/*
	Copyright NetFoundry, Inc.

	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

	https://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 handler_edge_ctrl

import (
	"encoding/json"
	"errors"
	"fmt"
	"github.com/golang/protobuf/proto"
	"github.com/michaelquigley/pfxlog"
	"github.com/openziti/edge/controller/env"
	"github.com/openziti/edge/controller/sync_strats"
	"github.com/openziti/edge/pb/edge_ctrl_pb"
	"github.com/openziti/edge/router/fabric"
	"github.com/openziti/foundation/channel2"
	"sync"
	"time"
)

type apiSessionAddedHandler struct {
	control     channel2.Channel
	sm          fabric.StateManager
	syncTracker *apiSessionSyncTracker

	reqChan   chan *apiSessionAddedWithState
	syncReady chan *apiSessionSyncTracker
	syncFail  chan error

	stop chan struct{}
}

func NewApiSessionAddedHandler(sm fabric.StateManager, control channel2.Channel) *apiSessionAddedHandler {
	handler := &apiSessionAddedHandler{
		control: control,
		sm:      sm,
		reqChan: make(chan *apiSessionAddedWithState, 100),

		syncReady: make(chan *apiSessionSyncTracker, 0),
		syncFail:  make(chan error, 0),

		stop: make(chan struct{}, 0),
	}

	go handler.startReceiveSync()
	go handler.startSyncApplier()
	go handler.startSyncFail()

	control.AddCloseHandler(handler)

	return handler
}

func (h *apiSessionAddedHandler) HandleClose(_ channel2.Channel) {
	if h.stop != nil {
		close(h.stop)
		h.stop = nil
	}
}

func (h *apiSessionAddedHandler) ContentType() int32 {
	return env.ApiSessionAddedType
}

func (h *apiSessionAddedHandler) HandleReceive(msg *channel2.Message, _ channel2.Channel) {
	go func() {
		req := &edge_ctrl_pb.ApiSessionAdded{}
		if err := proto.Unmarshal(msg.Body, req); err == nil {
			if req.IsFullState {

				reqWithState := &apiSessionAddedWithState{
					ApiSessionAdded: req,
				}

				if syncStrategyType, syncState, err := parseInstantSyncHeaders(msg); err == nil {
					reqWithState.SyncStrategyType = syncStrategyType
					reqWithState.InstantSyncState = syncState
				} else {
					pfxlog.Logger().WithField("msgContentType", msg.ContentType).WithError(err).Errorf("sync headers not present (old controller) or only partial present(error), treating as legacy: %v", err)
				}

				h.reqChan <- reqWithState
			} else {
				for _, session := range req.ApiSessions {
					h.sm.AddApiSession(session)
				}
			}
		} else {
			pfxlog.Logger().Panic("could not convert message as api session added")
		}
	}()
}

func (h *apiSessionAddedHandler) startSyncApplier() {
	for {
		select {
		case <-h.stop:
			return
		case sync := <-h.syncReady:
			lastId := ""
			apiSessions := sync.all()
			for _, apiSession := range apiSessions {
				if lastId == "" || apiSession.Id > lastId {
					lastId = apiSession.Id
				}

				h.sm.AddApiSession(apiSession)
			}

			h.sm.RemoveMissingApiSessions(apiSessions, lastId)

			pfxlog.Logger().Infof("finished sychronizing api sessions [count: %d, syncId: %s]", len(apiSessions), sync.syncId)
		}
	}
}

func (h *apiSessionAddedHandler) startSyncFail() {
	for {
		select {
		case <-h.stop:
			return
		case err := <-h.syncFail:
			pfxlog.Logger().Errorf("failed to synchronize api sessions: %v", err)

			h.syncTracker.Stop()
			h.syncTracker = nil

			resync := &edge_ctrl_pb.RequestClientReSync{
				Reason: fmt.Sprintf("error during api session sync: %v", err),
			}

			resyncProto, _ := proto.Marshal(resync)

			resyncMsg := channel2.NewMessage(env.RequestClientReSyncType, resyncProto)
			_ = h.control.Send(resyncMsg)
		}
	}
}

func (h *apiSessionAddedHandler) legacySync(reqWithState *apiSessionAddedWithState) {
	pfxlog.Logger().Warn("using legacy sync logic some connections may be dropped")
	for _, apiSession := range reqWithState.ApiSessions {
		h.sm.AddApiSession(apiSession)
	}

	h.sm.RemoveMissingApiSessions(reqWithState.ApiSessions, "")
}

func (h *apiSessionAddedHandler) startReceiveSync() {
	for {
		select {
		case <-h.stop:
			return
		case reqWithState := <-h.reqChan:
			switch reqWithState.SyncStrategyType {
			case string(sync_strats.RouterSyncStrategyInstant):
				h.instantSync(reqWithState)
			case "":
				pfxlog.Logger().Warn("syncStrategy is not specified, old controller?")
				h.legacySync(reqWithState)
			default:
				pfxlog.Logger().Warnf("syncStrategy [%s] is not supported", reqWithState.SyncStrategyType)
				h.legacySync(reqWithState)
			}
		}
	}
}

func (h *apiSessionAddedHandler) instantSync(reqWithState *apiSessionAddedWithState) {
	logger := pfxlog.Logger().WithField("strategy", reqWithState.SyncStrategyType)

	if reqWithState.InstantSyncState == nil {
		logger.Panic("syncState is empty, cannot continue")
	}

	if reqWithState.InstantSyncState.Id == "" {
		logger.Panic("syncState id is empty, cannot continue")
	}

