// 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 (
	"errors"
	"fmt"
	"io"
	"math/big"
	mrand "math/rand"
	"sort"
	"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/consensus"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/trie"
	lru "github.com/hashicorp/golang-lru"
)

var (
	headBlockGauge     = metrics.NewRegisteredGauge("chain/head/block", nil)
	headHeaderGauge    = metrics.NewRegisteredGauge("chain/head/header", nil)
	headFastBlockGauge = metrics.NewRegisteredGauge("chain/head/receipt", nil)

	accountReadTimer   = metrics.NewRegisteredTimer("chain/account/reads", nil)
	accountHashTimer   = metrics.NewRegisteredTimer("chain/account/hashes", nil)
	accountUpdateTimer = metrics.NewRegisteredTimer("chain/account/updates", nil)
	accountCommitTimer = metrics.NewRegisteredTimer("chain/account/commits", nil)

	storageReadTimer   = metrics.NewRegisteredTimer("chain/storage/reads", nil)
	storageHashTimer   = metrics.NewRegisteredTimer("chain/storage/hashes", nil)
	storageUpdateTimer = metrics.NewRegisteredTimer("chain/storage/updates", nil)
	storageCommitTimer = metrics.NewRegisteredTimer("chain/storage/commits", nil)

	blockInsertTimer     = metrics.NewRegisteredTimer("chain/inserts", nil)
	blockValidationTimer = metrics.NewRegisteredTimer("chain/validation", nil)
	blockExecutionTimer  = metrics.NewRegisteredTimer("chain/execution", nil)
	blockWriteTimer      = metrics.NewRegisteredTimer("chain/write", nil)
	blockReorgAddMeter   = metrics.NewRegisteredMeter("chain/reorg/drop", nil)
	blockReorgDropMeter  = metrics.NewRegisteredMeter("chain/reorg/add", nil)

	blockPrefetchExecuteTimer   = metrics.NewRegisteredTimer("chain/prefetch/executes", nil)
	blockPrefetchInterruptMeter = metrics.NewRegisteredMeter("chain/prefetch/interrupts", nil)

	errInsertionInterrupted = errors.New("insertion is interrupted")
)

const (
	bodyCacheLimit      = 256
	blockCacheLimit     = 256
	receiptsCacheLimit  = 32
	txLookupCacheLimit  = 1024
	maxFutureBlocks     = 256
	maxTimeFutureBlocks = 30
	badBlockLimit       = 10
	TriesInMemory       = 128

	// BlockChainVersion ensures that an incompatible database forces a resync from scratch.
	//
	// Changelog:
	//
	// - Version 4
	//   The following incompatible database changes were added:
	//   * the `BlockNumber`, `TxHash`, `TxIndex`, `BlockHash` and `Index` fields of log are deleted
	//   * the `Bloom` field of receipt is deleted
	//   * the `BlockIndex` and `TxIndex` fields of txlookup are deleted
	// - Version 5
	//  The following incompatible database changes were added:
	//    * the `TxHash`, `GasCost`, and `ContractAddress` fields are no longer stored for a receipt
	//    * the `TxHash`, `GasCost`, and `ContractAddress` fields are computed by looking up the
	//      receipts' corresponding block
	// - Version 6
	//  The following incompatible database changes were added:
	//    * Transaction lookup information stores the corresponding block number instead of block hash
	// - Version 7
	//  The following incompatible database changes were added:
	//    * Use freezer as the ancient database to maintain all ancient data
	BlockChainVersion uint64 = 7
)

// CacheConfig contains the configuration values for the trie caching/pruning
// that's resident in a blockchain.
type CacheConfig struct {
	TrieCleanLimit      int           // Memory allowance (MB) to use for caching trie nodes in memory
	TrieCleanNoPrefetch bool          // Whether to disable heuristic state prefetching for followup blocks
	TrieDirtyLimit      int           // Memory limit (MB) at which to start flushing dirty trie nodes to disk
	TrieDirtyDisabled   bool          // Whether to disable trie write caching and GC altogether (archive node)
	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
	blockProcFeed event.Feed
	scope         event.SubscriptionScope
	genesisBlock  *types.Block

	chainmu sync.RWMutex // blockchain insertion lock

	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
	txLookupCache *lru.Cache     // Cache for the most recent transaction lookup data.
	futureBlocks  *lru.Cache     // future blocks are blocks added for later processing

	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
	validator  Validator  // Block and state validator interface
	prefetcher Prefetcher // Block state prefetcher interface
	processor  Processor  // Block transaction processor 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.
	terminateInsert func(common.Hash, uint64) bool // Testing hook used to terminate ancient receipt chain insertion.
}

// 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, vmConfig vm.Config, shouldPreserve func(block *types.Block) bool) (*BlockChain, error) {
	if cacheConfig == nil {
		cacheConfig = &CacheConfig{
			TrieCleanLimit: 256,
			TrieDirtyLimit: 256,
			TrieTimeLimit:  5 * time.Minute,
		}
	}
	bodyCache, _ := lru.New(bodyCacheLimit)
	bodyRLPCache, _ := lru.New(bodyCacheLimit)
	receiptsCache, _ := lru.New(receiptsCacheLimit)
	blockCache, _ := lru.New(blockCacheLimit)
	txLookupCache, _ := lru.New(txLookupCacheLimit)
	futureBlocks, _ := lru.New(maxFutureBlocks)
	badBlocks, _ := lru.New(badBlockLimit)

	bc := &BlockChain{
		chainConfig:    chainConfig,
		cacheConfig:    cacheConfig,
		db:             db,
		triegc:         prque.New(nil),
		stateCache:     state.NewDatabaseWithCache(db, cacheConfig.TrieCleanLimit),
		quit:           make(chan struct{}),
		shouldPreserve: shouldPreserve,
		bodyCache:      bodyCache,
		bodyRLPCache:   bodyRLPCache,
		receiptsCache:  receiptsCache,
		blockCache:     blockCache,
		txLookupCache:  txLookupCache,
		futureBlocks:   futureBlocks,
		engine:         engine,
		vmConfig:       vmConfig,
		badBlocks:      badBlocks,
	}
	bc.validator = NewBlockValidator(chainConfig, bc, engine)
	bc.prefetcher = newStatePrefetcher(chainConfig, bc, engine)
	bc.processor = 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)

	// Initialize the chain with ancient data if it isn't empty.
	if bc.empty() {
		rawdb.InitDatabaseFromFreezer(bc.db)
	}

	if err := bc.loadLastState(); err != nil {
		return nil, err
	}
	// The first thing the node will do is reconstruct the verification data for
	// the head block (ethash cache or clique voting snapshot). Might as well do
	// it in advance.
	bc.engine.VerifyHeader(bc, bc.CurrentHeader(), true)

	if frozen, err := bc.db.Ancients(); err == nil && frozen > 0 {
		var (
			needRewind bool
			low        uint64
		)
		// The head full block may be rolled back to a very low height due to
		// blockchain repair. If the head full block is even lower than the ancient
		// chain, truncate the ancient store.
		fullBlock := bc.CurrentBlock()
		if fullBlock != nil && fullBlock != bc.genesisBlock && fullBlock.NumberU64() < frozen-1 {
			needRewind = true
			low = fullBlock.NumberU64()
		}
		// In fast sync, it may happen that ancient data has been written to the
		// ancient store, but the LastFastBlock has not been updated, truncate the
		// extra data here.
		fastBlock := bc.CurrentFastBlock()
		if fastBlock != nil && fastBlock.NumberU64() < frozen-1 {
			needRewind = true
			if fastBlock.NumberU64() < low || low == 0 {
				low = fastBlock.NumberU64()
			}
		}
		if needRewind {
			var hashes []common.Hash
			previous := bc.CurrentHeader().Number.Uint64()
			for i := low + 1; i <= bc.CurrentHeader().Number.Uint64(); i++ {
				hashes = append(hashes, rawdb.ReadCanonicalHash(bc.db, i))
			}
			bc.Rollback(hashes)
			log.Warn("Truncate ancient chain", "from", previous, "to", low)
		}
	}
	// Check the current state of the block hashes and make sure that we do not have any of the bad blocks in our chain
	for hash := range BadHashes {
		if header := bc.GetHeaderByHash(hash); header != nil {
			// get the canonical block corresponding to the offending header's number
			headerByNumber := bc.GetHeaderByNumber(header.Number.Uint64())
			// make sure the headerByNumber (if present) is in our current canonical chain
			if headerByNumber != nil && headerByNumber.Hash() == header.Hash() {
				log.Error("Found bad hash, rewinding chain", "number", header.Number, "hash", header.ParentHash)
				bc.SetHead(header.Number.Uint64() - 1)
				log.Error("Chain rewind was successful, resuming normal operation")
			}
		}
	}
	// Take ownership of this particular state
	go bc.update()
	return bc, nil
}

