package client

import (
	"context"
	"fmt"
	"io"
	"net"
	"sync"
	"time"

	log "github.com/sirupsen/logrus"

	auth "github.com/netbirdio/netbird/relay/auth/hmac"
	"github.com/netbirdio/netbird/relay/client/dialer/ws"
	"github.com/netbirdio/netbird/relay/healthcheck"
	"github.com/netbirdio/netbird/relay/messages"
)

const (
	bufferSize            = 8820
	serverResponseTimeout = 8 * time.Second
)

var (
	ErrConnAlreadyExists = fmt.Errorf("connection already exists")
)

type internalStopFlag struct {
	sync.Mutex
	stop bool
}

func newInternalStopFlag() *internalStopFlag {
	return &internalStopFlag{}
}

func (isf *internalStopFlag) set() {
	isf.Lock()
	defer isf.Unlock()
	isf.stop = true
}

func (isf *internalStopFlag) isSet() bool {
	isf.Lock()
	defer isf.Unlock()
	return isf.stop
}

// Msg carry the payload from the server to the client. With this struct, the net.Conn can free the buffer.
type Msg struct {
	Payload []byte

	bufPool *sync.Pool
	bufPtr  *[]byte
}

func (m *Msg) Free() {
	m.bufPool.Put(m.bufPtr)
}

type connContainer struct {
	conn        *Conn
	messages    chan Msg
	msgChanLock sync.Mutex
	closed      bool // flag to check if channel is closed
	ctx         context.Context
	cancel      context.CancelFunc
}

func newConnContainer(conn *Conn, messages chan Msg) *connContainer {
	ctx, cancel := context.WithCancel(context.Background())

	return &connContainer{
		conn:     conn,
		messages: messages,
		ctx:      ctx,
		cancel:   cancel,
	}
}

func (cc *connContainer) writeMsg(msg Msg) {
	cc.msgChanLock.Lock()
	defer cc.msgChanLock.Unlock()

	if cc.closed {
		msg.Free()
		return
	}

	select {
	case cc.messages <- msg:
	case <-cc.ctx.Done():
		msg.Free()
	}
}

func (cc *connContainer) close() {
	cc.cancel()

	cc.msgChanLock.Lock()
	defer cc.msgChanLock.Unlock()

	if cc.closed {
		return
	}

	cc.closed = true
	close(cc.messages)

	for msg := range cc.messages {
		msg.Free()
	}
}

// Client is a client for the relay server. It is responsible for establishing a connection to the relay server and
// managing connections to other peers. All exported functions are safe to call concurrently. After close the connection,
// the client can be reused by calling Connect again. When the client is closed, all connections are closed too.
// While the Connect is in progress, the OpenConn function will block until the connection is established with relay server.
type Client struct {
	log            *log.Entry
	parentCtx      context.Context
	connectionURL  string
	authTokenStore *auth.TokenStore
	hashedID       []byte

	bufPool *sync.Pool

	relayConn        net.Conn
	conns            map[string]*connContainer
	serviceIsRunning bool
	mu               sync.Mutex // protect serviceIsRunning and conns
	readLoopMutex    sync.Mutex
	wgReadLoop       sync.WaitGroup
	instanceURL      *RelayAddr
	muInstanceURL    sync.Mutex

	onDisconnectListener func()
	listenerMutex        sync.Mutex
}

// NewClient creates a new client for the relay server. The client is not connected to the server until the Connect
func NewClient(ctx context.Context, serverURL string, authTokenStore *auth.TokenStore, peerID string) *Client {
	hashedID, hashedStringId := messages.HashID(peerID)
	return &Client{
		log:            log.WithField("client_id", hashedStringId),
		parentCtx:      ctx,
		connectionURL:  serverURL,
		authTokenStore: authTokenStore,
		hashedID:       hashedID,
		bufPool: &sync.Pool{
			New: func() any {
				buf := make([]byte, bufferSize)
				return &buf
			},
		},
		conns: make(map[string]*connContainer),
	}
}

