// Copyright 2017 Vector Creations Ltd
// Copyright 2018 New Vector Ltd
// Copyright 2019-2020 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.

package input

import (
	"bytes"
	"context"
	"fmt"
	"time"

	fedapi "github.com/matrix-org/dendrite/federationapi/api"
	"github.com/matrix-org/dendrite/internal/eventutil"
	"github.com/matrix-org/dendrite/roomserver/api"
	"github.com/matrix-org/dendrite/roomserver/internal/helpers"
	"github.com/matrix-org/dendrite/roomserver/state"
	"github.com/matrix-org/dendrite/roomserver/types"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/matrix-org/util"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/sirupsen/logrus"
)

func init() {
	prometheus.MustRegister(processRoomEventDuration)
}

var processRoomEventDuration = prometheus.NewHistogramVec(
	prometheus.HistogramOpts{
		Namespace: "dendrite",
		Subsystem: "roomserver",
		Name:      "processroomevent_duration_millis",
		Help:      "How long it takes the roomserver to process an event",
		Buckets: []float64{ // milliseconds
			5, 10, 25, 50, 75, 100, 250, 500,
			1000, 2000, 3000, 4000, 5000, 6000,
			7000, 8000, 9000, 10000, 15000, 20000,
		},
	},
	[]string{"room_id"},
)

// processRoomEvent can only be called once at a time
//
// TODO(#375): This should be rewritten to allow concurrent calls. The
// difficulty is in ensuring that we correctly annotate events with the correct
// state deltas when sending to kafka streams
// TODO: Break up function - we should probably do transaction ID checks before calling this.
// nolint:gocyclo
func (r *Inputer) processRoomEvent(
	ctx context.Context,
	input *api.InputRoomEvent,
) (eventID string, err error) {
	// Measure how long it takes to process this event.
	started := time.Now()
	defer func() {
		timetaken := time.Since(started)
		processRoomEventDuration.With(prometheus.Labels{
			"room_id": input.Event.RoomID(),
		}).Observe(float64(timetaken.Milliseconds()))
	}()

	// Parse and validate the event JSON
	headered := input.Event
	event := headered.Unwrap()

	// if we have already got this event then do not process it again, if the input kind is an outlier.
	// Outliers contain no extra information which may warrant a re-processing.
	if input.Kind == api.KindOutlier {
		evs, err2 := r.DB.EventsFromIDs(ctx, []string{event.EventID()})
		if err2 == nil && len(evs) == 1 {
			// check hash matches if we're on early room versions where the event ID was a random string
			idFormat, err2 := headered.RoomVersion.EventIDFormat()
			if err2 == nil {
				switch idFormat {
				case gomatrixserverlib.EventIDFormatV1:
					if bytes.Equal(event.EventReference().EventSHA256, evs[0].EventReference().EventSHA256) {
						util.GetLogger(ctx).WithField("event_id", event.EventID()).Infof("Already processed event; ignoring")
						return event.EventID(), nil
					}
				default:
					util.GetLogger(ctx).WithField("event_id", event.EventID()).Infof("Already processed event; ignoring")
					return event.EventID(), nil
				}
			}
		}
	}

	// First of all, check that the auth events of the event are known.
	// If they aren't then we will ask the federation API for them.
	isRejected := false
	authEvents := gomatrixserverlib.NewAuthEvents(nil)
	knownAuthEvents := map[string]types.Event{}
	if err = r.checkForMissingAuthEvents(ctx, input.Event, &authEvents, knownAuthEvents); err != nil {
		return "", fmt.Errorf("r.checkForMissingAuthEvents: %w", err)
	}

	// Check if the event is allowed by its auth events. If it isn't then
	// we consider the event to be "rejected" — it will still be persisted.
	var rejectionErr error
	if rejectionErr = gomatrixserverlib.Allowed(event, &authEvents); rejectionErr != nil {
		isRejected = true
		logrus.WithError(rejectionErr).Warnf("Event %s rejected", event.EventID())
	}

	// Accumulate the auth event NIDs.
	authEventIDs := event.AuthEventIDs()
	authEventNIDs := make([]types.EventNID, 0, len(authEventIDs))
	for _, authEventID := range authEventIDs {
		authEventNIDs = append(authEventNIDs, knownAuthEvents[authEventID].EventNID)
	}

	var softfail bool
	if input.Kind == api.KindNew {
		// Check that the event passes authentication checks based on the
		// current room state.
		softfail, err = helpers.CheckForSoftFail(ctx, r.DB, headered, input.StateEventIDs)
		if err != nil {
			logrus.WithFields(logrus.Fields{
				"event_id": event.EventID(),
				"type":     event.Type(),
				"room":     event.RoomID(),
			}).WithError(err).Info("Error authing soft-failed event")
		}
	}

	// Store the event.
	_, _, stateAtEvent, redactionEvent, redactedEventID, err := r.DB.StoreEvent(ctx, event, authEventNIDs, isRejected)
	if err != nil {
		return "", fmt.Errorf("r.DB.StoreEvent: %w", err)
	}

