package parlia

import (
	"bytes"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"math/big"
	"os"
	"sort"
	"strings"
	"sync"
	"time"

	lru "github.com/hashicorp/golang-lru"
	"github.com/holiman/uint256"
	"github.com/ledgerwatch/erigon-lib/kv"
	"github.com/ledgerwatch/log/v3"
	"golang.org/x/crypto/sha3"

	"github.com/ledgerwatch/erigon/accounts/abi"
	"github.com/ledgerwatch/erigon/common"
	"github.com/ledgerwatch/erigon/common/hexutil"
	"github.com/ledgerwatch/erigon/common/math"
	"github.com/ledgerwatch/erigon/common/u256"
	"github.com/ledgerwatch/erigon/consensus"
	"github.com/ledgerwatch/erigon/consensus/misc"
	"github.com/ledgerwatch/erigon/core"
	"github.com/ledgerwatch/erigon/core/forkid"
	"github.com/ledgerwatch/erigon/core/state"
	"github.com/ledgerwatch/erigon/core/systemcontracts"
	"github.com/ledgerwatch/erigon/core/types"
	"github.com/ledgerwatch/erigon/core/vm"
	"github.com/ledgerwatch/erigon/crypto"
	"github.com/ledgerwatch/erigon/params"
	"github.com/ledgerwatch/erigon/rlp"
	"github.com/ledgerwatch/erigon/rpc"
	"github.com/ledgerwatch/erigon/turbo/snapshotsync"
)

const (
	inMemorySnapshots  = 128  // Number of recent snapshots to keep in memory
	inMemorySignatures = 4096 // Number of recent block signatures to keep in memory

	checkpointInterval = 1024        // Number of blocks after which to save the snapshot to the database
	defaultEpochLength = uint64(100) // Default number of blocks of checkpoint to update validatorSet from contract

	extraVanity      = 32 // Fixed number of extra-data prefix bytes reserved for signer vanity
	extraSeal        = 65 // Fixed number of extra-data suffix bytes reserved for signer seal
	nextForkHashSize = 4  // Fixed number of extra-data suffix bytes reserved for nextForkHash.

	validatorBytesLength = common.AddressLength
	wiggleTime           = uint64(1) // second, Random delay (per signer) to allow concurrent signers
	initialBackOffTime   = uint64(1) // second
	processBackOffTime   = uint64(1) // second

	systemRewardPercent = 4 // it means 1/2^4 = 1/16 percentage of gas fee incoming will be distributed to system
)

var (
	uncleHash  = types.CalcUncleHash(nil) // Always Keccak256(RLP([])) as uncles are meaningless outside of PoW.
	diffInTurn = big.NewInt(2)            // Block difficulty for in-turn signatures
	diffNoTurn = big.NewInt(1)            // Block difficulty for out-of-turn signatures
	// 100 native token
	maxSystemBalance = new(uint256.Int).Mul(uint256.NewInt(100), uint256.NewInt(params.Ether))

	systemContracts = map[common.Address]struct{}{
		systemcontracts.ValidatorContract:          {},
		systemcontracts.SlashContract:              {},
		systemcontracts.SystemRewardContract:       {},
		systemcontracts.LightClientContract:        {},
		systemcontracts.RelayerHubContract:         {},
		systemcontracts.GovHubContract:             {},
		systemcontracts.TokenHubContract:           {},
		systemcontracts.RelayerIncentivizeContract: {},
		systemcontracts.CrossChainContract:         {},
	}
)

// Various error messages to mark blocks invalid. These should be private to
// prevent engine specific errors from being referenced in the remainder of the
// codebase, inherently breaking if the engine is swapped out. Please put common
// error types into the consensus package.
var (
	// errUnknownBlock is returned when the list of validators is requested for a block
	// that is not part of the local blockchain.
	errUnknownBlock = errors.New("unknown block")

	// errMissingVanity is returned if a block's extra-data section is shorter than
	// 32 bytes, which is required to store the signer vanity.
	errMissingVanity = errors.New("extra-data 32 byte vanity prefix missing")

	// errMissingSignature is returned if a block's extra-data section doesn't seem
	// to contain a 65 byte secp256k1 signature.
	errMissingSignature = errors.New("extra-data 65 byte signature suffix missing")

	// errExtraValidators is returned if non-sprint-end block contain validator data in
	// their extra-data fields.
	errExtraValidators = errors.New("non-sprint-end block contains extra validator list")

	// errInvalidSpanValidators is returned if a block contains an
	// invalid list of validators (i.e. non divisible by 20 bytes).
	errInvalidSpanValidators = errors.New("invalid validator list on sprint end block")

	// errInvalidMixDigest is returned if a block's mix digest is non-zero.
	errInvalidMixDigest = errors.New("non-zero mix digest")

	// errInvalidUncleHash is returned if a block contains an non-empty uncle list.
	errInvalidUncleHash = errors.New("non empty uncle hash")

	// errMismatchingEpochValidators is returned if a sprint block contains a
	// list of validators different than the one the local node calculated.
	errMismatchingEpochValidators = errors.New("mismatching validator list on epoch block")

	// errInvalidDifficulty is returned if the difficulty of a block is missing.
	errInvalidDifficulty = errors.New("invalid difficulty")

	// errWrongDifficulty is returned if the difficulty of a block doesn't match the
	// turn of the signer.
	errWrongDifficulty = errors.New("wrong difficulty")

	// errOutOfRangeChain is returned if an authorization list is attempted to
	// be modified via out-of-range or non-contiguous headers.
	errOutOfRangeChain = errors.New("out of range or non-contiguous chain")

	// errBlockHashInconsistent is returned if an authorization list is attempted to
	// insert an inconsistent block.
	errBlockHashInconsistent = errors.New("the block hash is inconsistent")

	// errUnauthorizedValidator is returned if a header is signed by a non-authorized entity.
	errUnauthorizedValidator = errors.New("unauthorized validator")

