// Package blockchain defines the life-cycle and status of the beacon chain
// as well as the Ethereum Serenity beacon chain fork-choice rule based on
// Casper Proof of Stake finality.
package blockchain

import (
	"context"
	"fmt"
	"time"

	"github.com/prysmaticlabs/prysm/beacon-chain/attestation"
	b "github.com/prysmaticlabs/prysm/beacon-chain/core/blocks"
	"github.com/prysmaticlabs/prysm/beacon-chain/db"
	"github.com/prysmaticlabs/prysm/beacon-chain/powchain"
	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	"github.com/prysmaticlabs/prysm/shared/event"
	"github.com/prysmaticlabs/prysm/shared/hashutil"
	"github.com/sirupsen/logrus"
)

var log = logrus.WithField("prefix", "blockchain")

type operationService interface {
	IncomingProcessedBlockFeed() *event.Feed
}

// ChainService represents a service that handles the internal
// logic of managing the full PoS beacon chain.
type ChainService struct {
	ctx                  context.Context
	cancel               context.CancelFunc
	beaconDB             *db.BeaconDB
	web3Service          *powchain.Web3Service
	attsService          *attestation.Service
	opsPoolService       operationService
	chainStartChan       chan time.Time
	canonicalBlockChan   chan *pb.BeaconBlock
	canonicalBlockFeed   *event.Feed
	genesisTime          time.Time
	enablePOWChain       bool
	finalizedEpoch       uint64
	stateInitializedFeed *event.Feed
}

// Config options for the service.
type Config struct {
	BeaconBlockBuf int
	Web3Service    *powchain.Web3Service
	AttsService    *attestation.Service
	BeaconDB       *db.BeaconDB
	OpsPoolService operationService
	DevMode        bool
	EnablePOWChain bool
}

// attestationTarget consists of validator index and block, it's
// used to represent which validator index has voted which block.
type attestationTarget struct {
	validatorIndex uint64
	block          *pb.BeaconBlock
}

// NewChainService instantiates a new service instance that will
// be registered into a running beacon node.
func NewChainService(ctx context.Context, cfg *Config) (*ChainService, error) {
	ctx, cancel := context.WithCancel(ctx)
	return &ChainService{
		ctx:                  ctx,
		cancel:               cancel,
		beaconDB:             cfg.BeaconDB,
		web3Service:          cfg.Web3Service,
		opsPoolService:       cfg.OpsPoolService,
		attsService:          cfg.AttsService,
		canonicalBlockFeed:   new(event.Feed),
		canonicalBlockChan:   make(chan *pb.BeaconBlock, cfg.BeaconBlockBuf),
		chainStartChan:       make(chan time.Time),
		stateInitializedFeed: new(event.Feed),
		enablePOWChain:       cfg.EnablePOWChain,
	}, nil
}

// Start a blockchain service's main event loop.
func (c *ChainService) Start() {
	beaconState, err := c.beaconDB.State(c.ctx)
	if err != nil {
		log.Fatalf("Could not fetch beacon state: %v", err)
	}
	// If the chain has already been initialized, simply start the block processing routine.
	if beaconState != nil {
		log.Info("Beacon chain data already exists, starting service")
		c.genesisTime = time.Unix(int64(beaconState.GenesisTime), 0)
		c.finalizedEpoch = beaconState.FinalizedEpoch
	} else {
		log.Info("Waiting for ChainStart log from the Validator Deposit Contract to start the beacon chain...")
		if c.web3Service == nil {
			log.Fatal("Not configured web3Service for POW chain")
			return // return need for TestStartUninitializedChainWithoutConfigPOWChain.
		}
		subChainStart := c.web3Service.ChainStartFeed().Subscribe(c.chainStartChan)
		go func() {
			genesisTime := <-c.chainStartChan
			c.processChainStartTime(genesisTime, subChainStart)
			return
		}()
	}
}

