package parlia

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

	"github.com/bits-and-blooms/bitset"
	"github.com/ethereum/go-ethereum/common/lru"
	"github.com/ethereum/go-ethereum/common/pepper8"
	"github.com/ethereum/go-ethereum/common/pipe8"
	"github.com/holiman/uint256"
	"github.com/prysmaticlabs/prysm/v5/crypto/bls"
	"golang.org/x/crypto/sha3"

	"github.com/ethereum/go-ethereum/accounts"
	"github.com/ethereum/go-ethereum/accounts/abi"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/gopool"
	"github.com/ethereum/go-ethereum/common/hexutil"
	cmath "github.com/ethereum/go-ethereum/common/math"
	"github.com/ethereum/go-ethereum/common/systemcontract"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/consensus/misc/eip1559"
	"github.com/ethereum/go-ethereum/consensus/misc/eip4844"
	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/core/forkid"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/systemcontracts"
	"github.com/ethereum/go-ethereum/core/tracing"
	"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/internal/ethapi"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/rpc"
	"github.com/ethereum/go-ethereum/trie"
)

const (
	inMemorySnapshots   = 1280 // Number of recent snapshots to keep in memory; a buffer exceeding the EpochLength
	inMemorySignatures  = 4096 // Number of recent block signatures to keep in memory
	inMemoryFrequencies = 128  // Number of post-Snake8Fix frequency-data entries to memoize by parent hash

	inMemoryHeaders = 86400 // Number of recent headers to keep in memory for double sign detection,

	checkpointInterval = 1024 // Number of blocks after which to save the snapshot to the database

	lorentzEpochLength   uint64 = 500  // Epoch length starting from the Lorentz hard fork
	maxwellEpochLength   uint64 = 1000 // Epoch length starting from the Maxwell hard fork
	defaultBlockInterval uint64 = 3000 // Default block interval in milliseconds
	lorentzBlockInterval uint64 = 1500 // Block interval starting from the Lorentz hard fork
	maxwellBlockInterval uint64 = 750  // Block interval starting from the Maxwell hard fork
	fermiBlockInterval   uint64 = 450  // Block interval starting from the Fermi hard fork
	defaultTurnLength    uint8  = 1    // Default consecutive number of blocks a validator receives priority for block production
	snake8TurnLength     uint8  = 50   // Chiliz Snake8 forces this turn length whenever the fork is active

	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.
	turnLengthSize   = 1  // Fixed number of extra-data suffix bytes reserved for turnLength

	validatorBytesLengthBeforeLuban = common.AddressLength
	validatorBytesLength            = common.AddressLength + types.BLSPublicKeyLength
	validatorNumberSize             = 1 // Fixed number of extra prefix bytes reserved for validator number after Luban

	wiggleTime                uint64 = 1000 // milliseconds, Random delay (per signer) to allow concurrent signers
	defaultInitialBackOffTime uint64 = 1000 // milliseconds, Default backoff time for the second validator permitted to produce blocks
	lorentzInitialBackOffTime uint64 = 2000 // milliseconds, Backoff time for the second validator permitted to produce blocks from the Lorentz hard fork

	systemRewardPercent = 5 // it means 1/3  percentage of gas fee incoming will be distributed to system

	collectAdditionalVotesRewardRatio = 100 // ratio of additional reward for collecting more votes than needed, the denominator is 100

	gasLimitBoundDivisorBeforeLorentz uint64 = 256 // The bound divisor of the gas limit, used in update calculations before lorentz hard fork.

	// `finalityRewardInterval` should be smaller than `inMemorySnapshots`, otherwise, it will result in excessive computation.
	finalityRewardInterval = 200

	kAncestorGenerationDepth = 3
)

var (
	defaultEpochLength           = uint64(200)   // Default number of blocks of checkpoint to update validatorSet from contract
	diffInTurn                   = big.NewInt(2) // Block difficulty for in-turn signatures
	diffNoTurn                   = big.NewInt(1) // Block difficulty for out-of-turn signatures
	validatorFrequencyDataPrefix = []byte("VFQ") // Prefix for validator frequency data in the header.Extra field
	// 100 native token
	maxSystemBalance                  = new(uint256.Int).Mul(uint256.NewInt(100), uint256.NewInt(params.Ether))
	verifyVoteAttestationErrorCounter = metrics.NewRegisteredCounter("parlia/verifyVoteAttestation/error", nil)
	updateAttestationErrorCounter     = metrics.NewRegisteredCounter("parlia/updateAttestation/error", nil)
	validVotesfromSelfCounter         = metrics.NewRegisteredCounter("parlia/VerifyVote/self", nil)
	doubleSignCounter                 = metrics.NewRegisteredCounter("parlia/doublesign", nil)
	snake8FreqVerifySkippedCounter    = metrics.NewRegisteredCounter("parlia/snake8fix/verifySkipped", nil)
	intentionalDelayMiningCounter     = metrics.NewRegisteredCounter("parlia/intentionalDelayMining", nil)
	attestationVoteCountGauge         = metrics.NewRegisteredGauge("parlia/attestation/voteCount", nil)
)

// 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")

	// errInvalidTurnLength is returned if a block contains an
	// invalid length of turn (i.e. no data left after parsing validators).
	errInvalidTurnLength = errors.New("invalid turnLength")

	// errInvalidSnake8Extra is returned if a Snake8 block's extra-data does not
	// contain a well-formed validator-frequency block (missing/short/misplaced
	// prefix or embedded parent timestamp).
	errInvalidSnake8Extra = errors.New("invalid snake8 frequency extra data")

	// errMismatchedSnake8ParentTime is returned if the parent timestamp embedded
	// in a Snake8 block's extra-data does not match the real parent.Time. This
	// guards against forged activation timestamps causing a consensus split.
	errMismatchedSnake8ParentTime = errors.New("snake8 embedded parent timestamp mismatch")

	// errMismatchedSnake8FrequencyData is returned (post-Snake8Fix, COR-173) if the
	// validator-frequency bytes embedded in a header do not match the recomputation
	// from the parent block's state. Pre-Snake8Fix the embedded bytes are
	// producer-controlled and unverified (historical behavior).
	errMismatchedSnake8FrequencyData = errors.New("snake8 embedded frequency data mismatch")

	// errSnake8StakeLookup marks a NODE-LOCAL failure to read validator stakes for
	// the Snake8 frequency data (RPC timeout under load, gas cap, missing historical
	// state during tracing replay, engine built without an RPC backend). It says
	// nothing about the block's validity: sealing treats it as fatal, verification
	// fails open on it (verifySnake8FrequencyData).
	errSnake8StakeLookup = errors.New("snake8fix stake lookup failed")

	// 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")

	// errMismatchingEpochTurnLength is returned if a sprint block contains a
	// turn length different than the one the local node calculated.
	errMismatchingEpochTurnLength = errors.New("mismatching turn length 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 = func(val string) error {
		return errors.New("unauthorized validator: " + val)
	}

	// 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")
)

// SignerFn is a signer callback function to request a header to be signed by a
// backing account.
type SignerFn func(accounts.Account, string, []byte) ([]byte, error)
type SignerTxFn func(accounts.Account, *types.Transaction, *big.Int) (*types.Transaction, error)

func isToSystemContract(to common.Address) bool {
	return systemcontract.IsSystemContract(to) || to == pepper8.Pepper8RecipientAddress || to == pipe8.Pipe8RecipientAddress
}

// ecrecover extracts the Ethereum account address from a signed header.
func ecrecover(header *types.Header, sigCache *lru.Cache[common.Hash, common.Address], 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, 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(types.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
}

// 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)
	types.EncodeSigHeader(b, header, chainId)
	return b.Bytes()
}

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

	recentSnaps   *lru.Cache[common.Hash, *Snapshot]      // Snapshots for recent block to speed up
	signatures    *lru.Cache[common.Hash, common.Address] // Signatures of recent blocks to speed up mining
	recentHeaders *lru.Cache[string, common.Hash]
	// Recent headers to check for double signing: key includes block number and miner. value is the block header
	// If same key's value already exists for different block header roots then double sign is detected

	signer types.Signer

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

	lock sync.RWMutex // Protects the signer fields

	ethAPI                     *ethapi.BlockChainAPI
	VotePool                   consensus.VotePool
	validatorSetABIBeforeLuban abi.ABI
	validatorSetABI            abi.ABI
	slashABI                   abi.ABI
	tokenomicsABI              abi.ABI
	stakeHubABI                abi.ABI

	// stakeReader fetches a validator's total delegated stake for the Snake8
	// frequency data. Defaults to getValidatorTotalDelegated (refreshFrequencyRLP
	// also falls back to it when nil, so struct-literal engines don't trap); tests
	// substitute a deterministic source since engines built without an RPC backend
	// cannot perform contract calls.
	stakeReader func(validator common.Address, blockNumber uint64, state *rpc.BlockNumberOrHash) (*big.Int, error)

	// frequencyCache memoizes post-Snake8Fix frequency bytes by parent hash — see
	// refreshFrequencyRLP for why this is sound and why pre-fork bytes never enter it.
	frequencyCache *lru.Cache[common.Hash, []byte]
}

// New creates a Parlia consensus engine.
func New(
	chainConfig *params.ChainConfig,
	db ethdb.Database,
	ethAPI *ethapi.BlockChainAPI,
	genesisHash common.Hash,
) *Parlia {
	// get parlia config
	parliaConfig := chainConfig.Parlia
	log.Info("Parlia", "chainConfig", chainConfig)

	// Override default epoch length with value from genesis config
	defaultEpochLength = parliaConfig.Epoch

	vABIBeforeLuban, err := abi.JSON(strings.NewReader(validatorSetABIBeforeLuban))
	if err != nil {
		panic(err)
	}
	vABI, err := abi.JSON(strings.NewReader(validatorSetABI))
	if err != nil {
		panic(err)
	}
	// signableSystemTxSelectors exists only for BEP-675 bid blocks, and covers BSC
	// validator-set methods that Chiliz's BAS validator set does not implement.
	// Assert the selectors only on chains that schedule the forks which pack them.
	if chainConfig.PlatoBlock != nil && chainConfig.FeynmanTime != nil {
		for methodName, selector := range signableSystemTxSelectors {
			method, ok := vABI.Methods[methodName]
			if !ok || !bytes.Equal(method.ID, selector[:]) {
				panic(fmt.Sprintf("invalid validator set ABI selector for %s", methodName))
			}
		}
	}
	sABI, err := abi.JSON(strings.NewReader(slashABI))
	if err != nil {
		panic(err)
	}
	tABI, err := abi.JSON(strings.NewReader(tokenomicsABI))
	if err != nil {
		panic(err)
	}
	stABI, err := abi.JSON(strings.NewReader(stakeABI))
	if err != nil {
		panic(err)
	}
	c := &Parlia{
		chainConfig:                chainConfig,
		config:                     parliaConfig,
		genesisHash:                genesisHash,
		db:                         db,
		ethAPI:                     ethAPI,
		recentSnaps:                lru.NewCache[common.Hash, *Snapshot](inMemorySnapshots),
		recentHeaders:              lru.NewCache[string, common.Hash](inMemoryHeaders),
		frequencyCache:             lru.NewCache[common.Hash, []byte](inMemoryFrequencies),
		signatures:                 lru.NewCache[common.Hash, common.Address](inMemorySignatures),
		validatorSetABIBeforeLuban: vABIBeforeLuban,
		validatorSetABI:            vABI,
		slashABI:                   sABI,
		tokenomicsABI:              tABI,
		stakeHubABI:                stABI,
		signer:                     types.LatestSigner(chainConfig),
	}
	c.stakeReader = c.getValidatorTotalDelegated

	return c
}

func (p *Parlia) IsSystemTransaction(tx *types.Transaction, header *types.Header) (bool, error) {
	if tx.To() == nil || !isToSystemContract(*tx.To()) {
		return false, nil
	}
	if tx.EffectiveGasPriceForBSC().Sign() != 0 {
		return false, nil
	}
	sender, err := types.Sender(p.signer, tx)
	if err != nil {
		return false, errors.New("UnAuthorized transaction")
	}
	return sender == header.Coinbase, nil
}

// tokenomicsDepositSelector is the 4-byte ABI selector of
// Tokenomics.deposit(address,uint256,uint256) (keccak256 prefix 0x0efe6a8b).
var tokenomicsDepositSelector = [4]byte{0x0e, 0xfe, 0x6a, 0x8b}

// IsTokenomicsDeposit returns true if to address is the tokenomics contract and tx data
// starts with Tokenomics.deposit() method signature.
//
// to must be non-nil: every caller reaches this only for a transaction that
// IsSystemTransaction / IsSystemContract already accepted, both of which reject
// a nil destination. The guard enforces that rather than trusting it: CLAUDE.md
// section 5 anticipates new replay and simulation paths calling in here, and a
// caller that forgets it would panic the node on a contract-creation tx instead
// of getting false.
func (p *Parlia) IsTokenomicsDeposit(to *common.Address, data []byte) bool {
	return to != nil && *to == systemcontract.TokenomicsContractAddress &&
		len(data) >= len(tokenomicsDepositSelector) &&
		bytes.Equal(data[:len(tokenomicsDepositSelector)], tokenomicsDepositSelector[:])
}

// IsPepper8Deposit returns true if to address is the pepper8 recipient and from
// address is coinbase. Nil-total, for the reason on IsTokenomicsDeposit.
func (p *Parlia) IsPepper8Deposit(from *common.Address, to *common.Address, coinbase *common.Address) bool {
	if from == nil || to == nil || coinbase == nil {
		return false
	}
	isDestinationPepper8Recipient := bytes.Equal(to.Bytes(), pepper8.Pepper8RecipientAddress.Bytes())
	isFromCoinbase := bytes.Equal(from.Bytes(), coinbase.Bytes())

	return isDestinationPepper8Recipient && isFromCoinbase
}

// IsPipe8Deposit returns true if to address is the pipe8 recipient and from
// address is coinbase. Nil-total, for the reason on IsTokenomicsDeposit.
func (p *Parlia) IsPipe8Deposit(from *common.Address, to *common.Address, coinbase common.Address) bool {
	if from == nil || to == nil {
		return false
	}
	isDestinationPipe8Recipient := bytes.Equal(to.Bytes(), pipe8.Pipe8RecipientAddress.Bytes())
	isFromCoinbase := bytes.Equal(from.Bytes(), coinbase.Bytes())

	return isDestinationPipe8Recipient && isFromCoinbase
}

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

// Author implements consensus.Engine, returning the SystemAddress
func (p *Parlia) Author(header *types.Header) (common.Address, error) {
	return header.Coinbase, nil
}

// ConsensusAddress returns the consensus address of the validator
func (p *Parlia) ConsensusAddress() common.Address {
	return p.val
}

// VerifyHeader checks whether a header conforms to the consensus rules.
func (p *Parlia) VerifyHeader(chain consensus.ChainHeaderReader, header *types.Header) error {
	return p.verifyHeader(chain, header, nil)
}

// VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers. 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) (chan<- struct{}, <-chan error) {
	abort := make(chan struct{})
	results := make(chan error, len(headers))

	gopool.Submit(func() {
		for i, header := range headers {
			err := p.verifyHeader(chain, header, headers[:i])

			select {
			case <-abort:
				return
			case results <- err:
			}
		}
	})
	return abort, results
}

