// Package initialsync is run by the beacon node when the local chain is
// behind the network's longest chain. Initial sync works as follows:
// The node requests for the slot number of the most recent finalized block.
// The node then builds from the most recent finalized block by requesting for subsequent
// blocks by slot number. Once the service detects that the local chain is caught up with
// the network, the service hands over control to the regular sync service.
// Note: The behavior of initialsync will likely change as the specification changes.
// The most significant and highly probable change will be determining where to sync from.
// The beacon chain may sync from a block in the pasts X months in order to combat long-range attacks
// (see here: https://github.com/ethereum/wiki/wiki/Proof-of-Stake-FAQs#what-is-weak-subjectivity)
package initialsync

import (
	"context"
	"errors"
	"fmt"
	"math/big"
	"runtime/debug"
	"strings"
	"sync"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/gogo/protobuf/proto"
	peer "github.com/libp2p/go-libp2p-peer"
	"github.com/prysmaticlabs/prysm/beacon-chain/db"
	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"github.com/prysmaticlabs/prysm/shared/event"
	"github.com/prysmaticlabs/prysm/shared/hashutil"
	"github.com/prysmaticlabs/prysm/shared/p2p"
	"github.com/prysmaticlabs/prysm/shared/params"
	"github.com/sirupsen/logrus"
	"go.opencensus.io/trace"
)

var log = logrus.WithField("prefix", "initial-sync")
var debugError = "debug:"

// Config defines the configurable properties of InitialSync.
//
type Config struct {
	SyncPollingInterval     time.Duration
	BlockBufferSize         int
	BlockAnnounceBufferSize int
	BatchedBlockBufferSize  int
	StateBufferSize         int
	BeaconDB                *db.BeaconDB
	P2P                     p2pAPI
	SyncService             syncService
	ChainService            chainService
	PowChain                powChainService
}

// DefaultConfig provides the default configuration for a sync service.
// SyncPollingInterval determines how frequently the service checks that initial sync is complete.
// BlockBufferSize determines that buffer size of the `blockBuf` channel.
// StateBufferSize determines the buffer size of the `stateBuf` channel.
func DefaultConfig() *Config {
	return &Config{
		SyncPollingInterval:     time.Duration(params.BeaconConfig().SyncPollingInterval) * time.Second,
		BlockBufferSize:         params.BeaconConfig().DefaultBufferSize,
		BatchedBlockBufferSize:  params.BeaconConfig().DefaultBufferSize,
		BlockAnnounceBufferSize: params.BeaconConfig().DefaultBufferSize,
		StateBufferSize:         params.BeaconConfig().DefaultBufferSize,
	}
}

type p2pAPI interface {
	p2p.Broadcaster
	p2p.Sender
	Subscribe(msg proto.Message, channel chan p2p.Message) event.Subscription
}

type chainService interface {
	ReceiveBlock(ctx context.Context, block *pb.BeaconBlock) (*pb.BeaconState, error)
	ApplyForkChoiceRule(ctx context.Context, block *pb.BeaconBlock, computedState *pb.BeaconState) error
}

type powChainService interface {
	BlockExists(ctx context.Context, hash common.Hash) (bool, *big.Int, error)
}

// SyncService is the interface for the Sync service.
// InitialSync calls `Start` when initial sync completes.
type syncService interface {
	Start()
	ResumeSync()
}

// InitialSync defines the main class in this package.
// See the package comments for a general description of the service's functions.
type InitialSync struct {
	ctx                            context.Context
	cancel                         context.CancelFunc
	p2p                            p2pAPI
	syncService                    syncService
	chainService                   chainService
	db                             *db.BeaconDB
	powchain                       powChainService
	blockAnnounceBuf               chan p2p.Message
	batchedBlockBuf                chan p2p.Message
	blockBuf                       chan p2p.Message
	stateBuf                       chan p2p.Message
	currentSlot                    uint64
	highestObservedSlot            uint64
	beaconStateSlot                uint64
	syncPollingInterval            time.Duration
	inMemoryBlocks                 map[uint64]*pb.BeaconBlock
	syncedFeed                     *event.Feed
	reqState                       bool
	stateRootOfHighestObservedSlot [32]byte
	mutex                          *sync.Mutex
}

