// 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/celo-org/celo-blockchain/common"
	"github.com/celo-org/celo-blockchain/common/mclock"
	"github.com/celo-org/celo-blockchain/common/prque"
	"github.com/celo-org/celo-blockchain/consensus"
	"github.com/celo-org/celo-blockchain/core/rawdb"
	"github.com/celo-org/celo-blockchain/core/state"
	"github.com/celo-org/celo-blockchain/core/state/snapshot"
	"github.com/celo-org/celo-blockchain/core/types"
	"github.com/celo-org/celo-blockchain/core/vm"
	"github.com/celo-org/celo-blockchain/core/vm/vmcontext"
	"github.com/celo-org/celo-blockchain/ethdb"
	"github.com/celo-org/celo-blockchain/event"
	"github.com/celo-org/celo-blockchain/internal/syncx"
	"github.com/celo-org/celo-blockchain/log"
	"github.com/celo-org/celo-blockchain/metrics"
	"github.com/celo-org/celo-blockchain/params"
	"github.com/celo-org/celo-blockchain/rlp"
	"github.com/celo-org/celo-blockchain/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)
	headBlockBaseFee   = metrics.NewRegisteredGauge("chain/head/basefee", 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)

	snapshotAccountReadTimer = metrics.NewRegisteredTimer("chain/snapshot/account/reads", nil)
	snapshotStorageReadTimer = metrics.NewRegisteredTimer("chain/snapshot/storage/reads", nil)
	snapshotCommitTimer      = metrics.NewRegisteredTimer("chain/snapshot/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)

	blockReorgMeter         = metrics.NewRegisteredMeter("chain/reorg/executes", nil)
	blockReorgAddMeter      = metrics.NewRegisteredMeter("chain/reorg/add", nil)
	blockReorgDropMeter     = metrics.NewRegisteredMeter("chain/reorg/drop", nil)
	blockReorgInvalidatedTx = metrics.NewRegisteredMeter("chain/reorg/invalidTx", nil)

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

	errInsertionInterrupted = errors.New("insertion is interrupted")
	errCommitmentNotFound   = errors.New("randomness commitment not found")
	errChainStopped         = errors.New("blockchain is stopped")
)

const (
	bodyCacheLimit      = 256
	blockCacheLimit     = 256
	receiptsCacheLimit  = 32
	txLookupCacheLimit  = 1024
	maxFutureBlocks     = 256
	maxTimeFutureBlocks = 30
	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
	// - Version 8
	//  The following incompatible database changes were added:
	//    * New scheme for contract code in order to separate the codes and trie nodes
	BlockChainVersion uint64 = 8
)

// 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
	TrieCleanJournal    string        // Disk journal for saving clean cache entries.
	TrieCleanRejournal  time.Duration // Time interval to dump clean cache to disk periodically
	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
	SnapshotLimit       int           // Memory allowance (MB) to use for caching snapshot entries in memory
	Preimages           bool          // Whether to store preimage of trie key to the disk

	SnapshotWait bool // Wait for snapshot construction on startup. TODO(karalabe): This is a dirty hack for testing, nuke it
}

// defaultCacheConfig are the default caching values if none are specified by the
// user (also used during testing).
var defaultCacheConfig = &CacheConfig{
	TrieCleanLimit: 256,
	TrieDirtyLimit: 256,
	TrieTimeLimit:  5 * time.Minute,
	SnapshotLimit:  256,
	SnapshotWait:   true,
}

// 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
	snaps  *snapshot.Tree // Snapshot tree for fast trie leaf access
	triegc *prque.Prque   // Priority queue mapping block numbers to tries to gc
	gcproc time.Duration  // Accumulates canonical block processing for trie dumping

	// txLookupLimit is the maximum number of blocks from head whose tx indices
	// are reserved:
	//  * 0:   means no limit and regenerate any missing indexes
	//  * N:   means N block limit [HEAD-N+1, HEAD] and delete extra indexes
	//  * nil: disable tx reindexer/deleter, but still index new blocks
	txLookupLimit uint64

	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

	// This mutex synchronizes chain write operations.
	// Readers don't need to take it, they can just read the database.
	chainmu *syncx.ClosableMutex

	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

	wg            sync.WaitGroup //
	quit          chan struct{}  // shutdown signal, closed in Stop.
	running       int32          // 0 if chain is running, 1 when stopped
	procInterrupt int32          // interrupt signaler for block processing

	engine     consensus.Engine
	validator  Validator // Block and state validator interface
	prefetcher Prefetcher
	processor  Processor // Block transaction processor interface
	vmConfig   vm.Config

	shouldPreserve func(*types.Block) bool // Function used to determine whether should preserve the given block.
}

// 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, txLookupLimit *uint64) (*BlockChain, error) {
	if cacheConfig == nil {
		cacheConfig = defaultCacheConfig
	}
	bodyCache, _ := lru.New(bodyCacheLimit)
	bodyRLPCache, _ := lru.New(bodyCacheLimit)
	receiptsCache, _ := lru.New(receiptsCacheLimit)
	blockCache, _ := lru.New(blockCacheLimit)
	txLookupCache, _ := lru.New(txLookupCacheLimit)
	futureBlocks, _ := lru.New(maxFutureBlocks)

