// 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"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/beacon"
	"github.com/ethereum/go-ethereum/core/rawdb"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/eth"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/node"
	"github.com/ethereum/go-ethereum/rpc"
)

// 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),
			Public:        true,
			Authenticated: true,
		},
		{
			Namespace:     "engine",
			Version:       "1.0",
			Service:       NewConsensusAPI(backend),
			Public:        true,
			Authenticated: false,
		},
	})
	return nil
}

type ConsensusAPI struct {
	eth          *eth.Ethereum
	remoteBlocks *headerQueue  // Cache of remote payloads received
	localBlocks  *payloadQueue // Cache of local payloads generated
}

// NewConsensusAPI creates a new consensus api for the given backend.
// The underlying blockchain needs to have a valid terminal total difficulty set.
func NewConsensusAPI(eth *eth.Ethereum) *ConsensusAPI {
	if eth.BlockChain().Config().TerminalTotalDifficulty == nil {
		panic("Catalyst started without valid total difficulty")
	}
	return &ConsensusAPI{
		eth:          eth,
		remoteBlocks: newHeaderQueue(),
		localBlocks:  newPayloadQueue(),
	}
}

// ForkchoiceUpdatedV1 has several responsibilities:
// If the method is called with an empty head block:
// 		we return success, which can be used to check if the catalyst mode is enabled
// If the total difficulty was not reached:
// 		we return INVALID
// If the finalizedBlockHash is set:
// 		we check if we have the finalizedBlockHash in our db, if not we start a sync
// We try to set our blockchain to the headBlock
// If there are payloadAttributes:
// 		we try to assemble a block with the payloadAttributes and return its payloadID
func (api *ConsensusAPI) ForkchoiceUpdatedV1(update beacon.ForkchoiceStateV1, payloadAttributes *beacon.PayloadAttributesV1) (beacon.ForkChoiceResponse, error) {
	log.Trace("Engine API request received", "method", "ForkChoiceUpdated", "head", update.HeadBlockHash, "finalized", update.FinalizedBlockHash, "safe", update.SafeBlockHash)
	if update.HeadBlockHash == (common.Hash{}) {
		log.Warn("Forkchoice requested update to zero hash")
		return beacon.ForkChoiceResponse{Status: beacon.INVALID}, nil // TODO(karalabe): Why does someone send us this?
	}
	// Check whether we have the block yet in our database or not. If not, we'll
	// need to either trigger a sync, or to reject this forkchoice update for a
	// reason.
	block := api.eth.BlockChain().GetBlockByHash(update.HeadBlockHash)
	if block == nil {
		// If the head hash is unknown (was not given to us in a newPayload request),
		// we cannot resolve the header, so not much to do. This could be extended in
		// the future to resolve from the `eth` network, but it's an unexpected case
		// that should be fixed, not papered over.
		header := api.remoteBlocks.get(update.HeadBlockHash)
		if header == nil {
			log.Warn("Forkcoice requested unknown head", "hash", update.HeadBlockHash)
			return beacon.ForkChoiceResponse{Status: beacon.INVALID}, errors.New("head hash never advertised")
		}
		// Header advertised via a past newPayload request. Start syncing to it.
		// Before we do however, make sure any legacy sync in switched off so we
		// don't accidentally have 2 cycles running.
		if merger := api.eth.Merger(); !merger.TDDReached() {
			merger.ReachTTD()
			api.eth.Downloader().Cancel()
		}
		log.Info("Forkchoice requested sync to new head", "number", header.Number, "hash", header.Hash())
		if err := api.eth.Downloader().BeaconSync(api.eth.SyncMode(), header); err != nil {
			return beacon.ForkChoiceResponse{Status: beacon.SYNCING}, err
		}
		return beacon.ForkChoiceResponse{Status: beacon.SYNCING}, nil
	}
	// Block is known locally, just sanity check that the beacon client does not
	// attempt to push as back to before the merge.
	if block.Difficulty().BitLen() > 0 {
		var (
			td  = api.eth.BlockChain().GetTd(update.HeadBlockHash, block.NumberU64())
			ptd = api.eth.BlockChain().GetTd(block.ParentHash(), block.NumberU64()-1)
			ttd = api.eth.BlockChain().Config().TerminalTotalDifficulty
		)
		if td == nil || (block.NumberU64() > 0 && ptd == nil) {
			log.Error("TDs unavailable for TTD check", "number", block.NumberU64(), "hash", update.HeadBlockHash, "td", td, "parent", block.ParentHash(), "ptd", ptd)
			return beacon.ForkChoiceResponse{Status: beacon.INVALID}, errors.New("TDs unavailable for TDD check")
		}
		if td.Cmp(ttd) < 0 || (block.NumberU64() > 0 && ptd.Cmp(ttd) >= 0) {
			log.Error("Refusing beacon update to pre-merge", "number", block.NumberU64(), "hash", update.HeadBlockHash, "diff", block.Difficulty(), "age", common.PrettyAge(time.Unix(int64(block.Time()), 0)))
			return beacon.ForkChoiceResponse{Status: beacon.INVALID}, errors.New("refusing reorg to pre-merge")
		}
	}
	// If the head block is already in our canonical chain, the beacon client is
	// probably resyncing. Ignore the update.
	if rawdb.ReadCanonicalHash(api.eth.ChainDb(), block.NumberU64()) == update.HeadBlockHash {
		log.Warn("Ignoring beacon update to old head", "number", block.NumberU64(), "hash", update.HeadBlockHash, "age", common.PrettyAge(time.Unix(int64(block.Time()), 0)), "have", api.eth.BlockChain().CurrentBlock().NumberU64())
		return beacon.ForkChoiceResponse{Status: beacon.VALID}, nil
	}
	if err := api.eth.BlockChain().SetChainHead(block); err != nil {
		return beacon.ForkChoiceResponse{Status: beacon.INVALID}, err
	}
	api.eth.SetSynced()

