package eth

import (
	"bytes"
	"math"
	"math/big"

	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/ethutil"
	"github.com/ethereum/go-ethereum/p2p"
	"github.com/ethereum/go-ethereum/rlp"
)

// ethProtocol represents the ethereum wire protocol
// instance is running on each peer
type ethProtocol struct {
	eth  backend
	peer *p2p.Peer
	id   string
	rw   p2p.MsgReadWriter
}

// backend is the interface the ethereum protocol backend should implement
// used as an argument to EthProtocol
type backend interface {
	GetTransactions() (txs []*types.Transaction)
	AddTransactions([]*types.Transaction)
	GetBlockHashes(hash []byte, amount uint32) (hashes [][]byte)
	AddBlockHashes(next func() ([]byte, bool), peerId string)
	GetBlock(hash []byte) (block *types.Block)
	AddBlock(block *types.Block, peerId string) (err error)
	AddPeer(td *big.Int, currentBlock []byte, peerId string, requestHashes func([]byte) error, requestBlocks func([][]byte) error, invalidBlock func(error)) (best bool)
	RemovePeer(peerId string)
	Status() (td *big.Int, currentBlock []byte, genesisBlock []byte)
}

const (
	ProtocolVersion    = 43
	NetworkId          = 0
	ProtocolLength     = uint64(8)
	ProtocolMaxMsgSize = 10 * 1024 * 1024
)

// eth protocol message codes
const (
	StatusMsg = iota
	GetTxMsg  // unused
	TxMsg
	GetBlockHashesMsg
	BlockHashesMsg
	GetBlocksMsg
	BlocksMsg
	NewBlockMsg
)

// message structs used for rlp decoding
type newBlockMsgData struct {
	Block *types.Block
	TD    *big.Int
}

type getBlockHashesMsgData struct {
	Hash   []byte
	Amount uint32
}

// main entrypoint, wrappers starting a server running the eth protocol
// use this constructor to attach the protocol ("class") to server caps
// the Dev p2p layer then runs the protocol instance on each peer
func EthProtocol(eth backend) *p2p.Protocol {
	return &p2p.Protocol{
		Name:    "eth",
		Version: ProtocolVersion,
		Length:  ProtocolLength,
		Run: func(peer *p2p.Peer, rw p2p.MsgReadWriter) error {
			return runEthProtocol(eth, peer, rw)
		},
	}
}

// the main loop that handles incoming messages
// note RemovePeer in the post-disconnect hook
func runEthProtocol(eth backend, peer *p2p.Peer, rw p2p.MsgReadWriter) (err error) {
	self := &ethProtocol{
		eth:  eth,
		rw:   rw,
		peer: peer,
		id:   (string)(peer.Identity().Pubkey()),
	}
	err = self.handleStatus()
	if err == nil {
		go func() {
			for {
				err = self.handle()
				if err != nil {
					self.eth.RemovePeer(self.id)
					break
				}
			}
		}()
	}
	return
}

func (self *ethProtocol) handle() error {
	msg, err := self.rw.ReadMsg()
	if err != nil {
		return err
	}
	if msg.Size > ProtocolMaxMsgSize {
		return ProtocolError(ErrMsgTooLarge, "%v > %v", msg.Size, ProtocolMaxMsgSize)
	}
	// make sure that the payload has been fully consumed
	defer msg.Discard()

	switch msg.Code {

	case StatusMsg:
		return ProtocolError(ErrExtraStatusMsg, "")

	case GetTxMsg:
		txs := self.eth.GetTransactions()
		// TODO: rewrite using rlp flat
		txsInterface := make([]interface{}, len(txs))
		for i, tx := range txs {
			txsInterface[i] = tx.RlpData()
		}
		return self.rw.EncodeMsg(TxMsg, txsInterface...)

	case TxMsg:
		// TODO: rework using lazy RLP stream
		var txs []*types.Transaction
		if err := msg.Decode(&txs); err != nil {
			return ProtocolError(ErrDecode, "%v", err)
		}
		self.eth.AddTransactions(txs)

	case GetBlockHashesMsg:
		var request getBlockHashesMsgData
		if err := msg.Decode(&request); err != nil {
			return ProtocolError(ErrDecode, "%v", err)
		}
		hashes := self.eth.GetBlockHashes(request.Hash, request.Amount)
		return self.rw.EncodeMsg(BlockHashesMsg, ethutil.ByteSliceToInterface(hashes)...)

	case BlockHashesMsg:
		// TODO: redo using lazy decode , this way very inefficient on known chains
		msgStream := rlp.NewListStream(msg.Payload, uint64(msg.Size))
		var err error
		iter := func() (hash []byte, ok bool) {
			hash, err = msgStream.Bytes()
			if err == nil {
				ok = true
			}
			return
		}
		self.eth.AddBlockHashes(iter, self.id)
		if err != nil && err != rlp.EOL {
			return ProtocolError(ErrDecode, "%v", err)
		}

	case GetBlocksMsg:
		var blockHashes [][]byte
		if err := msg.Decode(&blockHashes); err != nil {
			return ProtocolError(ErrDecode, "%v", err)
		}
		max := int(math.Min(float64(len(blockHashes)), blockHashesBatchSize))
		var blocks []interface{}
		for i, hash := range blockHashes {
			if i >= max {
				break
			}
			block := self.eth.GetBlock(hash)
			if block != nil {
				blocks = append(blocks, block.Value().Raw())
			}
		}
		return self.rw.EncodeMsg(BlocksMsg, blocks...)