	bc := &BlockChain{
		chainConfig: chainConfig,
		cacheConfig: cacheConfig,
		db:          db,
		triegc:      prque.New(nil),
		stateCache: state.NewDatabaseWithConfig(db, &trie.Config{
			Cache:     cacheConfig.TrieCleanLimit,
			Journal:   cacheConfig.TrieCleanJournal,
			Preimages: cacheConfig.Preimages,
		}),
		quit:           make(chan struct{}),
		chainmu:        syncx.NewClosableMutex(),
		shouldPreserve: shouldPreserve,
		bodyCache:      bodyCache,
		bodyRLPCache:   bodyRLPCache,
		receiptsCache:  receiptsCache,
		blockCache:     blockCache,
		txLookupCache:  txLookupCache,
		futureBlocks:   futureBlocks,
		engine:         engine,
		vmConfig:       vmConfig,
	}
	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.insertStopped)
	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.
	var txIndexBlock uint64

	if bc.empty() {
		rawdb.InitDatabaseFromFreezer(bc.db)
		// If ancient database is not empty, reconstruct all missing
		// indices in the background.
		frozen, _ := bc.db.Ancients()
		if frozen > 0 {
			txIndexBlock = frozen
		}
	}
	if err := bc.loadLastState(); err != nil {
		return nil, err
	}

	// Make sure the state associated with the block is available
	head := bc.CurrentBlock()
	if _, err := state.New(head.Root(), bc.stateCache, bc.snaps); err != nil {
		// Head state is missing, before the state recovery, find out the
		// disk layer point of snapshot(if it's enabled). Make sure the
		// rewound point is lower than disk layer.
		var diskRoot common.Hash
		if bc.cacheConfig.SnapshotLimit > 0 {
			diskRoot = rawdb.ReadSnapshotRoot(bc.db)
		}
		if diskRoot != (common.Hash{}) {
			log.Warn("Head state missing, repairing", "number", head.Number(), "hash", head.Hash(), "snaproot", diskRoot)

			snapDisk, err := bc.SetHeadBeyondRoot(head.NumberU64(), diskRoot)
			if err != nil {
				return nil, err
			}
			// Chain rewound, persist old snapshot number to indicate recovery procedure
			if snapDisk != 0 {
				rawdb.WriteSnapshotRecoveryNumber(bc.db, snapDisk)
			}
		} else {
			log.Warn("Head state missing, repairing", "number", head.Number(), "hash", head.Hash())
			if err := bc.SetHead(head.NumberU64()); err != nil {
				return nil, err
			}
		}
	}

	// Ensure that a previous crash in SetHead doesn't leave extra ancients
	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.Hash() != bc.genesisBlock.Hash() && 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 {
			log.Error("Truncating ancient chain", "from", bc.CurrentHeader().Number.Uint64(), "to", low)
			if err := bc.SetHead(low); 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)

	// 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)
				if err := bc.SetHead(header.Number.Uint64() - 1); err != nil {
					return nil, err
				}
				log.Error("Chain rewind was successful, resuming normal operation")
			}
		}
	}

	// Load any existing snapshot, regenerating it if loading failed
	if bc.cacheConfig.SnapshotLimit > 0 {
		// If the chain was rewound past the snapshot persistent layer (causing
		// a recovery block number to be persisted to disk), check if we're still
		// in recovery mode and in that case, don't invalidate the snapshot on a
		// head mismatch.
		var recover bool

		head := bc.CurrentBlock()
		if layer := rawdb.ReadSnapshotRecoveryNumber(bc.db); layer != nil && *layer > head.NumberU64() {
			log.Warn("Enabling snapshot recovery", "chainhead", head.NumberU64(), "diskbase", *layer)
			recover = true
		}
		bc.snaps, _ = snapshot.New(bc.db, bc.stateCache.TrieDB(), bc.cacheConfig.SnapshotLimit, head.Root(), !bc.cacheConfig.SnapshotWait, true, recover)
	}

	// Start future block processor.
	bc.wg.Add(1)
	go bc.futureBlocksLoop()

	// Start tx indexer/unindexer.
	if txLookupLimit != nil {
		bc.txLookupLimit = *txLookupLimit

		bc.wg.Add(1)
		go bc.maintainTxIndex(txIndexBlock)
	}

	// If periodic cache journal is required, spin it up.
	if bc.cacheConfig.TrieCleanRejournal > 0 {
		if bc.cacheConfig.TrieCleanRejournal < time.Minute {
			log.Warn("Sanitizing invalid trie cache journal time", "provided", bc.cacheConfig.TrieCleanRejournal, "updated", time.Minute)
			bc.cacheConfig.TrieCleanRejournal = time.Minute
		}
		triedb := bc.stateCache.TrieDB()
		bc.wg.Add(1)
		go func() {
			defer bc.wg.Done()
			triedb.SaveCachePeriodically(bc.cacheConfig.TrieCleanJournal, bc.cacheConfig.TrieCleanRejournal, bc.quit)
		}()
	}
	return bc, nil
}

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

// NewEVMRunner creates the System's EVMRunner for given header & sttate
func (bc *BlockChain) NewEVMRunner(header *types.Header, state vm.StateDB) vm.EVMRunner {
	return vmcontext.NewEVMRunner(bc, header, state)
}

// NewEVMRunnerForCurrentBlock creates the System's EVMRunner for current block & state
func (bc *BlockChain) NewEVMRunnerForCurrentBlock() (vm.EVMRunner, error) {
	block := bc.CurrentBlock()
	state, err := bc.StateAt(block.Header().Root)
	if err != nil {
		log.Error("Can't create EVMRunner for current block (error fetching state)", "number", block.Number(), "stateRoot", block.Root().Hex(), "err", err)
		return nil, err
	}
	return vmcontext.NewEVMRunner(bc, block.Header(), state), nil
}

