package gateway

import (
	"context"
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"strings"
	"sync"
	"time"

	"github.com/coder/websocket"
	"github.com/coder/websocket/wsjson"

	"realtime-gateway/internal/channel"
	"realtime-gateway/internal/config"
	"realtime-gateway/internal/model"
	"realtime-gateway/internal/plugin"
	"realtime-gateway/internal/router"
	"realtime-gateway/internal/session"
)

type client struct {
	conn     *websocket.Conn
	logger   *slog.Logger
	cfg      config.GatewayConfig
	hub      *router.Hub
	channels *channel.Manager
	plugins  *plugin.Bus
	session  *session.Session
	auth     config.AuthConfig

	writeMu sync.Mutex
}

func serveClient(
	w http.ResponseWriter,
	r *http.Request,
	logger *slog.Logger,
	cfg config.Config,
	hub *router.Hub,
	channels *channel.Manager,
	plugins *plugin.Bus,
	sessions *session.Manager,
) {
	conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{
		InsecureSkipVerify: true,
	})
	if err != nil {
		logger.Error("websocket accept failed", "error", err)
		return
	}

	sess := sessions.Create()
	c := &client{
		conn:     conn,
		logger:   logger.With("sessionId", sess.ID),
		cfg:      cfg.Gateway,
		hub:      hub,
		channels: channels,
		plugins:  plugins,
		session:  sess,
		auth:     cfg.Auth,
	}

	hub.Register(c, nil)
	defer func() {
		if sess.ChannelID != "" {
			channels.Unbind(sess.ChannelID, sess.Role)
		}
		hub.Unregister(sess.ID)
		sessions.Delete(sess.ID)
		_ = conn.Close(websocket.StatusNormalClosure, "session closed")
	}()

	if err := c.run(r.Context()); err != nil && !errors.Is(err, context.Canceled) {
		c.logger.Warn("client closed", "error", err)
	}
}

func (c *client) ID() string {
	return c.session.ID
}

func (c *client) Send(message model.ServerMessage) error {
	c.writeMu.Lock()
	defer c.writeMu.Unlock()

	ctx, cancel := context.WithTimeout(context.Background(), c.cfg.WriteWait())
	defer cancel()
	return wsjson.Write(ctx, c.conn, message)
}

func (c *client) run(ctx context.Context) error {
	if err := c.Send(model.ServerMessage{
		Type:      "welcome",
		SessionID: c.session.ID,
	}); err != nil {
		return err
	}

	pingCtx, cancelPing := context.WithCancel(ctx)
	defer cancelPing()
	go c.pingLoop(pingCtx)

	for {
		readCtx, cancel := context.WithTimeout(ctx, c.cfg.PongWait())
		var message model.ClientMessage
		err := wsjson.Read(readCtx, c.conn, &message)
		cancel()
		if err != nil {
			return err
		}
		if err := c.handleMessage(message); err != nil {
			_ = c.Send(model.ServerMessage{
				Type:  "error",
				Error: err.Error(),
			})
		}
	}
}

func (c *client) handleMessage(message model.ClientMessage) error {
	switch message.Type {
	case "authenticate":
		return c.handleAuthenticate(message)
	case "join_channel":
		return c.handleJoinChannel(message)
	case "subscribe":
		return c.handleSubscribe(message)
	case "publish":
		return c.handlePublish(message)
	case "snapshot":
		return c.handleSnapshot(message)
	default:
		return errors.New("unsupported message type")
	}
}

func (c *client) handleJoinChannel(message model.ClientMessage) error {
	if strings.TrimSpace(message.ChannelID) == "" {
		return errors.New("channelId is required")
	}

	snapshot, err := c.channels.Join(message.ChannelID, message.Token, message.Role)
	if err != nil {
		return err
	}

	if c.session.ChannelID != "" {
		c.channels.Unbind(c.session.ChannelID, c.session.Role)
	}
	if err := c.channels.Bind(snapshot.ID, message.Role); err != nil {
		return err
	}