	// errCoinBaseMisMatch is returned if a header's coinbase do not match with signature
	errCoinBaseMisMatch = errors.New("coinbase do not match with signature")

	// errRecentlySigned is returned if a header is signed by an authorized entity
	// that already signed a header recently, thus is temporarily not allowed to.
	errRecentlySigned = errors.New("recently signed")
)

// SignFn is a signer callback function to request a header to be signed by a
// backing account.
type SignFn func(validator common.Address, payload []byte, chainId *big.Int) ([]byte, error)

// ecrecover extracts the Ethereum account address from a signed header.
func ecrecover(header *types.Header, sigCache *lru.ARCCache, chainId *big.Int) (common.Address, error) {
	// If the signature's already cached, return that
	hash := header.Hash()
	if address, known := sigCache.Get(hash); known {
		return address.(common.Address), nil
	}
	// Retrieve the signature from the header extra-data
	if len(header.Extra) < extraSeal {
		return common.Address{}, errMissingSignature
	}
	signature := header.Extra[len(header.Extra)-extraSeal:]

	// Recover the public key and the Ethereum address
	pubkey, err := crypto.Ecrecover(SealHash(header, chainId).Bytes(), signature)
	if err != nil {
		return common.Address{}, err
	}
	var signer common.Address
	copy(signer[:], crypto.Keccak256(pubkey[1:])[12:])

	sigCache.Add(hash, signer)
	return signer, nil
}

// SealHash returns the hash of a block prior to it being sealed.
func SealHash(header *types.Header, chainId *big.Int) (hash common.Hash) {
	hasher := sha3.NewLegacyKeccak256()
	encodeSigHeader(hasher, header, chainId)
	hasher.Sum(hash[:0])
	return hash
}

func encodeSigHeader(w io.Writer, header *types.Header, chainId *big.Int) {
	err := rlp.Encode(w, []interface{}{
		chainId,
		header.ParentHash,
		header.UncleHash,
		header.Coinbase,
		header.Root,
		header.TxHash,
		header.ReceiptHash,
		header.Bloom,
		header.Difficulty,
		header.Number,
		header.GasLimit,
		header.GasUsed,
		header.Time,
		header.Extra[:len(header.Extra)-65], // this will panic if extra is too short, should check before calling encodeSigHeader
		header.MixDigest,
		header.Nonce,
	})
	if err != nil {
		panic("can't encode: " + err.Error())
	}
}

// parliaRLP returns the rlp bytes which needs to be signed for the parlia
// sealing. The RLP to sign consists of the entire header apart from the 65 byte signature
// contained at the end of the extra data.
//
// Note, the method requires the extra data to be at least 65 bytes, otherwise it
// panics. This is done to avoid accidentally using both forms (signature present
// or not), which could be abused to produce different hashes for the same header.
func parliaRLP(header *types.Header, chainId *big.Int) []byte {
	b := new(bytes.Buffer)
	encodeSigHeader(b, header, chainId)
	return b.Bytes()
}

type Parlia struct {
	chainConfig *params.ChainConfig  // Chain config
	config      *params.ParliaConfig // Consensus engine configuration parameters for parlia consensus
	genesisHash common.Hash
	db          kv.RwDB // Database to store and retrieve snapshot checkpoints

	recentSnaps *lru.ARCCache // Snapshots for recent block to speed up
	signatures  *lru.ARCCache // Signatures of recent blocks to speed up mining

	signer *types.Signer

	val    common.Address // Ethereum address of the signing key
	signFn SignFn         // Signer function to authorize hashes with

	lock sync.RWMutex // Protects the signer fields

	validatorSetABI abi.ABI
	slashABI        abi.ABI

	// The fields below are for testing only
	fakeDiff  bool     // Skip difficulty verifications
	forks     []uint64 // Forks extracted from the chainConfig
	snapshots *snapshotsync.RoSnapshots
}

// New creates a Parlia consensus engine.
func New(
	chainConfig *params.ChainConfig,
	db kv.RwDB,
	snapshots *snapshotsync.RoSnapshots,
) *Parlia {
	// get parlia config
	parliaConfig := chainConfig.Parlia

	// Set any missing consensus parameters to their defaults
	if parliaConfig != nil && parliaConfig.Epoch == 0 {
		parliaConfig.Epoch = defaultEpochLength
	}

	// Allocate the snapshot caches and create the engine
	recentSnaps, err := lru.NewARC(inMemorySnapshots)
	if err != nil {
		panic(err)
	}
	signatures, err := lru.NewARC(inMemorySignatures)
	if err != nil {
		panic(err)
	}
	vABI, err := abi.JSON(strings.NewReader(validatorSetABI))
	if err != nil {
		panic(err)
	}
	sABI, err := abi.JSON(strings.NewReader(slashABI))
	if err != nil {
		panic(err)
	}
	c := &Parlia{
		chainConfig:     chainConfig,
		config:          parliaConfig,
		db:              db,
		recentSnaps:     recentSnaps,
		signatures:      signatures,
		validatorSetABI: vABI,
		slashABI:        sABI,
		signer:          types.LatestSigner(chainConfig),
		forks:           forkid.GatherForks(chainConfig),
		snapshots:       snapshots,
	}

	return c
}

// Type returns underlying consensus engine
func (p *Parlia) Type() params.ConsensusType {
	return params.ParliaConsensus
}

// Author retrieves the Ethereum address of the account that minted the given
// block, which may be different from the header's coinbase if a consensus
// engine is based on signatures.
func (p *Parlia) Author(header *types.Header) (common.Address, error) {
	return header.Coinbase, nil
}

// VerifyHeader checks whether a header conforms to the consensus rules of a
// given engine. Verifying the seal may be done optionally here, or explicitly
// via the VerifySeal method.
func (p *Parlia) VerifyHeader(chain consensus.ChainHeaderReader, header *types.Header, seal bool) error {
	return p.verifyHeader(chain, header, nil)
}

// VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers
// concurrently. The method returns a quit channel to abort the operations and
// a results channel to retrieve the async verifications (the order is that of
// the input slice).
func (p *Parlia) VerifyHeaders(chain consensus.ChainHeaderReader, headers []*types.Header, seals []bool) error {
	for i, header := range headers {
		err := p.verifyHeader(chain, header, headers[:i])
		if err != nil {
			return err
		}
	}
	return nil
}

// verifyHeader checks whether a header conforms to the consensus rules.The
// caller may optionally pass in a batch of parents (ascending order) to avoid
// looking those up from the database. This is useful for concurrently verifying
// a batch of new headers.
func (p *Parlia) verifyHeader(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) error {
	if header.Number == nil {
		return errUnknownBlock
	}
	number := header.Number.Uint64()

	// Don't waste time checking blocks from the future
	if header.Time > uint64(time.Now().Unix()) {
		return consensus.ErrFutureBlock
	}
	// Check that the extra-data contains the vanity, validators and signature.
	if len(header.Extra) < extraVanity {
		return errMissingVanity
	}
	if len(header.Extra) < extraVanity+extraSeal {
		return errMissingSignature
	}
	// check extra data
	isEpoch := number%p.config.Epoch == 0

	// Ensure that the extra-data contains a signer list on checkpoint, but none otherwise
	signersBytes := len(header.Extra) - extraVanity - extraSeal
	if !isEpoch && signersBytes != 0 {
		return errExtraValidators
	}

	if isEpoch && signersBytes%validatorBytesLength != 0 {
		return errInvalidSpanValidators
	}

	// Ensure that the mix digest is zero as we don't have fork protection currently
	if header.MixDigest != (common.Hash{}) {
		return errInvalidMixDigest
	}
	// Ensure that the block doesn't contain any uncles which are meaningless in PoA
	if header.UncleHash != uncleHash {
		return errInvalidUncleHash
	}
	// Ensure that the block's difficulty is meaningful (may not be correct at this point)
	if number > 0 {
		if header.Difficulty == nil {
			return errInvalidDifficulty
		}
	}
	// If all checks passed, validate any special fields for hard forks
	if err := misc.VerifyForkHashes(chain.Config(), header, false); err != nil {
		return err
	}
	// All basic checks passed, verify cascading fields
	return p.verifyCascadingFields(chain, header, parents)
}

// verifyCascadingFields verifies all the header fields that are not standalone,
// rather depend on a batch of previous headers. The caller may optionally pass
// in a batch of parents (ascending order) to avoid looking those up from the
// database. This is useful for concurrently verifying a batch of new headers.
func (p *Parlia) verifyCascadingFields(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) error {
	// The genesis block is the always valid dead-end
	number := header.Number.Uint64()
	if number == 0 {
		return nil
	}

	var parent *types.Header
	if len(parents) > 0 {
		parent = parents[len(parents)-1]
	} else {
		parent = chain.GetHeader(header.ParentHash, number-1)
	}

	if parent == nil || parent.Number.Uint64() != number-1 || parent.Hash() != header.ParentHash {
		return consensus.ErrUnknownAncestor
	}

	snap, err := p.snapshot(chain, number-1, header.ParentHash, parents, true /* verify */)
	if err != nil {
		return err
	}

	err = p.blockTimeVerifyForRamanujanFork(snap, header, parent)
	if err != nil {
		return err
	}

	// Verify that the gas limit is <= 2^63-1
	capacity := uint64(0x7fffffffffffffff)
	if header.GasLimit > capacity {
		return fmt.Errorf("invalid gasLimit: have %v, max %v", header.GasLimit, capacity)
	}
	// Verify that the gasUsed is <= gasLimit
	if header.GasUsed > header.GasLimit {
		return fmt.Errorf("invalid gasUsed: have %d, gasLimit %d", header.GasUsed, header.GasLimit)
	}

	// Verify that the gas limit remains within allowed bounds
	diff := int64(parent.GasLimit) - int64(header.GasLimit)
	if diff < 0 {
		diff *= -1
	}
	limit := parent.GasLimit / params.GasLimitBoundDivisor

	if uint64(diff) >= limit || header.GasLimit < params.MinGasLimit {
		return fmt.Errorf("invalid gas limit: have %d, want %d += %d", header.GasLimit, parent.GasLimit, limit)
	}

	// All basic checks passed, verify the seal and return
	return p.verifySeal(chain, header, parents)
}

// verifySeal checks whether the signature contained in the header satisfies the
// consensus protocol requirements. The method accepts an optional list of parent
// headers that aren't yet part of the local blockchain to generate the snapshots
// from.
func (p *Parlia) verifySeal(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) error {
	// Verifying the genesis block is not supported
	number := header.Number.Uint64()
	if number == 0 {
		return errUnknownBlock
	}
	// Retrieve the snapshot needed to verify this header and cache it
	snap, err := p.snapshot(chain, number-1, header.ParentHash, parents, true /* verify */)
	if err != nil {
		return err
	}

	// Resolve the authorization key and check against validators
	signer, err := ecrecover(header, p.signatures, p.chainConfig.ChainID)
	if err != nil {
		return err
	}

	if signer != header.Coinbase {
		return errCoinBaseMisMatch
	}

	if _, ok := snap.Validators[signer]; !ok {
		return errUnauthorizedValidator
	}

	for seen, recent := range snap.Recents {
		if recent == signer {
			// Signer is among recents, only fail if the current block doesn't shift it out
			if limit := uint64(len(snap.Validators)/2 + 1); seen > number-limit {
				return errRecentlySigned
			}
		}
	}

