// Copyright 2015 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 raft

import (
	"fmt"
	"sync"
	"sync/atomic"
	"time"

	"github.com/eapache/channels"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/consensus/ethash"
	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/core/state"
	"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/event"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
)

var (
	extraVanity = 32 // Fixed number of extra-data prefix bytes reserved for arbitrary signer vanity
)

// Current state information for building the next block
type work struct {
	config       *params.ChainConfig
	publicState  *state.StateDB
	privateState *state.StateDB
	Block        *types.Block
	header       *types.Header
}

type minter struct {
	config           *params.ChainConfig
	mu               sync.Mutex
	mux              *event.TypeMux
	eth              *RaftService
	chain            *core.BlockChain
	chainDb          ethdb.Database
	coinbase         common.Address
	minting          int32 // Atomic status counter
	shouldMine       *channels.RingChannel
	blockTime        time.Duration
	speculativeChain *speculativeChain

	invalidRaftOrderingChan chan InvalidRaftOrdering
	chainHeadChan           chan core.ChainHeadEvent
	chainHeadSub            event.Subscription
	txPreChan               chan core.NewTxsEvent
	txPreSub                event.Subscription
}

type extraSeal struct {
	RaftId    []byte // RaftID of the block minter
	Signature []byte // Signature of the block minter
}

func newMinter(config *params.ChainConfig, eth *RaftService, blockTime time.Duration) *minter {
	minter := &minter{
		config:           config,
		eth:              eth,
		mux:              eth.EventMux(),
		chainDb:          eth.ChainDb(),
		chain:            eth.BlockChain(),
		shouldMine:       channels.NewRingChannel(1),
		blockTime:        blockTime,
		speculativeChain: newSpeculativeChain(),

		invalidRaftOrderingChan: make(chan InvalidRaftOrdering, 1),
		chainHeadChan:           make(chan core.ChainHeadEvent, core.GetChainHeadChannleSize()),
		txPreChan:               make(chan core.NewTxsEvent, 4096),
	}

	minter.chainHeadSub = eth.BlockChain().SubscribeChainHeadEvent(minter.chainHeadChan)
	minter.txPreSub = eth.TxPool().SubscribeNewTxsEvent(minter.txPreChan)

	minter.speculativeChain.clear(minter.chain.CurrentBlock())

	go minter.eventLoop()
	go minter.mintingLoop()

	return minter
}

func (minter *minter) start() {
	atomic.StoreInt32(&minter.minting, 1)
	minter.requestMinting()
}

func (minter *minter) stop() {
	minter.mu.Lock()
	defer minter.mu.Unlock()

	minter.speculativeChain.clear(minter.chain.CurrentBlock())
	atomic.StoreInt32(&minter.minting, 0)
}

// Notify the minting loop that minting should occur, if it's not already been
// requested. Due to the use of a RingChannel, this function is idempotent if
// called multiple times before the minting occurs.
func (minter *minter) requestMinting() {
	minter.shouldMine.In() <- struct{}{}
}

type AddressTxes map[common.Address]types.Transactions

func (minter *minter) updateSpeculativeChainPerNewHead(newHeadBlock *types.Block) {
	minter.mu.Lock()
	defer minter.mu.Unlock()

	minter.speculativeChain.accept(newHeadBlock)
}

func (minter *minter) updateSpeculativeChainPerInvalidOrdering(headBlock *types.Block, invalidBlock *types.Block) {
	invalidHash := invalidBlock.Hash()

	log.Info("Handling InvalidRaftOrdering", "invalid block", invalidHash, "current head", headBlock.Hash())

	minter.mu.Lock()
	defer minter.mu.Unlock()

	// 1. if the block is not in our db, exit. someone else mined this.
	if !minter.chain.HasBlock(invalidHash, invalidBlock.NumberU64()) {
		log.Info("Someone else mined invalid block; ignoring", "block", invalidHash)

		return
	}

	minter.speculativeChain.unwindFrom(invalidHash, headBlock)
}

func (minter *minter) eventLoop() {
	defer minter.chainHeadSub.Unsubscribe()
	defer minter.txPreSub.Unsubscribe()

	for {
		select {
		case ev := <-minter.chainHeadChan:
			newHeadBlock := ev.Block

			if atomic.LoadInt32(&minter.minting) == 1 {
				minter.updateSpeculativeChainPerNewHead(newHeadBlock)