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

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

// empty returns an indicator whether the blockchain is empty.
// Note, it's a special case that we connect a non-empty ancient
// database with an empty node, so that we can plugin the ancient
// into node seamlessly.
func (bc *BlockChain) empty() bool {
	genesis := bc.genesisBlock.Hash()
	for _, hash := range []common.Hash{rawdb.ReadHeadBlockHash(bc.db), rawdb.ReadHeadHeaderHash(bc.db), rawdb.ReadHeadFastBlockHash(bc.db)} {
		if hash != genesis {
			return false
		}
	}
	return true
}

// 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
		log.Warn("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
		log.Warn("Head block missing, resetting chain", "hash", head)
		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
		log.Warn("Head state missing, repairing chain", "number", currentBlock.Number(), "hash", currentBlock.Hash())
		if err := bc.repair(&currentBlock); err != nil {
			return err
		}
		rawdb.WriteHeadBlockHash(bc.db, currentBlock.Hash())
	}
	// Everything seems to be fine, set as the head block
	bc.currentBlock.Store(currentBlock)
	headBlockGauge.Update(int64(currentBlock.NumberU64()))

	// 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
		}
	}
	bc.hc.SetCurrentHeader(currentHeader)

	// Restore the last known head fast block
	bc.currentFastBlock.Store(currentBlock)
	headFastBlockGauge.Update(int64(currentBlock.NumberU64()))

	if head := rawdb.ReadHeadFastBlockHash(bc.db); head != (common.Hash{}) {
		if block := bc.GetBlockByHash(head); block != nil {
			bc.currentFastBlock.Store(block)
			headFastBlockGauge.Update(int64(block.NumberU64()))
		}
	}
	// 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())

	log.Info("Loaded most recent local header", "number", currentHeader.Number, "hash", currentHeader.Hash(), "td", headerTd, "age", common.PrettyAge(time.Unix(int64(currentHeader.Time), 0)))
	log.Info("Loaded most recent local full block", "number", currentBlock.Number(), "hash", currentBlock.Hash(), "td", blockTd, "age", common.PrettyAge(time.Unix(int64(currentBlock.Time()), 0)))
	log.Info("Loaded most recent local fast block", "number", currentFastBlock.Number(), "hash", currentFastBlock.Hash(), "td", fastTd, "age", common.PrettyAge(time.Unix(int64(currentFastBlock.Time()), 0)))

	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 {
	log.Warn("Rewinding blockchain", "target", head)

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

	updateFn := func(db ethdb.KeyValueWriter, header *types.Header) {
		// Rewind the block chain, ensuring we don't end up with a stateless head block
		if currentBlock := bc.CurrentBlock(); currentBlock != nil && header.Number.Uint64() < currentBlock.NumberU64() {
			newHeadBlock := bc.GetBlock(header.Hash(), header.Number.Uint64())
			if newHeadBlock == nil {
				newHeadBlock = bc.genesisBlock
			} else {
				if _, err := state.New(newHeadBlock.Root(), bc.stateCache); err != nil {
					// Rewound state missing, rolled back to before pivot, reset to genesis
					newHeadBlock = bc.genesisBlock
				}
			}
			rawdb.WriteHeadBlockHash(db, newHeadBlock.Hash())

			// Degrade the chain markers if they are explicitly reverted.
			// In theory we should update all in-memory markers in the
			// last step, however the direction of SetHead is from high
			// to low, so it's safe the update in-memory markers directly.
			bc.currentBlock.Store(newHeadBlock)
			headBlockGauge.Update(int64(newHeadBlock.NumberU64()))
		}

		// Rewind the fast block in a simpleton way to the target head
		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock != nil && header.Number.Uint64() < currentFastBlock.NumberU64() {
			newHeadFastBlock := bc.GetBlock(header.Hash(), header.Number.Uint64())
			// If either blocks reached nil, reset to the genesis state
			if newHeadFastBlock == nil {
				newHeadFastBlock = bc.genesisBlock
			}
			rawdb.WriteHeadFastBlockHash(db, newHeadFastBlock.Hash())

			// Degrade the chain markers if they are explicitly reverted.
			// In theory we should update all in-memory markers in the
			// last step, however the direction of SetHead is from high
			// to low, so it's safe the update in-memory markers directly.
			bc.currentFastBlock.Store(newHeadFastBlock)
			headFastBlockGauge.Update(int64(newHeadFastBlock.NumberU64()))
		}
	}

	// Rewind the header chain, deleting all block bodies until then
	delFn := func(db ethdb.KeyValueWriter, hash common.Hash, num uint64) {
		// Ignore the error here since light client won't hit this path
		frozen, _ := bc.db.Ancients()
		if num+1 <= frozen {
			// Truncate all relative data(header, total difficulty, body, receipt
			// and canonical hash) from ancient store.
			if err := bc.db.TruncateAncients(num + 1); err != nil {
				log.Crit("Failed to truncate ancient data", "number", num, "err", err)
			}

			// Remove the hash <-> number mapping from the active store.
			rawdb.DeleteHeaderNumber(db, hash)
		} else {
			// Remove relative body and receipts from the active store.
			// The header, total difficulty and canonical hash will be
			// removed in the hc.SetHead function.
			rawdb.DeleteBody(db, hash, num)
			rawdb.DeleteReceipts(db, hash, num)
		}
		// Todo(rjl493456442) txlookup, bloombits, etc
	}
	bc.hc.SetHead(head, updateFn, delFn)

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

	return bc.loadLastState()
}

// FastSyncCommitHead sets the current head block to the one defined by the hash
// irrelevant what the chain contents were prior.
func (bc *BlockChain) FastSyncCommitHead(hash common.Hash) error {
	// Make sure that both the block as well at its state trie exists
	block := bc.GetBlockByHash(hash)
	if block == nil {
		return fmt.Errorf("non existent block [%x…]", hash[:4])
	}
	if _, err := trie.NewSecure(block.Root(), bc.stateCache.TrieDB()); err != nil {
		return err
	}
	// If all checks out, manually set the head block
	bc.chainmu.Lock()
	bc.currentBlock.Store(block)
	headBlockGauge.Update(int64(block.NumberU64()))
	bc.chainmu.Unlock()

	log.Info("Committed new head block", "number", block.Number(), "hash", hash)
	return nil
}

// 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)
}

// SetCurrentBlock is used for testing
func (bc *BlockChain) SetCurrentBlock(block *types.Block) {
	bc.currentBlock.Store(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)
}

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

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

// State returns a new mutable state based on the current HEAD block.
func (bc *BlockChain) State() (*state.StateDB, 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.StateDB, error) {
	return state.New(root, bc.stateCache)
}

// StateCache returns the caching database underpinning the blockchain instance.
func (bc *BlockChain) StateCache() state.Database {
	return 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.chainmu.Lock()
	defer bc.chainmu.Unlock()

	// Prepare the genesis block and reinitialise the chain
	batch := bc.db.NewBatch()
	rawdb.WriteTd(batch, genesis.Hash(), genesis.NumberU64(), genesis.Difficulty())
	rawdb.WriteBlock(batch, genesis)
	if err := batch.Write(); err != nil {
		log.Crit("Failed to write genesis block", "err", err)
	}
	bc.writeHeadBlock(genesis)