	// Ensure that the difficulty corresponds to the turn-ness of the signer
	if !p.fakeDiff {
		inturn := snap.inturn(signer)
		if inturn && header.Difficulty.Cmp(diffInTurn) != 0 {
			return errWrongDifficulty
		}
		if !inturn && header.Difficulty.Cmp(diffNoTurn) != 0 {
			return errWrongDifficulty
		}
	}

	return nil
}

// snapshot retrieves the authorization snapshot at a given point in time.
func (p *Parlia) snapshot(chain consensus.ChainHeaderReader, number uint64, hash common.Hash, parents []*types.Header, verify bool) (*Snapshot, error) {
	// Search for a snapshot in memory or on disk for checkpoints
	var (
		headers []*types.Header
		snap    *Snapshot
	)

	for snap == nil {
		// If an in-memory snapshot was found, use that
		if s, ok := p.recentSnaps.Get(hash); ok {
			snap = s.(*Snapshot)
			break
		}

		// If an on-disk checkpoint snapshot can be found, use that
		if number%checkpointInterval == 0 {
			if s, err := loadSnapshot(p.config, p.signatures, p.db, number, hash); err == nil {
				//log.Trace("Loaded snapshot from disk", "number", number, "hash", hash)
				snap = s
				if !verify || snap != nil {
					break
				}
			}
		}
		if (verify && number%p.config.Epoch == 0) || number == 0 {
			if (p.snapshots != nil && number <= p.snapshots.BlocksAvailable()) || number == 0 {
				// Headers included into the snapshots have to be trusted as checkpoints
				checkpoint := chain.GetHeader(hash, number)
				if checkpoint != nil {
					validatorBytes := checkpoint.Extra[extraVanity : len(checkpoint.Extra)-extraSeal]
					// get validators from headers
					validators, err := ParseValidators(validatorBytes)
					if err != nil {
						return nil, err
					}
					// new snapshot
					snap = newSnapshot(p.config, p.signatures, number, hash, validators)
					break
				}
			}
		}

		// No snapshot for this header, gather the header and move backward
		var header *types.Header
		if len(parents) > 0 {
			// If we have explicit parents, pick from there (enforced)
			header = parents[len(parents)-1]
			if header.Hash() != hash || header.Number.Uint64() != number {
				return nil, consensus.ErrUnknownAncestor
			}
			parents = parents[:len(parents)-1]
		} else {
			// No explicit parents (or no more left), reach out to the database
			header = chain.GetHeader(hash, number)
			if header == nil {
				return nil, consensus.ErrUnknownAncestor
			}
		}
		headers = append(headers, header)
		number, hash = number-1, header.ParentHash
	}

	// check if snapshot is nil
	if snap == nil {
		return nil, fmt.Errorf("unknown error while retrieving snapshot at block number %v", number)
	}

	// Previous snapshot found, apply any pending headers on top of it
	for i := 0; i < len(headers)/2; i++ {
		headers[i], headers[len(headers)-1-i] = headers[len(headers)-1-i], headers[i]
	}
	snap, err := snap.apply(headers, chain, parents, p.chainConfig.ChainID)
	if err != nil {
		return nil, err
	}
	p.recentSnaps.Add(snap.Hash, snap)

	// If we've generated a new checkpoint snapshot, save to disk
	if snap.Number%checkpointInterval == 0 && len(headers) > 0 {
		if err = snap.store(p.db); err != nil {
			return nil, err
		}
		//log.Trace("Stored snapshot to disk", "number", snap.Number, "hash", snap.Hash)
	}
	return snap, err
}

// VerifyUncles verifies that the given block's uncles conform to the consensus
// rules of a given engine.
func (p *Parlia) VerifyUncles(chain consensus.ChainReader, header *types.Header, uncles []*types.Header) error {
	if len(uncles) > 0 {
		return errors.New("uncles not allowed")
	}
	return nil
}

// Prepare initializes the consensus fields of a block header according to the
// rules of a particular engine. The changes are executed inline.
func (p *Parlia) Prepare(chain consensus.ChainHeaderReader, header *types.Header, ibs *state.IntraBlockState) error {
	header.Coinbase = p.val
	header.Nonce = types.BlockNonce{}

	number := header.Number.Uint64()
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, false /* verify */)
	if err != nil {
		return err
	}

	// Set the correct difficulty
	header.Difficulty = CalcDifficulty(snap, p.val)

	// Ensure the extra data has all it's components
	if len(header.Extra) < extraVanity-nextForkHashSize {
		header.Extra = append(header.Extra, bytes.Repeat([]byte{0x00}, extraVanity-nextForkHashSize-len(header.Extra))...)
	}
	header.Extra = header.Extra[:extraVanity-nextForkHashSize]
	nextForkHash := forkid.NextForkHashFromForks(p.forks, p.genesisHash, number)
	header.Extra = append(header.Extra, nextForkHash[:]...)

	parent := chain.GetHeader(header.ParentHash, number-1)
	if parent == nil {
		return consensus.ErrUnknownAncestor
	}

	if number%p.config.Epoch == 0 {
		newValidators, err := p.getCurrentValidators(parent, ibs)
		if err != nil {
			return err
		}
		// sort validator by address
		sort.Sort(validatorsAscending(newValidators))
		for _, validator := range newValidators {
			header.Extra = append(header.Extra, validator.Bytes()...)
		}
	}

	// add extra seal space
	header.Extra = append(header.Extra, make([]byte, extraSeal)...)

