// 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"
	"runtime"
	"sync"
	"sync/atomic"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/mclock"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/event"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/pow"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/trie"
	"github.com/hashicorp/golang-lru"
)

var (
	blockInsertTimer = metrics.NewTimer("chain/inserts")

	ErrNoGenesis = errors.New("Genesis not found in chain")
)

const (
	bodyCacheLimit      = 256
	blockCacheLimit     = 256
	maxFutureBlocks     = 256
	maxTimeFutureBlocks = 30
	// must be bumped when consensus algorithm is changed, this forces the upgradedb
	// command to be run (forces the blocks to be imported again using the new algorithm)
	BlockChainVersion = 3
	badBlockLimit     = 10
)

// 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 {
	config *params.ChainConfig // chain & network configuration

	hc           *HeaderChain
	chainDb      ethdb.Database
	eventMux     *event.TypeMux
	genesisBlock *types.Block

	mu      sync.RWMutex // global mutex for locking chain operations
	chainmu sync.RWMutex // blockchain insertion lock
	procmu  sync.RWMutex // block processor lock

	checkpoint       int          // checkpoint counts towards the new checkpoint
	currentBlock     *types.Block // Current head of the block chain
	currentFastBlock *types.Block // Current head of the fast-sync chain (may be above the block chain!)

	stateCache   *state.StateDB // 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
	blockCache   *lru.Cache     // Cache for the most recent entire blocks
	futureBlocks *lru.Cache     // future blocks are blocks added for later processing

	quit    chan struct{} // blockchain quit channel
	running int32         // running must be called atomically
	// procInterrupt must be atomically called
	procInterrupt int32          // interrupt signaler for block processing
	wg            sync.WaitGroup // chain processing wait group for shutting down

	pow       pow.PoW
	processor Processor // block processor interface
	validator Validator // block and state validator interface
	vmConfig  vm.Config

	badBlocks *lru.Cache // Bad block cache
}

// NewBlockChain returns a fully initialised block chain using information
// available in the database. It initialiser the default Ethereum Validator and
// Processor.
func NewBlockChain(chainDb ethdb.Database, config *params.ChainConfig, pow pow.PoW, mux *event.TypeMux, vmConfig vm.Config) (*BlockChain, error) {
	bodyCache, _ := lru.New(bodyCacheLimit)
	bodyRLPCache, _ := lru.New(bodyCacheLimit)
	blockCache, _ := lru.New(blockCacheLimit)
	futureBlocks, _ := lru.New(maxFutureBlocks)
	badBlocks, _ := lru.New(badBlockLimit)

	bc := &BlockChain{
		config:       config,
		chainDb:      chainDb,
		eventMux:     mux,
		quit:         make(chan struct{}),
		bodyCache:    bodyCache,
		bodyRLPCache: bodyRLPCache,
		blockCache:   blockCache,
		futureBlocks: futureBlocks,
		pow:          pow,
		vmConfig:     vmConfig,
		badBlocks:    badBlocks,
	}
	bc.SetValidator(NewBlockValidator(config, bc, pow))
	bc.SetProcessor(NewStateProcessor(config, bc))

	gv := func() HeaderValidator { return bc.Validator() }
	var err error
	bc.hc, err = NewHeaderChain(chainDb, config, gv, bc.getProcInterrupt)
	if err != nil {
		return nil, err
	}

	bc.genesisBlock = bc.GetBlockByNumber(0)
	if bc.genesisBlock == nil {
		return nil, ErrNoGenesis
	}

	if err := bc.loadLastState(); err != nil {
		return nil, err
	}
	// 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(fmt.Sprintf("Found bad hash, rewinding chain to block #%d [%x…]", header.Number, header.ParentHash[:4]))
				bc.SetHead(header.Number.Uint64() - 1)
				log.Error(fmt.Sprint("Chain rewind was successful, resuming normal operation"))
			}
		}
	}
	// Take ownership of this particular state
	go bc.update()
	return bc, nil
}

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

// loadLastState loads the last known chain state from the database. This method
// assumes that the chain manager mutex is held.
func (self *BlockChain) loadLastState() error {
	// Restore the last known head block
	head := GetHeadBlockHash(self.chainDb)
	if head == (common.Hash{}) {
		// Corrupt or empty database, init from scratch
		self.Reset()
	} else {
		if block := self.GetBlockByHash(head); block != nil {
			// Block found, set as the current head
			self.currentBlock = block
		} else {
			// Corrupt or empty database, init from scratch
			self.Reset()
		}
	}
	// Restore the last known head header
	currentHeader := self.currentBlock.Header()
	if head := GetHeadHeaderHash(self.chainDb); head != (common.Hash{}) {
		if header := self.GetHeaderByHash(head); header != nil {
			currentHeader = header
		}
	}
	self.hc.SetCurrentHeader(currentHeader)
	// Restore the last known head fast block
	self.currentFastBlock = self.currentBlock
	if head := GetHeadFastBlockHash(self.chainDb); head != (common.Hash{}) {
		if block := self.GetBlockByHash(head); block != nil {
			self.currentFastBlock = block
		}
	}
	// Initialize a statedb cache to ensure singleton account bloom filter generation
	statedb, err := state.New(self.currentBlock.Root(), self.chainDb)
	if err != nil {
		return err
	}
	self.stateCache = statedb