// Connect establishes a connection to the relay server. It blocks until the connection is established or an error occurs.
func (c *Client) Connect() error {
	c.log.Infof("connecting to relay server: %s", c.connectionURL)
	c.readLoopMutex.Lock()
	defer c.readLoopMutex.Unlock()

	c.mu.Lock()
	defer c.mu.Unlock()

	if c.serviceIsRunning {
		return nil
	}

	err := c.connect()
	if err != nil {
		return err
	}

	c.serviceIsRunning = true

	c.wgReadLoop.Add(1)
	go c.readLoop(c.relayConn)

	c.log.Infof("relay connection established with: %s", c.connectionURL)
	return nil
}

// OpenConn create a new net.Conn for the destination peer ID. In case if the connection is in progress
// to the relay server, the function will block until the connection is established or timed out. Otherwise,
// it will return immediately.
// todo: what should happen if call with the same peerID with multiple times?
func (c *Client) OpenConn(dstPeerID string) (net.Conn, error) {
	c.mu.Lock()
	defer c.mu.Unlock()

	if !c.serviceIsRunning {
		return nil, fmt.Errorf("relay connection is not established")
	}

	hashedID, hashedStringID := messages.HashID(dstPeerID)
	_, ok := c.conns[hashedStringID]
	if ok {
		return nil, ErrConnAlreadyExists
	}

	log.Infof("open connection to peer: %s", hashedStringID)
	msgChannel := make(chan Msg, 2)
	conn := NewConn(c, hashedID, hashedStringID, msgChannel, c.instanceURL)

	c.conns[hashedStringID] = newConnContainer(conn, msgChannel)
	return conn, nil
}

// ServerInstanceURL returns the address of the relay server. It could change after the close and reopen the connection.
func (c *Client) ServerInstanceURL() (string, error) {
	c.muInstanceURL.Lock()
	defer c.muInstanceURL.Unlock()
	if c.instanceURL == nil {
		return "", fmt.Errorf("relay connection is not established")
	}
	return c.instanceURL.String(), nil
}

// SetOnDisconnectListener sets a function that will be called when the connection to the relay server is closed.
func (c *Client) SetOnDisconnectListener(fn func()) {
	c.listenerMutex.Lock()
	defer c.listenerMutex.Unlock()
	c.onDisconnectListener = fn
}

// HasConns returns true if there are connections.
func (c *Client) HasConns() bool {
	c.mu.Lock()
	defer c.mu.Unlock()
	return len(c.conns) > 0
}

// Close closes the connection to the relay server and all connections to other peers.
func (c *Client) Close() error {
	return c.close(true)
}

func (c *Client) connect() error {
	conn, err := ws.Dial(c.connectionURL)
	if err != nil {
		return err
	}
	c.relayConn = conn

	err = c.handShake()
	if err != nil {
		cErr := conn.Close()
		if cErr != nil {
			log.Errorf("failed to close connection: %s", cErr)
		}
		return err
	}

	return nil
}

func (c *Client) handShake() error {
	msg, err := messages.MarshalAuthMsg(c.hashedID, c.authTokenStore.TokenBinary())
	if err != nil {
		log.Errorf("failed to marshal auth message: %s", err)
		return err
	}

	_, err = c.relayConn.Write(msg)
	if err != nil {
		log.Errorf("failed to send auth message: %s", err)
		return err
	}
	buf := make([]byte, messages.MaxHandshakeRespSize)
	n, err := c.readWithTimeout(buf)
	if err != nil {
		log.Errorf("failed to read auth response: %s", err)
		return err
	}