	// Last update all in-memory chain markers
	bc.genesisBlock = genesis
	bc.currentBlock.Store(bc.genesisBlock)
	headBlockGauge.Update(int64(bc.genesisBlock.NumberU64()))
	bc.hc.SetGenesis(bc.genesisBlock.Header())
	bc.hc.SetCurrentHeader(bc.genesisBlock.Header())
	bc.currentFastBlock.Store(bc.genesisBlock)
	headFastBlockGauge.Update(int64(bc.genesisBlock.NumberU64()))
	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 {
			log.Info("Rewound blockchain to past state", "number", (*head).Number(), "hash", (*head).Hash())
			return nil
		}
		// Otherwise rewind one block and recheck state availability there
		block := bc.GetBlock((*head).ParentHash(), (*head).NumberU64()-1)
		if block == nil {
			return fmt.Errorf("missing block %d [%x]", (*head).NumberU64()-1, (*head).ParentHash())
		}
		*head = block
	}
}

// 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.chainmu.RLock()
	defer bc.chainmu.RUnlock()

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

	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 {
			log.Info("Exporting blocks", "exported", block.NumberU64()-first, "elapsed", common.PrettyDuration(time.Since(start)))
			reported = time.Now()
		}
	}
	return nil
}

// writeHeadBlock 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) writeHeadBlock(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
	batch := bc.db.NewBatch()
	rawdb.WriteCanonicalHash(batch, block.Hash(), block.NumberU64())
	rawdb.WriteTxLookupEntries(batch, block)
	rawdb.WriteHeadBlockHash(batch, block.Hash())

	// If the block is better than our head or is on a different chain, force update heads
	if updateHeads {
		rawdb.WriteHeadHeaderHash(batch, block.Hash())
		rawdb.WriteHeadFastBlockHash(batch, block.Hash())
	}
	// Flush the whole batch into the disk, exit the node if failed
	if err := batch.Write(); err != nil {
		log.Crit("Failed to update chain indexes and markers", "err", err)
	}
	// Update all in-memory chain markers in the last step
	if updateHeads {
		bc.hc.SetCurrentHeader(block.Header())
		bc.currentFastBlock.Store(block)
		headFastBlockGauge.Update(int64(block.NumberU64()))
	}
	bc.currentBlock.Store(block)
	headBlockGauge.Update(int64(block.NumberU64()))
}

// 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)
}

// HasFastBlock checks if a fast block is fully present in the database or not.
func (bc *BlockChain) HasFastBlock(hash common.Hash, number uint64) bool {
	if !bc.HasBlock(hash, number) {
		return false
	}
	if bc.receiptsCache.Contains(hash) {
		return true
	}
	return rawdb.HasReceipts(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.chainConfig)
	if receipts == nil {
		return nil
	}
	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(block *types.Block, length int) []*types.Header {
	uncles := []*types.Header{}
	for i := 0; block != nil && i < length; i++ {
		uncles = append(uncles, block.Uncles()...)
		block = bc.GetBlock(block.ParentHash(), block.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.TrieDirtyDisabled {
		triedb := bc.stateCache.TrieDB()

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

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

	log.Info("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 {
		sort.Slice(blocks, func(i, j int) bool {
			return blocks[i].NumberU64() < blocks[j].NumberU64()
		})
		// Insert one by one as chain insertion needs contiguous ancestry between blocks
		for i := range blocks {
			bc.InsertChain(blocks[i : i+1])
		}
	}
}

// WriteStatus status of write
type WriteStatus byte

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

	batch := bc.db.NewBatch()
	for i := len(chain) - 1; i >= 0; i-- {
		hash := chain[i]

		// Degrade the chain markers if they are explicitly reverted.
		// In theory we should update all in-memory markers in the
		// last step, however the direction of rollback is from high
		// to low, so it's safe the update in-memory markers directly.
		currentHeader := bc.hc.CurrentHeader()
		if currentHeader.Hash() == hash {
			newHeadHeader := bc.GetHeader(currentHeader.ParentHash, currentHeader.Number.Uint64()-1)
			rawdb.WriteHeadHeaderHash(batch, currentHeader.ParentHash)
			bc.hc.SetCurrentHeader(newHeadHeader)
		}
		if currentFastBlock := bc.CurrentFastBlock(); currentFastBlock.Hash() == hash {
			newFastBlock := bc.GetBlock(currentFastBlock.ParentHash(), currentFastBlock.NumberU64()-1)
			rawdb.WriteHeadFastBlockHash(batch, currentFastBlock.ParentHash())
			bc.currentFastBlock.Store(newFastBlock)
			headFastBlockGauge.Update(int64(newFastBlock.NumberU64()))
		}
		if currentBlock := bc.CurrentBlock(); currentBlock.Hash() == hash {
			newBlock := bc.GetBlock(currentBlock.ParentHash(), currentBlock.NumberU64()-1)
			rawdb.WriteHeadBlockHash(batch, currentBlock.ParentHash())
			bc.currentBlock.Store(newBlock)
			headBlockGauge.Update(int64(newBlock.NumberU64()))
		}
	}
	if err := batch.Write(); err != nil {
		log.Crit("Failed to rollback chain markers", "err", err)
	}
	// Truncate ancient data which exceeds the current header.
	//
	// Notably, it can happen that system crashes without truncating the ancient data
	// but the head indicator has been updated in the active store. Regarding this issue,
	// system will self recovery by truncating the extra data during the setup phase.
	if err := bc.truncateAncient(bc.hc.CurrentHeader().Number.Uint64()); err != nil {
		log.Crit("Truncate ancient store failed", "err", err)
	}
}

// truncateAncient rewinds the blockchain to the specified header and deletes all
// data in the ancient store that exceeds the specified header.
func (bc *BlockChain) truncateAncient(head uint64) error {
	frozen, err := bc.db.Ancients()
	if err != nil {
		return err
	}
	// Short circuit if there is no data to truncate in ancient store.
	if frozen <= head+1 {
		return nil
	}
	// Truncate all the data in the freezer beyond the specified head
	if err := bc.db.TruncateAncients(head + 1); err != nil {
		return err
	}
	// Clear out any stale content from the caches
	bc.hc.headerCache.Purge()
	bc.hc.tdCache.Purge()
	bc.hc.numberCache.Purge()

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

	log.Info("Rewind ancient data", "number", head)
	return nil
}

// numberHash is just a container for a number and a hash, to represent a block
type numberHash struct {
	number uint64
	hash   common.Hash
}

// InsertReceiptChain attempts to complete an already existing header chain with
// transaction and receipt data.
func (bc *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain []types.Receipts, ancientLimit uint64) (int, error) {
	// We don't require the chainMu here since we want to maximize the
	// concurrency of header insertion and receipt insertion.
	bc.wg.Add(1)
	defer bc.wg.Done()

	var (
		ancientBlocks, liveBlocks     types.Blocks
		ancientReceipts, liveReceipts []types.Receipts
	)
	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 0; i < len(blockChain); i++ {
		if i != 0 {
			if blockChain[i].NumberU64() != blockChain[i-1].NumberU64()+1 || blockChain[i].ParentHash() != blockChain[i-1].Hash() {
				log.Error("Non contiguous receipt insert", "number", blockChain[i].Number(), "hash", blockChain[i].Hash(), "parent", blockChain[i].ParentHash(),
					"prevnumber", blockChain[i-1].Number(), "prevhash", blockChain[i-1].Hash())
				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])
			}
		}
		if blockChain[i].NumberU64() <= ancientLimit {
			ancientBlocks, ancientReceipts = append(ancientBlocks, blockChain[i]), append(ancientReceipts, receiptChain[i])
		} else {
			liveBlocks, liveReceipts = append(liveBlocks, blockChain[i]), append(liveReceipts, receiptChain[i])
		}
	}

	var (
		stats = struct{ processed, ignored int32 }{}
		start = time.Now()
		size  = 0
	)
	// updateHead updates the head fast sync block if the inserted blocks are better
	// and returns a indicator whether the inserted blocks are canonical.
	updateHead := func(head *types.Block) bool {
		bc.chainmu.Lock()