// getValidatorBytesFromHeader returns the validators bytes extracted from the header's extra field if exists.
// The validators bytes would be contained only in the epoch block's header, and its each validator bytes length is fixed.
// On luban fork, we introduce vote attestation into the header's extra field, so extra format is different from before.
// Before luban fork: |---Extra Vanity---|---Validators Bytes (or Empty)---|---Extra Seal---|
// After luban fork:  |---Extra Vanity---|---Validators Number and Validators Bytes (or Empty)---|---Vote Attestation (or Empty)---|---Extra Seal---|
// After bohr fork:   |---Extra Vanity---|---Validators Number and Validators Bytes (or Empty)---|---Turn Length (or Empty)---|---Vote Attestation (or Empty)---|---Extra Seal---|
// After snake8 fork:   |---Extra Vanity---|---Validators Bytes (or Empty) ---|---Turn Length (or Empty)---/---Vote Attestation (or Empty)---/---Frequency Data Prefix---|---Parent Timestamp---|---Frequency data---|---Extra Seal---|
func getValidatorBytesFromHeader(header *types.Header, chainConfig *params.ChainConfig, epochLength uint64) []byte {
	if len(header.Extra) <= extraVanity+extraSeal {
		return nil
	}

	if !chainConfig.IsLuban(header.Number) {
		start := extraVanity
		end := len(header.Extra) - extraSeal
		body := header.Extra[start:end]

		// Legacy quirks, preserved byte-for-byte on BOTH epoch and non-epoch
		// headers. The pre-COR-213 parser rejected a header outright when
		//
		//   a) the body began with "VFQ", or
		//   b) the first "VFQ" occurrence in header.Extra began inside the vanity,
		//      including one straddling the vanity end into the first validator
		//      address — the scan started at offset 0, so such an occurrence set
		//      end < start and fell into the `end <= start` return.
		//
		// Both are consensus rules on the live networks, not artefacts of the
		// scan: relaxing either accepts an epoch header that every 2.10.6 node
		// rejects, which splits the chain across a rolling upgrade instead of
		// halting it uniformly. They are therefore checked ahead of the
		// epoch/non-epoch split rather than inside the non-epoch branch.
		//
		// The residual cost is narrow and deliberate: an epoch header whose
		// lowest-sorted validator address itself begins with 0x564651 stays
		// unparseable. Legacy rejected it too, so this is not a regression — it is
		// the one corner of COR-213 that cannot be fixed without a hardfork.
		//
		// The legacy loop ran i over [0, end-3], i.e. it never read prefix bytes
		// from the seal; the straddle window is therefore bounded by end.
		legacyScanEnd := start + len(validatorFrequencyDataPrefix) - 1
		if legacyScanEnd > end {
			legacyScanEnd = end
		}
		if bytes.HasPrefix(body, validatorFrequencyDataPrefix) ||
			bytes.Contains(header.Extra[:legacyScanEnd], validatorFrequencyDataPrefix) {
			return nil
		}

		if header.Number.Uint64()%epochLength != 0 {
			// Non-epoch headers carry no validator list: the body is either the
			// frequency block (caught by the HasPrefix guard above) or something
			// verifyHeader rejects as errExtraValidators.
			return body
		}

		// Epoch header: |validators (n*20 bytes)|"VFQ"|parent ts|frequency RLP|
		// once Snake8 is active, |validators| before. The frequency block is
		// located structurally (validator-aligned prefix + well-formed tail), never
		// by a byte-wise scan for "VFQ": an address containing those three bytes
		// used to truncate the list (COR-213).
		switch off, found, hostile := preLubanFrequencyBlockOffset(body); {
		case hostile:
			return nil
		case found && off == 0:
			// The frequency block starts immediately: no validator entries.
			return nil
		case found:
			end = start + off
		}

		if (end-start)%validatorBytesLengthBeforeLuban != 0 {
			return nil
		}

		return header.Extra[start:end]
	}

	if header.Number.Uint64()%epochLength != 0 {
		return nil
	}
	num := int(header.Extra[extraVanity])
	start := extraVanity + validatorNumberSize
	end := start + num*validatorBytesLength
	extraMinLen := end + extraSeal
	if chainConfig.IsBohr(header.Number, header.Time) {
		extraMinLen += turnLengthSize
	}
	if num == 0 || len(header.Extra) < extraMinLen {
		return nil
	}
	return header.Extra[start:end]
}

// frequencyBlockEntry is the wire shape of one Snake8 frequency-data entry:
// what calcFrequencyRLP encodes and selectValidatorFromFrequencyRLP decodes.
type frequencyBlockEntry struct {
	Address   common.Address
	Frequency *big.Int
}

// maxFrequencyBlockCandidates bounds the structural decodes attempted while
// locating the frequency block in one header, so a hostile header cannot make
// the parser do quadratic work. An honest epoch header has exactly one
// candidate; one candidate per validator entry is already absurd.
const maxFrequencyBlockCandidates = 256

// decodesAsFrequencyList reports whether tail is exactly one NON-EMPTY RLP list
// of (address, frequency) entries, the encoding calcFrequencyRLP produces.
// Trailing bytes, a different structure, or an empty input all fail.
//
// The empty list (0xc0) is rejected on purpose: calcFrequencyRLP returns an
// error rather than an empty list when there are no eligible candidates, so the
// producer emits either a list with at least one entry or nothing at all — an
// empty list is not a shape any honest header carries. Accepting it would make
// a second decodable candidate cost an attacker a single byte: with "VFQ" at
// bytes 11..13 of their own (freely ground) address, a frequency whose encoding
// ends in 0xc0 and a list length ≡ 1 (mod 20), the last twelve bytes of the
// honest frequency list form a 20-aligned candidate with tail 0xc0. Two
// decodable candidates are reported hostile, getValidatorBytesFromHeader
// returns nil, and every node rejects the epoch block — the COR-213 halt the
// structural search exists to prevent. Requiring an entry raises the bar to 25
// attacker-controlled bytes at the very end of the body, which the producer's
// encoding never places there. See TestPreLubanFrequencyEmptyListDecoy.
func decodesAsFrequencyList(tail []byte) bool {
	if len(tail) == 0 {
		return false
	}
	var entries []frequencyBlockEntry
	return rlp.DecodeBytes(tail, &entries) == nil && len(entries) > 0
}

// preLubanFrequencyBlockOffset locates the Snake8 frequency block inside the
// body (vanity and seal stripped) of a pre-Luban epoch header, where it follows
// the fixed-width 20-byte validator entries:
//
//	|validator 1|...|validator n|"VFQ"|LE parent timestamp|frequency RLP|
//
// The prefix alone is not a delimiter: a validator address may contain, or even
// start with, the bytes 0x564651, and the previous byte-wise scan for their
// first occurrence truncated the validator list there (COR-213). The block is
// therefore located structurally. A candidate is an offset that is a multiple
// of the validator width (zero included: a first address may itself start with
// the prefix), starts with "VFQ" and has room for the 8-byte timestamp. Its tail
// is everything up to the seal, and refreshFrequencyRLP only ever embeds two
// tail shapes: the RLP list of entries, or nothing at all when calcFrequencyRLP
// failed. So:
//
//   - exactly one candidate whose tail decodesAsFrequencyList: that is the
//     block. The bytes after a validator address are the remaining raw
//     20-byte entries, which never form such a list, so an address is told
//     apart from the block in every realistic layout;
//   - more than one such candidate: unreachable for an honest producer and
//     not constructible by an attacker who controls only their own address.
//     Reported as hostile and rejected;
//   - none, but a candidate whose tail is empty (necessarily the last offset):
//     the degraded block with no frequency data. It only counts when no
//     decodable candidate exists, because an attacker can cheaply forge one:
//     their address appears inside the honest frequency list, and placing
//     "VFQ" at the right position in it puts the prefix exactly eleven bytes
//     before the seal, on an aligned offset. FuzzHeaderExtraRoundTrip found
//     that shape (see its testdata) against an earlier rule that let it win;
//   - none at all: a pre-Snake8 header, the whole body is validator entries.
//
// Only a bounded number of prefixed offsets is examined, so a hostile header
// cannot make the parser do quadratic work; exceeding the bound is hostile.
func preLubanFrequencyBlockOffset(body []byte) (offset int, found bool, hostile bool) {
	blockHeader := len(validatorFrequencyDataPrefix) + 8 // "VFQ" + parent timestamp
	attempts, decodable, emptyAtEnd := 0, 0, -1
	for off := 0; off+blockHeader <= len(body); off += validatorBytesLengthBeforeLuban {
		if !bytes.HasPrefix(body[off:], validatorFrequencyDataPrefix) {
			continue
		}
		tail := body[off+blockHeader:]
		if len(tail) == 0 {
			emptyAtEnd = off
			continue
		}
		attempts++
		if attempts > maxFrequencyBlockCandidates {
			return 0, false, true
		}
		if decodesAsFrequencyList(tail) {
			offset = off
			decodable++
			if decodable > 1 {
				// The verdict can no longer change; stop decoding. Identical
				// result to falling through to the switch below, but it caps
				// the RLP work a hostile header can provoke at two decodes.
				return 0, false, true
			}
		}
	}
	switch {
	case decodable == 1:
		return offset, true, false
	case decodable > 1:
		return 0, false, true
	case emptyAtEnd >= 0:
		return emptyAtEnd, true, false
	}
	return 0, false, false
}

// getVoteAttestationFromHeader returns the vote attestation extracted from the header's extra field if exists.
func getVoteAttestationFromHeader(header *types.Header, chainConfig *params.ChainConfig, epochLength uint64) (*types.VoteAttestation, error) {
	if len(header.Extra) <= extraVanity+extraSeal {
		return nil, nil
	}

	if !chainConfig.IsLuban(header.Number) {
		return nil, nil
	}

	var attestationBytes []byte
	if header.Number.Uint64()%epochLength != 0 {
		attestationBytes = header.Extra[extraVanity : len(header.Extra)-extraSeal]
	} else {
		num := int(header.Extra[extraVanity])
		start := extraVanity + validatorNumberSize + num*validatorBytesLength
		if chainConfig.IsBohr(header.Number, header.Time) {
			start += turnLengthSize
		}
		end := len(header.Extra) - extraSeal
		if end <= start {
			return nil, nil
		}
		attestationBytes = header.Extra[start:end]
	}

	var attestation types.VoteAttestation
	if err := rlp.Decode(bytes.NewReader(attestationBytes), &attestation); err != nil {
		return nil, fmt.Errorf("block %d has vote attestation info, decode err: %s", header.Number.Uint64(), err)
	}
	return &attestation, nil
}

// getParent returns the parent of a given block.
func (p *Parlia) getParent(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) (*types.Header, error) {
	var parent *types.Header
	number := header.Number.Uint64()
	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 nil, consensus.ErrUnknownAncestor
	}
	return parent, nil
}

// isSnake8Enabled returns true if the parent block's timestamp >= snake8Time.
//
// When the parent header is available locally (the common case) the decision is
// made from the trusted parent.Time. During batch sync the parent may not yet be
// in the local store, in which case we provisionally fall back to the parent
// timestamp embedded in header.Extra. That embedded value is producer-controlled
// and MUST NOT be trusted on its own; verifySnake8Extra cross-validates it
// against the real parent.Time during full verification, so a forged value can
// never make a block accepted on the wrong side of the fork boundary.
func (p *Parlia) isSnake8Enabled(chain consensus.ChainHeaderReader, header *types.Header) bool {
	parent := chain.GetHeaderByHash(header.ParentHash)
	if parent != nil {
		return p.chainConfig.IsSnake8(parent.Time)
	}

	// Parent not in cache: provisionally read the embedded parent timestamp using
	// the strict, bounds-checked extractor. Any malformed layout yields false
	// rather than an out-of-bounds read on attacker-controlled bytes.
	ts, ok := extractSnake8ParentTimestamp(header, p.chainConfig)
	if !ok {
		log.Trace("failed to extract parent timestamp from extra", "number", header.Number.Uint64())
		return false
	}
	return p.chainConfig.IsSnake8(ts)
}

// verifySnake8Extra authoritatively validates the Snake8 fork data embedded in a
// header's extra-data against the real (now-known) parent header. Fork
// activation is decided solely from the trusted parent.Time, never from
// producer-controlled bytes:
//
//   - When Snake8 is active for this block, the header must carry a well-formed
//     validator-frequency block whose embedded parent timestamp equals
//     parent.Time. A forged or absent timestamp is rejected here, so a malicious
//     producer cannot push syncing nodes onto the wrong side of the fork.
//   - When Snake8 is not yet active, the header must not carry a frequency block.
func (p *Parlia) verifySnake8Extra(header, parent *types.Header) error {
	ts, ok := extractSnake8ParentTimestamp(header, p.chainConfig)

	if !p.chainConfig.IsSnake8(parent.Time) {
		// Pre-fork block: it must not carry a Snake8 frequency block.
		if ok {
			return errInvalidSnake8Extra
		}
		return nil
	}

	// Snake8 is active: a well-formed frequency block is mandatory and its
	// embedded parent timestamp must match the real parent.
	if !ok {
		return errInvalidSnake8Extra
	}
	if ts != parent.Time {
		return errMismatchedSnake8ParentTime
	}
	return nil
}

// verifySnake8FrequencyData authoritatively validates the validator-frequency
// bytes embedded in a Snake8 header against their recomputation from the parent
// block's state (COR-173, Snake8Fix fork). Pre-Snake8Fix the bytes are accepted
// as-is: historical blocks were produced with unpinned latest-state stake reads
// (and soft degradation to zero stakes on lookup failure), so a strict
// recomputation could reject valid history — the check is therefore gated on the
// parent's timestamp, mirroring Snake8's own activation rule.
//
// The check is state-dependent, so it runs from Finalize (like verifyValidators),
// not from VerifyHeader: a node executing block N necessarily has state N-1.
// refreshFrequencyRLP is deterministic post-fork (stakes pinned to the parent
// block, candidates from the parent snapshot's Recents), so every honest node
// recomputes exactly the bytes an honest producer embedded.
//
// Error classification: only a byte MISMATCH condemns the block. A node-local
// inability to read stakes (errSnake8StakeLookup: RPC timeout under load, gas cap,
// no historical state during tracing replay, nil-ethAPI engines like `geth import`)
// fails OPEN — logged loudly and counted — because an error out of Finalize is
// treated as a bad block by insertChain: failing closed would let a local condition
// (or RPC-load DoS) make a node reject the honest head and stall. Fail-open only
// relaxes the check on nodes that could not have evaluated it; sealing keeps the
// hard failure, so an honest producer never emits unverifiable blocks.
func (p *Parlia) verifySnake8FrequencyData(chain consensus.ChainHeaderReader, header, parent *types.Header) error {
	if !p.chainConfig.IsSnake8Fix(parent.Time) {
		return nil
	}

	embedded, err := parseValidatorFrequencies(header, p.chainConfig)
	if err != nil {
		return err
	}

	number := header.Number.Uint64()
	// isSnake8Fork=true so snapshot() returns a caller-owned copy (COR-174) that
	// refreshFrequencyRLP may write to; extraHeader=nil because the embedded
	// bytes under judgment must not pre-stamp the snapshot we recompute into.
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, true, nil)
	if err != nil {
		return err
	}
	if err := p.refreshFrequencyRLP(snap, number, parent); err != nil {
		if errors.Is(err, errSnake8StakeLookup) {
			snake8FreqVerifySkippedCounter.Inc(1)
			log.Error("Skipping Snake8 frequency verification: cannot read stakes locally",
				"number", number, "hash", header.Hash(), "err", err)
			return nil
		}
		return err
	}

	if !bytes.Equal(embedded, snap.FrequencyRLP) {
		log.Warn("Snake8 embedded frequency data does not match state recomputation",
			"number", number, "hash", header.Hash(), "coinbase", header.Coinbase,
			"embedded", hex.EncodeToString(embedded), "recomputed", hex.EncodeToString(snap.FrequencyRLP))
		return errMismatchedSnake8FrequencyData
	}
	return nil
}

