package rollup_sync_service

import (
	"encoding/binary"
	"errors"
	"fmt"
	"math"
	"math/big"

	"github.com/scroll-tech/go-ethereum/common"
	"github.com/scroll-tech/go-ethereum/common/hexutil"
	"github.com/scroll-tech/go-ethereum/core/types"
)

const blockContextByteSize = 60

// WrappedBlock contains the block's Header, Transactions and WithdrawTrieRoot hash.
type WrappedBlock struct {
	Header *types.Header `json:"header"`
	// Transactions is only used for recover types.Transactions, the from of types.TransactionData field is missing.
	Transactions []*types.TransactionData `json:"transactions"`
	WithdrawRoot common.Hash              `json:"withdraw_trie_root,omitempty"`
}

// BlockContext represents the essential data of a block in the ScrollChain.
// It provides an overview of block attributes including hash values, block numbers, gas details, and transaction counts.
type BlockContext struct {
	BlockHash       common.Hash
	ParentHash      common.Hash
	BlockNumber     uint64
	Timestamp       uint64
	BaseFee         *big.Int
	GasLimit        uint64
	NumTransactions uint16
	NumL1Messages   uint16
}

// numL1Messages returns the number of L1 messages in this block.
// This number is the sum of included and skipped L1 messages.
func (w *WrappedBlock) numL1Messages(totalL1MessagePoppedBefore uint64) uint64 {
	var lastQueueIndex *uint64
	for _, txData := range w.Transactions {
		if txData.Type == types.L1MessageTxType {
			lastQueueIndex = &txData.Nonce
		}
	}
	if lastQueueIndex == nil {
		return 0
	}
	// note: last queue index included before this block is totalL1MessagePoppedBefore - 1
	// TODO: cache results
	return *lastQueueIndex - totalL1MessagePoppedBefore + 1
}

// Encode encodes the WrappedBlock into RollupV2 BlockContext Encoding.
func (w *WrappedBlock) Encode(totalL1MessagePoppedBefore uint64) ([]byte, error) {
	bytes := make([]byte, 60)

	if !w.Header.Number.IsUint64() {
		return nil, errors.New("block number is not uint64")
	}

	// note: numL1Messages includes skipped messages
	numL1Messages := w.numL1Messages(totalL1MessagePoppedBefore)
	if numL1Messages > math.MaxUint16 {
		return nil, errors.New("number of L1 messages exceeds max uint16")
	}

	// note: numTransactions includes skipped messages
	numL2Transactions := w.numL2Transactions()
	numTransactions := numL1Messages + numL2Transactions
	if numTransactions > math.MaxUint16 {
		return nil, errors.New("number of transactions exceeds max uint16")
	}

	binary.BigEndian.PutUint64(bytes[0:], w.Header.Number.Uint64())
	binary.BigEndian.PutUint64(bytes[8:], w.Header.Time)
	// TODO: [16:47] Currently, baseFee is 0, because we disable EIP-1559.
	binary.BigEndian.PutUint64(bytes[48:], w.Header.GasLimit)
	binary.BigEndian.PutUint16(bytes[56:], uint16(numTransactions))
	binary.BigEndian.PutUint16(bytes[58:], uint16(numL1Messages))

	return bytes, nil
}

func txsToTxsData(txs types.Transactions) []*types.TransactionData {
	txsData := make([]*types.TransactionData, len(txs))
	for i, tx := range txs {
		v, r, s := tx.RawSignatureValues()

		nonce := tx.Nonce()

		// We need QueueIndex in `NewBatchHeader`. However, `TransactionData`
		// does not have this field. Since `L1MessageTx` do not have a nonce,
		// we reuse this field for storing the queue index.
		if msg := tx.AsL1MessageTx(); msg != nil {
			nonce = msg.QueueIndex
		}

		txsData[i] = &types.TransactionData{
			Type:     tx.Type(),
			TxHash:   tx.Hash().String(),
			Nonce:    nonce,
			ChainId:  (*hexutil.Big)(tx.ChainId()),
			Gas:      tx.Gas(),
			GasPrice: (*hexutil.Big)(tx.GasPrice()),
			To:       tx.To(),
			Value:    (*hexutil.Big)(tx.Value()),
			Data:     hexutil.Encode(tx.Data()),
			IsCreate: tx.To() == nil,
			V:        (*hexutil.Big)(v),
			R:        (*hexutil.Big)(r),
			S:        (*hexutil.Big)(s),
		}
	}
	return txsData
}

func convertTxDataToRLPEncoding(txData *types.TransactionData) ([]byte, error) {
	data, err := hexutil.Decode(txData.Data)
	if err != nil {
		return nil, fmt.Errorf("failed to decode txData.Data: %s, err: %w", txData.Data, err)
	}

	tx := types.NewTx(&types.LegacyTx{
		Nonce:    txData.Nonce,
		To:       txData.To,
		Value:    txData.Value.ToInt(),
		Gas:      txData.Gas,
		GasPrice: txData.GasPrice.ToInt(),
		Data:     data,
		V:        txData.V.ToInt(),
		R:        txData.R.ToInt(),
		S:        txData.S.ToInt(),
	})

	rlpTxData, err := tx.MarshalBinary()
	if err != nil {
		return nil, fmt.Errorf("failed to marshal binary of the tx: %+v, err: %w", tx, err)
	}

	return rlpTxData, nil
}

func (w *WrappedBlock) numL2Transactions() uint64 {
	var count uint64
	for _, txData := range w.Transactions {
		if txData.Type != types.L1MessageTxType {
			count++
		}
	}
	return count
}

func decodeBlockContext(encodedBlockContext []byte) (*BlockContext, error) {
	if len(encodedBlockContext) != blockContextByteSize {
		return nil, errors.New("block encoding is not 60 bytes long")
	}

	return &BlockContext{
		BlockNumber:     binary.BigEndian.Uint64(encodedBlockContext[0:8]),
		Timestamp:       binary.BigEndian.Uint64(encodedBlockContext[8:16]),
		GasLimit:        binary.BigEndian.Uint64(encodedBlockContext[48:56]),
		NumTransactions: binary.BigEndian.Uint16(encodedBlockContext[56:58]),
		NumL1Messages:   binary.BigEndian.Uint16(encodedBlockContext[58:60]),
	}, nil
}