		// Rewind may have occurred, skip in that case.
		if bc.CurrentHeader().Number.Cmp(head.Number()) >= 0 {
			currentFastBlock, td := bc.CurrentFastBlock(), bc.GetTd(head.Hash(), head.NumberU64())
			if bc.GetTd(currentFastBlock.Hash(), currentFastBlock.NumberU64()).Cmp(td) < 0 {
				rawdb.WriteHeadFastBlockHash(bc.db, head.Hash())
				bc.currentFastBlock.Store(head)
				headFastBlockGauge.Update(int64(head.NumberU64()))
				bc.chainmu.Unlock()
				return true
			}
		}
		bc.chainmu.Unlock()
		return false
	}
	// writeAncient writes blockchain and corresponding receipt chain into ancient store.
	//
	// this function only accepts canonical chain data. All side chain will be reverted
	// eventually.
	writeAncient := func(blockChain types.Blocks, receiptChain []types.Receipts) (int, error) {
		var (
			previous = bc.CurrentFastBlock()
			batch    = bc.db.NewBatch()
		)
		// If any error occurs before updating the head or we are inserting a side chain,
		// all the data written this time wll be rolled back.
		defer func() {
			if previous != nil {
				if err := bc.truncateAncient(previous.NumberU64()); err != nil {
					log.Crit("Truncate ancient store failed", "err", err)
				}
			}
		}()
		var deleted []*numberHash
		for i, block := range blockChain {
			// Short circuit insertion if shutting down or processing failed
			if atomic.LoadInt32(&bc.procInterrupt) == 1 {
				return 0, errInsertionInterrupted
			}
			// Short circuit insertion if it is required(used in testing only)
			if bc.terminateInsert != nil && bc.terminateInsert(block.Hash(), block.NumberU64()) {
				return i, errors.New("insertion is terminated for testing purpose")
			}
			// 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])
			}
			var (
				start  = time.Now()
				logged = time.Now()
				count  int
			)
			// Migrate all ancient blocks. This can happen if someone upgrades from Geth
			// 1.8.x to 1.9.x mid-fast-sync. Perhaps we can get rid of this path in the
			// long term.
			for {
				// We can ignore the error here since light client won't hit this code path.
				frozen, _ := bc.db.Ancients()
				if frozen >= block.NumberU64() {
					break
				}
				h := rawdb.ReadCanonicalHash(bc.db, frozen)
				b := rawdb.ReadBlock(bc.db, h, frozen)
				size += rawdb.WriteAncientBlock(bc.db, b, rawdb.ReadReceipts(bc.db, h, frozen, bc.chainConfig), rawdb.ReadTd(bc.db, h, frozen))
				count += 1

				// Always keep genesis block in active database.
				if b.NumberU64() != 0 {
					deleted = append(deleted, &numberHash{b.NumberU64(), b.Hash()})
				}
				if time.Since(logged) > 8*time.Second {
					log.Info("Migrating ancient blocks", "count", count, "elapsed", common.PrettyDuration(time.Since(start)))
					logged = time.Now()
				}
				// Don't collect too much in-memory, write it out every 100K blocks
				if len(deleted) > 100000 {
					// Sync the ancient store explicitly to ensure all data has been flushed to disk.
					if err := bc.db.Sync(); err != nil {
						return 0, err
					}
					// Wipe out canonical block data.
					for _, nh := range deleted {
						rawdb.DeleteBlockWithoutNumber(batch, nh.hash, nh.number)
						rawdb.DeleteCanonicalHash(batch, nh.number)
					}
					if err := batch.Write(); err != nil {
						return 0, err
					}
					batch.Reset()
					// Wipe out side chain too.
					for _, nh := range deleted {
						for _, hash := range rawdb.ReadAllHashes(bc.db, nh.number) {
							rawdb.DeleteBlock(batch, hash, nh.number)
						}
					}
					if err := batch.Write(); err != nil {
						return 0, err
					}
					batch.Reset()
					deleted = deleted[0:]
				}
			}
			if count > 0 {
				log.Info("Migrated ancient blocks", "count", count, "elapsed", common.PrettyDuration(time.Since(start)))
			}
			// Flush data into ancient database.
			size += rawdb.WriteAncientBlock(bc.db, block, receiptChain[i], bc.GetTd(block.Hash(), block.NumberU64()))
			rawdb.WriteTxLookupEntries(batch, block)

			stats.processed++
		}
		// Flush all tx-lookup index data.
		size += batch.ValueSize()
		if err := batch.Write(); err != nil {
			return 0, err
		}
		batch.Reset()

		// Sync the ancient store explicitly to ensure all data has been flushed to disk.
		if err := bc.db.Sync(); err != nil {
			return 0, err
		}
		if !updateHead(blockChain[len(blockChain)-1]) {
			return 0, errors.New("side blocks can't be accepted as the ancient chain data")
		}
		previous = nil // disable rollback explicitly

		// Wipe out canonical block data.
		for _, nh := range deleted {
			rawdb.DeleteBlockWithoutNumber(batch, nh.hash, nh.number)
			rawdb.DeleteCanonicalHash(batch, nh.number)
		}
		for _, block := range blockChain {
			// Always keep genesis block in active database.
			if block.NumberU64() != 0 {
				rawdb.DeleteBlockWithoutNumber(batch, block.Hash(), block.NumberU64())
				rawdb.DeleteCanonicalHash(batch, block.NumberU64())
			}
		}
		if err := batch.Write(); err != nil {
			return 0, err
		}
		batch.Reset()

		// Wipe out side chain too.
		for _, nh := range deleted {
			for _, hash := range rawdb.ReadAllHashes(bc.db, nh.number) {
				rawdb.DeleteBlock(batch, hash, nh.number)
			}
		}
		for _, block := range blockChain {
			// Always keep genesis block in active database.
			if block.NumberU64() != 0 {
				for _, hash := range rawdb.ReadAllHashes(bc.db, block.NumberU64()) {
					rawdb.DeleteBlock(batch, hash, block.NumberU64())
				}
			}
		}
		if err := batch.Write(); err != nil {
			return 0, err
		}
		return 0, nil
	}
	// writeLive writes blockchain and corresponding receipt chain into active store.
	writeLive := func(blockChain types.Blocks, receiptChain []types.Receipts) (int, error) {
		batch := bc.db.NewBatch()
		for i, block := range blockChain {
			// Short circuit insertion if shutting down or processing failed
			if atomic.LoadInt32(&bc.procInterrupt) == 1 {
				return 0, errInsertionInterrupted
			}
			// 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])
			}
			if bc.HasBlock(block.Hash(), block.NumberU64()) {
				stats.ignored++
				continue
			}
			// Write all the data out into the database
			rawdb.WriteBody(batch, block.Hash(), block.NumberU64(), block.Body())
			rawdb.WriteReceipts(batch, block.Hash(), block.NumberU64(), receiptChain[i])
			rawdb.WriteTxLookupEntries(batch, block)
			for _, tx := range block.Transactions() {
				rawdb.WriteTransactionMeta(batch, block.NumberU64(), tx.GetMeta())
			}

			// Write everything belongs to the blocks into the database. So that
			// we can ensure all components of body is completed(body, receipts,
			// tx indexes)
			if batch.ValueSize() >= ethdb.IdealBatchSize {
				if err := batch.Write(); err != nil {
					return 0, err
				}
				size += batch.ValueSize()
				batch.Reset()
			}
			stats.processed++
		}
		// Write everything belongs to the blocks into the database. So that
		// we can ensure all components of body is completed(body, receipts,
		// tx indexes)
		if batch.ValueSize() > 0 {
			size += batch.ValueSize()
			if err := batch.Write(); err != nil {
				return 0, err
			}
		}
		updateHead(blockChain[len(blockChain)-1])
		return 0, nil
	}
	// Write downloaded chain data and corresponding receipt chain data.
	if len(ancientBlocks) > 0 {
		if n, err := writeAncient(ancientBlocks, ancientReceipts); err != nil {
			if err == errInsertionInterrupted {
				return 0, nil
			}
			return n, err
		}
	}
	if len(liveBlocks) > 0 {
		if n, err := writeLive(liveBlocks, liveReceipts); err != nil {
			if err == errInsertionInterrupted {
				return 0, nil
			}
			return n, err
		}
	}

	head := blockChain[len(blockChain)-1]
	context := []interface{}{
		"count", stats.processed, "elapsed", common.PrettyDuration(time.Since(start)),
		"number", head.Number(), "hash", head.Hash(), "age", common.PrettyAge(time.Unix(int64(head.Time()), 0)),
		"size", common.StorageSize(size),
	}
	if stats.ignored > 0 {
		context = append(context, []interface{}{"ignored", stats.ignored}...)
	}
	log.Info("Imported new block receipts", context...)

