package core

import (
	"bytes"
	"context"
	"fmt"
	"sort"
	"time"

	"github.com/pkg/errors"
	"github.com/prysmaticlabs/prysm/v5/beacon-chain/cache"
	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/altair"
	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/epoch/precompute"
	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/feed"
	opfeed "github.com/prysmaticlabs/prysm/v5/beacon-chain/core/feed/operation"
	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/helpers"
	coreTime "github.com/prysmaticlabs/prysm/v5/beacon-chain/core/time"
	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/transition"
	forkchoicetypes "github.com/prysmaticlabs/prysm/v5/beacon-chain/forkchoice/types"
	beaconState "github.com/prysmaticlabs/prysm/v5/beacon-chain/state"
	fieldparams "github.com/prysmaticlabs/prysm/v5/config/fieldparams"
	"github.com/prysmaticlabs/prysm/v5/config/params"
	"github.com/prysmaticlabs/prysm/v5/consensus-types/primitives"
	"github.com/prysmaticlabs/prysm/v5/consensus-types/validator"
	"github.com/prysmaticlabs/prysm/v5/crypto/bls"
	"github.com/prysmaticlabs/prysm/v5/encoding/bytesutil"
	ethpb "github.com/prysmaticlabs/prysm/v5/proto/prysm/v1alpha1"
	"github.com/prysmaticlabs/prysm/v5/runtime/version"
	prysmTime "github.com/prysmaticlabs/prysm/v5/time"
	"github.com/prysmaticlabs/prysm/v5/time/slots"
	"github.com/sirupsen/logrus"
	"go.opencensus.io/trace"
	"golang.org/x/sync/errgroup"
)

var errOptimisticMode = errors.New("the node is currently optimistic and cannot serve validators")

// AggregateBroadcastFailedError represents an error scenario where
// broadcasting an aggregate selection proof failed.
type AggregateBroadcastFailedError struct {
	err error
}

// NewAggregateBroadcastFailedError creates a new error instance.
func NewAggregateBroadcastFailedError(err error) AggregateBroadcastFailedError {
	return AggregateBroadcastFailedError{
		err: err,
	}
}

// Error returns the underlying error message.
func (e *AggregateBroadcastFailedError) Error() string {
	return fmt.Sprintf("could not broadcast signed aggregated attestation: %s", e.err.Error())
}

// ComputeValidatorPerformance reports the validator's latest balance along with other important metrics on
// rewards and penalties throughout its lifecycle in the beacon chain.
func (s *Service) ComputeValidatorPerformance(
	ctx context.Context,
	req *ethpb.ValidatorPerformanceRequest,
) (*ethpb.ValidatorPerformanceResponse, *RpcError) {
	ctx, span := trace.StartSpan(ctx, "coreService.ComputeValidatorPerformance")
	defer span.End()

	if s.SyncChecker.Syncing() {
		return nil, &RpcError{Reason: Unavailable, Err: errors.New("Syncing to latest head, not ready to respond")}
	}

