woop/core/blockchain.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package core implements the Ethereum consensus protocol.
package core

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"math/big"
	"sync"
	"sync/atomic"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/mclock"
	"github.com/ethereum/go-ethereum/common/prque"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/harmony-one/harmony/block"
	consensus_engine "github.com/harmony-one/harmony/consensus/engine"
	"github.com/harmony-one/harmony/consensus/reward"
	"github.com/harmony-one/harmony/consensus/votepower"
	"github.com/harmony-one/harmony/core/rawdb"
	"github.com/harmony-one/harmony/core/state"
	"github.com/harmony-one/harmony/core/types"
	"github.com/harmony-one/harmony/core/vm"
	"github.com/harmony-one/harmony/internal/params"
	"github.com/harmony-one/harmony/internal/utils"
	"github.com/harmony-one/harmony/numeric"
	"github.com/harmony-one/harmony/shard"
	"github.com/harmony-one/harmony/shard/committee"
	"github.com/harmony-one/harmony/staking/apr"
	"github.com/harmony-one/harmony/staking/effective"
	"github.com/harmony-one/harmony/staking/slash"
	staking "github.com/harmony-one/harmony/staking/types"
	lru "github.com/hashicorp/golang-lru"
	"github.com/pkg/errors"
)

var (
	// blockInsertTimer
	blockInsertTimer = metrics.NewRegisteredTimer("chain/inserts", nil)
	// ErrNoGenesis is the error when there is no genesis.
	ErrNoGenesis = errors.New("Genesis not found in chain")
	// errExceedMaxPendingSlashes ..
	errExceedMaxPendingSlashes = errors.New("exceeed max pending slashes")
	errNilEpoch                = errors.New("nil epoch for voting power computation")
)

const (
	bodyCacheLimit                     = 256
	blockCacheLimit                    = 256
	receiptsCacheLimit                 = 32
	maxFutureBlocks                    = 256
	maxTimeFutureBlocks                = 30
	badBlockLimit                      = 10
	triesInMemory                      = 128
	shardCacheLimit                    = 10
	commitsCacheLimit                  = 10
	epochCacheLimit                    = 10
	randomnessCacheLimit               = 10
	validatorCacheLimit                = 1024
	validatorStatsCacheLimit           = 1024
	validatorListCacheLimit            = 10
	validatorListByDelegatorCacheLimit = 1024
	pendingCrossLinksCacheLimit        = 2
	blockAccumulatorCacheLimit         = 256
	maxPendingSlashes                  = 512
	// BlockChainVersion ensures that an incompatible database forces a resync from scratch.
	BlockChainVersion = 3
	pendingCLCacheKey = "pendingCLs"
)

// CacheConfig contains the configuration values for the trie caching/pruning
// that's resident in a blockchain.
type CacheConfig struct {
	Disabled      bool          // Whether to disable trie write caching (archive node)
	TrieNodeLimit int           // Memory limit (MB) at which to flush the current in-memory trie to disk
	TrieTimeLimit time.Duration // Time limit after which to flush the current in-memory trie to disk
}

// BlockChain represents the canonical chain given a database with a genesis
// block. The Blockchain manages chain imports, reverts, chain reorganisations.
//
// Importing blocks in to the block chain happens according to the set of rules
// defined by the two stage Validator. Processing of blocks is done using the
// Processor which processes the included transaction. The validation of the state
// is done in the second part of the Validator. Failing results in aborting of
// the import.
//
// The BlockChain also helps in returning blocks from **any** chain included
// in the database as well as blocks that represents the canonical chain. It's
// important to note that GetBlock can return any block and does not need to be
// included in the canonical one where as GetBlockByNumber always represents the
// canonical chain.
type BlockChain struct {
	chainConfig *params.ChainConfig // Chain & network configuration
	cacheConfig *CacheConfig        // Cache configuration for pruning

	db     ethdb.Database // Low level persistent database to store final content in
	triegc *prque.Prque   // Priority queue mapping block numbers to tries to gc
	gcproc time.Duration  // Accumulates canonical block processing for trie dumping

	hc            *HeaderChain
	rmLogsFeed    event.Feed
	chainFeed     event.Feed
	chainSideFeed event.Feed
	chainHeadFeed event.Feed
	logsFeed      event.Feed
	scope         event.SubscriptionScope
	genesisBlock  *types.Block

	mu                          sync.RWMutex // global mutex for locking chain operations
	chainmu                     sync.RWMutex // blockchain insertion lock
	procmu                      sync.RWMutex // block processor lock
	pendingCrossLinksMutex      sync.RWMutex // pending crosslinks lock
	pendingSlashingCandidatesMU sync.RWMutex // pending slashing candidates

	currentBlock     atomic.Value // Current head of the block chain
	currentFastBlock atomic.Value // Current head of the fast-sync chain (may be above the block chain!)

	stateCache                    state.Database // State database to reuse between imports (contains state cache)
	bodyCache                     *lru.Cache     // Cache for the most recent block bodies
	bodyRLPCache                  *lru.Cache     // Cache for the most recent block bodies in RLP encoded format
	receiptsCache                 *lru.Cache     // Cache for the most recent receipts per block
	blockCache                    *lru.Cache     // Cache for the most recent entire blocks
	futureBlocks                  *lru.Cache     // future blocks are blocks added for later processing
	shardStateCache               *lru.Cache
	lastCommitsCache              *lru.Cache
	epochCache                    *lru.Cache    // Cache epoch number → first block number
	randomnessCache               *lru.Cache    // Cache for vrf/vdf
	validatorSnapshotCache        *lru.Cache    // Cache for validator snapshot
	validatorStatsCache           *lru.Cache    // Cache for validator stats
	validatorListCache            *lru.Cache    // Cache of validator list
	validatorListByDelegatorCache *lru.Cache    // Cache of validator list by delegator
	pendingCrossLinksCache        *lru.Cache    // Cache of last pending crosslinks
	blockAccumulatorCache         *lru.Cache    // Cache of block accumulators
	quit                          chan struct{} // blockchain quit channel
	running                       int32         // running must be called atomically
	// procInterrupt must be atomically called
	procInterrupt int32          // interrupt signaler for block processing
	wg            sync.WaitGroup // chain processing wait group for shutting down

	engine         consensus_engine.Engine
	processor      Processor // block processor interface
	validator      Validator // block and state validator interface
	vmConfig       vm.Config
	badBlocks      *lru.Cache              // Bad block cache
	shouldPreserve func(*types.Block) bool // Function used to determine whether should preserve the given block.
	pendingSlashes slash.Records
}

// NewBlockChain returns a fully initialised block chain using information
// available in the database. It initialises the default Ethereum Validator and
// Processor.
func NewBlockChain(
	db ethdb.Database, cacheConfig *CacheConfig, chainConfig *params.ChainConfig,
	engine consensus_engine.Engine, vmConfig vm.Config,
	shouldPreserve func(block *types.Block) bool,
) (*BlockChain, error) {
	if cacheConfig == nil {
		cacheConfig = &CacheConfig{
			TrieNodeLimit: 256 * 1024 * 1024,
			TrieTimeLimit: 2 * time.Minute,
		}
	}
	bodyCache, _ := lru.New(bodyCacheLimit)
	bodyRLPCache, _ := lru.New(bodyCacheLimit)
	receiptsCache, _ := lru.New(receiptsCacheLimit)
	blockCache, _ := lru.New(blockCacheLimit)
	futureBlocks, _ := lru.New(maxFutureBlocks)
	badBlocks, _ := lru.New(badBlockLimit)
	shardCache, _ := lru.New(shardCacheLimit)
	commitsCache, _ := lru.New(commitsCacheLimit)
	epochCache, _ := lru.New(epochCacheLimit)
	randomnessCache, _ := lru.New(randomnessCacheLimit)
	validatorCache, _ := lru.New(validatorCacheLimit)
	validatorStatsCache, _ := lru.New(validatorStatsCacheLimit)
	validatorListCache, _ := lru.New(validatorListCacheLimit)
	validatorListByDelegatorCache, _ := lru.New(validatorListByDelegatorCacheLimit)
	pendingCrossLinksCache, _ := lru.New(pendingCrossLinksCacheLimit)
	blockAccumulatorCache, _ := lru.New(blockAccumulatorCacheLimit)

	bc := &BlockChain{
		chainConfig:                   chainConfig,
		cacheConfig:                   cacheConfig,
		db:                            db,
		triegc:                        prque.New(nil),
		stateCache:                    state.NewDatabase(db),
		quit:                          make(chan struct{}),
		shouldPreserve:                shouldPreserve,
		bodyCache:                     bodyCache,
		bodyRLPCache:                  bodyRLPCache,
		receiptsCache:                 receiptsCache,
		blockCache:                    blockCache,
		futureBlocks:                  futureBlocks,
		shardStateCache:               shardCache,
		lastCommitsCache:              commitsCache,
		epochCache:                    epochCache,
		randomnessCache:               randomnessCache,
		validatorSnapshotCache:        validatorCache,
		validatorStatsCache:           validatorStatsCache,
		validatorListCache:            validatorListCache,
		validatorListByDelegatorCache: validatorListByDelegatorCache,
		pendingCrossLinksCache:        pendingCrossLinksCache,
		blockAccumulatorCache:         blockAccumulatorCache,
		engine:                        engine,
		vmConfig:                      vmConfig,
		badBlocks:                     badBlocks,
		pendingSlashes:                slash.Records{},
	}
	bc.SetValidator(NewBlockValidator(chainConfig, bc, engine))
	bc.SetProcessor(NewStateProcessor(chainConfig, bc, engine))

	var err error
	bc.hc, err = NewHeaderChain(db, chainConfig, engine, bc.getProcInterrupt)
	if err != nil {
		return nil, err
	}
	bc.genesisBlock = bc.GetBlockByNumber(0)
	if bc.genesisBlock == nil {
		return nil, ErrNoGenesis
	}
	var nilBlock *types.Block
	bc.currentBlock.Store(nilBlock)
	bc.currentFastBlock.Store(nilBlock)
	if err := bc.loadLastState(); err != nil {
		return nil, err
	}
	// Take ownership of this particular state
	go bc.update()
	return bc, nil
}

// ValidateNewBlock validates new block.
func (bc *BlockChain) ValidateNewBlock(block *types.Block) error {
	state, err := state.New(bc.CurrentBlock().Root(), bc.stateCache)

	if err != nil {
		return err
	}

	// NOTE Order of mutating state here matters.
	// Process block using the parent state as reference point.
	receipts, cxReceipts, _, usedGas, _, err := bc.processor.Process(
		block, state, bc.vmConfig,
	)
	if err != nil {
		bc.reportBlock(block, receipts, err)
		return err
	}

	// Verify all the hash roots (state, txns, receipts, cross-shard)
	if err := bc.Validator().ValidateState(
		block, state, receipts, cxReceipts, usedGas,
	); err != nil {
		bc.reportBlock(block, receipts, err)
		return err
	}
	return nil
}

// IsEpochBlock returns whether this block is the first block of an epoch.
// by checking if the previous block is the last block of the previous epoch
func IsEpochBlock(block *types.Block) bool {
	if block.NumberU64() == 0 {
		// genesis block is the first epoch block
		return true
	}
	return shard.Schedule.IsLastBlock(block.NumberU64() - 1)
}

// EpochFirstBlock returns the block number of the first block of an epoch.
// TODO: instead of using fixed epoch schedules, determine the first block by epoch changes.
func EpochFirstBlock(epoch *big.Int) *big.Int {
	if epoch.Cmp(big.NewInt(GenesisEpoch)) == 0 {
		return big.NewInt(GenesisEpoch)
	}
	return big.NewInt(int64(shard.Schedule.EpochLastBlock(epoch.Uint64()-1) + 1))
}

func (bc *BlockChain) getProcInterrupt() bool {
	return atomic.LoadInt32(&bc.procInterrupt) == 1
}

// loadLastState loads the last known chain state from the database. This method
// assumes that the chain manager mutex is held.
func (bc *BlockChain) loadLastState() error {
	// Restore the last known head block
	head := rawdb.ReadHeadBlockHash(bc.db)
	if head == (common.Hash{}) {
		// Corrupt or empty database, init from scratch
		utils.Logger().Warn().Msg("Empty database, resetting chain")
		return bc.Reset()
	}
	// Make sure the entire head block is available
	currentBlock := bc.GetBlockByHash(head)
	if currentBlock == nil {
		// Corrupt or empty database, init from scratch
		utils.Logger().Warn().Str("hash", head.Hex()).Msg("Head block missing, resetting chain")
		return bc.Reset()
	}
	// Make sure the state associated with the block is available
	if _, err := state.New(currentBlock.Root(), bc.stateCache); err != nil {
		// Dangling block without a state associated, init from scratch
		utils.Logger().Warn().
			Str("number", currentBlock.Number().String()).
			Str("hash", currentBlock.Hash().Hex()).
			Msg("Head state missing, repairing chain")
		if err := bc.repair(&currentBlock); err != nil {
			return err
		}
	}
	// Everything seems to be fine, set as the head block
	bc.currentBlock.Store(currentBlock)