	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()

	batch := bc.db.NewBatch()
	rawdb.WriteTd(batch, block.Hash(), block.NumberU64(), td)
	rawdb.WriteBlock(batch, block)
	if err := batch.Write(); err != nil {
		log.Crit("Failed to write block into disk", "err", err)
	}
	return nil
}

// writeKnownBlock updates the head block flag with a known block
// and introduces chain reorg if necessary.
func (bc *BlockChain) writeKnownBlock(block *types.Block) error {
	bc.wg.Add(1)
	defer bc.wg.Done()

	current := bc.CurrentBlock()
	if block.ParentHash() != current.Hash() {
		if err := bc.reorg(current, block); err != nil {
			return err
		}
	}
	bc.writeHeadBlock(block)
	return nil
}

// WriteBlockWithState writes the block and all associated state to the database.
func (bc *BlockChain) WriteBlockWithState(block *types.Block, receipts []*types.Receipt, logs []*types.Log, state *state.StateDB, emitHeadEvent bool) (status WriteStatus, err error) {
	bc.chainmu.Lock()
	defer bc.chainmu.Unlock()

	return bc.writeBlockWithState(block, receipts, logs, state, emitHeadEvent)
}

// writeBlockWithState writes the block and all associated state to the database,
// but is expects the chain mutex to be held.
func (bc *BlockChain) writeBlockWithState(block *types.Block, receipts []*types.Receipt, logs []*types.Log, state *state.StateDB, emitHeadEvent bool) (status WriteStatus, err error) {
	bc.wg.Add(1)
	defer bc.wg.Done()

	// Calculate the total difficulty of the block
	ptd := bc.GetTd(block.ParentHash(), block.NumberU64()-1)
	if ptd == nil {
		return NonStatTy, consensus.ErrUnknownAncestor
	}
	// Make sure no inconsistent state is leaked during insertion
	currentBlock := bc.CurrentBlock()
	localTd := bc.GetTd(currentBlock.Hash(), currentBlock.NumberU64())
	externTd := new(big.Int).Add(block.Difficulty(), ptd)

	// Irrelevant of the canonical status, write the block itself to the database.
	//
	// Note all the components of block(td, hash->number map, header, body, receipts)
	// should be written atomically. BlockBatch is used for containing all components.
	blockBatch := bc.db.NewBatch()
	rawdb.WriteTd(blockBatch, block.Hash(), block.NumberU64(), externTd)
	rawdb.WriteBlock(blockBatch, block)
	for _, tx := range block.Transactions() {
		rawdb.WriteTransactionMeta(blockBatch, block.NumberU64(), tx.GetMeta())
	}
	rawdb.WriteReceipts(blockBatch, block.Hash(), block.NumberU64(), receipts)
	rawdb.WritePreimages(blockBatch, state.Preimages())
	if err := blockBatch.Write(); err != nil {
		log.Crit("Failed to write block into disk", "err", err)
	}
	// Commit all cached state changes into underlying memory database.
	root, err := state.Commit(bc.chainConfig.IsEIP158(block.Number()))
	if err != nil {
		return NonStatTy, err
	}
	triedb := bc.stateCache.TrieDB()

	// If we're running an archive node, always flush
	if bc.cacheConfig.TrieDirtyDisabled {
		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.TrieDirtyLimit) * 1024 * 1024
			)
			if nodes > limit || imgs > 4*1024*1024 {
				triedb.Cap(limit - ethdb.IdealBatchSize)
			}
			// Find the next state trie we need to commit
			chosen := current - TriesInMemory

			// If we exceeded out time allowance, flush an entire trie to disk
			if bc.gcproc > bc.cacheConfig.TrieTimeLimit {
				// If the header is missing (canonical chain behind), we're reorging a low
				// diff sidechain. Suspend committing until this operation is completed.
				header := bc.GetHeaderByNumber(chosen)
				if header == nil {
					log.Warn("Reorg in progress, trie commit postponed", "number", chosen)
				} else {
					// 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 {
						log.Info("State in memory for too long, committing", "time", bc.gcproc, "allowance", bc.cacheConfig.TrieTimeLimit, "optimum", float64(chosen-lastWrite)/TriesInMemory)
					}
					// 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))
			}
		}
	}
	// If the total difficulty is higher than our known, add it to the canonical chain
	// Second clause in the if statement reduces the vulnerability to selfish mining.
	// Please refer to http://www.cs.cornell.edu/~ie53/publications/btcProcFC.pdf
	reorg := externTd.Cmp(localTd) > 0
	currentBlock = bc.CurrentBlock()
	if !reorg && externTd.Cmp(localTd) == 0 {
		// Split same-difficulty blocks by number, then preferentially select
		// the block generated by the local miner as the canonical block.
		if block.NumberU64() < currentBlock.NumberU64() {
			reorg = true
		} else if block.NumberU64() == currentBlock.NumberU64() {
			var currentPreserve, blockPreserve bool
			if bc.shouldPreserve != nil {
				currentPreserve, blockPreserve = bc.shouldPreserve(currentBlock), bc.shouldPreserve(block)
			}
			reorg = !currentPreserve && (blockPreserve || mrand.Float64() < 0.5)
		}
	}
	if reorg {
		// Reorganise the chain if the parent is not the head block
		if block.ParentHash() != currentBlock.Hash() {
			if err := bc.reorg(currentBlock, block); err != nil {
				return NonStatTy, err
			}
		}
		status = CanonStatTy
	} else {
		status = SideStatTy
	}
	// Set new head.
	if status == CanonStatTy {
		bc.writeHeadBlock(block)
	}
	bc.futureBlocks.Remove(block.Hash())

	if status == CanonStatTy {
		bc.chainFeed.Send(ChainEvent{Block: block, Hash: block.Hash(), Logs: logs})
		if len(logs) > 0 {
			bc.logsFeed.Send(logs)
		}
		// In theory we should fire a ChainHeadEvent when we inject
		// a canonical block, but sometimes we can insert a batch of
		// canonicial blocks. Avoid firing too much ChainHeadEvents,
		// we will fire an accumulated ChainHeadEvent and disable fire
		// event here.
		if emitHeadEvent {
			bc.chainHeadFeed.Send(ChainHeadEvent{Block: block})
		}
	} else {
		bc.chainSideFeed.Send(ChainSideEvent{Block: block})
	}
	return status, nil
}

// addFutureBlock checks if the block is within the max allowed window to get
// accepted for future processing, and returns an error if the block is too far
// ahead and was not added.
func (bc *BlockChain) addFutureBlock(block *types.Block) error {
	max := uint64(time.Now().Unix() + maxTimeFutureBlocks)
	if block.Time() > max {
		return fmt.Errorf("future block timestamp %v > allowed %v", block.Time(), max)
	}
	bc.futureBlocks.Add(block.Hash(), block)
	return 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) (int, error) {
	// Sanity check that we have something meaningful to import
	if len(chain) == 0 {
		return 0, nil
	}

	bc.blockProcFeed.Send(true)
	defer bc.blockProcFeed.Send(false)

	// Remove already known canon-blocks
	var (
		block, prev *types.Block
	)
	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 1; i < len(chain); i++ {
		block = chain[i]
		prev = chain[i-1]
		if block.NumberU64() != prev.NumberU64()+1 || block.ParentHash() != prev.Hash() {
			// Chain broke ancestry, log a message (programming error) and skip insertion
			log.Error("Non contiguous block insert", "number", block.Number(), "hash", block.Hash(),
				"parent", block.ParentHash(), "prevnumber", prev.Number(), "prevhash", prev.Hash())

