package tunnel

import (
	"crypto/sha256"
	"errors"
	"fmt"
	"sync"

	"github.com/google/uuid"
	"github.com/micro/go-micro/network/link"
	"github.com/micro/go-micro/transport"
)

// tun represents a network tunnel
type tun struct {
	// the link on top of which we build a tunnel
	link link.Link

	sync.RWMutex

	// to indicate if we're connected or not
	connected bool

	// the send channel for all messages
	send chan *message

	// close channel
	closed chan bool

	// a map of sockets based on Micro-Tunnel-Id
	sockets map[string]*socket
}

// create new tunnel on top of a link
func newTunnel(link link.Link) *tun {
	return &tun{
		link:    link,
		send:    make(chan *message, 128),
		closed:  make(chan bool),
		sockets: make(map[string]*socket),
	}
}

// getSocket returns a socket from the internal socket map.
// It does this based on the Micro-Tunnel-Id and Micro-Tunnel-Session
func (t *tun) getSocket(id, session string) (*socket, bool) {
	// get the socket
	t.RLock()
	s, ok := t.sockets[id+session]
	t.RUnlock()
	return s, ok
}

// newSocket creates a new socket and saves it
func (t *tun) newSocket(id, session string) (*socket, bool) {
	// hash the id
	h := sha256.New()
	h.Write([]byte(id))
	id = fmt.Sprintf("%x", h.Sum(nil))

	// new socket
	s := &socket{
		id:      id,
		session: session,
		closed:  make(chan bool),
		recv:    make(chan *message, 128),
		send:    t.send,
		wait:    make(chan bool),
	}

	// save socket
	t.Lock()
	_, ok := t.sockets[id+session]
	if ok {
		// socket already exists
		t.Unlock()
		return nil, false
	}
	t.sockets[id+session] = s
	t.Unlock()

	// return socket
	return s, true
}

// TODO: use tunnel id as part of the session
func (t *tun) newSession() string {
	return uuid.New().String()
}

// process outgoing messages sent by all local sockets
func (t *tun) process() {
	// manage the send buffer
	// all pseudo sockets throw everything down this
	for {
		select {
		case msg := <-t.send:
			nmsg := &transport.Message{
				Header: msg.data.Header,
				Body:   msg.data.Body,
			}

			// set the tunnel id on the outgoing message
			nmsg.Header["Micro-Tunnel-Id"] = msg.id

			// set the session id
			nmsg.Header["Micro-Tunnel-Session"] = msg.session

			// send the message via the interface
			if err := t.link.Send(nmsg); err != nil {
				// no op
				// TODO: do something
			}
		case <-t.closed:
			return
		}
	}
}

// process incoming messages
func (t *tun) listen() {
	for {
		// process anything via the net interface
		msg := new(transport.Message)
		err := t.link.Recv(msg)
		if err != nil {
			return
		}

		// first check Micro-Tunnel
		switch msg.Header["Micro-Tunnel"] {
		case "connect":
			// assuming new connection
			// TODO: do something with this
			continue
		case "close":
			// assuming connection closed
			// TODO: do something with this
			continue
		}

		// the tunnel id
		id := msg.Header["Micro-Tunnel-Id"]

		// the session id
		session := msg.Header["Micro-Tunnel-Session"]

		// if the session id is blank there's nothing we can do
		// TODO: check this is the case, is there any reason
		// why we'd have a blank session? Is the tunnel
		// used for some other purpose?
		if len(id) == 0 || len(session) == 0 {
			continue
		}

		// get the socket based on the tunnel id and session
		// this could be something we dialed in which case
		// we have a session for it otherwise its a listener
		s, exists := t.getSocket(id, session)
		if !exists {
			// try get it based on just the tunnel id
			// the assumption here is that a listener
			// has no session but its set a listener session
			s, exists = t.getSocket(id, "listener")
			if !exists {
				// drop it, we don't care about
				// messages we don't know about
				continue
			}
		}

		// is the socket closed?
		select {
		case <-s.closed:
			// closed
			delete(t.sockets, id)
			continue
		default:
			// process
		}

		// is the socket new?
		select {
		// if its new the socket is actually blocked waiting
		// for a connection. so we check if its waiting.
		case <-s.wait:
		// if its waiting e.g its new then we close it
		default:
			// set remote address of the socket
			s.remote = msg.Header["Remote"]
			close(s.wait)
		}

		// construct a new transport message
		tmsg := &transport.Message{
			Header: msg.Header,
			Body:   msg.Body,
		}

		// construct the internal message
		imsg := &message{
			id:      id,
			session: session,
			data:    tmsg,
		}

		// append to recv backlog
		// we don't block if we can't pass it on
		select {
		case s.recv <- imsg:
		default:
		}
	}
}

func (t *tun) connect() error {
	return t.link.Send(&transport.Message{
		Header: map[string]string{
			"Micro-Tunnel": "connect",
		},
	})
}

func (t *tun) close() error {
	return t.link.Send(&transport.Message{
		Header: map[string]string{
			"Micro-Tunnel": "close",
		},
	})
}

// Close the tunnel
func (t *tun) Close() error {
	t.Lock()
	defer t.Unlock()

	if !t.connected {
		return nil
	}

	select {
	case <-t.closed:
		return nil
	default:
		// close all the sockets
		for _, s := range t.sockets {
			s.Close()
		}
		// close the connection
		close(t.closed)
		t.connected = false

		// send a close message
		// we don't close the link
		// just the tunnel
		return t.close()
	}

	return nil
}

// Connect the tunnel
func (t *tun) Connect() error {
	t.Lock()
	defer t.Unlock()

	// already connected
	if t.connected {
		return nil
	}

	// send the connect message
	if err := t.connect(); err != nil {
		return err
	}

	// set as connected
	t.connected = true
	// create new close channel
	t.closed = make(chan bool)

	// process messages to be sent
	go t.process()
	// process incoming messages
	go t.listen()

	return nil
}

// Dial an address
func (t *tun) Dial(addr string) (Conn, error) {
	c, ok := t.newSocket(addr, t.newSession())
	if !ok {
		return nil, errors.New("error dialing " + addr)
	}
	// set remote
	c.remote = addr
	// set local
	c.local = t.link.Local()

	return c, nil
}

// Accept a connection on the address
func (t *tun) Listen(addr string) (Listener, error) {
	// create a new socket by hashing the address
	c, ok := t.newSocket(addr, "listener")
	if !ok {
		return nil, errors.New("already listening on " + addr)
	}

	// set remote. it will be replaced by the first message received
	c.remote = t.link.Remote()
	// set local
	c.local = addr

	tl := &tunListener{
		addr: addr,
		// the accept channel
		accept: make(chan *socket, 128),
		// the channel to close
		closed: make(chan bool),
		// the connection
		conn: c,
		// the listener socket
		socket: c,
	}

	// this kicks off the internal message processor
	// for the listener so it can create pseudo sockets
	// per session if they do not exist or pass messages
	// to the existign sessions
	go tl.process()

	// return the listener
	return tl, nil
}