 400 <= e.code < 500:
                    raise

                logger.info(
                    "Failed to get PDU %s from %s because %s",
                    event_id, destination, e,
                )
                continue
            except NotRetryingDestination as e:
                logger.info(e.message)
                continue
            except Exception as e:
                logger.info(
                    "Failed to get PDU %s from %s because %s",
                    event_id, destination, e,
                )
                continue

        if self._get_pdu_cache is not None and pdu:
            self._get_pdu_cache[event_id] = pdu

        defer.returnValue(pdu)

    @defer.inlineCallbacks
    @log_function
    def get_state_for_room(self, destination, room_id, event_id):
        """Requests all of the `current` state PDUs for a given room from
        a remote home server.

        Args:
            destination (str): The remote homeserver to query for the state.
            room_id (str): The id of the room we're interested in.
            event_id (str): The id of the event we want the state at.

        Returns:
            Deferred: Results in a list of PDUs.
        """

        result = yield self.transport_layer.get_room_state(
            destination, room_id, event_id=event_id,
        )

        pdus = [
            self.event_from_pdu_json(p, outlier=True) for p in result["pdus"]
        ]

        auth_chain = [
            self.event_from_pdu_json(p, outlier=True)
            for p in result.get("auth_chain", [])
        ]

        signed_pdus = yield self._check_sigs_and_hash_and_fetch(
            destination, pdus, outlier=True
        )

        signed_auth = yield self._check_sigs_and_hash_and_fetch(
            destination, auth_chain, outlier=True
        )

        signed_auth.sort(key=lambda e: e.depth)

        defer.returnValue((signed_pdus, signed_auth))

    @defer.inlineCallbacks
    @log_function
    def get_event_auth(self, destination, room_id, event_id):
        res = yield self.transport_layer.get_event_auth(
            destination, room_id, event_id,
        )

        auth_chain = [
            self.event_from_pdu_json(p, outlier=True)
            for p in res["auth_chain"]
        ]

        signed_auth = yield self._check_sigs_and_hash_and_fetch(
            destination, auth_chain, outlier=True
        )

        signed_auth.sort(key=lambda e: e.depth)

        defer.returnValue(signed_auth)

    @defer.inlineCallbacks
    def make_join(self, destinations, room_id, user_id):
        for destination in destinations:
            if destination == self.server_name:
                continue

            try:
                ret = yield self.transport_layer.make_join(
                    destination, room_id, user_id
                )

                pdu_dict = ret["event"]

                logger.debug("Got response to make_join: %s", pdu_dict)

                defer.returnValue(
                    (destination, self.event_from_pdu_json(pdu_dict))
                )
                break
            except CodeMessageException:
                raise
            except Exception as e:
                logger.warn(
                    "Failed to make_join via %s: %s",
                    destination, e.message
                )

        raise RuntimeError("Failed to send to any server.")

    @defer.inlineCallbacks
    def send_join(self, destinations, pdu):
        for destination in destinations:
            if destination == self.server_name:
                continue

            try:
                time_now = self._clock.time_msec()
                _, content = yield self.transport_layer.send_join(
                    destination=destination,
                    room_id=pdu.room_id,
                    event_id=pdu.event_id,
                    content=pdu.get_pdu_json(time_now),
                )

                logger.debug("Got content: %s", content)

                state = [
                    self.event_from_pdu_json(p, outlier=True)
                    for p in content.get("state", [])
                ]

                auth_chain = [
                    self.event_from_pdu_json(p, outlier=True)
                    for p in content.get("auth_chain", [])
                ]

                signed_state, signed_auth = yield defer.gatherResults(
                    [
                        self._check_sigs_and_hash_and_fetch(
                            destination, state, outlier=True
                        ),
                        self._check_sigs_and_hash_and_fetch(
                            destination, auth_chain, outlier=True
                        )
                    ],
                    consumeErrors=True
                ).addErrback(unwrapFirstError)

                auth_chain.sort(key=lambda e: e.depth)

                defer.returnValue({
                    "state": signed_state,
                    "auth_chain": signed_auth,
                    "origin": destination,
                })
            except CodeMessageException:
                raise
            except Exception as e:
                logger.exception(
                    "Failed to send_join via %s: %s",
                    destination, e.message
                )

        raise RuntimeError("Failed to send to any server.")