	// If the beacon client also advertised a finalized block, mark the local
	// chain final and completely in PoS mode.
	if update.FinalizedBlockHash != (common.Hash{}) {
		if merger := api.eth.Merger(); !merger.PoSFinalized() {
			merger.FinalizePoS()
		}
	}
	// If payload generation was requested, create a new block to be potentially
	// sealed by the beacon client. The payload will be requested later, and we
	// might replace it arbitrarily many times in between.
	if payloadAttributes != nil {
		log.Info("Creating new payload for sealing")
		start := time.Now()

		data, err := api.assembleBlock(update.HeadBlockHash, payloadAttributes)
		if err != nil {
			log.Error("Failed to create sealing payload", "err", err)
			return beacon.ForkChoiceResponse{Status: beacon.VALID}, err // Valid as setHead was accepted
		}
		id := computePayloadId(update.HeadBlockHash, payloadAttributes)
		api.localBlocks.put(id, data)

		log.Info("Created payload for sealing", "id", id, "elapsed", time.Since(start))
		return beacon.ForkChoiceResponse{Status: beacon.VALID, PayloadID: &id}, nil
	}
	return beacon.ForkChoiceResponse{Status: beacon.VALID}, nil
}

// GetPayloadV1 returns a cached payload by id.
func (api *ConsensusAPI) GetPayloadV1(payloadID beacon.PayloadID) (*beacon.ExecutableDataV1, error) {
	log.Trace("Engine API request received", "method", "GetPayload", "id", payloadID)
	data := api.localBlocks.get(payloadID)
	if data == nil {
		return nil, &beacon.UnknownPayload
	}
	return data, nil
}

// ExecutePayloadV1 creates an Eth1 block, inserts it in the chain, and returns the status of the chain.
func (api *ConsensusAPI) ExecutePayloadV1(params beacon.ExecutableDataV1) (beacon.ExecutePayloadResponse, error) {
	log.Trace("Engine API request received", "method", "ExecutePayload", "number", params.Number, "hash", params.BlockHash)
	block, err := beacon.ExecutableDataToBlock(params)
	if err != nil {
		return api.invalid(), err
	}
	// If we already have the block locally, ignore the entire execution and just
	// return a fake success.
	if block := api.eth.BlockChain().GetBlockByHash(params.BlockHash); block != nil {
		log.Warn("Ignoring already known beacon payload", "number", params.Number, "hash", params.BlockHash, "age", common.PrettyAge(time.Unix(int64(block.Time()), 0)))
		return beacon.ExecutePayloadResponse{Status: beacon.VALID, LatestValidHash: block.Hash()}, nil
	}
	// If the parent is missing, we - in theory - could trigger a sync, but that
	// would also entail a reorg. That is problematic if multiple sibling blocks
	// are being fed to us, and even more so, if some semi-distant uncle shortens
	// our live chain. As such, payload execution will not permit reorgs and thus
	// will not trigger a sync cycle. That is fine though, if we get a fork choice
	// update after legit payload executions.
	parent := api.eth.BlockChain().GetBlock(block.ParentHash(), block.NumberU64()-1)
	if parent == nil {
		// Stash the block away for a potential forced forckchoice update to it
		// at a later time.
		api.remoteBlocks.put(block.Hash(), block.Header())

