package rpc

import (
	"context"
	"errors"
	"fmt"
	"time"

	"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/hashutil"
	"github.com/prysmaticlabs/prysm/shared/params"
)

// ValidatorServer defines a server implementation of the gRPC Validator service,
// providing RPC endpoints for obtaining validator assignments per epoch, the slots
// and shards in which particular validators need to perform their responsibilities,
// and more.
type ValidatorServer struct {
	ctx                context.Context
	beaconDB           *db.BeaconDB
	chainService       chainService
	canonicalStateChan chan *pbp2p.BeaconState
}

// WaitForActivation checks if a validator public key exists in the active validator registry of the current
// beacon state, if not, then it creates a stream which listens for canonical states which contain
// the validator with the public key as an active validator record.
func (vs *ValidatorServer) WaitForActivation(req *pb.ValidatorActivationRequest, stream pb.ValidatorService_WaitForActivationServer) error {
	if vs.beaconDB.HasValidator(req.Pubkey) {
		beaconState, err := vs.beaconDB.HeadState(vs.ctx)
		if err != nil {
			return fmt.Errorf("could not retrieve beacon state: %v", err)
		}
		activeVal, err := vs.retrieveActiveValidator(beaconState, req.Pubkey)
		if err != nil {
			return fmt.Errorf("could not retrieve active validator from state: %v", err)
		}
		res := &pb.ValidatorActivationResponse{
			Validator: activeVal,
		}
		return stream.Send(res)
	}
	for {
		select {
		case <-time.After(3 * time.Second):
			if !vs.beaconDB.HasValidator(req.Pubkey) {
				continue
			}
			beaconState, err := vs.beaconDB.HeadState(vs.ctx)
			if err != nil {
				return fmt.Errorf("could not retrieve beacon state: %v", err)
			}
			activeVal, err := vs.retrieveActiveValidator(beaconState, req.Pubkey)
			if err != nil {
				return fmt.Errorf("could not retrieve active validator from state: %v", err)
			}
			res := &pb.ValidatorActivationResponse{
				Validator: activeVal,
			}
			return stream.Send(res)
		case <-vs.ctx.Done():
			return errors.New("rpc context closed, exiting goroutine")
		}
	}
}

// ValidatorIndex is called by a validator to get its index location that corresponds
// to the attestation bit fields.
func (vs *ValidatorServer) ValidatorIndex(ctx context.Context, req *pb.ValidatorIndexRequest) (*pb.ValidatorIndexResponse, error) {
	index, err := vs.beaconDB.ValidatorIndex(req.PublicKey)
	if err != nil {
		return nil, fmt.Errorf("could not get validator index: %v", err)
	}

	return &pb.ValidatorIndexResponse{Index: uint64(index)}, nil
}

// ValidatorPerformance reports the validator's latest balance along with other important metrics on
// rewards and penalties throughout its lifecycle in the beacon chain.
func (vs *ValidatorServer) ValidatorPerformance(
	ctx context.Context, req *pb.ValidatorPerformanceRequest,
) (*pb.ValidatorPerformanceResponse, error) {
	index, err := vs.beaconDB.ValidatorIndex(req.PublicKey)
	if err != nil {
		return nil, fmt.Errorf("could not get validator index: %v", err)
	}
	beaconState, err := vs.beaconDB.HeadState(ctx)
	if err != nil {
		return nil, fmt.Errorf("could not retrieve beacon state: %v", err)
	}
	totalBalance := float32(0)
	for _, val := range beaconState.ValidatorBalances {
		totalBalance += float32(val)
	}
	avgBalance := totalBalance / float32(len(beaconState.ValidatorBalances))
	balance := beaconState.ValidatorBalances[index]
	activeIndices := helpers.ActiveValidatorIndices(beaconState.ValidatorRegistry, helpers.SlotToEpoch(req.Slot))
	return &pb.ValidatorPerformanceResponse{
		Balance:                 balance,
		AverageValidatorBalance: avgBalance,
		TotalValidators:         uint64(len(beaconState.ValidatorRegistry)),
		TotalActiveValidators:   uint64(len(activeIndices)),
	}, nil
}

// CommitteeAssignment returns the committee assignment response from a given validator public key.
// The committee assignment response contains the following fields for the current and previous epoch:
//	1.) The list of validators in the committee.
//	2.) The shard to which the committee is assigned.
//	3.) The slot at which the committee is assigned.
//	4.) The bool signalling if the validator is expected to propose a block at the assigned slot.
func (vs *ValidatorServer) CommitteeAssignment(
	ctx context.Context,
	req *pb.CommitteeAssignmentsRequest) (*pb.CommitteeAssignmentResponse, error) {
	beaconState, err := vs.beaconDB.HeadState(ctx)
	if err != nil {
		return nil, fmt.Errorf("could not fetch beacon state: %v", err)
	}
	var assignments []*pb.CommitteeAssignmentResponse_CommitteeAssignment
	for _, pk := range req.PublicKeys {
		a, err := vs.assignment(ctx, pk, beaconState, req.EpochStart)
		if err != nil {
			return nil, err
		}
		assignments = append(assignments, a)
	}
	return &pb.CommitteeAssignmentResponse{
		Assignment: assignments,
	}, nil
}

