package websocket

import (
	"encoding/json"
	"fmt"
	"sync"

	log "github.com/sirupsen/logrus"

	"github.com/vapor/event"
	"github.com/vapor/protocol"
	"github.com/vapor/protocol/bc"
	"github.com/vapor/protocol/bc/types"
)

// Notification types
type notificationBlockConnected types.Block
type notificationBlockDisconnected types.Block
type notificationTxDescAcceptedByMempool protocol.TxDesc

// Notification control requests
type notificationRegisterClient WSClient
type notificationUnregisterClient WSClient
type notificationRegisterBlocks WSClient
type notificationUnregisterBlocks WSClient
type notificationRegisterNewMempoolTxs WSClient
type notificationUnregisterNewMempoolTxs WSClient

// NotificationType represents the type of a notification message.
type NotificationType int

// Constants for the type of a notification message.
const (
	// NTBlockConnected indicates the associated block was connected to the main chain.
	NTRawBlockConnected NotificationType = iota
	// NTBlockDisconnected indicates the associated block was disconnected  from the main chain.
	NTRawBlockDisconnected
	NTNewTransaction
	NTRequestStatus
)

// notificationTypeStrings is a map of notification types back to their constant
// names for pretty printing.
var notificationTypeStrings = map[NotificationType]string{
	NTRawBlockConnected:    "raw_blocks_connected",
	NTRawBlockDisconnected: "raw_blocks_disconnected",
	NTNewTransaction:       "new_transaction",
	NTRequestStatus:        "request_status",
}

// String returns the NotificationType in human-readable form.
func (n NotificationType) String() string {
	if s, ok := notificationTypeStrings[n]; ok {
		return s
	}
	return fmt.Sprintf("Unknown Notification Type (%d)", int(n))
}

type statusInfo struct {
	BestHeight uint64
	BestHash   bc.Hash
}

// WSNotificationManager is a connection and notification manager used for
// websockets.  It allows websocket clients to register for notifications they
// are interested in.  When an event happens elsewhere in the code such as
// transactions being added to the memory pool or block connects/disconnects,
// the notification manager is provided with the relevant details needed to
// figure out which websocket clients need to be notified based on what they
// have registered for and notifies them accordingly.  It is also used to keep
// track of all connected websocket clients.
type WSNotificationManager struct {
	// queueNotification queues a notification for handling.
	queueNotification chan interface{}

	// notificationMsgs feeds notificationHandler with notifications
	// and client (un)registeration requests from a queue as well as
	// registeration and unregisteration requests from clients.
	notificationMsgs chan interface{}

	// Access channel for current number of connected clients.
	numClients chan int

	// Shutdown handling
	wg                   sync.WaitGroup
	quit                 chan struct{}
	MaxNumWebsockets     int
	maxNumConcurrentReqs int
	status               statusInfo
	chain                *protocol.Chain
	eventDispatcher      *event.Dispatcher
	txMsgSub             *event.Subscription
}

// NewWsNotificationManager returns a new notification manager ready for use. See WSNotificationManager for more details.
func NewWsNotificationManager(maxNumWebsockets int, maxNumConcurrentReqs int, chain *protocol.Chain, dispatcher *event.Dispatcher) *WSNotificationManager {
	// init status
	var status statusInfo
	header := chain.BestBlockHeader()
	status.BestHeight = header.Height
	status.BestHash = header.Hash()

	return &WSNotificationManager{
		queueNotification:    make(chan interface{}),
		notificationMsgs:     make(chan interface{}),
		numClients:           make(chan int),
		quit:                 make(chan struct{}),
		MaxNumWebsockets:     maxNumWebsockets,
		maxNumConcurrentReqs: maxNumConcurrentReqs,
		status:               status,
		chain:                chain,
		eventDispatcher:      dispatcher,
	}
}