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

	return n, err
}

// insertChain is the internal implementation of InsertChain, which assumes that
// 1) chains are contiguous, and 2) The chain mutex is held.
//
// This method is split out so that import batches that require re-injecting
// historical blocks can do so without releasing the lock, which could lead to
// racey behaviour. If a sidechain import is in progress, and the historic state
// is imported, but then new canon-head is added before the actual sidechain
// completes, then the historic state could be pruned again
func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, error) {
	// If the chain is terminating, don't even bother starting up
	if atomic.LoadInt32(&bc.procInterrupt) == 1 {
		return 0, nil
	}
	// Start a parallel signature recovery (signer will fluke on fork transition, minimal perf loss)
	senderCacher.recoverFromBlocks(types.MakeSigner(bc.chainConfig, chain[0].Number()), chain)

	var (
		stats     = insertStats{startTime: mclock.Now()}
		lastCanon *types.Block
	)
	// Fire a single chain head event if we've progressed the chain
	defer func() {
		if lastCanon != nil && bc.CurrentBlock().Hash() == lastCanon.Hash() {
			bc.chainHeadFeed.Send(ChainHeadEvent{lastCanon})
		}
	}()
	// Start the parallel header verifier
	headers := make([]*types.Header, len(chain))
	seals := make([]bool, len(chain))

	for i, block := range chain {
		headers[i] = block.Header()
		seals[i] = verifySeals
	}
	abort, results := bc.engine.VerifyHeaders(bc, headers, seals)
	defer close(abort)

	// Peek the error for the first block to decide the directing import logic
	it := newInsertIterator(chain, results, bc.validator)

	block, err := it.next()

	// Left-trim all the known blocks
	if err == ErrKnownBlock {
		// First block (and state) is known
		//   1. We did a roll-back, and should now do a re-import
		//   2. The block is stored as a sidechain, and is lying about it's stateroot, and passes a stateroot
		// 	    from the canonical chain, which has not been verified.
		// Skip all known blocks that are behind us
		var (
			current  = bc.CurrentBlock()
			localTd  = bc.GetTd(current.Hash(), current.NumberU64())
			externTd = bc.GetTd(block.ParentHash(), block.NumberU64()-1) // The first block can't be nil
		)
		for block != nil && err == ErrKnownBlock {
			externTd = new(big.Int).Add(externTd, block.Difficulty())
			if localTd.Cmp(externTd) < 0 {
				break
			}
			log.Debug("Ignoring already known block", "number", block.Number(), "hash", block.Hash())
			stats.ignored++

			block, err = it.next()
		}
		// The remaining blocks are still known blocks, the only scenario here is:
		// During the fast sync, the pivot point is already submitted but rollback
		// happens. Then node resets the head full block to a lower height via `rollback`
		// and leaves a few known blocks in the database.
		//
		// When node runs a fast sync again, it can re-import a batch of known blocks via
		// `insertChain` while a part of them have higher total difficulty than current
		// head full block(new pivot point).
		for block != nil && err == ErrKnownBlock {
			log.Debug("Writing previously known block", "number", block.Number(), "hash", block.Hash())
			if err := bc.writeKnownBlock(block); err != nil {
				return it.index, err
			}
			lastCanon = block

			block, err = it.next()
		}
		// Falls through to the block import
	}
	switch {
	// First block is pruned, insert as sidechain and reorg only if TD grows enough
	case err == consensus.ErrPrunedAncestor:
		log.Debug("Pruned ancestor, inserting as sidechain", "number", block.Number(), "hash", block.Hash())
		return bc.insertSideChain(block, it)

	// First block is future, shove it (and all children) to the future queue (unknown ancestor)
	case err == consensus.ErrFutureBlock || (err == consensus.ErrUnknownAncestor && bc.futureBlocks.Contains(it.first().ParentHash())):
		for block != nil && (it.index == 0 || err == consensus.ErrUnknownAncestor) {
			log.Debug("Future block, postponing import", "number", block.Number(), "hash", block.Hash())
			if err := bc.addFutureBlock(block); err != nil {
				return it.index, err
			}
			block, err = it.next()
		}
		stats.queued += it.processed()
		stats.ignored += it.remaining()

		// If there are any still remaining, mark as ignored
		return it.index, err

	// Some other error occurred, abort
	case err != nil:
		bc.futureBlocks.Remove(block.Hash())
		stats.ignored += len(it.chain)
		bc.reportBlock(block, nil, err)
		return it.index, err
	}
	// No validation errors for the first block (or chain prefix skipped)
	for ; block != nil && err == nil || err == ErrKnownBlock; block, err = it.next() {
		// If the chain is terminating, stop processing blocks
		if atomic.LoadInt32(&bc.procInterrupt) == 1 {
			log.Debug("Premature abort during blocks processing")
			break
		}
		// If the header is a banned one, straight out abort
		if BadHashes[block.Hash()] {
			bc.reportBlock(block, nil, ErrBlacklistedHash)
			return it.index, ErrBlacklistedHash
		}
		// If the block is known (in the middle of the chain), it's a special case for
		// Clique blocks where they can share state among each other, so importing an
		// older block might complete the state of the subsequent one. In this case,
		// just skip the block (we already validated it once fully (and crashed), since
		// its header and body was already in the database).
		if err == ErrKnownBlock {
			logger := log.Debug
			if bc.chainConfig.Clique == nil {
				logger = log.Warn
			}
			logger("Inserted known block", "number", block.Number(), "hash", block.Hash(),
				"uncles", len(block.Uncles()), "txs", len(block.Transactions()), "gas", block.GasUsed(),
				"root", block.Root())

			if err := bc.writeKnownBlock(block); err != nil {
				return it.index, err
			}
			stats.processed++

			// We can assume that logs are empty here, since the only way for consecutive
			// Clique blocks to have the same state is if there are no transactions.
			lastCanon = block
			continue
		}
		// Retrieve the parent block and it's state to execute on top
		start := time.Now()

		parent := it.previous()
		if parent == nil {
			parent = bc.GetHeader(block.ParentHash(), block.NumberU64()-1)
		}
		statedb, err := state.New(parent.Root, bc.stateCache)
		if err != nil {
			return it.index, err
		}
		// If we have a followup block, run that against the current state to pre-cache
		// transactions and probabilistically some of the account/storage trie nodes.
		var followupInterrupt uint32

		if !bc.cacheConfig.TrieCleanNoPrefetch {
			if followup, err := it.peek(); followup != nil && err == nil {
				go func(start time.Time) {
					throwaway, _ := state.New(parent.Root, bc.stateCache)
					bc.prefetcher.Prefetch(followup, throwaway, bc.vmConfig, &followupInterrupt)

					blockPrefetchExecuteTimer.Update(time.Since(start))
					if atomic.LoadUint32(&followupInterrupt) == 1 {
						blockPrefetchInterruptMeter.Mark(1)
					}
				}(time.Now())
			}
		}
		// Process block using the parent state as reference point
		substart := time.Now()
		receipts, logs, usedGas, err := bc.processor.Process(block, statedb, bc.vmConfig)
		if err != nil {
			bc.reportBlock(block, receipts, err)
			atomic.StoreUint32(&followupInterrupt, 1)
			return it.index, err
		}
		// Update the metrics touched during block processing
		accountReadTimer.Update(statedb.AccountReads)     // Account reads are complete, we can mark them
		storageReadTimer.Update(statedb.StorageReads)     // Storage reads are complete, we can mark them
		accountUpdateTimer.Update(statedb.AccountUpdates) // Account updates are complete, we can mark them
		storageUpdateTimer.Update(statedb.StorageUpdates) // Storage updates are complete, we can mark them

		triehash := statedb.AccountHashes + statedb.StorageHashes // Save to not double count in validation
		trieproc := statedb.AccountReads + statedb.AccountUpdates
		trieproc += statedb.StorageReads + statedb.StorageUpdates

		blockExecutionTimer.Update(time.Since(substart) - trieproc - triehash)

		// Validate the state using the default validator
		substart = time.Now()
		if err := bc.validator.ValidateState(block, statedb, receipts, usedGas); err != nil {
			bc.reportBlock(block, receipts, err)
			atomic.StoreUint32(&followupInterrupt, 1)
			return it.index, err
		}
		proctime := time.Since(start)

		// Update the metrics touched during block validation
		accountHashTimer.Update(statedb.AccountHashes) // Account hashes are complete, we can mark them
		storageHashTimer.Update(statedb.StorageHashes) // Storage hashes are complete, we can mark them

		blockValidationTimer.Update(time.Since(substart) - (statedb.AccountHashes + statedb.StorageHashes - triehash))

