// Copyright 2017 Vector Creations 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.

package sync

import (
	"net/http"
	"sync"
	"time"

	log "github.com/Sirupsen/logrus"
	"github.com/matrix-org/dendrite/clientapi/auth"
	"github.com/matrix-org/dendrite/clientapi/httputil"
	"github.com/matrix-org/dendrite/clientapi/jsonerror"
	"github.com/matrix-org/dendrite/syncapi/storage"
	"github.com/matrix-org/dendrite/syncapi/types"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/matrix-org/util"
)

// RequestPool manages HTTP long-poll connections for /sync
type RequestPool struct {
	db *storage.SyncServerDatabase
	// The latest sync stream position: guarded by 'cond'.
	currPos types.StreamPosition
	// A condition variable to notify all waiting goroutines of a new sync stream position
	cond *sync.Cond
}

// NewRequestPool makes a new RequestPool
func NewRequestPool(db *storage.SyncServerDatabase) (*RequestPool, error) {
	pos, err := db.SyncStreamPosition()
	if err != nil {
		return nil, err
	}
	return &RequestPool{db, types.StreamPosition(pos), sync.NewCond(&sync.Mutex{})}, nil
}

// OnIncomingSyncRequest is called when a client makes a /sync request. This function MUST be
// called in a dedicated goroutine for this request. This function will block the goroutine
// until a response is ready, or it times out.
func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request) util.JSONResponse {
	// Extract values from request
	logger := util.GetLogger(req.Context())
	userID, resErr := auth.VerifyAccessToken(req)
	if resErr != nil {
		return *resErr
	}
	syncReq, err := newSyncRequest(req, userID)
	if err != nil {
		return util.JSONResponse{
			Code: 400,
			JSON: jsonerror.Unknown(err.Error()),
		}
	}
	logger.WithFields(log.Fields{
		"userID":  userID,
		"since":   syncReq.since,
		"timeout": syncReq.timeout,
	}).Info("Incoming /sync request")

	// Fork off 2 goroutines: one to do the work, and one to serve as a timeout.
	// Whichever returns first is the one we will serve back to the client.
	// TODO: Currently this means that cpu work is timed, which may not be what we want long term.
	timeoutChan := make(chan struct{})
	timer := time.AfterFunc(syncReq.timeout, func() {
		close(timeoutChan) // signal that the timeout has expired
	})

	done := make(chan util.JSONResponse)
	go func() {
		syncData, err := rp.currentSyncForUser(*syncReq)
		timer.Stop()
		var res util.JSONResponse
		if err != nil {
			res = httputil.LogThenError(req, err)
		} else {
			res = util.JSONResponse{
				Code: 200,
				JSON: syncData,
			}
		}
		done <- res
		close(done)
	}()

	select {
	case <-timeoutChan: // timeout fired
		return util.JSONResponse{
			Code: 200,
			JSON: types.NewResponse(syncReq.since),
		}
	case res := <-done: // received a response
		return res
	}
}

// OnNewEvent is called when a new event is received from the room server. Must only be
// called from a single goroutine, to avoid races between updates which could set the
// current position in the stream incorrectly.
func (rp *RequestPool) OnNewEvent(ev *gomatrixserverlib.Event, pos types.StreamPosition) {
	// update the current position in a guard and then notify all /sync streams
	rp.cond.L.Lock()
	rp.currPos = pos
	rp.cond.L.Unlock()

	rp.cond.Broadcast() // notify ALL waiting goroutines
}

func (rp *RequestPool) waitForEvents(req syncRequest) types.StreamPosition {
	// In a guard, check if the /sync request should block, and block it until we get a new position
	rp.cond.L.Lock()
	currentPos := rp.currPos
	for req.since == currentPos {
		// we need to wait for a new event.
		// TODO: This waits for ANY new event, we need to only wait for events which we care about.
		rp.cond.Wait() // atomically unlocks and blocks goroutine, then re-acquires lock on unblock
		currentPos = rp.currPos
	}
	rp.cond.L.Unlock()
	return currentPos
}

func (rp *RequestPool) currentSyncForUser(req syncRequest) (*types.Response, error) {
	currentPos := rp.waitForEvents(req)

	if req.since == types.StreamPosition(0) {
		pos, data, err := rp.db.CompleteSync(req.userID, req.limit)
		if err != nil {
			return nil, err
		}
		res := types.NewResponse(pos)
		for roomID, d := range data {
			jr := types.NewJoinResponse()
			jr.Timeline.Events = gomatrixserverlib.ToClientEvents(d.RecentEvents, gomatrixserverlib.FormatSync)
			jr.Timeline.Limited = true
			jr.State.Events = gomatrixserverlib.ToClientEvents(d.State, gomatrixserverlib.FormatSync)
			res.Rooms.Join[roomID] = *jr
		}
		return res, nil
	}

	// TODO: handle ignored users

	data, err := rp.db.IncrementalSync(req.userID, req.since, currentPos, req.limit)
	if err != nil {
		return nil, err
	}

	res := types.NewResponse(currentPos)
	for roomID, d := range data {
		jr := types.NewJoinResponse()
		jr.Timeline.Events = gomatrixserverlib.ToClientEvents(d.RecentEvents, gomatrixserverlib.FormatSync)
		jr.Timeline.Limited = false // TODO: if len(events) >= numRecents + 1 and then set limited:true
		jr.State.Events = gomatrixserverlib.ToClientEvents(d.State, gomatrixserverlib.FormatSync)
		res.Rooms.Join[roomID] = *jr
	}
	return res, nil
}