// VulcanizeDB
// Copyright © 2022 Vulcanize

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.

// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.
// This package will handle all event subscriptions that utilize SSE.

package beaconclient

import (
	"encoding/json"
	"github.com/pkg/errors"
	"time"

	log "github.com/sirupsen/logrus"
	"github.com/vulcanize/ipld-eth-beacon-indexer/pkg/loghelper"
	"golang.org/x/sync/errgroup"
)

var (
	shutdownWaitInterval = time.Duration(5) * time.Second
)

// This function will capture all the SSE events for a given SseEvents object.
// When new messages come in, it will ensure that they are decoded into JSON.
// If any errors occur, it log the error information.
func handleIncomingSseEvent[P ProcessedEvents](eventHandler *SseEvents[P], errMetricInc func(uint64), idleTimeout time.Duration) {
	go func() {
		errG := new(errgroup.Group)
		errG.Go(func() error {
			err := eventHandler.Connect()
			if err != nil {
				return err
			}
			return nil
		})
		if err := errG.Wait(); err != nil {
			log.WithFields(log.Fields{
				"err":      err,
				"endpoint": eventHandler.Endpoint,
			}).Error("Unable to subscribe to the SSE endpoint.")
			return
		} else {
			loghelper.LogEndpoint(eventHandler.Endpoint).Info("Successfully subscribed to the event stream.")
		}

	}()

	// TODO(telackey): Doesn't there need to be a check here that the handler hasn't been shutdown?
	for {
		var idleTimer *time.Timer = nil
		var idleTimerC <-chan time.Time = nil
		if idleTimeout > 0 {
			idleTimer = time.NewTimer(idleTimeout)
			idleTimerC = idleTimer.C
		}

		select {
		case message := <-eventHandler.MessagesCh:
			if nil != idleTimer {
				idleTimer.Stop()
			}
			// Message can be nil if its a keep-alive message
			if len(message.Data) != 0 {
				log.WithFields(log.Fields{"msg": string(message.Data)}).Debug("We are going to send the following message to be processed.")
				go processMsg(message.Data, eventHandler.ProcessCh, eventHandler.ErrorCh)
			}

		case headErr := <-eventHandler.ErrorCh:
			if nil != idleTimer {
				idleTimer.Stop()
			}
			log.WithFields(log.Fields{
				"endpoint": eventHandler.Endpoint,
				"err":      headErr.err,
				"msg":      headErr.msg,
			},
			).Error("Unable to handle event.")
			errMetricInc(1)

		case <-idleTimerC:
			err := errors.New("SSE idle timeout")
			log.WithFields(log.Fields{
				"endpoint": eventHandler.Endpoint,
				"err":      err,
				"msg":      err.Error(),
			},
			).Error("TIMEOUT - Attempting to resubscribe")
			errMetricInc(1)
			eventHandler.Disconnect()
			err = eventHandler.Connect()
			if err != nil {
				log.Error("Unable to re-subscribe.", err)
			}
		}
	}
}

// Turn the data object into a Struct.
func processMsg[P ProcessedEvents](msg []byte, processCh chan<- *P, errorCh chan<- *SseError) {
	var msgMarshaled P
	err := json.Unmarshal(msg, &msgMarshaled)
	if err != nil {
		loghelper.LogError(err).Error("Unable to parse message")
		errorCh <- &SseError{
			err: err,
			msg: msg,
		}
		return
	}
	processCh <- &msgMarshaled
}

// Capture all of the event topics.
func (bc *BeaconClient) captureEventTopic() {
	log.Info("We are capturing all SSE events")
	go handleIncomingSseEvent(bc.HeadTracking, bc.Metrics.IncrementHeadError, time.Second*30)
	go handleIncomingSseEvent(bc.ReOrgTracking, bc.Metrics.IncrementReorgError, 0)
}