	// Mix digest is reserved for now, set to empty
	header.MixDigest = common.Hash{}

	// Ensure the timestamp has the correct delay
	header.Time = p.blockTimeForRamanujanFork(snap, header, parent)
	if header.Time < uint64(time.Now().Unix()) {
		header.Time = uint64(time.Now().Unix())
	}
	return nil
}

// Initialize runs any pre-transaction state modifications (e.g. epoch start)
func (p *Parlia) Initialize(config *params.ChainConfig, chain consensus.ChainHeaderReader, e consensus.EpochReader, header *types.Header, txs []types.Transaction, uncles []*types.Header, syscall consensus.SystemCall) {
}

func (p *Parlia) splitTxs(txs types.Transactions, header *types.Header) (userTxs types.Transactions, systemTxs types.Transactions, err error) {
	for _, tx := range txs {
		isSystemTx, err2 := p.IsSystemTransaction(tx, header)
		if err2 != nil {
			err = err2
			return
		}
		if isSystemTx {
			systemTxs = append(systemTxs, tx)
		} else {
			userTxs = append(userTxs, tx)
		}
	}
	if userTxs == nil {
		userTxs = types.Transactions{}
	}
	if systemTxs == nil {
		systemTxs = types.Transactions{}
	}
	return
}

// Finalize runs any post-transaction state modifications (e.g. block rewards)
// but does not assemble the block.
//
// Note: The block header and state database might be updated to reflect any
// consensus rules that happen at finalization (e.g. block rewards).
func (p *Parlia) Finalize(_ *params.ChainConfig, header *types.Header, state *state.IntraBlockState,
	txs types.Transactions, _ []*types.Header, receipts types.Receipts, e consensus.EpochReader,
	chain consensus.ChainHeaderReader, syscall consensus.SystemCall,
) (types.Transactions, types.Receipts, error) {
	return p.finalize(header, state, txs, receipts, chain, false)
}

func (p *Parlia) finalize(header *types.Header, state *state.IntraBlockState, txs types.Transactions,
	receipts types.Receipts, chain consensus.ChainHeaderReader, mining bool,
) (types.Transactions, types.Receipts, error) {
	userTxs, systemTxs, err := p.splitTxs(txs, header)
	if err != nil {
		return nil, nil, err
	}
	txs = userTxs
	// warn if not in majority fork
	number := header.Number.Uint64()
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, false /* verify */)
	if err != nil {
		return nil, nil, err
	}
	/*
		nextForkHash := forkid.NextForkHashFromForks(p.forks, p.genesisHash, number)
		nextForkHashStr := hex.EncodeToString(nextForkHash[:])
		if !snap.isMajorityFork(nextForkHashStr) {
			log.Debug("[parlia] there is a possible fork, and your client is not the majority. Please check...", "nextForkHash", nextForkHashStr)
		}
	*/
	// If the block is an epoch end block, verify the validator list
	// The verification can only be done when the state is ready, it can't be done in VerifyHeader.
	if number%p.config.Epoch == 0 {
		parentHeader := chain.GetHeader(header.ParentHash, number-1)
		newValidators, err := p.getCurrentValidators(parentHeader, state)
		if err != nil {
			return nil, nil, err
		}
		// sort validator by address
		sort.Sort(validatorsAscending(newValidators))
		validatorsBytes := make([]byte, len(newValidators)*validatorBytesLength)
		for i, validator := range newValidators {
			copy(validatorsBytes[i*validatorBytesLength:], validator.Bytes())
		}

		extraSuffix := len(header.Extra) - extraSeal
		if !bytes.Equal(header.Extra[extraVanity:extraSuffix], validatorsBytes) {
			return nil, nil, errMismatchingEpochValidators
		}
	}
	// No block rewards in PoA, so the state remains as is and uncles are dropped
	if number == 1 {
		var err error
		if txs, systemTxs, receipts, err = p.initContract(state, header, txs, receipts, systemTxs, &header.GasUsed, mining); err != nil {
			log.Error("[parlia] init contract failed: %+v", err)
			os.Exit(1)
		}
	}
	if header.Difficulty.Cmp(diffInTurn) != 0 {
		spoiledVal := snap.supposeValidator()
		signedRecently := false
		for _, recent := range snap.Recents {
			if recent == spoiledVal {
				signedRecently = true
				break
			}
		}
		if !signedRecently {
			//log.Trace("slash validator", "block hash", header.Hash(), "address", spoiledVal)
			var tx types.Transaction
			var receipt *types.Receipt
			if systemTxs, tx, receipt, err = p.slash(spoiledVal, state, header, len(txs), systemTxs, &header.GasUsed, mining); err != nil {
				// it is possible that slash validator failed because of the slash channel is disabled.
				log.Error("slash validator failed", "block hash", header.Hash(), "address", spoiledVal)
			} else {
				txs = append(txs, tx)
				receipts = append(receipts, receipt)
			}
		}
	}
	if txs, systemTxs, receipts, err = p.distributeIncoming(header.Coinbase, state, header, txs, receipts, systemTxs, &header.GasUsed, mining); err != nil {
		return nil, nil, err
	}
	if len(systemTxs) > 0 {
		return nil, nil, fmt.Errorf("the length of systemTxs is still %d", len(systemTxs))
	}
	// Re-order receipts so that are in right order
	sort.Slice(receipts, func(i int, j int) bool {
		return receipts[i].TransactionIndex < receipts[j].TransactionIndex
	})
	return txs, receipts, nil
}

// FinalizeAndAssemble runs any post-transaction state modifications (e.g. block
// rewards) and assembles the final block.
//
// Note: The block header and state database might be updated to reflect any
// consensus rules that happen at finalization (e.g. block rewards).
func (p *Parlia) FinalizeAndAssemble(_ *params.ChainConfig, header *types.Header, state *state.IntraBlockState,
	txs types.Transactions, _ []*types.Header, receipts types.Receipts, e consensus.EpochReader,
	chain consensus.ChainHeaderReader, syscall consensus.SystemCall, call consensus.Call,
) (*types.Block, types.Transactions, types.Receipts, error) {
	outTxs, outReceipts, err := p.finalize(header, state, txs, receipts, chain, true)
	if err != nil {
		return nil, nil, nil, err
	}
	return types.NewBlock(header, outTxs, nil, outReceipts), outTxs, outReceipts, nil
}