// trimParents safely removes last element if exists.
func trimParents(parents []*types.Header) []*types.Header {
	if len(parents) > 1 {
		return parents[:len(parents)-1]
	}
	return nil
}

// verifyVoteAttestation checks whether the vote attestation in the header is valid.
func (p *Parlia) verifyVoteAttestation(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) error {
	// === Step 1: Extract attestation ===
	epochLength, err := p.epochLength(chain, header, parents)
	if err != nil {
		return err
	}
	attestation, err := getVoteAttestationFromHeader(header, chain.Config(), epochLength)
	if err != nil {
		return err
	}
	if attestation == nil {
		return nil
	}
	if attestation.Data == nil {
		return errors.New("invalid attestation, vote data is nil")
	}
	if len(attestation.Extra) > types.MaxAttestationExtraLength {
		return fmt.Errorf("invalid attestation, too large extra length: %d", len(attestation.Extra))
	}
	if attestation.Data.SourceNumber >= attestation.Data.TargetNumber {
		return errors.New("invalid attestation, SourceNumber not lower than TargetNumber")
	}

	// === Step 2: Verify source block ===
	parent, err := p.getParent(chain, header, parents)
	if err != nil {
		return err
	}
	// The source block should be the highest justified block.
	sourceNumber := attestation.Data.SourceNumber
	sourceHash := attestation.Data.SourceHash
	headers := []*types.Header{parent}
	if len(parents) > 0 {
		headers = parents
	}
	justifiedBlockNumber, justifiedBlockHash, err := p.GetJustifiedNumberAndHash(chain, headers)
	if err != nil {
		return errors.New("unexpected error when getting the highest justified number and hash")
	}
	if sourceNumber != justifiedBlockNumber || sourceHash != justifiedBlockHash {
		return fmt.Errorf("invalid attestation, source mismatch, expected block: %d, hash: %s; real block: %d, hash: %s",
			justifiedBlockNumber, justifiedBlockHash, sourceNumber, sourceHash)
	}

	// === Step 3: Verify target block ===
	targetNumber := attestation.Data.TargetNumber
	targetHash := attestation.Data.TargetHash
	match := false
	ancestor := parent
	ancestorParents := trimParents(parents)
	for range p.GetAncestorGenerationDepth(header) {
		if targetNumber == ancestor.Number.Uint64() && targetHash == ancestor.Hash() {
			match = true
			break
		}

		ancestor, err = p.getParent(chain, ancestor, ancestorParents)
		if err != nil {
			return err
		}
		ancestorParents = trimParents(ancestorParents)
	}
	if !match {
		return fmt.Errorf("invalid attestation, target mismatch, real block: %d, hash: %s", targetNumber, targetHash)
	}

	// === Step 4: Check quorum ===
	// The snapshot should be the targetNumber-1 block's snapshot.
	snap, err := p.snapshot(chain, ancestor.Number.Uint64()-1, ancestor.ParentHash, ancestorParents, p.isSnake8Enabled(chain, ancestor), ancestor)
	if err != nil {
		return err
	}
	// Filter out valid validator from attestation.
	validators := snap.validators()
	validatorsBitSet := bitset.From([]uint64{uint64(attestation.VoteAddressSet)})
	if validatorsBitSet.Count() > uint(len(validators)) {
		return errors.New("invalid attestation, vote number larger than validators number")
	}
	votedAddrs := make([]bls.PublicKey, 0, validatorsBitSet.Count())
	for index, val := range validators {
		if !validatorsBitSet.Test(uint(index)) {
			continue
		}

		voteAddr, err := bls.PublicKeyFromBytes(snap.Validators[val].VoteAddress[:])
		if err != nil {
			return fmt.Errorf("BLS public key converts failed: %v", err)
		}
		votedAddrs = append(votedAddrs, voteAddr)
	}
	// The valid voted validators should be no less than 2/3 validators.
	if len(votedAddrs) < cmath.CeilDiv(len(snap.Validators)*2, 3) {
		return errors.New("invalid attestation, not enough validators voted")
	}

	// === Step 5: Signature verification ===
	aggSig, err := bls.SignatureFromBytes(attestation.AggSignature[:])
	if err != nil {
		return fmt.Errorf("BLS signature converts failed: %v", err)
	}
	if !aggSig.FastAggregateVerify(votedAddrs, attestation.Data.Hash()) {
		return errors.New("invalid attestation, signature verify failed")
	}

	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 {
	// Don't waste time checking blocks from the future
	if header.Time > uint64(time.Now().Unix()+time.Second.Milliseconds()/1000) {
		return consensus.ErrFutureBlock
	}

	if err := p.VerifyUnsealedHeader(chain, header, parents); err != nil {
		return err
	}

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

// VerifyUnsealedHeader performs all header validity checks that do not require
// a valid seal signature. It is used to validate a locally proposed block before
// sealing: it runs the same structural, fork-rule, and cascading-field checks as
// VerifyHeader but skips verifySeal (no signature yet) and verifyVoteAttestation
// (vote attestation is embedded by the sealer and not present before sealing).
func (p *Parlia) VerifyUnsealedHeader(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) error {
	// check extra data
	if len(header.Extra) < extraVanity {
		return errMissingVanity
	}
	if len(header.Extra) < extraVanity+extraSeal {
		return errMissingSignature
	}
	if header.Number == nil {
		return errUnknownBlock
	}
	number := header.Number.Uint64()
	epochLength, err := p.epochLength(chain, header, parents)
	if err != nil {
		return err
	}
	// Ensure that the extra-data contains a signer list on checkpoint, but none otherwise
	signersBytes := getValidatorBytesFromHeader(header, p.chainConfig, epochLength)
	isEpoch := number%epochLength == 0
	if !isEpoch && len(signersBytes) != 0 && !bytes.HasPrefix(signersBytes, []byte("VFQ")) {
		return errExtraValidators
	}
	if isEpoch && len(signersBytes) == 0 {
		return errInvalidSpanValidators
	}

	lorentz := chain.Config().IsLorentz(header.Number, header.Time)
	if !lorentz {
		if header.MixDigest != (common.Hash{}) {
			return errInvalidMixDigest
		}
	} else {
		if header.MilliTimestamp()/1000 != header.Time {
			return fmt.Errorf("invalid MixDigest, have %#x, expected the last two bytes to represent milliseconds", header.MixDigest)
		}
	}

	// Ensure that the block doesn't contain any uncles which are meaningless in PoA
	if header.UncleHash != types.EmptyUncleHash {
		return errInvalidUncleHash
	}

	prague := chain.Config().IsPrague(header.Number, header.Time)
	if !prague {
		if header.ParentBeaconRoot != nil {
			return fmt.Errorf("invalid parentBeaconRoot, have %#x, expected nil", header.ParentBeaconRoot)
		}
		if header.RequestsHash != nil {
			return fmt.Errorf("invalid RequestsHash, have %#x, expected nil", header.RequestsHash)
		}
	} else {
		if header.ParentBeaconRoot == nil || *header.ParentBeaconRoot != (common.Hash{}) {
			return fmt.Errorf("invalid parentBeaconRoot, have %#x, expected zero hash", header.ParentBeaconRoot)
		}
		if header.RequestsHash == nil {
			return errors.New("header has nil RequestsHash after Prague")
		}
	}

	// 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
	}

	parent, err := p.getParent(chain, header, parents)
	if err != nil {
		return err
	}

	// Now that the real parent is known, authoritatively validate the Snake8
	// fork-activation data embedded in the header's extra-data. This rejects
	// forged embedded parent timestamps that would otherwise split consensus
	// between syncing and fully-synced nodes (BLK-3750).
	if err := p.verifySnake8Extra(header, parent); err != nil {
		return err
	}

	snap, err := p.snapshot(chain, number-1, header.ParentHash, parents, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		return err
	}

	if _, ok := snap.Validators[header.Coinbase]; !ok {
		return errUnauthorizedValidator(header.Coinbase.String())
	}
	if snap.SignRecently(header.Coinbase) {
		return errRecentlySigned
	}

	if header.Difficulty == nil {
		return errInvalidDifficulty
	}
	inturn := snap.inturn(header.Coinbase)
	if inturn && header.Difficulty.Cmp(diffInTurn) != 0 {
		return errWrongDifficulty
	}
	if !inturn && header.Difficulty.Cmp(diffNoTurn) != 0 {
		return errWrongDifficulty
	}

	if diff := new(big.Int).Sub(header.Number, parent.Number); diff.Cmp(big.NewInt(1)) != 0 {
		return consensus.ErrInvalidNumber
	}

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

	// Verify the block's gas usage and (if applicable) verify the base fee.
	if !chain.Config().IsLondon(header.Number) {
		// Verify BaseFee not present before EIP-1559 fork.
		if header.BaseFee != nil {
			return fmt.Errorf("invalid baseFee before fork: have %d, expected 'nil'", header.BaseFee)
		}
	} else if err := eip1559.VerifyEIP1559Header(chain.Config(), parent, header); err != nil {
		// Verify the header's EIP-1559 attributes.
		return err
	}

	cancun := chain.Config().IsCancun(header.Number, header.Time)
	if !cancun {
		switch {
		case header.ExcessBlobGas != nil:
			return fmt.Errorf("invalid excessBlobGas: have %d, expected nil", header.ExcessBlobGas)
		case header.BlobGasUsed != nil:
			return fmt.Errorf("invalid blobGasUsed: have %d, expected nil", header.BlobGasUsed)
		case header.WithdrawalsHash != nil:
			return fmt.Errorf("invalid WithdrawalsHash, have %#x, expected nil", header.WithdrawalsHash)
		}
	} else {
		if !header.EmptyWithdrawalsHash() {
			return errors.New("header has wrong WithdrawalsHash")
		}
		if err := eip4844.VerifyEIP4844Header(chain.Config(), parent, header); 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
	}
	gasLimitBoundDivisor := gasLimitBoundDivisorBeforeLorentz
	if p.chainConfig.IsLorentz(header.Number, header.Time) {
		gasLimitBoundDivisor = params.GasLimitBoundDivisor
	}
	limit := parent.GasLimit / 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-1)
	}

	return nil
}

// snapshot retrieves the authorization snapshot at a given point in time.
// !!! be careful
// the block with `number` and `hash` is just the last element of `parents`,
// unlike other interfaces such as verifyCascadingFields, `parents` are real parents
func (p *Parlia) snapshot(chain consensus.ChainHeaderReader, number uint64, hash common.Hash, parents []*types.Header, isSnake8Fork bool, extraHeader *types.Header) (*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
			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, hash, p.ethAPI, isSnake8Fork); err == nil {
				log.Trace("Loaded snapshot from disk", "number", number, "hash", hash)
				snap = s
				break
			}
		}

		// If we're at the genesis, snapshot the initial state. Alternatively if we have
		// piled up more headers than allowed to be reorged (chain reinit from a freezer),
		// consider the checkpoint trusted and snapshot it.

		// Unable to retrieve the exact EpochLength here.
		// As known
		// 		defaultEpochLength = 200 && turnLength = 1 or 4
		// 		lorentzEpochLength = 500 && turnLength = 8
		// 		maxwellEpochLength = 1000 && turnLength = 16
		// So just select block number like 1200, 2200, 3200, we can always get the right validators from `number - 200`
		offset := uint64(200)
		if number == 0 || (number%maxwellEpochLength == offset && (len(headers) > int(params.FullImmutabilityThreshold))) {
			var (
				checkpoint    *types.Header
				blockHash     common.Hash
				blockInterval = defaultBlockInterval
				epochLength   = defaultEpochLength
			)
			if number == 0 {
				checkpoint = chain.GetHeaderByNumber(0)
				if checkpoint != nil {
					blockHash = checkpoint.Hash()
				}
			} else {
				checkpoint = chain.GetHeaderByNumber(number - offset)
				blockHeader := chain.GetHeaderByNumber(number)
				if blockHeader != nil {
					blockHash = blockHeader.Hash()
					if p.chainConfig.IsFermi(blockHeader.Number, blockHeader.Time) {
						blockInterval = fermiBlockInterval
					} else if p.chainConfig.IsMaxwell(blockHeader.Number, blockHeader.Time) {
						blockInterval = maxwellBlockInterval
					} else if p.chainConfig.IsLorentz(blockHeader.Number, blockHeader.Time) {
						blockInterval = lorentzBlockInterval
					}
				}
				if number > offset { // exclude `number == 200`
					blockBeforeCheckpoint := chain.GetHeaderByNumber(number - offset - 1)
					if blockBeforeCheckpoint != nil {
						if p.chainConfig.IsMaxwell(blockBeforeCheckpoint.Number, blockBeforeCheckpoint.Time) {
							epochLength = maxwellEpochLength
						} else if p.chainConfig.IsLorentz(blockBeforeCheckpoint.Number, blockBeforeCheckpoint.Time) {
							epochLength = lorentzEpochLength
						}
					}
				}
			}
			if checkpoint != nil && blockHash != (common.Hash{}) {
				// get validators from headers
				validators, voteAddrs, err := parseValidators(checkpoint, p.chainConfig, epochLength)
				if err != nil {
					return nil, err
				}

				// new snapshot
				snap = newSnapshot(p.config, p.signatures, number, blockHash, validators, voteAddrs, p.ethAPI, isSnake8Fork)

				// get turnLength from headers and use that for new turnLength
				turnLength, err := parseTurnLength(checkpoint, p.chainConfig, epochLength)
				if err != nil {
					return nil, err
				}
				if turnLength != nil {
					snap.TurnLength = *turnLength
				}
				snap.BlockInterval = blockInterval
				snap.EpochLength = epochLength

				// snap.Recents is currently empty, which affects the following:
				// a. The function SignRecently - This is acceptable since an empty snap.Recents results in a more lenient check.
				// b. The function blockTimeVerifyForRamanujanFork - This is also acceptable as it won't be invoked during `snap.apply`.
				// c. This may cause a mismatch in the slash systemtx, but the transaction list is not verified during `snap.apply`.