// NewInitialSyncService constructs a new InitialSyncService.
// This method is normally called by the main node.
func NewInitialSyncService(ctx context.Context,
	cfg *Config,
) *InitialSync {
	ctx, cancel := context.WithCancel(ctx)

	blockBuf := make(chan p2p.Message, cfg.BlockBufferSize)
	stateBuf := make(chan p2p.Message, cfg.StateBufferSize)
	blockAnnounceBuf := make(chan p2p.Message, cfg.BlockAnnounceBufferSize)
	batchedBlockBuf := make(chan p2p.Message, cfg.BatchedBlockBufferSize)

	return &InitialSync{
		ctx:                            ctx,
		cancel:                         cancel,
		p2p:                            cfg.P2P,
		syncService:                    cfg.SyncService,
		chainService:                   cfg.ChainService,
		db:                             cfg.BeaconDB,
		powchain:                       cfg.PowChain,
		currentSlot:                    params.BeaconConfig().GenesisSlot,
		highestObservedSlot:            params.BeaconConfig().GenesisSlot,
		beaconStateSlot:                params.BeaconConfig().GenesisSlot,
		blockBuf:                       blockBuf,
		stateBuf:                       stateBuf,
		batchedBlockBuf:                batchedBlockBuf,
		blockAnnounceBuf:               blockAnnounceBuf,
		syncPollingInterval:            cfg.SyncPollingInterval,
		inMemoryBlocks:                 map[uint64]*pb.BeaconBlock{},
		syncedFeed:                     new(event.Feed),
		reqState:                       false,
		stateRootOfHighestObservedSlot: [32]byte{},
		mutex:                          new(sync.Mutex),
	}
}

// Start begins the goroutine.
func (s *InitialSync) Start() {
	cHead, err := s.db.ChainHead()
	if err != nil {
		log.Errorf("Unable to get chain head %v", err)
	}
	s.currentSlot = cHead.Slot

	var reqState bool
	// setting genesis bool
	if cHead.Slot == params.BeaconConfig().GenesisSlot || s.isSlotDiffLarge() {
		reqState = true
	}
	s.reqState = reqState

	go func() {
		ticker := time.NewTicker(s.syncPollingInterval)
		s.run(ticker.C)
		ticker.Stop()
	}()
	go s.checkInMemoryBlocks()
}

// Stop kills the initial sync goroutine.
func (s *InitialSync) Stop() error {
	log.Info("Stopping service")
	s.cancel()
	return nil
}

// InitializeObservedSlot sets the highest observed slot.
func (s *InitialSync) InitializeObservedSlot(slot uint64) {
	s.highestObservedSlot = slot
}

// InitializeStateRoot sets the state root of the highest observed slot.
func (s *InitialSync) InitializeStateRoot(root [32]byte) {
	s.stateRootOfHighestObservedSlot = root
}

// SyncedFeed returns a feed which fires a message once the node is synced
func (s *InitialSync) SyncedFeed() *event.Feed {
	return s.syncedFeed
}

// run is the main goroutine for the initial sync service.
// delayChan is explicitly passed into this function to facilitate tests that don't require a timeout.
// It is assumed that the goroutine `run` is only called once per instance.
func (s *InitialSync) run(delayChan <-chan time.Time) {