	// We don't need the following as we want the current header and block to be consistent
	// Restore the last known head header
	//currentHeader := currentBlock.Header()
	//if head := rawdb.ReadHeadHeaderHash(bc.db); head != (common.Hash{}) {
	//	if header := bc.GetHeaderByHash(head); header != nil {
	//		currentHeader = header
	//	}
	//}
	utils.Logger().Info().
		Str("number", currentBlock.Number().String()).
		Str("hash", currentBlock.Hash().Hex()).
		Msg("Head state missing, repairing chain")
	currentHeader := currentBlock.Header()
	bc.hc.SetCurrentHeader(currentHeader)

	// Restore the last known head fast block
	bc.currentFastBlock.Store(currentBlock)
	if head := rawdb.ReadHeadFastBlockHash(bc.db); head != (common.Hash{}) {
		if block := bc.GetBlockByHash(head); block != nil {
			bc.currentFastBlock.Store(block)
		}
	}

	// Issue a status log for the user
	currentFastBlock := bc.CurrentFastBlock()

	headerTd := bc.GetTd(currentHeader.Hash(), currentHeader.Number().Uint64())
	blockTd := bc.GetTd(currentBlock.Hash(), currentBlock.NumberU64())
	fastTd := bc.GetTd(currentFastBlock.Hash(), currentFastBlock.NumberU64())

	utils.Logger().Info().
		Str("number", currentHeader.Number().String()).
		Str("hash", currentHeader.Hash().Hex()).
		Str("td", headerTd.String()).
		Str("age", common.PrettyAge(time.Unix(currentHeader.Time().Int64(), 0)).String()).
		Msg("Loaded most recent local header")
	utils.Logger().Info().
		Str("number", currentBlock.Number().String()).
		Str("hash", currentBlock.Hash().Hex()).
		Str("td", blockTd.String()).
		Str("age", common.PrettyAge(time.Unix(currentBlock.Time().Int64(), 0)).String()).
		Msg("Loaded most recent local full block")
	utils.Logger().Info().
		Str("number", currentFastBlock.Number().String()).
		Str("hash", currentFastBlock.Hash().Hex()).
		Str("td", fastTd.String()).
		Str("age", common.PrettyAge(time.Unix(currentFastBlock.Time().Int64(), 0)).String()).
		Msg("Loaded most recent local fast block")

	return nil
}

// SetHead rewinds the local chain to a new head. In the case of headers, everything
// above the new head will be deleted and the new one set. In the case of blocks
// though, the head may be further rewound if block bodies are missing (non-archive
// nodes after a fast sync).
func (bc *BlockChain) SetHead(head uint64) error {
	utils.Logger().Warn().Uint64("target", head).Msg("Rewinding blockchain")

	bc.mu.Lock()
	defer bc.mu.Unlock()

	// Rewind the header chain, deleting all block bodies until then
	delFn := func(db rawdb.DatabaseDeleter, hash common.Hash, num uint64) {
		rawdb.DeleteBody(db, hash, num)
	}
	bc.hc.SetHead(head, delFn)
	currentHeader := bc.hc.CurrentHeader()

	// Clear out any stale content from the caches
	bc.bodyCache.Purge()
	bc.bodyRLPCache.Purge()
	bc.receiptsCache.Purge()
	bc.blockCache.Purge()
	bc.futureBlocks.Purge()
	bc.shardStateCache.Purge()

	// Rewind the block chain, ensuring we don't end up with a stateless head block
	if currentBlock := bc.CurrentBlock(); currentBlock != nil && currentHeader.Number().Uint64() < currentBlock.NumberU64() {
		bc.currentBlock.Store(bc.GetBlock(currentHeader.Hash(), currentHeader.Number().Uint64()))
	}
	if currentBlock := bc.CurrentBlock(); currentBlock != nil {
		if _, err := state.New(currentBlock.Root(), bc.stateCache); err != nil {
			// Rewound state missing, rolled back to before pivot, reset to genesis
			bc.currentBlock.Store(bc.genesisBlock)
		}
	}
	// Rewind the fast block in a simpleton way to the target head
	if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock != nil && currentHeader.Number().Uint64() < currentFastBlock.NumberU64() {
		bc.currentFastBlock.Store(bc.GetBlock(currentHeader.Hash(), currentHeader.Number().Uint64()))
	}
	// If either blocks reached nil, reset to the genesis state
	if currentBlock := bc.CurrentBlock(); currentBlock == nil {
		bc.currentBlock.Store(bc.genesisBlock)
	}
	if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock == nil {
		bc.currentFastBlock.Store(bc.genesisBlock)
	}
	currentBlock := bc.CurrentBlock()
	currentFastBlock := bc.CurrentFastBlock()

	rawdb.WriteHeadBlockHash(bc.db, currentBlock.Hash())
	rawdb.WriteHeadFastBlockHash(bc.db, currentFastBlock.Hash())

	return bc.loadLastState()
}

// ShardID returns the shard Id of the blockchain.
// TODO: use a better solution before resharding shuffle nodes to different shards
func (bc *BlockChain) ShardID() uint32 {
	return bc.CurrentBlock().ShardID()
}

// GasLimit returns the gas limit of the current HEAD block.
func (bc *BlockChain) GasLimit() uint64 {
	return bc.CurrentBlock().GasLimit()
}

// CurrentBlock retrieves the current head block of the canonical chain. The
// block is retrieved from the blockchain's internal cache.
func (bc *BlockChain) CurrentBlock() *types.Block {
	return bc.currentBlock.Load().(*types.Block)
}

// CurrentFastBlock retrieves the current fast-sync head block of the canonical
// chain. The block is retrieved from the blockchain's internal cache.
func (bc *BlockChain) CurrentFastBlock() *types.Block {
	return bc.currentFastBlock.Load().(*types.Block)
}

// SetProcessor sets the processor required for making state modifications.
func (bc *BlockChain) SetProcessor(processor Processor) {
	bc.procmu.Lock()
	defer bc.procmu.Unlock()
	bc.processor = processor
}

// SetValidator sets the validator which is used to validate incoming blocks.
func (bc *BlockChain) SetValidator(validator Validator) {
	bc.procmu.Lock()
	defer bc.procmu.Unlock()
	bc.validator = validator
}

// Validator returns the current validator.
func (bc *BlockChain) Validator() Validator {
	bc.procmu.RLock()
	defer bc.procmu.RUnlock()
	return bc.validator
}

// Processor returns the current processor.
func (bc *BlockChain) Processor() Processor {
	bc.procmu.RLock()
	defer bc.procmu.RUnlock()
	return bc.processor
}

// State returns a new mutable state based on the current HEAD block.
func (bc *BlockChain) State() (*state.DB, error) {
	return bc.StateAt(bc.CurrentBlock().Root())
}

// StateAt returns a new mutable state based on a particular point in time.
func (bc *BlockChain) StateAt(root common.Hash) (*state.DB, error) {
	return state.New(root, bc.stateCache)
}

// Reset purges the entire blockchain, restoring it to its genesis state.
func (bc *BlockChain) Reset() error {
	return bc.ResetWithGenesisBlock(bc.genesisBlock)
}

// ResetWithGenesisBlock purges the entire blockchain, restoring it to the
// specified genesis state.
func (bc *BlockChain) ResetWithGenesisBlock(genesis *types.Block) error {
	// Dump the entire block chain and purge the caches
	if err := bc.SetHead(0); err != nil {
		return err
	}
	bc.mu.Lock()
	defer bc.mu.Unlock()

	// Prepare the genesis block and reinitialise the chain
	rawdb.WriteBlock(bc.db, genesis)

	bc.genesisBlock = genesis
	bc.insert(bc.genesisBlock)
	bc.currentBlock.Store(bc.genesisBlock)
	bc.hc.SetGenesis(bc.genesisBlock.Header())
	bc.hc.SetCurrentHeader(bc.genesisBlock.Header())
	bc.currentFastBlock.Store(bc.genesisBlock)

	return nil
}

// repair tries to repair the current blockchain by rolling back the current block
// until one with associated state is found. This is needed to fix incomplete db
// writes caused either by crashes/power outages, or simply non-committed tries.
//
// This method only rolls back the current block. The current header and current
// fast block are left intact.
func (bc *BlockChain) repair(head **types.Block) error {
	for {
		// Abort if we've rewound to a head block that does have associated state
		if _, err := state.New((*head).Root(), bc.stateCache); err == nil {
			utils.Logger().Info().
				Str("number", (*head).Number().String()).
				Str("hash", (*head).Hash().Hex()).
				Msg("Rewound blockchain to past state")
			return nil
		}
		// Repair last commit sigs
		lastSig := (*head).Header().LastCommitSignature()
		sigAndBitMap := append(lastSig[:], (*head).Header().LastCommitBitmap()...)
		bc.WriteLastCommits(sigAndBitMap)

		// Otherwise rewind one block and recheck state availability there
		(*head) = bc.GetBlock((*head).ParentHash(), (*head).NumberU64()-1)
	}
}

// Export writes the active chain to the given writer.
func (bc *BlockChain) Export(w io.Writer) error {
	return bc.ExportN(w, uint64(0), bc.CurrentBlock().NumberU64())
}

// ExportN writes a subset of the active chain to the given writer.
func (bc *BlockChain) ExportN(w io.Writer, first uint64, last uint64) error {
	bc.mu.RLock()
	defer bc.mu.RUnlock()

	if first > last {
		return fmt.Errorf("export failed: first (%d) is greater than last (%d)", first, last)
	}
	utils.Logger().Info().Uint64("count", last-first+1).Msg("Exporting batch of blocks")

	start, reported := time.Now(), time.Now()
	for nr := first; nr <= last; nr++ {
		block := bc.GetBlockByNumber(nr)
		if block == nil {
			return fmt.Errorf("export failed on #%d: not found", nr)
		}
		if err := block.EncodeRLP(w); err != nil {
			return err
		}
		if time.Since(reported) >= statsReportLimit {
			utils.Logger().Info().
				Uint64("exported", block.NumberU64()-first).
				Str("elapsed", common.PrettyDuration(time.Since(start)).String()).
				Msg("Exporting blocks")
			reported = time.Now()
		}
	}

	return nil
}

// similar to insert, but add to the db writer.
func (bc *BlockChain) insertWithWriter(batch rawdb.DatabaseWriter, block *types.Block) {
	// If the block is on a side chain or an unknown one, force other heads onto it too
	updateHeads := rawdb.ReadCanonicalHash(bc.db, block.NumberU64()) != block.Hash()

	// Add the block to the canonical chain number scheme and mark as the head
	rawdb.WriteCanonicalHash(batch, block.Hash(), block.NumberU64())
	rawdb.WriteHeadBlockHash(batch, block.Hash())

	bc.currentBlock.Store(block)

	// If the block is better than our head or is on a different chain, force update heads
	if updateHeads {
		bc.hc.SetCurrentHeader(block.Header())
		rawdb.WriteHeadFastBlockHash(batch, block.Hash())

		bc.currentFastBlock.Store(block)
	}
}

// insert injects a new head block into the current block chain. This method
// assumes that the block is indeed a true head. It will also reset the head
// header and the head fast sync block to this very same block if they are older
// or if they are on a different side chain.
//
// Note, this function assumes that the `mu` mutex is held!
func (bc *BlockChain) insert(block *types.Block) {
	bc.insertWithWriter(bc.db, block)
}

// Genesis retrieves the chain's genesis block.
func (bc *BlockChain) Genesis() *types.Block {
	return bc.genesisBlock
}

// GetBody retrieves a block body (transactions and uncles) from the database by
// hash, caching it if found.
func (bc *BlockChain) GetBody(hash common.Hash) *types.Body {
	// Short circuit if the body's already in the cache, retrieve otherwise
	if cached, ok := bc.bodyCache.Get(hash); ok {
		body := cached.(*types.Body)
		return body
	}
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	body := rawdb.ReadBody(bc.db, hash, *number)
	if body == nil {
		return nil
	}
	// Cache the found body for next time and return
	bc.bodyCache.Add(hash, body)
	return body
}

// GetBodyRLP retrieves a block body in RLP encoding from the database by hash,
// caching it if found.
func (bc *BlockChain) GetBodyRLP(hash common.Hash) rlp.RawValue {
	// Short circuit if the body's already in the cache, retrieve otherwise
	if cached, ok := bc.bodyRLPCache.Get(hash); ok {
		return cached.(rlp.RawValue)
	}
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	body := rawdb.ReadBodyRLP(bc.db, hash, *number)
	if len(body) == 0 {
		return nil
	}
	// Cache the found body for next time and return
	bc.bodyRLPCache.Add(hash, body)
	return body
}

// HasBlock checks if a block is fully present in the database or not.
func (bc *BlockChain) HasBlock(hash common.Hash, number uint64) bool {
	if bc.blockCache.Contains(hash) {
		return true
	}
	return rawdb.HasBody(bc.db, hash, number)
}

// HasState checks if state trie is fully present in the database or not.
func (bc *BlockChain) HasState(hash common.Hash) bool {
	_, err := bc.stateCache.OpenTrie(hash)
	return err == nil
}