				//
				// TODO(bts): not sure if this is the place, but we're going to
				// want to put an upper limit on our speculative mining chain
				// length.
				//

				minter.requestMinting()
			} else {
				minter.mu.Lock()
				minter.speculativeChain.setHead(newHeadBlock)
				minter.mu.Unlock()
			}

		case <-minter.txPreChan:
			if atomic.LoadInt32(&minter.minting) == 1 {
				minter.requestMinting()
			}

		case ev := <-minter.invalidRaftOrderingChan:
			headBlock := ev.headBlock
			invalidBlock := ev.invalidBlock

			minter.updateSpeculativeChainPerInvalidOrdering(headBlock, invalidBlock)

		// system stopped
		case <-minter.chainHeadSub.Err():
			return
		case <-minter.txPreSub.Err():
			return
		}
	}
}

// Returns a wrapper around no-arg func `f` which can be called without limit
// and returns immediately: this will call the underlying func `f` at most once
// every `rate`. If this function is called more than once before the underlying
// `f` is invoked (per this rate limiting), `f` will only be called *once*.
//
// TODO(joel): this has a small bug in that you can't call it *immediately* when
// first allocated.
func throttle(rate time.Duration, f func()) func() {
	request := channels.NewRingChannel(1)

	// every tick, block waiting for another request. then serve it immediately
	go func() {
		ticker := time.NewTicker(rate)
		defer ticker.Stop()

		for range ticker.C {
			<-request.Out()
			f()
		}
	}()

	return func() {
		request.In() <- struct{}{}
	}
}

// This function spins continuously, blocking until a block should be created
// (via requestMinting()). This is throttled by `minter.blockTime`:
//
//   1. A block is guaranteed to be minted within `blockTime` of being
//      requested.
//   2. We never mint a block more frequently than `blockTime`.
func (minter *minter) mintingLoop() {
	throttledMintNewBlock := throttle(minter.blockTime, func() {
		if atomic.LoadInt32(&minter.minting) == 1 {
			minter.mintNewBlock()
		}
	})

	for range minter.shouldMine.Out() {
		throttledMintNewBlock()
	}
}

func generateNanoTimestamp(parent *types.Block) (tstamp int64) {
	parentTime := int64(parent.Time())
	tstamp = time.Now().UnixNano()

	if parentTime >= tstamp {
		// Each successive block needs to be after its predecessor.
		tstamp = parentTime + 1
	}

	return
}

// Assumes mu is held.
func (minter *minter) createWork() *work {
	parent := minter.speculativeChain.head
	parentNumber := parent.Number()
	tstamp := generateNanoTimestamp(parent)

	header := &types.Header{
		ParentHash: parent.Hash(),
		Number:     parentNumber.Add(parentNumber, common.Big1),
		Difficulty: ethash.CalcDifficulty(minter.config, uint64(tstamp), parent.Header()),
		GasLimit:   minter.eth.calcGasLimitFunc(parent),
		GasUsed:    0,
		Coinbase:   minter.coinbase,
		Time:       uint64(tstamp),
	}

	publicState, privateState, err := minter.chain.StateAt(parent.Root())
	if err != nil {
		panic(fmt.Sprint("failed to get parent state: ", err))
	}

	return &work{
		config:       minter.config,
		publicState:  publicState,
		privateState: privateState,
		header:       header,
	}
}

func (minter *minter) getTransactions() *types.TransactionsByPriceAndNonce {
	allAddrTxes, err := minter.eth.TxPool().Pending()
	if err != nil { // TODO: handle
		panic(err)
	}
	addrTxes := minter.speculativeChain.withoutProposedTxes(allAddrTxes)
	signer := types.MakeSigner(minter.chain.Config(), minter.chain.CurrentBlock().Number())
	return types.NewTransactionsByPriceAndNonce(signer, addrTxes)
}

// Sends-off events asynchronously.
func (minter *minter) firePendingBlockEvents(logs []*types.Log) {
	// Copy logs before we mutate them, adding a block hash.
	copiedLogs := make([]*types.Log, len(logs))
	for i, l := range logs {
		copiedLogs[i] = new(types.Log)
		*copiedLogs[i] = *l
	}

	go func() {
		minter.mux.Post(core.PendingLogsEvent{Logs: copiedLogs})
		minter.mux.Post(core.PendingStateEvent{})
	}()
}

func (minter *minter) mintNewBlock() {
	minter.mu.Lock()
	defer minter.mu.Unlock()

	work := minter.createWork()
	transactions := minter.getTransactions()

	committedTxes, publicReceipts, _, logs := work.commitTransactions(transactions, minter.chain)
	txCount := len(committedTxes)

	if txCount == 0 {
		log.Info("Not minting a new block since there are no pending transactions")
		return
	}

	minter.firePendingBlockEvents(logs)

	header := work.header

	// commit state root after all state transitions.
	ethash.AccumulateRewards(minter.chain.Config(), work.publicState, header, nil)
	header.Root = work.publicState.IntermediateRoot(minter.chain.Config().IsEIP158(work.header.Number))