	headState, err := s.HeadFetcher.HeadState(ctx)
	if err != nil {
		return nil, &RpcError{Err: errors.Wrap(err, "could not get head state"), Reason: Internal}
	}
	currSlot := s.GenesisTimeFetcher.CurrentSlot()
	if currSlot > headState.Slot() {
		headRoot, err := s.HeadFetcher.HeadRoot(ctx)
		if err != nil {
			return nil, &RpcError{Err: errors.Wrap(err, "could not get head root"), Reason: Internal}
		}
		headState, err = transition.ProcessSlotsUsingNextSlotCache(ctx, headState, headRoot, currSlot)
		if err != nil {
			return nil, &RpcError{Err: errors.Wrapf(err, "could not process slots up to %d", currSlot), Reason: Internal}
		}
	}
	var validatorSummary []*precompute.Validator
	if headState.Version() == version.Phase0 {
		vp, bp, err := precompute.New(ctx, headState)
		if err != nil {
			return nil, &RpcError{Err: err, Reason: Internal}
		}
		vp, bp, err = precompute.ProcessAttestations(ctx, headState, vp, bp)
		if err != nil {
			return nil, &RpcError{Err: err, Reason: Internal}
		}
		headState, err = precompute.ProcessRewardsAndPenaltiesPrecompute(headState, bp, vp, precompute.AttestationsDelta, precompute.ProposersDelta)
		if err != nil {
			return nil, &RpcError{Err: err, Reason: Internal}
		}
		validatorSummary = vp
	} else if headState.Version() >= version.Altair {
		vp, bp, err := altair.InitializePrecomputeValidators(ctx, headState)
		if err != nil {
			return nil, &RpcError{Err: err, Reason: Internal}
		}
		vp, bp, err = altair.ProcessEpochParticipation(ctx, headState, bp, vp)
		if err != nil {
			return nil, &RpcError{Err: err, Reason: Internal}
		}
		headState, vp, err = altair.ProcessInactivityScores(ctx, headState, vp)
		if err != nil {
			return nil, &RpcError{Err: err, Reason: Internal}
		}
		headState, err = altair.ProcessRewardsAndPenaltiesPrecompute(headState, bp, vp)
		if err != nil {
			return nil, &RpcError{Err: err, Reason: Internal}
		}
		validatorSummary = vp
	} else {
		return nil, &RpcError{Err: errors.Wrapf(err, "head state version %d not supported", headState.Version()), Reason: Internal}
	}

	responseCap := len(req.Indices) + len(req.PublicKeys)
	validatorIndices := make([]primitives.ValidatorIndex, 0, responseCap)
	missingValidators := make([][]byte, 0, responseCap)

	filtered := map[primitives.ValidatorIndex]bool{} // Track filtered validators to prevent duplication in the response.
	// Convert the list of validator public keys to validator indices and add to the indices set.
	for _, pubKey := range req.PublicKeys {
		// Skip empty public key.
		if len(pubKey) == 0 {
			continue
		}
		pubkeyBytes := bytesutil.ToBytes48(pubKey)
		idx, ok := headState.ValidatorIndexByPubkey(pubkeyBytes)
		if !ok {
			// Validator index not found, track as missing.
			missingValidators = append(missingValidators, pubKey)
			continue
		}
		if !filtered[idx] {
			validatorIndices = append(validatorIndices, idx)
			filtered[idx] = true
		}
	}
	// Add provided indices to the indices set.
	for _, idx := range req.Indices {
		if !filtered[idx] {
			validatorIndices = append(validatorIndices, idx)
			filtered[idx] = true
		}
	}
	// Depending on the indices and public keys given, results might not be sorted.
	sort.Slice(validatorIndices, func(i, j int) bool {
		return validatorIndices[i] < validatorIndices[j]
	})

	currentEpoch := coreTime.CurrentEpoch(headState)
	responseCap = len(validatorIndices)
	pubKeys := make([][]byte, 0, responseCap)
	beforeTransitionBalances := make([]uint64, 0, responseCap)
	afterTransitionBalances := make([]uint64, 0, responseCap)
	effectiveBalances := make([]uint64, 0, responseCap)
	correctlyVotedSource := make([]bool, 0, responseCap)
	correctlyVotedTarget := make([]bool, 0, responseCap)
	correctlyVotedHead := make([]bool, 0, responseCap)
	inactivityScores := make([]uint64, 0, responseCap)
	// Append performance summaries.
	// Also track missing validators using public keys.
	for _, idx := range validatorIndices {
		val, err := headState.ValidatorAtIndexReadOnly(idx)
		if err != nil {
			return nil, &RpcError{Err: errors.Wrap(err, "could not get validator"), Reason: Internal}
		}
		pubKey := val.PublicKey()
		if uint64(idx) >= uint64(len(validatorSummary)) {
			// Not listed in validator summary yet; treat it as missing.
			missingValidators = append(missingValidators, pubKey[:])
			continue
		}
		if !helpers.IsActiveValidatorUsingTrie(val, currentEpoch) {
			// Inactive validator; treat it as missing.
			missingValidators = append(missingValidators, pubKey[:])
			continue
		}