	// Issue a status log for the user
	headerTd := self.GetTd(currentHeader.Hash(), currentHeader.Number.Uint64())
	blockTd := self.GetTd(self.currentBlock.Hash(), self.currentBlock.NumberU64())
	fastTd := self.GetTd(self.currentFastBlock.Hash(), self.currentFastBlock.NumberU64())

	log.Info(fmt.Sprintf("Last header: #%d [%x…] TD=%v", currentHeader.Number, currentHeader.Hash().Bytes()[:4], headerTd))
	log.Info(fmt.Sprintf("Last block: #%d [%x…] TD=%v", self.currentBlock.Number(), self.currentBlock.Hash().Bytes()[:4], blockTd))
	log.Info(fmt.Sprintf("Fast block: #%d [%x…] TD=%v", self.currentFastBlock.Number(), self.currentFastBlock.Hash().Bytes()[:4], fastTd))

	return nil
}

// SetHead rewinds the local chain to a new head. In the case of headers, everything
// above the new head will be deleted and the new one set. In the case of blocks
// though, the head may be further rewound if block bodies are missing (non-archive
// nodes after a fast sync).
func (bc *BlockChain) SetHead(head uint64) {
	bc.mu.Lock()
	defer bc.mu.Unlock()

	delFn := func(hash common.Hash, num uint64) {
		DeleteBody(bc.chainDb, hash, num)
	}
	bc.hc.SetHead(head, delFn)

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

	// Update all computed fields to the new head
	currentHeader := bc.hc.CurrentHeader()
	if bc.currentBlock != nil && currentHeader.Number.Uint64() < bc.currentBlock.NumberU64() {
		bc.currentBlock = bc.GetBlock(currentHeader.Hash(), currentHeader.Number.Uint64())
	}
	if bc.currentFastBlock != nil && currentHeader.Number.Uint64() < bc.currentFastBlock.NumberU64() {
		bc.currentFastBlock = bc.GetBlock(currentHeader.Hash(), currentHeader.Number.Uint64())
	}

	if bc.currentBlock == nil {
		bc.currentBlock = bc.genesisBlock
	}
	if bc.currentFastBlock == nil {
		bc.currentFastBlock = bc.genesisBlock
	}

	if err := WriteHeadBlockHash(bc.chainDb, bc.currentBlock.Hash()); err != nil {
		log.Crit(fmt.Sprintf("failed to reset head block hash: %v", err))
	}
	if err := WriteHeadFastBlockHash(bc.chainDb, bc.currentFastBlock.Hash()); err != nil {
		log.Crit(fmt.Sprintf("failed to reset head fast block hash: %v", err))
	}
	bc.loadLastState()
}

// FastSyncCommitHead sets the current head block to the one defined by the hash
// irrelevant what the chain contents were prior.
func (self *BlockChain) FastSyncCommitHead(hash common.Hash) error {
	// Make sure that both the block as well at its state trie exists
	block := self.GetBlockByHash(hash)
	if block == nil {
		return fmt.Errorf("non existent block [%x…]", hash[:4])
	}
	if _, err := trie.NewSecure(block.Root(), self.chainDb, 0); err != nil {
		return err
	}
	// If all checks out, manually set the head block
	self.mu.Lock()
	self.currentBlock = block
	self.mu.Unlock()

	log.Info(fmt.Sprintf("committed block #%d [%x…] as new head", block.Number(), hash[:4]))
	return nil
}

// GasLimit returns the gas limit of the current HEAD block.
func (self *BlockChain) GasLimit() *big.Int {
	self.mu.RLock()
	defer self.mu.RUnlock()

	return self.currentBlock.GasLimit()
}

// LastBlockHash return the hash of the HEAD block.
func (self *BlockChain) LastBlockHash() common.Hash {
	self.mu.RLock()
	defer self.mu.RUnlock()

	return self.currentBlock.Hash()
}

// CurrentBlock retrieves the current head block of the canonical chain. The
// block is retrieved from the blockchain's internal cache.
func (self *BlockChain) CurrentBlock() *types.Block {
	self.mu.RLock()
	defer self.mu.RUnlock()

	return self.currentBlock
}

// CurrentFastBlock retrieves the current fast-sync head block of the canonical
// chain. The block is retrieved from the blockchain's internal cache.
func (self *BlockChain) CurrentFastBlock() *types.Block {
	self.mu.RLock()
	defer self.mu.RUnlock()

	return self.currentFastBlock
}

// Status returns status information about the current chain such as the HEAD Td,
// the HEAD hash and the hash of the genesis block.
func (self *BlockChain) Status() (td *big.Int, currentBlock common.Hash, genesisBlock common.Hash) {
	self.mu.RLock()
	defer self.mu.RUnlock()

	return self.GetTd(self.currentBlock.Hash(), self.currentBlock.NumberU64()), self.currentBlock.Hash(), self.genesisBlock.Hash()
}