// 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()
	}
	// 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
		}
	}
	log.Debug(fmt.Sprintf("Loading Last State: %v", currentHeader.Number))
	bc.hc.SetCurrentHeader(currentHeader)
	// Update the head block basefee gauge metric (after EIP-1559)
	if currentHeader.BaseFee != nil {
		headBlockBaseFee.Update(currentHeader.BaseFee.Int64())
	}

	// 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)))
	if pivot := rawdb.ReadLastPivotNumber(bc.db); pivot != nil {
		log.Info("Loaded last fast-sync pivot marker", "number", *pivot)
	}
	return nil
}

// SetHead rewinds the local chain to a new head. Depending on whether the node
// was fast synced or full synced and in which state, the method will try to
// delete minimal data from disk whilst retaining chain consistency.
func (bc *BlockChain) SetHead(head uint64) error {
	_, err := bc.SetHeadBeyondRoot(head, common.Hash{})
	return err
}

// SetHeadBeyondRoot rewinds the local chain to a new head with the extra condition
// that the rewind must pass the specified state root. This method is meant to be
// used when rewinding with snapshots enabled to ensure that we go back further than
// persistent disk layer. Depending on whether the node was fast synced or full, and
// in which state, the method will try to delete minimal data from disk whilst
// retaining chain consistency.
//
// The method returns the block number where the requested root cap was found.
func (bc *BlockChain) SetHeadBeyondRoot(head uint64, root common.Hash) (uint64, error) {
	if !bc.chainmu.TryLock() {
		return 0, errChainStopped
	}
	defer bc.chainmu.Unlock()

	// Track the block number of the requested root hash
	var rootNumber uint64 // (no root == always 0)

	// Retrieve the last pivot block to short circuit rollbacks beyond it and the
	// current freezer limit to start nuking id underflown
	pivot := rawdb.ReadLastPivotNumber(bc.db)
	frozen, _ := bc.db.Ancients()

	updateFn := func(db ethdb.KeyValueWriter, header *types.Header) (uint64, bool) {
		// Rewind the block chain, ensuring we don't end up with a stateless head
		// block. Note, depth equality is permitted to allow using SetHead as a
		// chain reparation mechanism without deleting any data!
		if currentBlock := bc.CurrentBlock(); currentBlock != nil && header.Number.Uint64() <= currentBlock.NumberU64() {
			newHeadBlock := bc.GetBlock(header.Hash(), header.Number.Uint64())
			if newHeadBlock == nil {
				log.Error("Gap in the chain, rewinding to genesis", "number", header.Number, "hash", header.Hash())
				newHeadBlock = bc.genesisBlock
			} else {
				// Block exists, keep rewinding until we find one with state,
				// keeping rewinding until we exceed the optional threshold
				// root hash
				beyondRoot := (root == common.Hash{}) // Flag whether we're beyond the requested root (no root, always true)

				for {
					// If a root threshold was requested but not yet crossed, check
					if root != (common.Hash{}) && !beyondRoot && newHeadBlock.Root() == root {
						beyondRoot, rootNumber = true, newHeadBlock.NumberU64()
					}
					if _, err := state.New(newHeadBlock.Root(), bc.stateCache, bc.snaps); err != nil {
						log.Trace("Block state missing, rewinding further", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash())
						if pivot == nil || newHeadBlock.NumberU64() > *pivot {
							parent := bc.GetBlock(newHeadBlock.ParentHash(), newHeadBlock.NumberU64()-1)
							if parent != nil {
								newHeadBlock = parent
								continue
							}
							log.Error("Missing block in the middle, aiming genesis", "number", newHeadBlock.NumberU64()-1, "hash", newHeadBlock.ParentHash())
							newHeadBlock = bc.genesisBlock
						} else {
							log.Trace("Rewind passed pivot, aiming genesis", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash(), "pivot", *pivot)
							newHeadBlock = bc.genesisBlock
						}
					}
					if beyondRoot || newHeadBlock.NumberU64() == 0 {
						log.Debug("Rewound to block with state", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash())
						break
					}
					log.Debug("Skipping block with threshold state", "number", newHeadBlock.NumberU64(), "hash", newHeadBlock.Hash(), "root", newHeadBlock.Root())
					newHeadBlock = bc.GetBlock(newHeadBlock.ParentHash(), newHeadBlock.NumberU64()-1) // Keep rewinding
				}
			}
			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()))
			log.Info("Rewound fast block", "number", newHeadFastBlock.NumberU64())
		}
		head := bc.CurrentBlock().NumberU64()

		// If setHead underflown the freezer threshold and the block processing
		// intent afterwards is full block importing, delete the chain segment
		// between the stateful-block and the sethead target.
		var wipe bool
		if head+1 < frozen {
			wipe = pivot == nil || head >= *pivot
		}
		return head, wipe // Only force wipe if full synced
	}
	// 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); 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
	}
	// If SetHead was only called as a chain reparation method, try to skip
	// touching the header chain altogether, unless the freezer is broken
	if block := bc.CurrentBlock(); block.NumberU64() == head {
		if target, force := updateFn(bc.db, block.Header()); force {
			bc.hc.SetHead(target, updateFn, delFn)
		}
	} else {
		// Rewind the chain to the requested head and keep going backwards until a
		// block with a state is found or fast sync pivot is passed
		log.Warn("Rewinding blockchain", "target", head)
		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 rootNumber, 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.
	if !bc.chainmu.TryLock() {
		return errChainStopped
	}
	bc.currentBlock.Store(block)
	headBlockGauge.Update(int64(block.NumberU64()))
	bc.chainmu.Unlock()

