package slasher

import (
	"context"
	"time"

	"github.com/pkg/errors"
	slashertypes "github.com/prysmaticlabs/prysm/v5/beacon-chain/slasher/types"
	fieldparams "github.com/prysmaticlabs/prysm/v5/config/fieldparams"
	"github.com/prysmaticlabs/prysm/v5/consensus-types/primitives"
	ethpb "github.com/prysmaticlabs/prysm/v5/proto/prysm/v1alpha1"
	"github.com/prysmaticlabs/prysm/v5/time/slots"
	"github.com/sirupsen/logrus"
)

const (
	couldNotSaveAttRecord            = "Could not save attestation records to DB"
	couldNotCheckSlashableAtt        = "Could not check slashable attestations"
	couldNotProcessAttesterSlashings = "Could not process attester slashings"
)

// Receive indexed attestations from some source event feed,
// validating their integrity before appending them to an attestation queue
// for batch processing in a separate routine.
func (s *Service) receiveAttestations(ctx context.Context, indexedAttsChan chan *ethpb.IndexedAttestation) {
	defer s.wg.Done()

	sub := s.serviceCfg.IndexedAttestationsFeed.Subscribe(indexedAttsChan)
	defer sub.Unsubscribe()
	for {
		select {
		case att := <-indexedAttsChan:
			if !validateAttestationIntegrity(att) {
				continue
			}
			dataRoot, err := att.Data.HashTreeRoot()
			if err != nil {
				log.WithError(err).Error("Could not get hash tree root of attestation")
				continue
			}
			attWrapper := &slashertypes.IndexedAttestationWrapper{
				IndexedAttestation: att,
				DataRoot:           dataRoot,
			}
			s.attsQueue.push(attWrapper)
		case err := <-sub.Err():
			log.WithError(err).Debug("Subscriber closed with error")
			return
		case <-ctx.Done():
			return
		}
	}
}

// Receive beacon blocks from some source event feed,
func (s *Service) receiveBlocks(ctx context.Context, beaconBlockHeadersChan chan *ethpb.SignedBeaconBlockHeader) {
	defer s.wg.Done()

	sub := s.serviceCfg.BeaconBlockHeadersFeed.Subscribe(beaconBlockHeadersChan)
	defer sub.Unsubscribe()
	for {
		select {
		case blockHeader := <-beaconBlockHeadersChan:
			if !validateBlockHeaderIntegrity(blockHeader) {
				continue
			}
			headerRoot, err := blockHeader.Header.HashTreeRoot()
			if err != nil {
				log.WithError(err).Error("Could not get hash tree root of signed block header")
				continue
			}
			wrappedProposal := &slashertypes.SignedBlockHeaderWrapper{
				SignedBeaconBlockHeader: blockHeader,
				HeaderRoot:              headerRoot,
			}
			s.blksQueue.push(wrappedProposal)
		case err := <-sub.Err():
			log.WithError(err).Debug("Subscriber closed with error")
			return
		case <-ctx.Done():
			return
		}
	}
}

// Process queued attestations every time a slot ticker fires. We retrieve
// these attestations from a queue, then group them all by validator chunk index.
// This grouping will allow us to perform detection on batches of attestations
// per validator chunk index which can be done concurrently.
func (s *Service) processQueuedAttestations(ctx context.Context, slotTicker <-chan primitives.Slot) {
	defer s.wg.Done()

	for {
		select {
		case currentSlot := <-slotTicker:
			// Retrieve all attestations from the queue.
			attestations := s.attsQueue.dequeue()

			// Process the retrieved attestations.
			s.processAttestations(ctx, attestations, currentSlot)
		case <-ctx.Done():
			return
		}
	}
}

func (s *Service) processAttestations(
	ctx context.Context,
	attestations []*slashertypes.IndexedAttestationWrapper,
	currentSlot primitives.Slot,
) map[[fieldparams.RootLength]byte]*ethpb.AttesterSlashing {
	// Get the current epoch from the current slot.
	currentEpoch := slots.ToEpoch(currentSlot)

	// Take all the attestations in the queue and filter out
	// those which are valid now and valid in the future.
	validAttestations, validInFutureAttestations, numDropped := s.filterAttestations(attestations, currentEpoch)

	// Increase corresponding prometheus metrics.
	deferredAttestationsTotal.Add(float64(len(validInFutureAttestations)))
	droppedAttestationsTotal.Add(float64(numDropped))
	processedAttestationsTotal.Add(float64(len(validAttestations)))

	// We add back those attestations that are valid in the future to the queue.
	s.attsQueue.extend(validInFutureAttestations)

	// Compute some counts.
	queuedAttestationsCount := s.attsQueue.size()
	validAttestationsCount := len(validAttestations)
	validInFutureAttestationsCount := len(validInFutureAttestations)

	// Log useful information.
	log.WithFields(logrus.Fields{
		"currentSlot":     currentSlot,
		"currentEpoch":    currentEpoch,
		"numValidAtts":    validAttestationsCount,
		"numDeferredAtts": validInFutureAttestationsCount,
		"numDroppedAtts":  numDropped,
		"attsQueueSize":   queuedAttestationsCount,
	}).Info("Start processing queued attestations")

	start := time.Now()