		summary := validatorSummary[idx]
		pubKeys = append(pubKeys, pubKey[:])
		effectiveBalances = append(effectiveBalances, summary.CurrentEpochEffectiveBalance)
		beforeTransitionBalances = append(beforeTransitionBalances, summary.BeforeEpochTransitionBalance)
		afterTransitionBalances = append(afterTransitionBalances, summary.AfterEpochTransitionBalance)
		correctlyVotedTarget = append(correctlyVotedTarget, summary.IsPrevEpochTargetAttester)
		correctlyVotedHead = append(correctlyVotedHead, summary.IsPrevEpochHeadAttester)

		if headState.Version() == version.Phase0 {
			correctlyVotedSource = append(correctlyVotedSource, summary.IsPrevEpochAttester)
		} else {
			correctlyVotedSource = append(correctlyVotedSource, summary.IsPrevEpochSourceAttester)
			inactivityScores = append(inactivityScores, summary.InactivityScore)
		}
	}

	return &ethpb.ValidatorPerformanceResponse{
		PublicKeys:                    pubKeys,
		CorrectlyVotedSource:          correctlyVotedSource,
		CorrectlyVotedTarget:          correctlyVotedTarget, // In altair, when this is true then the attestation was definitely included.
		CorrectlyVotedHead:            correctlyVotedHead,
		CurrentEffectiveBalances:      effectiveBalances,
		BalancesBeforeEpochTransition: beforeTransitionBalances,
		BalancesAfterEpochTransition:  afterTransitionBalances,
		MissingValidators:             missingValidators,
		InactivityScores:              inactivityScores, // Only populated in Altair
	}, nil
}

// SubmitSignedContributionAndProof is called by a sync committee aggregator
// to submit signed contribution and proof object.
func (s *Service) SubmitSignedContributionAndProof(
	ctx context.Context,
	req *ethpb.SignedContributionAndProof,
) *RpcError {
	ctx, span := trace.StartSpan(ctx, "coreService.SubmitSignedContributionAndProof")
	defer span.End()

	errs, ctx := errgroup.WithContext(ctx)

	// Broadcasting and saving contribution into the pool in parallel. As one fail should not affect another.
	errs.Go(func() error {
		return s.Broadcaster.Broadcast(ctx, req)
	})

	if err := s.SyncCommitteePool.SaveSyncCommitteeContribution(req.Message.Contribution); err != nil {
		return &RpcError{Err: err, Reason: Internal}
	}

	// Wait for p2p broadcast to complete and return the first error (if any)
	err := errs.Wait()
	if err != nil {
		return &RpcError{Err: err, Reason: Internal}
	}

	s.OperationNotifier.OperationFeed().Send(&feed.Event{
		Type: opfeed.SyncCommitteeContributionReceived,
		Data: &opfeed.SyncCommitteeContributionReceivedData{
			Contribution: req,
		},
	})

	return nil
}

// SubmitSignedAggregateSelectionProof verifies given aggregate and proofs and publishes them on appropriate gossipsub topic.
func (s *Service) SubmitSignedAggregateSelectionProof(
	ctx context.Context,
	req *ethpb.SignedAggregateSubmitRequest,
) *RpcError {
	ctx, span := trace.StartSpan(ctx, "coreService.SubmitSignedAggregateSelectionProof")
	defer span.End()

	if req.SignedAggregateAndProof == nil || req.SignedAggregateAndProof.Message == nil ||
		req.SignedAggregateAndProof.Message.Aggregate == nil || req.SignedAggregateAndProof.Message.Aggregate.Data == nil {
		return &RpcError{Err: errors.New("signed aggregate request can't be nil"), Reason: BadRequest}
	}
	emptySig := make([]byte, fieldparams.BLSSignatureLength)
	if bytes.Equal(req.SignedAggregateAndProof.Signature, emptySig) ||
		bytes.Equal(req.SignedAggregateAndProof.Message.SelectionProof, emptySig) {
		return &RpcError{Err: errors.New("signed signatures can't be zero hashes"), Reason: BadRequest}
	}

