// Package gateway provides WebSocket client integration with the OpenClaw
// gateway using WS protocol v3. The WSClient handles connection, handshake,
// frame routing, request/response correlation, and automatic reconnection
// with exponential backoff.
package gateway

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"sync"
	"time"

	"code.cubecraftcreations.com/CubeCraft-Creations/Control-Center/go-backend/internal/handler"
	"code.cubecraftcreations.com/CubeCraft-Creations/Control-Center/go-backend/internal/repository"

	"github.com/gorilla/websocket"
	"github.com/google/uuid"
)

// WSConfig holds WebSocket client configuration, typically loaded from
// environment variables. AuthToken must be set to a valid OpenClaw gateway
// operator token.
type WSConfig struct {
	URL       string // e.g. "ws://host.docker.internal:18789/"
	AuthToken string // from OPENCLAW_GATEWAY_TOKEN
}

// DefaultWSConfig returns sensible defaults for local development.
func DefaultWSConfig() WSConfig {
	return WSConfig{
		URL:       "ws://localhost:18789/",
		AuthToken: "",
	}
}

// eventHandler is a callback invoked when a named event arrives from the
// gateway.
type eventHandler func(json.RawMessage)

// WSClient connects to the OpenClaw gateway over WebSocket, completes the
// v3 handshake, routes incoming frames, and automatically reconnects on
// disconnect with exponential backoff.
type WSClient struct {
	config  WSConfig
	conn    *websocket.Conn
	connMu  sync.Mutex // protects conn for writes
	pending map[string]chan<- json.RawMessage
	mu      sync.Mutex // protects pending and handlers
	agents  repository.AgentRepo
	broker  *handler.Broker
	logger  *slog.Logger

	handlers map[string][]eventHandler
}

// NewWSClient returns a WSClient wired to the given repository and broker.
func NewWSClient(cfg WSConfig, agents repository.AgentRepo, broker *handler.Broker, logger *slog.Logger) *WSClient {
	if logger == nil {
		logger = slog.Default()
	}
	return &WSClient{
		config:   cfg,
		pending:  make(map[string]chan<- json.RawMessage),
		agents:   agents,
		broker:   broker,
		logger:   logger,
		handlers: make(map[string][]eventHandler),
	}
}

// OnEvent registers a handler for the given event name. Handlers are called
// when an incoming frame with type "event" and matching event name is
// received. This is safe to call before Start.
func (c *WSClient) OnEvent(event string, handler func(json.RawMessage)) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.handlers[event] = append(c.handlers[event], handler)
}

// ── Frame types ──────────────────────────────────────────────────────────

// wsFrame represents a generic WebSocket frame in the OpenClaw v3 protocol.
type wsFrame struct {
	Type   string          `json:"type"`             // "req", "res", "event"
	ID     string          `json:"id,omitempty"`      // request/response correlation
	Method string          `json:"method,omitempty"` // method name (req frames)
	Event  string          `json:"event,omitempty"`  // event name (event frames)
	Params json.RawMessage `json:"params,omitempty"`
	Result json.RawMessage `json:"result,omitempty"`
	Error  *wsError        `json:"error,omitempty"`
}

// wsError represents an error in a response frame.
type wsError struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

// connectRequest builds the initial connect handshake payload.
type connectRequest struct {
	MinProtocol int              `json:"minProtocol"`
	MaxProtocol int              `json:"maxProtocol"`
	Client      connectClientInfo `json:"client"`
	Role        string           `json:"role"`
	Scopes      []string         `json:"scopes"`
	Auth        connectAuth      `json:"auth"`
}

type connectClientInfo struct {
	ID       string `json:"id"`
	Version  string `json:"version"`
	Platform string `json:"platform"`
	Mode     string `json:"mode"`
}

type connectAuth struct {
	Token string `json:"token"`
}

// helloOKResponse represents the expected response to a successful connect.
type helloOKResponse struct {
	ConnID  string `json:"connId"`
	Features struct {
		Methods []string `json:"methods"`
		Events  []string `json:"events"`
	} `json:"features"`
}