	blockSub := s.p2p.Subscribe(&pb.BeaconBlockResponse{}, s.blockBuf)
	batchedBlocksub := s.p2p.Subscribe(&pb.BatchedBeaconBlockResponse{}, s.batchedBlockBuf)
	blockAnnounceSub := s.p2p.Subscribe(&pb.BeaconBlockAnnounce{}, s.blockAnnounceBuf)
	beaconStateSub := s.p2p.Subscribe(&pb.BeaconStateResponse{}, s.stateBuf)
	defer func() {
		blockSub.Unsubscribe()
		blockAnnounceSub.Unsubscribe()
		beaconStateSub.Unsubscribe()
		batchedBlocksub.Unsubscribe()
		close(s.batchedBlockBuf)
		close(s.blockBuf)
		close(s.stateBuf)
	}()

	if s.reqState {
		if err := s.requestStateFromPeer(s.ctx, s.stateRootOfHighestObservedSlot[:], p2p.AnyPeer); err != nil {
			log.Errorf("Could not request state from peer %v", err)
		}
	} else {
		// Send out a batch request
		s.requestBatchedBlocks(s.currentSlot+1, s.highestObservedSlot)
	}

	for {
		select {
		case <-s.ctx.Done():
			log.Debug("Exiting goroutine")
			return
		case <-delayChan:
			if s.checkSyncStatus() {
				return
			}
		case msg := <-s.blockAnnounceBuf:
			safelyHandleMessage(s.processBlockAnnounce, msg)
		case msg := <-s.blockBuf:
			safelyHandleMessage(func(message p2p.Message) {
				data := message.Data.(*pb.BeaconBlockResponse)
				s.processBlock(message.Ctx, data.Block, message.Peer)
			}, msg)
		case msg := <-s.stateBuf:
			safelyHandleMessage(s.processState, msg)
		case msg := <-s.batchedBlockBuf:
			safelyHandleMessage(s.processBatchedBlocks, msg)
		}
	}
}

// safelyHandleMessage will recover and log any panic that occurs from the
// function argument.
func safelyHandleMessage(fn func(p2p.Message), msg p2p.Message) {
	defer func() {
		if r := recover(); r != nil {
			printedMsg := "message contains no data"
			if msg.Data != nil {
				printedMsg = proto.MarshalTextString(msg.Data)
			}
			log.WithFields(logrus.Fields{
				"r":   r,
				"msg": printedMsg,
			}).Error("Panicked when handling p2p message! Recovering...")

			debug.PrintStack()

			if msg.Ctx == nil {
				return
			}
			if span := trace.FromContext(msg.Ctx); span != nil {
				span.SetStatus(trace.Status{
					Code:    trace.StatusCodeInternal,
					Message: fmt.Sprintf("Panic: %v", r),
				})
			}
		}
	}()

	// Fingers crossed that it doesn't panic...
	fn(msg)
}

// checkInMemoryBlocks is another routine which will run concurrently with the
// main routine for initial sync, where it checks the blocks saved in memory regularly
// to see if the blocks are valid enough to be processed.
func (s *InitialSync) checkInMemoryBlocks() {
	for {
		select {
		case <-s.ctx.Done():
			return
		default:
			if s.currentSlot == s.highestObservedSlot {
				return
			}
			s.mutex.Lock()
			if block, ok := s.inMemoryBlocks[s.currentSlot+1]; ok && s.currentSlot+1 <= s.highestObservedSlot {
				s.processBlock(s.ctx, block, p2p.AnyPeer)
			}
			s.mutex.Unlock()
		}
	}
}

// checkSyncStatus verifies if the beacon node is correctly synced with its peers up to their
// latest canonical head. If not, then it requests batched blocks up to the highest observed slot.
func (s *InitialSync) checkSyncStatus() bool {
	if s.reqState {
		if err := s.requestStateFromPeer(s.ctx, s.stateRootOfHighestObservedSlot[:], p2p.AnyPeer); err != nil {
			log.Errorf("Could not request state from peer %v", err)
		}
		return false
	}
	if s.highestObservedSlot == s.currentSlot {
		log.Info("Exiting initial sync and starting normal sync")
		s.syncedFeed.Send(s.currentSlot)
		s.syncService.ResumeSync()
		return true
	}
	// requests multiple blocks so as to save and sync quickly.
	s.requestBatchedBlocks(s.currentSlot+1, s.highestObservedSlot)
	return false
}

