// Copyright 2016 The go-ethereum Authors
// This file is part of go-ethereum.
//
// go-ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// go-ethereum 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.

package mailserver

import (
	"bytes"
	"encoding/binary"

	"github.com/ethereum/go-ethereum/cmd/utils"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/logger"
	"github.com/ethereum/go-ethereum/logger/glog"
	"github.com/ethereum/go-ethereum/rlp"
	whisper "github.com/ethereum/go-ethereum/whisper/whisperv5"
	"github.com/syndtr/goleveldb/leveldb"
	"github.com/syndtr/goleveldb/leveldb/util"
)

const MailServerKeyName = "958e04ab302fb36ad2616a352cbac79d"

type WMailServer struct {
	db  *leveldb.DB
	w   *whisper.Whisper
	pow float64
	key []byte
}

type DBKey struct {
	timestamp uint32
	hash      common.Hash
	raw       []byte
}

func NewDbKey(t uint32, h common.Hash) *DBKey {
	const sz = common.HashLength + 4
	var k DBKey
	k.timestamp = t
	k.hash = h
	k.raw = make([]byte, sz)
	binary.BigEndian.PutUint32(k.raw, k.timestamp)
	copy(k.raw[4:], k.hash[:])
	return &k
}

func (s *WMailServer) Init(shh *whisper.Whisper, path string, password string, pow float64) {
	var err error
	if len(path) == 0 {
		utils.Fatalf("DB file is not specified")
	}

	if len(password) == 0 {
		utils.Fatalf("Password is not specified for MailServer")
	}

	s.db, err = leveldb.OpenFile(path, nil)
	if err != nil {
		utils.Fatalf("Failed to open DB file: %s", err)
	}

	s.w = shh
	s.pow = pow

	err = s.w.AddSymKey(MailServerKeyName, []byte(password))
	if err != nil {
		utils.Fatalf("Failed to create symmetric key for MailServer: %s", err)
	}
	s.key = s.w.GetSymKey(MailServerKeyName)
}

func (s *WMailServer) Close() {
	if s.db != nil {
		s.db.Close()
	}
}

func (s *WMailServer) Archive(env *whisper.Envelope) {
	key := NewDbKey(env.Expiry-env.TTL, env.Hash())
	rawEnvelope, err := rlp.EncodeToBytes(env)
	if err != nil {
		glog.V(logger.Error).Infof("rlp.EncodeToBytes failed: %s", err)
	} else {
		err = s.db.Put(key.raw, rawEnvelope, nil)
		if err != nil {
			glog.V(logger.Error).Infof("Writing to DB failed: %s", err)
		}
	}
}

func (s *WMailServer) DeliverMail(peer *whisper.Peer, request *whisper.Envelope) {
	ok, lower, upper, topic := s.validate(peer, request)
	if !ok {
		return
	}

	var err error
	var zero common.Hash
	var empty whisper.TopicType
	kl := NewDbKey(lower, zero)
	ku := NewDbKey(upper, zero)
	i := s.db.NewIterator(&util.Range{Start: kl.raw, Limit: ku.raw}, nil)
	defer i.Release()

	for i.Next() {
		var envelope whisper.Envelope
		err = rlp.DecodeBytes(i.Value(), &envelope)
		if err != nil {
			glog.V(logger.Error).Infof("RLP decoding failed: %s", err)
		}

		if topic == empty || envelope.Topic == topic {
			err = s.w.SendP2PDirect(peer, &envelope)
			if err != nil {
				glog.V(logger.Error).Infof("Failed to send direct message to peer: %s", err)
				return
			}
		}
	}

	err = i.Error()
	if err != nil {
		glog.V(logger.Error).Infof("Level DB iterator error: %s", err)
	}
}

func (s *WMailServer) validate(peer *whisper.Peer, request *whisper.Envelope) (bool, uint32, uint32, whisper.TopicType) {
	var topic whisper.TopicType
	if s.pow > 0.0 && request.PoW() < s.pow {
		return false, 0, 0, topic
	}

	f := whisper.Filter{KeySym: s.key}
	decrypted := request.Open(&f)
	if decrypted == nil {
		glog.V(logger.Warn).Infof("Failed to decrypt p2p request")
		return false, 0, 0, topic
	}

	if len(decrypted.Payload) < 8 {
		glog.V(logger.Warn).Infof("Undersized p2p request")
		return false, 0, 0, topic
	}

	if bytes.Equal(peer.ID(), decrypted.Signature) {
		glog.V(logger.Warn).Infof("Wrong signature of p2p request")
		return false, 0, 0, topic
	}

	lower := binary.BigEndian.Uint32(decrypted.Payload[:4])
	upper := binary.BigEndian.Uint32(decrypted.Payload[4:8])

	if len(decrypted.Payload) >= 8+whisper.TopicLength {
		topic = whisper.BytesToTopic(decrypted.Payload[8:])
	}

	return true, lower, upper, topic
}