	_, err = messages.ValidateVersion(buf[:n])
	if err != nil {
		return fmt.Errorf("validate version: %w", err)
	}

	msgType, err := messages.DetermineServerMessageType(buf[messages.SizeOfVersionByte:n])
	if err != nil {
		log.Errorf("failed to determine message type: %s", err)
		return err
	}

	if msgType != messages.MsgTypeAuthResponse {
		log.Errorf("unexpected message type: %s", msgType)
		return fmt.Errorf("unexpected message type")
	}

	addr, err := messages.UnmarshalAuthResponse(buf[messages.SizeOfProtoHeader:n])
	if err != nil {
		return err
	}

	c.muInstanceURL.Lock()
	c.instanceURL = &RelayAddr{addr: addr}
	c.muInstanceURL.Unlock()
	return nil
}

func (c *Client) readLoop(relayConn net.Conn) {
	internallyStoppedFlag := newInternalStopFlag()
	hc := healthcheck.NewReceiver()
	go c.listenForStopEvents(hc, relayConn, internallyStoppedFlag)

	var (
		errExit error
		n       int
	)
	for {
		bufPtr := c.bufPool.Get().(*[]byte)
		buf := *bufPtr
		n, errExit = relayConn.Read(buf)
		if errExit != nil {
			c.mu.Lock()
			if c.serviceIsRunning && !internallyStoppedFlag.isSet() {
				c.log.Debugf("failed to read message from relay server: %s", errExit)
			}
			c.mu.Unlock()
			break
		}

		_, err := messages.ValidateVersion(buf[:n])
		if err != nil {
			c.log.Errorf("failed to validate protocol version: %s", err)
			c.bufPool.Put(bufPtr)
			continue
		}

		msgType, err := messages.DetermineServerMessageType(buf[messages.SizeOfVersionByte:n])
		if err != nil {
			c.log.Errorf("failed to determine message type: %s", err)
			c.bufPool.Put(bufPtr)
			continue
		}

		if !c.handleMsg(msgType, buf[messages.SizeOfProtoHeader:n], bufPtr, hc, internallyStoppedFlag) {
			break
		}
	}

	hc.Stop()

	c.muInstanceURL.Lock()
	c.instanceURL = nil
	c.muInstanceURL.Unlock()

	c.notifyDisconnected()
	c.wgReadLoop.Done()
	_ = c.close(false)
}

func (c *Client) handleMsg(msgType messages.MsgType, buf []byte, bufPtr *[]byte, hc *healthcheck.Receiver, internallyStoppedFlag *internalStopFlag) (continueLoop bool) {
	switch msgType {
	case messages.MsgTypeHealthCheck:
		c.handleHealthCheck(hc, internallyStoppedFlag)
		c.bufPool.Put(bufPtr)
	case messages.MsgTypeTransport:
		return c.handleTransportMsg(buf, bufPtr, internallyStoppedFlag)
	case messages.MsgTypeClose:
		log.Debugf("relay connection close by server")
		c.bufPool.Put(bufPtr)
		return false
	}

	return true
}

func (c *Client) handleHealthCheck(hc *healthcheck.Receiver, internallyStoppedFlag *internalStopFlag) {
	msg := messages.MarshalHealthcheck()
	_, wErr := c.relayConn.Write(msg)
	if wErr != nil {
		if c.serviceIsRunning && !internallyStoppedFlag.isSet() {
			c.log.Errorf("failed to send heartbeat: %s", wErr)
		}
	}
	hc.Heartbeat()
}

func (c *Client) handleTransportMsg(buf []byte, bufPtr *[]byte, internallyStoppedFlag *internalStopFlag) bool {
	peerID, payload, err := messages.UnmarshalTransportMsg(buf)
	if err != nil {
		if c.serviceIsRunning && !internallyStoppedFlag.isSet() {
			c.log.Errorf("failed to parse transport message: %v", err)
		}

		c.bufPool.Put(bufPtr)
		return true
	}

	stringID := messages.HashIDToString(peerID)