    @defer.inlineCallbacks
    def send_invite(self, destination, room_id, event_id, pdu):
        time_now = self._clock.time_msec()
        code, content = yield self.transport_layer.send_invite(
            destination=destination,
            room_id=room_id,
            event_id=event_id,
            content=pdu.get_pdu_json(time_now),
        )

        pdu_dict = content["event"]

        logger.debug("Got response to send_invite: %s", pdu_dict)

        pdu = self.event_from_pdu_json(pdu_dict)

        # Check signatures are correct.
        pdu = yield self._check_sigs_and_hash(pdu)

        # FIXME: We should handle signature failures more gracefully.

        defer.returnValue(pdu)

    @defer.inlineCallbacks
    def query_auth(self, destination, room_id, event_id, local_auth):
        """
        Params:
            destination (str)
            event_it (str)
            local_auth (list)
        """
        time_now = self._clock.time_msec()

        send_content = {
            "auth_chain": [e.get_pdu_json(time_now) for e in local_auth],
        }

        code, content = yield self.transport_layer.send_query_auth(
            destination=destination,
            room_id=room_id,
            event_id=event_id,
            content=send_content,
        )

        auth_chain = [
            self.event_from_pdu_json(e)
            for e in content["auth_chain"]
        ]

        signed_auth = yield self._check_sigs_and_hash_and_fetch(
            destination, auth_chain, outlier=True
        )

        signed_auth.sort(key=lambda e: e.depth)

        ret = {
            "auth_chain": signed_auth,
            "rejects": content.get("rejects", []),
            "missing": content.get("missing", []),
        }

        defer.returnValue(ret)

    @defer.inlineCallbacks
    def get_missing_events(self, destination, room_id, earliest_events_ids,
                           latest_events, limit, min_depth):
        """Tries to fetch events we are missing. This is called when we receive
        an event without having received all of its ancestors.

        Args:
            destination (str)
            room_id (str)
            earliest_events_ids (list): List of event ids. Effectively the
                events we expected to receive, but haven't. `get_missing_events`
                should only return events that didn't happen before these.
            latest_events (list): List of events we have received that we don't
                have all previous events for.
            limit (int): Maximum number of events to return.
            min_depth (int): Minimum depth of events tor return.
        """
        try:
            content = yield self.transport_layer.get_missing_events(
                destination=destination,
                room_id=room_id,
                earliest_events=earliest_events_ids,
                latest_events=[e.event_id for e in latest_events],
                limit=limit,
                min_depth=min_depth,
            )

            events = [
                self.event_from_pdu_json(e)
                for e in content.get("events", [])
            ]

            signed_events = yield self._check_sigs_and_hash_and_fetch(
                destination, events, outlier=False
            )

            have_gotten_all_from_destination = True
        except HttpResponseException as e:
            if not e.code == 400:
                raise

            # We are probably hitting an old server that doesn't support
            # get_missing_events
            signed_events = []
            have_gotten_all_from_destination = False

        if len(signed_events) >= limit:
            defer.returnValue(signed_events)

        servers = yield self.store.get_joined_hosts_for_room(room_id)

        servers = set(servers)
        servers.discard(self.server_name)

        failed_to_fetch = set()

        while len(signed_events) < limit:
            # Are we missing any?

            seen_events = set(earliest_events_ids)
            seen_events.update(e.event_id for e in signed_events if e)

            missing_events = {}
            for e in itertools.chain(latest_events, signed_events):
                if e.depth > min_depth:
                    missing_events.update({
                        e_id: e.depth for e_id, _ in e.prev_events
                        if e_id not in seen_events
                        and e_id not in failed_to_fetch
                    })

            if not missing_events:
                break

            have_seen = yield self.store.have_events(missing_events)

            for k in have_seen:
                missing_events.pop(k, None)

            if not missing_events:
                break

            # Okay, we haven't gotten everything yet. Lets get them.
            ordered_missing = sorted(missing_events.items(), key=lambda x: x[0])

            if have_gotten_all_from_destination:
                servers.discard(destination)

            def random_server_list():
                srvs = list(servers)
                random.shuffle(srvs)
                return srvs

            deferreds = [
                self.get_pdu(
                    destinations=random_server_list(),
                    event_id=e_id,
                )
                for e_id, depth in ordered_missing[:limit - len(signed_events)]
            ]

            res = yield defer.DeferredList(deferreds, consumeErrors=True)
            for (result, val), (e_id, _) in zip(res, ordered_missing):
                if result and val:
                    signed_events.append(val)
                else:
                    failed_to_fetch.add(e_id)

        defer.returnValue(signed_events)

    def event_from_pdu_json(self, pdu_json, outlier=False):
        event = FrozenEvent(
            pdu_json
        )

        event.internal_metadata.outlier = outlier

        return event