	// if storing this event results in it being redacted then do so.
	if !isRejected && redactedEventID == event.EventID() {
		r, rerr := eventutil.RedactEvent(redactionEvent, event)
		if rerr != nil {
			return "", fmt.Errorf("eventutil.RedactEvent: %w", rerr)
		}
		event = r
	}

	// For outliers we can stop after we've stored the event itself as it
	// doesn't have any associated state to store and we don't need to
	// notify anyone about it.
	if input.Kind == api.KindOutlier {
		logrus.WithFields(logrus.Fields{
			"event_id": event.EventID(),
			"type":     event.Type(),
			"room":     event.RoomID(),
			"sender":   event.Sender(),
		}).Debug("Stored outlier")
		return event.EventID(), nil
	}

	roomInfo, err := r.DB.RoomInfo(ctx, event.RoomID())
	if err != nil {
		return "", fmt.Errorf("r.DB.RoomInfo: %w", err)
	}
	if roomInfo == nil {
		return "", fmt.Errorf("r.DB.RoomInfo missing for room %s", event.RoomID())
	}

	if stateAtEvent.BeforeStateSnapshotNID == 0 {
		// We haven't calculated a state for this event yet.
		// Lets calculate one.
		err = r.calculateAndSetState(ctx, input, *roomInfo, &stateAtEvent, event, isRejected)
		if err != nil && input.Kind != api.KindOld {
			return "", fmt.Errorf("r.calculateAndSetState: %w", err)
		}
	}

	// We stop here if the event is rejected: We've stored it but won't update forward extremities or notify anyone about it.
	if isRejected || softfail {
		logrus.WithFields(logrus.Fields{
			"event_id":  event.EventID(),
			"type":      event.Type(),
			"room":      event.RoomID(),
			"soft_fail": softfail,
			"sender":    event.Sender(),
		}).Debug("Stored rejected event")
		return event.EventID(), rejectionErr
	}

	switch input.Kind {
	case api.KindNew:
		if err = r.updateLatestEvents(
			ctx,                 // context
			roomInfo,            // room info for the room being updated
			stateAtEvent,        // state at event (below)
			event,               // event
			input.SendAsServer,  // send as server
			input.TransactionID, // transaction ID
			input.HasState,      // rewrites state?
		); err != nil {
			return "", fmt.Errorf("r.updateLatestEvents: %w", err)
		}
	case api.KindOld:
		err = r.WriteOutputEvents(event.RoomID(), []api.OutputEvent{
			{
				Type: api.OutputTypeOldRoomEvent,
				OldRoomEvent: &api.OutputOldRoomEvent{
					Event: headered,
				},
			},
		})
		if err != nil {
			return "", fmt.Errorf("r.WriteOutputEvents (old): %w", err)
		}
	}

	// processing this event resulted in an event (which may not be the one we're processing)
	// being redacted. We are guaranteed to have both sides (the redaction/redacted event),
	// so notify downstream components to redact this event - they should have it if they've
	// been tracking our output log.
	if redactedEventID != "" {
		err = r.WriteOutputEvents(event.RoomID(), []api.OutputEvent{
			{
				Type: api.OutputTypeRedactedEvent,
				RedactedEvent: &api.OutputRedactedEvent{
					RedactedEventID: redactedEventID,
					RedactedBecause: redactionEvent.Headered(headered.RoomVersion),
				},
			},
		})
		if err != nil {
			return "", fmt.Errorf("r.WriteOutputEvents (redactions): %w", err)
		}
	}

	// Update the extremities of the event graph for the room
	return event.EventID(), nil
}

func (r *Inputer) checkForMissingAuthEvents(
	ctx context.Context,
	event *gomatrixserverlib.HeaderedEvent,
	auth *gomatrixserverlib.AuthEvents,
	known map[string]types.Event,
) error {
	authEventIDs := event.AuthEventIDs()
	if len(authEventIDs) == 0 {
		return nil
	}

	unknown := map[string]struct{}{}

	authEvents, err := r.DB.EventsFromIDs(ctx, authEventIDs)
	if err != nil {
		return fmt.Errorf("r.DB.EventsFromIDs: %w", err)
	}
	for _, event := range authEvents {
		if event.Event != nil {
			known[event.EventID()] = event
			if err = auth.AddEvent(event.Event); err != nil {
				return fmt.Errorf("auth.AddEvent: %w", err)
			}
		} else {
			unknown[event.EventID()] = struct{}{}
		}
	}

	if len(unknown) > 0 {
		logrus.Printf("XXX: There are %d missing auth events", len(unknown))

		serverReq := &fedapi.QueryJoinedHostServerNamesInRoomRequest{
			RoomID: event.RoomID(),
		}
		serverRes := &fedapi.QueryJoinedHostServerNamesInRoomResponse{}
		if err = r.FSAPI.QueryJoinedHostServerNamesInRoom(ctx, serverReq, serverRes); err != nil {
			return fmt.Errorf("r.FSAPI.QueryJoinedHostServerNamesInRoom: %w", err)
		}

		logrus.Printf("XXX: Asking servers %+v", serverRes.ServerNames)

