package rpc

import (
	"context"
	"fmt"

	"github.com/prysmaticlabs/prysm/beacon-chain/core/blocks"
	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
	"github.com/prysmaticlabs/prysm/beacon-chain/core/state"
	"github.com/prysmaticlabs/prysm/beacon-chain/db"
	pbp2p "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	pb "github.com/prysmaticlabs/prysm/proto/beacon/rpc/v1"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"github.com/prysmaticlabs/prysm/shared/featureconfig"
	"github.com/prysmaticlabs/prysm/shared/hashutil"
	"github.com/prysmaticlabs/prysm/shared/params"
	"github.com/sirupsen/logrus"
)

// ProposerServer defines a server implementation of the gRPC Proposer service,
// providing RPC endpoints for computing state transitions and state roots, proposing
// beacon blocks to a beacon node, and more.
type ProposerServer struct {
	beaconDB           *db.BeaconDB
	chainService       chainService
	powChainService    powChainService
	operationService   operationService
	canonicalStateChan chan *pbp2p.BeaconState
}

// ProposerIndex sends a response to the client which returns the proposer index for a given slot. Validators
// are shuffled and assigned slots to attest/propose to. This method will look for the validator that is assigned
// to propose a beacon block at the given slot.
func (ps *ProposerServer) ProposerIndex(ctx context.Context, req *pb.ProposerIndexRequest) (*pb.ProposerIndexResponse, error) {
	beaconState, err := ps.beaconDB.HeadState(ctx)
	if err != nil {
		return nil, fmt.Errorf("could not get beacon state: %v", err)
	}

	head, err := ps.beaconDB.ChainHead()
	if err != nil {
		return nil, fmt.Errorf("could not get chain head: %v", err)
	}
	headRoot, err := hashutil.HashBeaconBlock(head)
	if err != nil {
		return nil, fmt.Errorf("could not hash block: %v", err)
	}
	for beaconState.Slot < req.SlotNumber {
		if ctx.Err() != nil {
			return nil, ctx.Err()
		}

		beaconState, err = state.ExecuteStateTransition(
			ctx, beaconState, nil /* block */, headRoot, state.DefaultConfig(),
		)
		if err != nil {
			return nil, fmt.Errorf("could not execute head transition: %v", err)
		}
	}

	proposerIndex, err := helpers.BeaconProposerIndex(
		beaconState,
		req.SlotNumber,
	)
	if err != nil {
		return nil, fmt.Errorf("could not get index of previous proposer: %v", err)
	}

	return &pb.ProposerIndexResponse{
		Index: proposerIndex,
	}, nil
}

// ProposeBlock is called by a proposer during its assigned slot to create a block in an attempt
// to get it processed by the beacon node as the canonical head.
func (ps *ProposerServer) ProposeBlock(ctx context.Context, blk *pbp2p.BeaconBlock) (*pb.ProposeResponse, error) {
	h, err := hashutil.HashBeaconBlock(blk)
	if err != nil {
		return nil, fmt.Errorf("could not tree hash block: %v", err)
	}
	log.WithField("blockRoot", fmt.Sprintf("%#x", bytesutil.Trunc(h[:]))).Debugf(
		"Block proposal received via RPC")
	beaconState, err := ps.chainService.ReceiveBlock(ctx, blk)
	if err != nil {
		return nil, fmt.Errorf("could not process beacon block: %v", err)
	}
	if err := ps.beaconDB.UpdateChainHead(ctx, blk, beaconState); err != nil {
		return nil, fmt.Errorf("failed to update chain: %v", err)
	}
	ps.chainService.UpdateCanonicalRoots(blk, h)
	log.WithFields(logrus.Fields{
		"headRoot": fmt.Sprintf("%#x", bytesutil.Trunc(h[:])),
		"headSlot": blk.Slot - params.BeaconConfig().GenesisSlot,
	}).Info("Chain head block and state updated")
	return &pb.ProposeResponse{BlockRootHash32: h[:]}, nil
}

