// Package node contains node logic.
package node

// @todo this is a very rough implementation that needs cleanup

import (
	"context"
	"database/sql"
	"encoding/hex"
	"fmt"
	"math/rand"
	"sync"
	"sync/atomic"
	"time"

	"go.uber.org/zap"

	"github.com/status-im/mvds/peers"
	"github.com/status-im/mvds/protobuf"
	"github.com/status-im/mvds/state"
	"github.com/status-im/mvds/store"
	"github.com/status-im/mvds/transport"
)

// Mode represents the synchronization mode.
type Mode int

const (
	INTERACTIVE Mode = iota
	BATCH
)

// CalculateNextEpoch is a function used to calculate the next `SendEpoch` for a given message.
type CalculateNextEpoch func(count uint64, epoch int64) int64

type EventStatus int

const (
	OnlineStatus EventStatus = iota
	OfflineStatus
)

const FreshEventPeriod = 10 // seconds
const MaxSendCount = 14     // stop resend the message after 14 times (~10 days)

type PeerStatusChangeEvent struct {
	PeerID    state.PeerID
	Status    EventStatus
	EventTime uint64
}

// Node represents an MVDS node, it runs all the logic like sending and receiving protocol messages.
type Node struct {
	// This needs to be declared first: https://github.com/golang/go/issues/9959
	epoch  int64
	ctx    context.Context
	cancel context.CancelFunc
	wg     sync.WaitGroup

	store     store.MessageStore
	transport transport.Transport

	syncState state.SyncState

	peers peers.Persistence

	payloads payloads

	nextEpoch CalculateNextEpoch

	ID state.PeerID

	epochPersistence EpochPersistence
	mode             Mode

	subscription chan protobuf.Message

	peerStatusChangeEvent chan PeerStatusChangeEvent

	logger *zap.Logger
}

type Persistence interface {
	MessageStore() store.MessageStore
	PeersStore() peers.Persistence
	StateStore() state.SyncState
	EpochStore() EpochPersistence
}

type sqlitePersistence struct {
	db *sql.DB
}

var _ Persistence = (*sqlitePersistence)(nil)

func NewSQLitePersistence(db *sql.DB) Persistence {
	return &sqlitePersistence{db: db}
}

func (p *sqlitePersistence) MessageStore() store.MessageStore {
	return store.NewPersistentMessageStore(p.db)
}

func (p *sqlitePersistence) PeersStore() peers.Persistence {
	return peers.NewSQLitePersistence(p.db)
}

func (p *sqlitePersistence) StateStore() state.SyncState {
	return state.NewPersistentSyncState(p.db)
}

func (p *sqlitePersistence) EpochStore() EpochPersistence {
	return NewEpochSQLitePersistence(p.db)
}

func NewPersistentNode(
	persistence Persistence,
	st transport.Transport,
	id state.PeerID,
	mode Mode,
	nextEpoch CalculateNextEpoch,
	peerStatusChangeEvent chan PeerStatusChangeEvent,
	logger *zap.Logger,
) (*Node, error) {
	ctx, cancel := context.WithCancel(context.Background())
	if logger == nil {
		logger = zap.NewNop()
	}

	node := Node{
		ID:                    id,
		ctx:                   ctx,
		cancel:                cancel,
		store:                 persistence.MessageStore(),
		transport:             st,
		peers:                 persistence.PeersStore(),
		syncState:             persistence.StateStore(),
		payloads:              newPayloads(),
		epochPersistence:      persistence.EpochStore(),
		nextEpoch:             nextEpoch,
		peerStatusChangeEvent: peerStatusChangeEvent,
		logger:                logger.Named("mvds"),
		mode:                  mode,
	}
	if currentEpoch, err := node.epochPersistence.Get(id); err != nil {
		return nil, err
	} else {
		node.epoch = currentEpoch
	}
	return &node, nil
}

func NewEphemeralNode(
	id state.PeerID,
	t transport.Transport,
	nextEpoch CalculateNextEpoch,
	currentEpoch int64,
	mode Mode,
	logger *zap.Logger,
) *Node {
	ctx, cancel := context.WithCancel(context.Background())
	if logger == nil {
		logger = zap.NewNop()
	}

	return &Node{
		ID:        id,
		ctx:       ctx,
		cancel:    cancel,
		store:     store.NewDummyStore(),
		transport: t,
		syncState: state.NewSyncState(),
		peers:     peers.NewMemoryPersistence(),
		payloads:  newPayloads(),
		nextEpoch: nextEpoch,
		epoch:     currentEpoch,
		logger:    logger.Named("mvds"),
		mode:      mode,
	}
}