// HasBlockAndState checks if a block and associated state trie is fully present
// in the database or not, caching it if present.
func (bc *BlockChain) HasBlockAndState(hash common.Hash, number uint64) bool {
	// Check first that the block itself is known
	block := bc.GetBlock(hash, number)
	if block == nil {
		return false
	}
	return bc.HasState(block.Root())
}

// GetBlock retrieves a block from the database by hash and number,
// caching it if found.
func (bc *BlockChain) GetBlock(hash common.Hash, number uint64) *types.Block {
	// Short circuit if the block's already in the cache, retrieve otherwise
	if block, ok := bc.blockCache.Get(hash); ok {
		return block.(*types.Block)
	}
	block := rawdb.ReadBlock(bc.db, hash, number)
	if block == nil {
		return nil
	}
	// Cache the found block for next time and return
	bc.blockCache.Add(block.Hash(), block)
	return block
}

// GetBlockByHash retrieves a block from the database by hash, caching it if found.
func (bc *BlockChain) GetBlockByHash(hash common.Hash) *types.Block {
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	return bc.GetBlock(hash, *number)
}

// GetBlockByNumber retrieves a block from the database by number, caching it
// (associated with its hash) if found.
func (bc *BlockChain) GetBlockByNumber(number uint64) *types.Block {
	hash := rawdb.ReadCanonicalHash(bc.db, number)
	if hash == (common.Hash{}) {
		return nil
	}
	return bc.GetBlock(hash, number)
}

// GetReceiptsByHash retrieves the receipts for all transactions in a given block.
func (bc *BlockChain) GetReceiptsByHash(hash common.Hash) types.Receipts {
	if receipts, ok := bc.receiptsCache.Get(hash); ok {
		return receipts.(types.Receipts)
	}

	number := rawdb.ReadHeaderNumber(bc.db, hash)
	if number == nil {
		return nil
	}

	receipts := rawdb.ReadReceipts(bc.db, hash, *number)
	bc.receiptsCache.Add(hash, receipts)
	return receipts
}

// GetBlocksFromHash returns the block corresponding to hash and up to n-1 ancestors.
// [deprecated by eth/62]
func (bc *BlockChain) GetBlocksFromHash(hash common.Hash, n int) (blocks []*types.Block) {
	number := bc.hc.GetBlockNumber(hash)
	if number == nil {
		return nil
	}
	for i := 0; i < n; i++ {
		block := bc.GetBlock(hash, *number)
		if block == nil {
			break
		}
		blocks = append(blocks, block)
		hash = block.ParentHash()
		*number--
	}
	return
}

// GetUnclesInChain retrieves all the uncles from a given block backwards until
// a specific distance is reached.
func (bc *BlockChain) GetUnclesInChain(b *types.Block, length int) []*block.Header {
	uncles := []*block.Header{}
	for i := 0; b != nil && i < length; i++ {
		uncles = append(uncles, b.Uncles()...)
		b = bc.GetBlock(b.ParentHash(), b.NumberU64()-1)
	}
	return uncles
}

// TrieNode retrieves a blob of data associated with a trie node (or code hash)
// either from ephemeral in-memory cache, or from persistent storage.
func (bc *BlockChain) TrieNode(hash common.Hash) ([]byte, error) {
	return bc.stateCache.TrieDB().Node(hash)
}

// Stop stops the blockchain service. If any imports are currently in progress
// it will abort them using the procInterrupt.
func (bc *BlockChain) Stop() {
	if !atomic.CompareAndSwapInt32(&bc.running, 0, 1) {
		return
	}
	// Unsubscribe all subscriptions registered from blockchain
	bc.scope.Close()
	close(bc.quit)
	atomic.StoreInt32(&bc.procInterrupt, 1)

	bc.wg.Wait()

	// Ensure the state of a recent block is also stored to disk before exiting.
	// We're writing three different states to catch different restart scenarios:
	//  - HEAD:     So we don't need to reprocess any blocks in the general case
	//  - HEAD-1:   So we don't do large reorgs if our HEAD becomes an uncle
	//  - HEAD-127: So we have a hard limit on the number of blocks reexecuted
	if !bc.cacheConfig.Disabled {
		triedb := bc.stateCache.TrieDB()

		for _, offset := range []uint64{0, 1, triesInMemory - 1} {
			if number := bc.CurrentBlock().NumberU64(); number > offset {
				recent := bc.GetHeaderByNumber(number - offset)

				utils.Logger().Info().
					Str("block", recent.Number().String()).
					Str("hash", recent.Hash().Hex()).
					Str("root", recent.Root().Hex()).
					Msg("Writing cached state to disk")
				if err := triedb.Commit(recent.Root(), true); err != nil {
					utils.Logger().Error().Err(err).Msg("Failed to commit recent state trie")
				}
			}
		}
		for !bc.triegc.Empty() {
			triedb.Dereference(bc.triegc.PopItem().(common.Hash))
		}
		if size, _ := triedb.Size(); size != 0 {
			utils.Logger().Error().Msg("Dangling trie nodes after full cleanup")
		}
	}
	utils.Logger().Info().Msg("Blockchain manager stopped")
}

func (bc *BlockChain) procFutureBlocks() {
	blocks := make([]*types.Block, 0, bc.futureBlocks.Len())
	for _, hash := range bc.futureBlocks.Keys() {
		if block, exist := bc.futureBlocks.Peek(hash); exist {
			blocks = append(blocks, block.(*types.Block))
		}
	}
	if len(blocks) > 0 {
		types.BlockBy(types.Number).Sort(blocks)

		// Insert one by one as chain insertion needs contiguous ancestry between blocks
		for i := range blocks {
			bc.InsertChain(blocks[i:i+1], true /* verifyHeaders */)
		}
	}
}

// WriteStatus status of write
type WriteStatus byte

// Constants for WriteStatus
const (
	NonStatTy WriteStatus = iota
	CanonStatTy
	SideStatTy
)

// Rollback is designed to remove a chain of links from the database that aren't
// certain enough to be valid.
func (bc *BlockChain) Rollback(chain []common.Hash) {
	bc.mu.Lock()
	defer bc.mu.Unlock()

	for i := len(chain) - 1; i >= 0; i-- {
		hash := chain[i]

		currentHeader := bc.hc.CurrentHeader()
		if currentHeader != nil && currentHeader.Hash() == hash {
			parentHeader := bc.GetHeader(currentHeader.ParentHash(), currentHeader.Number().Uint64()-1)
			if parentHeader != nil {
				bc.hc.SetCurrentHeader(parentHeader)
			}
		}
		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock != nil && currentFastBlock.Hash() == hash {
			newFastBlock := bc.GetBlock(currentFastBlock.ParentHash(), currentFastBlock.NumberU64()-1)
			if newFastBlock != nil {
				bc.currentFastBlock.Store(newFastBlock)
				rawdb.WriteHeadFastBlockHash(bc.db, newFastBlock.Hash())
			}
		}
		if currentBlock := bc.CurrentBlock(); currentBlock != nil && currentBlock.Hash() == hash {
			newBlock := bc.GetBlock(currentBlock.ParentHash(), currentBlock.NumberU64()-1)
			if newBlock != nil {
				bc.currentBlock.Store(newBlock)
				rawdb.WriteHeadBlockHash(bc.db, newBlock.Hash())
			}
		}
	}
}

// SetReceiptsData computes all the non-consensus fields of the receipts
func SetReceiptsData(config *params.ChainConfig, block *types.Block, receipts types.Receipts) error {
	signer := types.MakeSigner(config, block.Epoch())

	transactions, stakingTransactions, logIndex := block.Transactions(), block.StakingTransactions(), uint(0)
	if len(transactions)+len(stakingTransactions) != len(receipts) {
		return errors.New("transaction+stakingTransactions and receipt count mismatch")
	}

	// The used gas can be calculated based on previous receipts
	if len(receipts) > 0 && len(transactions) > 0 {
		receipts[0].GasUsed = receipts[0].CumulativeGasUsed
	}
	for j := 1; j < len(transactions); j++ {
		// The transaction hash can be retrieved from the transaction itself
		receipts[j].TxHash = transactions[j].Hash()
		receipts[j].GasUsed = receipts[j].CumulativeGasUsed - receipts[j-1].CumulativeGasUsed
		// The contract address can be derived from the transaction itself
		if transactions[j].To() == nil {
			// Deriving the signer is expensive, only do if it's actually needed
			from, _ := types.Sender(signer, transactions[j])
			receipts[j].ContractAddress = crypto.CreateAddress(from, transactions[j].Nonce())
		}
		// The derived log fields can simply be set from the block and transaction
		for k := 0; k < len(receipts[j].Logs); k++ {
			receipts[j].Logs[k].BlockNumber = block.NumberU64()
			receipts[j].Logs[k].BlockHash = block.Hash()
			receipts[j].Logs[k].TxHash = receipts[j].TxHash
			receipts[j].Logs[k].TxIndex = uint(j)
			receipts[j].Logs[k].Index = logIndex
			logIndex++
		}
	}

	// The used gas can be calculated based on previous receipts
	if len(receipts) > len(transactions) && len(stakingTransactions) > 0 {
		receipts[len(transactions)].GasUsed = receipts[len(transactions)].CumulativeGasUsed
	}
	// in a block, txns are processed before staking txns
	for j := len(transactions) + 1; j < len(transactions)+len(stakingTransactions); j++ {
		// The transaction hash can be retrieved from the staking transaction itself
		receipts[j].TxHash = stakingTransactions[j].Hash()
		receipts[j].GasUsed = receipts[j].CumulativeGasUsed - receipts[j-1].CumulativeGasUsed
		// The derived log fields can simply be set from the block and transaction
		for k := 0; k < len(receipts[j].Logs); k++ {
			receipts[j].Logs[k].BlockNumber = block.NumberU64()
			receipts[j].Logs[k].BlockHash = block.Hash()
			receipts[j].Logs[k].TxHash = receipts[j].TxHash
			receipts[j].Logs[k].TxIndex = uint(j) + uint(len(transactions))
			receipts[j].Logs[k].Index = logIndex
			logIndex++
		}
	}
	return nil
}

// InsertReceiptChain attempts to complete an already existing header chain with
// transaction and receipt data.
func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain []types.Receipts) (int, error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 1; i < len(blockChain); i++ {
		if blockChain[i].NumberU64() != blockChain[i-1].NumberU64()+1 || blockChain[i].ParentHash() != blockChain[i-1].Hash() {
			utils.Logger().Error().
				Str("number", blockChain[i].Number().String()).
				Str("hash", blockChain[i].Hash().Hex()).
				Str("parent", blockChain[i].ParentHash().Hex()).
				Str("prevnumber", blockChain[i-1].Number().String()).
				Str("prevhash", blockChain[i-1].Hash().Hex()).
				Msg("Non contiguous receipt insert")
			return 0, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, blockChain[i-1].NumberU64(),
				blockChain[i-1].Hash().Bytes()[:4], i, blockChain[i].NumberU64(), blockChain[i].Hash().Bytes()[:4], blockChain[i].ParentHash().Bytes()[:4])
		}
	}

	var (
		stats = struct{ processed, ignored int32 }{}
		start = time.Now()
		bytes = 0
		batch = bc.db.NewBatch()
	)
	for i, block := range blockChain {
		receipts := receiptChain[i]
		// Short circuit insertion if shutting down or processing failed
		if atomic.LoadInt32(&bc.procInterrupt) == 1 {
			return 0, nil
		}
		// Short circuit if the owner header is unknown
		if !bc.HasHeader(block.Hash(), block.NumberU64()) {
			return i, fmt.Errorf("containing header #%d [%x…] unknown", block.Number(), block.Hash().Bytes()[:4])
		}
		// Skip if the entire data is already known
		if bc.HasBlock(block.Hash(), block.NumberU64()) {
			stats.ignored++
			continue
		}
		// Compute all the non-consensus fields of the receipts
		if err := SetReceiptsData(bc.chainConfig, block, receipts); err != nil {
			return i, fmt.Errorf("failed to set receipts data: %v", err)
		}
		// Write all the data out into the database
		rawdb.WriteBody(batch, block.Hash(), block.NumberU64(), block.Body())
		rawdb.WriteReceipts(batch, block.Hash(), block.NumberU64(), receipts)
		rawdb.WriteTxLookupEntries(batch, block)

		stats.processed++

		if batch.ValueSize() >= ethdb.IdealBatchSize {
			if err := batch.Write(); err != nil {
				return 0, err
			}
			bytes += batch.ValueSize()
			batch.Reset()
		}
	}
	if batch.ValueSize() > 0 {
		bytes += batch.ValueSize()
		if err := batch.Write(); err != nil {
			return 0, err
		}
	}

