package rpc

import (
	"context"
	"fmt"
	"time"

	ptypes "github.com/gogo/protobuf/types"
	"github.com/pkg/errors"
	"github.com/prysmaticlabs/prysm/beacon-chain/blockchain"
	"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"
	ethpb "github.com/prysmaticlabs/prysm/proto/eth/v1alpha1"
	"github.com/prysmaticlabs/prysm/shared/event"
	"github.com/prysmaticlabs/prysm/shared/trieutil"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

type stateFeedListener interface {
	StateInitializedFeed() *event.Feed
}

// BeaconServer defines a server implementation of the gRPC Beacon service,
// providing RPC endpoints for obtaining the canonical beacon chain head,
// fetching latest observed attestations, and more.
type BeaconServer struct {
	beaconDB            db.Database
	ctx                 context.Context
	powChainService     powChainService
	chainService        stateFeedListener
	operationService    operationService
	incomingAttestation chan *ethpb.Attestation
	canonicalStateChan  chan *pbp2p.BeaconState
	chainStartChan      chan time.Time
}

// WaitForChainStart queries the logs of the Deposit Contract in order to verify the beacon chain
// has started its runtime and validators begin their responsibilities. If it has not, it then
// subscribes to an event stream triggered by the powchain service whenever the ChainStart log does
// occur in the Deposit Contract on ETH 1.0.
func (bs *BeaconServer) WaitForChainStart(req *ptypes.Empty, stream pb.BeaconService_WaitForChainStartServer) error {
	ok := bs.powChainService.HasChainStarted()

	if ok {
		genesisTime, _ := bs.powChainService.ETH2GenesisTime()

		res := &pb.ChainStartResponse{
			Started:     true,
			GenesisTime: genesisTime,
		}
		return stream.Send(res)
	}

	sub := bs.chainService.StateInitializedFeed().Subscribe(bs.chainStartChan)
	defer sub.Unsubscribe()
	for {
		select {
		case chainStartTime := <-bs.chainStartChan:
			log.Info("Sending ChainStart log and genesis time to connected validator clients")
			res := &pb.ChainStartResponse{
				Started:     true,
				GenesisTime: uint64(chainStartTime.Unix()),
			}
			return stream.Send(res)
		case <-sub.Err():
			return errors.New("subscriber closed, exiting goroutine")
		case <-bs.ctx.Done():
			return errors.New("rpc context closed, exiting goroutine")
		}
	}
}

// CanonicalHead of the current beacon chain. This method is requested on-demand
// by a validator when it is their time to propose or attest.
func (bs *BeaconServer) CanonicalHead(ctx context.Context, req *ptypes.Empty) (*ethpb.BeaconBlock, error) {
	var headBlock *ethpb.BeaconBlock
	var err error
	if d, isLegacyDB := bs.beaconDB.(*db.BeaconDB); isLegacyDB {
		headBlock, err = d.ChainHead()
		if err != nil {
			return nil, errors.Wrap(err, "could not get canonical head block")
		}
	} else {
		headBlock = bs.chainService.(blockchain.HeadRetriever).HeadBlock()
	}
	return headBlock, nil
}

// BlockTree returns the current tree of saved blocks and their votes starting from the justified state.
func (bs *BeaconServer) BlockTree(ctx context.Context, _ *ptypes.Empty) (*pb.BlockTreeResponse, error) {
	// TODO(3219): Add after new fork choice service.
	return nil, status.Error(codes.Unimplemented, "not implemented")
}

// BlockTreeBySlots returns the current tree of saved blocks and their
// votes starting from the justified state.
func (bs *BeaconServer) BlockTreeBySlots(ctx context.Context, req *pb.TreeBlockSlotRequest) (*pb.BlockTreeResponse, error) {
	// TODO(3219): Add after new fork choice service.
	return nil, status.Error(codes.Unimplemented, "not implemented")
}

func constructMerkleProof(trie *trieutil.MerkleTrie, index int, deposit *ethpb.Deposit) (*ethpb.Deposit, error) {
	proof, err := trie.MerkleProof(index)
	if err != nil {
		return nil, fmt.Errorf(
			"could not generate merkle proof for deposit at index %d: %v",
			index,
			err,
		)
	}
	// For every deposit, we construct a Merkle proof using the powchain service's
	// in-memory deposits trie, which is updated only once the state's LatestETH1Data
	// property changes during a state transition after a voting period.
	deposit.Proof = proof
	return deposit, nil
}