	// As a preventive measure, a beacon node shouldn't broadcast an attestation whose slot is out of range.
	if err := helpers.ValidateAttestationTime(req.SignedAggregateAndProof.Message.Aggregate.Data.Slot,
		s.GenesisTimeFetcher.GenesisTime(), params.BeaconConfig().MaximumGossipClockDisparityDuration()); err != nil {
		return &RpcError{Err: errors.New("attestation slot is no longer valid from current time"), Reason: BadRequest}
	}

	if err := s.Broadcaster.Broadcast(ctx, req.SignedAggregateAndProof); err != nil {
		return &RpcError{Err: &AggregateBroadcastFailedError{err: err}, Reason: Internal}
	}

	log.WithFields(logrus.Fields{
		"slot":            req.SignedAggregateAndProof.Message.Aggregate.Data.Slot,
		"committeeIndex":  req.SignedAggregateAndProof.Message.Aggregate.Data.CommitteeIndex,
		"validatorIndex":  req.SignedAggregateAndProof.Message.AggregatorIndex,
		"aggregatedCount": req.SignedAggregateAndProof.Message.Aggregate.AggregationBits.Count(),
	}).Debug("Broadcasting aggregated attestation and proof")

	return nil
}

// AggregatedSigAndAggregationBits returns the aggregated signature and aggregation bits
// associated with a particular set of sync committee messages.
func (s *Service) AggregatedSigAndAggregationBits(
	ctx context.Context,
	req *ethpb.AggregatedSigAndAggregationBitsRequest) ([]byte, []byte, error) {
	subCommitteeSize := params.BeaconConfig().SyncCommitteeSize / params.BeaconConfig().SyncCommitteeSubnetCount
	sigs := make([][]byte, 0, subCommitteeSize)
	bits := ethpb.NewSyncCommitteeAggregationBits()
	for _, msg := range req.Msgs {
		if bytes.Equal(req.BlockRoot, msg.BlockRoot) {
			headSyncCommitteeIndices, err := s.HeadFetcher.HeadSyncCommitteeIndices(ctx, msg.ValidatorIndex, req.Slot)
			if err != nil {
				return nil, nil, errors.Wrapf(err, "could not get sync subcommittee index")
			}
			for _, index := range headSyncCommitteeIndices {
				i := uint64(index)
				subnetIndex := i / subCommitteeSize
				indexMod := i % subCommitteeSize
				if subnetIndex == req.SubnetId && !bits.BitAt(indexMod) {
					bits.SetBitAt(indexMod, true)
					sigs = append(sigs, msg.Signature)
				}
			}
		}
	}
	aggregatedSig := make([]byte, 96)
	aggregatedSig[0] = 0xC0
	if len(sigs) != 0 {
		uncompressedSigs, err := bls.MultipleSignaturesFromBytes(sigs)
		if err != nil {
			return nil, nil, errors.Wrapf(err, "could not decompress signatures")
		}
		aggregatedSig = bls.AggregateSignatures(uncompressedSigs).Marshal()
	}
	return aggregatedSig, bits, nil
}