	// Update the head fast sync block if better
	bc.mu.Lock()
	head := blockChain[len(blockChain)-1]
	if td := bc.GetTd(head.Hash(), head.NumberU64()); td != nil { // Rewind may have occurred, skip in that case
		currentFastBlock := bc.CurrentFastBlock()
		if bc.GetTd(currentFastBlock.Hash(), currentFastBlock.NumberU64()).Cmp(td) < 0 {
			rawdb.WriteHeadFastBlockHash(bc.db, head.Hash())
			bc.currentFastBlock.Store(head)
		}
	}
	bc.mu.Unlock()

	utils.Logger().Info().
		Int32("count", stats.processed).
		Str("elapsed", common.PrettyDuration(time.Since(start)).String()).
		Str("age", common.PrettyAge(time.Unix(head.Time().Int64(), 0)).String()).
		Str("head", head.Number().String()).
		Str("hash", head.Hash().Hex()).
		Str("size", common.StorageSize(bytes).String()).
		Int32("ignored", stats.ignored).
		Msg("Imported new block receipts")

	return 0, nil
}

var lastWrite uint64

// WriteBlockWithoutState writes only the block and its metadata to the database,
// but does not write any state. This is used to construct competing side forks
// up to the point where they exceed the canonical total difficulty.
func (bc *BlockChain) WriteBlockWithoutState(block *types.Block, td *big.Int) (err error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	if err := bc.hc.WriteTd(block.Hash(), block.NumberU64(), td); err != nil {
		return err
	}
	rawdb.WriteBlock(bc.db, block)

	return nil
}

// WriteBlockWithState writes the block and all associated state to the database.
func (bc *BlockChain) WriteBlockWithState(
	block *types.Block, receipts []*types.Receipt,
	cxReceipts []*types.CXReceipt,
	paid reward.Reader,
	state *state.DB,
) (status WriteStatus, err error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	// Make sure no inconsistent state is leaked during insertion
	bc.mu.Lock()
	defer bc.mu.Unlock()

	currentBlock := bc.CurrentBlock()
	if currentBlock == nil || block.ParentHash() != currentBlock.Hash() {
		return NonStatTy, errors.New("Hash of parent block doesn't match the current block hash")
	}

	// Commit state object changes to in-memory trie
	root, err := state.Commit(bc.chainConfig.IsS3(block.Epoch()))
	if err != nil {
		return NonStatTy, err
	}

	// Flush trie state into disk if it's archival node or the block is epoch block
	triedb := bc.stateCache.TrieDB()
	if bc.cacheConfig.Disabled || len(block.Header().ShardState()) > 0 {
		if err := triedb.Commit(root, false); err != nil {
			return NonStatTy, err
		}
	} else {
		// Full but not archive node, do proper garbage collection
		triedb.Reference(root, common.Hash{}) // metadata reference to keep trie alive
		bc.triegc.Push(root, -int64(block.NumberU64()))

		if current := block.NumberU64(); current > triesInMemory {
			// If we exceeded our memory allowance, flush matured singleton nodes to disk
			var (
				nodes, imgs = triedb.Size()
				limit       = common.StorageSize(bc.cacheConfig.TrieNodeLimit) * 1024 * 1024
			)
			if nodes > limit || imgs > 4*1024*1024 {
				triedb.Cap(limit - ethdb.IdealBatchSize)
			}
			// Find the next state trie we need to commit
			header := bc.GetHeaderByNumber(current - triesInMemory)
			chosen := header.Number().Uint64()

			// If we exceeded out time allowance, flush an entire trie to disk
			if bc.gcproc > bc.cacheConfig.TrieTimeLimit {
				// If we're exceeding limits but haven't reached a large enough memory gap,
				// warn the user that the system is becoming unstable.
				if chosen < lastWrite+triesInMemory && bc.gcproc >= 2*bc.cacheConfig.TrieTimeLimit {
					utils.Logger().Info().
						Dur("time", bc.gcproc).
						Dur("allowance", bc.cacheConfig.TrieTimeLimit).
						Float64("optimum", float64(chosen-lastWrite)/triesInMemory).
						Msg("State in memory for too long, committing")
				}
				// Flush an entire trie and restart the counters
				triedb.Commit(header.Root(), true)
				lastWrite = chosen
				bc.gcproc = 0
			}
			// Garbage collect anything below our required write retention
			for !bc.triegc.Empty() {
				root, number := bc.triegc.Pop()
				if uint64(-number) > chosen {
					bc.triegc.Push(root, number)
					break
				}
				triedb.Dereference(root.(common.Hash))
			}
		}
	}

	batch := bc.db.NewBatch()
	// Write the raw block
	rawdb.WriteBlock(batch, block)

	// Write offchain data
	if status, err := bc.CommitOffChainData(
		batch, block, receipts,
		cxReceipts, paid, state,
	); err != nil {
		return status, err
	}

	// Write the positional metadata for transaction/receipt lookups and preimages
	rawdb.WriteTxLookupEntries(batch, block)
	rawdb.WriteCxLookupEntries(batch, block)
	rawdb.WritePreimages(batch, block.NumberU64(), state.Preimages())

	// Update current block
	bc.insertWithWriter(batch, block)

	if err := batch.Write(); err != nil {
		return NonStatTy, err
	}

	bc.futureBlocks.Remove(block.Hash())
	return CanonStatTy, nil
}

// InsertChain attempts to insert the given batch of blocks in to the canonical
// chain or, otherwise, create a fork. If an error is returned it will return
// the index number of the failing block as well an error describing what went
// wrong.
//
// After insertion is done, all accumulated events will be fired.
func (bc *BlockChain) InsertChain(chain types.Blocks, verifyHeaders bool) (int, error) {
	n, events, logs, err := bc.insertChain(chain, verifyHeaders)
	bc.PostChainEvents(events, logs)
	return n, err
}

// insertChain will execute the actual chain insertion and event aggregation. The
// only reason this method exists as a separate one is to make locking cleaner
// with deferred statements.
func (bc *BlockChain) insertChain(chain types.Blocks, verifyHeaders bool) (int, []interface{}, []*types.Log, error) {
	// Sanity check that we have something meaningful to import
	if len(chain) == 0 {
		return 0, nil, nil, nil
	}
	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 1; i < len(chain); i++ {
		if chain[i].NumberU64() != chain[i-1].NumberU64()+1 || chain[i].ParentHash() != chain[i-1].Hash() {
			// Chain broke ancestry, log a message (programming error) and skip insertion
			utils.Logger().Error().
				Str("number", chain[i].Number().String()).
				Str("hash", chain[i].Hash().Hex()).
				Str("parent", chain[i].ParentHash().Hex()).
				Str("prevnumber", chain[i-1].Number().String()).
				Str("prevhash", chain[i-1].Hash().Hex()).
				Msg("insertChain: non contiguous block insert")

			return 0, nil, nil, fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])", i-1, chain[i-1].NumberU64(),
				chain[i-1].Hash().Bytes()[:4], i, chain[i].NumberU64(), chain[i].Hash().Bytes()[:4], chain[i].ParentHash().Bytes()[:4])
		}
	}
	// Pre-checks passed, start the full block imports
	bc.wg.Add(1)
	defer bc.wg.Done()

	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	// A queued approach to delivering events. This is generally
	// faster than direct delivery and requires much less mutex
	// acquiring.
	var (
		stats         = insertStats{startTime: mclock.Now()}
		events        = make([]interface{}, 0, len(chain))
		lastCanon     *types.Block
		coalescedLogs []*types.Log
	)

	var verifyHeadersResults <-chan error

	// If the block header chain has not been verified, conduct header verification here.
	if verifyHeaders {
		headers := make([]*block.Header, len(chain))
		seals := make([]bool, len(chain))

		for i, block := range chain {
			headers[i] = block.Header()
			seals[i] = true
		}
		// Note that VerifyHeaders verifies headers in the chain in parallel
		abort, results := bc.Engine().VerifyHeaders(bc, headers, seals)
		verifyHeadersResults = results
		defer close(abort)
	}

	// Start a parallel signature recovery (signer will fluke on fork transition, minimal perf loss)
	//senderCacher.recoverFromBlocks(types.MakeSigner(bc.chainConfig, chain[0].Number()), chain)

	// Iterate over the blocks and insert when the verifier permits
	for i, block := range chain {
		// If the chain is terminating, stop processing blocks
		if atomic.LoadInt32(&bc.procInterrupt) == 1 {
			utils.Logger().Debug().Msg("Premature abort during blocks processing")
			break
		}
		// Wait for the block's verification to complete
		bstart := time.Now()

		var err error
		if verifyHeaders {
			err = <-verifyHeadersResults
		}
		if err == nil {
			err = bc.Validator().ValidateBody(block)
		}
		switch {
		case err == ErrKnownBlock:
			// Block and state both already known. However if the current block is below
			// this number we did a rollback and we should reimport it nonetheless.
			if bc.CurrentBlock().NumberU64() >= block.NumberU64() {
				stats.ignored++
				continue
			}

		case err == consensus_engine.ErrFutureBlock:
			// Allow up to MaxFuture second in the future blocks. If this limit is exceeded
			// the chain is discarded and processed at a later time if given.
			max := big.NewInt(time.Now().Unix() + maxTimeFutureBlocks)
			if block.Time().Cmp(max) > 0 {
				return i, events, coalescedLogs, fmt.Errorf("future block: %v > %v", block.Time(), max)
			}
			bc.futureBlocks.Add(block.Hash(), block)
			stats.queued++
			continue

		case err == consensus_engine.ErrUnknownAncestor && bc.futureBlocks.Contains(block.ParentHash()):
			bc.futureBlocks.Add(block.Hash(), block)
			stats.queued++
			continue

		case err == consensus_engine.ErrPrunedAncestor:
			// TODO: add fork choice mechanism
			// Block competing with the canonical chain, store in the db, but don't process
			// until the competitor TD goes above the canonical TD
			//currentBlock := bc.CurrentBlock()
			//localTd := bc.GetTd(currentBlock.Hash(), currentBlock.NumberU64())
			//externTd := new(big.Int).Add(bc.GetTd(block.ParentHash(), block.NumberU64()-1), block.Difficulty())
			//if localTd.Cmp(externTd) > 0 {
			//	if err = bc.WriteBlockWithoutState(block, externTd); err != nil {
			//		return i, events, coalescedLogs, err
			//	}
			//	continue
			//}
			// Competitor chain beat canonical, gather all blocks from the common ancestor
			var winner []*types.Block

			parent := bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
			for parent != nil && !bc.HasState(parent.Root()) {
				winner = append(winner, parent)
				parent = bc.GetBlock(parent.ParentHash(), parent.NumberU64()-1)
			}
			for j := 0; j < len(winner)/2; j++ {
				winner[j], winner[len(winner)-1-j] = winner[len(winner)-1-j], winner[j]
			}
			// Prune in case non-empty winner chain
			if len(winner) > 0 {
				// Import all the pruned blocks to make the state available
				bc.chainmu.Unlock()
				_, evs, logs, err := bc.insertChain(winner, true /* verifyHeaders */)
				bc.chainmu.Lock()
				events, coalescedLogs = evs, logs

				if err != nil {
					return i, events, coalescedLogs, err
				}
			}

		case err != nil:
			bc.reportBlock(block, nil, err)
			return i, events, coalescedLogs, err
		}

		// Create a new statedb using the parent block and report an
		// error if it fails.
		var parent *types.Block
		if i == 0 {
			parent = bc.GetBlock(block.ParentHash(), block.NumberU64()-1)
		} else {
			parent = chain[i-1]
		}
		state, err := state.New(parent.Root(), bc.stateCache)
		if err != nil {
			return i, events, coalescedLogs, err
		}

		// Process block using the parent state as reference point.
		receipts, cxReceipts, logs, usedGas, payout, err := bc.processor.Process(
			block, state, bc.vmConfig,
		)
		if err != nil {
			bc.reportBlock(block, receipts, err)
			return i, events, coalescedLogs, err
		}

		// Validate the state using the default validator
		if err := bc.Validator().ValidateState(
			block, state, receipts, cxReceipts, usedGas,
		); err != nil {
			bc.reportBlock(block, receipts, err)
			return i, events, coalescedLogs, err
		}
		proctime := time.Since(bstart)

		// Write the block to the chain and get the status.
		status, err := bc.WriteBlockWithState(
			block, receipts, cxReceipts, payout, state,
		)
		if err != nil {
			return i, events, coalescedLogs, err
		}
		logger := utils.Logger().With().
			Str("number", block.Number().String()).
			Str("hash", block.Hash().Hex()).
			Int("uncles", len(block.Uncles())).
			Int("txs", len(block.Transactions())).
			Int("stakingTxs", len(block.StakingTransactions())).
			Uint64("gas", block.GasUsed()).
			Str("elapsed", common.PrettyDuration(time.Since(bstart)).String()).
			Logger()

		switch status {
		case CanonStatTy:
			logger.Info().Msg("Inserted new block")
			coalescedLogs = append(coalescedLogs, logs...)
			blockInsertTimer.UpdateSince(bstart)
			events = append(events, ChainEvent{block, block.Hash(), logs})
			lastCanon = block