	// update block hash since it is now available, but was not when the
	// receipt/log of individual transactions were created:
	headerHash := header.Hash()
	for _, l := range logs {
		l.BlockHash = headerHash
	}

	//Sign the block and build the extraSeal struct
	extraSealBytes := minter.buildExtraSeal(headerHash)

	// add vanity and seal to header
	// NOTE: leaving vanity blank for now as a space for any future data
	header.Extra = make([]byte, extraVanity+len(extraSealBytes))
	copy(header.Extra[extraVanity:], extraSealBytes)

	block := types.NewBlock(header, committedTxes, nil, publicReceipts)

	log.Info("Generated next block", "block num", block.Number(), "num txes", txCount)

	deleteEmptyObjects := minter.chain.Config().IsEIP158(block.Number())
	if err := minter.chain.CommitBlockWithState(deleteEmptyObjects, work.publicState, work.privateState); err != nil {
		panic(err)
	}

	minter.speculativeChain.extend(block)

	minter.mux.Post(core.NewMinedBlockEvent{Block: block})

	elapsed := time.Since(time.Unix(0, int64(header.Time)))
	log.Info("🔨  Mined block", "number", block.Number(), "hash", fmt.Sprintf("%x", block.Hash().Bytes()[:4]), "elapsed", elapsed)
}

func (env *work) commitTransactions(txes *types.TransactionsByPriceAndNonce, bc *core.BlockChain) (types.Transactions, types.Receipts, types.Receipts, []*types.Log) {
	var allLogs []*types.Log
	var committedTxes types.Transactions
	var publicReceipts types.Receipts
	var privateReceipts types.Receipts

	gp := new(core.GasPool).AddGas(env.header.GasLimit)
	txCount := 0

	for {
		tx := txes.Peek()
		if tx == nil {
			break
		}

		env.publicState.Prepare(tx.Hash(), common.Hash{}, txCount)

		publicReceipt, privateReceipt, err := env.commitTransaction(tx, bc, gp)
		switch {
		case err != nil:
			log.Info("TX failed, will be removed", "hash", tx.Hash(), "err", err)
			txes.Pop() // skip rest of txes from this account
		default:
			txCount++
			committedTxes = append(committedTxes, tx)

			publicReceipts = append(publicReceipts, publicReceipt)
			allLogs = append(allLogs, publicReceipt.Logs...)

			if privateReceipt != nil {
				privateReceipts = append(privateReceipts, privateReceipt)
				allLogs = append(allLogs, privateReceipt.Logs...)
			}

			txes.Shift()
		}
	}

	return committedTxes, publicReceipts, privateReceipts, allLogs
}

func (env *work) commitTransaction(tx *types.Transaction, bc *core.BlockChain, gp *core.GasPool) (*types.Receipt, *types.Receipt, error) {
	publicSnapshot := env.publicState.Snapshot()
	privateSnapshot := env.privateState.Snapshot()

	var author *common.Address
	var vmConf vm.Config
	publicReceipt, privateReceipt, err := core.ApplyTransaction(env.config, bc, author, gp, env.publicState, env.privateState, env.header, tx, &env.header.GasUsed, vmConf)
	if err != nil {
		env.publicState.RevertToSnapshot(publicSnapshot)
		env.privateState.RevertToSnapshot(privateSnapshot)

		return nil, nil, err
	}

	return publicReceipt, privateReceipt, nil
}

func (minter *minter) buildExtraSeal(headerHash common.Hash) []byte {
	//Sign the headerHash
	nodeKey := minter.eth.nodeKey
	sig, err := crypto.Sign(headerHash.Bytes(), nodeKey)
	if err != nil {
		log.Warn("Block sealing failed", "err", err)
	}

	//build the extraSeal struct
	raftIdString := hexutil.EncodeUint64(uint64(minter.eth.raftProtocolManager.raftId))

	extra := extraSeal{
		RaftId:    []byte(raftIdString[2:]), //remove the 0x prefix
		Signature: sig,
	}

	//encode to byte array for storage
	extraDataBytes, err := rlp.EncodeToBytes(extra)
	if err != nil {
		log.Warn("Header.Extra Data Encoding failed", "err", err)
	}

	return extraDataBytes
}