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

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

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

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

// AuxValidator returns the auxiliary validator (Proof of work atm)
func (self *BlockChain) AuxValidator() pow.PoW { return self.pow }

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

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

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

// ResetWithGenesisBlock purges the entire blockchain, restoring it to the
// specified genesis state.
func (bc *BlockChain) ResetWithGenesisBlock(genesis *types.Block) {
	// Dump the entire block chain and purge the caches
	bc.SetHead(0)

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

	// Prepare the genesis block and reinitialise the chain
	if err := bc.hc.WriteTd(genesis.Hash(), genesis.NumberU64(), genesis.Difficulty()); err != nil {
		log.Crit(fmt.Sprintf("failed to write genesis block TD: %v", err))
	}
	if err := WriteBlock(bc.chainDb, genesis); err != nil {
		log.Crit(fmt.Sprintf("failed to write genesis block: %v", err))
	}
	bc.genesisBlock = genesis
	bc.insert(bc.genesisBlock)
	bc.currentBlock = bc.genesisBlock
	bc.hc.SetGenesis(bc.genesisBlock.Header())
	bc.hc.SetCurrentHeader(bc.genesisBlock.Header())
	bc.currentFastBlock = bc.genesisBlock
}

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

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

	if first > last {
		return fmt.Errorf("export failed: first (%d) is greater than last (%d)", first, last)
	}

	log.Info(fmt.Sprintf("exporting %d blocks...\n", last-first+1))

	for nr := first; nr <= last; nr++ {
		block := self.GetBlockByNumber(nr)
		if block == nil {
			return fmt.Errorf("export failed on #%d: not found", nr)
		}

		if err := block.EncodeRLP(w); err != nil {
			return err
		}
	}

	return nil
}

// insert injects a new head block into the current block chain. This method
// assumes that the block is indeed a true head. It will also reset the head
// header and the head fast sync block to this very same block if they are older
// or if they are on a different side chain.
//
// Note, this function assumes that the `mu` mutex is held!
func (bc *BlockChain) insert(block *types.Block) {
	// If the block is on a side chain or an unknown one, force other heads onto it too
	updateHeads := GetCanonicalHash(bc.chainDb, block.NumberU64()) != block.Hash()

	// Add the block to the canonical chain number scheme and mark as the head
	if err := WriteCanonicalHash(bc.chainDb, block.Hash(), block.NumberU64()); err != nil {
		log.Crit(fmt.Sprintf("failed to insert block number: %v", err))
	}
	if err := WriteHeadBlockHash(bc.chainDb, block.Hash()); err != nil {
		log.Crit(fmt.Sprintf("failed to insert head block hash: %v", err))
	}
	bc.currentBlock = block

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

		if err := WriteHeadFastBlockHash(bc.chainDb, block.Hash()); err != nil {
			log.Crit(fmt.Sprintf("failed to insert head fast block hash: %v", err))
		}
		bc.currentFastBlock = block
	}
}

// Accessors
func (bc *BlockChain) Genesis() *types.Block {
	return bc.genesisBlock
}

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

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

// HasBlock checks if a block is fully present in the database or not, caching
// it if present.
func (bc *BlockChain) HasBlock(hash common.Hash) bool {
	return bc.GetBlockByHash(hash) != 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) bool {
	// Check first that the block itself is known
	block := bc.GetBlockByHash(hash)
	if block == nil {
		return false
	}
	// Ensure the associated state is also present
	_, err := state.New(block.Root(), bc.chainDb)
	return err == nil
}

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

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

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

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

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

// 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
	}
	close(bc.quit)
	atomic.StoreInt32(&bc.procInterrupt, 1)

	bc.wg.Wait()

	log.Info(fmt.Sprint("Chain manager stopped"))
}

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

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

type WriteStatus byte

const (
	NonStatTy WriteStatus = iota
	CanonStatTy
	SplitStatTy
	SideStatTy
)