	// Destroy any existing state snapshot and regenerate it in the background,
	// also resuming the normal maintenance of any previously paused snapshot.
	if bc.snaps != nil {
		bc.snaps.Rebuild(block.Root())
	}
	log.Info("Committed new head block", "number", block.Number(), "hash", hash)
	return nil
}

// 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)
}

// Snapshots returns the blockchain snapshot tree.
func (bc *BlockChain) Snapshots() *snapshot.Tree {
	return bc.snaps
}

// 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, bc.snaps)
}

// 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
	}
	if !bc.chainmu.TryLock() {
		return errChainStopped
	}
	defer bc.chainmu.Unlock()

	// Prepare the genesis block and reinitialise the chain
	batch := bc.db.NewBatch()
	rawdb.WriteTd(batch, genesis.Hash(), genesis.NumberU64(), genesis.TotalDifficulty())
	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
}

// 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 {
	if !bc.chainmu.TryLock() {
		return errChainStopped
	}
	defer bc.chainmu.Unlock()

	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.WriteTxLookupEntriesByBlock(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) 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
}

// TrieNode retrieves a blob of data associated with a trie node
// 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)
}

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

// ContractCodeWithPrefix retrieves a blob of data associated with a contract
// hash either from ephemeral in-memory cache, or from persistent storage.
//
// If the code doesn't exist in the in-memory cache, check the storage with
// new code scheme.
func (bc *BlockChain) ContractCodeWithPrefix(hash common.Hash) ([]byte, error) {
	type codeReader interface {
		ContractCodeWithPrefix(addrHash, codeHash common.Hash) ([]byte, error)
	}
	return bc.stateCache.(codeReader).ContractCodeWithPrefix(common.Hash{}, 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()

	// Signal shutdown to all goroutines.
	close(bc.quit)
	bc.StopInsert()

	// Now wait for all chain modifications to end and persistent goroutines to exit.
	//
	// Note: Close waits for the mutex to become available, i.e. any running chain
	// modification will have exited when Close returns. Since we also called StopInsert,
	// the mutex should become available quickly. It cannot be taken again after Close has
	// returned.
	bc.chainmu.Close()
	bc.wg.Wait()

	// Ensure that the entirety of the state snapshot is journalled to disk.
	var snapBase common.Hash
	if bc.snaps != nil {
		var err error
		if snapBase, err = bc.snaps.Journal(bc.CurrentBlock().Root()); err != nil {
			log.Error("Failed to journal state snapshot", "err", err)
		}
	}

	// 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, nil); err != nil {
					log.Error("Failed to commit recent state trie", "err", err)
				}
			}
		}
		if snapBase != (common.Hash{}) {
			log.Info("Writing snapshot state to disk", "root", snapBase)
			if err := triedb.Commit(snapBase, true, nil); 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")
		}
	}
	// Ensure all live cached entries be saved into disk, so that we can skip
	// cache warmup when node restarts.
	if bc.cacheConfig.TrieCleanJournal != "" {
		triedb := bc.stateCache.TrieDB()
		triedb.SaveCache(bc.cacheConfig.TrieCleanJournal)
	}
	log.Info("Blockchain stopped")
}

// StopInsert interrupts all insertion methods, causing them to return
// errInsertionInterrupted as soon as possible. Insertion is permanently disabled after
// calling this method.
func (bc *BlockChain) StopInsert() {
	atomic.StoreInt32(&bc.procInterrupt, 1)
}

// insertStopped returns true after StopInsert has been called.
func (bc *BlockChain) insertStopped() bool {
	return atomic.LoadInt32(&bc.procInterrupt) == 1
}

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
)

// 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  = int64(0)
	)

	// updateHead updates the head fast sync block if the inserted blocks are better
	// and returns an indicator whether the inserted blocks are canonical.
	updateHead := func(head *types.Block) bool {
		if !bc.chainmu.TryLock() {
			return false
		}
		defer bc.chainmu.Unlock()

		// 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())
			fastBlockTd := bc.GetTd(currentFastBlock.Hash(), currentFastBlock.NumberU64())

			// These two should not be nil under normal circumstances,
			// but it apparently can happen in edge cases. See
			// https://github.com/celo-org/celo-blockchain/issues/1920
			if fastBlockTd == nil {
				log.Warn("InsertReceiptChain: fastBlockTd is nil")
				return false
			}
			if td == nil {
				log.Warn("InsertReceiptChain: td is nil")
				return false
			}

			if fastBlockTd.Cmp(td) < 0 {
				rawdb.WriteHeadFastBlockHash(bc.db, head.Hash())
				bc.currentFastBlock.Store(head)
				headFastBlockGauge.Update(int64(head.NumberU64()))
				return true
			}
		}
		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) {
		first := blockChain[0]
		last := blockChain[len(blockChain)-1]

		// Ensure genesis is in ancients.
		if first.NumberU64() == 1 {
			if frozen, _ := bc.db.Ancients(); frozen == 0 {
				b := bc.genesisBlock
				writeSize, err := rawdb.WriteAncientBlocks(bc.db, []*types.Block{b}, []types.Receipts{nil}, big.NewInt(1))
				size += writeSize
				if err != nil {
					log.Error("Error writing genesis to ancients", "err", err)
					return 0, err
				}
				log.Info("Wrote genesis to ancients")
			}
		}
		// Before writing the blocks to the ancients, we need to ensure that
		// they correspond to the what the headerchain 'expects'.
		// We only check the last block/header, since it's a contiguous chain.
		if !bc.HasHeader(last.Hash(), last.NumberU64()) {
			return 0, fmt.Errorf("containing header #%d [%x..] unknown", last.Number(), last.Hash().Bytes()[:4])
		}

