package sync

import (
	"context"
	"time"

	libp2pcore "github.com/libp2p/go-libp2p-core"
	"github.com/pkg/errors"
	types "github.com/prysmaticlabs/eth2-types"
	"github.com/prysmaticlabs/prysm/beacon-chain/db/filters"
	p2ptypes "github.com/prysmaticlabs/prysm/beacon-chain/p2p/types"
	"github.com/prysmaticlabs/prysm/cmd/beacon-chain/flags"
	"github.com/prysmaticlabs/prysm/config/params"
	"github.com/prysmaticlabs/prysm/monitoring/tracing"
	pb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"go.opencensus.io/trace"
)

// beaconBlocksByRangeRPCHandler looks up the request blocks from the database from a given start block.
func (s *Service) beaconBlocksByRangeRPCHandler(ctx context.Context, msg interface{}, stream libp2pcore.Stream) error {
	ctx, span := trace.StartSpan(ctx, "sync.BeaconBlocksByRangeHandler")
	defer span.End()
	ctx, cancel := context.WithTimeout(ctx, respTimeout)
	defer cancel()
	SetRPCStreamDeadlines(stream)

	// Ticker to stagger out large requests.
	ticker := time.NewTicker(time.Second)
	defer ticker.Stop()

	m, ok := msg.(*pb.BeaconBlocksByRangeRequest)
	if !ok {
		return errors.New("message is not type *pb.BeaconBlockByRangeRequest")
	}
	if err := s.validateRangeRequest(m); err != nil {
		s.writeErrorResponseToStream(responseCodeInvalidRequest, err.Error(), stream)
		s.cfg.P2P.Peers().Scorers().BadResponsesScorer().Increment(stream.Conn().RemotePeer())
		tracing.AnnotateError(span, err)
		return err
	}

	// The initial count for the first batch to be returned back.
	count := m.Count
	allowedBlocksPerSecond := uint64(flags.Get().BlockBatchLimit)
	if count > allowedBlocksPerSecond {
		count = allowedBlocksPerSecond
	}
	// initial batch start and end slots to be returned to remote peer.
	startSlot := m.StartSlot
	endSlot := startSlot.Add(m.Step * (count - 1))

	// The final requested slot from remote peer.
	endReqSlot := startSlot.Add(m.Step * (m.Count - 1))

	blockLimiter, err := s.rateLimiter.topicCollector(string(stream.Protocol()))
	if err != nil {
		return err
	}
	remainingBucketCapacity := blockLimiter.Remaining(stream.Conn().RemotePeer().String())
	span.AddAttributes(
		trace.Int64Attribute("start", int64(startSlot)),
		trace.Int64Attribute("end", int64(endReqSlot)),
		trace.Int64Attribute("step", int64(m.Step)),
		trace.Int64Attribute("count", int64(m.Count)),
		trace.StringAttribute("peer", stream.Conn().RemotePeer().Pretty()),
		trace.Int64Attribute("remaining_capacity", remainingBucketCapacity),
	)
	// prevRoot is used to ensure that returned chains are strictly linear for singular steps
	// by comparing the previous root of the block in the list with the current block's parent.
	var prevRoot [32]byte
	for startSlot <= endReqSlot {
		if err := s.rateLimiter.validateRequest(stream, allowedBlocksPerSecond); err != nil {
			tracing.AnnotateError(span, err)
			return err
		}

		if endSlot-startSlot > rangeLimit {
			s.writeErrorResponseToStream(responseCodeInvalidRequest, p2ptypes.ErrInvalidRequest.Error(), stream)
			err := p2ptypes.ErrInvalidRequest
			tracing.AnnotateError(span, err)
			return err
		}

		err := s.writeBlockRangeToStream(ctx, startSlot, endSlot, m.Step, &prevRoot, stream)
		if err != nil && !errors.Is(err, p2ptypes.ErrInvalidParent) {
			return err
		}
		// Reduce capacity of peer in the rate limiter first.
		// Decrease allowed blocks capacity by the number of streamed blocks.
		if startSlot <= endSlot {
			s.rateLimiter.add(stream, int64(1+endSlot.SubSlot(startSlot).Div(m.Step)))
		}
		// Exit in the event we have a disjoint chain to
		// return.
		if errors.Is(err, p2ptypes.ErrInvalidParent) {
			break
		}

		// Recalculate start and end slots for the next batch to be returned to the remote peer.
		startSlot = endSlot.Add(m.Step)
		endSlot = startSlot.Add(m.Step * (allowedBlocksPerSecond - 1))
		if endSlot > endReqSlot {
			endSlot = endReqSlot
		}

		// do not wait if all blocks have already been sent.
		if startSlot > endReqSlot {
			break
		}