	c.session.Role = message.Role
	c.session.Authenticated = true
	c.session.ChannelID = snapshot.ID
	c.session.Subscriptions = nil
	c.hub.UpdateSubscriptions(c.session.ID, nil)

	return c.Send(model.ServerMessage{
		Type:      "joined_channel",
		SessionID: c.session.ID,
		State: json.RawMessage([]byte(
			`{"channelId":"` + snapshot.ID + `","deliveryMode":"` + snapshot.DeliveryMode + `"}`,
		)),
	})
}

func (c *client) handleAuthenticate(message model.ClientMessage) error {
	if !authorize(c.auth, message.Role, message.Token) {
		return errors.New("authentication failed")
	}

	c.session.Role = message.Role
	c.session.Authenticated = true
	return c.Send(model.ServerMessage{
		Type:      "authenticated",
		SessionID: c.session.ID,
	})
}

func (c *client) handleSubscribe(message model.ClientMessage) error {
	if !c.session.Authenticated && !c.auth.AllowAnonymousConsumers {
		return errors.New("consumer must authenticate before subscribe")
	}

	subscriptions := normalizeSubscriptions(c.session.ChannelID, message.Subscriptions)
	c.session.Subscriptions = subscriptions
	c.hub.UpdateSubscriptions(c.session.ID, subscriptions)
	return c.Send(model.ServerMessage{
		Type:      "subscribed",
		SessionID: c.session.ID,
	})
}

func (c *client) handlePublish(message model.ClientMessage) error {
	if !c.session.Authenticated {
		return errors.New("authentication required")
	}
	if c.session.Role != model.RoleProducer && c.session.Role != model.RoleController {
		return errors.New("publish is only allowed for producer or controller")
	}
	if message.Envelope == nil {
		return errors.New("envelope is required")
	}

	envelope := *message.Envelope
	if envelope.Source.Kind == "" {
		envelope.Source.Kind = c.session.Role
	}

	if c.session.ChannelID != "" {
		envelope.Target.ChannelID = c.session.ChannelID
	}
	deliveryMode := channel.DeliveryModeCacheLatest
	if envelope.Target.ChannelID != "" {
		deliveryMode = c.channels.DeliveryMode(envelope.Target.ChannelID)
	}
	result := c.hub.Publish(envelope, deliveryMode)
	if !result.Dropped {
		c.plugins.Publish(envelope)
	}
	return c.Send(model.ServerMessage{
		Type:      "published",
		SessionID: c.session.ID,
	})
}

func (c *client) handleSnapshot(message model.ClientMessage) error {
	if len(message.Subscriptions) == 0 || message.Subscriptions[0].DeviceID == "" {
		return errors.New("snapshot requires deviceId in first subscription")
	}
	channelID := message.Subscriptions[0].ChannelID
	if channelID == "" {
		channelID = c.session.ChannelID
	}
	state, ok := c.hub.Snapshot(channelID, message.Subscriptions[0].DeviceID)
	if !ok {
		return errors.New("snapshot not found")
	}
	return c.Send(model.ServerMessage{
		Type:      "snapshot",
		SessionID: c.session.ID,
		State:     json.RawMessage(state),
	})
}

func (c *client) pingLoop(ctx context.Context) {
	ticker := time.NewTicker(c.cfg.PingInterval())
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			pingCtx, cancel := context.WithTimeout(ctx, c.cfg.WriteWait())
			_ = c.conn.Ping(pingCtx)
			cancel()
		}
	}
}

func normalizeSubscriptions(channelID string, subscriptions []model.Subscription) []model.Subscription {
	items := make([]model.Subscription, 0, len(subscriptions))
	for _, entry := range subscriptions {
		if channelID != "" && strings.TrimSpace(entry.ChannelID) == "" {
			entry.ChannelID = channelID
		}
		items = append(items, entry)
	}
	return items
}