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

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

		currentHeader := self.hc.CurrentHeader()
		if currentHeader.Hash() == hash {
			self.hc.SetCurrentHeader(self.GetHeader(currentHeader.ParentHash, currentHeader.Number.Uint64()-1))
		}
		if self.currentFastBlock.Hash() == hash {
			self.currentFastBlock = self.GetBlock(self.currentFastBlock.ParentHash(), self.currentFastBlock.NumberU64()-1)
			WriteHeadFastBlockHash(self.chainDb, self.currentFastBlock.Hash())
		}
		if self.currentBlock.Hash() == hash {
			self.currentBlock = self.GetBlock(self.currentBlock.ParentHash(), self.currentBlock.NumberU64()-1)
			WriteHeadBlockHash(self.chainDb, self.currentBlock.Hash())
		}
	}
}

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

	transactions, logIndex := block.Transactions(), uint(0)

	for j := 0; j < len(receipts); j++ {
		// The transaction hash can be retrieved from the transaction itself
		receipts[j].TxHash = transactions[j].Hash()

		tx, _ := transactions[j].AsMessage(signer)
		// The contract address can be derived from the transaction itself
		if MessageCreatesContract(tx) {
			receipts[j].ContractAddress = crypto.CreateAddress(tx.From(), tx.Nonce())
		}
		// The used gas can be calculated based on previous receipts
		if j == 0 {
			receipts[j].GasUsed = new(big.Int).Set(receipts[j].CumulativeGasUsed)
		} else {
			receipts[j].GasUsed = new(big.Int).Sub(receipts[j].CumulativeGasUsed, receipts[j-1].CumulativeGasUsed)
		}
		// The derived log fields can simply be set from the block and transaction
		for k := 0; k < len(receipts[j].Logs); k++ {
			receipts[j].Logs[k].BlockNumber = block.NumberU64()
			receipts[j].Logs[k].BlockHash = block.Hash()
			receipts[j].Logs[k].TxHash = receipts[j].TxHash
			receipts[j].Logs[k].TxIndex = uint(j)
			receipts[j].Logs[k].Index = logIndex
			logIndex++
		}
	}
}

// InsertReceiptChain attempts to complete an already existing header chain with
// transaction and receipt data.
// XXX should this be moved to the test?
func (self *BlockChain) InsertReceiptChain(blockChain types.Blocks, receiptChain []types.Receipts) (int, error) {
	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 1; i < len(blockChain); i++ {
		if blockChain[i].NumberU64() != blockChain[i-1].NumberU64()+1 || blockChain[i].ParentHash() != blockChain[i-1].Hash() {
			// Chain broke ancestry, log a messge (programming error) and skip insertion
			failure := 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])

			log.Error(fmt.Sprint(failure.Error()))
			return 0, failure
		}
	}
	// Pre-checks passed, start the block body and receipt imports
	self.wg.Add(1)
	defer self.wg.Done()

	// Collect some import statistics to report on
	stats := struct{ processed, ignored int32 }{}
	start := time.Now()

	// Create the block importing task queue and worker functions
	tasks := make(chan int, len(blockChain))
	for i := 0; i < len(blockChain) && i < len(receiptChain); i++ {
		tasks <- i
	}
	close(tasks)

	errs, failed := make([]error, len(tasks)), int32(0)
	process := func(worker int) {
		for index := range tasks {
			block, receipts := blockChain[index], receiptChain[index]

			// Short circuit insertion if shutting down or processing failed
			if atomic.LoadInt32(&self.procInterrupt) == 1 {
				return
			}
			if atomic.LoadInt32(&failed) > 0 {
				return
			}
			// Short circuit if the owner header is unknown
			if !self.HasHeader(block.Hash()) {
				errs[index] = fmt.Errorf("containing header #%d [%x…] unknown", block.Number(), block.Hash().Bytes()[:4])
				atomic.AddInt32(&failed, 1)
				return
			}
			// Skip if the entire data is already known
			if self.HasBlock(block.Hash()) {
				atomic.AddInt32(&stats.ignored, 1)
				continue
			}
			// Compute all the non-consensus fields of the receipts
			SetReceiptsData(self.config, block, receipts)
			// Write all the data out into the database
			if err := WriteBody(self.chainDb, block.Hash(), block.NumberU64(), block.Body()); err != nil {
				errs[index] = fmt.Errorf("failed to write block body: %v", err)
				atomic.AddInt32(&failed, 1)
				log.Crit(fmt.Sprint(errs[index]))
				return
			}
			if err := WriteBlockReceipts(self.chainDb, block.Hash(), block.NumberU64(), receipts); err != nil {
				errs[index] = fmt.Errorf("failed to write block receipts: %v", err)
				atomic.AddInt32(&failed, 1)
				log.Crit(fmt.Sprint(errs[index]))
				return
			}
			if err := WriteMipmapBloom(self.chainDb, block.NumberU64(), receipts); err != nil {
				errs[index] = fmt.Errorf("failed to write log blooms: %v", err)
				atomic.AddInt32(&failed, 1)
				log.Crit(fmt.Sprint(errs[index]))
				return
			}
			if err := WriteTransactions(self.chainDb, block); err != nil {
				errs[index] = fmt.Errorf("failed to write individual transactions: %v", err)
				atomic.AddInt32(&failed, 1)
				log.Crit(fmt.Sprint(errs[index]))
				return
			}
			if err := WriteReceipts(self.chainDb, receipts); err != nil {
				errs[index] = fmt.Errorf("failed to write individual receipts: %v", err)
				atomic.AddInt32(&failed, 1)
				log.Crit(fmt.Sprint(errs[index]))
				return
			}
			atomic.AddInt32(&stats.processed, 1)
		}
	}
	// Start as many worker threads as goroutines allowed
	pending := new(sync.WaitGroup)
	for i := 0; i < runtime.GOMAXPROCS(0); i++ {
		pending.Add(1)
		go func(id int) {
			defer pending.Done()
			process(id)
		}(i)
	}
	pending.Wait()