				// snap.Attestation is nil, but Snapshot.updateAttestation will handle it correctly.
				if err := snap.store(p.db); err != nil {
					return nil, err
				}
				log.Info("Stored checkpoint snapshot to disk", "number", number, "hash", blockHash)
				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, isSnake8Fork)
	if err != nil {
		return nil, err
	}
	p.recentSnaps.Add(snap.Hash, snap)

	// If we've generated a new checkpoint snapshot, save to disk. Deliberately before
	// the Snake8 stamping below (COR-174) so nothing caller-dependent reaches 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)
	}

	// FrequencyRLP is a per-caller view, so it goes on a copy the caller owns and never
	// on the shared cache entry (COR-174). Three reasons this matters:
	//   - the verify path passes a not-yet-validated candidate header, which must not
	//     be able to write into consensus state other code paths read;
	//   - in-turn selection is derived from FrequencyRLP, so a cached value stamped by
	//     an unrelated caller made the selected validator depend on call order;
	//   - snapshot() is reached concurrently from header verification, the miner and
	//     RPC handlers, so writing to the cached pointer was also a data race.
	// parlia_getSnapshot and friends (api.go) become read-only diagnostics by
	// construction: they receive a copy like everyone else.
	//
	// IsSnake8Fork and TurnLength are re-asserted here for the caller's view, but note
	// they are NOT caller-local — apply() and loadSnapshot() already installed them on
	// the cached entry, because the header loop depends on both. Do not "fix" that by
	// moving them here only; see the note in Snapshot.apply.
	//
	// Non-Snake8 callers have nothing to stamp and still get the shared entry, so the
	// standing rule for every caller is unchanged: treat the returned snapshot as
	// read-only unless you know it is a copy.
	if isSnake8Fork {
		snap = snap.copy()
		snap.IsSnake8Fork = true
		snap.TurnLength = snake8TurnLength
		if extraHeader != nil {
			if freq, err := parseValidatorFrequencies(extraHeader, p.chainConfig); err == nil {
				snap.FrequencyRLP = freq
			}
		}
	}

	var validators []string
	for v := range snap.Validators {
		validators = append(validators, v.Hex())
	}
	log.Trace("loaded snapshot", "number", snap.Number, "hash", snap.Hash, "validators", strings.Join(validators, ","), "len", len(snap.Validators))

	return snap, nil
}

// VerifyUncles implements consensus.Engine, always returning an error for any
// uncles as this consensus mechanism doesn't permit uncles.
func (p *Parlia) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {
	if len(block.Uncles()) > 0 {
		return errors.New("uncles not allowed")
	}
	return nil
}

func (p *Parlia) VerifyRequests(header *types.Header, Requests [][]byte) error {
	return nil
}

// 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
	}

	// Verify vote attestation for fast finality.
	if err := p.verifyVoteAttestation(chain, header, parents); err != nil {
		log.Warn("Verify vote attestation failed", "error", err, "hash", header.Hash(), "number", header.Number,
			"parent", header.ParentHash, "coinbase", header.Coinbase, "extra", common.Bytes2Hex(header.Extra))
		verifyVoteAttestationErrorCounter.Inc(1)
		if chain.Config().IsPlato(header.Number) {
			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
	}

	// check for double sign & add to cache
	key := proposalKey(*header)
	preHash, ok := p.recentHeaders.Get(key)
	if ok && preHash != header.Hash() {
		doubleSignCounter.Inc(1)
		log.Warn("DoubleSign detected", " block", header.Number, " miner", header.Coinbase,
			"hash1", preHash, "hash2", header.Hash())
	} else {
		p.recentHeaders.Add(key, header.Hash())
	}

	return nil
}

func (p *Parlia) prepareValidators(chain consensus.ChainHeaderReader, header *types.Header) error {
	epochLength, err := p.epochLength(chain, header, nil)
	if err != nil {
		return err
	}
	if header.Number.Uint64()%epochLength != 0 {
		return nil
	}

	newValidators, voteAddressMap, err := p.getCurrentValidators(header.ParentHash, new(big.Int).Sub(header.Number, big.NewInt(1)))
	if err != nil {
		return err
	}
	// sort validator by address
	sort.Sort(validatorsAscending(newValidators))
	if !p.chainConfig.IsLuban(header.Number) {
		for _, validator := range newValidators {
			header.Extra = append(header.Extra, validator.Bytes()...)
		}
	} else {
		header.Extra = append(header.Extra, byte(len(newValidators)))
		if p.chainConfig.IsOnLuban(header.Number) {
			voteAddressMap = make(map[common.Address]*types.BLSPublicKey, len(newValidators))
			var zeroBlsKey types.BLSPublicKey
			for _, validator := range newValidators {
				voteAddressMap[validator] = &zeroBlsKey
			}
		}
		for _, validator := range newValidators {
			header.Extra = append(header.Extra, validator.Bytes()...)
			header.Extra = append(header.Extra, voteAddressMap[validator].Bytes()...)
		}
	}
	return nil
}

func (p *Parlia) prepareTurnLength(chain consensus.ChainHeaderReader, header *types.Header) error {
	epochLength, err := p.epochLength(chain, header, nil)
	if err != nil {
		return err
	}
	if header.Number.Uint64()%epochLength != 0 ||
		!p.chainConfig.IsBohr(header.Number, header.Time) {
		return nil
	}

	turnLength, err := p.getTurnLength(chain, header)
	if err != nil {
		return err
	}

	if turnLength != nil {
		header.Extra = append(header.Extra, *turnLength)
	}

	return nil
}

// assembleVoteAttestation collects votes and assembles the vote attestation into the block header.
func (p *Parlia) assembleVoteAttestation(chain consensus.ChainHeaderReader, header *types.Header) error {
	// === Step 1: Preconditions ===
	if !p.chainConfig.IsLuban(header.Number) || header.Number.Uint64() < 3 || p.VotePool == nil {
		return nil
	}

	// === Step 2: Find target header with quorum votes ===
	parent := chain.GetHeaderByHash(header.ParentHash)
	if parent == nil {
		return errors.New("parent not found")
	}
	justifiedBlockNumber, justifiedBlockHash, err := p.GetJustifiedNumberAndHash(chain, []*types.Header{parent})
	if err != nil {
		return errors.New("unexpected error when getting the highest justified number and hash")
	}
	var (
		votes                  []*types.VoteEnvelope
		targetHeader           = parent
		targetHeaderParentSnap *Snapshot
	)
	for range p.GetAncestorGenerationDepth(header) {
		snap, err := p.snapshot(chain, targetHeader.Number.Uint64()-1, targetHeader.ParentHash, nil, p.isSnake8Enabled(chain, targetHeader), targetHeader)
		if err != nil {
			return err
		}
		votes = p.VotePool.FetchVotesByBlockHash(targetHeader.Hash(), justifiedBlockNumber)
		quorum := cmath.CeilDiv(len(snap.Validators)*2, 3)
		if len(votes) >= quorum {
			targetHeaderParentSnap = snap
			break
		}

		targetHeader = chain.GetHeaderByHash(targetHeader.ParentHash)
		if targetHeader == nil {
			return errors.New("parent not found")
		}
		if targetHeader.Number.Uint64() <= justifiedBlockNumber {
			break
		}
	}
	if targetHeaderParentSnap == nil {
		return nil
	}

	// === Step 3: Build vote attestation ===
	attestation := &types.VoteAttestation{
		Data: &types.VoteData{
			SourceNumber: justifiedBlockNumber,
			SourceHash:   justifiedBlockHash,
			TargetNumber: targetHeader.Number.Uint64(),
			TargetHash:   targetHeader.Hash(),
		},
	}
	// Validate vote data consistency
	for _, vote := range votes {
		if vote.Data.Hash() != attestation.Data.Hash() {
			return fmt.Errorf("vote check error, expected: %v, real: %v", attestation.Data, vote.Data)
		}
	}
	// Prepare aggregated vote signature
	voteAddrSet := make(map[types.BLSPublicKey]struct{}, len(votes))
	signatures := make([][]byte, len(votes))
	for i, vote := range votes {
		voteAddrSet[vote.VoteAddress] = struct{}{}
		signatures[i] = vote.Signature[:]
	}
	sigs, err := bls.MultipleSignaturesFromBytes(signatures)
	if err != nil {
		return err
	}
	copy(attestation.AggSignature[:], bls.AggregateSignatures(sigs).Marshal())
	// Prepare vote address bitset.
	for _, valInfo := range targetHeaderParentSnap.Validators {
		if _, ok := voteAddrSet[valInfo.VoteAddress]; ok {
			attestation.VoteAddressSet |= 1 << (valInfo.Index - 1) // Index is offset by 1
		}
	}
	bitsetCount := bitset.From([]uint64{uint64(attestation.VoteAddressSet)}).Count()
	if bitsetCount < uint(len(signatures)) {
		log.Warn(fmt.Sprintf("assembleVoteAttestation, check VoteAddress Set failed, expected:%d, real:%d", len(signatures), bitsetCount))
		return errors.New("invalid attestation, check VoteAddress Set failed")
	}

	// === Step 4: Encode & insert into header extra ===
	buf := new(bytes.Buffer)
	if err = rlp.Encode(buf, attestation); err != nil {
		return fmt.Errorf("attestation: failed to encode: %w", err)
	}
	extraSealStart := len(header.Extra) - extraSeal
	extraSealBytes := header.Extra[extraSealStart:]
	header.Extra = append(header.Extra[:extraSealStart], buf.Bytes()...)
	header.Extra = append(header.Extra, extraSealBytes...)

	return nil
}

// NextInTurnValidator return the next in-turn validator for header
func (p *Parlia) NextInTurnValidator(chain consensus.ChainHeaderReader, header *types.Header) (common.Address, error) {
	snap, err := p.snapshot(chain, header.Number.Uint64(), header.Hash(), nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		return common.Address{}, err
	}

	return snap.inturnValidator(), nil
}

// Prepare implements consensus.Engine, preparing all the consensus fields of the
// header for running the transactions on top.
func (p *Parlia) Prepare(chain consensus.ChainHeaderReader, header *types.Header) error {
	header.Coinbase = p.val
	return p.prepare(chain, header)
}

// prepare is shared by Prepare and PrepareForBidBlock; caller sets Coinbase/Number/ParentHash.
func (p *Parlia) prepare(chain consensus.ChainHeaderReader, header *types.Header) error {
	header.Nonce = types.BlockNonce{}

	number := header.Number.Uint64()
	parent := chain.GetHeader(header.ParentHash, number-1)
	if parent == nil {
		return consensus.ErrUnknownAncestor
	}
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), nil)
	if err != nil {
		return err
	}

	// CONSENSUS-CRITICAL ORDERING (Chiliz Snake8): the difficulty stamped below
	// must be derived from the SAME frequency data that SetExtraData embeds in
	// this header — verifiers (and our own Seal) judge in-turn-ness from the
	// embedded data, so install the fresh FrequencyRLP on the snapshot BEFORE
	// computing difficulty and the Ramanujan backoff. Stamping difficulty from
	// the stale cached FrequencyRLP produces blocks that are invalid by
	// construction (diff=1 while the embedded data says in-turn) and forks the
	// chain — this regressed in the v1.7.6 prepare/SetExtraData split (COR-37).
	if p.isSnake8Enabled(chain, header) {
		if err := p.refreshFrequencyRLP(snap, number, parent); err != nil {
			// Post-Snake8Fix only: refuse to seal rather than emit a header
			// whose embedded bytes a verifier's recomputation would reject.
			return err
		}
	}
	// TODO: delete this log
	log.Trace("Prepare_start", "number", header.Number, "time", header.Time, "isSnake8", p.isSnake8Enabled(chain, header), "isSnake8Snap", snap.IsSnake8Fork, "inturnVal", snap.inturnValidator())

	// Set the correct difficulty. header.Coinbase, not p.val: Prepare sets
	// Coinbase = p.val, but PrepareForBidBlock prepares for the in-turn
	// validator — the difficulty must describe the block's actual signer.
	header.Difficulty = calcDifficulty(snap, header.Coinbase)
	if header.Difficulty.Cmp(diffInTurn) != 0 && header.Number.Uint64() == 1 {
		return fmt.Errorf("not your turn for block producing")
	}

	// 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))...)
	}

	// Ensure the timestamp has the correct delay
	blockTime := p.blockTimeForRamanujanFork(snap, header, parent)

	header.Time = blockTime / 1000 // get seconds
	if p.chainConfig.IsLorentz(header.Number, header.Time) {
		header.SetMilliseconds(blockTime % 1000)
	} else {
		header.MixDigest = common.Hash{}
	}
	return p.SetExtraData(chain, header)
}

// refreshFrequencyRLP computes the fresh Snake8 validator-frequency data for
// the child of snap (block `number`, whose parent header is `parent`) and installs
// it on the snapshot. `snap` must be a caller-owned snapshot — Parlia.snapshot()
// returns a copy under Snake8, so this write stays local and never reaches the
// shared LRU entry (COR-174).
//
// Pre-Snake8Fix (historical behavior): stakes are read at the node's latest state
// and every failure is soft — on a lookup error the stake degrades to zero, on a
// calcFrequencyRLP error FrequencyRLP ends up nil and validator selection degrades
// to round-robin. Because both prepare() (difficulty) and SetExtraData (embedded
// data) go through this same helper, they degrade together and the produced header
// stays self-consistent. Never returns an error on this path.
//
// Post-Snake8Fix (COR-173): the embedded bytes are consensus-verified, so they must
// be reproducible by every node. Stake reads are pinned to the parent block's state
// (by hash, so side chains resolve correctly) and a failed lookup is reported as
// errSnake8StakeLookup — a NODE-LOCAL failure, not a statement about the block.
// Sealing treats it as fatal (refuse to produce rather than embed bytes a verifier
// would reject); verification fails open on it (see verifySnake8FrequencyData). The
// one remaining soft failure is calcFrequencyRLP's "no eligible validators": it is a
// deterministic function of the pinned stakes and snap.Recents, so producer and
// verifier degrade to the same nil bytes (round-robin selection) and the header
// still verifies.
//
// Pinned bytes are a pure function of the parent (stakes at the parent's state,
// candidates from the parent's snapshot), so they are memoized in frequencyCache by
// parent hash: prepare + SetExtraData + the Finalize verification all share one
// stake sweep per parent. The unpinned pre-fork path must never be cached.
func (p *Parlia) refreshFrequencyRLP(snap *Snapshot, number uint64, parent *types.Header) error {
	pinned := p.chainConfig.IsSnake8Fix(parent.Time)
	var state *rpc.BlockNumberOrHash
	if pinned {
		// Nil-guarded like stakeReader below: struct-literal engines have no cache.
		if p.frequencyCache != nil {
			if cached, ok := p.frequencyCache.Get(parent.Hash()); ok {
				snap.FrequencyRLP = bytes.Clone(cached)
				return nil
			}
		}
		parentState := rpc.BlockNumberOrHashWithHash(parent.Hash(), false)
		state = &parentState
	}

	// Fall back for engines assembled as struct literals (tests, tooling), which
	// bypass New() and leave the stakeReader seam nil.
	stakeReader := p.stakeReader
	if stakeReader == nil {
		stakeReader = p.getValidatorTotalDelegated
	}

	stakes := make(map[common.Address]*big.Int)
	for addr := range snap.Validators {
		totalDelegated, err := stakeReader(addr, number-1, state)
		if err != nil || totalDelegated == nil {
			if pinned {
				if err == nil {
					return fmt.Errorf("%w: validator %s at block %d: contract returned no stake", errSnake8StakeLookup, addr, number-1)
				}
				return fmt.Errorf("%w: validator %s at block %d: %v", errSnake8StakeLookup, addr, number-1, err)
			}
			log.Error("error when fetching total delegated amount", "validator", addr, "err", err)
			// Zero, not nil: calcFrequencyRLP dereferences every stake, so a
			// nil entry would crash the sealer on a transient RPC failure.
			// A zero stake excludes the validator from the frequency set,
			// which is the intended degradation.
			totalDelegated = big.NewInt(0)
		}
		stakes[addr] = totalDelegated
	}
	freqRlp, err := snap.calcFrequencyRLP(stakes)
	if err != nil {
		log.Error("error when calculating frequency rlp", "error", err, "block", number-1)
	}
	snap.FrequencyRLP = freqRlp
	if pinned && p.frequencyCache != nil {
		p.frequencyCache.Add(parent.Hash(), bytes.Clone(freqRlp))
	}
	return nil
}

// SetExtraData rebuilds the validator-controlled extra-data section:
// 28-byte vanity (caller-supplied, zero-padded) + 4-byte nextForkHash +
// validators bytes (epoch only) + turnLength (epoch only, post-Bohr) + 65 reserved seal bytes.
// Caller supplies the desired vanity in header.Extra; this function pads/truncates it.
func (p *Parlia) SetExtraData(chain consensus.ChainHeaderReader, header *types.Header) error {
	// 32-byte vanity prefix: pad/truncate caller's vanity bytes, then append nextForkHash.
	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.NextForkHash(p.chainConfig, p.genesisHash, chain.GenesisHeader().Time, header.Number.Uint64(), header.Time)
	header.Extra = append(header.Extra, nextForkHash[:]...)

