// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package catalyst implements the temporary eth1/eth2 RPC integration.
package catalyst

import (
	"crypto/sha256"
	"encoding/binary"
	"errors"
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/eth"
	"github.com/ethereum/go-ethereum/les"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/node"
	"github.com/ethereum/go-ethereum/rpc"
	"github.com/ethereum/go-ethereum/trie"
)

var (
	VALID              = GenericStringResponse{"VALID"}
	SUCCESS            = GenericStringResponse{"SUCCESS"}
	INVALID            = ForkChoiceResponse{Status: "INVALID", PayloadID: nil}
	SYNCING            = ForkChoiceResponse{Status: "SYNCING", PayloadID: nil}
	GenericServerError = rpc.CustomError{Code: -32000, ValidationError: "Server error"}
	UnknownPayload     = rpc.CustomError{Code: -32001, ValidationError: "Unknown payload"}
	InvalidTB          = rpc.CustomError{Code: -32002, ValidationError: "Invalid terminal block"}
)

// Register adds catalyst APIs to the full node.
func Register(stack *node.Node, backend *eth.Ethereum) error {
	log.Warn("Catalyst mode enabled", "protocol", "eth")
	stack.RegisterAPIs([]rpc.API{
		{
			Namespace: "engine",
			Version:   "1.0",
			Service:   NewConsensusAPI(backend, nil),
			Public:    true,
		},
	})
	return nil
}

// RegisterLight adds catalyst APIs to the light client.
func RegisterLight(stack *node.Node, backend *les.LightEthereum) error {
	log.Warn("Catalyst mode enabled", "protocol", "les")
	stack.RegisterAPIs([]rpc.API{
		{
			Namespace: "engine",
			Version:   "1.0",
			Service:   NewConsensusAPI(nil, backend),
			Public:    true,
		},
	})
	return nil
}

type ConsensusAPI struct {
	light          bool
	eth            *eth.Ethereum
	les            *les.LightEthereum
	preparedBlocks *payloadQueue // preparedBlocks caches payloads (*ExecutableDataV1) by payload ID (PayloadID)
}

func NewConsensusAPI(eth *eth.Ethereum, les *les.LightEthereum) *ConsensusAPI {
	if eth == nil {
		if les.BlockChain().Config().TerminalTotalDifficulty == nil {
			panic("Catalyst started without valid total difficulty")
		}
	} else {
		if eth.BlockChain().Config().TerminalTotalDifficulty == nil {
			panic("Catalyst started without valid total difficulty")
		}
	}

	return &ConsensusAPI{
		light:          eth == nil,
		eth:            eth,
		les:            les,
		preparedBlocks: newPayloadQueue(),
	}
}

func (api *ConsensusAPI) GetPayloadV1(payloadID PayloadID) (*ExecutableDataV1, error) {
	log.Trace("Engine API request received", "method", "GetPayload", "id", payloadID)
	data := api.preparedBlocks.get(payloadID)
	if data == nil {
		return nil, &UnknownPayload
	}
	return data, nil
}