// GetAttestationData requests that the beacon node produces attestation data for
// the requested committee index and slot based on the nodes current head.
func (s *Service) GetAttestationData(
	ctx context.Context, req *ethpb.AttestationDataRequest,
) (*ethpb.AttestationData, *RpcError) {
	ctx, span := trace.StartSpan(ctx, "coreService.GetAttestationData")
	defer span.End()

	if req.Slot != s.GenesisTimeFetcher.CurrentSlot() {
		return nil, &RpcError{Reason: BadRequest, Err: errors.Errorf("invalid request: slot %d is not the current slot %d", req.Slot, s.GenesisTimeFetcher.CurrentSlot())}
	}
	if err := helpers.ValidateAttestationTime(
		req.Slot,
		s.GenesisTimeFetcher.GenesisTime(),
		params.BeaconConfig().MaximumGossipClockDisparityDuration(),
	); err != nil {
		return nil, &RpcError{Reason: BadRequest, Err: errors.Errorf("invalid request: %v", err)}
	}

	s.AttestationCache.RLock()
	res := s.AttestationCache.Get()
	if res != nil && res.Slot == req.Slot {
		s.AttestationCache.RUnlock()
		return &ethpb.AttestationData{
			Slot:            res.Slot,
			CommitteeIndex:  req.CommitteeIndex,
			BeaconBlockRoot: res.HeadRoot,
			Source: &ethpb.Checkpoint{
				Epoch: res.Source.Epoch,
				Root:  res.Source.Root[:],
			},
			Target: &ethpb.Checkpoint{
				Epoch: res.Target.Epoch,
				Root:  res.Target.Root[:],
			},
		}, nil
	}
	s.AttestationCache.RUnlock()

	s.AttestationCache.Lock()
	defer s.AttestationCache.Unlock()

	// We check the cache again as in the event there are multiple inflight requests for
	// the same attestation data, the cache might have been filled while we were waiting
	// to acquire the lock.
	res = s.AttestationCache.Get()
	if res != nil && res.Slot == req.Slot {
		return &ethpb.AttestationData{
			Slot:            res.Slot,
			CommitteeIndex:  req.CommitteeIndex,
			BeaconBlockRoot: res.HeadRoot,
			Source: &ethpb.Checkpoint{
				Epoch: res.Source.Epoch,
				Root:  res.Source.Root[:],
			},
			Target: &ethpb.Checkpoint{
				Epoch: res.Target.Epoch,
				Root:  res.Target.Root[:],
			},
		}, nil
	}
	// cache miss, we need to check for optimistic status before proceeding
	optimistic, err := s.OptimisticModeFetcher.IsOptimistic(ctx)
	if err != nil {
		return nil, &RpcError{Reason: Internal, Err: err}
	}
	if optimistic {
		return nil, &RpcError{Reason: Unavailable, Err: errOptimisticMode}
	}

	headRoot, err := s.HeadFetcher.HeadRoot(ctx)
	if err != nil {
		return nil, &RpcError{Reason: Internal, Err: errors.Wrap(err, "could not get head root")}
	}
	targetEpoch := slots.ToEpoch(req.Slot)
	targetRoot, err := s.HeadFetcher.TargetRootForEpoch(bytesutil.ToBytes32(headRoot), targetEpoch)
	if err != nil {
		return nil, &RpcError{Reason: Internal, Err: errors.Wrap(err, "could not get target root")}
	}

	headState, err := s.HeadFetcher.HeadState(ctx)
	if err != nil {
		return nil, &RpcError{Reason: Internal, Err: errors.Wrap(err, "could not get head state")}
	}
	if coreTime.CurrentEpoch(headState) < slots.ToEpoch(req.Slot) { // Ensure justified checkpoint safety by processing head state across the boundary.
		headState, err = transition.ProcessSlotsUsingNextSlotCache(ctx, headState, headRoot, req.Slot)
		if err != nil {
			return nil, &RpcError{Reason: Internal, Err: errors.Errorf("could not process slots up to %d: %v", req.Slot, err)}
		}
	}
	justifiedCheckpoint := headState.CurrentJustifiedCheckpoint()

	if err = s.AttestationCache.Put(&cache.AttestationConsensusData{
		Slot:     req.Slot,
		HeadRoot: headRoot,
		Target: forkchoicetypes.Checkpoint{
			Epoch: targetEpoch,
			Root:  targetRoot,
		},
		Source: forkchoicetypes.Checkpoint{
			Epoch: justifiedCheckpoint.Epoch,
			Root:  bytesutil.ToBytes32(justifiedCheckpoint.Root),
		},
	}); err != nil {
		log.WithError(err).Error("Failed to put attestation data into cache")
	}