		// Write all chain data to ancients.
		td := bc.GetTd(first.Hash(), first.NumberU64())
		writeSize, err := rawdb.WriteAncientBlocks(bc.db, blockChain, receiptChain, td)
		size += writeSize
		if err != nil {
			log.Error("Error importing chain data to ancients", "err", err)
			return 0, err
		}

		// Write tx indices if any condition is satisfied:
		// * If user requires to reserve all tx indices(txlookuplimit=0)
		// * If all ancient tx indices are required to be reserved(txlookuplimit is even higher than ancientlimit)
		// * If block number is large enough to be regarded as a recent block
		// It means blocks below the ancientLimit-txlookupLimit won't be indexed.
		//
		// But if the `TxIndexTail` is not nil, e.g. Geth is initialized with
		// an external ancient database, during the setup, blockchain will start
		// a background routine to re-indexed all indices in [ancients - txlookupLimit, ancients)
		// range. In this case, all tx indices of newly imported blocks should be
		// generated.
		var batch = bc.db.NewBatch()
		for _, block := range blockChain {
			if bc.txLookupLimit == 0 || ancientLimit <= bc.txLookupLimit || block.NumberU64() >= ancientLimit-bc.txLookupLimit {
				rawdb.WriteTxLookupEntriesByBlock(batch, block)
			} else if rawdb.ReadTxIndexTail(bc.db) != nil {
				rawdb.WriteTxLookupEntriesByBlock(batch, block)
			}
			stats.processed++
		}

		// Flush all tx-lookup index data.
		size += int64(batch.ValueSize())
		if err := batch.Write(); err != nil {
			// The tx index data could not be written.
			// Roll back the ancient store update.
			fastBlock := bc.CurrentFastBlock().NumberU64()
			if err := bc.db.TruncateAncients(fastBlock + 1); err != nil {
				log.Error("Can't truncate ancient store after failed insert", "err", err)
			}
			return 0, err
		}

		// Sync the ancient store explicitly to ensure all data has been flushed to disk.
		if err := bc.db.Sync(); err != nil {
			return 0, err
		}

		// Update the current fast block because all block data is now present in DB.
		previousFastBlock := bc.CurrentFastBlock().NumberU64()
		if !updateHead(blockChain[len(blockChain)-1]) {
			// We end up here if the header chain has reorg'ed, and the blocks/receipts
			// don't match the canonical chain.
			if err := bc.db.TruncateAncients(previousFastBlock + 1); err != nil {
				log.Error("Can't truncate ancient store after failed insert", "err", err)
			}
			return 0, errSideChainReceipts
		}

		// Delete block data from the main database.
		batch.Reset()
		canonHashes := make(map[common.Hash]struct{})
		for _, block := range blockChain {
			canonHashes[block.Hash()] = struct{}{}
			if block.NumberU64() == 0 {
				continue
			}
			rawdb.DeleteCanonicalHash(batch, block.NumberU64())
			rawdb.DeleteBlockWithoutNumber(batch, block.Hash(), block.NumberU64())
		}
		// Delete side chain hash-to-number mappings.
		for _, nh := range rawdb.ReadAllHashesInRange(bc.db, first.NumberU64(), last.NumberU64()) {
			if _, canon := canonHashes[nh.Hash]; !canon {
				rawdb.DeleteHeader(batch, nh.Hash, nh.Number)
			}
		}
		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) {
		skipPresenceCheck := false
		batch := bc.db.NewBatch()
		for i, block := range blockChain {
			// Short circuit insertion if shutting down or processing failed
			if bc.insertStopped() {
				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 !skipPresenceCheck {
				// Ignore if the entire data is already known
				if bc.HasBlock(block.Hash(), block.NumberU64()) {
					stats.ignored++
					continue
				} else {
					// If block N is not present, neither are the later blocks.
					// This should be true, but if we are mistaken, the shortcut
					// here will only cause overwriting of some existing data
					skipPresenceCheck = true
				}
			}
			// 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.WriteTxLookupEntriesByBlock(batch, block) // Always write tx indices for live blocks, we assume they are needed

			// 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 += int64(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 += int64(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
		}
	}
	// Write the tx index tail (block number from where we index) before write any live blocks
	if len(liveBlocks) > 0 && liveBlocks[0].NumberU64() == ancientLimit+1 {
		// The tx index tail can only be one of the following two options:
		// * 0: all ancient blocks have been indexed
		// * ancient-limit: the indices of blocks before ancient-limit are ignored
		if tail := rawdb.ReadTxIndexTail(bc.db); tail == nil {
			if bc.txLookupLimit == 0 || ancientLimit <= bc.txLookupLimit {
				rawdb.WriteTxIndexTail(bc.db, 0)
			} else {
				rawdb.WriteTxIndexTail(bc.db, ancientLimit-bc.txLookupLimit)
			}
		}
	}
	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
}

// SetTxLookupLimit is responsible for updating the txlookup limit to the
// original one stored in db if the new mismatches with the old one.
func (bc *BlockChain) SetTxLookupLimit(limit uint64) {
	bc.txLookupLimit = limit
}

// TxLookupLimit retrieves the txlookup limit used by blockchain to prune
// stale transaction indices.
func (bc *BlockChain) TxLookupLimit() uint64 {
	return bc.txLookupLimit
}

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) {
	if bc.insertStopped() {
		return errInsertionInterrupted
	}