	if err := p.prepareValidators(chain, header); err != nil {
		return err
	}

	if err := p.prepareTurnLength(chain, header); err != nil {
		return err
	}

	// Add RLP-encoded validator+frequency data (Chiliz Snake8). SetExtraData is
	// also called standalone (e.g. from the miner MEV path), so recompute the
	// parent and the frequency snapshot here rather than relying on prepare's
	// locals. refreshFrequencyRLP is deterministic for a given parent, so this
	// recomputation yields exactly the bytes prepare() derived the difficulty
	// from — the header stays coherent (see the ordering note in prepare).
	if p.isSnake8Enabled(chain, header) {
		number := header.Number.Uint64()
		parent := chain.GetHeader(header.ParentHash, number-1)
		if parent == nil {
			return consensus.ErrUnknownAncestor
		}
		snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, true, nil)
		if err != nil {
			return err
		}
		if err := p.refreshFrequencyRLP(snap, number, parent); err != nil {
			return err
		}

		ts := make([]byte, 8)
		binary.LittleEndian.PutUint64(ts, parent.Time)
		log.Trace("Prepare", "append snake8 data", parent.Time, "number", header.Number.Uint64(), "len(validatorFrequencyDataPrefix)", len(validatorFrequencyDataPrefix), "len(ts)", len(ts), "len(snap.FrequencyRLP)", len(snap.FrequencyRLP))
		header.Extra = append(header.Extra, validatorFrequencyDataPrefix...)
		header.Extra = append(header.Extra, ts...)
		header.Extra = append(header.Extra, snap.FrequencyRLP...)
	}

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

	return nil
}

func (p *Parlia) verifyValidators(chain consensus.ChainHeaderReader, header *types.Header) error {
	epochLength, err := p.epochLength(chain, header, nil)
	if err != nil {
		return err
	}
	if header.Number.Uint64()%epochLength != 0 {
		return nil
	}

	newValidators, voteAddressMap, err := p.getCurrentValidators(header.ParentHash, new(big.Int).Sub(header.Number, big.NewInt(1)))
	if err != nil {
		return err
	}
	// sort validator by address
	sort.Sort(validatorsAscending(newValidators))
	var validatorsBytes []byte
	validatorsNumber := len(newValidators)
	if !p.chainConfig.IsLuban(header.Number) {
		validatorsBytes = make([]byte, validatorsNumber*validatorBytesLengthBeforeLuban)
		for i, validator := range newValidators {
			copy(validatorsBytes[i*validatorBytesLengthBeforeLuban:], validator.Bytes())
		}
	} else {
		if uint8(validatorsNumber) != header.Extra[extraVanity] {
			return errMismatchingEpochValidators
		}
		validatorsBytes = make([]byte, validatorsNumber*validatorBytesLength)
		if p.chainConfig.IsOnLuban(header.Number) {
			voteAddressMap = make(map[common.Address]*types.BLSPublicKey, len(newValidators))
			var zeroBlsKey types.BLSPublicKey
			for _, validator := range newValidators {
				voteAddressMap[validator] = &zeroBlsKey
			}
		}
		for i, validator := range newValidators {
			copy(validatorsBytes[i*validatorBytesLength:], validator.Bytes())
			copy(validatorsBytes[i*validatorBytesLength+common.AddressLength:], voteAddressMap[validator].Bytes())
		}
	}
	if !bytes.Equal(getValidatorBytesFromHeader(header, p.chainConfig, epochLength), validatorsBytes) {
		return errMismatchingEpochValidators
	}
	return nil
}

func (p *Parlia) verifyTurnLength(chain consensus.ChainHeaderReader, header *types.Header) error {
	epochLength, err := p.epochLength(chain, header, nil)
	if err != nil {
		return err
	}
	if header.Number.Uint64()%epochLength != 0 ||
		!p.chainConfig.IsBohr(header.Number, header.Time) {
		return nil
	}

	turnLengthFromHeader, err := parseTurnLength(header, p.chainConfig, epochLength)
	if err != nil {
		return err
	}
	if turnLengthFromHeader != nil {
		turnLength, err := p.getTurnLength(chain, header)
		if err != nil {
			return err
		}
		if turnLength != nil && *turnLength == *turnLengthFromHeader {
			log.Debug("verifyTurnLength", "turnLength", *turnLength)
			return nil
		}
	}

	return errMismatchingEpochTurnLength
}

func (p *Parlia) distributeFinalityReward(chain consensus.ChainHeaderReader, state vm.StateDB, header *types.Header,
	cx core.ChainContext, txs *[]*types.Transaction, receipts *[]*types.Receipt, systemTxs *[]*types.Transaction,
	usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	currentHeight := header.Number.Uint64()
	if currentHeight%finalityRewardInterval != 0 {
		return nil
	}

	head := header
	accumulatedWeights := make(map[common.Address]uint64)
	for height := currentHeight - 1; height+finalityRewardInterval >= currentHeight && height >= 1; height-- {
		head = chain.GetHeaderByHash(head.ParentHash)
		if head == nil {
			return fmt.Errorf("header is nil at height %d", height)
		}
		epochLength, err := p.epochLength(chain, head, nil)
		if err != nil {
			return err
		}
		voteAttestation, err := getVoteAttestationFromHeader(head, chain.Config(), epochLength)
		if err != nil {
			return err
		}
		if voteAttestation == nil {
			continue
		}
		justifiedBlock := chain.GetHeaderByHash(voteAttestation.Data.TargetHash)
		if justifiedBlock == nil {
			log.Warn("justifiedBlock is nil at height %d", voteAttestation.Data.TargetNumber)
			continue
		}
		parent := chain.GetHeaderByHash(justifiedBlock.ParentHash)
		if parent == nil {
			return consensus.ErrUnknownAncestor
		}
		snap, err := p.snapshot(chain, justifiedBlock.Number.Uint64()-1, justifiedBlock.ParentHash, nil, p.isSnake8Enabled(chain, head), head)
		if err != nil {
			return err
		}
		validators := snap.validators()
		validatorsBitSet := bitset.From([]uint64{uint64(voteAttestation.VoteAddressSet)})
		if validatorsBitSet.Count() > uint(len(validators)) {
			log.Error("invalid attestation, vote number larger than validators number")
			continue
		}
		validVoteCount := 0
		for index, val := range validators {
			if validatorsBitSet.Test(uint(index)) {
				accumulatedWeights[val] += 1
				validVoteCount += 1
			}
		}
		quorum := cmath.CeilDiv(len(snap.Validators)*2, 3)
		if validVoteCount > quorum {
			accumulatedWeights[head.Coinbase] += uint64((validVoteCount - quorum) * collectAdditionalVotesRewardRatio / 100)
		}
	}

	validators := make([]common.Address, 0, len(accumulatedWeights))
	weights := make([]*big.Int, 0, len(accumulatedWeights))
	for val := range accumulatedWeights {
		validators = append(validators, val)
	}
	sort.Sort(validatorsAscending(validators))
	for _, val := range validators {
		weights = append(weights, big.NewInt(int64(accumulatedWeights[val])))
	}

	// generate system transaction
	method := "distributeFinalityReward"
	data, err := p.validatorSetABI.Pack(method, validators, weights)
	if err != nil {
		log.Error("Unable to pack tx for distributeFinalityReward", "error", err)
		return err
	}
	msg := p.getSystemMessage(header.Coinbase, common.HexToAddress(systemcontracts.ValidatorContract), data, common.Big0)
	return p.applyTransaction(msg, state, header, cx, txs, receipts, systemTxs, usedGas, mode, tracer)
}

func (p *Parlia) EstimateGasReservedForSystemTxs(chain consensus.ChainHeaderReader, header *types.Header) uint64 {
	parent := chain.GetHeaderByHash(header.ParentHash)
	if parent != nil {
		// Mainnet and Chapel have both passed Feynman. Now, simplify the logic before and during the Feynman hard fork.
		if p.chainConfig.IsFeynman(header.Number, header.Time) &&
			!p.chainConfig.IsOnFeynman(header.Number, parent.Time, header.Time) {
			// const (
			// 	the following values represent the maximum values found in the most recent blocks on the mainnet
			// 	depositTxGas         = uint64(60_000)
			// 	slashTxGas           = uint64(140_000)
			// 	finalityRewardTxGas  = uint64(350_000)
			// 	updateValidatorTxGas = uint64(12_160_000)
			// )
			// suggestReservedGas := depositTxGas
			// if header.Difficulty.Cmp(diffInTurn) != 0 {
			// 	snap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, nil)
			// 	if err != nil || !snap.SignRecently(snap.inturnValidator()) {
			// 		suggestReservedGas += slashTxGas
			// 	}
			// }
			// if header.Number.Uint64()%p.config.Epoch == 0 {
			// 	suggestReservedGas += finalityRewardTxGas
			// }
			// if isBreatheBlock(parent.Time, header.Time) {
			// 	suggestReservedGas += updateValidatorTxGas
			// }
			// return suggestReservedGas * 150 / 100
			if !isBreatheBlock(parent.Time, header.Time) {
				// params.SystemTxsGasSoftLimit > (depositTxGas+slashTxGas+finalityRewardTxGas)*150/100
				return params.SystemTxsGasSoftLimit
			}
		}
	}

	// params.SystemTxsGasHardLimit > (depositTxGas+slashTxGas+finalityRewardTxGas+updateValidatorTxGas)*150/100
	return params.SystemTxsGasHardLimit
}

// Finalize implements consensus.Engine, ensuring no uncles are set, nor block
// rewards given.
func (p *Parlia) Finalize(chain consensus.ChainHeaderReader, header *types.Header, state vm.StateDB, txs *[]*types.Transaction,
	uncles []*types.Header, _ []*types.Withdrawal, receipts *[]*types.Receipt, systemTxs *[]*types.Transaction, usedGas *uint64, tracer *tracing.Hooks) error {
	// warn if not in majority fork
	p.detectNewVersionWithFork(chain, header, state)

	// 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 err := p.verifyValidators(chain, header); err != nil {
		return err
	}

	if err := p.verifyTurnLength(chain, header); err != nil {
		return err
	}

	cx := chainContext{ChainHeaderReader: chain, parlia: p}

	parent := chain.GetHeaderByHash(header.ParentHash)
	if parent == nil {
		return consensus.ErrUnknownAncestor
	}

	// Snake8Fix (COR-173): with state now available, verify the embedded
	// validator-frequency data against its recomputation from the parent
	// block's state. Like verifyValidators above, this cannot run in
	// VerifyHeader because it needs a contract call against parent state.
	if err := p.verifySnake8FrequencyData(chain, header, parent); err != nil {
		return err
	}

	systemcontracts.TryUpdateBuildInSystemContract(p.chainConfig, header.Number, parent.Time, header.Time, state, false)

	if p.chainConfig.IsOnFeynman(header.Number, parent.Time, header.Time) {
		err := p.initializeFeynmanContract(state, header, cx, txs, receipts, systemTxs, usedGas, systemTxImporting, tracer)
		if err != nil {
			return fmt.Errorf("init feynman contract failed: %v", err)
		}
	}

	// No block rewards in PoA, so the state remains as is and uncles are dropped
	if header.Number.Cmp(common.Big1) == 0 {
		err := p.initContract(state, header, cx, txs, receipts, systemTxs, usedGas, systemTxImporting, tracer)
		if err != nil {
			log.Error("init contract failed", "error", err)
			return err
		}
	}
	if header.Difficulty.Cmp(diffInTurn) != 0 {
		snap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
		if err != nil {
			return err
		}
		spoiledVal := snap.inturnValidator()
		signedRecently := false
		if p.chainConfig.IsPlato(header.Number) {
			signedRecently = snap.SignRecently(spoiledVal)
		} else {
			for _, recent := range snap.Recents {
				if recent == spoiledVal {
					signedRecently = true
					break
				}
			}
		}

		if !signedRecently {
			log.Trace("slash validator", "block hash", header.Hash(), "address", spoiledVal)
			err = p.slash(spoiledVal, state, header, cx, txs, receipts, systemTxs, usedGas, systemTxImporting, tracer)
			if err != nil {
				log.Error("slash validator failed", "block hash", header.Hash(), "address", spoiledVal, "err", err)
			}
		}
	}

	val := header.Coinbase
	PenalizeForDelayMining, err := p.isIntentionalDelayMining(chain, header)
	if err != nil {
		log.Debug("unexpected error happened when detecting intentional delay mining", "err", err)
	}
	if PenalizeForDelayMining {
		intentionalDelayMiningCounter.Inc(1)
		log.Warn("intentional delay mining detected", "validator", val, "number", header.Number, "hash", header.Hash())
	}
	err = p.distributeIncoming(val, state, header, cx, txs, receipts, systemTxs, usedGas, systemTxImporting, tracer)
	if err != nil {
		return err
	}

	if p.chainConfig.IsPlato(header.Number) {
		if err := p.distributeFinalityReward(chain, state, header, cx, txs, receipts, systemTxs, usedGas, systemTxImporting, tracer); err != nil {
			return err
		}
	}

	// update validators every day
	if p.chainConfig.IsFeynman(header.Number, header.Time) && isBreatheBlock(parent.Time, header.Time) {
		// we should avoid update validators in the Feynman upgrade block
		if !p.chainConfig.IsOnFeynman(header.Number, parent.Time, header.Time) {
			if err := p.updateValidatorSetV2(state, header, cx, txs, receipts, systemTxs, usedGas, systemTxImporting, tracer); err != nil {
				return err
			}
		}
	}

	if len(*systemTxs) > 0 {
		return errors.New("the length of systemTxs do not match")
	}
	return nil
}

type systemTxMode uint8

const (
	systemTxImporting systemTxMode = iota
	systemTxMining
	systemTxPacking
)

func (p *Parlia) FinalizeAndAssemble(chain consensus.ChainHeaderReader, header *types.Header, state *state.StateDB,
	body *types.Body, receipts []*types.Receipt, tracer *tracing.Hooks) (*types.Block, []*types.Receipt, error) {
	return p.finalizeAndAssemble(chain, header, state, body, receipts, tracer, systemTxMining)
}

func (p *Parlia) finalizeAndAssemble(chain consensus.ChainHeaderReader, header *types.Header, state *state.StateDB,
	body *types.Body, receipts []*types.Receipt, tracer *tracing.Hooks, mode systemTxMode) (*types.Block, []*types.Receipt, error) {
	// No block rewards in PoA, so the state remains as is and uncles are dropped
	cx := chainContext{ChainHeaderReader: chain, parlia: p}

	if body.Transactions == nil {
		body.Transactions = make([]*types.Transaction, 0)
	}
	if receipts == nil {
		receipts = make([]*types.Receipt, 0)
	}

	parent := chain.GetHeaderByHash(header.ParentHash)
	if parent == nil {
		return nil, nil, errors.New("parent not found")
	}

	systemcontracts.TryUpdateBuildInSystemContract(p.chainConfig, header.Number, parent.Time, header.Time, state, false)

	if p.chainConfig.IsOnFeynman(header.Number, parent.Time, header.Time) {
		err := p.initializeFeynmanContract(state, header, cx, &body.Transactions, &receipts, nil, &header.GasUsed, mode, tracer)
		if err != nil {
			return nil, nil, fmt.Errorf("init feynman contract failed: %v", err)
		}
	}

	if header.Number.Cmp(common.Big1) == 0 {
		err := p.initContract(state, header, cx, &body.Transactions, &receipts, nil, &header.GasUsed, mode, tracer)
		if err != nil {
			log.Error("init contract failed", "error", err)
			return nil, nil, err
		}
	}
	if header.Difficulty.Cmp(diffInTurn) != 0 {
		number := header.Number.Uint64()
		snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
		if err != nil {
			return nil, nil, err
		}
		spoiledVal := snap.inturnValidator()
		signedRecently := false
		if p.chainConfig.IsPlato(header.Number) {
			signedRecently = snap.SignRecently(spoiledVal)
		} else {
			for _, recent := range snap.Recents {
				if recent == spoiledVal {
					signedRecently = true
					break
				}
			}
		}
		if !signedRecently {
			err = p.slash(spoiledVal, state, header, cx, &body.Transactions, &receipts, nil, &header.GasUsed, mode, tracer)
			if err != nil {
				log.Error("slash validator failed", "block hash", header.Hash(), "address", spoiledVal)
			}
		}
	}

	err := p.distributeIncoming(header.Coinbase, state, header, cx, &body.Transactions, &receipts, nil, &header.GasUsed, mode, tracer)
	if err != nil {
		return nil, nil, err
	}

	if p.chainConfig.IsPlato(header.Number) {
		if err := p.distributeFinalityReward(chain, state, header, cx, &body.Transactions, &receipts, nil, &header.GasUsed, mode, tracer); err != nil {
			return nil, nil, err
		}
	}

