package notify

import (
	cryptorand "crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
	"time"
)

const (
	systemPeerAttachKey = "_notify_peer_attach"
	peerAttachTimeout   = 5 * time.Second
)

type peerAttachRequest struct {
	PeerID string
}

type peerAttachResponse struct {
	PeerID   string
	Accepted bool
	Reused   bool
	Error    string
}

func newClientPeerIdentity() string {
	var buf [16]byte
	if _, err := cryptorand.Read(buf[:]); err == nil {
		return "peer-" + hex.EncodeToString(buf[:])
	}
	return fmt.Sprintf("peer-%d", time.Now().UnixNano())
}

func (c *ClientCommon) ensureClientPeerIdentity() string {
	if c == nil {
		return ""
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	if strings.TrimSpace(c.peerIdentity) == "" {
		c.peerIdentity = newClientPeerIdentity()
	}
	return c.peerIdentity
}

func (c *ClientCommon) setClientPeerIdentity(peerID string) {
	if c == nil {
		return
	}
	peerID = strings.TrimSpace(peerID)
	if peerID == "" {
		return
	}
	c.mu.Lock()
	c.peerIdentity = peerID
	c.mu.Unlock()
}

func decodePeerAttachRequest(decodeFn func([]byte) (interface{}, error), data []byte) (peerAttachRequest, error) {
	if decodeFn == nil {
		decodeFn = Decode
	}
	value, err := decodeFn(data)
	if err != nil {
		return peerAttachRequest{}, err
	}
	switch req := value.(type) {
	case peerAttachRequest:
		return req, nil
	case *peerAttachRequest:
		if req == nil {
			return peerAttachRequest{}, errors.New("peer attach request is nil")
		}
		return *req, nil
	default:
		return peerAttachRequest{}, fmt.Errorf("unexpected peer attach request type %T", value)
	}
}

func decodePeerAttachResponse(decodeFn func([]byte) (interface{}, error), data []byte) (peerAttachResponse, error) {
	if decodeFn == nil {
		decodeFn = Decode
	}
	value, err := decodeFn(data)
	if err != nil {
		return peerAttachResponse{}, err
	}
	switch resp := value.(type) {
	case peerAttachResponse:
		return resp, nil
	case *peerAttachResponse:
		if resp == nil {
			return peerAttachResponse{}, errors.New("peer attach response is nil")
		}
		return *resp, nil
	default:
		return peerAttachResponse{}, fmt.Errorf("unexpected peer attach response type %T", value)
	}
}

func (c *ClientCommon) announceClientPeerIdentity() error {
	if c == nil {
		return errors.New("client is nil")
	}
	peerID := c.ensureClientPeerIdentity()
	if peerID == "" {
		return errors.New("peer identity is empty")
	}
	encoded, err := c.sequenceEn(peerAttachRequest{PeerID: peerID})
	if err != nil {
		return err
	}
	reply, err := c.sendWait(TransferMsg{
		Key:   systemPeerAttachKey,
		Value: encoded,
		Type:  MSG_SYS_WAIT,
	}, peerAttachTimeout)
	if err != nil {
		return err
	}
	resp, err := decodePeerAttachResponse(c.sequenceDe, reply.Value)
	if err != nil {
		return err
	}
	if resp.PeerID != "" {
		c.setClientPeerIdentity(resp.PeerID)
	}
	if !resp.Accepted {
		if strings.TrimSpace(resp.Error) != "" {
			return errors.New(resp.Error)
		}
		return errors.New("peer attach rejected")
	}
	return nil
}

func (s *ServerCommon) bindAcceptedClientIdentity(current *LogicalConn, peerID string) (*LogicalConn, bool, error) {
	if s == nil {
		return nil, false, errors.New("server is nil")
	}
	if current == nil {
		return nil, false, errors.New("client is nil")
	}
	peerID = strings.TrimSpace(peerID)
	if peerID == "" {
		return nil, false, errors.New("peer id is empty")
	}
	if current.ID() == peerID {
		current.markIdentityBound()
		return current, false, nil
	}
	existing := s.GetLogicalConn(peerID)
	if existing == nil {
		if err := s.renameAcceptedLogical(current, peerID); err != nil {
			return nil, false, err
		}
		current.markIdentityBound()
		return current, false, nil
	}
	if existing == current {
		existing.markIdentityBound()
		return existing, false, nil
	}
	if err := s.handoffAcceptedLogicalTransport(existing, current); err != nil {
		return nil, true, err
	}
	existing.markIdentityBound()
	return existing, true, nil
}

func (s *ServerCommon) replyPeerAttach(client *LogicalConn, message Message, resp peerAttachResponse) error {
	if s == nil {
		return errors.New("server is nil")
	}
	if client == nil {
		return errors.New("client is nil")
	}
	encoded, err := s.sequenceEn(resp)
	if err != nil {
		return err
	}
	reply := TransferMsg{
		ID:    message.ID,
		Key:   systemPeerAttachKey,
		Value: encoded,
		Type:  MSG_SYS_REPLY,
	}
	if message.inboundConn != nil {
		return s.sendTransferInbound(client, messageTransportConnSnapshot(&message), message.inboundConn, reply)
	}
	_, err = s.sendLogical(client, reply)
	return err
}

func (s *ServerCommon) handlePeerAttachSystemMessage(message Message) bool {
	if message.Key != systemPeerAttachKey {
		return false
	}
	message = hydrateServerMessagePeerFields(message)
	current := messageLogicalConnSnapshot(&message)
	req, err := decodePeerAttachRequest(s.sequenceDe, message.Value)
	if err != nil {
		if current != nil {
			_ = s.replyPeerAttach(current, message, peerAttachResponse{
				Accepted: false,
				Error:    err.Error(),
			})
		}
		return true
	}
	bound, reused, err := s.bindAcceptedClientIdentity(current, req.PeerID)
	if err != nil {
		if current != nil {
			_ = s.replyPeerAttach(current, message, peerAttachResponse{
				PeerID:   req.PeerID,
				Accepted: false,
				Error:    err.Error(),
			})
		}
		return true
	}
	if err := s.replyPeerAttach(bound, message, peerAttachResponse{
		PeerID:   bound.ID(),
		Accepted: true,
		Reused:   reused,
	}); err != nil && bound != nil {
		s.stopLogicalSession(bound, "peer attach reply failed", err)
	}
	return true
}