package p2p

import (
	"bytes"
	"context"
	"fmt"
	"reflect"

	"github.com/gogo/protobuf/proto"
	"github.com/pkg/errors"
	eth "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
	"github.com/prysmaticlabs/prysm/shared/hashutil"
	"github.com/prysmaticlabs/prysm/shared/traceutil"
	"go.opencensus.io/trace"
)

// ErrMessageNotMapped occurs on a Broadcast attempt when a message has not been defined in the
// GossipTypeMapping.
var ErrMessageNotMapped = errors.New("message type is not mapped to a PubSub topic")

const attestationSubnetTopicFormat = "/eth2/%x/beacon_attestation_%d"

// Broadcast a message to the p2p network.
func (s *Service) Broadcast(ctx context.Context, msg proto.Message) error {
	ctx, span := trace.StartSpan(ctx, "p2p.Broadcast")
	defer span.End()
	forkDigest, err := s.forkDigest()
	if err != nil {
		err := errors.Wrap(err, "could not retrieve fork digest")
		traceutil.AnnotateError(span, err)
		return err
	}

	topic, ok := GossipTypeMapping[reflect.TypeOf(msg)]
	if !ok {
		traceutil.AnnotateError(span, ErrMessageNotMapped)
		return ErrMessageNotMapped
	}
	return s.broadcastObject(ctx, msg, fmt.Sprintf(topic, forkDigest))
}

// BroadcastAttestation broadcasts an attestation to the p2p network.
func (s *Service) BroadcastAttestation(ctx context.Context, subnet uint64, att *eth.Attestation) error {
	ctx, span := trace.StartSpan(ctx, "p2p.BroadcastAttestation")
	defer span.End()
	forkDigest, err := s.forkDigest()
	if err != nil {
		err := errors.Wrap(err, "could not retrieve fork digest")
		traceutil.AnnotateError(span, err)
		return err
	}
	return s.broadcastObject(ctx, att, attestationToTopic(subnet, forkDigest))
}

// method to broadcast messages to other peers in our gossip mesh.
func (s *Service) broadcastObject(ctx context.Context, obj interface{}, topic string) error {
	_, span := trace.StartSpan(ctx, "p2p.broadcastObject")
	defer span.End()

	span.AddAttributes(trace.StringAttribute("topic", topic))

	buf := new(bytes.Buffer)
	if _, err := s.Encoding().EncodeGossip(buf, obj); err != nil {
		err := errors.Wrap(err, "could not encode message")
		traceutil.AnnotateError(span, err)
		return err
	}

	if span.IsRecordingEvents() {
		id := hashutil.FastSum64(buf.Bytes())
		messageLen := int64(buf.Len())
		span.AddMessageSendEvent(int64(id), messageLen /*uncompressed*/, messageLen /*compressed*/)
	}

	if err := s.pubsub.Publish(topic+s.Encoding().ProtocolSuffix(), buf.Bytes()); err != nil {
		err := errors.Wrap(err, "could not publish message")
		traceutil.AnnotateError(span, err)
		return err
	}
	return nil
}

func attestationToTopic(subnet uint64, forkDigest [4]byte) string {
	return fmt.Sprintf(attestationSubnetTopicFormat, forkDigest, subnet)
}