	// update validators every day
	if p.chainConfig.IsFeynman(header.Number, header.Time) && isBreatheBlock(parent.Time, header.Time) {
		// we should avoid update validators in the Feynman upgrade block
		if !p.chainConfig.IsOnFeynman(header.Number, parent.Time, header.Time) {
			if err := p.updateValidatorSetV2(state, header, cx, &body.Transactions, &receipts, nil, &header.GasUsed, mode, tracer); err != nil {
				return nil, nil, err
			}
		}
	}

	// should not happen. Once happen, stop the node is better than broadcast the block
	if header.GasLimit < header.GasUsed {
		return nil, nil, errors.New("gas consumption of system txs exceed the gas limit")
	}
	header.UncleHash = types.EmptyUncleHash
	var blk *types.Block
	var rootHash common.Hash
	wg := sync.WaitGroup{}
	wg.Add(2)
	go func() {
		rootHash = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
		wg.Done()
	}()
	go func() {
		blk = types.NewBlock(header, body, receipts, trie.NewStackTrie(nil))
		wg.Done()
	}()
	wg.Wait()
	blk.SetRoot(rootHash)
	// Assemble and return the final block for sealing
	return blk, receipts, nil
}

func (p *Parlia) IsActiveValidatorAt(chain consensus.ChainHeaderReader, header *types.Header, checkVoteKeyFn func(bLSPublicKey *types.BLSPublicKey) bool) bool {
	number := header.Number.Uint64()
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		log.Error("failed to get the snapshot from consensus", "error", err)
		return false
	}
	validators := snap.Validators
	validatorInfo, ok := validators[p.val]

	return ok && (checkVoteKeyFn == nil || (validatorInfo != nil && checkVoteKeyFn(&validatorInfo.VoteAddress)))
}

// VerifyVote will verify: 1. If the vote comes from valid validators 2. If the vote's sourceNumber and sourceHash are correct
func (p *Parlia) VerifyVote(chain consensus.ChainHeaderReader, vote *types.VoteEnvelope) error {
	targetNumber := vote.Data.TargetNumber
	targetHash := vote.Data.TargetHash
	header := chain.GetVerifiedBlockByHash(targetHash)
	if header == nil {
		log.Warn("BlockHeader at current voteBlockNumber is nil", "targetNumber", targetNumber, "targetHash", targetHash)
		return errors.New("BlockHeader at current voteBlockNumber is nil")
	}
	if header.Number.Uint64() != targetNumber {
		log.Warn("unexpected target number", "expect", header.Number.Uint64(), "real", targetNumber)
		return errors.New("target number mismatch")
	}

	justifiedBlockNumber, justifiedBlockHash, err := p.GetJustifiedNumberAndHash(chain, []*types.Header{header})
	if err != nil {
		log.Error("failed to get the highest justified number and hash", "headerNumber", header.Number, "headerHash", header.Hash())
		return errors.New("unexpected error when getting the highest justified number and hash")
	}
	if vote.Data.SourceNumber != justifiedBlockNumber || vote.Data.SourceHash != justifiedBlockHash {
		return errors.New("vote source block mismatch")
	}

	number := header.Number.Uint64()
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		log.Error("failed to get the snapshot from consensus", "error", err)
		return errors.New("failed to get the snapshot from consensus")
	}

	validators := snap.Validators
	voteAddress := vote.VoteAddress
	for addr, validator := range validators {
		if validator.VoteAddress == voteAddress {
			if addr == p.val {
				validVotesfromSelfCounter.Inc(1)
			}
			metrics.GetOrRegisterCounter(fmt.Sprintf("parlia/VerifyVote/%s", addr.String()), nil).Inc(1)
			return nil
		}
	}

	return errors.New("vote verification failed")
}

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

	p.val = val
	p.signFn = signFn
	p.signTxFn = signTxFn
}

// IsLastBlockInTurn reports whether header is the last block in the current validator's turn.
func (p *Parlia) IsLastBlockInTurn(chain consensus.ChainReader, header *types.Header) bool {
	snap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		return false
	}
	return snap.lastBlockInOneTurn(header.Number.Uint64())
}

// Argument leftOver is the time reserved for block finalize(calculate root, distribute income...)
func (p *Parlia) Delay(chain consensus.ChainReader, header *types.Header, leftOver *time.Duration) *time.Duration {
	snap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		return nil
	}

	delay := p.delayForRamanujanFork(snap, header)
	timeForMining := time.Duration(snap.BlockInterval) * time.Millisecond
	if delay > timeForMining {
		delay = timeForMining
	}

	if *leftOver >= time.Duration(snap.BlockInterval)*time.Millisecond {
		// ignore invalid leftOver
		log.Error("Delay invalid argument", "leftOver", leftOver.String(), "Period", snap.BlockInterval)
	} else if *leftOver >= delay {
		delay = time.Duration(0)
		return &delay
	} else {
		delay = delay - *leftOver
	}

	return &delay
}

// Seal implements consensus.Engine, attempting to create a sealed block using
// the local signing credentials.
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
	}
	// Don't hold the val fields for the entire sealing procedure
	p.lock.RLock()
	val, signFn := p.val, p.signFn
	p.lock.RUnlock()

	isSnake8 := p.isSnake8Enabled(chain, header)
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, isSnake8, header)
	if err != nil {
		return err
	}

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

	// If we're amongst the recent signers, wait for the next block
	if snap.SignRecently(val) {
		log.Info("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(), "isSnake8", isSnake8, "isSnake8Snap", snap.IsSnake8Fork, "inturnVal", snap.inturnValidator())

	// Wait until sealing is terminated or delay timeout.
	log.Info("Waiting for slot to sign and propagate", "delay", common.PrettyDuration(delay))
	go func() {
		select {
		case <-stop:
			return
		case <-time.After(delay):
		}

		err := p.assembleVoteAttestation(chain, header)
		if err != nil {
			/* If the vote attestation can't be assembled successfully, the blockchain won't get
			   fast finalized, but it can be tolerated, so just report this error here. */
			log.Debug("Assemble vote attestation failed when sealing", "err", err)
		}

		// Sign all the things!
		sig, err := signFn(accounts.Account{Address: val}, accounts.MimetypeParlia, ParliaRLP(header, p.chainConfig.ChainID))
		if err != nil {
			log.Error("Sign for the block header failed when sealing", "err", err)
			return
		}
		copy(header.Extra[len(header.Extra)-extraSeal:], sig)

		if p.shouldWaitForCurrentBlockProcess(chain, header, snap) {
			highestVerifiedHeader := chain.GetHighestVerifiedHeader()
			// including time for writing and committing blocks
			waitProcessEstimate := math.Ceil(float64(highestVerifiedHeader.GasUsed) / float64(100_000_000))
			log.Info("Waiting for received in turn block to process", "waitProcessEstimate(Seconds)", waitProcessEstimate)
			select {
			case <-stop:
				log.Info("Received block process finished, abort block seal")
				return
			case <-time.After(time.Duration(waitProcessEstimate) * time.Second):
				if chain.CurrentHeader().Number.Uint64() >= header.Number.Uint64() {
					log.Info("Process backoff time exhausted, and current header has updated to abort this seal")
					return
				}
				log.Info("Process backoff time exhausted, start to seal block")
			}
		}

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

	return nil
}

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

	highestVerifiedHeader := chain.GetHighestVerifiedHeader()
	if highestVerifiedHeader == nil {
		log.Warn("Shouldn't wait for block process, because there is no highest verified header")
		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, p.isSnake8Enabled(chain, header), header)
	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) SignRecently(chain consensus.ChainReader, parent *types.Header) (bool, error) {
	snap, err := p.snapshot(chain, parent.Number.Uint64(), parent.Hash(), nil, p.isSnake8Enabled(chain, parent), parent)
	if err != nil {
		return true, err
	}

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

	return snap.SignRecently(p.val), nil
}

// 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.
//
// Snake8 in-turn rule (COR-173): block N's in-turn-ness — and therefore its
// consensus-verified difficulty — is judged from the frequency bytes embedded in
// header N itself (verifyCascadingFields stamps the candidate header's bytes onto
// the snapshot). Post-Snake8Fix those bytes are in turn forced to equal the
// recomputation from state at N-1 (verifySnake8FrequencyData), which is what the
// producer embeds via prepare()/SetExtraData. This function is only a scheduling
// hint for the miner: it approximates block N+1's difficulty using the bytes
// embedded in parent header N (state N-1 derived) rather than the state-N-derived
// bytes the actual block will carry. That approximation is not consensus-relevant
// — Prepare recomputes the authoritative difficulty before sealing.
func (p *Parlia) CalcDifficulty(chain consensus.ChainHeaderReader, time uint64, parent *types.Header) *big.Int {
	snap, err := p.snapshot(chain, parent.Number.Uint64(), parent.Hash(), nil, p.isSnake8Enabled(chain, parent), parent)
	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 encodeSigHeaderWithoutVoteAttestation(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[:extraVanity], // this will panic if extra is too short, should check before calling encodeSigHeaderWithoutVoteAttestation
		header.MixDigest,
		header.Nonce,
	})
	if err != nil {
		panic("can't encode: " + err.Error())
	}
}

// SealHash returns the hash of a block without vote attestation prior to it being sealed.
// So it's not the real hash of a block, just used as unique id to distinguish task
func (p *Parlia) SealHash(header *types.Header) (hash common.Hash) {
	hasher := sha3.NewLegacyKeccak256()
	encodeSigHeaderWithoutVoteAttestation(hasher, header, p.chainConfig.ChainID)
	hasher.Sum(hash[:0])
	return hash
}

// APIs implements consensus.Engine, returning the user facing RPC API to query snapshot.
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,
	}}
}

// Close implements consensus.Engine. It's a noop for parlia as there are no background threads.
func (p *Parlia) Close() error {
	return nil
}

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

// Returns the inflation % for years passed
// years are estimated based on the seconds passed since the fork block's timestamp
// If year > 13: pct = 1.88, Otherwise  pct = 9.24e^(-0.250x) + 1.60
// Note: result is rounded to 1e18 decimal places and returned as int (percent * 1e18)
func getInflationPct(secondsPassed uint64) *big.Int {
	// convert seconds to years
	year := big.NewFloat(0)
	year.Mul(big.NewFloat(0).SetUint64(secondsPassed), big.NewFloat(1.0/31536000))
	year.Add(year, big.NewFloat(1))
	yearF, _ := year.Float64()

	log.Trace("inflation year", "year", yearF)

	var inflationPct float64
	if year.Cmp(big.NewFloat(13)) > 0 {
		inflationPct = 1.88
	} else {
		initDecayMag := 9.24
		decayRate := -0.25
		offset := 1.6

		inflationPct = initDecayMag*math.Pow(math.E, decayRate*yearF) + offset
	}
	inflationPct = math.Round(inflationPct*1e18) / 1e18
	return big.NewInt(int64(inflationPct * 1e18))
}

// Returns amount of chz & inflation pct for specific block (part of dragon8)
func getNewSupplyForBlock(forkTs uint64, currentTs uint64, lastSupply *big.Int) (*big.Int, *big.Int) {
	// Calculate the new supply
	secondsPassed := currentTs - forkTs
	newIntroducedSupply := big.NewInt(0)
	inflationPct := getInflationPct(secondsPassed)
	newIntroducedSupply.Mul(lastSupply, inflationPct)
	newIntroducedSupply.Div(newIntroducedSupply, big.NewInt(1e18))
	newIntroducedSupply.Div(newIntroducedSupply, big.NewInt(100)) // inflPct is percent*1e18

	// Calculate amount for 1 block
	blockAmount := big.NewInt(0)
	blockAmount.Div(newIntroducedSupply, big.NewInt(10512000)) // 10512000 blocks = ~1y

	log.Trace("inflation details", "secondsSinceFork", secondsPassed, "newIntroducedSupply", newIntroducedSupply, "blockAmount", blockAmount)

	return blockAmount, inflationPct
}

// Returns inflation %, supply, amount for the block (part of dragon8Fix)
func getNewSupplyForBlockDragon8Fix(forkTime uint64, currentTime uint64) (*big.Int, *big.Int, *big.Int) {
	var (
		// inflation %, supply, amount per block
		inflationData = [][]*big.Int{
			{big.NewInt(87961192355797800), cmath.MustParseBig256("8888888888000000000000000000"), cmath.MustParseBig256("74379496319128800000")}, // year 0
			{big.NewInt(72043432957447300), cmath.MustParseBig256("9670766153000000000000000000"), cmath.MustParseBig256("66278081527102500000")}, // year 1
			// one time inflation of 148600000 CHZ during year 1 + og schedule
			// new supply after year1 = 10367481346 + 148600000 = 10516081346
			// year 3 to year 8 have changed
			{big.NewInt(55304937824698300), cmath.MustParseBig256("10516081346000000000000000000"), cmath.MustParseBig256("55326410292998500000")}, // year 2
			{big.NewInt(46543801590000000), cmath.MustParseBig256("11097672571000000000000000000"), cmath.MustParseBig256("49136973934551000000")}, // year 3
			{big.NewInt(39673708820000000), cmath.MustParseBig256("11614200441000000000000000000"), cmath.MustParseBig256("43833562214611900000")}, // year 4
			{big.NewInt(39673708820000000), cmath.MustParseBig256("12074978847000000000000000000"), cmath.MustParseBig256("39395232686453600000")}, // year 5
			{big.NewInt(34295934680000000), cmath.MustParseBig256("12489101533000000000000000000"), cmath.MustParseBig256("35751611491628600000")}, // year 6
			{big.NewInt(30091911660000000), cmath.MustParseBig256("12864922473000000000000000000"), cmath.MustParseBig256("34885308219178100000")}, // year 7
			//
			{big.NewInt(25738888349516300), cmath.MustParseBig256("13231636833000000000000000000"), cmath.MustParseBig256("32397985455982600000")}, // year 8
			{big.NewInt(23584653872848300), cmath.MustParseBig256("13572204456000000000000000000"), cmath.MustParseBig256("30450508407284500000")}, // year 9
			{big.NewInt(21906934375499800), cmath.MustParseBig256("13892300200000000000000000000"), cmath.MustParseBig256("28951456317173600000")}, // year 10
			{big.NewInt(20600325117190600), cmath.MustParseBig256("14196637909000000000000000000"), cmath.MustParseBig256("27821095556737700000")}, // year 11
			{big.NewInt(19582736803651100), cmath.MustParseBig256("14489093265000000000000000000"), cmath.MustParseBig256("26991638121944800000")}, // year 12
			{big.NewInt(18800000000000000), cmath.MustParseBig256("14772829365000000000000000000"), cmath.MustParseBig256("26420204724736900000")}, // year 13
		}
		yearInSecs = uint64(31536000)
	)
	var year uint64

