package beacon

import (
	"bytes"
	"context"
	"strconv"

	types "github.com/prysmaticlabs/eth2-types"
	"github.com/prysmaticlabs/prysm/beacon-chain/rpc/eth/helpers"
	"github.com/prysmaticlabs/prysm/beacon-chain/rpc/statefetcher"
	"github.com/prysmaticlabs/prysm/beacon-chain/state"
	"github.com/prysmaticlabs/prysm/config/params"
	ethpb "github.com/prysmaticlabs/prysm/proto/eth/v1"
	eth "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
	"github.com/prysmaticlabs/prysm/time/slots"
	"go.opencensus.io/trace"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
	"google.golang.org/protobuf/types/known/emptypb"
	"google.golang.org/protobuf/types/known/timestamppb"
)

type stateRequest struct {
	epoch   *types.Epoch
	stateId []byte
}

// GetGenesis retrieves details of the chain's genesis which can be used to identify chain.
func (bs *Server) GetGenesis(ctx context.Context, _ *emptypb.Empty) (*ethpb.GenesisResponse, error) {
	_, span := trace.StartSpan(ctx, "beacon.GetGenesis")
	defer span.End()

	genesisTime := bs.GenesisTimeFetcher.GenesisTime()
	if genesisTime.IsZero() {
		return nil, status.Errorf(codes.NotFound, "Chain genesis info is not yet known")
	}
	validatorRoot := bs.ChainInfoFetcher.GenesisValidatorRoot()
	if bytes.Equal(validatorRoot[:], params.BeaconConfig().ZeroHash[:]) {
		return nil, status.Errorf(codes.NotFound, "Chain genesis info is not yet known")
	}
	forkVersion := params.BeaconConfig().GenesisForkVersion

	return &ethpb.GenesisResponse{
		Data: &ethpb.GenesisResponse_Genesis{
			GenesisTime: &timestamppb.Timestamp{
				Seconds: genesisTime.Unix(),
				Nanos:   0,
			},
			GenesisValidatorsRoot: validatorRoot[:],
			GenesisForkVersion:    forkVersion,
		},
	}, nil
}

// GetStateRoot calculates HashTreeRoot for state with given 'stateId'. If stateId is root, same value will be returned.
func (bs *Server) GetStateRoot(ctx context.Context, req *ethpb.StateRequest) (*ethpb.StateRootResponse, error) {
	ctx, span := trace.StartSpan(ctx, "beacon.GetStateRoot")
	defer span.End()

	var (
		root []byte
		err  error
	)

	root, err = bs.StateFetcher.StateRoot(ctx, req.StateId)
	if err != nil {
		if rootNotFoundErr, ok := err.(*statefetcher.StateRootNotFoundError); ok {
			return nil, status.Errorf(codes.NotFound, "State root not found: %v", rootNotFoundErr)
		} else if parseErr, ok := err.(*statefetcher.StateIdParseError); ok {
			return nil, status.Errorf(codes.InvalidArgument, "Invalid state ID: %v", parseErr)
		}
		return nil, status.Errorf(codes.Internal, "Could not get state root: %v", err)
	}

	return &ethpb.StateRootResponse{
		Data: &ethpb.StateRootResponse_StateRoot{
			Root: root,
		},
	}, nil
}

// GetStateFork returns Fork object for state with given 'stateId'.
func (bs *Server) GetStateFork(ctx context.Context, req *ethpb.StateRequest) (*ethpb.StateForkResponse, error) {
	ctx, span := trace.StartSpan(ctx, "beacon.GetStateFork")
	defer span.End()

	var (
		st  state.BeaconState
		err error
	)

	st, err = bs.StateFetcher.State(ctx, req.StateId)
	if err != nil {
		return nil, helpers.PrepareStateFetchGRPCError(err)
	}

	fork := st.Fork()
	return &ethpb.StateForkResponse{
		Data: &ethpb.Fork{
			PreviousVersion: fork.PreviousVersion,
			CurrentVersion:  fork.CurrentVersion,
			Epoch:           fork.Epoch,
		},
	}, nil
}

// GetFinalityCheckpoints returns finality checkpoints for state with given 'stateId'. In case finality is
// not yet achieved, checkpoint should return epoch 0 and ZERO_HASH as root.
func (bs *Server) GetFinalityCheckpoints(ctx context.Context, req *ethpb.StateRequest) (*ethpb.StateFinalityCheckpointResponse, error) {
	ctx, span := trace.StartSpan(ctx, "beacon.GetFinalityCheckpoints")
	defer span.End()

	var (
		st  state.BeaconState
		err error
	)

	st, err = bs.StateFetcher.State(ctx, req.StateId)
	if err != nil {
		if stateNotFoundErr, ok := err.(*statefetcher.StateNotFoundError); ok {
			return nil, status.Errorf(codes.NotFound, "State not found: %v", stateNotFoundErr)
		} else if parseErr, ok := err.(*statefetcher.StateIdParseError); ok {
			return nil, status.Errorf(codes.InvalidArgument, "Invalid state ID: %v", parseErr)
		}
		return nil, status.Errorf(codes.Internal, "Could not get state: %v", err)
	}

	return &ethpb.StateFinalityCheckpointResponse{
		Data: &ethpb.StateFinalityCheckpointResponse_StateFinalityCheckpoint{
			PreviousJustified: checkpoint(st.PreviousJustifiedCheckpoint()),
			CurrentJustified:  checkpoint(st.CurrentJustifiedCheckpoint()),
			Finalized:         checkpoint(st.FinalizedCheckpoint()),
		},
	}, nil
}

func (bs *Server) stateFromRequest(ctx context.Context, req *stateRequest) (state.BeaconState, error) {
	if req.epoch != nil {
		slot, err := slots.EpochStart(*req.epoch)
		if err != nil {
			return nil, status.Errorf(
				codes.Internal,
				"Could not calculate start slot for epoch %d: %v",
				*req.epoch,
				err,
			)
		}
		st, err := bs.StateFetcher.State(ctx, []byte(strconv.FormatUint(uint64(slot), 10)))
		if err != nil {
			return nil, helpers.PrepareStateFetchGRPCError(err)
		}
		return st, nil
	}
	var err error
	st, err := bs.StateFetcher.State(ctx, req.stateId)
	if err != nil {
		return nil, helpers.PrepareStateFetchGRPCError(err)
	}
	return st, nil
}

func checkpoint(sourceCheckpoint *eth.Checkpoint) *ethpb.Checkpoint {
	if sourceCheckpoint != nil {
		return &ethpb.Checkpoint{
			Epoch: sourceCheckpoint.Epoch,
			Root:  sourceCheckpoint.Root,
		}
	}
	return &ethpb.Checkpoint{
		Epoch: 0,
		Root:  params.BeaconConfig().ZeroHash[:],
	}
}