func (api *ConsensusAPI) ForkchoiceUpdatedV1(heads ForkchoiceStateV1, payloadAttributes *PayloadAttributesV1) (ForkChoiceResponse, error) {
	log.Trace("Engine API request received", "method", "ForkChoiceUpdated", "head", heads.HeadBlockHash, "finalized", heads.FinalizedBlockHash, "safe", heads.SafeBlockHash)
	if heads.HeadBlockHash == (common.Hash{}) {
		return ForkChoiceResponse{Status: SUCCESS.Status, PayloadID: nil}, nil
	}
	if err := api.checkTerminalTotalDifficulty(heads.HeadBlockHash); err != nil {
		if api.light {
			if header := api.les.BlockChain().GetHeaderByHash(heads.HeadBlockHash); header == nil {
				// TODO (MariusVanDerWijden) trigger sync
				return SYNCING, nil
			}
			return INVALID, err
		} else {
			if block := api.eth.BlockChain().GetBlockByHash(heads.HeadBlockHash); block == nil {
				// TODO (MariusVanDerWijden) trigger sync
				return SYNCING, nil
			}
			return INVALID, err
		}
	}
	// If the finalized block is set, check if it is in our blockchain
	if heads.FinalizedBlockHash != (common.Hash{}) {
		if api.light {
			if header := api.les.BlockChain().GetHeaderByHash(heads.FinalizedBlockHash); header == nil {
				// TODO (MariusVanDerWijden) trigger sync
				return SYNCING, nil
			}
		} else {
			if block := api.eth.BlockChain().GetBlockByHash(heads.FinalizedBlockHash); block == nil {
				// TODO (MariusVanDerWijden) trigger sync
				return SYNCING, nil
			}
		}
	}
	// SetHead
	if err := api.setHead(heads.HeadBlockHash); err != nil {
		return INVALID, err
	}
	// Assemble block (if needed). It only works for full node.
	if !api.light && payloadAttributes != nil {
		data, err := api.assembleBlock(heads.HeadBlockHash, payloadAttributes)
		if err != nil {
			return INVALID, err
		}
		id := computePayloadId(heads.HeadBlockHash, payloadAttributes)
		api.preparedBlocks.put(id, data)
		log.Info("Created payload", "payloadID", id)
		return ForkChoiceResponse{Status: SUCCESS.Status, PayloadID: &id}, nil
	}
	return ForkChoiceResponse{Status: SUCCESS.Status, PayloadID: nil}, nil
}

func computePayloadId(headBlockHash common.Hash, params *PayloadAttributesV1) PayloadID {
	// Hash
	hasher := sha256.New()
	hasher.Write(headBlockHash[:])
	binary.Write(hasher, binary.BigEndian, params.Timestamp)
	hasher.Write(params.Random[:])
	hasher.Write(params.SuggestedFeeRecipient[:])
	var out PayloadID
	copy(out[:], hasher.Sum(nil)[:8])
	return out
}

func (api *ConsensusAPI) invalid() ExecutePayloadResponse {
	if api.light {
		return ExecutePayloadResponse{Status: INVALID.Status, LatestValidHash: api.les.BlockChain().CurrentHeader().Hash()}
	}
	return ExecutePayloadResponse{Status: INVALID.Status, LatestValidHash: api.eth.BlockChain().CurrentHeader().Hash()}
}

// ExecutePayloadV1 creates an Eth1 block, inserts it in the chain, and returns the status of the chain.
func (api *ConsensusAPI) ExecutePayloadV1(params ExecutableDataV1) (ExecutePayloadResponse, error) {
	log.Trace("Engine API request received", "method", "ExecutePayload", params.BlockHash, "number", params.Number)
	block, err := ExecutableDataToBlock(params)
	if err != nil {
		return api.invalid(), err
	}
	if api.light {
		if !api.les.BlockChain().HasHeader(block.ParentHash(), block.NumberU64()-1) {
			/*
				TODO (MariusVanDerWijden) reenable once sync is merged
				if err := api.eth.Downloader().BeaconSync(api.eth.SyncMode(), block.Header()); err != nil {
					return SYNCING, err
				}
			*/
			// TODO (MariusVanDerWijden) we should return nil here not empty hash
			return ExecutePayloadResponse{Status: SYNCING.Status, LatestValidHash: common.Hash{}}, nil
		}
		parent := api.les.BlockChain().GetHeaderByHash(params.ParentHash)
		td := api.les.BlockChain().GetTd(parent.Hash(), block.NumberU64()-1)
		ttd := api.les.BlockChain().Config().TerminalTotalDifficulty
		if td.Cmp(ttd) < 0 {
			return api.invalid(), fmt.Errorf("can not execute payload on top of block with low td got: %v threshold %v", td, ttd)
		}
		if err = api.les.BlockChain().InsertHeader(block.Header()); err != nil {
			return api.invalid(), err
		}
		if merger := api.merger(); !merger.TDDReached() {
			merger.ReachTTD()
		}
		return ExecutePayloadResponse{Status: VALID.Status, LatestValidHash: block.Hash()}, nil
	}
	if !api.eth.BlockChain().HasBlock(block.ParentHash(), block.NumberU64()-1) {
		/*
			TODO (MariusVanDerWijden) reenable once sync is merged
			if err := api.eth.Downloader().BeaconSync(api.eth.SyncMode(), block.Header()); err != nil {
				return SYNCING, err
			}
		*/
		// TODO (MariusVanDerWijden) we should return nil here not empty hash
		return ExecutePayloadResponse{Status: SYNCING.Status, LatestValidHash: common.Hash{}}, nil
	}
	parent := api.eth.BlockChain().GetBlockByHash(params.ParentHash)
	td := api.eth.BlockChain().GetTd(parent.Hash(), block.NumberU64()-1)
	ttd := api.eth.BlockChain().Config().TerminalTotalDifficulty
	if td.Cmp(ttd) < 0 {
		return api.invalid(), fmt.Errorf("can not execute payload on top of block with low td got: %v threshold %v", td, ttd)
	}
	log.Trace("Inserting block without head", "hash", block.Hash(), "number", block.Number)
	if err := api.eth.BlockChain().InsertBlockWithoutSetHead(block); err != nil {
		return api.invalid(), err
	}