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

// InsertPreprocessedBlock inserts a block which is already processed. This is
// only called by validators when committing, since that is the only flow where
// a block would have previously been preprocessed. It can happen that the
// validator has already inserted the block that they attempt to insert here,
// in the case that they received it over the network while the engine was
// processing a message that caused a validator to commit. This is possible
// because there is no synchronisation between the area of code that inserts
// blocks received from the network and the engine.
func (bc *BlockChain) InsertPreprocessedBlock(block *types.Block, receipts []*types.Receipt, logs []*types.Log, state *state.StateDB) error {
	if !bc.chainmu.TryLock() {
		return errInsertionInterrupted
	}
	defer bc.chainmu.Unlock()

	current := bc.CurrentHeader()
	currentNum := current.Number.Uint64()
	blockNum := block.NumberU64()

	switch {
	case blockNum > currentNum+1:
		// If the block we are trying to insert is a future block, then something
		// is badly wrong since validators should only start working on a block
		// once they have agreed they previous block.
		return fmt.Errorf(
			"tried to insert preprocessed block that is in the future, current: (num:%d,hash:%v), preprocessed: (num:%d, hash:%v)",
			currentNum,
			current.Hash(),
			blockNum,
			block.Hash(),
		)
	case blockNum <= currentNum:
		// We expect this to ocur sometimes, we log an info.
		log.Info("Tried to insert preprocessed bock but it has already been inserted", "preprocessedNum", blockNum, "currentNum", currentNum)
		return nil
	default: // blockNum == currentNum + 1
		if block.Header().ParentHash != current.Hash() {
			return fmt.Errorf(
				"tried to insert preprocessed block but parent-hash does not match parent, current: (num:%d, hash:%v), preprocessed: (num:%d, hash:%v, parentHash:%v)",
				currentNum,
				current.Hash(),
				blockNum,
				block.Hash(),
				block.ParentHash(),
			)
		}
		// Insert the block and return any error
		_, err := bc.insertPreprocessedBlock(block, receipts, logs, state, true)
		return err
	}
}

// insertPreprocessedBlock writes the block and all associated state to the database,
// but is expects the chain mutex to be held.
func (bc *BlockChain) insertPreprocessedBlock(block *types.Block, receipts []*types.Receipt, logs []*types.Log, state *state.StateDB, emitHeadEvent bool) (status WriteStatus, err error) {
	if bc.insertStopped() {
		return NonStatTy, errInsertionInterrupted
	}

	randomCommitment := common.Hash{}
	if istEngine, isIstanbul := bc.engine.(consensus.Istanbul); isIstanbul {

		if hash := bc.GetCanonicalHash(block.NumberU64()); (hash != common.Hash{} && hash != block.Hash()) {
			log.Error("Found two blocks with same height", "old", hash, "new", block.Hash())
		}
		err := istEngine.OnBlockInsertion(block.Header(), state)
		if err != nil {
			return NonStatTy, err
		}

		blockAuthor, err := istEngine.Author(block.Header())
		if err != nil {
			log.Warn("Unable to retrieve the author for block", "blockNum", block.NumberU64(), "err", err)
		}

		if blockAuthor == istEngine.ValidatorAddress() && !istEngine.IsProxy() {
			// Calculate the randomness commitment
			_, randomCommitment, err = istEngine.GenerateRandomness(block.ParentHash())

			if err != nil {
				log.Error("Couldn't generate the randomness for the block", "blockNum", block.NumberU64(), "err", err)
				return NonStatTy, err
			}
		}
	}

	// 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 := big.NewInt(int64(block.NumberU64() + 1))

	// 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)
	rawdb.WriteReceipts(blockBatch, block.Hash(), block.NumberU64(), receipts)
	rawdb.WritePreimages(blockBatch, state.Preimages())
	if (randomCommitment != common.Hash{}) {
		// Note that the random commitment cache entry is never transferred over to the freezer,
		// unlike all of the other saved data within this batch write
		rawdb.WriteRandomCommitmentCache(blockBatch, randomCommitment, block.ParentHash())
	}
	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, nil); 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, nil)
					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)

	// Do a sanity check that the provided chain is actually ordered and linked.
	for i := 1; i < len(chain); i++ {
		block, prev := chain[i], 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-check passed, start the full block imports.
	if !bc.chainmu.TryLock() {
		return 0, errChainStopped
	}
	defer bc.chainmu.Unlock()
	return bc.insertChain(chain, true)
}

// InsertChainWithoutSealVerification works exactly the same
// except for seal verification, seal verification is omitted
func (bc *BlockChain) InsertChainWithoutSealVerification(block *types.Block) (int, error) {
	bc.blockProcFeed.Send(true)
	defer bc.blockProcFeed.Send(false)

	if !bc.chainmu.TryLock() {
		return 0, errChainStopped
	}
	defer bc.chainmu.Unlock()
	return bc.insertChain(types.Blocks([]*types.Block{block}), false)
}