// processChainStartTime initializes a series of deposits from the ChainStart deposits in the eth1
// deposit contract, initializes the beacon chain's state, and kicks off the beacon chain.
func (c *ChainService) processChainStartTime(genesisTime time.Time, chainStartSub event.Subscription) {
	initialDepositsData := c.web3Service.ChainStartDeposits()
	initialDeposits := make([]*pb.Deposit, len(initialDepositsData))
	for i := range initialDepositsData {
		initialDeposits[i] = &pb.Deposit{DepositData: initialDepositsData[i]}
	}

	depositRoot := c.web3Service.DepositRoot()
	latestBlockHash := c.web3Service.LatestBlockHash()
	eth1Data := &pb.Eth1Data{
		DepositRootHash32: depositRoot[:],
		BlockHash32:       latestBlockHash[:],
	}
	beaconState, err := c.initializeBeaconChain(genesisTime, initialDeposits, eth1Data)
	if err != nil {
		log.Fatalf("Could not initialize beacon chain: %v", err)
	}
	c.finalizedEpoch = beaconState.FinalizedEpoch
	c.stateInitializedFeed.Send(genesisTime)
	chainStartSub.Unsubscribe()
}

// initializes the state and genesis block of the beacon chain to persistent storage
// based on a genesis timestamp value obtained from the ChainStart event emitted
// by the ETH1.0 Deposit Contract and the POWChain service of the node.
func (c *ChainService) initializeBeaconChain(genesisTime time.Time, deposits []*pb.Deposit,
	eth1data *pb.Eth1Data) (*pb.BeaconState, error) {
	log.Info("ChainStart time reached, starting the beacon chain!")
	c.genesisTime = genesisTime
	unixTime := uint64(genesisTime.Unix())
	if err := c.beaconDB.InitializeState(unixTime, deposits, eth1data); err != nil {
		return nil, fmt.Errorf("could not initialize beacon state to disk: %v", err)
	}
	beaconState, err := c.beaconDB.State(c.ctx)
	if err != nil {
		return nil, fmt.Errorf("could not attempt fetch beacon state: %v", err)
	}
	stateRoot, err := hashutil.HashProto(beaconState)
	if err != nil {
		return nil, fmt.Errorf("could not hash beacon state: %v", err)
	}
	genBlock := b.NewGenesisBlock(stateRoot[:])
	if err := c.beaconDB.SaveBlock(genBlock); err != nil {
		return nil, fmt.Errorf("could not save genesis block to disk: %v", err)
	}
	if err := c.beaconDB.UpdateChainHead(genBlock, beaconState); err != nil {
		return nil, fmt.Errorf("could not set chain head, %v", err)
	}
	return beaconState, nil
}

// Stop the blockchain service's main event loop and associated goroutines.
func (c *ChainService) Stop() error {
	defer c.cancel()

	log.Info("Stopping service")
	return nil
}

// Status always returns nil.
// TODO(1202): Add service health checks.
func (c *ChainService) Status() error {
	return nil
}

// CanonicalBlockFeed returns a channel that is written to
// whenever a new block is determined to be canonical in the chain.
func (c *ChainService) CanonicalBlockFeed() *event.Feed {
	return c.canonicalBlockFeed
}

// StateInitializedFeed returns a feed that is written to
// when the beacon state is first initialized.
func (c *ChainService) StateInitializedFeed() *event.Feed {
	return c.stateInitializedFeed
}

// ChainHeadRoot returns the hash root of the last beacon block processed by the
// block chain service.
func (c *ChainService) ChainHeadRoot() ([32]byte, error) {
	head, err := c.beaconDB.ChainHead()
	if err != nil {
		return [32]byte{}, fmt.Errorf("could not retrieve chain head: %v", err)
	}

	root, err := hashutil.HashBeaconBlock(head)
	if err != nil {
		return [32]byte{}, fmt.Errorf("could not tree hash parent block: %v", err)
	}
	return root, nil
}

// doesPoWBlockExist checks if the referenced PoW block exists.
func (c *ChainService) doesPoWBlockExist(hash [32]byte) bool {
	powBlock, err := c.web3Service.Client().BlockByHash(c.ctx, hash)
	if err != nil {
		log.Debugf("fetching PoW block corresponding to mainchain reference failed: %v", err)
		return false
	}

	return powBlock != nil
}