// ── Start loop ───────────────────────────────────────────────────────────

// Start connects to the gateway, completes the handshake, and begins the
// read loop. On disconnect it reconnects with exponential backoff. On
// ctx cancellation it performs a clean shutdown.
func (c *WSClient) Start(ctx context.Context) {
	backoff := 1 * time.Second
	maxBackoff := 30 * time.Second

	for {
		err := c.connectAndRun(ctx)
		if err != nil {
			if ctx.Err() != nil {
				c.logger.Info("ws client stopped (context cancelled)")
				return
			}
			c.logger.Warn("ws client disconnected, reconnecting",
				"error", err,
				"backoff", backoff)
		}

		select {
		case <-ctx.Done():
			c.logger.Info("ws client stopped during backoff (context cancelled)")
			return
		case <-time.After(backoff):
			// Exponential backoff: 1s, 2s, 4s, 8s, 16s, max 30s
			backoff = backoff * 2
			if backoff > maxBackoff {
				backoff = maxBackoff
			}
		}
	}
}

// connectAndRun dials the gateway, completes the handshake, and runs the
// read loop until an error occurs or ctx is cancelled.
func (c *WSClient) connectAndRun(ctx context.Context) error {
	c.logger.Info("ws client connecting", "url", c.config.URL)

	dialer := websocket.Dialer{
		HandshakeTimeout: 10 * time.Second,
	}

	conn, _, err := dialer.DialContext(ctx, c.config.URL, nil)
	if err != nil {
		return fmt.Errorf("dial failed: %w", err)
	}

	c.connMu.Lock()
	c.conn = conn
	c.connMu.Unlock()

	// Reset backoff on successful connect
	defer func() {
		conn.Close()
	}()

	// Step 1: Read the connect.challenge frame
	if err := c.readChallenge(conn); err != nil {
		return fmt.Errorf("handshake challenge: %w", err)
	}

	// Step 2: Send connect request
	helloOK, err := c.sendConnect(conn)
	if err != nil {
		return fmt.Errorf("handshake connect: %w", err)
	}

	c.logger.Info("ws client handshake complete",
		"connId", helloOK.ConnID,
		"methods", helloOK.Features.Methods,
		"events", helloOK.Features.Events)

	// Step 3: Read loop
	return c.readLoop(ctx, conn)
}

// readChallenge reads the first frame from the gateway, which must be a
// connect.challenge event.
func (c *WSClient) readChallenge(conn *websocket.Conn) error {
	var frame wsFrame
	if err := conn.ReadJSON(&frame); err != nil {
		return fmt.Errorf("read challenge: %w", err)
	}

	if frame.Type != "event" || frame.Event != "connect.challenge" {
		return fmt.Errorf("expected connect.challenge, got type=%s event=%s", frame.Type, frame.Event)
	}

	c.logger.Debug("received connect.challenge", "params", string(frame.Params))
	return nil
}

// sendConnect sends the connect request and waits for the hello-ok response.
func (c *WSClient) sendConnect(conn *websocket.Conn) (*helloOKResponse, error) {
	reqID := uuid.New().String()
	params := connectRequest{
		MinProtocol: 3,
		MaxProtocol: 3,
		Client: connectClientInfo{
			ID:       "control-center",
			Version:  "1.0",
			Platform: "server",
			Mode:     "operator",
		},
		Role:   "operator",
		Scopes: []string{"operator.read"},
		Auth: connectAuth{
			Token: c.config.AuthToken,
		},
	}

	paramsJSON, err := json.Marshal(params)
	if err != nil {
		return nil, fmt.Errorf("marshal connect params: %w", err)
	}

	reqFrame := wsFrame{
		Type:   "req",
		ID:     reqID,
		Method: "connect",
		Params: paramsJSON,
	}

	if err := conn.WriteJSON(reqFrame); err != nil {
		return nil, fmt.Errorf("write connect request: %w", err)
	}

	// Read response
	var resFrame wsFrame
	if err := conn.ReadJSON(&resFrame); err != nil {
		return nil, fmt.Errorf("read connect response: %w", err)
	}

	if resFrame.Error != nil {
		return nil, fmt.Errorf("connect rejected: code=%d msg=%s", resFrame.Error.Code, resFrame.Error.Message)
	}

	if resFrame.ID != reqID {
		return nil, fmt.Errorf("response id mismatch: expected %s, got %s", reqID, resFrame.ID)
	}