// Authorize injects a private key into the consensus engine to mint new blocks
// with.
func (p *Parlia) Authorize(val common.Address, signFn SignFn) {
	p.lock.Lock()
	defer p.lock.Unlock()

	p.val = val
	p.signFn = signFn
}

// Seal generates a new sealing request for the given input block and pushes
// the result into the given channel.
//
// Note, the method returns immediately and will send the result async. More
// than one result may also be returned depending on the consensus algorithm.
func (p *Parlia) Seal(chain consensus.ChainHeaderReader, block *types.Block, results chan<- *types.Block, stop <-chan struct{}) error {
	header := block.Header()

	// Sealing the genesis block is not supported
	number := header.Number.Uint64()
	if number == 0 {
		return errUnknownBlock
	}
	// For 0-period chains, refuse to seal empty blocks (no reward but would spin sealing)
	if p.config.Period == 0 && len(block.Transactions()) == 0 {
		log.Info("[parlia] Sealing paused, waiting for transactions")
		return nil
	}
	// Don't hold the val fields for the entire sealing procedure
	p.lock.RLock()
	val, signFn := p.val, p.signFn
	p.lock.RUnlock()

	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, false /* verify */)
	if err != nil {
		return err
	}

	// Bail out if we're unauthorized to sign a block
	if _, authorized := snap.Validators[val]; !authorized {
		return errUnauthorizedValidator
	}

	// If we're amongst the recent signers, wait for the next block
	for seen, recent := range snap.Recents {
		if recent == val {
			// Signer is among recent, only wait if the current block doesn't shift it out
			if limit := uint64(len(snap.Validators)/2 + 1); number < limit || seen > number-limit {
				log.Info("[parlia] Signed recently, must wait for others")
				return nil
			}
		}
	}

	// Sweet, the protocol permits us to sign the block, wait for our time
	delay := p.delayForRamanujanFork(snap, header)

	log.Info("Sealing block with", "number", number, "delay", delay, "headerDifficulty", header.Difficulty, "val", val.Hex())

	// Sign all the things!
	sig, err := signFn(val, crypto.Keccak256(parliaRLP(header, p.chainConfig.ChainID)), p.chainConfig.ChainID)
	if err != nil {
		return err
	}
	copy(header.Extra[len(header.Extra)-extraSeal:], sig)

	// Wait until sealing is terminated or delay timeout.
	//log.Trace("Waiting for slot to sign and propagate", "delay", common.PrettyDuration(delay))
	go func() {
		select {
		case <-stop:
			return
		case <-time.After(delay):
		}
		if p.shouldWaitForCurrentBlockProcess(chain, header, snap) {
			log.Info("[parlia] Waiting for received in turn block to process")
			select {
			case <-stop:
				log.Info("[parlia] Received block process finished, abort block seal")
				return
			case <-time.After(time.Duration(processBackOffTime) * time.Second):
				log.Info("[parlia] Process backoff time exhausted, start to seal block")
			}
		}

		select {
		case results <- block.WithSeal(header):
		default:
			log.Warn("[parlia] Sealing result is not read by miner", "sealhash", SealHash(header, p.chainConfig.ChainID))
		}
	}()

	return nil
}

// SealHash returns the hash of a block prior to it being sealed.
func (p *Parlia) SealHash(header *types.Header) common.Hash {
	return SealHash(header, p.chainConfig.ChainID)
}

// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
// that a new block should have.
func (p *Parlia) CalcDifficulty(chain consensus.ChainHeaderReader, time, parentTime uint64, parentDifficulty *big.Int, parentNumber uint64, parentHash, parentUncleHash common.Hash, parentSeal []rlp.RawValue) *big.Int {
	snap, err := p.snapshot(chain, parentNumber, parentHash, nil, false /* verify */)
	if err != nil {
		return nil
	}
	return CalcDifficulty(snap, p.val)
}

// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
// that a new block should have based on the previous blocks in the chain and the
// current signer.
func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
	if snap.inturn(signer) {
		return new(big.Int).Set(diffInTurn)
	}
	return new(big.Int).Set(diffNoTurn)
}

func (p *Parlia) GenerateSeal(chain consensus.ChainHeaderReader, current, parent *types.Header, call consensus.Call) []rlp.RawValue {
	return nil
}

// APIs returns the RPC APIs this consensus engine provides.
func (p *Parlia) APIs(chain consensus.ChainHeaderReader) []rpc.API {
	return []rpc.API{{
		Namespace: "parlia",
		Version:   "1.0",
		Service:   &API{chain: chain, parlia: p},
		Public:    false,
	}}
}

func (p *Parlia) IsSystemTransaction(tx types.Transaction, header *types.Header) (bool, error) {
	// deploy a contract
	if tx.GetTo() == nil {
		return false, nil
	}
	sender, err := tx.Sender(*p.signer)
	if err != nil {
		return false, errors.New("UnAuthorized transaction")
	}
	if sender == header.Coinbase && isToSystemContract(*tx.GetTo()) && tx.GetPrice().IsZero() {
		return true, nil
	}
	return false, nil
}

func isToSystemContract(to common.Address) bool {
	_, ok := systemContracts[to]
	return ok
}

func (p *Parlia) IsSystemContract(to *common.Address) bool {
	if to == nil {
		return false
	}
	return isToSystemContract(*to)
}

func (p *Parlia) shouldWaitForCurrentBlockProcess(chain consensus.ChainHeaderReader, header *types.Header, snap *Snapshot) bool {
	if header.Difficulty.Cmp(diffInTurn) == 0 {
		return false
	}

	highestVerifiedHeader := chain.CurrentHeader()
	if highestVerifiedHeader == nil {
		return false
	}

	if header.ParentHash == highestVerifiedHeader.ParentHash {
		return true
	}
	return false
}

func (p *Parlia) EnoughDistance(chain consensus.ChainReader, header *types.Header) bool {
	snap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, nil, false /* verify */)
	if err != nil {
		return true
	}
	return snap.enoughDistance(p.val, header)
}

func (p *Parlia) IsLocalBlock(header *types.Header) bool {
	return p.val == header.Coinbase
}

func (p *Parlia) AllowLightProcess(chain consensus.ChainReader, currentHeader *types.Header) bool {
	snap, err := p.snapshot(chain, currentHeader.Number.Uint64()-1, currentHeader.ParentHash, nil, false /* verify */)
	if err != nil {
		return true
	}

	idx := snap.indexOfVal(p.val)
	// validator is not allowed to diff sync
	return idx < 0
}