// 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 bc.insertStopped() {
		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, big.NewInt(1))
			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 errors.Is(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 errors.Is(err, consensus.ErrFutureBlock) || (errors.Is(err, consensus.ErrUnknownAncestor) && bc.futureBlocks.Contains(it.first().ParentHash())):
		for block != nil && (it.index == 0 || errors.Is(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)
	var activeState *state.StateDB
	defer func() {
		// The chain importer is starting and stopping trie prefetchers. If a bad
		// block or other error is hit however, an early return may not properly
		// terminate the background threads. This defer ensures that we clean up
		// and dangling prefetcher, without defering each and holding on live refs.
		if activeState != nil {
			activeState.StopPrefetcher()
		}
	}()

	for ; block != nil && err == nil || err == ErrKnownBlock; block, err = it.next() {
		// If the chain is terminating, stop processing blocks
		if bc.insertStopped() {
			log.Debug("Abort during block processing")
			break
		}
		// If the header is a banned one, straight out abort
		if BadHashes[block.Hash()] {
			bc.reportBlock(block, nil, ErrBannedHash)
			return it.index, ErrBannedHash
		}
		// 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.Warn
			logger("Inserted known block", "number", block.Number(), "hash", block.Hash(), "txs", len(block.Transactions()), "gas", block.GasUsed(),
				"root", block.Root())

			// Special case. Commit the empty receipt slice if we meet the known
			// block in the middle. It can only happen in the clique chain. Whenever
			// we insert blocks via `insertSideChain`, we only commit `td`, `header`
			// and `body` if it's non-existent. Since we don't have receipts without
			// reexecution, so nothing to commit. But if the sidechain will be adpoted
			// as the canonical chain eventually, it needs to be reexecuted for missing
			// state, but if it's this special case here(skip reexecution) we will lose
			// the empty receipt entry.
			if len(block.Transactions()) == 0 {
				rawdb.WriteReceipts(bc.db, block.Hash(), block.NumberU64(), nil)
			} else {
				log.Error("Please file an issue, skip known block execution without receipt",
					"hash", block.Hash(), "number", block.NumberU64())
			}
			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
			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, bc.snaps)
		if err != nil {
			return it.index, err
		}
		// Enable prefetching to pull in trie node paths while processing transactions
		statedb.StartPrefetcher("chain")
		activeState = statedb
		// 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 {
				throwaway, _ := state.New(parent.Root, bc.stateCache, bc.snaps)

				go func(start time.Time, followup *types.Block, throwaway *state.StateDB, interrupt *uint32) {
					bc.prefetcher.Prefetch(followup, throwaway, bc.vmConfig, &followupInterrupt)

					blockPrefetchExecuteTimer.Update(time.Since(start))
					if atomic.LoadUint32(interrupt) == 1 {
						blockPrefetchInterruptMeter.Mark(1)
					}
				}(time.Now(), followup, throwaway, &followupInterrupt)
			}
		}

		// 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
		snapshotAccountReadTimer.Update(statedb.SnapshotAccountReads) // Account reads are complete, we can mark them
		snapshotStorageReadTimer.Update(statedb.SnapshotStorageReads) // Storage reads are complete, we can mark them
		triehash := statedb.AccountHashes + statedb.StorageHashes     // Save to not double count in validation
		trieproc := statedb.SnapshotAccountReads + statedb.AccountReads + statedb.AccountUpdates
		trieproc += statedb.SnapshotStorageReads + 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.insertPreprocessedBlock(block, receipts, logs, statedb, false)
		atomic.StoreUint32(&followupInterrupt, 1)
		if err != nil {
			return it.index, err
		}
		// 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
		snapshotCommitTimer.Update(statedb.SnapshotCommits) // Snapshot commits are complete, we can mark them

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

		switch status {
		case CanonStatTy:
			log.Debug("Inserted new block", "number", block.Number(), "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(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(),
				"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(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(),
				"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 && errors.Is(err, consensus.ErrFutureBlock) {
		if err := bc.addFutureBlock(block); err != nil {
			return it.index, err
		}
		block, err = it.next()

		for ; block != nil && errors.Is(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 && errors.Is(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

				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")
			}
		}

		externTd = big.NewInt(int64(block.NumberU64() + 1))

		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(),
				"elapsed", common.PrettyDuration(time.Since(start)),
				"txs", len(block.Transactions()), "gas", block.GasUsed(),
				"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 {
		log.Info("Found orphaned sidechain, removing", "length", len(hashes))
		batch := bc.db.NewBatch()

		for i := 0; i < len(hashes); i++ {
			rawdb.DeleteBlock(batch, hashes[i], numbers[i])
		}

		if err := batch.Write(); err != nil {
			log.Error("Error when removing sidechain", "err", err)
		}

		// Clear out any stale content from the caches
		bc.purge()

		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 bc.insertStopped() {
				log.Debug("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
}

func (bc *BlockChain) purge() {
	// 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()
}

// 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
					}
					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")
		}
	}
	// Reorgs should not happen with Istanbul consensus. Warn the user.
	if len(oldChain) > 0 && len(newChain) > 0 {
		log.Error("Chain reorg detected", "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)))
		blockReorgMeter.Mark(1)
	} 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
}

// futureBlocksLoop processes the 'future block' queue.
func (bc *BlockChain) futureBlocksLoop() {
	defer bc.wg.Done()

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

// maintainTxIndex is responsible for the construction and deletion of the
// transaction index.
//
// User can use flag `txlookuplimit` to specify a "recentness" block, below
// which ancient tx indices get deleted. If `txlookuplimit` is 0, it means
// all tx indices will be reserved.
//
// The user can adjust the txlookuplimit value for each launch after fast
// sync, Geth will automatically construct the missing indices and delete
// the extra indices.
func (bc *BlockChain) maintainTxIndex(ancients uint64) {
	defer bc.wg.Done()

	// Before starting the actual maintenance, we need to handle a special case,
	// where user might init Geth with an external ancient database. If so, we
	// need to reindex all necessary transactions before starting to process any
	// pruning requests.
	if ancients > 0 {
		var from = uint64(0)
		if bc.txLookupLimit != 0 && ancients > bc.txLookupLimit {
			from = ancients - bc.txLookupLimit
		}
		rawdb.IndexTransactions(bc.db, from, ancients, bc.quit)
	}