func (s *InitialSync) processBlockAnnounce(msg p2p.Message) {
	ctx, span := trace.StartSpan(msg.Ctx, "beacon-chain.sync.initial-sync.processBlockAnnounce")
	defer span.End()
	data := msg.Data.(*pb.BeaconBlockAnnounce)
	recBlockAnnounce.Inc()

	if s.reqState {
		if err := s.requestStateFromPeer(ctx, s.stateRootOfHighestObservedSlot[:], msg.Peer); err != nil {
			log.Errorf("Could not request state from peer %v", err)
		}
		return
	}

	if data.SlotNumber > s.highestObservedSlot {
		s.highestObservedSlot = data.SlotNumber
	}

	s.requestBatchedBlocks(s.currentSlot+1, s.highestObservedSlot)
	log.Debugf("Successfully requested the next block with slot: %d", data.SlotNumber-params.BeaconConfig().GenesisSlot)
}

// processBlock is the main method that validates each block which is received
// for initial sync. It checks if the blocks are valid and then will continue to
// process and save it into the db.
func (s *InitialSync) processBlock(ctx context.Context, block *pb.BeaconBlock, peerID peer.ID) {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.sync.initial-sync.processBlock")
	defer span.End()
	recBlock.Inc()
	if block.Slot > s.highestObservedSlot {
		s.highestObservedSlot = block.Slot
	}

	if block.Slot < s.currentSlot {
		return
	}

	// requesting beacon state if there is no saved state.
	if s.reqState {
		if err := s.requestStateFromPeer(s.ctx, s.stateRootOfHighestObservedSlot[:], peerID); err != nil {
			log.Errorf("Could not request beacon state from peer: %v", err)
		}
		return
	}
	// if it isn't the block in the next slot we check if it is a skipped slot.
	// if it isn't skipped we save it in memory.
	if block.Slot != (s.currentSlot + 1) {
		// if parent exists we validate the block.
		if s.doesParentExist(block) {
			if err := s.validateAndSaveNextBlock(ctx, block); err != nil {
				// Debug error so as not to have noisy error logs
				if strings.HasPrefix(err.Error(), debugError) {
					log.Debug(strings.TrimPrefix(err.Error(), debugError))
					return
				}
				log.Errorf("Unable to save block: %v", err)
			}
			return
		}
		s.mutex.Lock()
		defer s.mutex.Unlock()
		if _, ok := s.inMemoryBlocks[block.Slot]; !ok {
			s.inMemoryBlocks[block.Slot] = block
		}
		return
	}

	if err := s.validateAndSaveNextBlock(ctx, block); err != nil {
		// Debug error so as not to have noisy error logs
		if strings.HasPrefix(err.Error(), debugError) {
			log.Debug(strings.TrimPrefix(err.Error(), debugError))
			return
		}
		log.Errorf("Unable to save block: %v", err)
	}
}

// processBatchedBlocks processes all the received blocks from
// the p2p message.
func (s *InitialSync) processBatchedBlocks(msg p2p.Message) {
	ctx, span := trace.StartSpan(msg.Ctx, "beacon-chain.sync.initial-sync.processBatchedBlocks")
	defer span.End()
	batchedBlockReq.Inc()

	response := msg.Data.(*pb.BatchedBeaconBlockResponse)
	batchedBlocks := response.BatchedBlocks
	if len(batchedBlocks) == 0 {
		// Do not process empty response
		return
	}

	log.Debug("Processing batched block response")
	for _, block := range batchedBlocks {
		s.processBlock(ctx, block, msg.Peer)
	}
	log.Debug("Finished processing batched blocks")
}

func (s *InitialSync) processState(msg p2p.Message) {
	ctx, span := trace.StartSpan(msg.Ctx, "beacon-chain.sync.initial-sync.processState")
	defer span.End()
	data := msg.Data.(*pb.BeaconStateResponse)
	beaconState := data.BeaconState
	recState.Inc()