// Close terminates any background threads maintained by the consensus engine.
func (p *Parlia) Close() error {
	return nil
}

// ==========================  interaction with contract/account =========

// getCurrentValidators get current validators
func (p *Parlia) getCurrentValidators(header *types.Header, ibs *state.IntraBlockState) ([]common.Address, error) {
	// method
	method := "getValidators"
	data, err := p.validatorSetABI.Pack(method)
	if err != nil {
		log.Error("Unable to pack tx for getValidators", "err", err)
		return nil, err
	}
	// call
	msgData := hexutil.Bytes(data)
	_, returnData, err := p.systemCall(header.Coinbase, systemcontracts.ValidatorContract, msgData[:], ibs, header, u256.Num0)
	if err != nil {
		return nil, err
	}
	var ret0 = new([]common.Address)
	out := ret0
	if err := p.validatorSetABI.UnpackIntoInterface(out, method, returnData); err != nil {
		return nil, err
	}
	valz := make([]common.Address, len(*ret0))
	copy(valz, *ret0)
	//for i, a := range *ret0 {
	//	valz[i] = a
	//}
	return valz, nil
}

// slash spoiled validators
func (p *Parlia) distributeIncoming(val common.Address, state *state.IntraBlockState, header *types.Header,
	txs types.Transactions, receipts types.Receipts, systemTxs types.Transactions,
	usedGas *uint64, mining bool,
) (types.Transactions, types.Transactions, types.Receipts, error) {
	coinbase := header.Coinbase
	balance := state.GetBalance(consensus.SystemAddress).Clone()
	if balance.Cmp(u256.Num0) <= 0 {
		return txs, systemTxs, receipts, nil
	}
	state.SetBalance(consensus.SystemAddress, u256.Num0)
	state.AddBalance(coinbase, balance)

	doDistributeSysReward := state.GetBalance(systemcontracts.SystemRewardContract).Cmp(maxSystemBalance) < 0
	if doDistributeSysReward {
		var rewards = new(uint256.Int)
		rewards = rewards.Rsh(balance, systemRewardPercent)
		if rewards.Cmp(u256.Num0) > 0 {
			var err error
			var tx types.Transaction
			var receipt *types.Receipt
			if systemTxs, tx, receipt, err = p.distributeToSystem(rewards, state, header, len(txs), systemTxs, usedGas, mining); err != nil {
				return nil, nil, nil, err
			}
			txs = append(txs, tx)
			receipts = append(receipts, receipt)
			//log.Debug("[parlia] distribute to system reward pool", "block hash", header.Hash(), "amount", rewards)
			balance = balance.Sub(balance, rewards)
		}
	}
	//log.Debug("[parlia] distribute to validator contract", "block hash", header.Hash(), "amount", balance)
	var err error
	var tx types.Transaction
	var receipt *types.Receipt
	if systemTxs, tx, receipt, err = p.distributeToValidator(balance, val, state, header, len(txs), systemTxs, usedGas, mining); err != nil {
		return nil, nil, nil, err
	}
	txs = append(txs, tx)
	receipts = append(receipts, receipt)
	return txs, systemTxs, receipts, nil
}

// slash spoiled validators
func (p *Parlia) slash(spoiledVal common.Address, state *state.IntraBlockState, header *types.Header,
	txIndex int, systemTxs types.Transactions, usedGas *uint64, mining bool,
) (types.Transactions, types.Transaction, *types.Receipt, error) {
	// method
	method := "slash"

	// get packed data
	data, err := p.slashABI.Pack(method,
		spoiledVal,
	)
	if err != nil {
		log.Error("[parlia] Unable to pack tx for slash", "err", err)
		return nil, nil, nil, err
	}
	// apply message
	return p.applyTransaction(header.Coinbase, systemcontracts.SlashContract, u256.Num0, data, state, header, txIndex, systemTxs, usedGas, mining)
}

// init contract
func (p *Parlia) initContract(state *state.IntraBlockState, header *types.Header,
	txs types.Transactions, receipts types.Receipts, systemTxs types.Transactions,
	usedGas *uint64, mining bool,
) (types.Transactions, types.Transactions, types.Receipts, error) {
	// method
	method := "init"
	// contracts
	contracts := []common.Address{
		systemcontracts.ValidatorContract,
		systemcontracts.SlashContract,
		systemcontracts.LightClientContract,
		systemcontracts.RelayerHubContract,
		systemcontracts.TokenHubContract,
		systemcontracts.RelayerIncentivizeContract,
		systemcontracts.CrossChainContract,
	}
	// get packed data
	data, err := p.validatorSetABI.Pack(method)
	if err != nil {
		log.Error("[parlia] Unable to pack tx for init validator set", "err", err)
		return nil, nil, nil, err
	}
	for _, c := range contracts {
		log.Info("[parlia] init contract", "block hash", header.Hash(), "contract", c)
		var tx types.Transaction
		var receipt *types.Receipt
		if systemTxs, tx, receipt, err = p.applyTransaction(header.Coinbase, c, u256.Num0, data, state, header, len(txs), systemTxs, usedGas, mining); err != nil {
			return nil, nil, nil, err
		}
		txs = append(txs, tx)
		receipts = append(receipts, receipt)
	}
	return txs, systemTxs, receipts, nil
}

func (p *Parlia) distributeToSystem(amount *uint256.Int, state *state.IntraBlockState, header *types.Header,
	txIndex int, systemTxs types.Transactions,
	usedGas *uint64, mining bool,
) (types.Transactions, types.Transaction, *types.Receipt, error) {
	return p.applyTransaction(header.Coinbase, systemcontracts.SystemRewardContract, amount, nil, state, header,
		txIndex, systemTxs, usedGas, mining)
}