		// Although we don't want to trigger a sync, if there is one already in
		// progress, try to extend if with the current payload request to relieve
		// some strain from the forkchoice update.
		if err := api.eth.Downloader().BeaconExtend(api.eth.SyncMode(), block.Header()); err == nil {
			log.Debug("Payload accepted for sync extension", "number", params.Number, "hash", params.BlockHash)
			return beacon.ExecutePayloadResponse{Status: beacon.SYNCING, LatestValidHash: api.eth.BlockChain().CurrentBlock().Hash()}, nil
		}
		// Either no beacon sync was started yet, or it rejected the delivered
		// payload as non-integratable on top of the existing sync. We'll just
		// have to rely on the beacon client to forcefully update the head with
		// a forkchoice update request.
		log.Warn("Ignoring payload with missing parent", "number", params.Number, "hash", params.BlockHash, "parent", params.ParentHash)
		return beacon.ExecutePayloadResponse{Status: beacon.SYNCING, LatestValidHash: common.Hash{}}, nil // TODO(karalabe): Switch to ACCEPTED
	}
	// We have an existing parent, do some sanity checks to avoid the beacon client
	// triggering too early
	var (
		td  = api.eth.BlockChain().GetTd(parent.Hash(), parent.NumberU64())
		ttd = api.eth.BlockChain().Config().TerminalTotalDifficulty
	)
	if td.Cmp(ttd) < 0 {
		log.Warn("Ignoring pre-merge payload", "number", params.Number, "hash", params.BlockHash, "td", td, "ttd", ttd)
		return api.invalid(), fmt.Errorf("cannot execute payload on top of pre-merge blocks: td %v, ttd %v", td, ttd)
	}
	log.Trace("Inserting block without sethead", "hash", block.Hash(), "number", block.Number)
	if err := api.eth.BlockChain().InsertBlockWithoutSetHead(block); err != nil {
		return api.invalid(), err
	}
	// We've accepted a valid payload from the beacon client. Mark the local
	// chain transitions to notify other subsystems (e.g. downloader) of the
	// behavioral change.
	if merger := api.eth.Merger(); !merger.TDDReached() {
		merger.ReachTTD()
		api.eth.Downloader().Cancel()
	}
	return beacon.ExecutePayloadResponse{Status: beacon.VALID, LatestValidHash: block.Hash()}, nil
}

// computePayloadId computes a pseudo-random payloadid, based on the parameters.
func computePayloadId(headBlockHash common.Hash, params *beacon.PayloadAttributesV1) beacon.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 beacon.PayloadID
	copy(out[:], hasher.Sum(nil)[:8])
	return out
}

// invalid returns a response "INVALID" with the latest valid hash set to the current head.
func (api *ConsensusAPI) invalid() beacon.ExecutePayloadResponse {
	return beacon.ExecutePayloadResponse{Status: beacon.INVALID, LatestValidHash: api.eth.BlockChain().CurrentHeader().Hash()}
}

// assembleBlock creates a new block and returns the "execution
// data" required for beacon clients to process the new block.
func (api *ConsensusAPI) assembleBlock(parentHash common.Hash, params *beacon.PayloadAttributesV1) (*beacon.ExecutableDataV1, error) {
	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 beacon.BlockToExecutableData(block), nil
}

// 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.eth.Merger().PoSFinalized() {
		return nil
	}
	// make sure the parent has enough terminal total difficulty
	newHeadBlock := api.eth.BlockChain().GetBlockByHash(head)
	if newHeadBlock == nil {
		return &beacon.GenericServerError
	}
	td := api.eth.BlockChain().GetTd(newHeadBlock.Hash(), newHeadBlock.NumberU64())
	if td != nil && td.Cmp(api.eth.BlockChain().Config().TerminalTotalDifficulty) < 0 {
		return &beacon.InvalidTB
	}
	return nil
}