			// Only count canonical blocks for GC processing time
			bc.gcproc += proctime
		}

		stats.processed++
		stats.usedGas += usedGas
		cache, _ := bc.stateCache.TrieDB().Size()
		stats.report(chain, i, cache)
	}
	// Append a single chain head event if we've progressed the chain
	if lastCanon != nil && bc.CurrentBlock().Hash() == lastCanon.Hash() {
		events = append(events, ChainHeadEvent{lastCanon})
	}

	return 0, events, coalescedLogs, nil
}

// insertStats tracks and reports on block insertion.
type insertStats struct {
	queued, processed, ignored int
	usedGas                    uint64
	lastIndex                  int
	startTime                  mclock.AbsTime
}

// statsReportLimit is the time limit during import and export after which we
// always print out progress. This avoids the user wondering what's going on.
const statsReportLimit = 8 * time.Second

// report prints statistics if some number of blocks have been processed
// or more than a few seconds have passed since the last message.
func (st *insertStats) report(chain []*types.Block, index int, cache common.StorageSize) {
	// Fetch the timings for the batch
	var (
		now     = mclock.Now()
		elapsed = time.Duration(now) - time.Duration(st.startTime)
	)
	// If we're at the last block of the batch or report period reached, log
	if index == len(chain)-1 || elapsed >= statsReportLimit {
		var (
			end = chain[index]
			txs = countTransactions(chain[st.lastIndex : index+1])
		)

		context := utils.Logger().With().
			Int("blocks", st.processed).
			Int("txs", txs).
			Float64("mgas", float64(st.usedGas)/1000000).
			Str("elapsed", common.PrettyDuration(elapsed).String()).
			Float64("mgasps", float64(st.usedGas)*1000/float64(elapsed)).
			Str("number", end.Number().String()).
			Str("hash", end.Hash().Hex()).
			Str("cache", cache.String())

		if timestamp := time.Unix(end.Time().Int64(), 0); time.Since(timestamp) > time.Minute {
			context = context.Str("age", common.PrettyAge(timestamp).String())
		}

		if st.queued > 0 {
			context = context.Int("queued", st.queued)
		}
		if st.ignored > 0 {
			context = context.Int("ignored", st.ignored)
		}

		logger := context.Logger()
		logger.Info().Msg("Imported new chain segment")

		*st = insertStats{startTime: now, lastIndex: index + 1}
	}
}

func countTransactions(chain []*types.Block) (c int) {
	for _, b := range chain {
		c += len(b.Transactions())
	}
	return c
}

// PostChainEvents iterates over the events generated by a chain insertion and
// posts them into the event feed.
// TODO: Should not expose PostChainEvents. The chain events should be posted in WriteBlock.
func (bc *BlockChain) PostChainEvents(events []interface{}, logs []*types.Log) {
	// post event logs for further processing
	if logs != nil {
		bc.logsFeed.Send(logs)
	}
	for _, event := range events {
		switch ev := event.(type) {
		case ChainEvent:
			bc.chainFeed.Send(ev)

		case ChainHeadEvent:
			bc.chainHeadFeed.Send(ev)

		case ChainSideEvent:
			bc.chainSideFeed.Send(ev)
		}
	}
}

func (bc *BlockChain) update() {
	futureTimer := time.NewTicker(5 * time.Second)
	defer futureTimer.Stop()
	for {
		select {
		case <-futureTimer.C:
			bc.procFutureBlocks()
		case <-bc.quit:
			return
		}
	}
}

// BadBlock ..
type BadBlock struct {
	Block  *types.Block
	Reason error
}

// MarshalJSON ..
func (b BadBlock) MarshalJSON() ([]byte, error) {
	return json.Marshal(struct {
		Block  *block.Header `json:"header"`
		Reason string        `json:"error-cause"`
	}{
		b.Block.Header(),
		b.Reason.Error(),
	})
}

// BadBlocks returns a list of the last 'bad blocks' that
// the client has seen on the network
func (bc *BlockChain) BadBlocks() []BadBlock {
	blocks := make([]BadBlock, bc.badBlocks.Len())
	for _, hash := range bc.badBlocks.Keys() {
		if blk, exist := bc.badBlocks.Peek(hash); exist {
			blocks = append(blocks, blk.(BadBlock))
		}
	}
	return blocks
}

// addBadBlock adds a bad block to the bad-block LRU cache
func (bc *BlockChain) addBadBlock(block *types.Block, reason error) {
	bc.badBlocks.Add(block.Hash(), BadBlock{block, reason})
}

// reportBlock logs a bad block error.
func (bc *BlockChain) reportBlock(
	block *types.Block, receipts types.Receipts, err error,
) {
	bc.addBadBlock(block, err)
	var receiptString string
	for _, receipt := range receipts {
		receiptString += fmt.Sprintf("\t%v\n", receipt)
	}
	utils.Logger().Error().Msgf(`
########## BAD BLOCK #########
Chain config: %v

Number: %v
Epoch: %v
NumTxn: %v
NumStkTxn: %v
Hash: 0x%x
%v

Error: %v
##############################
`, bc.chainConfig,
		block.Number(),
		block.Epoch(),
		len(block.Transactions()),
		len(block.StakingTransactions()),
		block.Hash(),
		receiptString,
		err,
	)
	for i, tx := range block.StakingTransactions() {
		utils.Logger().Error().
			Msgf("StakingTxn %d: %s, %v", i, tx.StakingType().String(), tx.StakingMessage())
	}
}

// InsertHeaderChain attempts to insert the given header chain in to the local
// chain, possibly creating a reorg. If an error is returned, it will return the
// index number of the failing header as well an error describing what went wrong.
//
// The verify parameter can be used to fine tune whether nonce verification
// should be done or not. The reason behind the optional check is because some
// of the header retrieval mechanisms already need to verify nonces, as well as
// because nonces can be verified sparsely, not needing to check each.
func (bc *BlockChain) InsertHeaderChain(chain []*block.Header, checkFreq int) (int, error) {
	start := time.Now()
	if i, err := bc.hc.ValidateHeaderChain(chain, checkFreq); err != nil {
		return i, err
	}

	// Make sure only one thread manipulates the chain at once
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	bc.wg.Add(1)
	defer bc.wg.Done()

	whFunc := func(header *block.Header) error {
		bc.mu.Lock()
		defer bc.mu.Unlock()

		_, err := bc.hc.WriteHeader(header)
		return err
	}

	return bc.hc.InsertHeaderChain(chain, whFunc, start)
}

// CurrentHeader retrieves the current head header of the canonical chain. The
// header is retrieved from the HeaderChain's internal cache.
func (bc *BlockChain) CurrentHeader() *block.Header {
	return bc.hc.CurrentHeader()
}

// GetTd retrieves a block's total difficulty in the canonical chain from the
// database by hash and number, caching it if found.
func (bc *BlockChain) GetTd(hash common.Hash, number uint64) *big.Int {
	return bc.hc.GetTd(hash, number)
}

// GetTdByHash retrieves a block's total difficulty in the canonical chain from the
// database by hash, caching it if found.
func (bc *BlockChain) GetTdByHash(hash common.Hash) *big.Int {
	return bc.hc.GetTdByHash(hash)
}

// GetHeader retrieves a block header from the database by hash and number,
// caching it if found.
func (bc *BlockChain) GetHeader(hash common.Hash, number uint64) *block.Header {
	return bc.hc.GetHeader(hash, number)
}

// GetHeaderByHash retrieves a block header from the database by hash, caching it if
// found.
func (bc *BlockChain) GetHeaderByHash(hash common.Hash) *block.Header {
	return bc.hc.GetHeaderByHash(hash)
}

// HasHeader checks if a block header is present in the database or not, caching
// it if present.
func (bc *BlockChain) HasHeader(hash common.Hash, number uint64) bool {
	return bc.hc.HasHeader(hash, number)
}

// GetBlockHashesFromHash retrieves a number of block hashes starting at a given
// hash, fetching towards the genesis block.
func (bc *BlockChain) GetBlockHashesFromHash(hash common.Hash, max uint64) []common.Hash {
	return bc.hc.GetBlockHashesFromHash(hash, max)
}

// GetAncestor retrieves the Nth ancestor of a given block. It assumes that either the given block or
// a close ancestor of it is canonical. maxNonCanonical points to a downwards counter limiting the
// number of blocks to be individually checked before we reach the canonical chain.
//
// Note: ancestor == 0 returns the same block, 1 returns its parent and so on.
func (bc *BlockChain) GetAncestor(hash common.Hash, number, ancestor uint64, maxNonCanonical *uint64) (common.Hash, uint64) {
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	return bc.hc.GetAncestor(hash, number, ancestor, maxNonCanonical)
}

// GetHeaderByNumber retrieves a block header from the database by number,
// caching it (associated with its hash) if found.
func (bc *BlockChain) GetHeaderByNumber(number uint64) *block.Header {
	return bc.hc.GetHeaderByNumber(number)
}

// Config retrieves the blockchain's chain configuration.
func (bc *BlockChain) Config() *params.ChainConfig { return bc.chainConfig }

// Engine retrieves the blockchain's consensus engine.
func (bc *BlockChain) Engine() consensus_engine.Engine { return bc.engine }

// SubscribeRemovedLogsEvent registers a subscription of RemovedLogsEvent.
func (bc *BlockChain) SubscribeRemovedLogsEvent(ch chan<- RemovedLogsEvent) event.Subscription {
	return bc.scope.Track(bc.rmLogsFeed.Subscribe(ch))
}

// SubscribeChainEvent registers a subscription of ChainEvent.
func (bc *BlockChain) SubscribeChainEvent(ch chan<- ChainEvent) event.Subscription {
	return bc.scope.Track(bc.chainFeed.Subscribe(ch))
}

// SubscribeChainHeadEvent registers a subscription of ChainHeadEvent.
func (bc *BlockChain) SubscribeChainHeadEvent(ch chan<- ChainHeadEvent) event.Subscription {
	return bc.scope.Track(bc.chainHeadFeed.Subscribe(ch))
}

// SubscribeChainSideEvent registers a subscription of ChainSideEvent.
func (bc *BlockChain) SubscribeChainSideEvent(ch chan<- ChainSideEvent) event.Subscription {
	return bc.scope.Track(bc.chainSideFeed.Subscribe(ch))
}

// SubscribeLogsEvent registers a subscription of []*types.Log.
func (bc *BlockChain) SubscribeLogsEvent(ch chan<- []*types.Log) event.Subscription {
	return bc.scope.Track(bc.logsFeed.Subscribe(ch))
}

// ReadShardState retrieves sharding state given the epoch number.
func (bc *BlockChain) ReadShardState(epoch *big.Int) (*shard.State, error) {
	cacheKey := string(epoch.Bytes())
	if cached, ok := bc.shardStateCache.Get(cacheKey); ok {
		shardState := cached.(*shard.State)
		return shardState, nil
	}
	shardState, err := rawdb.ReadShardState(bc.db, epoch)
	if err != nil {
		return nil, err
	}
	bc.shardStateCache.Add(cacheKey, shardState)
	return shardState, nil
}

// WriteShardStateBytes saves the given sharding state under the given epoch number.
func (bc *BlockChain) WriteShardStateBytes(db rawdb.DatabaseWriter,
	epoch *big.Int, shardState []byte,
) (*shard.State, error) {
	decodeShardState, err := shard.DecodeWrapper(shardState)
	if err != nil {
		return nil, err
	}
	err = rawdb.WriteShardStateBytes(db, epoch, shardState)
	if err != nil {
		return nil, err
	}
	cacheKey := string(epoch.Bytes())
	bc.shardStateCache.Add(cacheKey, decodeShardState)
	return decodeShardState, nil
}

// ReadLastCommits retrieves last commits.
func (bc *BlockChain) ReadLastCommits() ([]byte, error) {
	if cached, ok := bc.lastCommitsCache.Get("lastCommits"); ok {
		lastCommits := cached.([]byte)
		return lastCommits, nil
	}
	lastCommits, err := rawdb.ReadLastCommits(bc.db)
	if err != nil {
		return nil, err
	}
	return lastCommits, nil
}

// WriteLastCommits saves the commits of last block.
func (bc *BlockChain) WriteLastCommits(lastCommits []byte) error {
	err := rawdb.WriteLastCommits(bc.db, lastCommits)
	if err != nil {
		return err
	}
	bc.lastCommitsCache.Add("lastCommits", lastCommits)
	return nil
}

// GetVdfByNumber retrieves the rand seed given the block number, return 0 if not exist
func (bc *BlockChain) GetVdfByNumber(number uint64) []byte {
	header := bc.GetHeaderByNumber(number)
	if header == nil {
		return []byte{}
	}

	return header.Vdf()
}

// GetVrfByNumber retrieves the randomness preimage given the block number, return 0 if not exist
func (bc *BlockChain) GetVrfByNumber(number uint64) []byte {
	header := bc.GetHeaderByNumber(number)
	if header == nil {
		return []byte{}
	}
	return header.Vrf()
}

// ChainDb returns the database
func (bc *BlockChain) ChainDb() ethdb.Database { return bc.db }