	// If anything failed, report
	if failed > 0 {
		for i, err := range errs {
			if err != nil {
				return i, err
			}
		}
	}
	if atomic.LoadInt32(&self.procInterrupt) == 1 {
		log.Debug(fmt.Sprint("premature abort during receipt chain processing"))
		return 0, nil
	}
	// Update the head fast sync block if better
	self.mu.Lock()
	head := blockChain[len(errs)-1]
	if self.GetTd(self.currentFastBlock.Hash(), self.currentFastBlock.NumberU64()).Cmp(self.GetTd(head.Hash(), head.NumberU64())) < 0 {
		if err := WriteHeadFastBlockHash(self.chainDb, head.Hash()); err != nil {
			log.Crit(fmt.Sprintf("failed to update head fast block hash: %v", err))
		}
		self.currentFastBlock = head
	}
	self.mu.Unlock()

	// Report some public statistics so the user has a clue what's going on
	first, last := blockChain[0], blockChain[len(blockChain)-1]

	ignored := ""
	if stats.ignored > 0 {
		ignored = fmt.Sprintf(" (%d ignored)", stats.ignored)
	}
	log.Info(fmt.Sprintf("imported %4d receipts in %9v. #%d [%x… / %x…]%s", stats.processed, common.PrettyDuration(time.Since(start)), last.Number(), first.Hash().Bytes()[:4], last.Hash().Bytes()[:4], ignored))

	return 0, nil
}

// WriteBlock writes the block to the chain.
func (self *BlockChain) WriteBlock(block *types.Block) (status WriteStatus, err error) {
	self.wg.Add(1)
	defer self.wg.Done()

	// Calculate the total difficulty of the block
	ptd := self.GetTd(block.ParentHash(), block.NumberU64()-1)
	if ptd == nil {
		return NonStatTy, ParentError(block.ParentHash())
	}
	// Make sure no inconsistent state is leaked during insertion
	self.mu.Lock()
	defer self.mu.Unlock()

	localTd := self.GetTd(self.currentBlock.Hash(), self.currentBlock.NumberU64())
	externTd := new(big.Int).Add(block.Difficulty(), ptd)

	// Irrelevant of the canonical status, write the block itself to the database
	if err := self.hc.WriteTd(block.Hash(), block.NumberU64(), externTd); err != nil {
		log.Crit(fmt.Sprintf("failed to write block total difficulty: %v", err))
	}
	if err := WriteBlock(self.chainDb, block); err != nil {
		log.Crit(fmt.Sprintf("failed to write block contents: %v", err))
	}

	// 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
	if externTd.Cmp(localTd) > 0 || (externTd.Cmp(localTd) == 0 && mrand.Float64() < 0.5) {
		// Reorganise the chain if the parent is not the head block
		if block.ParentHash() != self.currentBlock.Hash() {
			if err := self.reorg(self.currentBlock, block); err != nil {
				return NonStatTy, err
			}
		}
		self.insert(block) // Insert the block as the new head of the chain
		status = CanonStatTy
	} else {
		status = SideStatTy
	}

	self.futureBlocks.Remove(block.Hash())

	return
}

// InsertChain will attempt to insert the given chain 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 (for possible errors see core/errors.go).
func (self *BlockChain) InsertChain(chain types.Blocks) (int, error) {
	// Do a sanity check that the provided chain is actually ordered and linked
	for i := 1; i < len(chain); i++ {
		if chain[i].NumberU64() != chain[i-1].NumberU64()+1 || chain[i].ParentHash() != chain[i-1].Hash() {
			// Chain broke ancestry, log a messge (programming error) and skip insertion
			failure := fmt.Errorf("non contiguous insert: item %d is #%d [%x…], item %d is #%d [%x…] (parent [%x…])",
				i-1, chain[i-1].NumberU64(), chain[i-1].Hash().Bytes()[:4], i, chain[i].NumberU64(), chain[i].Hash().Bytes()[:4], chain[i].ParentHash().Bytes()[:4])

			log.Error(fmt.Sprint(failure.Error()))
			return 0, failure
		}
	}
	// Pre-checks passed, start the full block imports
	self.wg.Add(1)
	defer self.wg.Done()

	self.chainmu.Lock()
	defer self.chainmu.Unlock()