	// Check for hello-ok method in the result
	// The gateway responds with method "hello-ok" on success
	var helloOK helloOKResponse
	if err := json.Unmarshal(resFrame.Result, &helloOK); err != nil {
		return nil, fmt.Errorf("parse hello-ok: %w", err)
	}

	return &helloOK, nil
}

// readLoop continuously reads frames from the connection and routes them.
// It returns on read error or context cancellation.
func (c *WSClient) readLoop(ctx context.Context, conn *websocket.Conn) error {
	for {
		select {
		case <-ctx.Done():
			// Clean shutdown: send close frame
			c.connMu.Lock()
			c.conn.WriteControl(
				websocket.CloseMessage,
				websocket.FormatCloseMessage(websocket.CloseNormalClosure, "shutdown"),
				time.Now().Add(5*time.Second),
			)
			c.connMu.Unlock()
			return ctx.Err()
		default:
		}

		var frame wsFrame
		if err := conn.ReadJSON(&frame); err != nil {
			// Check if it's a close error
			if websocket.IsCloseError(err, websocket.CloseNormalClosure, websocket.CloseGoingAway) {
				c.logger.Info("ws connection closed by server")
				return nil
			}
			if websocket.IsUnexpectedCloseError(err) {
				c.logger.Warn("ws connection unexpectedly closed", "error", err)
				return err
			}
			return fmt.Errorf("read frame: %w", err)
		}

		c.routeFrame(frame)
	}
}

// routeFrame dispatches a received frame to the appropriate handler.
func (c *WSClient) routeFrame(frame wsFrame) {
	switch frame.Type {
	case "res":
		c.handleResponse(frame)
	case "event":
		c.handleEvent(frame)
	default:
		c.logger.Warn("unknown frame type", "type", frame.Type, "id", frame.ID)
	}
}

// handleResponse correlates a response frame to a pending request channel.
func (c *WSClient) handleResponse(frame wsFrame) {
	c.mu.Lock()
	ch, ok := c.pending[frame.ID]
	if ok {
		delete(c.pending, frame.ID)
	}
	c.mu.Unlock()

	if !ok {
		c.logger.Warn("received response for unknown request", "id", frame.ID)
		return
	}

	if frame.Error != nil {
		// Send nil to signal error; caller checks via Send return
		ch <- nil
		return
	}

	ch <- frame.Result
}

// handleEvent dispatches an event frame to registered handlers.
func (c *WSClient) handleEvent(frame wsFrame) {
	c.mu.Lock()
	handlers := c.handlers[frame.Event]
	c.mu.Unlock()

	if len(handlers) == 0 {
		c.logger.Debug("unhandled event", "event", frame.Event)
		return
	}

	for _, h := range handlers {
		h(frame.Params)
	}
}

// ── Send ─────────────────────────────────────────────────────────────────

// Send sends a JSON request to the gateway and returns the response payload.
// It is safe for concurrent use. The caller should check for errors in the
// returned payload. A nil payload with nil error means the gateway sent an
// error response (check via the response frame's error field, which is logged).
func (c *WSClient) Send(method string, params any) (json.RawMessage, error) {
	reqID := uuid.New().String()

	paramsJSON, err := json.Marshal(params)
	if err != nil {
		return nil, fmt.Errorf("marshal params: %w", err)
	}

	// Register pending response channel
	respCh := make(chan json.RawMessage, 1)
	c.mu.Lock()
	c.pending[reqID] = respCh
	c.mu.Unlock()

	defer func() {
		c.mu.Lock()
		delete(c.pending, reqID)
		c.mu.Unlock()
	}()

	// Build and send frame
	frame := wsFrame{
		Type:   "req",
		ID:     reqID,
		Method: method,
		Params: paramsJSON,
	}

	c.connMu.Lock()
	err = c.conn.WriteJSON(frame)
	c.connMu.Unlock()

	if err != nil {
		return nil, fmt.Errorf("write request: %w", err)
	}

	// Wait for response with timeout
	select {
	case resp := <-respCh:
		if resp == nil {
			return nil, fmt.Errorf("gateway returned error for request %s", reqID)
		}
		return resp, nil
	case <-time.After(30 * time.Second):
		return nil, fmt.Errorf("request %s timed out", reqID)
	}
}