		// wait for ticker before resuming streaming blocks to remote peer.
		<-ticker.C
	}
	closeStream(stream, log)
	return nil
}

func (s *Service) writeBlockRangeToStream(ctx context.Context, startSlot, endSlot types.Slot, step uint64,
	prevRoot *[32]byte, stream libp2pcore.Stream) error {
	ctx, span := trace.StartSpan(ctx, "sync.WriteBlockRangeToStream")
	defer span.End()

	filter := filters.NewFilter().SetStartSlot(startSlot).SetEndSlot(endSlot).SetSlotStep(step)
	blks, roots, err := s.cfg.DB.Blocks(ctx, filter)
	if err != nil {
		log.WithError(err).Debug("Could not retrieve blocks")
		s.writeErrorResponseToStream(responseCodeServerError, p2ptypes.ErrGeneric.Error(), stream)
		tracing.AnnotateError(span, err)
		return err
	}
	// handle genesis case
	if startSlot == 0 {
		genBlock, genRoot, err := s.retrieveGenesisBlock(ctx)
		if err != nil {
			log.WithError(err).Debug("Could not retrieve genesis block")
			s.writeErrorResponseToStream(responseCodeServerError, p2ptypes.ErrGeneric.Error(), stream)
			tracing.AnnotateError(span, err)
			return err
		}
		blks = append([]block.SignedBeaconBlock{genBlock}, blks...)
		roots = append([][32]byte{genRoot}, roots...)
	}
	// Filter and sort our retrieved blocks, so that
	// we only return valid sets of blocks.
	blks, roots, err = s.dedupBlocksAndRoots(blks, roots)
	if err != nil {
		s.writeErrorResponseToStream(responseCodeServerError, p2ptypes.ErrGeneric.Error(), stream)
		tracing.AnnotateError(span, err)
		return err
	}
	blks, roots = s.sortBlocksAndRoots(blks, roots)

	blks, err = s.filterBlocks(ctx, blks, roots, prevRoot, step, startSlot)
	if err != nil && err != p2ptypes.ErrInvalidParent {
		s.writeErrorResponseToStream(responseCodeServerError, p2ptypes.ErrGeneric.Error(), stream)
		tracing.AnnotateError(span, err)
		return err
	}
	for _, b := range blks {
		if b == nil || b.IsNil() || b.Block().IsNil() {
			continue
		}
		if chunkErr := s.chunkBlockWriter(stream, b); chunkErr != nil {
			log.WithError(chunkErr).Debug("Could not send a chunked response")
			s.writeErrorResponseToStream(responseCodeServerError, p2ptypes.ErrGeneric.Error(), stream)
			tracing.AnnotateError(span, chunkErr)
			return chunkErr
		}

	}
	// Return error in the event we have an invalid parent.
	return err
}

func (s *Service) validateRangeRequest(r *pb.BeaconBlocksByRangeRequest) error {
	startSlot := r.StartSlot
	count := r.Count
	step := r.Step

	maxRequestBlocks := params.BeaconNetworkConfig().MaxRequestBlocks
	// Add a buffer for possible large range requests from nodes syncing close to the
	// head of the chain.
	buffer := rangeLimit * 2
	highestExpectedSlot := s.cfg.Chain.CurrentSlot().Add(uint64(buffer))

	// Ensure all request params are within appropriate bounds
	if count == 0 || count > maxRequestBlocks {
		return p2ptypes.ErrInvalidRequest
	}

	if step == 0 || step > rangeLimit {
		return p2ptypes.ErrInvalidRequest
	}

	if startSlot > highestExpectedSlot {
		return p2ptypes.ErrInvalidRequest
	}

	endSlot := startSlot.Add(step * (count - 1))
	if endSlot-startSlot > rangeLimit {
		return p2ptypes.ErrInvalidRequest
	}
	return nil
}

// filters all the provided blocks to ensure they are canonical
// and are strictly linear.
func (s *Service) filterBlocks(ctx context.Context, blks []block.SignedBeaconBlock, roots [][32]byte, prevRoot *[32]byte,
	step uint64, startSlot types.Slot) ([]block.SignedBeaconBlock, error) {
	if len(blks) != len(roots) {
		return nil, errors.New("input blks and roots are diff lengths")
	}

	newBlks := make([]block.SignedBeaconBlock, 0, len(blks))
	for i, b := range blks {
		isCanonical, err := s.cfg.Chain.IsCanonical(ctx, roots[i])
		if err != nil {
			return nil, err
		}
		parentValid := *prevRoot != [32]byte{}
		isLinear := *prevRoot == bytesutil.ToBytes32(b.Block().ParentRoot())
		isSingular := step == 1
		slotDiff, err := b.Block().Slot().SafeSubSlot(startSlot)
		if err != nil {
			return nil, err
		}
		slotDiff, err = slotDiff.SafeMod(step)
		if err != nil {
			return nil, err
		}
		isRequestedSlotStep := slotDiff == 0
		if isRequestedSlotStep && isCanonical {
			// Exit early if our valid block is non linear.
			if parentValid && isSingular && !isLinear {
				return newBlks, p2ptypes.ErrInvalidParent
			}
			newBlks = append(newBlks, blks[i])
			// Set the previous root as the
			// newly added block's root
			currRoot := roots[i]
			prevRoot = &currRoot
		}
	}
	return newBlks, nil
}

func (s *Service) writeErrorResponseToStream(responseCode byte, reason string, stream libp2pcore.Stream) {
	writeErrorResponseToStream(responseCode, reason, stream, s.cfg.P2P)
}

func (s *Service) retrieveGenesisBlock(ctx context.Context) (block.SignedBeaconBlock, [32]byte, error) {
	genBlock, err := s.cfg.DB.GenesisBlock(ctx)
	if err != nil {
		return nil, [32]byte{}, err
	}
	genRoot, err := genBlock.Block().HashTreeRoot()
	if err != nil {
		return nil, [32]byte{}, err
	}
	return genBlock, genRoot, nil
}