	// Check for attestatinos slashings (double, sourrounding, surrounded votes).
	slashings, err := s.checkSlashableAttestations(ctx, currentEpoch, validAttestations)
	if err != nil {
		log.WithError(err).Error(couldNotCheckSlashableAtt)
		return nil
	}

	// Process attester slashings by verifying their signatures, submitting
	// to the beacon node's operations pool, and logging them.
	processedAttesterSlashings, err := s.processAttesterSlashings(ctx, slashings)
	if err != nil {
		log.WithError(err).Error(couldNotProcessAttesterSlashings)
		return nil
	}

	end := time.Since(start)
	log.WithField("elapsed", end).Info("Done processing queued attestations")

	if len(slashings) > 0 {
		log.WithField("numSlashings", len(slashings)).Warn("Slashable attestation offenses found")
	}

	return processedAttesterSlashings
}

// Process queued blocks every time an epoch ticker fires. We retrieve
// these blocks from a queue, then perform double proposal detection.
func (s *Service) processQueuedBlocks(ctx context.Context, slotTicker <-chan primitives.Slot) {
	defer s.wg.Done()

	for {
		select {
		case currentSlot := <-slotTicker:
			blocks := s.blksQueue.dequeue()
			currentEpoch := slots.ToEpoch(currentSlot)

			receivedBlocksTotal.Add(float64(len(blocks)))

			log.WithFields(logrus.Fields{
				"currentSlot":  currentSlot,
				"currentEpoch": currentEpoch,
				"numBlocks":    len(blocks),
			}).Info("Processing queued blocks for slashing detection")

			start := time.Now()
			// Check for slashings.
			slashings, err := s.detectProposerSlashings(ctx, blocks)
			if err != nil {
				log.WithError(err).Error("Could not detect proposer slashings")
				continue
			}

			// Process proposer slashings by verifying their signatures, submitting
			// to the beacon node's operations pool, and logging them.
			if err := s.processProposerSlashings(ctx, slashings); err != nil {
				log.WithError(err).Error("Could not process proposer slashings")
				continue
			}

			log.WithField("elapsed", time.Since(start)).Debug("Done checking slashable blocks")

			processedBlocksTotal.Add(float64(len(blocks)))
		case <-ctx.Done():
			return
		}
	}
}

// Prunes slasher data on each slot tick to prevent unnecessary build-up of disk space usage.
func (s *Service) pruneSlasherData(ctx context.Context, slotTicker <-chan primitives.Slot) {
	defer s.wg.Done()

	for {
		select {
		case <-slotTicker:
			headEpoch := slots.ToEpoch(s.serviceCfg.HeadStateFetcher.HeadSlot())
			if err := s.pruneSlasherDataWithinSlidingWindow(ctx, headEpoch); err != nil {
				log.WithError(err).Error("Could not prune slasher data")
				continue
			}
		case <-ctx.Done():
			return
		}
	}
}

// Prunes slasher data by using a sliding window of [current_epoch - HISTORY_LENGTH, current_epoch].
// All data before that window is unnecessary for slasher, so can be periodically deleted.
// Say HISTORY_LENGTH is 4 and we have data for epochs 0, 1, 2, 3. Once we hit epoch 4, the sliding window
// we care about is 1, 2, 3, 4, so we can delete data for epoch 0.
func (s *Service) pruneSlasherDataWithinSlidingWindow(ctx context.Context, currentEpoch primitives.Epoch) error {
	var maxPruningEpoch primitives.Epoch
	if currentEpoch >= s.params.historyLength {
		maxPruningEpoch = currentEpoch - s.params.historyLength
	} else {
		// If the current epoch is less than the history length, we should not
		// attempt to prune at all.
		return nil
	}
	start := time.Now()
	log.WithFields(logrus.Fields{
		"currentEpoch":          currentEpoch,
		"pruningAllBeforeEpoch": maxPruningEpoch,
	}).Info("Pruning old attestations and proposals for slasher")
	numPrunedAtts, err := s.serviceCfg.Database.PruneAttestationsAtEpoch(
		ctx, maxPruningEpoch,
	)
	if err != nil {
		return errors.Wrap(err, "Could not prune attestations")
	}
	numPrunedProposals, err := s.serviceCfg.Database.PruneProposalsAtEpoch(
		ctx, maxPruningEpoch,
	)
	if err != nil {
		return errors.Wrap(err, "Could not prune proposals")
	}
	fields := logrus.Fields{}
	if numPrunedAtts > 0 {
		fields["numPrunedAtts"] = numPrunedAtts
	}
	if numPrunedProposals > 0 {
		fields["numPrunedProposals"] = numPrunedProposals
	}
	fields["elapsed"] = time.Since(start)
	log.WithFields(fields).Info("Done pruning old attestations and proposals for slasher")
	return nil
}