// GetEpochBlockNumber returns the first block number of the given epoch.
func (bc *BlockChain) GetEpochBlockNumber(epoch *big.Int) (*big.Int, error) {
	// Try cache first
	cacheKey := string(epoch.Bytes())
	if cachedValue, ok := bc.epochCache.Get(cacheKey); ok {
		return (&big.Int{}).SetBytes([]byte(cachedValue.(string))), nil
	}
	blockNum, err := rawdb.ReadEpochBlockNumber(bc.db, epoch)
	if err != nil {
		return nil, errors.Wrapf(
			err, "cannot read epoch block number from database",
		)
	}
	cachedValue := []byte(blockNum.Bytes())
	bc.epochCache.Add(cacheKey, cachedValue)
	return blockNum, nil
}

// StoreEpochBlockNumber stores the given epoch-first block number.
func (bc *BlockChain) StoreEpochBlockNumber(
	epoch *big.Int, blockNum *big.Int,
) error {
	cacheKey := string(epoch.Bytes())
	cachedValue := []byte(blockNum.Bytes())
	bc.epochCache.Add(cacheKey, cachedValue)
	if err := rawdb.WriteEpochBlockNumber(bc.db, epoch, blockNum); err != nil {
		return errors.Wrapf(
			err, "cannot write epoch block number to database",
		)
	}
	return nil
}

// ReadEpochVrfBlockNums retrieves block numbers with valid VRF for the specified epoch
func (bc *BlockChain) ReadEpochVrfBlockNums(epoch *big.Int) ([]uint64, error) {
	vrfNumbers := []uint64{}
	if cached, ok := bc.randomnessCache.Get("vrf-" + string(epoch.Bytes())); ok {
		encodedVrfNumbers := cached.([]byte)
		if err := rlp.DecodeBytes(encodedVrfNumbers, &vrfNumbers); err != nil {
			return nil, err
		}
		return vrfNumbers, nil
	}

	encodedVrfNumbers, err := rawdb.ReadEpochVrfBlockNums(bc.db, epoch)
	if err != nil {
		return nil, err
	}

	if err := rlp.DecodeBytes(encodedVrfNumbers, &vrfNumbers); err != nil {
		return nil, err
	}
	return vrfNumbers, nil
}

// WriteEpochVrfBlockNums saves block numbers with valid VRF for the specified epoch
func (bc *BlockChain) WriteEpochVrfBlockNums(epoch *big.Int, vrfNumbers []uint64) error {
	encodedVrfNumbers, err := rlp.EncodeToBytes(vrfNumbers)
	if err != nil {
		return err
	}

	err = rawdb.WriteEpochVrfBlockNums(bc.db, epoch, encodedVrfNumbers)
	if err != nil {
		return err
	}
	bc.randomnessCache.Add("vrf-"+string(epoch.Bytes()), encodedVrfNumbers)
	return nil
}

// ReadEpochVdfBlockNum retrieves block number with valid VDF for the specified epoch
func (bc *BlockChain) ReadEpochVdfBlockNum(epoch *big.Int) (*big.Int, error) {
	if cached, ok := bc.randomnessCache.Get("vdf-" + string(epoch.Bytes())); ok {
		encodedVdfNumber := cached.([]byte)
		return new(big.Int).SetBytes(encodedVdfNumber), nil
	}

	encodedVdfNumber, err := rawdb.ReadEpochVdfBlockNum(bc.db, epoch)
	if err != nil {
		return nil, err
	}
	return new(big.Int).SetBytes(encodedVdfNumber), nil
}

// WriteEpochVdfBlockNum saves block number with valid VDF for the specified epoch
func (bc *BlockChain) WriteEpochVdfBlockNum(epoch *big.Int, blockNum *big.Int) error {
	err := rawdb.WriteEpochVdfBlockNum(bc.db, epoch, blockNum.Bytes())
	if err != nil {
		return err
	}

	bc.randomnessCache.Add("vdf-"+string(epoch.Bytes()), blockNum.Bytes())
	return nil
}

// WriteCrossLinks saves the hashes of crosslinks by shardID and blockNum combination key
func (bc *BlockChain) WriteCrossLinks(batch rawdb.DatabaseWriter, cls []types.CrossLink) error {
	var err error
	for i := 0; i < len(cls); i++ {
		cl := cls[i]
		err = rawdb.WriteCrossLinkShardBlock(batch, cl.ShardID(), cl.BlockNum(), cl.Serialize())
	}
	return err
}

// DeleteCrossLinks removes the hashes of crosslinks by shardID and blockNum combination key
func (bc *BlockChain) DeleteCrossLinks(cls []types.CrossLink) error {
	var err error
	for i := 0; i < len(cls); i++ {
		cl := cls[i]
		err = rawdb.DeleteCrossLinkShardBlock(bc.db, cl.ShardID(), cl.BlockNum())
	}
	return err
}

// ReadCrossLink retrieves crosslink given shardID and blockNum.
func (bc *BlockChain) ReadCrossLink(shardID uint32, blockNum uint64) (*types.CrossLink, error) {
	bytes, err := rawdb.ReadCrossLinkShardBlock(bc.db, shardID, blockNum)
	if err != nil {
		return nil, err
	}
	crossLink, err := types.DeserializeCrossLink(bytes)

	return crossLink, err
}

// LastContinuousCrossLink saves the last crosslink of a shard
// This function will update the latest crosslink in the sense that
// any previous block's crosslink is received up to this point
// there is no missing hole between genesis to this crosslink of given shardID
func (bc *BlockChain) LastContinuousCrossLink(batch rawdb.DatabaseWriter, shardID uint32) error {
	oldLink, err := bc.ReadShardLastCrossLink(shardID)
	if oldLink == nil || err != nil {
		return err
	}
	newLink := oldLink
	// Starting from last checkpoint, keeping reading immediate next crosslink until there is a gap
	for i := oldLink.BlockNum() + 1; ; i++ {
		tmp, err := bc.ReadCrossLink(shardID, i)
		if err == nil && tmp != nil && tmp.BlockNum() == i {
			newLink = tmp
		} else {
			break
		}
	}

	if newLink.BlockNum() > oldLink.BlockNum() {
		utils.Logger().Debug().Msgf("LastContinuousCrossLink: latest checkpoint blockNum %d", newLink.BlockNum())
		return rawdb.WriteShardLastCrossLink(batch, shardID, newLink.Serialize())
	}
	return nil
}

// ReadShardLastCrossLink retrieves the last crosslink of a shard.
func (bc *BlockChain) ReadShardLastCrossLink(shardID uint32) (*types.CrossLink, error) {
	bytes, err := rawdb.ReadShardLastCrossLink(bc.db, shardID)
	if err != nil {
		return nil, err
	}
	return types.DeserializeCrossLink(bytes)
}

func (bc *BlockChain) writeSlashes(processed slash.Records) error {
	bytes, err := rlp.EncodeToBytes(processed)
	if err != nil {
		const msg = "failed to encode slashing candidates"
		utils.Logger().Error().Msg(msg)
		return err
	}
	if err := rawdb.WritePendingSlashingCandidates(bc.db, bytes); err != nil {
		return err
	}
	return nil
}

// DeleteFromPendingSlashingCandidates ..
func (bc *BlockChain) DeleteFromPendingSlashingCandidates(
	processed slash.Records,
) error {
	bc.pendingSlashingCandidatesMU.Lock()
	defer bc.pendingSlashingCandidatesMU.Unlock()
	current := bc.ReadPendingSlashingCandidates()
	bc.pendingSlashes = current.SetDifference(processed)
	return bc.writeSlashes(bc.pendingSlashes)
}

// ReadPendingSlashingCandidates retrieves pending slashing candidates
func (bc *BlockChain) ReadPendingSlashingCandidates() slash.Records {
	if !bc.Config().IsStaking(bc.CurrentHeader().Epoch()) {
		return slash.Records{}
	}
	return append(bc.pendingSlashes[0:0], bc.pendingSlashes...)
}

// ReadPendingCrossLinks retrieves pending crosslinks
func (bc *BlockChain) ReadPendingCrossLinks() ([]types.CrossLink, error) {
	bytes := []byte{}
	if cached, ok := bc.pendingCrossLinksCache.Get(pendingCLCacheKey); ok {
		bytes = cached.([]byte)
	} else {
		bytes, err := rawdb.ReadPendingCrossLinks(bc.db)
		if err != nil || len(bytes) == 0 {
			return nil, err
		}
	}
	cls := []types.CrossLink{}
	if err := rlp.DecodeBytes(bytes, &cls); err != nil {
		utils.Logger().Error().Err(err).Msg("Invalid pending crosslink RLP decoding")
		return nil, err
	}
	return cls, nil
}

// WritePendingCrossLinks saves the pending crosslinks
func (bc *BlockChain) WritePendingCrossLinks(crossLinks []types.CrossLink) error {
	// deduplicate crosslinks if any
	m := map[uint32]map[uint64](types.CrossLink){}
	for _, cl := range crossLinks {
		if _, ok := m[cl.ShardID()]; !ok {
			m[cl.ShardID()] = map[uint64](types.CrossLink){}
		}
		m[cl.ShardID()][cl.BlockNum()] = cl
	}

	cls := []types.CrossLink{}
	for _, m1 := range m {
		for _, cl := range m1 {
			cls = append(cls, cl)
		}
	}
	utils.Logger().Debug().Msgf("[WritePendingCrossLinks] Before Dedup has %d cls, after Dedup has %d cls", len(crossLinks), len(cls))

	bytes, err := rlp.EncodeToBytes(cls)
	if err != nil {
		utils.Logger().Error().Msg("[WritePendingCrossLinks] Failed to encode pending crosslinks")
		return err
	}
	if err := rawdb.WritePendingCrossLinks(bc.db, bytes); err != nil {
		return err
	}
	by, err := rlp.EncodeToBytes(cls)
	if err == nil {
		bc.pendingCrossLinksCache.Add(pendingCLCacheKey, by)
	}
	return nil

}

// AddPendingSlashingCandidates appends pending slashing candidates
func (bc *BlockChain) AddPendingSlashingCandidates(
	candidates slash.Records,
) error {
	bc.pendingSlashingCandidatesMU.Lock()
	defer bc.pendingSlashingCandidatesMU.Unlock()
	current := bc.ReadPendingSlashingCandidates()

	state, err := bc.State()
	if err != nil {
		return err
	}

	valid := slash.Records{}
	for i := range candidates {
		if err := slash.Verify(bc, state, &candidates[i]); err == nil {
			valid = append(valid, candidates[i])
		}
	}

	pendingSlashes := append(
		bc.pendingSlashes, current.SetDifference(valid)...,
	)

	if l, c := len(pendingSlashes), len(current); l > maxPendingSlashes {
		return errors.Wrapf(
			errExceedMaxPendingSlashes, "current %d with-additional %d", c, l,
		)
	}
	bc.pendingSlashes = pendingSlashes
	return bc.writeSlashes(bc.pendingSlashes)
}

// AddPendingCrossLinks appends pending crosslinks
func (bc *BlockChain) AddPendingCrossLinks(pendingCLs []types.CrossLink) (int, error) {
	bc.pendingCrossLinksMutex.Lock()
	defer bc.pendingCrossLinksMutex.Unlock()

	cls, err := bc.ReadPendingCrossLinks()
	if err != nil || len(cls) == 0 {
		err := bc.WritePendingCrossLinks(pendingCLs)
		return len(pendingCLs), err
	}
	cls = append(cls, pendingCLs...)
	err = bc.WritePendingCrossLinks(cls)
	return len(cls), err
}

// DeleteFromPendingCrossLinks delete pending crosslinks that already committed (i.e. passed in the params)
func (bc *BlockChain) DeleteFromPendingCrossLinks(crossLinks []types.CrossLink) (int, error) {
	bc.pendingCrossLinksMutex.Lock()
	defer bc.pendingCrossLinksMutex.Unlock()

	cls, err := bc.ReadPendingCrossLinks()
	if err != nil || len(cls) == 0 {
		return 0, err
	}

	m := map[uint32]map[uint64](struct{}){}
	for _, cl := range crossLinks {
		if _, ok := m[cl.ShardID()]; !ok {
			m[cl.ShardID()] = map[uint64](struct{}){}
		}
		m[cl.ShardID()][cl.BlockNum()] = struct{}{}
	}

	pendingCLs := []types.CrossLink{}

	for _, cl := range cls {
		if _, ok := m[cl.ShardID()]; ok {
			if _, ok1 := m[cl.ShardID()][cl.BlockNum()]; ok1 {
				continue
			}
		}
		pendingCLs = append(pendingCLs, cl)
	}
	err = bc.WritePendingCrossLinks(pendingCLs)
	return len(pendingCLs), err
}

// IsSameLeaderAsPreviousBlock retrieves a block from the database by number, caching it
func (bc *BlockChain) IsSameLeaderAsPreviousBlock(block *types.Block) bool {
	if IsEpochBlock(block) {
		return false
	}

	previousHeader := bc.GetHeaderByNumber(block.NumberU64() - 1)
	return block.Coinbase() == previousHeader.Coinbase()
}