// NewNode returns a new node.
func NewNode(
	ms store.MessageStore,
	st transport.Transport,
	ss state.SyncState,
	nextEpoch CalculateNextEpoch,
	currentEpoch int64,
	id state.PeerID,
	mode Mode,
	pp peers.Persistence,
	logger *zap.Logger,
) *Node {
	ctx, cancel := context.WithCancel(context.Background())
	if logger == nil {
		logger = zap.NewNop()
	}

	return &Node{
		ctx:       ctx,
		cancel:    cancel,
		store:     ms,
		transport: st,
		syncState: ss,
		peers:     pp,
		payloads:  newPayloads(),
		nextEpoch: nextEpoch,
		ID:        id,
		epoch:     currentEpoch,
		logger:    logger.Named("mvds"),
		mode:      mode,
	}
}

func (n *Node) CurrentEpoch() int64 {
	return atomic.LoadInt64(&n.epoch)
}

// Start listens for new messages received by the node and sends out those required every epoch.
func (n *Node) Start(duration time.Duration) {
	n.wg.Add(1)
	go func() {
		defer n.wg.Done()
		for {
			p, ok := n.transport.Watch(n.ctx)
			if !ok {
				n.logger.Debug("watching transport stopped")
				return
			}
			n.wg.Add(1)
			go func() {
				defer n.wg.Done()
				n.onPayload(p.Sender, p.Payload)
			}()
		}
	}()

	n.wg.Add(1)
	go func() {
		defer n.wg.Done()
		for {
			select {
			case <-n.ctx.Done():
				n.logger.Debug("reset data sync for peer stopped")
				return
			case event := <-n.peerStatusChangeEvent:
				if event.Status == OnlineStatus && event.EventTime > uint64(time.Now().Unix())-FreshEventPeriod {
					n.logger.Debug("resetting peer epoch", zap.String("peerID", hex.EncodeToString(event.PeerID[:4])))
					n.resetPeerEpoch(event.PeerID)
				}
			}
		}
	}()

	n.wg.Add(1)
	go func() {
		defer n.wg.Done()
		for {
			select {
			case <-n.ctx.Done():
				n.logger.Debug("epoch processing stopped")
				return
			case <-time.After(duration):
				err := n.sendMessages()
				if err != nil {
					n.logger.Error("error sending messages.", zap.Error(err))
				}
				err = n.syncState.Clear(MaxSendCount)
				if err != nil {
					n.logger.Error("error clearing sync state.", zap.Error(err))
				}
				atomic.AddInt64(&n.epoch, 1)
				// When a persistent node is used, the epoch needs to be saved.
				if n.epochPersistence != nil {
					if err := n.epochPersistence.Set(n.ID, n.epoch); err != nil {
						n.logger.Error("Failed to persisten epoch", zap.Error(err))
					}
				}
			}
		}
	}()
}

// Stop message reading and epoch processing
func (n *Node) Stop() {
	n.logger.Info("stopping node")
	n.Unsubscribe()
	n.cancel()
	n.wg.Wait()
}

// Subscribe subscribes to incoming messages.
func (n *Node) Subscribe() chan protobuf.Message {
	n.subscription = make(chan protobuf.Message)
	return n.subscription
}

// Unsubscribe closes the listening channels
func (n *Node) Unsubscribe() {
	if n.subscription != nil {
		close(n.subscription)
	}
	n.subscription = nil
}

// AppendMessage sends a message to a given group.
func (n *Node) AppendMessage(groupID state.GroupID, data []byte) (state.MessageID, error) {
	m := protobuf.Message{
		GroupId:   groupID[:],
		Timestamp: time.Now().Unix(),
		Body:      data,
	}

	id := m.ID()

	peers, err := n.peers.GetByGroupID(groupID)
	if err != nil {
		return state.MessageID{}, fmt.Errorf("trying to send to unknown group %x", groupID[:4])
	}

	err = n.store.Add(&m)
	if err != nil {
		return state.MessageID{}, err
	}

	for _, p := range peers {
		t := state.OFFER
		if n.mode == BATCH {
			t = state.MESSAGE
		}

		n.insertSyncState(&groupID, id, p, t)
	}

	n.logger.Debug("Sending message",
		zap.String("node", hex.EncodeToString(n.ID[:4])),
		zap.String("groupID", hex.EncodeToString(groupID[:4])),
		zap.String("id", hex.EncodeToString(id[:4])))
	// @todo think about a way to insta trigger send messages when send was selected, we don't wanna wait for ticks here