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

	// Start the parallel nonce verifier.
	nonceAbort, nonceResults := verifyNoncesFromBlocks(self.pow, chain)
	defer close(nonceAbort)

	for i, block := range chain {
		if atomic.LoadInt32(&self.procInterrupt) == 1 {
			log.Debug(fmt.Sprint("Premature abort during block chain processing"))
			break
		}
		bstart := time.Now()
		// Wait for block i's nonce to be verified before processing
		// its state transition.
		for !nonceChecked[i] {
			r := <-nonceResults
			nonceChecked[r.index] = true
			if !r.valid {
				block := chain[r.index]
				return r.index, &BlockNonceErr{Hash: block.Hash(), Number: block.Number(), Nonce: block.Nonce()}
			}
		}

		if BadHashes[block.Hash()] {
			err := BadHashError(block.Hash())
			self.reportBlock(block, nil, err)
			return i, err
		}
		// Stage 1 validation of the block using the chain's validator
		// interface.
		err := self.Validator().ValidateBlock(block)
		if err != nil {
			if IsKnownBlockErr(err) {
				stats.ignored++
				continue
			}

			if err == BlockFutureErr {
				// Allow up to MaxFuture second in the future blocks. If this limit
				// is exceeded the chain is discarded and processed at a later time
				// if given.
				max := big.NewInt(time.Now().Unix() + maxTimeFutureBlocks)
				if block.Time().Cmp(max) == 1 {
					return i, fmt.Errorf("%v: BlockFutureErr, %v > %v", BlockFutureErr, block.Time(), max)
				}

				self.futureBlocks.Add(block.Hash(), block)
				stats.queued++
				continue
			}

			if IsParentErr(err) && self.futureBlocks.Contains(block.ParentHash()) {
				self.futureBlocks.Add(block.Hash(), block)
				stats.queued++
				continue
			}

			self.reportBlock(block, nil, err)
			return i, err
		}
		// Create a new statedb using the parent block and report an
		// error if it fails.
		switch {
		case i == 0:
			err = self.stateCache.Reset(self.GetBlock(block.ParentHash(), block.NumberU64()-1).Root())
		default:
			err = self.stateCache.Reset(chain[i-1].Root())
		}
		if err != nil {
			self.reportBlock(block, nil, err)
			return i, err
		}
		// Process block using the parent state as reference point.
		receipts, logs, usedGas, err := self.processor.Process(block, self.stateCache, self.vmConfig)
		if err != nil {
			self.reportBlock(block, receipts, err)
			return i, err
		}
		// Validate the state using the default validator
		err = self.Validator().ValidateState(block, self.GetBlock(block.ParentHash(), block.NumberU64()-1), self.stateCache, receipts, usedGas)
		if err != nil {
			self.reportBlock(block, receipts, err)
			return i, err
		}
		// Write state changes to database
		_, err = self.stateCache.Commit(self.config.IsEIP158(block.Number()))
		if err != nil {
			return i, err
		}

		// coalesce logs for later processing
		coalescedLogs = append(coalescedLogs, logs...)

		if err := WriteBlockReceipts(self.chainDb, block.Hash(), block.NumberU64(), receipts); err != nil {
			return i, err
		}

		// write the block to the chain and get the status
		status, err := self.WriteBlock(block)
		if err != nil {
			return i, err
		}

		switch status {
		case CanonStatTy:
			log.Debug("", "msg", log.Lazy{Fn: func() string {
				return fmt.Sprintf("inserted block #%d [%x…] in %9v: %3d txs %7v gas %d uncles.", block.Number(), block.Hash().Bytes()[0:4], common.PrettyDuration(time.Since(bstart)), len(block.Transactions()), block.GasUsed(), len(block.Uncles()))
			}})
			blockInsertTimer.UpdateSince(bstart)
			events = append(events, ChainEvent{block, block.Hash(), logs})

