// Copyright 2022 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 streams

import (
	"context"
	"encoding/json"
	"sync"

	"github.com/matrix-org/gomatrixserverlib"

	"github.com/matrix-org/dendrite/syncapi/notifier"
	"github.com/matrix-org/dendrite/syncapi/storage"
	"github.com/matrix-org/dendrite/syncapi/types"
)

type PresenceStreamProvider struct {
	DefaultStreamProvider
	// cache contains previously sent presence updates to avoid unneeded updates
	cache    sync.Map
	notifier *notifier.Notifier
}

func (p *PresenceStreamProvider) Setup(
	ctx context.Context, snapshot storage.DatabaseTransaction,
) {
	p.DefaultStreamProvider.Setup(ctx, snapshot)

	p.latestMutex.Lock()
	defer p.latestMutex.Unlock()

	id, err := snapshot.MaxStreamPositionForPresence(ctx)
	if err != nil {
		panic(err)
	}
	p.latest = id
}

func (p *PresenceStreamProvider) CompleteSync(
	ctx context.Context,
	snapshot storage.DatabaseTransaction,
	req *types.SyncRequest,
) types.StreamPosition {
	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
}

func (p *PresenceStreamProvider) IncrementalSync(
	ctx context.Context,
	snapshot storage.DatabaseTransaction,
	req *types.SyncRequest,
	from, to types.StreamPosition,
) types.StreamPosition {
	// We pull out a larger number than the filter asks for, since we're filtering out events later
	presences, err := snapshot.PresenceAfter(ctx, from, gomatrixserverlib.EventFilter{Limit: 1000})
	if err != nil {
		req.Log.WithError(err).Error("p.DB.PresenceAfter failed")
		return from
	}

	// add newly joined rooms user presences
	if len(req.NewlyJoined) > 0 {
		newlyJoinedRoomIDs := make([]string, 0, len(req.NewlyJoined))
		for roomID := range req.NewlyJoined {
			newlyJoinedRoomIDs = append(newlyJoinedRoomIDs, roomID)
		}
		// TODO: Check if this is working better than before.
		if err = p.notifier.LoadRooms(ctx, p.DB, newlyJoinedRoomIDs); err != nil {
			req.Log.WithError(err).Error("unable to refresh notifier lists")
			return from
		}
	NewlyJoinedLoop:
		for _, roomID := range newlyJoinedRoomIDs {
			roomUsers := p.notifier.JoinedUsers(roomID)
			for i := range roomUsers {
				// we already got a presence from this user
				if _, ok := presences[roomUsers[i]]; ok {
					continue
				}
				// Bear in mind that this might return nil, but at least populating
				// a nil means that there's a map entry so we won't repeat this call.
				presences[roomUsers[i]], err = snapshot.GetPresence(ctx, roomUsers[i])
				if err != nil {
					req.Log.WithError(err).Error("unable to query presence for user")
					_ = snapshot.Rollback()
					return from
				}
				if len(presences) > req.Filter.Presence.Limit {
					break NewlyJoinedLoop
				}
			}
		}
	} else {
		return to
	}

	lastPos := from
	for _, presence := range presences {
		if presence == nil {
			continue
		}
		// Ignore users we don't share a room with
		if req.Device.UserID != presence.UserID && !p.notifier.IsSharedUser(req.Device.UserID, presence.UserID) {
			continue
		}
		cacheKey := req.Device.UserID + req.Device.ID + presence.UserID
		pres, ok := p.cache.Load(cacheKey)
		if ok {
			// skip already sent presence
			prevPresence := pres.(*types.PresenceInternal)
			currentlyActive := prevPresence.CurrentlyActive()
			skip := prevPresence.Equals(presence) && currentlyActive && req.Device.UserID != presence.UserID
			if skip {
				req.Log.Tracef("Skipping presence, no change (%s)", presence.UserID)
				continue
			}
		}

		if _, known := types.PresenceFromString(presence.ClientFields.Presence); known {
			presence.ClientFields.LastActiveAgo = presence.LastActiveAgo()
			if presence.ClientFields.Presence == "online" {
				currentlyActive := presence.CurrentlyActive()
				presence.ClientFields.CurrentlyActive = &currentlyActive
			}
		} else {
			presence.ClientFields.Presence = "offline"
		}

		content, err := json.Marshal(presence.ClientFields)
		if err != nil {
			return from
		}

		req.Response.Presence.Events = append(req.Response.Presence.Events, gomatrixserverlib.ClientEvent{
			Content: content,
			Sender:  presence.UserID,
			Type:    gomatrixserverlib.MPresence,
		})
		if presence.StreamPos > lastPos {
			lastPos = presence.StreamPos
		}
		if len(req.Response.Presence.Events) == req.Filter.Presence.Limit {
			break
		}
		p.cache.Store(cacheKey, presence)
	}

	if len(req.Response.Presence.Events) == 0 {
		return to
	}

	return lastPos
}