// ChainDB ...
// TODO(ricl): in eth, this is not exposed. I expose it here because I need it in Harmony object.
// In eth, chainDB is initialized within Ethereum object
func (bc *BlockChain) ChainDB() ethdb.Database {
	return bc.db
}

// GetVMConfig returns the block chain VM config.
func (bc *BlockChain) GetVMConfig() *vm.Config {
	return &bc.vmConfig
}

// ReadCXReceipts retrieves the cross shard transaction receipts of a given shard
func (bc *BlockChain) ReadCXReceipts(shardID uint32, blockNum uint64, blockHash common.Hash) (types.CXReceipts, error) {
	cxs, err := rawdb.ReadCXReceipts(bc.db, shardID, blockNum, blockHash)
	if err != nil || len(cxs) == 0 {
		return nil, err
	}
	return cxs, nil
}

// CXMerkleProof calculates the cross shard transaction merkle proof of a given destination shard
func (bc *BlockChain) CXMerkleProof(toShardID uint32, block *types.Block) (*types.CXMerkleProof, error) {
	proof := &types.CXMerkleProof{BlockNum: block.Number(), BlockHash: block.Hash(), ShardID: block.ShardID(), CXReceiptHash: block.Header().OutgoingReceiptHash(), CXShardHashes: []common.Hash{}, ShardIDs: []uint32{}}

	epoch := block.Header().Epoch()
	shardingConfig := shard.Schedule.InstanceForEpoch(epoch)
	shardNum := int(shardingConfig.NumShards())

	for i := 0; i < shardNum; i++ {
		receipts, err := bc.ReadCXReceipts(uint32(i), block.NumberU64(), block.Hash())
		if err != nil || len(receipts) == 0 {
			continue
		} else {
			hash := types.DeriveSha(receipts)
			proof.CXShardHashes = append(proof.CXShardHashes, hash)
			proof.ShardIDs = append(proof.ShardIDs, uint32(i))
		}
	}
	if len(proof.ShardIDs) == 0 {
		return nil, nil
	}
	return proof, nil
}

// WriteCXReceiptsProofSpent mark the CXReceiptsProof list with given unspent status
// true: unspent, false: spent
func (bc *BlockChain) WriteCXReceiptsProofSpent(db rawdb.DatabaseWriter, cxps []*types.CXReceiptsProof) {
	for _, cxp := range cxps {
		rawdb.WriteCXReceiptsProofSpent(db, cxp)
	}
}

// IsSpent checks whether a CXReceiptsProof is unspent
func (bc *BlockChain) IsSpent(cxp *types.CXReceiptsProof) bool {
	shardID := cxp.MerkleProof.ShardID
	blockNum := cxp.MerkleProof.BlockNum.Uint64()
	by, _ := rawdb.ReadCXReceiptsProofSpent(bc.db, shardID, blockNum)
	return by == rawdb.SpentByte
}

// ReadTxLookupEntry returns where the given transaction resides in the chain,
// as a (block hash, block number, index in transaction list) triple.
// returns 0, 0 if not found
func (bc *BlockChain) ReadTxLookupEntry(txID common.Hash) (common.Hash, uint64, uint64) {
	return rawdb.ReadTxLookupEntry(bc.db, txID)
}

// ReadValidatorInformationAt reads staking
// information of given validatorWrapper at a specific state root
func (bc *BlockChain) ReadValidatorInformationAt(
	addr common.Address, root common.Hash,
) (*staking.ValidatorWrapper, error) {
	state, err := bc.StateAt(root)
	if err != nil || state == nil {
		return nil, errors.Wrapf(err, "at root: %s", root.Hex())
	}
	wrapper, err := state.ValidatorWrapper(addr)
	if err != nil {
		return nil, errors.Wrapf(err, "at root: %s", root.Hex())
	}
	return wrapper, nil
}

// ReadValidatorInformation reads staking information of given validator address
func (bc *BlockChain) ReadValidatorInformation(
	addr common.Address,
) (*staking.ValidatorWrapper, error) {
	return bc.ReadValidatorInformationAt(addr, bc.CurrentBlock().Root())
}

// ReadValidatorSnapshotAtEpoch reads the snapshot
// staking validator information of given validator address
func (bc *BlockChain) ReadValidatorSnapshotAtEpoch(
	epoch *big.Int,
	addr common.Address,
) (*staking.ValidatorSnapshot, error) {
	return rawdb.ReadValidatorSnapshot(bc.db, addr, epoch)
}

// ReadValidatorSnapshot reads the snapshot staking information of given validator address
func (bc *BlockChain) ReadValidatorSnapshot(
	addr common.Address,
) (*staking.ValidatorSnapshot, error) {
	epoch := bc.CurrentBlock().Epoch()
	key := addr.Hex() + epoch.String()
	if cached, ok := bc.validatorSnapshotCache.Get(key); ok {
		return cached.(*staking.ValidatorSnapshot), nil
	}
	return rawdb.ReadValidatorSnapshot(bc.db, addr, epoch)
}

// WriteValidatorSnapshot writes the snapshot of provided validator
func (bc *BlockChain) WriteValidatorSnapshot(
	batch rawdb.DatabaseWriter, snapshot *staking.ValidatorSnapshot,
) error {
	// Batch write the current data as snapshot
	if err := rawdb.WriteValidatorSnapshot(batch, snapshot.Validator, snapshot.Epoch); err != nil {
		return err
	}

	// Update cache
	key := snapshot.Validator.Address.Hex() + snapshot.Epoch.String()
	bc.validatorSnapshotCache.Add(key, snapshot)
	return nil
}

// ReadValidatorStats reads the stats of a validator
func (bc *BlockChain) ReadValidatorStats(
	addr common.Address,
) (*staking.ValidatorStats, error) {
	return rawdb.ReadValidatorStats(bc.db, addr)
}

// UpdateValidatorVotingPower writes the voting power for the committees
func (bc *BlockChain) UpdateValidatorVotingPower(
	batch rawdb.DatabaseWriter,
	block *types.Block,
	newEpochSuperCommittee, currentEpochSuperCommittee *shard.State,
	state *state.DB,
) (map[common.Address]*staking.ValidatorStats, error) {
	if newEpochSuperCommittee == nil {
		return nil, shard.ErrSuperCommitteeNil
	}

	validatorStats := map[common.Address]*staking.ValidatorStats{}

	existing, replacing :=
		currentEpochSuperCommittee.StakedValidators(),
		newEpochSuperCommittee.StakedValidators()

	// TODO could also keep track of the BLS keys which
	// lost a slot because just losing slots doesn't mean that the
	// validator was booted, just that some of their keys lost slots
	for currentValidator := range existing.LookupSet {
		if _, keptSlot := replacing.LookupSet[currentValidator]; !keptSlot {
			// NOTE Think carefully about when time comes to delete offchain things
			// TODO Someone: collect and then delete every 30 epochs
			// rawdb.DeleteValidatorSnapshot(
			// 	bc.db, currentValidator, currentEpochSuperCommittee.Epoch,
			// )
			// rawdb.DeleteValidatorStats(bc.db, currentValidator)
			stats, err := rawdb.ReadValidatorStats(bc.db, currentValidator)
			if err != nil {
				stats = staking.NewEmptyStats()
			}
			// This means it's already in staking epoch
			if currentEpochSuperCommittee.Epoch != nil {
				wrapper, err := state.ValidatorWrapper(currentValidator)
				if err != nil {
					return nil, err
				}

				if slash.IsBanned(wrapper) {
					stats.BootedStatus = effective.BannedForDoubleSigning
				} else if wrapper.Status == effective.Inactive {
					stats.BootedStatus = effective.TurnedInactiveOrInsufficientUptime
				} else {
					stats.BootedStatus = effective.LostEPoSAuction
				}
			}
			validatorStats[currentValidator] = stats
		}
	}

	rosters := make([]*votepower.Roster, len(newEpochSuperCommittee.Shards))
	for i := range newEpochSuperCommittee.Shards {
		subCommittee := &newEpochSuperCommittee.Shards[i]
		if newEpochSuperCommittee.Epoch == nil {
			return nil, errors.Wrapf(
				errNilEpoch,
				"block epoch %v current-committee-epoch %v",
				block.Epoch(),
				currentEpochSuperCommittee.Epoch,
			)
		}
		roster, err := votepower.Compute(subCommittee, newEpochSuperCommittee.Epoch)
		if err != nil {
			return nil, err
		}
		rosters[i] = roster
	}

	networkWide := votepower.AggregateRosters(rosters)
	for key, value := range networkWide {
		stats, err := rawdb.ReadValidatorStats(bc.db, key)
		if err != nil {
			stats = staking.NewEmptyStats()
		}
		total := numeric.ZeroDec()
		for i := range value {
			total = total.Add(value[i].EffectiveStake)
		}
		stats.TotalEffectiveStake = total
		earningWrapping := make([]staking.VoteWithCurrentEpochEarning, len(value))
		for i := range value {
			earningWrapping[i] = staking.VoteWithCurrentEpochEarning{
				Vote:   value[i],
				Earned: big.NewInt(0),
			}
		}
		stats.MetricsPerShard = earningWrapping

		// This means it's already in staking epoch
		if currentEpochSuperCommittee.Epoch != nil {
			wrapper, err := state.ValidatorWrapper(key)
			if err != nil {
				return nil, err
			}

			stats.APR = numeric.ZeroDec()
			if wrapper.Delegations[0].Amount.Cmp(common.Big0) > 0 {
				if aprComputed, err := apr.ComputeForValidator(
					bc, block, wrapper,
				); err != nil {
					if errors.Cause(err) == apr.ErrInsufficientEpoch {
						utils.Logger().Info().Err(err).Msg("apr could not be computed")
					} else {
						return nil, err
					}
				} else {
					stats.APR = *aprComputed
				}
			} else {
				utils.Logger().Info().Msg("zero total delegation, skipping apr computation")
			}
		}
		validatorStats[key] = stats
	}

	return validatorStats, nil
}

// UpdateValidatorSnapshots updates the content snapshot of all validators
// Note: this should only be called within the blockchain insert process.
func (bc *BlockChain) UpdateValidatorSnapshots(
	batch rawdb.DatabaseWriter, epoch *big.Int, state *state.DB, newValidators []common.Address,
) error {
	// Note this is reading the validator list from last block.
	// It's fine since the new validators from this block is already snapshot when created.
	allValidators, err := bc.ReadValidatorList()
	if err != nil {
		return err
	}

	allValidators = append(allValidators, newValidators...)

	// Read all validator's current data and snapshot them
	for i := range allValidators {
		// The snapshot will be captured in the state after the last epoch block is finalized
		validator, err := state.ValidatorWrapper(allValidators[i])
		if err != nil {
			return err
		}

		snapshot := &staking.ValidatorSnapshot{validator, epoch}
		if err := bc.WriteValidatorSnapshot(batch, snapshot); err != nil {
			return err
		}
	}

	return nil
}

// ReadValidatorList reads the addresses of current all validators
func (bc *BlockChain) ReadValidatorList() ([]common.Address, error) {
	if cached, ok := bc.validatorListCache.Get("validatorList"); ok {
		by := cached.([]byte)
		m := []common.Address{}
		if err := rlp.DecodeBytes(by, &m); err != nil {
			return nil, err
		}
		return m, nil
	}
	return rawdb.ReadValidatorList(bc.db)
}

// WriteValidatorList writes the list of validator addresses to database
// Note: this should only be called within the blockchain insert process.
func (bc *BlockChain) WriteValidatorList(
	db rawdb.DatabaseWriter, addrs []common.Address,
) error {
	if err := rawdb.WriteValidatorList(db, addrs); err != nil {
		return err
	}
	bytes, err := rlp.EncodeToBytes(addrs)
	if err == nil {
		bc.validatorListCache.Add("validatorList", bytes)
	}
	return nil
}

// ReadDelegationsByDelegator reads the addresses of validators delegated by a delegator
func (bc *BlockChain) ReadDelegationsByDelegator(
	delegator common.Address,
) (m staking.DelegationIndexes, err error) {
	rawResult := staking.DelegationIndexes{}
	if cached, ok := bc.validatorListByDelegatorCache.Get(string(delegator.Bytes())); ok {
		by := cached.([]byte)
		if err := rlp.DecodeBytes(by, &rawResult); err != nil {
			return nil, err
		}
	} else {
		if rawResult, err = rawdb.ReadDelegationsByDelegator(bc.db, delegator); err != nil {
			return nil, err
		}
	}
	blockNum := bc.CurrentBlock().Number()
	for _, index := range rawResult {
		if index.BlockNum.Cmp(blockNum) <= 0 {
			m = append(m, index)
		} else {
			// Filter out index that's created beyond current height of chain.
			// This only happens when there is a chain rollback.
			utils.Logger().Warn().Msgf("Future delegation index encountered. Skip: %+v", index)
		}
	}
	return m, nil
}

// writeDelegationsByDelegator writes the list of validator addresses to database
func (bc *BlockChain) writeDelegationsByDelegator(
	batch rawdb.DatabaseWriter,
	delegator common.Address,
	indices []staking.DelegationIndex,
) error {
	if err := rawdb.WriteDelegationsByDelegator(
		batch, delegator, indices,
	); err != nil {
		return err
	}
	bytes, err := rlp.EncodeToBytes(indices)
	if err == nil {
		bc.validatorListByDelegatorCache.Add(string(delegator.Bytes()), bytes)
	}
	return nil
}