			// This puts transactions in a extra db for rpc
			if err := WriteTransactions(self.chainDb, block); err != nil {
				return i, err
			}
			// store the receipts
			if err := WriteReceipts(self.chainDb, receipts); err != nil {
				return i, err
			}
			// Write map map bloom filters
			if err := WriteMipmapBloom(self.chainDb, block.NumberU64(), receipts); err != nil {
				return i, err
			}
			// Write hash preimages
			if err := WritePreimages(self.chainDb, block.NumberU64(), self.stateCache.Preimages()); err != nil {
				return i, err
			}
		case SideStatTy:
			log.Trace("", "msg", log.Lazy{Fn: func() string {
				return fmt.Sprintf("inserted forked block #%d [%x…] (TD=%v) in %9v: %3d txs %d uncles.", block.Number(), block.Hash().Bytes()[0:4], block.Difficulty(), common.PrettyDuration(time.Since(bstart)), len(block.Transactions()), len(block.Uncles()))
			}})
			blockInsertTimer.UpdateSince(bstart)
			events = append(events, ChainSideEvent{block})

		case SplitStatTy:
			events = append(events, ChainSplitEvent{block, logs})
		}

		stats.processed++
		stats.usedGas += usedGas.Uint64()
		stats.report(chain, i)
	}

	go self.postChainEvents(events, coalescedLogs)

	return 0, nil
}

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

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

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

		var hashes, extra string
		if st.queued > 0 || st.ignored > 0 {
			extra = fmt.Sprintf(" (%d queued %d ignored)", st.queued, st.ignored)
		}
		if st.processed > 1 {
			hashes = fmt.Sprintf("%x… / %x…", start.Hash().Bytes()[:4], end.Hash().Bytes()[:4])
		} else {
			hashes = fmt.Sprintf("%x…", end.Hash().Bytes()[:4])
		}
		log.Info(fmt.Sprintf("imported %4d blocks, %5d txs (%7.3f Mg) in %9v (%6.3f Mg/s). #%v [%s]%s", st.processed, txcount, float64(st.usedGas)/1000000, common.PrettyDuration(elapsed), float64(st.usedGas)*1000/float64(elapsed), end.Number(), hashes, extra))

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

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

// reorgs 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 (self *BlockChain) reorg(oldBlock, newBlock *types.Block) error {
	var (
		newChain    types.Blocks
		oldChain    types.Blocks
		commonBlock *types.Block
		deletedTxs  types.Transactions
		deletedLogs []*types.Log
		// collectLogs collects the logs that were generated during the
		// processing of the block that corresponds with the given hash.
		// These logs are later announced as deleted.
		collectLogs = func(h common.Hash) {
			// Coalesce logs and set 'Removed'.
			receipts := GetBlockReceipts(self.chainDb, h, self.hc.GetBlockNumber(h))
			for _, receipt := range receipts {
				for _, log := range receipt.Logs {
					del := *log
					del.Removed = true
					deletedLogs = append(deletedLogs, &del)
				}
			}
		}
	)

	// first reduce whoever is higher bound
	if oldBlock.NumberU64() > newBlock.NumberU64() {
		// reduce old chain
		for ; oldBlock != nil && oldBlock.NumberU64() != newBlock.NumberU64(); oldBlock = self.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1) {
			oldChain = append(oldChain, oldBlock)
			deletedTxs = append(deletedTxs, oldBlock.Transactions()...)

			collectLogs(oldBlock.Hash())
		}
	} else {
		// reduce new chain and append new chain blocks for inserting later on
		for ; newBlock != nil && newBlock.NumberU64() != oldBlock.NumberU64(); newBlock = self.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")
	}

	for {
		if oldBlock.Hash() == newBlock.Hash() {
			commonBlock = oldBlock
			break
		}

		oldChain = append(oldChain, oldBlock)
		newChain = append(newChain, newBlock)
		deletedTxs = append(deletedTxs, oldBlock.Transactions()...)
		collectLogs(oldBlock.Hash())

		oldBlock, newBlock = self.GetBlock(oldBlock.ParentHash(), oldBlock.NumberU64()-1), self.GetBlock(newBlock.ParentHash(), newBlock.NumberU64()-1)
		if oldBlock == nil {
			return fmt.Errorf("Invalid old chain")
		}
		if newBlock == nil {
			return fmt.Errorf("Invalid new chain")
		}
	}
	// Ensure the user sees large reorgs
	logFn := log.Debug
	if len(oldChain) > 63 {
		logFn = log.Warn
	}
	logFn("", "msg", log.Lazy{Fn: func() string {
		oldLen, newLen := len(oldChain), len(newChain)
		newLast, newFirst := newChain[0], newChain[newLen-1]
		oldLast, oldFirst := oldChain[0], oldChain[oldLen-1]

		return fmt.Sprintf("Chain split detected after #%v [%x…]. Reorganising chain (-%v +%v blocks), rejecting #%v-#%v [%x…/%x…] in favour of #%v-#%v [%x…/%x…]",
			commonBlock.Number(), commonBlock.Hash().Bytes()[:4],
			oldLen, newLen,
			oldFirst.Number(), oldLast.Number(),
			oldFirst.Hash().Bytes()[:4], oldLast.Hash().Bytes()[:4],
			newFirst.Number(), newLast.Number(),
			newFirst.Hash().Bytes()[:4], newLast.Hash().Bytes()[:4])
	}})