// queueHandler manages a queue of empty interfaces, reading from in and
// sending the oldest unsent to out.  This handler stops when either of the
// in or quit channels are closed, and closes out before returning, without
// waiting to send any variables still remaining in the queue.
func queueHandler(in <-chan interface{}, out chan<- interface{}, quit <-chan struct{}) {
	var (
		q       []interface{}
		next    interface{}
		dequeue chan<- interface{}
	)

	skipQueue := out

out:
	for {
		select {
		case n, ok := <-in:
			if !ok {
				// Sender closed input channel.
				break out
			}

			// Either send to out immediately if skipQueue is
			// non-nil (queue is empty) and reader is ready,
			// or append to the queue and send later.
			select {
			case skipQueue <- n:

			default:
				q = append(q, n)
				dequeue = out
				skipQueue = nil
				next = q[0]
			}

		case dequeue <- next:
			copy(q, q[1:])
			q[len(q)-1] = nil // avoid leak
			q = q[:len(q)-1]
			if len(q) == 0 {
				dequeue = nil
				skipQueue = out
			} else {
				next = q[0]
			}

		case <-quit:
			break out
		}
	}
	close(out)
}

func (m *WSNotificationManager) sendNotification(typ NotificationType, data interface{}) {
	switch typ {
	case NTRawBlockConnected:
		block, ok := data.(*types.Block)
		if !ok {
			log.WithField("module", logModule).Error("Chain connected notification is not a block")
			break
		}
		m.status.BestHeight = block.Height
		m.status.BestHash = block.Hash()
		// Notify registered websocket clients of incoming block.
		m.NotifyBlockConnected(block)

	case NTRawBlockDisconnected:
		block, ok := data.(*types.Block)
		if !ok {
			log.WithField("module", logModule).Error("Chain disconnected notification is not a block")
			break
		}
		m.status.BestHeight = block.Height - 1
		m.status.BestHash = block.PreviousBlockHash
		// Notify registered websocket clients.
		m.NotifyBlockDisconnected(block)
	}
}

// queueHandler maintains a queue of notifications and notification handler
// control messages.
func (m *WSNotificationManager) queueHandler() {
	queueHandler(m.queueNotification, m.notificationMsgs, m.quit)
	m.wg.Done()
}

// NotifyBlockConnected passes a block newly-connected to the best chain
// to the notification manager for block and transaction notification
// processing.
func (m *WSNotificationManager) NotifyBlockConnected(block *types.Block) {
	select {
	case m.queueNotification <- (*notificationBlockConnected)(block):
	case <-m.quit:
	}
}

// NotifyBlockDisconnected passes a block disconnected from the best chain
// to the notification manager for block notification processing.
func (m *WSNotificationManager) NotifyBlockDisconnected(block *types.Block) {
	select {
	case m.queueNotification <- (*notificationBlockDisconnected)(block):
	case <-m.quit:
	}
}

// memPoolTxQueryLoop constantly pass a transaction accepted by mempool to the
// notification manager for transaction notification processing.
func (m *WSNotificationManager) memPoolTxQueryLoop() {
out:
	for {
		select {
		case obj, ok := <-m.txMsgSub.Chan():
			if !ok {
				log.WithFields(log.Fields{"module": logModule}).Warning("tx pool tx msg subscription channel closed")
				break out
			}

			ev, ok := obj.Data.(protocol.TxMsgEvent)
			if !ok {
				log.WithFields(log.Fields{"module": logModule}).Error("event type error")
				continue
			}

			if ev.TxMsg.MsgType == protocol.MsgNewTx {
				select {
				case m.queueNotification <- (*notificationTxDescAcceptedByMempool)(ev.TxMsg.TxDesc):
				default:
				}
			}
		case <-m.quit:
			break out
		}
	}

	m.wg.Done()
}

// notificationHandler reads notifications and control messages from the queue handler and processes one at a time.
func (m *WSNotificationManager) notificationHandler() {
	// clients is a map of all currently connected websocket clients.
	clients := make(map[chan struct{}]*WSClient)
	blockNotifications := make(map[chan struct{}]*WSClient)
	txNotifications := make(map[chan struct{}]*WSClient)