// slash spoiled validators
func (p *Parlia) distributeToValidator(amount *uint256.Int, validator common.Address, state *state.IntraBlockState, header *types.Header,
	txIndex int, systemTxs types.Transactions,
	usedGas *uint64, mining bool,
) (types.Transactions, types.Transaction, *types.Receipt, error) {
	// method
	method := "deposit"

	// get packed data
	data, err := p.validatorSetABI.Pack(method,
		validator,
	)
	if err != nil {
		log.Error("[parlia] Unable to pack tx for deposit", "err", err)
		return nil, nil, nil, err
	}
	// apply message
	return p.applyTransaction(header.Coinbase, systemcontracts.ValidatorContract, amount, data, state, header, txIndex, systemTxs, usedGas, mining)
}

func (p *Parlia) applyTransaction(from common.Address, to common.Address, value *uint256.Int, data []byte, ibs *state.IntraBlockState, header *types.Header,
	txIndex int, systemTxs types.Transactions, usedGas *uint64, mining bool,
) (types.Transactions, types.Transaction, *types.Receipt, error) {
	nonce := ibs.GetNonce(from)
	expectedTx := types.Transaction(types.NewTransaction(nonce, to, value, math.MaxUint64/2, u256.Num0, data))
	expectedHash := expectedTx.SigningHash(p.chainConfig.ChainID)
	if from == p.val && mining {
		signature, err := p.signFn(from, expectedTx.SigningHash(p.chainConfig.ChainID).Bytes(), p.chainConfig.ChainID)
		if err != nil {
			return nil, nil, nil, err
		}
		signer := types.LatestSignerForChainID(p.chainConfig.ChainID)
		expectedTx, err = expectedTx.WithSignature(*signer, signature)
		if err != nil {
			return nil, nil, nil, err
		}
	} else {
		if len(systemTxs) == 0 || systemTxs[0] == nil {
			return nil, nil, nil, fmt.Errorf("supposed to get a actual transaction, but get none")
		}
		actualTx := systemTxs[0]
		actualHash := actualTx.SigningHash(p.chainConfig.ChainID)
		if !bytes.Equal(actualHash.Bytes(), expectedHash.Bytes()) {
			return nil, nil, nil, fmt.Errorf("expected system tx (hash %v, nonce %d, to %s, value %s, gas %d, gasPrice %s, data %s), actual tx (hash %v, nonce %d, to %s, value %s, gas %d, gasPrice %s, data %s)",
				expectedHash.String(),
				expectedTx.GetNonce(),
				expectedTx.GetTo().String(),
				expectedTx.GetValue().String(),
				expectedTx.GetGas(),
				expectedTx.GetPrice().String(),
				hex.EncodeToString(expectedTx.GetData()),
				actualHash.String(),
				actualTx.GetNonce(),
				actualTx.GetTo().String(),
				actualTx.GetValue().String(),
				actualTx.GetGas(),
				actualTx.GetPrice().String(),
				hex.EncodeToString(actualTx.GetData()),
			)
		}
		expectedTx = actualTx
		// move to next
		systemTxs = systemTxs[1:]
	}
	ibs.Prepare(expectedTx.Hash(), common.Hash{}, txIndex)
	gasUsed, _, err := p.systemCall(from, to, data, ibs, header, value)
	if err != nil {
		return nil, nil, nil, err
	}
	*usedGas += gasUsed
	receipt := types.NewReceipt(false, *usedGas)
	receipt.TxHash = expectedTx.Hash()
	receipt.GasUsed = gasUsed
	if err := ibs.FinalizeTx(p.chainConfig.Rules(header.Number.Uint64()), state.NewNoopWriter()); err != nil {
		return nil, nil, nil, err
	}
	// Set the receipt logs and create a bloom for filtering
	receipt.Logs = ibs.GetLogs(expectedTx.Hash())
	receipt.Bloom = types.CreateBloom(types.Receipts{receipt})
	receipt.BlockHash = header.Hash()
	receipt.BlockNumber = header.Number
	receipt.TransactionIndex = uint(txIndex)
	ibs.SetNonce(from, nonce+1)
	return systemTxs, expectedTx, receipt, nil
}

func (p *Parlia) systemCall(from, contract common.Address, data []byte, ibs *state.IntraBlockState, header *types.Header, value *uint256.Int) (gasUsed uint64, returnData []byte, err error) {
	chainConfig := p.chainConfig
	if chainConfig.DAOForkSupport && chainConfig.DAOForkBlock != nil && chainConfig.DAOForkBlock.Cmp(header.Number) == 0 {
		misc.ApplyDAOHardFork(ibs)
	}
	msg := types.NewMessage(
		from,
		&contract,
		0, value,
		math.MaxUint64/2, u256.Num0,
		nil, nil,
		data, nil, false,
	)
	vmConfig := vm.Config{NoReceipts: true}
	// Create a new context to be used in the EVM environment
	blockContext := core.NewEVMBlockContext(header, nil, p, &from, nil)
	evm := vm.NewEVM(blockContext, core.NewEVMTxContext(msg), ibs, chainConfig, vmConfig)
	ret, leftOverGas, err := evm.Call(
		vm.AccountRef(msg.From()),
		*msg.To(),
		msg.Data(),
		msg.Gas(),
		msg.Value(),
		false,
	)
	if err != nil {
		return 0, nil, err
	}
	return msg.Gas() - leftOverGas, ret, nil
}