	if s.currentSlot > beaconState.FinalizedEpoch*params.BeaconConfig().SlotsPerEpoch {
		return
	}

	if err := s.db.SaveCurrentAndFinalizedState(beaconState); err != nil {
		log.Errorf("Unable to set beacon state for initial sync %v", err)
		return
	}

	if err := s.db.SaveFinalizedBlock(beaconState.LatestBlock); err != nil {
		log.Errorf("Could not save finalized block %v", err)
		return
	}

	if err := s.db.SaveBlock(beaconState.LatestBlock); err != nil {
		log.Errorf("Could not save block %v", err)
		return
	}

	if err := s.db.UpdateChainHead(beaconState.LatestBlock, beaconState); err != nil {
		log.Errorf("Could not update chainhead %v", err)
		return
	}

	if err := s.db.SaveJustifiedState(beaconState); err != nil {
		log.Errorf("Could not set beacon state for initial sync %v", err)
		return
	}

	if err := s.db.SaveJustifiedBlock(beaconState.LatestBlock); err != nil {
		log.Errorf("Could not save finalized block %v", err)
		return
	}

	h, err := hashutil.HashProto(beaconState)
	if err != nil {
		log.Error(err)
		return
	}

	exists, blkNum, err := s.powchain.BlockExists(ctx, bytesutil.ToBytes32(beaconState.LatestEth1Data.BlockHash32))
	if err != nil {
		log.Errorf("Unable to get powchain block %v", err)
	}

	if !exists {
		log.Error("Latest ETH1 block doesn't exist in the pow chain")
		return
	}

	s.db.PrunePendingDeposits(ctx, blkNum)

	if h == s.stateRootOfHighestObservedSlot {
		s.reqState = false
	}

	// sets the current slot to the last finalized slot of the
	// beacon state to begin our sync from.
	s.currentSlot = beaconState.FinalizedEpoch * params.BeaconConfig().SlotsPerEpoch
	s.beaconStateSlot = beaconState.Slot
	log.Debugf("Successfully saved beacon state with the last finalized slot: %d", beaconState.FinalizedEpoch*params.BeaconConfig().SlotsPerEpoch-params.BeaconConfig().GenesisSlot)

	s.requestBatchedBlocks(s.currentSlot+1, s.highestObservedSlot)
}

// requestStateFromPeer always requests for the last finalized slot from a peer.
func (s *InitialSync) requestStateFromPeer(ctx context.Context, stateRoot []byte, peerID peer.ID) error {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.sync.initial-sync.requestStateFromPeer")
	defer span.End()
	stateReq.Inc()
	log.Debugf("Successfully processed incoming block with state hash: %#x", stateRoot)
	return s.p2p.Send(ctx, &pb.BeaconStateRequest{FinalizedStateRootHash32S: stateRoot}, peerID)
}

// requestNextBlock broadcasts a request for a block with the entered slotnumber.
func (s *InitialSync) requestNextBlockBySlot(ctx context.Context, slotNumber uint64) {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.sync.initial-sync.requestBlockBySlot")
	defer span.End()
	log.Debugf("Requesting block %d ", slotNumber)
	blockReqSlot.Inc()
	s.mutex.Lock()
	defer s.mutex.Unlock()
	if block, ok := s.inMemoryBlocks[slotNumber]; ok {
		s.processBlock(ctx, block, p2p.AnyPeer)
		return
	}
	s.p2p.Broadcast(ctx, &pb.BeaconBlockRequestBySlotNumber{SlotNumber: slotNumber})
}