	return &ethpb.AttestationData{
		Slot:            req.Slot,
		CommitteeIndex:  req.CommitteeIndex,
		BeaconBlockRoot: headRoot,
		Source: &ethpb.Checkpoint{
			Epoch: justifiedCheckpoint.Epoch,
			Root:  justifiedCheckpoint.Root,
		},
		Target: &ethpb.Checkpoint{
			Epoch: targetEpoch,
			Root:  targetRoot[:],
		},
	}, nil
}

// SubmitSyncMessage submits the sync committee message to the network.
// It also saves the sync committee message into the pending pool for block inclusion.
func (s *Service) SubmitSyncMessage(ctx context.Context, msg *ethpb.SyncCommitteeMessage) *RpcError {
	ctx, span := trace.StartSpan(ctx, "coreService.SubmitSyncMessage")
	defer span.End()

	errs, ctx := errgroup.WithContext(ctx)

	headSyncCommitteeIndices, err := s.HeadFetcher.HeadSyncCommitteeIndices(ctx, msg.ValidatorIndex, msg.Slot)
	if err != nil {
		return &RpcError{Reason: Internal, Err: errors.Wrap(err, "could not get head sync committee indices")}
	}
	// Broadcasting and saving message into the pool in parallel. As one fail should not affect another.
	// This broadcasts for all subnets.
	for _, index := range headSyncCommitteeIndices {
		subCommitteeSize := params.BeaconConfig().SyncCommitteeSize / params.BeaconConfig().SyncCommitteeSubnetCount
		subnet := uint64(index) / subCommitteeSize
		errs.Go(func() error {
			return s.P2P.BroadcastSyncCommitteeMessage(ctx, subnet, msg)
		})
	}

	if err := s.SyncCommitteePool.SaveSyncCommitteeMessage(msg); err != nil {
		return &RpcError{Reason: Internal, Err: errors.Wrap(err, "could not save sync committee message")}
	}

	// Wait for p2p broadcast to complete and return the first error (if any)
	if err = errs.Wait(); err != nil {
		return &RpcError{Reason: Internal, Err: errors.Wrap(err, "could not broadcast sync committee message")}
	}
	return nil
}

// RegisterSyncSubnetCurrentPeriod registers a persistent subnet for the current sync committee period.
func RegisterSyncSubnetCurrentPeriod(s beaconState.BeaconState, epoch primitives.Epoch, pubKey []byte, status validator.Status) error {
	committee, err := s.CurrentSyncCommittee()
	if err != nil {
		return err
	}
	syncCommPeriod := slots.SyncCommitteePeriod(epoch)
	registerSyncSubnet(epoch, syncCommPeriod, pubKey, committee, status)
	return nil
}

// RegisterSyncSubnetCurrentPeriodProto registers a persistent subnet for the current sync committee period.
func RegisterSyncSubnetCurrentPeriodProto(s beaconState.BeaconState, epoch primitives.Epoch, pubKey []byte, status ethpb.ValidatorStatus) error {
	committee, err := s.CurrentSyncCommittee()
	if err != nil {
		return err
	}
	syncCommPeriod := slots.SyncCommitteePeriod(epoch)
	registerSyncSubnetProto(epoch, syncCommPeriod, pubKey, committee, status)
	return nil
}

// RegisterSyncSubnetNextPeriod registers a persistent subnet for the next sync committee period.
func RegisterSyncSubnetNextPeriod(s beaconState.BeaconState, epoch primitives.Epoch, pubKey []byte, status validator.Status) error {
	committee, err := s.NextSyncCommittee()
	if err != nil {
		return err
	}
	syncCommPeriod := slots.SyncCommitteePeriod(epoch)
	registerSyncSubnet(epoch, syncCommPeriod+1, pubKey, committee, status)
	return nil
}