		// Write the block to the chain and get the status.
		substart = time.Now()
		status, err := bc.writeBlockWithState(block, receipts, logs, statedb, false)
		if err != nil {
			atomic.StoreUint32(&followupInterrupt, 1)
			return it.index, err
		}
		atomic.StoreUint32(&followupInterrupt, 1)

		// Update the metrics touched during block commit
		accountCommitTimer.Update(statedb.AccountCommits) // Account commits are complete, we can mark them
		storageCommitTimer.Update(statedb.StorageCommits) // Storage commits are complete, we can mark them

		blockWriteTimer.Update(time.Since(substart) - statedb.AccountCommits - statedb.StorageCommits)
		blockInsertTimer.UpdateSince(start)

		switch status {
		case CanonStatTy:
			log.Debug("Inserted new block", "number", block.Number(), "hash", block.Hash(),
				"uncles", len(block.Uncles()), "txs", len(block.Transactions()), "gas", block.GasUsed(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"root", block.Root())

			lastCanon = block

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

		case SideStatTy:
			log.Debug("Inserted forked block", "number", block.Number(), "hash", block.Hash(),
				"diff", block.Difficulty(), "elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()),
				"root", block.Root())

		default:
			// This in theory is impossible, but lets be nice to our future selves and leave
			// a log, instead of trying to track down blocks imports that don't emit logs.
			log.Warn("Inserted block with unknown status", "number", block.Number(), "hash", block.Hash(),
				"diff", block.Difficulty(), "elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()),
				"root", block.Root())
		}
		stats.processed++
		stats.usedGas += usedGas

		dirty, _ := bc.stateCache.TrieDB().Size()
		stats.report(chain, it.index, dirty)
	}
	// Any blocks remaining here? The only ones we care about are the future ones
	if block != nil && err == consensus.ErrFutureBlock {
		if err := bc.addFutureBlock(block); err != nil {
			return it.index, err
		}
		block, err = it.next()

		for ; block != nil && err == consensus.ErrUnknownAncestor; block, err = it.next() {
			if err := bc.addFutureBlock(block); err != nil {
				return it.index, err
			}
			stats.queued++
		}
	}
	stats.ignored += it.remaining()

	return it.index, err
}

// insertSideChain is called when an import batch hits upon a pruned ancestor
// error, which happens when a sidechain with a sufficiently old fork-block is
// found.
//
// The method writes all (header-and-body-valid) blocks to disk, then tries to
// switch over to the new chain if the TD exceeded the current chain.
func (bc *BlockChain) insertSideChain(block *types.Block, it *insertIterator) (int, error) {
	var (
		externTd *big.Int
		current  = bc.CurrentBlock()
	)
	// The first sidechain block error is already verified to be ErrPrunedAncestor.
	// Since we don't import them here, we expect ErrUnknownAncestor for the remaining
	// ones. Any other errors means that the block is invalid, and should not be written
	// to disk.
	err := consensus.ErrPrunedAncestor
	for ; block != nil && (err == consensus.ErrPrunedAncestor); block, err = it.next() {
		// Check the canonical state root for that number
		if number := block.NumberU64(); current.NumberU64() >= number {
			canonical := bc.GetBlockByNumber(number)
			if canonical != nil && canonical.Hash() == block.Hash() {
				// Not a sidechain block, this is a re-import of a canon block which has it's state pruned

				// Collect the TD of the block. Since we know it's a canon one,
				// we can get it directly, and not (like further below) use
				// the parent and then add the block on top
				externTd = bc.GetTd(block.Hash(), block.NumberU64())
				continue
			}
			if canonical != nil && canonical.Root() == block.Root() {
				// This is most likely a shadow-state attack. When a fork is imported into the
				// database, and it eventually reaches a block height which is not pruned, we
				// just found that the state already exist! This means that the sidechain block
				// refers to a state which already exists in our canon chain.
				//
				// If left unchecked, we would now proceed importing the blocks, without actually
				// having verified the state of the previous blocks.
				log.Warn("Sidechain ghost-state attack detected", "number", block.NumberU64(), "sideroot", block.Root(), "canonroot", canonical.Root())

				// If someone legitimately side-mines blocks, they would still be imported as usual. However,
				// we cannot risk writing unverified blocks to disk when they obviously target the pruning
				// mechanism.
				return it.index, errors.New("sidechain ghost-state attack")
			}
		}
		if externTd == nil {
			externTd = bc.GetTd(block.ParentHash(), block.NumberU64()-1)
		}
		externTd = new(big.Int).Add(externTd, block.Difficulty())

		if !bc.HasBlock(block.Hash(), block.NumberU64()) {
			start := time.Now()
			if err := bc.writeBlockWithoutState(block, externTd); err != nil {
				return it.index, err
			}
			log.Debug("Injected sidechain block", "number", block.Number(), "hash", block.Hash(),
				"diff", block.Difficulty(), "elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(), "uncles", len(block.Uncles()),
				"root", block.Root())
		}
	}
	// At this point, we've written all sidechain blocks to database. Loop ended
	// either on some other error or all were processed. If there was some other
	// error, we can ignore the rest of those blocks.
	//
	// If the externTd was larger than our local TD, we now need to reimport the previous
	// blocks to regenerate the required state
	localTd := bc.GetTd(current.Hash(), current.NumberU64())
	if localTd.Cmp(externTd) > 0 {
		log.Info("Sidechain written to disk", "start", it.first().NumberU64(), "end", it.previous().Number, "sidetd", externTd, "localtd", localTd)
		return it.index, err
	}
	// Gather all the sidechain hashes (full blocks may be memory heavy)
	var (
		hashes  []common.Hash
		numbers []uint64
	)
	parent := it.previous()
	for parent != nil && !bc.HasState(parent.Root) {
		hashes = append(hashes, parent.Hash())
		numbers = append(numbers, parent.Number.Uint64())

		parent = bc.GetHeader(parent.ParentHash, parent.Number.Uint64()-1)
	}
	if parent == nil {
		return it.index, errors.New("missing parent")
	}
	// Import all the pruned blocks to make the state available
	var (
		blocks []*types.Block
		memory common.StorageSize
	)
	for i := len(hashes) - 1; i >= 0; i-- {
		// Append the next block to our batch
		block := bc.GetBlock(hashes[i], numbers[i])

		blocks = append(blocks, block)
		memory += block.Size()

		// If memory use grew too large, import and continue. Sadly we need to discard
		// all raised events and logs from notifications since we're too heavy on the
		// memory here.
		if len(blocks) >= 2048 || memory > 64*1024*1024 {
			log.Info("Importing heavy sidechain segment", "blocks", len(blocks), "start", blocks[0].NumberU64(), "end", block.NumberU64())
			if _, err := bc.insertChain(blocks, false); err != nil {
				return 0, err
			}
			blocks, memory = blocks[:0], 0

			// If the chain is terminating, stop processing blocks
			if atomic.LoadInt32(&bc.procInterrupt) == 1 {
				log.Debug("Premature abort during blocks processing")
				return 0, nil
			}
		}
	}
	if len(blocks) > 0 {
		log.Info("Importing sidechain segment", "start", blocks[0].NumberU64(), "end", blocks[len(blocks)-1].NumberU64())
		return bc.insertChain(blocks, false)
	}
	return 0, nil
}

