package blockchain

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"

	"github.com/pkg/errors"
	"github.com/prysmaticlabs/go-ssz"
	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
	ethpb "github.com/prysmaticlabs/prysm/proto/eth/v1alpha1"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"github.com/sirupsen/logrus"
	"go.opencensus.io/trace"
)

// AttestationReceiver interface defines the methods of chain service receive and processing new attestations.
type AttestationReceiver interface {
	ReceiveAttestation(ctx context.Context, att *ethpb.Attestation) error
	ReceiveAttestationNoPubsub(ctx context.Context, att *ethpb.Attestation) error
}

// ReceiveAttestation is a function that defines the operations that are preformed on
// attestation that is received from regular sync. The operations consist of:
//  1. Gossip attestation to other peers
//  2. Validate attestation, update validator's latest vote
//  3. Apply fork choice to the processed attestation
//  4. Save latest head info
func (s *Service) ReceiveAttestation(ctx context.Context, att *ethpb.Attestation) error {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.blockchain.ReceiveAttestation")
	defer span.End()

	// Broadcast the new attestation to the network.
	if err := s.p2p.Broadcast(ctx, att); err != nil {
		return errors.Wrap(err, "could not broadcast attestation")
	}

	attDataRoot, err := ssz.HashTreeRoot(att.Data)
	if err != nil {
		log.WithError(err).Error("Failed to hash attestation")
	}

	log.WithFields(logrus.Fields{
		"attRoot":   fmt.Sprintf("%#x", attDataRoot),
		"blockRoot": fmt.Sprintf("%#x", att.Data.BeaconBlockRoot),
	}).Debug("Broadcasting attestation")

	if err := s.ReceiveAttestationNoPubsub(ctx, att); err != nil {
		return err
	}

	processedAtt.Inc()
	return nil
}

// ReceiveAttestationNoPubsub is a function that defines the operations that are preformed on
// attestation that is received from regular sync. The operations consist of:
//  1. Validate attestation, update validator's latest vote
//  2. Apply fork choice to the processed attestation
//  3. Save latest head info
func (s *Service) ReceiveAttestationNoPubsub(ctx context.Context, att *ethpb.Attestation) error {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.blockchain.ReceiveAttestationNoPubsub")
	defer span.End()

	// Update forkchoice store for the new attestation
	attSlot, err := s.forkChoiceStore.OnAttestation(ctx, att)
	if err != nil {
		return errors.Wrap(err, "could not process attestation from fork choice service")
	}

	// Run fork choice for head block after updating fork choice store.
	headRoot, err := s.forkChoiceStore.Head(ctx)
	if err != nil {
		return errors.Wrap(err, "could not get head from fork choice service")
	}
	// Only save head if it's different than the current head.
	if !bytes.Equal(headRoot, s.HeadRoot()) {
		headBlk, err := s.beaconDB.Block(ctx, bytesutil.ToBytes32(headRoot))
		if err != nil {
			return errors.Wrap(err, "could not compute state from block head")
		}
		if err := s.saveHead(ctx, headBlk, bytesutil.ToBytes32(headRoot)); err != nil {
			return errors.Wrap(err, "could not save head")
		}
	}

	// Skip checking for competing attestation's target roots at epoch boundary.
	if !helpers.IsEpochStart(attSlot) {
		s.headLock.RLock()
		defer s.headLock.RUnlock()
		targetRoot, err := helpers.BlockRoot(s.headState, att.Data.Target.Epoch)
		if err != nil {
			return errors.Wrapf(err, "could not get target root for epoch %d", att.Data.Target.Epoch)
		}
		isCompetingAtts(targetRoot, att.Data.Target.Root[:])
	}

	processedAttNoPubsub.Inc()
	return nil
}

// This checks if the attestation is from a competing chain, emits warning and updates metrics.
func isCompetingAtts(headTargetRoot []byte, attTargetRoot []byte) {
	if !bytes.Equal(attTargetRoot, headTargetRoot) {
		log.WithFields(logrus.Fields{
			"attTargetRoot":  hex.EncodeToString(attTargetRoot),
			"headTargetRoot": hex.EncodeToString(headTargetRoot),
		}).Warn("target heads different from new attestation")
		competingAtts.Inc()
	}
}