	// calculate current inflation year from block number
	year = (currentTime - forkTime) / yearInSecs
	log.Debug("inflation year", "year", year)

	if year >= 13 {
		return inflationData[13][0], inflationData[13][1], inflationData[13][2]
	}

	return inflationData[year][0], inflationData[year][1], inflationData[year][2]
}

func (p *Parlia) getLastSupplyFromTokenomics(header *types.Header) (*big.Int, error) {
	method := "getTotalSupply"
	data, err := p.tokenomicsABI.Pack(method)
	if err != nil {
		return nil, err
	}
	msgData := (hexutil.Bytes)(data)
	gas := (hexutil.Uint64)(uint64(math.MaxUint64 / 2))
	args := ethapi.TransactionArgs{
		From: &header.Coinbase,
		To:   &systemcontract.TokenomicsContractAddress,
		Gas:  &gas,
		Data: &msgData,
	}
	// Pin to the parent by hash, never by number (COR-184): by-number resolution goes
	// through the canonical number->hash index, so a node-local gap in that index
	// becomes a hard error out of Finalize. RequireCanonical must stay false, so
	// re-execution off the canonical chain still resolves.
	blockNr := rpc.BlockNumberOrHashWithHash(header.ParentHash, false)
	res, err := p.ethAPI.Call(context.Background(), args, &blockNr, nil, nil)
	if err != nil {
		return nil, err
	}

	initialTotalSupply := big.NewInt(0)
	if err := p.tokenomicsABI.UnpackIntoInterface(&initialTotalSupply, method, res); err != nil {
		return nil, err
	}
	return initialTotalSupply, nil
}

func (p *Parlia) distributeToTokenomics(amount *big.Int, inflationPct *big.Int, validator common.Address, newTotalSupply *big.Int,
	state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	// method
	method := "deposit"

	// get packed data
	data, err := p.tokenomicsABI.Pack(method, validator, newTotalSupply, inflationPct)
	if err != nil {
		log.Error("Unable to pack tx for tokenomics deposit", "error", err)
		return err
	}
	// get system message
	msg := p.getSystemMessage(header.Coinbase, systemcontract.TokenomicsContractAddress, data, amount)
	// apply message
	return p.applyTransaction(msg, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
}

// getValidatorTotalDelegated returns the total delegated amount for a validator at
// the epoch containing blockNumber. `state` selects the state the contract call runs
// against: nil means latest (pre-Snake8Fix historical behavior — nondeterministic
// across nodes); post-Snake8Fix callers pin it to the parent block so producers and
// verifiers read identical values (COR-173).
func (p *Parlia) getValidatorTotalDelegated(validatorAddress common.Address, blockNumber uint64, state *rpc.BlockNumberOrHash) (*big.Int, error) {
	if p.ethAPI == nil {
		// Engines constructed without an RPC backend (tests, tooling) cannot
		// read stakes; report it as the same soft failure as an RPC error so
		// frequency selection degrades to round-robin instead of panicking.
		return nil, errors.New("ethAPI unavailable for stake lookup")
	}
	method := "getValidatorStatusAtEpoch"
	epoch := blockNumber / p.chainConfig.Parlia.Epoch
	data, err := p.validatorSetABI.Pack(method, validatorAddress, epoch)
	if err != nil {
		log.Error("Unable to pack tx for getValidatorStatusAtEpoch", "error", err)
		return nil, err
	}

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	msgData := (hexutil.Bytes)(data)
	toAddress := common.HexToAddress(systemcontracts.ValidatorContract)
	gas := (hexutil.Uint64)(uint64(math.MaxUint64 / 2))
	result, err := p.ethAPI.Call(ctx, ethapi.TransactionArgs{
		Gas:  &gas,
		To:   &toAddress,
		Data: &msgData,
	}, state, nil, nil)
	if err != nil {
		return nil, err
	}

	var status struct {
		OwnerAddress   common.Address `json:"ownerAddress"`   // Address of the owner
		Status         uint8          `json:"status"`         // Status of the validator
		TotalDelegated *big.Int       `json:"totalDelegated"` // Total amount delegated (uint256)
		SlashesCount   uint32         `json:"slashesCount"`   // Count of slashes (uint32)
		ChangedAt      uint64         `json:"changedAt"`      // Timestamp when status changed (uint64)
		JailedBefore   uint64         `json:"jailedBefore"`   // Timestamp when jailed (uint64)
		ClaimedAt      uint64         `json:"claimedAt"`      // Timestamp when rewards were claimed (uint64)
		CommissionRate uint16         `json:"commissionRate"` // Commission rate (uint16)
		TotalRewards   *big.Int       `json:"totalRewards"`   // Total rewards earned (uint96)
	}
	err = p.validatorSetABI.UnpackIntoInterface(&status, method, result)
	if err != nil {
		return nil, err
	}

	return status.TotalDelegated, nil
}

func (p *Parlia) distributePRB(state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	amount := p.GetPepper8MintAmount()
	recipient := pepper8.Pepper8RecipientAddress

	log.Info("distributePRB", "amount", amount, "recipient", recipient)
	// get system message
	msg := p.getSystemMessage(header.Coinbase, recipient, nil, amount)
	// apply message
	return p.applyTransaction(msg, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
}

func (p *Parlia) distributePipe8Mint(state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	amount := p.GetPipe8MintAmount()
	recipient := pipe8.Pipe8RecipientAddress

	log.Info("distributePipe8Mint", "amount", amount, "recipient", recipient)
	msg := p.getSystemMessage(header.Coinbase, recipient, nil, amount)
	return p.applyTransaction(msg, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
}

// getCurrentValidators get current validators
func (p *Parlia) getCurrentValidators(blockHash common.Hash, blockNum *big.Int) ([]common.Address, map[common.Address]*types.BLSPublicKey, error) {
	// block
	blockNr := rpc.BlockNumberOrHashWithHash(blockHash, false)

	if !p.chainConfig.IsLuban(blockNum) {
		validators, err := p.getCurrentValidatorsBeforeLuban(blockHash, blockNum)
		return validators, nil, err
	}

	// method
	method := "getMiningValidators"

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel() // cancel when we are finished consuming integers

	data, err := p.validatorSetABI.Pack(method)
	if err != nil {
		log.Error("Unable to pack tx for getMiningValidators", "error", err)
		return nil, nil, err
	}
	// call
	msgData := (hexutil.Bytes)(data)
	toAddress := common.HexToAddress(systemcontract.ValidatorContract)
	gas := (hexutil.Uint64)(uint64(math.MaxUint64 / 2))
	result, err := p.ethAPI.Call(ctx, ethapi.TransactionArgs{
		Gas:  &gas,
		To:   &toAddress,
		Data: &msgData,
	}, &blockNr, nil, nil)
	if err != nil {
		return nil, nil, err
	}

	var valSet []common.Address
	var voteAddrSet []types.BLSPublicKey
	if err := p.validatorSetABI.UnpackIntoInterface(&[]interface{}{&valSet, &voteAddrSet}, method, result); err != nil {
		return nil, nil, err
	}

	voteAddrMap := make(map[common.Address]*types.BLSPublicKey, len(valSet))
	for i := 0; i < len(valSet); i++ {
		voteAddrMap[valSet[i]] = &(voteAddrSet)[i]
	}
	return valSet, voteAddrMap, nil
}

func (p *Parlia) isIntentionalDelayMining(chain consensus.ChainHeaderReader, header *types.Header) (bool, error) {
	parent := chain.GetHeader(header.ParentHash, header.Number.Uint64()-1)
	if parent == nil {
		return false, errors.New("parent not found")
	}
	blockInterval, err := p.BlockInterval(chain, header)
	if err != nil {
		return false, err
	}
	isIntentional := header.Coinbase == parent.Coinbase &&
		header.Difficulty.Cmp(diffInTurn) == 0 && parent.Difficulty.Cmp(diffInTurn) == 0 &&
		parent.MilliTimestamp()+blockInterval < header.MilliTimestamp()
	return isIntentional, nil
}

// distributeIncoming distributes system incoming of the block
func (p *Parlia) distributeIncoming(val common.Address, state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	var (
		coinbase  = header.Coinbase
		isDragon8 = p.chainConfig.IsDragon8(header.Time) || p.chainConfig.IsDragon8Fix(header.Time)
	)

	parent := chain.GetHeader(header.ParentHash, header.Number.Uint64()-1)
	if parent == nil {
		return errors.New("parent not found")
	}

	if p.IsPepper8Block(header.Time, parent.Time) {
		// set the bytecode of the deterministic deployment proxy
		bytecode, err := hex.DecodeString(p.getPepper8DeterministicDeploymentProxyBytecode())
		if err != nil {
			return err
		}
		state.SetCode(p.getPepper8DeterministicDeploymentProxyAddress(), bytecode, tracing.CodeChangeSystemContractUpgrade)

		// distribute Pepper8
		log.Trace("distributePRB", "block hash", header.Number.Uint64())
		state.AddBalance(coinbase, uint256.MustFromBig(p.GetPepper8MintAmount()), tracing.BalanceChangeUnspecified)
		if err := p.distributePRB(state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer); err != nil {
			return err
		}
	}

	if p.IsPipe8Block(header.Time, parent.Time) {
		log.Trace("distributePipe8Mint", "block hash", header.Number.Uint64())
		state.AddBalance(coinbase, uint256.MustFromBig(p.GetPipe8MintAmount()), tracing.BalanceChangeUnspecified)
		if err := p.distributePipe8Mint(state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer); err != nil {
			return err
		}
	}

	if isDragon8 {
		var (
			blockAmount    *big.Int
			inflationPct   *big.Int
			lastSupply     *big.Int
			newTotalSupply *big.Int
		)

		if p.chainConfig.IsDragon8Fix(header.Time) {
			inflationPct, newTotalSupply, blockAmount = getNewSupplyForBlockDragon8Fix(*p.chainConfig.Dragon8FixTime, header.Time)
		} else if p.chainConfig.IsDragon8(header.Time) {
			// Only this schedule consumes lastSupply, so the Tokenomics read stays
			// confined to this branch (COR-184) — do not hoist it out.
			var err error
			lastSupply, err = p.getLastSupplyFromTokenomics(header)
			if err != nil {
				return err
			}
			blockAmount, inflationPct = getNewSupplyForBlock(*p.chainConfig.Dragon8Time, header.Time, lastSupply)
			newTotalSupply = big.NewInt(0).Add(lastSupply, blockAmount)
		}
		state.AddBalance(coinbase, uint256.MustFromBig(blockAmount), tracing.BalanceChangeUnspecified)

		// DEPOSIT to tokenomics
		// lastSupply is read only on the legacy branch, so it is not logged here.
		log.Trace("distribute to tokenomics", "block hash", header.Hash(), "amount", blockAmount, "inflation", inflationPct, "newTotalSupply", newTotalSupply)
		if err := p.distributeToTokenomics(blockAmount, inflationPct, val, newTotalSupply, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer); err != nil {
			return err
		}
	}

	balance := state.GetBalance(consensus.SystemAddress)
	if balance.Cmp(common.U2560) <= 0 {
		return nil
	}
	state.SetBalance(consensus.SystemAddress, common.U2560, tracing.BalanceChangeUnspecified)
	state.AddBalance(coinbase, balance, tracing.BalanceChangeUnspecified)

	doDistributeSysReward := !isDragon8 && state.GetBalance(common.HexToAddress(systemcontracts.SystemRewardContract)).Cmp(maxSystemBalance) < 0
	if doDistributeSysReward {
		rewards := new(big.Int)
		rewards = rewards.Div(balance.ToBig(), big.NewInt(systemRewardPercent))
		if rewards.Cmp(common.Big0) > 0 {
			err := p.distributeToSystem(rewards, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
			if err != nil {
				return err
			}
			log.Trace("distribute to system reward pool", "block hash", header.Hash(), "amount", rewards)
			balance = balance.Sub(balance, uint256.MustFromBig(rewards))
		}
	}
	log.Trace("distribute to validator contract", "block hash", header.Hash(), "amount", balance)
	return p.distributeToValidator(balance.ToBig(), val, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
}

// slash spoiled validators
func (p *Parlia) slash(spoiledVal common.Address, state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	// method
	method := "slash"

	// get packed data
	data, err := p.slashABI.Pack(method,
		spoiledVal,
	)
	if err != nil {
		log.Error("Unable to pack tx for slash", "error", err)
		return err
	}
	// get system message
	msg := p.getSystemMessage(header.Coinbase, common.HexToAddress(systemcontract.SlashContract), data, common.Big0)
	// apply message
	return p.applyTransaction(msg, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
}

// init contract
func (p *Parlia) initContract(state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	// method
	method := "init"
	// get packed data
	data, err := p.validatorSetABI.Pack(method)
	if err != nil {
		log.Error("Unable to pack tx for init validator set", "error", err)
		return err
	}
	contracts := []common.Address{
		common.HexToAddress(systemcontract.ValidatorContract),
		common.HexToAddress(systemcontract.SlashContract),
		common.HexToAddress(systemcontract.SystemRewardContract),
		common.HexToAddress(systemcontract.StakingPoolContract),
		common.HexToAddress(systemcontract.GovernanceContract),
		common.HexToAddress(systemcontract.ChainConfigContract),
		common.HexToAddress(systemcontract.RuntimeUpgradeContract),
	}
	if !p.chainConfig.IsDeployerProxySunsetTime(header.Time) {
		contracts = append(contracts, common.HexToAddress(systemcontract.DeployerProxyContract))
	}
	if p.chainConfig.IsDragon8(header.Time) || p.chainConfig.IsDragon8Fix(header.Time) {
		contracts = append(contracts, common.HexToAddress(systemcontract.TokenomicsContract))
	}
	for _, c := range contracts {
		msg := p.getSystemMessage(header.Coinbase, c, data, common.Big0)
		// apply message
		log.Trace("init contract", "block hash", header.Hash(), "contract", c)
		err = p.applyTransaction(msg, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
		if err != nil {
			return err
		}
	}
	return nil
}

func (p *Parlia) distributeToSystem(amount *big.Int, state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	// get system message
	msg := p.getSystemMessage(header.Coinbase, common.HexToAddress(systemcontract.SystemRewardContract), nil, amount)
	// apply message
	return p.applyTransaction(msg, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
}

// distributeToValidator deposits validator reward to validator contract
func (p *Parlia) distributeToValidator(amount *big.Int, validator common.Address,
	state vm.StateDB, header *types.Header, chain core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt, receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode, tracer *tracing.Hooks) error {
	// method
	method := "deposit"

	// get packed data
	data, err := p.validatorSetABI.Pack(method,
		validator,
	)
	if err != nil {
		log.Error("Unable to pack tx for deposit", "error", err)
		return err
	}
	// get system message
	msg := p.getSystemMessage(header.Coinbase, common.HexToAddress(systemcontract.ValidatorContract), data, amount)
	// apply message
	return p.applyTransaction(msg, state, header, chain, txs, receipts, receivedTxs, usedGas, mode, tracer)
}