		var res gomatrixserverlib.RespEventAuth
		var found bool
		for _, serverName := range serverRes.ServerNames {
			res, err = r.FSAPI.GetEventAuth(ctx, serverName, event.RoomID(), event.EventID())
			if err != nil {
				logrus.WithError(err).Warnf("Failed to get event auth from federation for %q: %s", event.EventID(), err)
				continue
			}
			logrus.Printf("XXX: Server %q provided us with %d auth events", serverName, len(res.AuthEvents))
			found = true
			break
		}
		if !found {
			logrus.Printf("XXX: None of the %d servers provided us with auth events", len(serverRes.ServerNames))
			return fmt.Errorf("no servers provided event auth")
		}

		for _, event := range gomatrixserverlib.ReverseTopologicalOrdering(
			res.AuthEvents,
			gomatrixserverlib.TopologicalOrderByAuthEvents,
		) {
			// If we already know about this event then we don't need to store
			// it or do anything further with it.
			if _, ok := known[event.EventID()]; ok {
				continue
			}

			// Check the signatures of the event.
			// TODO: It really makes sense for the federation API to be doing this,
			// because then it can attempt another server if one serves up an event
			// with an invalid signature. For now this will do.
			if err := event.VerifyEventSignatures(ctx, r.FSAPI.KeyRing()); err != nil {
				return fmt.Errorf("event.VerifyEventSignatures: %w", err)
			}

			// Otherwise, we need to store, and that means we need to know the
			// auth event NIDs. Let's see if we can find those.
			authEventNIDs := make([]types.EventNID, 0, len(event.AuthEventIDs()))
			for _, eventID := range event.AuthEventIDs() {
				knownEvent, ok := known[eventID]
				if !ok {
					return fmt.Errorf("missing auth event %s for %s", eventID, event.EventID())
				}
				authEventNIDs = append(authEventNIDs, knownEvent.EventNID)
			}

			// Let's take a note of the fact that we now know about this event.
			known[event.EventID()] = types.Event{}
			if err := auth.AddEvent(event); err != nil {
				return fmt.Errorf("auth.AddEvent: %w", err)
			}

			// Check if the auth event should be rejected.
			isRejected := false
			if err := gomatrixserverlib.Allowed(event, auth); err != nil {
				isRejected = true
				logrus.WithError(err).Warnf("Auth event %s rejected", event.EventID())
			}

			// Finally, store the event in the database.
			eventNID, _, _, _, _, err := r.DB.StoreEvent(ctx, event, authEventNIDs, isRejected)
			if err != nil {
				return fmt.Errorf("r.DB.StoreEvent: %w", err)
			}

			// Now we know about this event, too.
			known[event.EventID()] = types.Event{
				EventNID: eventNID,
				Event:    event,
			}
		}
	}

	return nil
}

func (r *Inputer) calculateAndSetState(
	ctx context.Context,
	input *api.InputRoomEvent,
	roomInfo types.RoomInfo,
	stateAtEvent *types.StateAtEvent,
	event *gomatrixserverlib.Event,
	isRejected bool,
) error {
	var err error
	roomState := state.NewStateResolution(r.DB, roomInfo)

	if input.HasState && !isRejected {
		// Check here if we think we're in the room already.
		stateAtEvent.Overwrite = true
		var joinEventNIDs []types.EventNID
		// Request join memberships only for local users only.
		if joinEventNIDs, err = r.DB.GetMembershipEventNIDsForRoom(ctx, roomInfo.RoomNID, true, true); err == nil {
			// If we have no local users that are joined to the room then any state about
			// the room that we have is quite possibly out of date. Therefore in that case
			// we should overwrite it rather than merge it.
			stateAtEvent.Overwrite = len(joinEventNIDs) == 0
		}

		// We've been told what the state at the event is so we don't need to calculate it.
		// Check that those state events are in the database and store the state.
		var entries []types.StateEntry
		if entries, err = r.DB.StateEntriesForEventIDs(ctx, input.StateEventIDs); err != nil {
			return fmt.Errorf("r.DB.StateEntriesForEventIDs: %w", err)
		}
		entries = types.DeduplicateStateEntries(entries)

		if stateAtEvent.BeforeStateSnapshotNID, err = r.DB.AddState(ctx, roomInfo.RoomNID, nil, entries); err != nil {
			return fmt.Errorf("r.DB.AddState: %w", err)
		}
	} else {
		stateAtEvent.Overwrite = false

		// We haven't been told what the state at the event is so we need to calculate it from the prev_events
		if stateAtEvent.BeforeStateSnapshotNID, err = roomState.CalculateAndStoreStateBeforeEvent(ctx, event, isRejected); err != nil {
			return fmt.Errorf("roomState.CalculateAndStoreStateBeforeEvent: %w", err)
		}
	}

	err = r.DB.SetState(ctx, stateAtEvent.EventNID, stateAtEvent.BeforeStateSnapshotNID)
	if err != nil {
		return fmt.Errorf("r.DB.SetState: %w", err)
	}
	return nil
}