// client2server - Go server with WebSocket + Redpanda
// Copyright (c) 2026 Luis Rosales - MIT License
//
// Build: go build -o client2server-server
// Run: ./client2server-server
// WebSocket: ws://localhost:3843
// HTTP API: http://localhost:3843

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/google/uuid"
	"github.com/redpanda-data/redpanda-sdk-go/redpanda"
	"github.com/redpanda-data/redpanda-sdk-go/schema"
	"nhooyr.io/websocket"
)

// Config
type Config struct {
	RedpandaBrokers []string
	WebsocketPort   int
	APIPort        int
	Token          string
}

var cfg = Config{
	RedpandaBrokers: []string{"localhost:9092"},
	WebsocketPort:   3843,
	APIPort:        3844, // HTTP API on next port
	Token:         "secret-token",
}

// Event from router
type RouterEvent struct {
	ID          string    `json:"id"`
	RouterID    string    `json:"router_id"`
	Hostname   string    `json:"hostname"`
	EventType  string    `json:"event_type"`
	Timestamp  time.Time `json:"timestamp"`
	Payload    map[string]interface{} `json:"payload"`
	ReceivedAt time.Time `json:"received_at"`
	Connection string    `json:"connection"` // "websocket" or "http"
}

// Command to router
type RouterCommand struct {
	ID        string          `json:"id"`
	RouterID string          `json:"router_id"`
	Command  string          `json:"command"`
	Args     map[string]string `json:"args,omitempty"`
	SentAt   time.Time       `json:"sent_at"`
}

// Router state
type Router struct {
	ID          string
	LastSeen   time.Time
	Conn      *websocket.Conn
	Connected bool
}

var routers = make(map[string]*Router)

// Redpanda
var rp *redpanda.Client

func initRedpanda() error {
	cfg.RedpandaBrokers = getEnvComma("REDPANDA_BROKERS", "localhost:9092")
	
	var err error
	rp, err = redpanda.NewClient(&redpanda.ClientConfig{
		Brokers: cfg.RedpandaBrokers,
	})
	if err != nil {
		return fmt.Errorf("redpanda: %v", err)
	}
	
	// Create topics if needed
	topics := []string{"router-events", "router-commands"}
	for _, topic := range topics {
		err := rp.CreateTopic(topic, 1, 3)
		if err != nil && !schema.ErrTopicExists.Exists(err) {
			log.Printf("Topic %s: %v", topic, err)
		}
	}
	
	return nil
}

func getEnvComma(key, def string) []string {
	val := os.Getenv(key)
	if val == "" {
		return []string{def}
	}
	return []string{val}
}

// Publish event to Redpanda
func publishEvent(event RouterEvent) error {
	data, err := json.Marshal(event)
	if err != nil {
		return err
	}
	
	return rp.Produce("router-events", []byte(event.ID), data)
}

// Publish command to Redpanda
func publishCommand(cmd RouterCommand) error {
	data, err := json.Marshal(cmd)
	if err != nil {
		return err
	}
	
	return rp.Produce("router-commands", []byte(cmd.ID), data)
}

// WebSocket handler
func handleWebSocket(w http.ResponseWriter, r *http.Request) {
	// Auth
	token := r.URL.Query().Get("token")
	if token != cfg.Token {
		http.Error(w, "Unauthorized", http.StatusUnauthorized)
		return
	}
	
	conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{
		CompressionMode: websocket.CompressionContextTakeover,
	})
	if err != nil {
		log.Printf("WS accept: %v", err)
		return
	}
	defer conn.Close(websocket.StatusNormalClosure, "")
	
	ctx := context.Background()
	
	// Read router registration
	var regMsg RouterEvent
	err = conn.Read(ctx, &regMsg)
	if err != nil {
		log.Printf("WS read reg: %v", err)
		return
	}
	
	routerID := regMsg.RouterID
	if routerID == "" {
		routerID = r.RemoteAddr
	}
	
	// Store router
	routers[routerID] = &Router{
		ID:          routerID,
		LastSeen:    time.Now(),
		Conn:       conn,
		Connected: true,
	}
	
	log.Printf("Router connected: %s", routerID)
	
	// Update router last seen
	routers[routerID].LastSeen = time.Now()
	
	// Message loop
	for {
		var event RouterEvent
		err := conn.Read(ctx, &event)
		if err != nil {
			break
		}
		
		event.ID = uuid.New().String()
		event.ReceivedAt = time.Now()
		event.Connection = "websocket"
		
		// Publish to Redpanda
		if err := publishEvent(event); err != nil {
			log.Printf("Publish error: %v", err)
		}
		
		log.Printf("[%s] %s", routerID, event.EventType)
		
		// Send ack
		conn.Write(ctx, []byte(`{"ack":true}`))
		
		// Update last seen
		routers[routerID].LastSeen = time.Now()
	}
	
	// Cleanup
	if routers[routerID] != nil {
		routers[routerID].Connected = false
	}
	log.Printf("Router disconnected: %s", routerID)
}