// get system message
func (p *Parlia) getSystemMessage(from, toAddress common.Address, data []byte, value *big.Int) *core.Message {
	return &core.Message{
		From:     from,
		GasLimit: math.MaxUint64 / 2,
		GasPrice: big.NewInt(0),
		Value:    value,
		To:       &toAddress,
		Data:     data,
	}
}

func (p *Parlia) applyTransaction(
	msg *core.Message,
	state vm.StateDB,
	header *types.Header,
	chainContext core.ChainContext,
	txs *[]*types.Transaction, receipts *[]*types.Receipt,
	receivedTxs *[]*types.Transaction, usedGas *uint64, mode systemTxMode,
	tracer *tracing.Hooks,
) (applyErr error) {
	nonce := state.GetNonce(msg.From)
	expectedTx := types.NewTransaction(nonce, *msg.To, msg.Value, msg.GasLimit, msg.GasPrice, msg.Data)
	expectedHash := p.signer.Hash(expectedTx)

	switch mode {
	case systemTxMining:
		var err error
		if msg.From != p.val {
			return fmt.Errorf("cannot sign system tx from %s with validator %s", msg.From, p.val)
		}
		expectedTx, err = p.signTxFn(accounts.Account{Address: msg.From}, expectedTx, p.chainConfig.ChainID)
		if err != nil {
			return err
		}
	case systemTxPacking:
	case systemTxImporting:
		if receivedTxs == nil || len(*receivedTxs) == 0 || (*receivedTxs)[0] == nil {
			return errors.New("supposed to get a actual transaction, but get none")
		}
		actualTx := (*receivedTxs)[0]
		if !bytes.Equal(p.signer.Hash(actualTx).Bytes(), expectedHash.Bytes()) {
			return fmt.Errorf("expected tx hash %v, nonce %d, to %s, value %s, gas %d, gasPrice %s, data %s\ngot tx hash %v, nonce %d, to %s, value %s, gas %d, gasPrice %s, data %s",
				expectedHash.String(),
				expectedTx.Nonce(),
				expectedTx.To().String(),
				expectedTx.Value().String(),
				expectedTx.Gas(),
				expectedTx.GasPrice().String(),
				hex.EncodeToString(expectedTx.Data()),
				actualTx.Hash().Hex(),
				actualTx.Nonce(),
				actualTx.To().String(),
				actualTx.Value().String(),
				actualTx.Gas(),
				actualTx.GasPrice().String(),
				hex.EncodeToString(actualTx.Data()),
			)
		}
		expectedTx = actualTx
		// move to next
		*receivedTxs = (*receivedTxs)[1:]
	default:
		return fmt.Errorf("unknown system tx mode %d", mode)
	}
	state.SetTxContext(expectedTx.Hash(), len(*txs))

	// Create a new context to be used in the EVM environment
	context := core.NewEVMBlockContext(header, chainContext, nil)
	// Create a new environment which holds all relevant information
	// about the transaction and calling mechanisms.
	evm := vm.NewEVM(context, state, p.chainConfig, vm.Config{Tracer: tracer})
	evm.SetTxContext(core.NewEVMTxContext(msg))

	// Tracing receipt will be set if there is no error and will be used to trace the transaction
	var tracingReceipt *types.Receipt
	if tracer != nil {
		if tracer.OnSystemTxStart != nil {
			tracer.OnSystemTxStart()
		}
		if tracer.OnTxStart != nil {
			tracer.OnTxStart(evm.GetVMContext(), expectedTx, msg.From)
		}

		// Defers are last in first out, so OnTxEnd will run before OnSystemTxEnd in this transaction,
		// which is what we want.
		if tracer.OnSystemTxEnd != nil {
			defer func() {
				tracer.OnSystemTxEnd()
			}()
		}
		if tracer.OnTxEnd != nil {
			defer func() {
				tracer.OnTxEnd(tracingReceipt, applyErr)
			}()
		}
	}

	gasUsed, err := applyMessage(msg, evm, state, header, p.chainConfig, chainContext)
	if err != nil {
		return err
	}
	*txs = append(*txs, expectedTx)
	// increment nonce only when tx is included
	state.SetNonce(msg.From, nonce+1, tracing.NonceChangeEoACall)
	var root []byte
	if p.chainConfig.IsByzantium(header.Number) {
		state.Finalise(true)
	} else {
		root = state.IntermediateRoot(p.chainConfig.IsEIP158(header.Number)).Bytes()
	}
	*usedGas += gasUsed
	tracingReceipt = types.NewReceipt(root, false, *usedGas)
	tracingReceipt.TxHash = expectedTx.Hash()
	tracingReceipt.GasUsed = gasUsed

	// Set the receipt logs and create a bloom for filtering
	tracingReceipt.Logs = state.GetLogs(expectedTx.Hash(), header.Number.Uint64(), header.Hash(), header.Time)
	tracingReceipt.Bloom = types.CreateBloom(tracingReceipt)
	tracingReceipt.BlockHash = header.Hash()
	tracingReceipt.BlockNumber = header.Number
	tracingReceipt.TransactionIndex = uint(state.TxIndex())
	*receipts = append(*receipts, tracingReceipt)
	return nil
}

// GetJustifiedNumberAndHash retrieves the number and hash of the highest justified block
// within the branch including `headers` and utilizing the latest element as the head.
func (p *Parlia) GetJustifiedNumberAndHash(chain consensus.ChainHeaderReader, headers []*types.Header) (uint64, common.Hash, error) {
	if chain == nil || len(headers) == 0 || headers[len(headers)-1] == nil {
		return 0, common.Hash{}, errors.New("illegal chain or header")
	}
	head := headers[len(headers)-1]
	snap, err := p.snapshot(chain, head.Number.Uint64(), head.Hash(), headers, p.isSnake8Enabled(chain, head), head)
	if err != nil {
		log.Error("GJ Unexpected error when getting snapshot",
			"error", err, "blockNumber", head.Number.Uint64(), "blockHash", head.Hash())
		return 0, common.Hash{}, err
	}

	if snap.Attestation == nil {
		if p.chainConfig.IsLuban(head.Number) {
			log.Debug("once one attestation generated, attestation of snap would not be nil forever basically")
		}
		return 0, chain.GetHeaderByNumber(0).Hash(), nil
	}
	return snap.Attestation.TargetNumber, snap.Attestation.TargetHash, nil
}

// GetFinalizedHeader returns highest finalized block header.
// It first checks VotePool for votes that may have reached quorum but not yet included in block headers,
// then falls back to the attestation in the snapshot.
func (p *Parlia) GetFinalizedHeader(chain consensus.ChainHeaderReader, header *types.Header) *types.Header {
	if chain == nil || header == nil {
		return nil
	}
	if !chain.Config().IsPlato(header.Number) {
		return chain.GetHeaderByNumber(0)
	}
	parent := chain.GetHeaderByHash(header.ParentHash)
	if parent == nil {
		log.Error("parent not found")
		return nil
	}
	snap, err := p.snapshot(chain, header.Number.Uint64(), header.Hash(), nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		log.Error("GF Unexpected error when getting snapshot",
			"error", err, "blockNumber", header.Number.Uint64(), "blockHash", header.Hash())
		return nil
	}

	if snap.Attestation == nil {
		return chain.GetHeaderByNumber(0) // keep consistent with GetJustifiedNumberAndHash
	}

	finalizedHash := snap.Attestation.SourceHash
	finalizedNumber := snap.Attestation.SourceNumber

	currentJustifiedHash := snap.Attestation.TargetHash
	currentJustifiedNumber := snap.Attestation.TargetNumber
	// Try to check if currentJustifiedNumber can become finalized by checking VotePool.
	// We only need to check currentJustifiedNumber + 1, since currentJustifiedNumber is already the latest justified.
	if p.VotePool != nil && currentJustifiedNumber == header.Number.Uint64()-1 {
		parentSnap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
		if err == nil {
			// Check if the next block (direct child) has reached quorum in VotePool
			votes := p.VotePool.FetchVotesByBlockHash(header.Hash(), currentJustifiedNumber)
			quorum := cmath.CeilDiv(len(parentSnap.Validators)*2, 3)

			if len(votes) >= quorum {
				finalizedHash = currentJustifiedHash
				finalizedNumber = currentJustifiedNumber
			}
		} else {
			log.Error("Failed to get parent snapshot for finality check",
				"error", err, "blockNumber", header.Number.Uint64()-1, "blockHash", header.ParentHash)
		}
	}

	return chain.GetHeader(finalizedHash, finalizedNumber)
}

// CheckFinalityAndNotify checks if votes for the target block have reached quorum,
// and if so, notifies the blockchain of early finalization via the notifyFn callback.
func (p *Parlia) CheckFinalityAndNotify(chain consensus.ChainHeaderReader, targetBlockHash common.Hash, notifyFn func(finalizedHeader *types.Header)) {
	// Get target block header directly by hash (don't rely on currentHeader which may have moved forward)
	targetHeader := chain.GetHeaderByHash(targetBlockHash)
	if targetHeader == nil {
		return
	}

	finalizedHeader := p.GetFinalizedHeader(chain, targetHeader)
	if finalizedHeader == nil || finalizedHeader.Number.Uint64() == 0 {
		return
	}

	// Notify via callback (NotifyFinalized has its own deduplication logic)
	notifyFn(finalizedHeader)
}

// ===========================     utility function        ==========================
func (p *Parlia) backOffTime(snap *Snapshot, parent, header *types.Header, val common.Address) uint64 {
	if snap.inturn(val) {
		log.Debug("backOffTime", "blockNumber", header.Number, "in turn validator", val)
		return 0
	} else {
		delay := defaultInitialBackOffTime
		// When mining blocks, `header.Time` is temporarily set to time.Now() + 1.
		// Therefore, using `header.Time` to determine whether a hard fork has occurred is incorrect.
		// As a result, during the Bohr and Lorentz hard forks, the network may experience some instability,
		// So use `parent.Time` instead.
		isParerntLorentz := p.chainConfig.IsLorentz(parent.Number, parent.Time)
		if isParerntLorentz {
			// If the in-turn validator has not signed recently, the expected backoff times are [2, 3, 4, ...].
			delay = lorentzInitialBackOffTime
		}
		validators := snap.validators()
		if p.chainConfig.IsPlanck(header.Number) {
			counts := snap.countRecents()
			for addr, seenTimes := range counts {
				log.Trace("backOffTime", "blockNumber", header.Number, "validator", addr, "seenTimes", seenTimes)
			}

			// The backOffTime does not matter when a validator has signed recently.
			if snap.signRecentlyByCounts(val, counts) {
				return 0
			}

			inTurnAddr := snap.inturnValidator()
			if snap.signRecentlyByCounts(inTurnAddr, counts) {
				log.Debug("in turn validator has recently signed, skip initialBackOffTime",
					"inTurnAddr", inTurnAddr)
				delay = 0
			}

			// Exclude the recently signed validators and the in turn validator
			temp := make([]common.Address, 0, len(validators))
			for _, addr := range validators {
				if snap.signRecentlyByCounts(addr, counts) {
					continue
				}
				if p.chainConfig.IsBohr(header.Number, header.Time) {
					if addr == inTurnAddr {
						continue
					}
				}
				temp = append(temp, addr)
			}
			validators = temp
		}

		// get the index of current validator and its shuffled backoff time.
		idx := -1
		for index, itemAddr := range validators {
			if val == itemAddr {
				idx = index
			}
		}
		if idx < 0 {
			log.Debug("The validator is not authorized", "addr", val)
			return 0
		}

		randSeed := snap.Number
		if p.chainConfig.IsBohr(header.Number, header.Time) {
			randSeed = header.Number.Uint64() / uint64(snap.TurnLength)
		}
		s := rand.NewSource(int64(randSeed))
		r := rand.New(s)
		n := len(validators)
		backOffSteps := make([]uint64, 0, n)

		for i := uint64(0); i < uint64(n); i++ {
			backOffSteps = append(backOffSteps, i)
		}

		r.Shuffle(n, func(i, j int) {
			backOffSteps[i], backOffSteps[j] = backOffSteps[j], backOffSteps[i]
		})

		if delay == 0 && isParerntLorentz {
			// If the in-turn validator has signed recently, the expected backoff times are [0, 2, 3, ...].
			if backOffSteps[idx] == 0 {
				return 0
			}
			return lorentzInitialBackOffTime + (backOffSteps[idx]-1)*wiggleTime
		}
		delay += backOffSteps[idx] * wiggleTime
		return delay
	}
}

// BlockInterval returns number of blocks in one epoch for the given header
func (p *Parlia) epochLength(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) (uint64, error) {
	if header == nil {
		return defaultEpochLength, errUnknownBlock
	}
	if header.Number.Uint64() == 0 {
		return defaultEpochLength, nil
	}
	// extraHeader is nil: this caller only reads EpochLength and has no candidate
	// header whose frequency data it would want stamped onto its snapshot view.
	snap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, parents, p.isSnake8Enabled(chain, header), nil)
	if err != nil {
		return defaultEpochLength, err
	}
	return snap.EpochLength, nil
}

// BlockInterval returns the block interval in milliseconds for the given header
func (p *Parlia) BlockInterval(chain consensus.ChainHeaderReader, header *types.Header) (uint64, error) {
	if header == nil {
		return defaultBlockInterval, errUnknownBlock
	}
	if header.Number.Uint64() == 0 {
		return defaultBlockInterval, nil
	}
	snap, err := p.snapshot(chain, header.Number.Uint64()-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), nil)
	if err != nil {
		return defaultBlockInterval, err
	}
	return snap.BlockInterval, nil
}

func (p *Parlia) NextProposalBlock(chain consensus.ChainHeaderReader, header *types.Header, proposer common.Address) (uint64, uint64, error) {
	snap, err := p.snapshot(chain, header.Number.Uint64(), header.Hash(), nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		return 0, 0, err
	}

	return snap.nextProposalBlock(proposer)
}

func (p *Parlia) detectNewVersionWithFork(chain consensus.ChainHeaderReader, header *types.Header, state vm.StateDB) {
	// Ignore blocks that are considered too old
	const maxBlockReceiveDelay = 10 * time.Second
	blockTime := time.UnixMilli(int64(header.MilliTimestamp()))
	if time.Since(blockTime) > maxBlockReceiveDelay {
		return
	}

	// If the fork is not a majority, log a warning or debug message
	number := header.Number.Uint64()
	snap, err := p.snapshot(chain, number-1, header.ParentHash, nil, p.isSnake8Enabled(chain, header), header)
	if err != nil {
		return
	}
	nextForkHash := forkid.NextForkHash(p.chainConfig, p.genesisHash, chain.GenesisHeader().Time, number, header.Time)
	forkHashHex := hex.EncodeToString(nextForkHash[:])
	if !snap.isMajorityFork(forkHashHex) {
		logFn := log.Debug
		if state.NoTries() {
			logFn = log.Warn
		}
		logFn("possible fork detected: client is not in majority", "nextForkHash", forkHashHex)
	}
}

// TODO(Nathan): use kAncestorGenerationDepth directly instead of this func once Fermi hardfork passed
func (p *Parlia) GetAncestorGenerationDepth(header *types.Header) uint64 {
	if p.chainConfig.IsFermi(header.Number, header.Time) {
		return kAncestorGenerationDepth
	}

	return 1
}

// chain context
type chainContext struct {
	consensus.ChainHeaderReader
	parlia consensus.Engine
}

func (c chainContext) Engine() consensus.Engine {
	return c.parlia
}

// apply message
func applyMessage(
	msg *core.Message,
	evm *vm.EVM,
	state vm.StateDB,
	header *types.Header,
	chainConfig *params.ChainConfig,
	chainContext core.ChainContext,
) (uint64, error) {
	// Apply the transaction to the current state (included in the env)
	if chainConfig.IsCancun(header.Number, header.Time) {
		rules := evm.ChainConfig().Rules(evm.Context.BlockNumber, evm.Context.Random != nil, evm.Context.Time)
		state.Prepare(rules, msg.From, evm.Context.Coinbase, msg.To, vm.ActivePrecompiles(rules), msg.AccessList)
	} else {
		state.ClearAccessList()
	}

	ret, returnGas, err := evm.Call(
		msg.From,
		*msg.To,
		msg.Data,
		msg.GasLimit,
		uint256.MustFromBig(msg.Value),
	)
	if err != nil && len(ret) > 64+4 {
		log.Error("apply message failed", "msg", string(ret[64+4:]), "err", err)
	}
	return msg.GasLimit - returnGas, err
}

// proposalKey build a key which is a combination of the block number and the proposer address.
func proposalKey(header types.Header) string {
	return header.ParentHash.String() + header.Coinbase.String()
}