// 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 snap

import (
	"fmt"
	"time"

	"github.com/ethereum/go-ethereum/core"
	"github.com/ethereum/go-ethereum/metrics"
	"github.com/ethereum/go-ethereum/p2p"
	"github.com/ethereum/go-ethereum/p2p/enode"
	"github.com/ethereum/go-ethereum/p2p/enr"
)

const (
	// softResponseLimit is the target maximum size of replies to data retrievals.
	softResponseLimit = 2 * 1024 * 1024

	// maxCodeLookups is the maximum number of bytecodes to serve. This number is
	// there to limit the number of disk lookups.
	maxCodeLookups = 1024

	// stateLookupSlack defines the ratio by how much a state response can exceed
	// the requested limit in order to try and avoid breaking up contracts into
	// multiple packages and proving them.
	stateLookupSlack = 0.1

	// maxTrieNodeLookups is the maximum number of state trie nodes to serve. This
	// number is there to limit the number of disk lookups.
	maxTrieNodeLookups = 1024

	// maxAccessListLookups is the maximum number of BALs to server. This number
	// is there to limit the number of disk lookups.
	maxAccessListLookups = 1024

	// maxTrieNodeTimeSpent is the maximum time we should spend on looking up trie nodes.
	// If we spend too much time, then it's a fairly high chance of timing out
	// at the remote side, which means all the work is in vain.
	maxTrieNodeTimeSpent = 5 * time.Second
)

// Handler is a callback to invoke from an outside runner after the boilerplate
// exchanges have passed.
type Handler func(peer *Peer) error

// Backend defines the data retrieval methods to serve remote requests and the
// callback methods to invoke on remote deliveries.
type Backend interface {
	// Chain retrieves the blockchain object to serve data.
	Chain() *core.BlockChain

	// RunPeer is invoked when a peer joins on the `eth` protocol. The handler
	// should do any peer maintenance work, handshakes and validations. If all
	// is passed, control should be given back to the `handler` to process the
	// inbound messages going forward.
	RunPeer(peer *Peer, handler Handler) error

	// PeerInfo retrieves all known `snap` information about a peer.
	PeerInfo(id enode.ID) interface{}

	// Handle is a callback to be invoked when a data packet is received from
	// the remote peer. Only packets not consumed by the protocol handler will
	// be forwarded to the backend.
	Handle(peer *Peer, packet Packet) error
}

// MakeProtocols constructs the P2P protocol definitions for `snap`.
func MakeProtocols(backend Backend) []p2p.Protocol {
	protocols := make([]p2p.Protocol, len(ProtocolVersions))
	for i, version := range ProtocolVersions {
		protocols[i] = p2p.Protocol{
			Name:    ProtocolName,
			Version: version,
			Length:  protocolLengths[version],
			Run: func(p *p2p.Peer, rw p2p.MsgReadWriter) error {
				return backend.RunPeer(NewPeer(version, p, rw), func(peer *Peer) error {
					defer peer.Close()
					return Handle(backend, peer)
				})
			},
			NodeInfo: func() interface{} {
				return nodeInfo(backend.Chain())
			},
			PeerInfo: func(id enode.ID) interface{} {
				return backend.PeerInfo(id)
			},
			Attributes: []enr.Entry{&enrEntry{}},
		}
	}
	return protocols
}

// Handle is the callback invoked to manage the life cycle of a `snap` peer.
// When this function terminates, the peer is disconnected.
func Handle(backend Backend, peer *Peer) error {
	for {
		if err := HandleMessage(backend, peer); err != nil {
			peer.Log().Debug("Message handling failed in `snap`", "err", err)
			return err
		}
	}
}

type msgHandler func(backend Backend, msg Decoder, peer *Peer) error
type Decoder interface {
	Decode(val interface{}) error
}

var snap1 = map[uint64]msgHandler{
	GetAccountRangeMsg:  handleGetAccountRange,
	AccountRangeMsg:     handleAccountRange,
	GetStorageRangesMsg: handleGetStorageRanges,
	StorageRangesMsg:    handleStorageRanges,
	GetByteCodesMsg:     handleGetByteCodes,
	ByteCodesMsg:        handleByteCodes,
	GetTrieNodesMsg:     handleGetTrienodes,
	TrieNodesMsg:        handleTrieNodes,
}

// nolint:unused
var snap2 = map[uint64]msgHandler{
	GetAccountRangeMsg:  handleGetAccountRange,
	AccountRangeMsg:     handleAccountRange,
	GetStorageRangesMsg: handleGetStorageRanges,
	StorageRangesMsg:    handleStorageRanges,
	GetByteCodesMsg:     handleGetByteCodes,
	ByteCodesMsg:        handleByteCodes,
	GetAccessListsMsg:   handleGetAccessLists,
	// AccessListsMsg: TODO
}

// HandleMessage is invoked whenever an inbound message is received from a
// remote peer on the `snap` protocol. The remote connection is torn down upon
// returning any error.
func HandleMessage(backend Backend, peer *Peer) error {
	// Read the next message from the remote peer, and ensure it's fully consumed
	msg, err := peer.rw.ReadMsg()
	if err != nil {
		return err
	}
	if msg.Size > maxMessageSize {
		return fmt.Errorf("%w: %v > %v", errMsgTooLarge, msg.Size, maxMessageSize)
	}
	defer msg.Discard()

	var handlers map[uint64]msgHandler
	switch peer.version {
	case SNAP1:
		handlers = snap1
	//case SNAP2:
	//	handlers = snap2
	default:
		return fmt.Errorf("unknown eth protocol version: %v", peer.version)
	}

	// Track the amount of time it takes to serve the request and run the handler
	start := time.Now()
	if metrics.Enabled() {
		h := fmt.Sprintf("%s/%s/%d/%#02x", p2p.HandleHistName, ProtocolName, peer.Version(), msg.Code)
		defer func(start time.Time) {
			sampler := func() metrics.Sample {
				return metrics.ResettingSample(
					metrics.NewExpDecaySample(1028, 0.015),
				)
			}
			metrics.GetOrRegisterHistogramLazy(h, nil, sampler).Update(time.Since(start).Microseconds())
		}(start)
	}

	if handler := handlers[msg.Code]; handler != nil {
		return handler(backend, msg, peer)
	}
	return fmt.Errorf("%w: %v", errInvalidMsgCode, msg.Code)
}

// NodeInfo represents a short summary of the `snap` sub-protocol metadata
// known about the host peer.
type NodeInfo struct{}

// nodeInfo retrieves some `snap` protocol metadata about the running host node.
func nodeInfo(chain *core.BlockChain) *NodeInfo {
	return &NodeInfo{}
}