// HTTP Event webhook (fallback)
func handleHTTPEvent(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}
	
	token := r.Header.Get("Authorization")
	if token != "Bearer "+cfg.Token && token != cfg.Token {
		http.Error(w, "Unauthorized", http.StatusUnauthorized)
		return
	}
	
	var event RouterEvent
	if err := json.NewDecoder(r.Body).Decode(&event); err != nil {
		http.Error(w, "Invalid JSON", http.StatusBadRequest)
		return
	}
	
	event.ID = uuid.New().String()
	event.ReceivedAt = time.Now()
	event.Connection = "http"
	
	// Publish to Redpanda
	if err := publishEvent(event); err != nil {
		log.Printf("Publish error: %v", err)
		w.WriteHeader(http.StatusInternalServerError)
		return
	}
	
	log.Printf("[%s] %s (HTTP)", event.RouterID, event.EventType)
	
	json.NewEncoder(w).Encode(map[string]string{"event_id": event.ID})
}

// Get routers list
func handleRouters(w http.ResponseWriter, r *http.Request) {
	json.NewEncoder(w).Encode(map[string]interface{}{
		"routers": func() []map[string]interface{} {
			list := []map[string]interface{}{}
			for id, router := range routers {
				list = append(list, map[string]interface{}{
					"id":           id,
					"last_seen":    router.LastSeen,
					"online":       time.Since(router.LastSeen) < 60*time.Second,
				})
			}
			return list
		}(),
	})
}

// Get events
func handleEvents(w http.ResponseWriter, r *http.Request) {
	// Simple consumer - in production use proper offset management
	consumer, err := rp.NewConsumer("router-events", "client2server-group")
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	defer consumer.Close()
	
	limit := 100
	if l := r.URL.Query().Get("limit"); l != "" {
		fmt.Sscanf(l, "%d", &limit)
	}
	
	events := []RouterEvent{}
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	
	for i := 0; i < limit; i++ {
		msg, err := consumer.Consume(ctx, 5*time.Second)
		if err != nil {
			break
		}
		
		var event RouterEvent
		if json.Unmarshal(msg.Value, &event) == nil {
			events = append(events, event)
		}
	}
	
	json.NewEncoder(w).Encode(map[string]interface{}{
		"events": events,
		"total": len(events),
	})
}

// Send command to router
func handleCommand(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}
	
	var cmd RouterCommand
	if err := json.NewDecoder(r.Body).Decode(&cmd); err != nil {
		http.Error(w, "Invalid JSON", http.StatusBadRequest)
		return
	}
	
	routerID := r.URL.Query().Get("router_id")
	if routerID == "" {
		routerID = cmd.RouterID
	}
	
	if routerID == "" {
		http.Error(w, "router_id required", http.StatusBadRequest)
		return
	}
	
	// Publish command
	cmd.ID = uuid.New().String()
	cmd.RouterID = routerID
	cmd.SentAt = time.Now()
	
	if err := publishCommand(cmd); err != nil {
		log.Printf("Publish command: %v", err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	
	log.Printf("Command to %s: %s", routerID, cmd.Command)
	
	json.NewEncoder(w).Encode(map[string]string{
		"command_id": cmd.ID,
		"status":     "sent",
	})
}

// Health check
func handleHealth(w http.ResponseWriter, r *http.Request) {
	json.NewEncoder(w).Encode(map[string]interface{}{
		"status":     "ok",
		"routers":   len(routers),
		"timestamp": time.Now(),
	})
}

// Main
func main() {
	// Config from env
	cfg.Token = getEnvStr("TOKEN", cfg.Token)
	cfg.WebsocketPort = getEnvInt("PORT", cfg.WebsocketPort)
	
	log.SetFlags(log.LstdFlags | log.Lshortfile)
	log.Printf("=== client2server Go Server ===")
	log.Printf("WebSocket: ws://localhost:%d", cfg.WebsocketPort)
	log.Printf("HTTP API:   http://localhost:%d", cfg.APIPort)
	
	// Init Redpanda
	if err := initRedpanda(); err != nil {
		log.Printf("Redpanda init failed (running without): %v", err)
	} else {
		log.Printf("Redpanda: %v", cfg.RedpandaBrokers)
	}
	
	// HTTP handlers
	http.HandleFunc("/", handleHealth)
	http.HandleFunc("/health", handleHealth)
	http.HandleFunc("/api/events", handleHTTPEvent)
	http.HandleFunc("/api/events/", handleHTTPEvent)
	http.HandleFunc("/api/routers", handleRouters)
	http.HandleFunc("/api/command", handleCommand)
	
	// WebSocket (HAProxy protocol)
	http.HandleFunc("/ws", handleWebSocket)
	
	// Graceful shutdown
	go func() {
		sigCh := make(chan os.Signal, 1)
		signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
		<-sigCh
		log.Println("Shutting down...")
		
		for _, router := range routers {
			router.Conn.Close(websocket.StatusNormalClosure, "server shutdown")
		}
		
		os.Exit(0)
	}()
	
	// Start (using HTTP for both WS and API - need haproxy or prefix)
	log.Printf("Server ready on port %d", cfg.WebiscrollPoint)
	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", cfg.WebsocketPort), nil))
}

func getEnvStr(key, def string) string {
	if val := os.Getenv(key); val != "" {
		return val
	}
	return def
}

func getEnvInt(key string, def int) int {
	if val := os.Getenv(key); val != "" {
		var v int
		fmt.Sscanf(val, "%d", &v)
		return v
	}
	return def
}