// PendingAttestations retrieves attestations kept in the beacon node's operations pool which have
// not yet been included into the beacon chain. Proposers include these pending attestations in their
// proposed blocks when performing their responsibility. If desired, callers can choose to filter pending
// attestations which are ready for inclusion. That is, attestations that satisfy:
// attestation.slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot.
func (ps *ProposerServer) PendingAttestations(ctx context.Context, req *pb.PendingAttestationsRequest) (*pb.PendingAttestationsResponse, error) {
	beaconState, err := ps.beaconDB.HeadState(ctx)
	if err != nil {
		return nil, fmt.Errorf("could not retrieve beacon state: %v", err)
	}
	atts, err := ps.operationService.PendingAttestations(ctx)
	if err != nil {
		return nil, fmt.Errorf("could not retrieve pending attestations from operations service: %v", err)
	}
	head, err := ps.beaconDB.ChainHead()
	if err != nil {
		return nil, fmt.Errorf("failed to retrieve chain head: %v", err)
	}
	blockRoot, err := hashutil.HashBeaconBlock(head)
	if err != nil {
		return nil, fmt.Errorf("could not hash beacon block: %v", err)
	}

	for beaconState.Slot < req.ProposalBlockSlot-1 {
		if ctx.Err() != nil {
			return nil, ctx.Err()
		}

		beaconState, err = state.ExecuteStateTransition(
			ctx, beaconState, nil /* block */, blockRoot, state.DefaultConfig(),
		)
		if err != nil {
			return nil, fmt.Errorf("could not execute head transition: %v", err)
		}
	}
	beaconState.Slot++

	var attsReadyForInclusion []*pbp2p.Attestation
	for _, att := range atts {
		if att.Data.Slot+params.BeaconConfig().MinAttestationInclusionDelay <= beaconState.Slot {
			attsReadyForInclusion = append(attsReadyForInclusion, att)
		}
	}

	validAtts := make([]*pbp2p.Attestation, 0, len(attsReadyForInclusion))
	for _, att := range attsReadyForInclusion {
		if err := blocks.VerifyAttestation(beaconState, att, false); err != nil {
			if ctx.Err() != nil {
				return nil, ctx.Err()
			}

			log.WithError(err).WithFields(logrus.Fields{
				"slot":     att.Data.Slot - params.BeaconConfig().GenesisSlot,
				"headRoot": bytesutil.Trunc(att.Data.BeaconBlockRootHash32)}).Warn(
				"Deleting failed pending attestation from DB")
			if err := ps.beaconDB.DeleteAttestation(att); err != nil {
				return nil, fmt.Errorf("could not delete failed attestation: %v", err)
			}
			continue
		}
		validAtts = append(validAtts, att)
	}

	return &pb.PendingAttestationsResponse{
		PendingAttestations: validAtts,
	}, nil
}

// ComputeStateRoot computes the state root after a block has been processed through a state transition and
// returns it to the validator client.
func (ps *ProposerServer) ComputeStateRoot(ctx context.Context, req *pbp2p.BeaconBlock) (*pb.StateRootResponse, error) {
	if !featureconfig.FeatureConfig().EnableComputeStateRoot {
		log.Debug("Compute state root disabled, returning no-op result")
		return &pb.StateRootResponse{StateRoot: []byte("no-op")}, nil
	}

	beaconState, err := ps.beaconDB.HeadState(ctx)
	if err != nil {
		return nil, fmt.Errorf("could not get beacon state: %v", err)
	}

	parentHash := bytesutil.ToBytes32(req.ParentRootHash32)
	// Check for skipped slots.
	for beaconState.Slot < req.Slot-1 {
		if ctx.Err() != nil {
			return nil, ctx.Err()
		}

		beaconState, err = state.ExecuteStateTransition(
			ctx,
			beaconState,
			nil,
			parentHash,
			state.DefaultConfig(),
		)
		if err != nil {
			return nil, fmt.Errorf("could not execute state transition %v", err)
		}
	}
	beaconState, err = state.ExecuteStateTransition(
		ctx,
		beaconState,
		req,
		parentHash,
		state.DefaultConfig(),
	)
	if err != nil {
		return nil, fmt.Errorf("could not execute state transition %v", err)
	}

	beaconStateHash, err := hashutil.HashProto(beaconState)
	if err != nil {
		return nil, fmt.Errorf("could not tree hash beacon state: %v", err)
	}
	log.WithField("beaconStateHash", fmt.Sprintf("%#x", beaconStateHash)).Debugf("Computed state hash")
	return &pb.StateRootResponse{
		StateRoot: beaconStateHash[:],
	}, nil
}