// RegisterSyncSubnetNextPeriodProto registers a persistent subnet for the next sync committee period.
func RegisterSyncSubnetNextPeriodProto(s beaconState.BeaconState, epoch primitives.Epoch, pubKey []byte, status ethpb.ValidatorStatus) error {
	committee, err := s.NextSyncCommittee()
	if err != nil {
		return err
	}
	syncCommPeriod := slots.SyncCommitteePeriod(epoch)
	registerSyncSubnetProto(epoch, syncCommPeriod+1, pubKey, committee, status)
	return nil
}

// registerSyncSubnet checks the status and pubkey of a particular validator
// to discern whether persistent subnets need to be registered for them.
func registerSyncSubnet(
	currEpoch primitives.Epoch,
	syncPeriod uint64,
	pubkey []byte,
	syncCommittee *ethpb.SyncCommittee,
	status validator.Status,
) {
	if status != validator.Active && status != validator.ActiveExiting {
		return
	}
	registerSyncSubnetInternal(currEpoch, syncPeriod, pubkey, syncCommittee)
}

func registerSyncSubnetProto(
	currEpoch primitives.Epoch,
	syncPeriod uint64,
	pubkey []byte,
	syncCommittee *ethpb.SyncCommittee,
	status ethpb.ValidatorStatus,
) {
	if status != ethpb.ValidatorStatus_ACTIVE && status != ethpb.ValidatorStatus_EXITING {
		return
	}
	registerSyncSubnetInternal(currEpoch, syncPeriod, pubkey, syncCommittee)
}

func registerSyncSubnetInternal(
	currEpoch primitives.Epoch,
	syncPeriod uint64,
	pubkey []byte,
	syncCommittee *ethpb.SyncCommittee,
) {
	startEpoch := primitives.Epoch(syncPeriod * uint64(params.BeaconConfig().EpochsPerSyncCommitteePeriod))
	currPeriod := slots.SyncCommitteePeriod(currEpoch)
	endEpoch := startEpoch + params.BeaconConfig().EpochsPerSyncCommitteePeriod
	_, _, ok, expTime := cache.SyncSubnetIDs.GetSyncCommitteeSubnets(pubkey, startEpoch)
	if ok && expTime.After(prysmTime.Now()) {
		return
	}
	firstValidEpoch, err := startEpoch.SafeSub(params.BeaconConfig().SyncCommitteeSubnetCount)
	if err != nil {
		firstValidEpoch = 0
	}
	// If we are processing for a future period, we only
	// add to the relevant subscription once we are at the valid
	// bound.
	if syncPeriod != currPeriod && currEpoch < firstValidEpoch {
		return
	}
	subs := subnetsFromCommittee(pubkey, syncCommittee)
	// Handle overflow in the event current epoch is less
	// than end epoch. This is an impossible condition, so
	// it is a defensive check.
	epochsToWatch, err := endEpoch.SafeSub(uint64(currEpoch))
	if err != nil {
		epochsToWatch = 0
	}
	epochDuration := time.Duration(params.BeaconConfig().SlotsPerEpoch.Mul(params.BeaconConfig().SecondsPerSlot))
	totalDuration := epochDuration * time.Duration(epochsToWatch) * time.Second
	cache.SyncSubnetIDs.AddSyncCommitteeSubnets(pubkey, startEpoch, subs, totalDuration)
}

// subnetsFromCommittee retrieves the relevant subnets for the chosen validator.
func subnetsFromCommittee(pubkey []byte, comm *ethpb.SyncCommittee) []uint64 {
	positions := make([]uint64, 0)
	for i, pkey := range comm.Pubkeys {
		if bytes.Equal(pubkey, pkey) {
			positions = append(positions, uint64(i)/(params.BeaconConfig().SyncCommitteeSize/params.BeaconConfig().SyncCommitteeSubnetCount))
		}
	}
	return positions
}