	//if no id or the sync id is newer, reset
	if h.syncTracker == nil || h.syncTracker.syncId == "" || h.syncTracker.isDone || h.syncTracker.syncId < reqWithState.Id {

		if h.syncTracker == nil || h.syncTracker.syncId == "" {
			logger.Infof("first api session syncId [%s], starting", reqWithState.Id)
		} else if h.syncTracker.isDone {
			logger.Infof("api session syncId [%s], starting", reqWithState.Id)
		} else {
			logger.Infof("api session with newer syncId [old: %s, new: %s], aborting old, starting new", h.syncTracker.syncId, reqWithState.Id)
		}

		if h.syncTracker != nil {
			h.syncTracker.Stop()
		}

		h.syncTracker = newApiSessionSyncTracker(reqWithState.Id)

		h.syncTracker.StartDeadline(h.syncReady, h.syncFail, 20*time.Second)
	}

	//ignore older syncs
	if h.syncTracker.syncId > reqWithState.Id {
		logger.Warnf("older syncId [%s], ignoring", reqWithState.Id)
		return
	}

	h.syncTracker.Add(reqWithState)

}

type apiSessionSyncTracker struct {
	syncId        string
	reqsWithState map[int]*apiSessionAddedWithState
	hasLast       bool
	lastSeq       int
	stop          chan struct{}
	deadline      sync.Once
	isDone        bool
}

func newApiSessionSyncTracker(id string) *apiSessionSyncTracker {
	return &apiSessionSyncTracker{
		syncId:        id,
		reqsWithState: map[int]*apiSessionAddedWithState{},
		stop:          make(chan struct{}, 0),
	}
}

func (tracker *apiSessionSyncTracker) Add(reqWithState *apiSessionAddedWithState) {
	tracker.reqsWithState[reqWithState.Sequence] = reqWithState

	if reqWithState.IsLast {
		tracker.hasLast = true
		tracker.lastSeq = reqWithState.Sequence
	}
}

func (tracker *apiSessionSyncTracker) Stop() {
	if tracker != nil && tracker.stop != nil {
		close(tracker.stop)
		tracker.stop = nil
	}
}

func (tracker *apiSessionSyncTracker) IsDone() bool {
	return tracker.isDone
}

func (tracker *apiSessionSyncTracker) StartDeadline(syncReady chan *apiSessionSyncTracker, syncFail chan error, timeout time.Duration) {
	tracker.deadline.Do(func() {
		go func() {
			ticker := time.NewTicker(1 * time.Second)
			select {
			case <-tracker.stop:
				tracker.reqsWithState = nil
				return
			case <-ticker.C:
				if tracker.HasAll() {
					syncReady <- tracker

					tracker.isDone = true
					return
				}
			case <-time.After(timeout):
				tracker.reqsWithState = nil
				syncFail <- errors.New("timeout, did not receive all updates in time")
				return
			}
		}()
	})
}

func (tracker *apiSessionSyncTracker) HasAll() bool {
	if !tracker.hasLast {
		return false
	}

	hasAll := true

	for i := 0; i <= tracker.lastSeq; i++ {
		if req, ok := tracker.reqsWithState[i]; !ok && req == nil {
			hasAll = false
			break
		}
	}

	return hasAll
}

func (tracker *apiSessionSyncTracker) all() []*edge_ctrl_pb.ApiSession {
	var result []*edge_ctrl_pb.ApiSession
	for i := 0; i <= tracker.lastSeq; i++ {
		if req, ok := tracker.reqsWithState[i]; ok {
			for _, apiSession := range req.ApiSessions {
				result = append(result, apiSession)
			}
		} else {
			pfxlog.Logger().WithField("strategy", sync_strats.RouterSyncStrategyInstant).Error("all failed to have all update sequences")
		}
	}

	return result
}

type apiSessionAddedWithState struct {
	SyncStrategyType string
	*sync_strats.InstantSyncState
	*edge_ctrl_pb.ApiSessionAdded
}

type apiSessionSync struct {
	syncId     string
	apiSession []*edge_ctrl_pb.ApiSession
}

func parseInstantSyncHeaders(msg *channel2.Message) (string, *sync_strats.InstantSyncState, error) {
	if syncStrategyType, ok := msg.Headers[env.SyncStrategyTypeHeader]; ok {
		if syncStrategyState, ok := msg.Headers[env.SyncStrategyStateHeader]; ok {
			state := &sync_strats.InstantSyncState{}
			if err := json.Unmarshal(syncStrategyState, state); err == nil {
				return string(syncStrategyType), state, nil
			} else {
				pfxlog.Logger().WithField("strategy", syncStrategyType).WithField("msgContentType", msg.ContentType).Panicf("could not parse sync state [%s], error: %v", syncStrategyState, err)
			}

		} else {
			return "", nil, errors.New("received sync message with a strategy type header, but no state")
		}
	}
	return "", nil, errors.New("received sync message with no strategy type header")
}