	c.mu.Lock()
	if !c.serviceIsRunning {
		c.mu.Unlock()
		c.bufPool.Put(bufPtr)
		return false
	}
	container, ok := c.conns[stringID]
	c.mu.Unlock()
	if !ok {
		c.log.Errorf("peer not found: %s", stringID)
		c.bufPool.Put(bufPtr)
		return true
	}
	msg := Msg{
		bufPool: c.bufPool,
		bufPtr:  bufPtr,
		Payload: payload,
	}
	container.writeMsg(msg)
	return true
}

func (c *Client) writeTo(connReference *Conn, id string, dstID []byte, payload []byte) (int, error) {
	c.mu.Lock()
	conn, ok := c.conns[id]
	c.mu.Unlock()
	if !ok {
		return 0, io.EOF
	}

	if conn.conn != connReference {
		return 0, io.EOF
	}

	// todo: use buffer pool instead of create new transport msg.
	msg, err := messages.MarshalTransportMsg(dstID, payload)
	if err != nil {
		log.Errorf("failed to marshal transport message: %s", err)
		return 0, err
	}

	// the write always return with 0 length because the underling does not support the size feedback.
	_, err = c.relayConn.Write(msg)
	if err != nil {
		log.Errorf("failed to write transport message: %s", err)
	}
	return len(payload), err
}

func (c *Client) listenForStopEvents(hc *healthcheck.Receiver, conn net.Conn, internalStopFlag *internalStopFlag) {
	for {
		select {
		case _, ok := <-hc.OnTimeout:
			if !ok {
				return
			}
			c.log.Errorf("health check timeout")
			internalStopFlag.set()
			_ = conn.Close() // ignore the err because the readLoop will handle it
			return
		case <-c.parentCtx.Done():
			err := c.close(true)
			if err != nil {
				log.Errorf("failed to teardown connection: %s", err)
			}
			return
		}
	}
}

func (c *Client) closeAllConns() {
	for _, container := range c.conns {
		container.close()
	}
	c.conns = make(map[string]*connContainer)
}

func (c *Client) closeConn(connReference *Conn, id string) error {
	c.mu.Lock()
	defer c.mu.Unlock()

	container, ok := c.conns[id]
	if !ok {
		return fmt.Errorf("connection already closed")
	}

	if container.conn != connReference {
		return fmt.Errorf("conn reference mismatch")
	}
	delete(c.conns, id)
	container.close()

	return nil
}

func (c *Client) close(gracefullyExit bool) error {
	c.readLoopMutex.Lock()
	defer c.readLoopMutex.Unlock()

	c.mu.Lock()
	var err error
	if !c.serviceIsRunning {
		c.mu.Unlock()
		return nil
	}

	c.serviceIsRunning = false
	c.closeAllConns()
	if gracefullyExit {
		c.writeCloseMsg()
	}
	err = c.relayConn.Close()
	c.mu.Unlock()

	c.wgReadLoop.Wait()
	c.log.Infof("relay connection closed with: %s", c.connectionURL)
	return err
}

func (c *Client) notifyDisconnected() {
	c.listenerMutex.Lock()
	defer c.listenerMutex.Unlock()

	if c.onDisconnectListener == nil {
		return
	}
	go c.onDisconnectListener()
}

func (c *Client) writeCloseMsg() {
	msg := messages.MarshalCloseMsg()
	_, err := c.relayConn.Write(msg)
	if err != nil {
		c.log.Errorf("failed to send close message: %s", err)
	}
}

func (c *Client) readWithTimeout(buf []byte) (int, error) {
	ctx, cancel := context.WithTimeout(c.parentCtx, serverResponseTimeout)
	defer cancel()

	readDone := make(chan struct{})
	var (
		n   int
		err error
	)

	go func() {
		n, err = c.relayConn.Read(buf)
		close(readDone)
	}()

	select {
	case <-ctx.Done():
		return 0, fmt.Errorf("read operation timed out")
	case <-readDone:
		return n, err
	}
}