out:
	for {
		select {
		case n, ok := <-m.notificationMsgs:
			if !ok {
				break out
			}
			switch n := n.(type) {
			case *notificationBlockConnected:
				block := (*types.Block)(n)
				if len(blockNotifications) != 0 {
					m.notifyBlockConnected(blockNotifications, block)
				}

			case *notificationBlockDisconnected:
				block := (*types.Block)(n)
				if len(blockNotifications) != 0 {
					m.notifyBlockDisconnected(blockNotifications, block)
				}

			case *notificationTxDescAcceptedByMempool:
				txDesc := (*protocol.TxDesc)(n)
				if len(txNotifications) != 0 {
					m.notifyForNewTx(txNotifications, txDesc)
				}

			case *notificationRegisterBlocks:
				wsc := (*WSClient)(n)
				blockNotifications[wsc.quit] = wsc

			case *notificationUnregisterBlocks:
				wsc := (*WSClient)(n)
				delete(blockNotifications, wsc.quit)

			case *notificationRegisterNewMempoolTxs:
				wsc := (*WSClient)(n)
				txNotifications[wsc.quit] = wsc

			case *notificationUnregisterNewMempoolTxs:
				wsc := (*WSClient)(n)
				delete(txNotifications, wsc.quit)

			case *notificationRegisterClient:
				wsc := (*WSClient)(n)
				clients[wsc.quit] = wsc

			case *notificationUnregisterClient:
				wsc := (*WSClient)(n)
				delete(blockNotifications, wsc.quit)
				delete(txNotifications, wsc.quit)
				delete(clients, wsc.quit)

			default:
				log.Warnf("Unhandled notification type")
			}

		case m.numClients <- len(clients):

		case <-m.quit:
			break out
		}
	}

	for _, c := range clients {
		c.Disconnect()
	}
	m.wg.Done()
}

// NumClients returns the number of clients actively being served.
func (m *WSNotificationManager) NumClients() (n int) {
	select {
	case n = <-m.numClients:
	case <-m.quit:
	}
	return
}

// IsMaxConnect returns whether the maximum connection is exceeded
func (m *WSNotificationManager) IsMaxConnect() bool {
	return m.NumClients() >= m.MaxNumWebsockets
}

// RegisterBlockUpdates requests block update notifications to the passed websocket client.
func (m *WSNotificationManager) RegisterBlockUpdates(wsc *WSClient) {
	m.queueNotification <- (*notificationRegisterBlocks)(wsc)
}

// UnregisterBlockUpdates removes block update notifications for the passed websocket client.
func (m *WSNotificationManager) UnregisterBlockUpdates(wsc *WSClient) {
	m.queueNotification <- (*notificationUnregisterBlocks)(wsc)
}

// notifyBlockConnected notifies websocket clients that have registered for block updates when a block is connected to the main chain.
func (*WSNotificationManager) notifyBlockConnected(clients map[chan struct{}]*WSClient, block *types.Block) {
	resp := NewWSResponse(NTRawBlockConnected.String(), block, nil)
	marshalledJSON, err := json.Marshal(resp)
	if err != nil {
		log.WithFields(log.Fields{"module": logModule, "error": err}).Error("Failed to marshal block connected notification")
		return
	}

	for _, wsc := range clients {
		wsc.QueueNotification(marshalledJSON)
	}
}

// notifyBlockDisconnected notifies websocket clients that have registered for block updates
// when a block is disconnected from the main chain (due to a reorganize).
func (*WSNotificationManager) notifyBlockDisconnected(clients map[chan struct{}]*WSClient, block *types.Block) {
	resp := NewWSResponse(NTRawBlockDisconnected.String(), block, nil)
	marshalledJSON, err := json.Marshal(resp)
	if err != nil {
		log.WithField("error", err).Error("Failed to marshal block Disconnected notification")
		return
	}

	for _, wsc := range clients {
		wsc.QueueNotification(marshalledJSON)
	}
}

// RegisterNewMempoolTxsUpdates requests notifications to the passed websocket
// client when new transactions are added to the memory pool.
func (m *WSNotificationManager) RegisterNewMempoolTxsUpdates(wsc *WSClient) {
	m.queueNotification <- (*notificationRegisterNewMempoolTxs)(wsc)
}