	var addedTxs types.Transactions
	// insert blocks. Order does not matter. Last block will be written in ImportChain itself which creates the new head properly
	for _, block := range newChain {
		// insert the block in the canonical way, re-writing history
		self.insert(block)
		// write canonical receipts and transactions
		if err := WriteTransactions(self.chainDb, block); err != nil {
			return err
		}
		receipts := GetBlockReceipts(self.chainDb, block.Hash(), block.NumberU64())
		// write receipts
		if err := WriteReceipts(self.chainDb, receipts); err != nil {
			return err
		}
		// Write map map bloom filters
		if err := WriteMipmapBloom(self.chainDb, block.NumberU64(), receipts); err != nil {
			return err
		}
		addedTxs = append(addedTxs, block.Transactions()...)
	}

	// calculate the difference between deleted and added transactions
	diff := types.TxDifference(deletedTxs, addedTxs)
	// When transactions get deleted from the database that means the
	// receipts that were created in the fork must also be deleted
	for _, tx := range diff {
		DeleteReceipt(self.chainDb, tx.Hash())
		DeleteTransaction(self.chainDb, tx.Hash())
	}
	// Must be posted in a goroutine because of the transaction pool trying
	// to acquire the chain manager lock
	if len(diff) > 0 {
		go self.eventMux.Post(RemovedTransactionEvent{diff})
	}
	if len(deletedLogs) > 0 {
		go self.eventMux.Post(RemovedLogsEvent{deletedLogs})
	}

	if len(oldChain) > 0 {
		go func() {
			for _, block := range oldChain {
				self.eventMux.Post(ChainSideEvent{Block: block})
			}
		}()
	}

	return nil
}

// postChainEvents iterates over the events generated by a chain insertion and
// posts them into the event mux.
func (self *BlockChain) postChainEvents(events []interface{}, logs []*types.Log) {
	// post event logs for further processing
	self.eventMux.Post(logs)
	for _, event := range events {
		if event, ok := event.(ChainEvent); ok {
			// We need some control over the mining operation. Acquiring locks and waiting for the miner to create new block takes too long
			// and in most cases isn't even necessary.
			if self.LastBlockHash() == event.Hash {
				self.eventMux.Post(ChainHeadEvent{event.Block})
			}
		}
		// Fire the insertion events individually too
		self.eventMux.Post(event)
	}
}

func (self *BlockChain) update() {
	futureTimer := time.Tick(5 * time.Second)
	for {
		select {
		case <-futureTimer:
			self.procFutureBlocks()
		case <-self.quit:
			return
		}
	}
}

// BadBlockArgs represents the entries in the list returned when bad blocks are queried.
type BadBlockArgs struct {
	Hash   common.Hash   `json:"hash"`
	Header *types.Header `json:"header"`
}

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

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

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

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

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

// InsertHeaderChain attempts to insert the given header chain in to the local
// chain, possibly creating a reorg. If an error is returned, it will return the
// index number of the failing header as well an error describing what went wrong.
//
// The verify parameter can be used to fine tune whether nonce verification
// should be done or not. The reason behind the optional check is because some
// of the header retrieval mechanisms already need to verify nonces, as well as
// because nonces can be verified sparsely, not needing to check each.
func (self *BlockChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
	// Make sure only one thread manipulates the chain at once
	self.chainmu.Lock()
	defer self.chainmu.Unlock()

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

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

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

	return self.hc.InsertHeaderChain(chain, checkFreq, whFunc)
}

// writeHeader writes a header into the local chain, given that its parent is
// already known. If the total difficulty of the newly inserted header becomes
// greater than the current known TD, the canonical chain is re-routed.
//
// Note: This method is not concurrent-safe with inserting blocks simultaneously
// into the chain, as side effects caused by reorganisations cannot be emulated
// without the real blocks. Hence, writing headers directly should only be done
// in two scenarios: pure-header mode of operation (light clients), or properly
// separated header/block phases (non-archive clients).
func (self *BlockChain) writeHeader(header *types.Header) error {
	self.wg.Add(1)
	defer self.wg.Done()

	self.mu.Lock()
	defer self.mu.Unlock()

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

// CurrentHeader retrieves the current head header of the canonical chain. The
// header is retrieved from the HeaderChain's internal cache.
func (self *BlockChain) CurrentHeader() *types.Header {
	self.mu.RLock()
	defer self.mu.RUnlock()

	return self.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 (self *BlockChain) GetTd(hash common.Hash, number uint64) *big.Int {
	return self.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 (self *BlockChain) GetTdByHash(hash common.Hash) *big.Int {
	return self.hc.GetTdByHash(hash)
}

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

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

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

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

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