package nixmsg

import (
	"context"
	"errors"
	"fmt"
	"net/url"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/eclipse/paho.golang/autopaho"
	"github.com/eclipse/paho.golang/paho"
)

type mqttTransport struct {
	mu       sync.Mutex
	cm       *autopaho.ConnectionManager
	cancel   context.CancelFunc
	cfg      transportConfig
	cred     atomic.Value // string
	upTopic  string
	downTopic string
	stopped  atomic.Bool
	ready    chan struct{}
}

func newMQTTTransport() *mqttTransport {
	t := &mqttTransport{ready: make(chan struct{})}
	t.cred.Store("")
	return t
}

func (t *mqttTransport) SetCredential(passwordOrToken string) {
	t.cred.Store(passwordOrToken)
}

func (t *mqttTransport) Start(ctx context.Context, cfg transportConfig) error {
	t.mu.Lock()
	defer t.mu.Unlock()
	if t.cm != nil {
		return errors.New("transport already started")
	}
	t.cfg = cfg
	t.upTopic = fmt.Sprintf("nix/c/%s/up", cfg.EndpointID)
	t.downTopic = fmt.Sprintf("nix/c/%s/down", cfg.EndpointID)

	u, err := normalizeMQTTURL(cfg.URL, cfg.AllowTCP)
	if err != nil {
		return err
	}

	innerCtx, cancel := context.WithCancel(ctx)
	t.cancel = cancel

	var sessionExpiry uint32 // 0；由 ConnectPacketBuilder 显式写入 Properties
	cliCfg := autopaho.ClientConfig{
		ServerUrls:                    []*url.URL{u},
		KeepAlive:                     30,
		ConnectTimeout:                cfg.ConnectTimeout,
		CleanStartOnInitialConnection: false, // 不要只靠这个；每次用 ConnectPacketBuilder
		SessionExpiryInterval:         sessionExpiry,
		ConnectUsername:               cfg.EndpointID,
		ReconnectBackoff:              cfg.Backoff.Func,
		OnConnectError: func(err error) {
			var ce *autopaho.ConnackError
			if errors.As(err, &ce) {
				if isAuthCONNACK(ce.ReasonCode) {
					reason := AuthBadCredentials
					if tok, _ := t.cred.Load().(string); strings.HasPrefix(tok, "nst_") {
						reason = AuthSessionInvalid
					}
					if cfg.OnAuthFailed != nil {
						cfg.OnAuthFailed(reason)
					}
					cancel()
				}
			}
		},
		OnConnectionDown: func() bool {
			if t.stopped.Load() {
				return false
			}
			if cfg.Backoff != nil {
				cfg.Backoff.MarkOffline()
			}
			if cfg.OnOffline != nil {
				cfg.OnOffline()
			}
			return !t.stopped.Load()
		},
		OnConnectionUp: func(cm *autopaho.ConnectionManager, _ *paho.Connack) {
			if cfg.Backoff != nil {
				cfg.Backoff.MarkOnline()
			}
			go func() {
				_, err := cm.Subscribe(innerCtx, &paho.Subscribe{
					Subscriptions: []paho.SubscribeOptions{{
						Topic: t.downTopic,
						QoS:   1,
					}},
				})
				if err != nil {
					return
				}
				if cfg.MQTTReady != nil {
					_ = cfg.MQTTReady(innerCtx)
				}
				if cfg.OnOnline != nil {
					cfg.OnOnline()
				}
			}()
		},
		ClientConfig: paho.ClientConfig{
			ClientID: cfg.EndpointID,
			OnServerDisconnect: func(d *paho.Disconnect) {
				if d != nil && d.ReasonCode == 0x8E {
					if cfg.OnKicked != nil {
						cfg.OnKicked()
					}
					cancel()
				}
			},
			OnPublishReceived: []func(paho.PublishReceived) (bool, error){
				func(pr paho.PublishReceived) (bool, error) {
					if cfg.OnDown != nil && pr.Packet != nil {
						cfg.OnDown(pr.Packet.Payload)
					}
					return true, nil
				},
			},
		},
	}

	cliCfg.ConnectPacketBuilder = func(c *paho.Connect, _ *url.URL) (*paho.Connect, error) {
		c.CleanStart = true
		zero := uint32(0)
		if c.Properties == nil {
			c.Properties = &paho.ConnectProperties{}
		}
		c.Properties.SessionExpiryInterval = &zero
		pass, _ := t.cred.Load().(string)
		c.UsernameFlag = true
		c.Username = cfg.EndpointID
		c.PasswordFlag = true
		c.Password = []byte(pass)
		if cfg.OnConnectPacket != nil {
			cfg.OnConnectPacket(c.CleanStart, zero)
		}
		return c, nil
	}

	cm, err := autopaho.NewConnection(innerCtx, cliCfg)
	if err != nil {
		cancel()
		return err
	}
	t.cm = cm
	return nil
}

func (t *mqttTransport) PublishUp(payload []byte) error {
	t.mu.Lock()
	cm := t.cm
	topic := t.upTopic
	t.mu.Unlock()
	if cm == nil {
		return apiErr(CodeNotConnected, "未连接")
	}
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()
	_, err := cm.Publish(ctx, &paho.Publish{
		Topic:   topic,
		QoS:     1,
		Payload: payload,
	})
	return err
}

func (t *mqttTransport) Stop(ctx context.Context) error {
	t.stopped.Store(true)
	t.mu.Lock()
	cm := t.cm
	cancel := t.cancel
	t.mu.Unlock()
	if cancel != nil {
		cancel()
	}
	if cm != nil {
		return cm.Disconnect(ctx)
	}
	return nil
}

func isAuthCONNACK(code byte) bool {
	switch code {
	case 0x86, 0x87, 0x8A, // MQTT 5
		4, 5: // MQTT 3.1.1 bad user/pass, not authorized
		return true
	default:
		return false
	}
}

func normalizeMQTTURL(raw string, allowTCP bool) (*url.URL, error) {
	u, err := url.Parse(raw)
	if err != nil {
		return nil, err
	}
	switch strings.ToLower(u.Scheme) {
	case "ws", "wss":
		if u.Path == "" || u.Path == "/" {
			u.Path = "/mqtt"
		}
		return u, nil
	case "http":
		u.Scheme = "ws"
		if u.Path == "" || u.Path == "/" {
			u.Path = "/mqtt"
		}
		return u, nil
	case "https":
		u.Scheme = "wss"
		if u.Path == "" || u.Path == "/" {
			u.Path = "/mqtt"
		}
		return u, nil
	case "mqtt", "tcp", "mqtts", "ssl", "tls":
		if !allowTCP {
			return nil, apiErr(CodeBadRequest, "裸 TCP 需在选项中显式打开 AllowTCP")
		}
		return u, nil
	default:
		return nil, fmt.Errorf("不支持的 URL scheme: %s", u.Scheme)
	}
}

// RegisterURLFromConnect 从连接地址推出注册 HTTP 地址（第 6.9 节）。
func RegisterURLFromConnect(connectURL string) (string, error) {
	u, err := url.Parse(connectURL)
	if err != nil {
		return "", err
	}
	out := *u
	switch strings.ToLower(u.Scheme) {
	case "wss", "https", "mqtts", "ssl", "tls":
		out.Scheme = "https"
	case "ws", "http", "mqtt", "tcp":
		out.Scheme = "http"
	default:
		return "", fmt.Errorf("无法从 %s 推出注册地址", u.Scheme)
	}
	out.Path = "/api/client/register"
	out.RawQuery = ""
	out.Fragment = ""
	return out.String(), nil
}