// UpdateStakingMetaData updates the metadata of validators and delegations,
// including the full validator list and delegation indexes.
// Note: this should only be called within the blockchain insert process.
func (bc *BlockChain) UpdateStakingMetaData(
	batch rawdb.DatabaseWriter, block *types.Block,
	state *state.DB, epoch, newEpoch *big.Int,
) (newValidators []common.Address, err error) {
	newValidators, newDelegations, err := bc.prepareStakingMetaData(block, state)
	if err != nil {
		utils.Logger().Warn().Msgf("oops, prepareStakingMetaData failed, err: %+v", err)
		return newValidators, err
	}

	if len(newValidators) > 0 {
		list, err := bc.ReadValidatorList()
		if err != nil {
			return newValidators, err
		}

		valMap := map[common.Address]struct{}{}
		for _, addr := range list {
			valMap[addr] = struct{}{}
		}

		newAddrs := []common.Address{}
		for _, addr := range newValidators {
			if _, ok := valMap[addr]; !ok {
				newAddrs = append(newAddrs, addr)
			}

			// Update validator snapshot for the new validator
			validator, err := state.ValidatorWrapper(addr)
			if err != nil {
				return newValidators, err
			}

			if err := bc.WriteValidatorSnapshot(batch, &staking.ValidatorSnapshot{validator, epoch}); err != nil {
				return newValidators, err
			}
			// For validator created at exactly the last block of an epoch, we should create the snapshot
			// for next epoch too.
			if newEpoch.Cmp(epoch) > 0 {
				if err := bc.WriteValidatorSnapshot(batch, &staking.ValidatorSnapshot{validator, newEpoch}); err != nil {
					return newValidators, err
				}
			}
		}

		// Update validator list
		list = append(list, newAddrs...)
		if err = bc.WriteValidatorList(batch, list); err != nil {
			return newValidators, err
		}
	}

	for addr, delegations := range newDelegations {
		if err := bc.writeDelegationsByDelegator(batch, addr, delegations); err != nil {
			return newValidators, err
		}
	}
	return newValidators, nil
}

// prepareStakingMetaData prepare the updates of validator's
// and the delegator's meta data according to staking transaction.
// The following return values are cached end state to be written to DB.
// The reason for the cached state is to solve the issue that batch DB changes
// won't be reflected immediately so the intermediary state can't be read from DB.
// newValidators - the addresses of the newly created validators
// newDelegations - the map of delegator address and their updated delegation indexes
func (bc *BlockChain) prepareStakingMetaData(
	block *types.Block, state *state.DB,
) (newValidators []common.Address,
	newDelegations map[common.Address]staking.DelegationIndexes,
	err error,
) {
	newDelegations = map[common.Address]staking.DelegationIndexes{}
	blockNum := block.Number()
	for _, txn := range block.StakingTransactions() {
		payload, err := txn.RLPEncodeStakeMsg()
		if err != nil {
			return nil, nil, err
		}
		decodePayload, err := staking.RLPDecodeStakeMsg(payload, txn.StakingType())
		if err != nil {
			return nil, nil, err
		}

		switch txn.StakingType() {
		case staking.DirectiveCreateValidator:
			createValidator := decodePayload.(*staking.CreateValidator)
			newList, appended := utils.AppendIfMissing(
				newValidators, createValidator.ValidatorAddress,
			)
			if !appended {
				return nil, nil, errValidatorExist
			}
			newValidators = newList

			// Add self delegation into the index
			selfIndex := staking.DelegationIndex{
				createValidator.ValidatorAddress,
				uint64(0),
				blockNum,
			}
			delegations, ok := newDelegations[createValidator.ValidatorAddress]
			if ok {
				delegations = append(delegations, selfIndex)
			} else {
				delegations = staking.DelegationIndexes{selfIndex}
			}
			newDelegations[createValidator.ValidatorAddress] = delegations
		case staking.DirectiveEditValidator:
		case staking.DirectiveDelegate:
			delegate := decodePayload.(*staking.Delegate)

			delegations, ok := newDelegations[delegate.DelegatorAddress]
			if !ok {
				// If the cache doesn't have it, load it from DB for the first time.
				delegations, err = bc.ReadDelegationsByDelegator(delegate.DelegatorAddress)
				if err != nil {
					return nil, nil, err
				}
			}
			if delegations, err = bc.addDelegationIndex(
				delegations, delegate.DelegatorAddress, delegate.ValidatorAddress, state, blockNum,
			); err != nil {
				return nil, nil, err
			}
			newDelegations[delegate.DelegatorAddress] = delegations
		case staking.DirectiveUndelegate:
		case staking.DirectiveCollectRewards:
		default:
		}
	}

	return newValidators, newDelegations, nil
}

// ReadBlockRewardAccumulator must only be called on beaconchain
func (bc *BlockChain) ReadBlockRewardAccumulator(number uint64) (*big.Int, error) {
	if !bc.chainConfig.IsStaking(shard.Schedule.CalcEpochNumber(number)) {
		return big.NewInt(0), nil
	}
	if cached, ok := bc.blockAccumulatorCache.Get(number); ok {
		return cached.(*big.Int), nil
	}
	return rawdb.ReadBlockRewardAccumulator(bc.db, number)
}

// WriteBlockRewardAccumulator directly writes the BlockRewardAccumulator value
// Note: this should only be called once during staking launch.
func (bc *BlockChain) WriteBlockRewardAccumulator(
	batch rawdb.DatabaseWriter, reward *big.Int, number uint64,
) error {
	if err := rawdb.WriteBlockRewardAccumulator(
		batch, reward, number,
	); err != nil {
		return err
	}
	bc.blockAccumulatorCache.Add(number, reward)
	return nil
}

// UpdateBlockRewardAccumulator ..
// Note: this should only be called within the blockchain insert process.
func (bc *BlockChain) UpdateBlockRewardAccumulator(
	batch rawdb.DatabaseWriter, diff *big.Int, number uint64,
) error {
	current, err := bc.ReadBlockRewardAccumulator(number - 1)
	if err != nil {
		// one-off fix for pangaea, return after pangaea enter staking.
		current = big.NewInt(0)
		bc.WriteBlockRewardAccumulator(batch, current, number)
	}
	return bc.WriteBlockRewardAccumulator(batch, new(big.Int).Add(current, diff), number)
}

// Note this should read from the state of current block in concern (root == newBlock.root)
func (bc *BlockChain) addDelegationIndex(
	delegations staking.DelegationIndexes,
	delegatorAddress, validatorAddress common.Address, state *state.DB, blockNum *big.Int,
) (staking.DelegationIndexes, error) {
	// If there is an existing delegation, just return
	validatorAddressBytes := validatorAddress.Bytes()
	for _, delegation := range delegations {
		if bytes.Equal(delegation.ValidatorAddress[:], validatorAddressBytes[:]) {
			return delegations, nil
		}
	}

	// Found the delegation from state and add the delegation index
	// Note this should read from the state of current block in concern
	wrapper, err := state.ValidatorWrapper(validatorAddress)
	if err != nil {
		return delegations, err
	}
	for i := range wrapper.Delegations {
		if bytes.Equal(
			wrapper.Delegations[i].DelegatorAddress[:], delegatorAddress[:],
		) {
			// TODO(audit): change the way of indexing if we allow delegation deletion.
			delegations = append(delegations, staking.DelegationIndex{
				validatorAddress,
				uint64(i),
				blockNum,
			})
		}
	}
	return delegations, nil
}

// ValidatorCandidates returns the up to date validator candidates for next epoch
func (bc *BlockChain) ValidatorCandidates() []common.Address {
	list, err := bc.ReadValidatorList()
	if err != nil {
		return make([]common.Address, 0)
	}
	return list
}

// DelegatorsInformation returns up to date information of delegators of a given validator address
func (bc *BlockChain) DelegatorsInformation(addr common.Address) []*staking.Delegation {
	return make([]*staking.Delegation, 0)
}

// GetECDSAFromCoinbase retrieve corresponding ecdsa address from Coinbase Address
func (bc *BlockChain) GetECDSAFromCoinbase(header *block.Header) (common.Address, error) {
	// backward compatibility: before isStaking epoch, coinbase address is the ecdsa address
	coinbase := header.Coinbase()
	isStaking := bc.Config().IsStaking(header.Epoch())
	if !isStaking {
		return coinbase, nil
	}

	shardState, err := bc.ReadShardState(header.Epoch())
	if err != nil {
		return common.Address{}, errors.Wrapf(
			err, "cannot read shard state",
		)
	}

	committee, err := shardState.FindCommitteeByID(header.ShardID())
	if err != nil {
		return common.Address{}, errors.Wrapf(
			err, "cannot find shard in the shard state",
		)
	}
	for _, member := range committee.Slots {
		// After staking the coinbase address will be the address of bls public key
		if bytes.Equal(member.EcdsaAddress[:], coinbase[:]) {
			return member.EcdsaAddress, nil
		}

		if utils.GetAddressFromBLSPubKeyBytes(member.BLSPublicKey[:]) == coinbase {
			return member.EcdsaAddress, nil
		}
	}
	return common.Address{}, errors.Errorf(
		"cannot find corresponding ECDSA Address for coinbase %s",
		header.Coinbase().Hash().Hex(),
	)
}

// SuperCommitteeForNextEpoch ...
// isVerify=true means validators use it to verify
// isVerify=false means leader is to propose
func (bc *BlockChain) SuperCommitteeForNextEpoch(
	beacon consensus_engine.ChainReader,
	header *block.Header,
	isVerify bool,
) (*shard.State, error) {
	var (
		nextCommittee = new(shard.State)
		err           error
		beaconEpoch   = new(big.Int)
		shardState    = shard.State{}
	)
	switch header.ShardID() {
	case shard.BeaconChainShardID:
		if shard.Schedule.IsLastBlock(header.Number().Uint64()) {
			nextCommittee, err = committee.WithStakingEnabled.Compute(
				new(big.Int).Add(header.Epoch(), common.Big1),
				beacon,
			)
		}
	default:
		// TODO: needs to make sure beacon chain sync works.
		if isVerify {
			//verify
			shardState, err = header.GetShardState()
			if err != nil {
				return &shard.State{}, err
			}
			// before staking epoch
			if shardState.Epoch == nil {
				beaconEpoch = new(big.Int).Add(header.Epoch(), common.Big1)
			} else { // after staking epoch
				beaconEpoch = shardState.Epoch
			}
		} else {
			//propose
			beaconEpoch = beacon.CurrentHeader().Epoch()
		}
		utils.Logger().Debug().Msgf("[SuperCommitteeCalculation] isVerify: %+v, realBeaconEpoch:%+v, beaconEpoch: %+v, headerEpoch:%+v, shardStateEpoch:%+v",
			isVerify, beacon.CurrentHeader().Epoch(), beaconEpoch, header.Epoch(), shardState.Epoch)
		nextEpoch := new(big.Int).Add(header.Epoch(), common.Big1)
		if bc.Config().IsStaking(nextEpoch) {
			// If next epoch is staking epoch, I should wait and listen for beacon chain for epoch changes
			switch beaconEpoch.Cmp(header.Epoch()) {
			case 1:
				// If beacon chain is bigger than shard chain in epoch, it means I should catch up with beacon chain now
				nextCommittee, err = committee.WithStakingEnabled.ReadFromDB(
					beaconEpoch, beacon,
				)

				utils.Logger().Debug().
					Uint64("blockNum", header.Number().Uint64()).
					Uint64("myCurEpoch", header.Epoch().Uint64()).
					Uint64("beaconEpoch", beaconEpoch.Uint64()).
					Msg("Propose new epoch as beacon chain's epoch")
			case 0:
				// If it's same epoch, no need to propose new shard state (new epoch change)
			case -1:
				// If beacon chain is behind, shard chain should wait for the beacon chain by not changing epochs.
			}
		} else {
			if bc.Config().IsStaking(beaconEpoch) {
				// If I am not even in the last epoch before staking epoch and beacon chain is already in staking epoch,
				// I should just catch up with beacon chain's epoch
				nextCommittee, err = committee.WithStakingEnabled.ReadFromDB(
					beaconEpoch, beacon,
				)

				utils.Logger().Debug().
					Uint64("blockNum", header.Number().Uint64()).
					Uint64("myCurEpoch", header.Epoch().Uint64()).
					Uint64("beaconEpoch", beaconEpoch.Uint64()).
					Msg("Propose entering staking along with beacon chain's epoch")
			} else {
				// If I are not in staking nor has beacon chain proposed a staking-based shard state,
				// do pre-staking committee calculation
				if shard.Schedule.IsLastBlock(header.Number().Uint64()) {
					nextCommittee, err = committee.WithStakingEnabled.Compute(
						nextEpoch,
						bc,
					)
				}
			}
		}

	}
	return nextCommittee, err
}