	return id, nil
}

// RequestMessage adds a REQUEST record to the next payload for a given message ID.
func (n *Node) RequestMessage(group state.GroupID, id state.MessageID) error {
	peers, err := n.peers.GetByGroupID(group)
	if err != nil {
		return fmt.Errorf("trying to request from an unknown group %x", group[:4])
	}

	for _, p := range peers {
		exist, err := n.IsPeerInGroup(group, p)
		if err != nil {
			return err
		}

		if exist {
			continue
		}

		n.insertSyncState(&group, id, p, state.REQUEST)
	}

	return nil
}

// AddPeer adds a peer to a specific group making it a recipient of messages.
func (n *Node) AddPeer(group state.GroupID, id state.PeerID) error {
	return n.peers.Add(group, id)
}

// IsPeerInGroup checks whether a peer is in the specified group.
func (n *Node) IsPeerInGroup(g state.GroupID, p state.PeerID) (bool, error) {
	return n.peers.Exists(g, p)
}

func (n *Node) sendMessages() error {
	err := n.syncState.Map(n.epoch, func(s state.State) state.State {
		m := s.MessageID
		p := s.PeerID
		switch s.Type {
		case state.OFFER:
			n.payloads.AddOffers(p, m[:])
		case state.REQUEST:
			n.payloads.AddRequests(p, m[:])
			n.logger.Debug("sending REQUEST",
				zap.String("from", hex.EncodeToString(n.ID[:4])),
				zap.String("to", hex.EncodeToString(p[:4])),
				zap.String("messageID", hex.EncodeToString(m[:4])),
			)

		case state.MESSAGE:
			g := *s.GroupID
			//  TODO: Handle errors
			exist, err := n.IsPeerInGroup(g, p)
			if err != nil {
				return s
			}

			if !exist {
				return s
			}

			msg, err := n.store.Get(m)
			if err != nil {
				n.logger.Error("failed to retreive message",
					zap.String("messageID", hex.EncodeToString(m[:4])),
					zap.Error(err),
				)

				return s
			}

			n.payloads.AddMessages(p, msg)
			n.logger.Debug("sending MESSAGE",
				zap.String("groupID", hex.EncodeToString(g[:4])),
				zap.String("from", hex.EncodeToString(n.ID[:4])),
				zap.String("to", hex.EncodeToString(p[:4])),
				zap.String("messageID", hex.EncodeToString(m[:4])),
			)

		}

		return n.updateSendEpoch(s)
	})

	if err != nil {
		n.logger.Error("error while mapping sync state", zap.Error(err))
		return err
	}

	return n.payloads.MapAndClear(func(peer state.PeerID, payload *protobuf.Payload) error {
		err := n.transport.Send(n.ID, peer, payload)
		if err != nil {
			n.logger.Error("error sending message", zap.Error(err))
			return err
		}
		return nil
	})

}

func (n *Node) onPayload(sender state.PeerID, payload *protobuf.Payload) {
	// Acks, Requests and Offers are all arrays of bytes as protobuf doesn't allow type aliases otherwise arrays of messageIDs would be nicer.
	if err := n.onAck(sender, payload.Acks); err != nil {
		n.logger.Error("error processing acks", zap.Error(err))
	}
	if err := n.onRequest(sender, payload.Requests); err != nil {
		n.logger.Error("error processing requests", zap.Error(err))
	}
	if err := n.onOffer(sender, payload.Offers); err != nil {
		n.logger.Error("error processing offers", zap.Error(err))
	}
	messageIds := n.onMessages(sender, payload.Messages)
	n.payloads.AddAcks(sender, messageIds)
}

func (n *Node) onOffer(sender state.PeerID, offers [][]byte) error {
	for _, raw := range offers {
		id := toMessageID(raw)
		n.logger.Debug("OFFER received",
			zap.String("from", hex.EncodeToString(sender[:4])),
			zap.String("to", hex.EncodeToString(n.ID[:4])),
			zap.String("messageID", hex.EncodeToString(id[:4])),
		)

		exist, err := n.store.Has(id)
		// @todo maybe ack?
		if err != nil {
			return err
		}

		if exist {
			continue
		}

		n.insertSyncState(nil, id, sender, state.REQUEST)
	}
	return nil
}

func (n *Node) onRequest(sender state.PeerID, requests [][]byte) error {
	for _, raw := range requests {
		id := toMessageID(raw)
		n.logger.Debug("REQUEST received",
			zap.String("from", hex.EncodeToString(sender[:4])),
			zap.String("to", hex.EncodeToString(n.ID[:4])),
			zap.String("messageID", hex.EncodeToString(id[:4])),
		)