// requestBatchedBlocks sends out a request for multiple blocks till a
// specified bound slot number.
func (s *InitialSync) requestBatchedBlocks(startSlot uint64, endSlot uint64) {
	ctx, span := trace.StartSpan(context.Background(), "beacon-chain.sync.initial-sync.requestBatchedBlocks")
	defer span.End()
	sentBatchedBlockReq.Inc()
	if startSlot > endSlot {
		log.Debugf("Invalid batched request from slot %d to %d", startSlot-params.BeaconConfig().GenesisSlot, endSlot-params.BeaconConfig().GenesisSlot)
		return
	}
	blockLimit := params.BeaconConfig().BatchBlockLimit
	if startSlot+blockLimit < endSlot {
		endSlot = startSlot + blockLimit
	}
	log.Debugf("Requesting batched blocks from slot %d to %d", startSlot-params.BeaconConfig().GenesisSlot, endSlot-params.BeaconConfig().GenesisSlot)
	s.p2p.Broadcast(ctx, &pb.BatchedBeaconBlockRequest{
		StartSlot: startSlot,
		EndSlot:   endSlot,
	})
}

// validateAndSaveNextBlock will validate whether blocks received from the blockfetcher
// routine can be added to the chain.
func (s *InitialSync) validateAndSaveNextBlock(ctx context.Context, block *pb.BeaconBlock) error {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.sync.initial-sync.validateAndSaveNextBlock")
	defer span.End()
	root, err := hashutil.HashBeaconBlock(block)
	if err != nil {
		return err
	}
	if err := s.checkBlockValidity(ctx, block); err != nil {
		return err
	}
	log.Infof("Saved block with root %#x and slot %d for initial sync", root, block.Slot)
	s.currentSlot = block.Slot

	s.mutex.Lock()
	defer s.mutex.Unlock()
	// delete block from memory.
	if _, ok := s.inMemoryBlocks[block.Slot]; ok {
		delete(s.inMemoryBlocks, block.Slot)
	}
	// since the block will not be processed by chainservice we save
	// the block and do not send it to chainservice.
	if s.beaconStateSlot >= block.Slot {
		if err := s.db.SaveBlock(block); err != nil {
			return err
		}
		return nil
	}

	// Send block to main chain service to be processed.
	beaconState, err := s.chainService.ReceiveBlock(ctx, block)
	if err != nil {
		return fmt.Errorf("could not process beacon block: %v", err)
	}
	if err := s.chainService.ApplyForkChoiceRule(ctx, block, beaconState); err != nil {
		return fmt.Errorf("could not apply fork choice rule: %v", err)
	}
	return nil
}

func (s *InitialSync) checkBlockValidity(ctx context.Context, block *pb.BeaconBlock) error {
	ctx, span := trace.StartSpan(ctx, "beacon-chain.sync.initial-sync.checkBlockValidity")
	defer span.End()
	blockRoot, err := hashutil.HashBeaconBlock(block)
	if err != nil {
		return fmt.Errorf("could not tree hash received block: %v", err)
	}

	if s.db.HasBlock(blockRoot) {
		return errors.New(debugError + "received a block that already exists. Exiting")
	}

	beaconState, err := s.db.State(ctx)
	if err != nil {
		return fmt.Errorf("failed to get beacon state: %v", err)
	}

	if block.Slot < beaconState.FinalizedEpoch*params.BeaconConfig().SlotsPerEpoch {
		return errors.New(debugError + "discarding received block with a slot number smaller than the last finalized slot")
	}
	// Attestation from proposer not verified as, other nodes only store blocks not proposer
	// attestations.
	return nil
}

// isSlotDiff large checks if the difference between the current slot and highest observed
// slot isnt too large.
func (s *InitialSync) isSlotDiffLarge() bool {
	slotsPerEpoch := params.BeaconConfig().SlotsPerEpoch
	epochLimit := params.BeaconConfig().SyncEpochLimit
	return s.currentSlot+slotsPerEpoch*epochLimit < s.highestObservedSlot
}

func (s *InitialSync) doesParentExist(block *pb.BeaconBlock) bool {
	parentHash := bytesutil.ToBytes32(block.ParentRootHash32)
	return s.db.HasBlock(parentHash)
}