// reorg takes two blocks, an old chain and a new chain and will reconstruct the
// blocks and inserts them to be part of the new canonical chain and accumulates
// potential missing transactions and post an event about them.
func (bc *BlockChain) reorg(oldBlock, newBlock *types.Block) error {
	var (
		newChain    types.Blocks
		oldChain    types.Blocks
		commonBlock *types.Block

		deletedTxs types.Transactions
		addedTxs   types.Transactions

		deletedLogs [][]*types.Log
		rebirthLogs [][]*types.Log

		// collectLogs collects the logs that were generated or removed during
		// the processing of the block that corresponds with the given hash.
		// These logs are later announced as deleted or reborn
		collectLogs = func(hash common.Hash, removed bool) {
			number := bc.hc.GetBlockNumber(hash)
			if number == nil {
				return
			}
			receipts := rawdb.ReadReceipts(bc.db, hash, *number, bc.chainConfig)

			var logs []*types.Log
			for _, receipt := range receipts {
				for _, log := range receipt.Logs {
					l := *log
					if removed {
						l.Removed = true
					} else {
					}
					logs = append(logs, &l)
				}
			}
			if len(logs) > 0 {
				if removed {
					deletedLogs = append(deletedLogs, logs)
				} else {
					rebirthLogs = append(rebirthLogs, logs)
				}
			}
		}
		// mergeLogs returns a merged log slice with specified sort order.
		mergeLogs = func(logs [][]*types.Log, reverse bool) []*types.Log {
			var ret []*types.Log
			if reverse {
				for i := len(logs) - 1; i >= 0; i-- {
					ret = append(ret, logs[i]...)
				}
			} else {
				for i := 0; i < len(logs); i++ {
					ret = append(ret, logs[i]...)
				}
			}
			return ret
		}
	)
	// Reduce the longer chain to the same number as the shorter one
	if oldBlock.NumberU64() > newBlock.NumberU64() {
		// Old chain is longer, gather all transactions and logs as deleted ones
		for ; oldBlock != nil && oldBlock.NumberU64() != newBlock.NumberU64(); oldBlock = bc.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1) {
			oldChain = append(oldChain, oldBlock)
			deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
			collectLogs(oldBlock.Hash(), true)
		}
	} else {
		// New chain is longer, stash all blocks away for subsequent insertion
		for ; newBlock != nil && newBlock.NumberU64() != oldBlock.NumberU64(); newBlock = bc.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1) {
			newChain = append(newChain, newBlock)
		}
	}
	if oldBlock == nil {
		return fmt.Errorf("invalid old chain")
	}
	if newBlock == nil {
		return fmt.Errorf("invalid new chain")
	}
	// Both sides of the reorg are at the same number, reduce both until the common
	// ancestor is found
	for {
		// If the common ancestor was found, bail out
		if oldBlock.Hash() == newBlock.Hash() {
			commonBlock = oldBlock
			break
		}
		// Remove an old block as well as stash away a new block
		oldChain = append(oldChain, oldBlock)
		deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
		collectLogs(oldBlock.Hash(), true)

		newChain = append(newChain, newBlock)

		// Step back with both chains
		oldBlock = bc.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1)
		if oldBlock == nil {
			return fmt.Errorf("invalid old chain")
		}
		newBlock = bc.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1)
		if newBlock == nil {
			return fmt.Errorf("invalid new chain")
		}
	}
	// Ensure the user sees large reorgs
	if len(oldChain) > 0 && len(newChain) > 0 {
		logFn := log.Info
		msg := "Chain reorg detected"
		if len(oldChain) > 63 {
			msg = "Large chain reorg detected"
			logFn = log.Warn
		}
		logFn(msg, "number", commonBlock.Number(), "hash", commonBlock.Hash(),
			"drop", len(oldChain), "dropfrom", oldChain[0].Hash(), "add", len(newChain), "addfrom", newChain[0].Hash())
		blockReorgAddMeter.Mark(int64(len(newChain)))
		blockReorgDropMeter.Mark(int64(len(oldChain)))
	} else {
		log.Error("Impossible reorg, please file an issue", "oldnum", oldBlock.Number(), "oldhash", oldBlock.Hash(), "newnum", newBlock.Number(), "newhash", newBlock.Hash())
	}
	// Insert the new chain(except the head block(reverse order)),
	// taking care of the proper incremental order.
	for i := len(newChain) - 1; i >= 1; i-- {
		// Insert the block in the canonical way, re-writing history
		bc.writeHeadBlock(newChain[i])

		// Collect reborn logs due to chain reorg
		collectLogs(newChain[i].Hash(), false)

		// Collect the new added transactions.
		addedTxs = append(addedTxs, newChain[i].Transactions()...)
	}
	// Delete useless indexes right now which includes the non-canonical
	// transaction indexes, canonical chain indexes which above the head.
	indexesBatch := bc.db.NewBatch()
	for _, tx := range types.TxDifference(deletedTxs, addedTxs) {
		rawdb.DeleteTxLookupEntry(indexesBatch, tx.Hash())
	}
	// Delete any canonical number assignments above the new head
	number := bc.CurrentBlock().NumberU64()
	for i := number + 1; ; i++ {
		hash := rawdb.ReadCanonicalHash(bc.db, i)
		if hash == (common.Hash{}) {
			break
		}
		rawdb.DeleteCanonicalHash(indexesBatch, i)
	}
	if err := indexesBatch.Write(); err != nil {
		log.Crit("Failed to delete useless indexes", "err", err)
	}
	// If any logs need to be fired, do it now. In theory we could avoid creating
	// this goroutine if there are no events to fire, but realistcally that only
	// ever happens if we're reorging empty blocks, which will only happen on idle
	// networks where performance is not an issue either way.
	if len(deletedLogs) > 0 {
		bc.rmLogsFeed.Send(RemovedLogsEvent{mergeLogs(deletedLogs, true)})
	}
	if len(rebirthLogs) > 0 {
		bc.logsFeed.Send(mergeLogs(rebirthLogs, false))
	}
	if len(oldChain) > 0 {
		for i := len(oldChain) - 1; i >= 0; i-- {
			bc.chainSideFeed.Send(ChainSideEvent{Block: oldChain[i]})
		}
	}
	return nil
}

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

// BadBlocks returns a list of the last 'bad blocks' that the client has seen on the network
func (bc *BlockChain) BadBlocks() []*types.Block {
	blocks := make([]*types.Block, 0, bc.badBlocks.Len())
	for _, hash := range bc.badBlocks.Keys() {
		if blk, exist := bc.badBlocks.Peek(hash); exist {
			block := blk.(*types.Block)
			blocks = append(blocks, block)
		}
	}
	return blocks
}

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

// reportBlock logs a bad block error.
func (bc *BlockChain) reportBlock(block *types.Block, receipts types.Receipts, err error) {
	bc.addBadBlock(block)

	var receiptString string
	for i, receipt := range receipts {
		receiptString += fmt.Sprintf("\t %d: cumulative: %v gas: %v contract: %v status: %v tx: %v logs: %v bloom: %x state: %x\n",
			i, receipt.CumulativeGasUsed, receipt.GasUsed, receipt.ContractAddress.Hex(),
			receipt.Status, receipt.TxHash.Hex(), receipt.Logs, receipt.Bloom, receipt.PostState)
	}
	log.Error(fmt.Sprintf(`
########## BAD BLOCK #########
Chain config: %v

Number: %v
Hash: 0x%x
%v

Error: %v
##############################
`, bc.chainConfig, block.Number(), block.Hash(), receiptString, err))
}

// 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 []*types.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 *types.Header) error {
		_, 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() *types.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) *types.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) *types.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)
}

// GetCanonicalHash returns the canonical hash for a given block number
func (bc *BlockChain) GetCanonicalHash(number uint64) common.Hash {
	return bc.hc.GetCanonicalHash(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) {
	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) *types.Header {
	return bc.hc.GetHeaderByNumber(number)
}

// GetTransactionLookup retrieves the lookup associate with the given transaction
// hash from the cache or database.
func (bc *BlockChain) GetTransactionLookup(hash common.Hash) *rawdb.LegacyTxLookupEntry {
	// Short circuit if the txlookup already in the cache, retrieve otherwise
	if lookup, exist := bc.txLookupCache.Get(hash); exist {
		return lookup.(*rawdb.LegacyTxLookupEntry)
	}
	tx, blockHash, blockNumber, txIndex := rawdb.ReadTransaction(bc.db, hash)
	if tx == nil {
		return nil
	}
	lookup := &rawdb.LegacyTxLookupEntry{BlockHash: blockHash, BlockIndex: blockNumber, Index: txIndex}
	bc.txLookupCache.Add(hash, lookup)
	return lookup
}

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

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

// SubscribeBlockProcessingEvent registers a subscription of bool where true means
// block processing has started while false means it has stopped.
func (bc *BlockChain) SubscribeBlockProcessingEvent(ch chan<- bool) event.Subscription {
	return bc.scope.Track(bc.blockProcFeed.Subscribe(ch))
}