func (vs *ValidatorServer) assignment(
	ctx context.Context,
	pubkey []byte,
	beaconState *pbp2p.BeaconState,
	epochStart uint64,
) (*pb.CommitteeAssignmentResponse_CommitteeAssignment, error) {

	if len(pubkey) != params.BeaconConfig().BLSPubkeyLength {
		return nil, fmt.Errorf(
			"expected public key to have length %d, received %d",
			params.BeaconConfig().BLSPubkeyLength,
			len(pubkey),
		)
	}

	idx, err := vs.beaconDB.ValidatorIndex(pubkey)
	if err != nil {
		return nil, fmt.Errorf("could not get active validator index: %v", err)
	}
	chainHead, err := vs.beaconDB.ChainHead()
	if err != nil {
		return nil, fmt.Errorf("could not get chain head: %v", err)
	}
	headRoot, err := hashutil.HashBeaconBlock(chainHead)
	if err != nil {
		return nil, fmt.Errorf("could not hash block: %v", err)
	}
	for beaconState.Slot < epochStart {
		beaconState, err = state.ExecuteStateTransition(
			ctx, beaconState, nil /* block */, headRoot, vs.beaconDB, state.DefaultConfig(),
		)
		if err != nil {
			return nil, fmt.Errorf("could not execute head transition: %v", err)
		}
	}

	committee, shard, slot, isProposer, err :=
		helpers.CommitteeAssignment(beaconState, epochStart, uint64(idx), false)
	if err != nil {
		return nil, err
	}
	status, err := vs.validatorStatus(pubkey, beaconState)
	if err != nil {
		return nil, err
	}
	return &pb.CommitteeAssignmentResponse_CommitteeAssignment{
		Committee:  committee,
		Shard:      shard,
		Slot:       slot,
		IsProposer: isProposer,
		PublicKey:  pubkey,
		Status:     status,
	}, nil
}

// ValidatorStatus returns the validator status of the current epoch.
// The status response can be one of the following:
//	PENDING_ACTIVE - validator is waiting to get activated.
//	ACTIVE - validator is active.
//	INITIATED_EXIT - validator has initiated an an exit request.
//	WITHDRAWABLE - validator's deposit can be withdrawn after lock up period.
//	EXITED - validator has exited, means the deposit has been withdrawn.
//	EXITED_SLASHED - validator was forcefully exited due to slashing.
func (vs *ValidatorServer) ValidatorStatus(
	ctx context.Context,
	req *pb.ValidatorIndexRequest) (*pb.ValidatorStatusResponse, error) {

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

	status, err := vs.validatorStatus(req.PublicKey, beaconState)
	if err != nil {
		return nil, err
	}

	return &pb.ValidatorStatusResponse{
		Status: status,
	}, nil
}

func (vs *ValidatorServer) validatorStatus(pubkey []byte, beaconState *pbp2p.BeaconState) (pb.ValidatorStatus, error) {
	idx, err := vs.beaconDB.ValidatorIndex(pubkey)
	if err != nil {
		return pb.ValidatorStatus_UNKNOWN_STATUS, fmt.Errorf("could not get active validator index: %v", err)
	}

	var status pb.ValidatorStatus
	v := beaconState.ValidatorRegistry[idx]
	farFutureEpoch := params.BeaconConfig().FarFutureEpoch
	epoch := helpers.CurrentEpoch(beaconState)

	if v.ActivationEpoch == farFutureEpoch {
		status = pb.ValidatorStatus_PENDING_ACTIVE
	} else if v.ActivationEpoch <= epoch && epoch < v.ExitEpoch {
		status = pb.ValidatorStatus_ACTIVE
	} else if v.StatusFlags == pbp2p.Validator_INITIATED_EXIT {
		status = pb.ValidatorStatus_INITIATED_EXIT
	} else if v.StatusFlags == pbp2p.Validator_WITHDRAWABLE {
		status = pb.ValidatorStatus_WITHDRAWABLE
	} else if epoch >= v.ExitEpoch && epoch >= v.SlashedEpoch {
		status = pb.ValidatorStatus_EXITED_SLASHED
	} else if epoch >= v.ExitEpoch {
		status = pb.ValidatorStatus_EXITED
	} else {
		status = pb.ValidatorStatus_UNKNOWN_STATUS
	}

	return status, nil
}

func (vs *ValidatorServer) retrieveActiveValidator(beaconState *pbp2p.BeaconState, pubkey []byte) (*pbp2p.Validator, error) {
	validatorIdx, err := vs.beaconDB.ValidatorIndex(pubkey)
	if err != nil {
		return nil, fmt.Errorf("could not retrieve validator index: %v", err)
	}
	return beaconState.ValidatorRegistry[validatorIdx], nil
}