	if merger := api.merger(); !merger.TDDReached() {
		merger.ReachTTD()
	}
	return ExecutePayloadResponse{Status: VALID.Status, LatestValidHash: block.Hash()}, nil
}

// AssembleBlock creates a new block, inserts it into the chain, and returns the "execution
// data" required for eth2 clients to process the new block.
func (api *ConsensusAPI) assembleBlock(parentHash common.Hash, params *PayloadAttributesV1) (*ExecutableDataV1, error) {
	if api.light {
		return nil, errors.New("not supported")
	}
	log.Info("Producing block", "parentHash", parentHash)
	block, err := api.eth.Miner().GetSealingBlock(parentHash, params.Timestamp, params.SuggestedFeeRecipient, params.Random)
	if err != nil {
		return nil, err
	}
	return BlockToExecutableData(block), nil
}

func encodeTransactions(txs []*types.Transaction) [][]byte {
	var enc = make([][]byte, len(txs))
	for i, tx := range txs {
		enc[i], _ = tx.MarshalBinary()
	}
	return enc
}

func decodeTransactions(enc [][]byte) ([]*types.Transaction, error) {
	var txs = make([]*types.Transaction, len(enc))
	for i, encTx := range enc {
		var tx types.Transaction
		if err := tx.UnmarshalBinary(encTx); err != nil {
			return nil, fmt.Errorf("invalid transaction %d: %v", i, err)
		}
		txs[i] = &tx
	}
	return txs, nil
}

func ExecutableDataToBlock(params ExecutableDataV1) (*types.Block, error) {
	txs, err := decodeTransactions(params.Transactions)
	if err != nil {
		return nil, err
	}
	if len(params.ExtraData) > 32 {
		return nil, fmt.Errorf("invalid extradata length: %v", len(params.ExtraData))
	}
	header := &types.Header{
		ParentHash:  params.ParentHash,
		UncleHash:   types.EmptyUncleHash,
		Coinbase:    params.FeeRecipient,
		Root:        params.StateRoot,
		TxHash:      types.DeriveSha(types.Transactions(txs), trie.NewStackTrie(nil)),
		ReceiptHash: params.ReceiptsRoot,
		Bloom:       types.BytesToBloom(params.LogsBloom),
		Difficulty:  common.Big0,
		Number:      new(big.Int).SetUint64(params.Number),
		GasLimit:    params.GasLimit,
		GasUsed:     params.GasUsed,
		Time:        params.Timestamp,
		BaseFee:     params.BaseFeePerGas,
		Extra:       params.ExtraData,
		MixDigest:   params.Random,
	}
	block := types.NewBlockWithHeader(header).WithBody(txs, nil /* uncles */)
	if block.Hash() != params.BlockHash {
		return nil, fmt.Errorf("blockhash mismatch, want %x, got %x", params.BlockHash, block.Hash())
	}
	return block, nil
}