	case BlocksMsg:
		msgStream := rlp.NewListStream(msg.Payload, uint64(msg.Size))
		for {
			var block *types.Block
			if err := msgStream.Decode(&block); err != nil {
				if err == rlp.EOL {
					break
				} else {
					return ProtocolError(ErrDecode, "%v", err)
				}
			}
			if err := self.eth.AddBlock(block, self.id); err != nil {
				return ProtocolError(ErrInvalidBlock, "%v", err)
			}
		}

	case NewBlockMsg:
		var request newBlockMsgData
		if err := msg.Decode(&request); err != nil {
			return ProtocolError(ErrDecode, "%v", err)
		}
		hash := request.Block.Hash()
		// to simplify backend interface adding a new block
		// uses AddPeer followed by AddHashes, AddBlock only if peer is the best peer
		// (or selected as new best peer)
		if self.eth.AddPeer(request.TD, hash, self.id, self.requestBlockHashes, self.requestBlocks, self.invalidBlock) {
			called := true
			iter := func() (hash []byte, ok bool) {
				if called {
					called = false
					return hash, true
				} else {
					return
				}
			}
			self.eth.AddBlockHashes(iter, self.id)
			if err := self.eth.AddBlock(request.Block, self.id); err != nil {
				return ProtocolError(ErrInvalidBlock, "%v", err)
			}
		}

	default:
		return ProtocolError(ErrInvalidMsgCode, "%v", msg.Code)
	}
	return nil
}

type statusMsgData struct {
	ProtocolVersion uint
	NetworkId       uint
	TD              *big.Int
	CurrentBlock    []byte
	GenesisBlock    []byte
}

func (self *ethProtocol) statusMsg() p2p.Msg {
	td, currentBlock, genesisBlock := self.eth.Status()

	return p2p.NewMsg(StatusMsg,
		uint32(ProtocolVersion),
		uint32(NetworkId),
		td,
		currentBlock,
		genesisBlock,
	)
}

func (self *ethProtocol) handleStatus() error {
	// send precanned status message
	if err := self.rw.WriteMsg(self.statusMsg()); err != nil {
		return err
	}

	// read and handle remote status
	msg, err := self.rw.ReadMsg()
	if err != nil {
		return err
	}

	if msg.Code != StatusMsg {
		return ProtocolError(ErrNoStatusMsg, "first msg has code %x (!= %x)", msg.Code, StatusMsg)
	}

	if msg.Size > ProtocolMaxMsgSize {
		return ProtocolError(ErrMsgTooLarge, "%v > %v", msg.Size, ProtocolMaxMsgSize)
	}

	var status statusMsgData
	if err := msg.Decode(&status); err != nil {
		return ProtocolError(ErrDecode, "%v", err)
	}

	_, _, genesisBlock := self.eth.Status()

	if bytes.Compare(status.GenesisBlock, genesisBlock) != 0 {
		return ProtocolError(ErrGenesisBlockMismatch, "%x (!= %x)", status.GenesisBlock, genesisBlock)
	}

	if status.NetworkId != NetworkId {
		return ProtocolError(ErrNetworkIdMismatch, "%d (!= %d)", status.NetworkId, NetworkId)
	}

	if ProtocolVersion != status.ProtocolVersion {
		return ProtocolError(ErrProtocolVersionMismatch, "%d (!= %d)", status.ProtocolVersion, ProtocolVersion)
	}

	self.peer.Infof("Peer is [eth] capable (%d/%d). TD = %v ~ %x", status.ProtocolVersion, status.NetworkId, status.CurrentBlock)

	self.eth.AddPeer(status.TD, status.CurrentBlock, self.id, self.requestBlockHashes, self.requestBlocks, self.invalidBlock)

	return nil
}

func (self *ethProtocol) requestBlockHashes(from []byte) error {
	self.peer.Debugf("fetching hashes (%d) %x...\n", blockHashesBatchSize, from[0:4])
	return self.rw.EncodeMsg(GetBlockHashesMsg, from, blockHashesBatchSize)
}

func (self *ethProtocol) requestBlocks(hashes [][]byte) error {
	self.peer.Debugf("fetching %v blocks", len(hashes))
	return self.rw.EncodeMsg(GetBlocksMsg, ethutil.ByteSliceToInterface(hashes))
}

func (self *ethProtocol) invalidBlock(err error) {
	ProtocolError(ErrInvalidBlock, "%v", err)
	self.peer.Disconnect(p2p.DiscSubprotocolError)
}

func (self *ethProtocol) protoError(code int, format string, params ...interface{}) (err *protocolError) {
	err = ProtocolError(code, format, params...)
	if err.Fatal() {
		self.peer.Errorln(err)
	} else {
		self.peer.Debugln(err)
	}
	return
}