// UnregisterNewMempoolTxsUpdates removes notifications to the passed websocket
// client when new transaction are added to the memory pool.
func (m *WSNotificationManager) UnregisterNewMempoolTxsUpdates(wsc *WSClient) {
	m.queueNotification <- (*notificationUnregisterNewMempoolTxs)(wsc)
}

// notifyForNewTx notifies websocket clients that have registered for updates
// when a new transaction is added to the memory pool.
func (m *WSNotificationManager) notifyForNewTx(clients map[chan struct{}]*WSClient, txDesc *protocol.TxDesc) {
	resp := NewWSResponse(NTNewTransaction.String(), txDesc, nil)
	marshalledJSON, err := json.Marshal(resp)
	if err != nil {
		log.WithFields(log.Fields{"module": logModule, "error": err}).Error("Failed to marshal tx notification")
		return
	}

	for _, wsc := range clients {
		wsc.QueueNotification(marshalledJSON)
	}
}

// AddClient adds the passed websocket client to the notification manager.
func (m *WSNotificationManager) AddClient(wsc *WSClient) {
	m.queueNotification <- (*notificationRegisterClient)(wsc)
}

// RemoveClient removes the passed websocket client and all notifications registered for it.
func (m *WSNotificationManager) RemoveClient(wsc *WSClient) {
	select {
	case m.queueNotification <- (*notificationUnregisterClient)(wsc):
	case <-m.quit:
	}
}

func (m *WSNotificationManager) blockNotify() {
out:
	for {
		select {
		case <-m.quit:
			break out

		default:
		}
		for !m.chain.InMainChain(m.status.BestHash) {
			block, err := m.chain.GetBlockByHash(&m.status.BestHash)
			if err != nil {
				log.WithFields(log.Fields{"module": logModule, "err": err}).Error("blockNotify GetBlockByHash")
				return
			}

			m.sendNotification(NTRawBlockDisconnected, block)
		}

		block, _ := m.chain.GetBlockByHeight(m.status.BestHeight + 1)
		if block == nil {
			m.blockWaiter()
			continue
		}

		if m.status.BestHash != block.PreviousBlockHash {
			log.WithFields(log.Fields{"module": logModule, "blockHeight": block.Height, "previousBlockHash": m.status.BestHash, "rcvBlockPrevHash": block.PreviousBlockHash}).Warning("The previousBlockHash of the received block is not the same as the hash of the previous block")
			continue
		}

		m.sendNotification(NTRawBlockConnected, block)
	}
	m.wg.Done()
}

func (m *WSNotificationManager) blockWaiter() {
	select {
	case <-m.chain.BlockWaiter(m.status.BestHeight + 1):
	case <-m.quit:
	}
}

// Start starts the goroutines required for the manager to queue and process websocket client notifications.
func (m *WSNotificationManager) Start() error {
	var err error
	m.txMsgSub, err = m.eventDispatcher.Subscribe(protocol.TxMsgEvent{})
	if err != nil {
		return err
	}

	m.wg.Add(4)
	go m.blockNotify()
	go m.queueHandler()
	go m.notificationHandler()
	go m.memPoolTxQueryLoop()
	return nil
}

// WaitForShutdown blocks until all notification manager goroutines have finished.
func (m *WSNotificationManager) WaitForShutdown() {
	m.wg.Wait()
}

// Shutdown shuts down the manager, stopping the notification queue and notification handler goroutines.
func (m *WSNotificationManager) Shutdown() {
	close(m.quit)
}