// BlockToExecutableData constructs the executableDataV1 structure by filling the
// fields from the given block. It assumes the given block is post-merge block.
func BlockToExecutableData(block *types.Block) *ExecutableDataV1 {
	return &ExecutableDataV1{
		BlockHash:     block.Hash(),
		ParentHash:    block.ParentHash(),
		FeeRecipient:  block.Coinbase(),
		StateRoot:     block.Root(),
		Number:        block.NumberU64(),
		GasLimit:      block.GasLimit(),
		GasUsed:       block.GasUsed(),
		BaseFeePerGas: block.BaseFee(),
		Timestamp:     block.Time(),
		ReceiptsRoot:  block.ReceiptHash(),
		LogsBloom:     block.Bloom().Bytes(),
		Transactions:  encodeTransactions(block.Transactions()),
		Random:        block.MixDigest(),
		ExtraData:     block.Extra(),
	}
}

// Used in tests to add a the list of transactions from a block to the tx pool.
func (api *ConsensusAPI) insertTransactions(txs types.Transactions) error {
	for _, tx := range txs {
		api.eth.TxPool().AddLocal(tx)
	}
	return nil
}

func (api *ConsensusAPI) checkTerminalTotalDifficulty(head common.Hash) error {
	// shortcut if we entered PoS already
	if api.merger().PoSFinalized() {
		return nil
	}
	if api.light {
		// make sure the parent has enough terminal total difficulty
		header := api.les.BlockChain().GetHeaderByHash(head)
		if header == nil {
			return &GenericServerError
		}
		td := api.les.BlockChain().GetTd(header.Hash(), header.Number.Uint64())
		if td != nil && td.Cmp(api.les.BlockChain().Config().TerminalTotalDifficulty) < 0 {
			return &InvalidTB
		}
		return nil
	}
	// make sure the parent has enough terminal total difficulty
	newHeadBlock := api.eth.BlockChain().GetBlockByHash(head)
	if newHeadBlock == nil {
		return &GenericServerError
	}
	td := api.eth.BlockChain().GetTd(newHeadBlock.Hash(), newHeadBlock.NumberU64())
	if td != nil && td.Cmp(api.eth.BlockChain().Config().TerminalTotalDifficulty) < 0 {
		return &InvalidTB
	}
	return nil
}

// setHead is called to perform a force choice.
func (api *ConsensusAPI) setHead(newHead common.Hash) error {
	log.Info("Setting head", "head", newHead)
	if api.light {
		headHeader := api.les.BlockChain().CurrentHeader()
		if headHeader.Hash() == newHead {
			return nil
		}
		newHeadHeader := api.les.BlockChain().GetHeaderByHash(newHead)
		if newHeadHeader == nil {
			return &GenericServerError
		}
		if err := api.les.BlockChain().SetChainHead(newHeadHeader); err != nil {
			return err
		}
		// Trigger the transition if it's the first `NewHead` event.
		if merger := api.merger(); !merger.PoSFinalized() {
			merger.FinalizePoS()
		}
		return nil
	}
	headBlock := api.eth.BlockChain().CurrentBlock()
	if headBlock.Hash() == newHead {
		return nil
	}
	newHeadBlock := api.eth.BlockChain().GetBlockByHash(newHead)
	if newHeadBlock == nil {
		return &GenericServerError
	}
	if err := api.eth.BlockChain().SetChainHead(newHeadBlock); err != nil {
		return err
	}
	// Trigger the transition if it's the first `NewHead` event.
	if merger := api.merger(); !merger.PoSFinalized() {
		merger.FinalizePoS()
	}
	// TODO (MariusVanDerWijden) are we really synced now?
	api.eth.SetSynced()
	return nil
}

// Helper function, return the merger instance.
func (api *ConsensusAPI) merger() *consensus.Merger {
	if api.light {
		return api.les.Merger()
	}
	return api.eth.Merger()
}