	// indexBlocks reindexes or unindexes transactions depending on user configuration
	indexBlocks := func(tail *uint64, head uint64, done chan struct{}) {
		defer func() { done <- struct{}{} }()

		// If the user just upgraded Geth to a new version which supports transaction
		// index pruning, write the new tail and remove anything older.
		if tail == nil {
			if bc.txLookupLimit == 0 || head < bc.txLookupLimit {
				// Nothing to delete, write the tail and return
				rawdb.WriteTxIndexTail(bc.db, 0)
			} else {
				// Prune all stale tx indices and record the tx index tail
				rawdb.UnindexTransactions(bc.db, 0, head-bc.txLookupLimit+1, bc.quit)
			}
			return
		}
		// If a previous indexing existed, make sure that we fill in any missing entries
		if bc.txLookupLimit == 0 || head < bc.txLookupLimit {
			if *tail > 0 {
				rawdb.IndexTransactions(bc.db, 0, *tail, bc.quit)
			}
			return
		}
		// Update the transaction index to the new chain state
		if head-bc.txLookupLimit+1 < *tail {
			// Reindex a part of missing indices and rewind index tail to HEAD-limit
			rawdb.IndexTransactions(bc.db, head-bc.txLookupLimit+1, *tail, bc.quit)
		} else {
			// Unindex a part of stale indices and forward index tail to HEAD-limit
			rawdb.UnindexTransactions(bc.db, *tail, head-bc.txLookupLimit+1, bc.quit)
		}
	}

	// Any reindexing done, start listening to chain events and moving the index window
	var (
		done   chan struct{}                  // Non-nil if background unindexing or reindexing routine is active.
		headCh = make(chan ChainHeadEvent, 1) // Buffered to avoid locking up the event feed
	)
	sub := bc.SubscribeChainHeadEvent(headCh)
	if sub == nil {
		return
	}
	defer sub.Unsubscribe()

	for {
		select {
		case head := <-headCh:
			if done == nil {
				done = make(chan struct{})
				go indexBlocks(rawdb.ReadTxIndexTail(bc.db), head.Block.NumberU64(), done)
			}
		case <-done:
			done = nil
		case <-bc.quit:
			if done != nil {
				log.Info("Waiting background transaction indexer to exit")
				<-done
			}
			return
		}
	}
}

// HasBadBlock returns whether the block with the hash is a bad block
func (bc *BlockChain) HasBadBlock(hash common.Hash) bool {
	return (rawdb.ReadBadBlock(bc.db, hash) != nil)
}

// reportBlock logs a bad block error.
func (bc *BlockChain) reportBlock(block *types.Block, receipts types.Receipts, err error) {
	rawdb.WriteBadBlock(bc.db, 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.
func (bc *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int, contiguousHeaders bool) (int, error) {
	start := time.Now()
	if i, err := bc.hc.ValidateHeaderChain(chain, checkFreq, true); err != nil {
		return i, err
	}

	if !bc.chainmu.TryLock() {
		return 0, errChainStopped
	}
	defer bc.chainmu.Unlock()

	_, err := bc.hc.InsertHeaderChain(chain, start)
	return 0, err
}

// 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 {
	// Blockchain might have cached the whole block, only if not go to headerchain
	if block, ok := bc.blockCache.Get(hash); ok {
		return block.(*types.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) *types.Header {
	// Blockchain might have cached the whole block, only if not go to headerchain
	if block, ok := bc.blockCache.Get(hash); ok {
		return block.(*types.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)
}

// 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))
}

// RecoverRandomnessCache will do a search for the block that was used to generate the given commitment.
// Specifically, it will find the block that this node authored and that block's parent hash is used to
// created the commitment.  The search is a reverse iteration of the node's local chain starting at
// the block where it's hash is the given commitmentBlockHash.
func (bc *BlockChain) RecoverRandomnessCache(commitment common.Hash, commitmentBlockHash common.Hash) error {
	istEngine, isIstanbul := bc.engine.(consensus.Istanbul)
	if !isIstanbul {
		return nil
	}

	log.Info("Recovering randomness cache entry", "commitment", commitment.Hex(), "initial block search", commitmentBlockHash.Hex())

	blockHashIter := commitmentBlockHash
	var parentHash common.Hash
	for {
		blockHeader := bc.GetHeaderByHash(blockHashIter)

		// We got to the genesis block, so search didn't find the latest
		// block authored by this validator.
		if blockHeader.Number.Uint64() == 0 {
			return errCommitmentNotFound
		}

		blockAuthor, err := istEngine.Author(blockHeader)
		if err != nil {
			log.Error("Error is retrieving block author", "block number", blockHeader.Number.Uint64(), "block hash", blockHeader.Hash(), "error", err)
			return err
		}

		if blockAuthor == istEngine.ValidatorAddress() {
			parentHash = blockHeader.ParentHash
			break
		}

		blockHashIter = blockHeader.ParentHash
	}

	// Calculate the randomness commitment
	// The calculation is stateless (e.g. it's just a hash operation of a string), so any passed in block header and state
	// will do. Will use the previously fetched current header and state.
	_, randomCommitment, err := istEngine.GenerateRandomness(parentHash)
	if err != nil {
		log.Error("Couldn't generate the randomness from the parent hash", "parent hash", parentHash, "err", err)
		return err
	}

	rawdb.WriteRandomCommitmentCache(bc.db, randomCommitment, parentHash)

	return nil
}