		message, err := n.store.Get(id)
		if err != nil {
			return err
		}

		if message == nil {
			n.logger.Error("message does not exist", zap.String("messageID", hex.EncodeToString(id[:4])))
			continue
		}

		groupID := toGroupID(message.GroupId)

		exist, err := n.IsPeerInGroup(groupID, sender)
		if err != nil {
			return err
		}

		if !exist {
			n.logger.Error("peer is not in group",
				zap.String("groupID", hex.EncodeToString(groupID[:4])),
				zap.String("peer", hex.EncodeToString(sender[:4])),
			)
			continue
		}

		n.insertSyncState(&groupID, id, sender, state.MESSAGE)
	}

	return nil
}

func (n *Node) onAck(sender state.PeerID, acks [][]byte) error {
	for _, ack := range acks {
		id := toMessageID(ack)

		err := n.syncState.Remove(id, sender)
		if err != nil {
			n.logger.Error("Error while removing sync state.", zap.Error(err))
			return err
		}

		n.logger.Debug("ACK received",
			zap.String("from", hex.EncodeToString(sender[:4])),
			zap.String("to", hex.EncodeToString(n.ID[:4])),
			zap.String("messageID", hex.EncodeToString(id[:4])),
		)

	}
	return nil
}

func (n *Node) onMessages(sender state.PeerID, messages []*protobuf.Message) [][]byte {
	a := make([][]byte, 0)

	for _, m := range messages {
		groupID := toGroupID(m.GroupId)
		err := n.onMessage(sender, *m)
		if err != nil {
			n.logger.Error("Error processing message", zap.Error(err))
			continue
		}

		id := m.ID()
		n.logger.Debug("sending ACK",
			zap.String("groupID", hex.EncodeToString(groupID[:4])),
			zap.String("from", hex.EncodeToString(n.ID[:4])),
			zap.String("", hex.EncodeToString(sender[:4])),
			zap.String("messageID", hex.EncodeToString(id[:4])),
		)

		a = append(a, id[:])
	}

	return a
}

func (n *Node) onMessage(sender state.PeerID, msg protobuf.Message) error {
	id := msg.ID()
	groupID := toGroupID(msg.GroupId)
	n.logger.Debug("MESSAGE received",
		zap.String("from", hex.EncodeToString(sender[:4])),
		zap.String("to", hex.EncodeToString(n.ID[:4])),
		zap.String("messageID", hex.EncodeToString(id[:4])),
	)

	err := n.syncState.Remove(id, sender)
	if err != nil && err != state.ErrStateNotFound {
		return err
	}

	err = n.store.Add(&msg)
	if err != nil {
		return err
		// @todo process, should this function ever even have an error?
	}

	peers, err := n.peers.GetByGroupID(groupID)
	if err != nil {
		return err
	}

	for _, peer := range peers {
		if peer == sender {
			continue
		}

		n.insertSyncState(&groupID, id, peer, state.OFFER)
	}

	if n.subscription != nil {
		n.subscription <- msg
	}

	return nil
}

func (n *Node) insertSyncState(groupID *state.GroupID, messageID state.MessageID, peerID state.PeerID, t state.RecordType) {
	s := state.State{
		GroupID:   groupID,
		MessageID: messageID,
		PeerID:    peerID,
		Type:      t,
		SendEpoch: n.epoch + 1,
	}

	err := n.syncState.Add(s)
	if err != nil {
		n.logger.Error("error setting sync states",
			zap.Error(err),
			zap.String("groupID", hex.EncodeToString(groupID[:4])),
			zap.String("messageID", hex.EncodeToString(messageID[:4])),
			zap.String("peerID", hex.EncodeToString(peerID[:4])),
		)

	}
}

func (n *Node) updateSendEpoch(s state.State) state.State {
	s.SendCount += 1
	s.SendEpoch = n.nextEpoch(s.SendCount, n.epoch)
	return s
}

func (n *Node) resetPeerEpoch(peerID state.PeerID) {
	n.syncState.MapWithPeerId(peerID, func(s state.State) state.State {
		s.SendEpoch = n.epoch + int64(rand.Intn(60))
		return s
	})
}

func toMessageID(b []byte) state.MessageID {
	var id state.MessageID
	copy(id[:], b)
	return id
}

func toGroupID(b []byte) state.GroupID {
	var id state.GroupID
	copy(id[:], b)
	return id
}