package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"os/user"
	"strconv"
	"strings"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/gin-gonic/gin"

	"monica-go-completion-backend/internal/api"
	"monica-go-completion-backend/internal/cluster"
	"monica-go-completion-backend/internal/completion"
	"monica-go-completion-backend/internal/lsp"
)

var requestIDSeed atomic.Int64

type config struct {
	Port            string
	WorkspaceDir    string
	AllowOrigin     string
	APIToken        string
	RequestTimeout  time.Duration
	MaxBodyBytes    int64
	SessionTTL      time.Duration
	CleanupInterval time.Duration
	MaxSessions     int
	InstanceID      string
	InstanceURL     string
	EnableRedis     bool
	RedisAddr       string
	RedisPassword   string
	RedisDB         int
	RedisKeyPrefix  string
	InstanceTTL     time.Duration
	Heartbeat       time.Duration
	Servers         []completion.LanguageServerSpec
}

func main() {
	cfg := loadConfig()

	var registry completion.SessionRegistry
	if cfg.EnableRedis {
		var err error
		registry, err = cluster.NewRedisRegistry(context.Background(), cluster.RedisRegistryConfig{
			Addr:              cfg.RedisAddr,
			Password:          cfg.RedisPassword,
			DB:                cfg.RedisDB,
			KeyPrefix:         cfg.RedisKeyPrefix,
			InstanceID:        cfg.InstanceID,
			InstanceEndpoint:  cfg.InstanceURL,
			SessionTTL:        cfg.SessionTTL,
			InstanceTTL:       cfg.InstanceTTL,
			HeartbeatInterval: cfg.Heartbeat,
		})
		if err != nil {
			log.Fatalf("create redis registry failed: %v", err)
		}
	}

	manager := completion.NewManager(completion.ManagerConfig{
		WorkspaceDir:    cfg.WorkspaceDir,
		MaxSessions:     cfg.MaxSessions,
		SessionTTL:      cfg.SessionTTL,
		CleanupInterval: cfg.CleanupInterval,
		InstanceID:      cfg.InstanceID,
		Registry:        registry,
	}, cfg.Servers, func(ctx context.Context, spec completion.LanguageServerSpec, workspaceDir string) (completion.RuntimeClient, error) {
		return lsp.NewClient(ctx, lsp.Config{
			Command:    spec.Command,
			Args:       spec.Args,
			RootPath:   workspaceDir,
			LanguageID: spec.LanguageID,
			ClientName: "monica-lsp-gateway",
		})
	})
	defer func() {
		_ = manager.Close()
	}()

	router := gin.New()
	router.Use(gin.Logger())
	router.Use(gin.Recovery())
	router.Use(requestIDMiddleware())
	router.Use(corsMiddleware(cfg.AllowOrigin))
	router.Use(apiTokenMiddleware(cfg.APIToken))

	api.RegisterRoutes(router, manager, api.RouteOptions{
		RequestTimeout: cfg.RequestTimeout,
		MaxBodyBytes:   cfg.MaxBodyBytes,
	})

	server := &http.Server{
		Addr:         ":" + cfg.Port,
		Handler:      router,
		ReadTimeout:  30 * time.Second,
		WriteTimeout: 30 * time.Second,
		IdleTimeout:  60 * time.Second,
	}

	go func() {
		log.Printf(
			"lsp gateway listening on :%s, workspace=%s, instanceID=%s, redis=%t",
			cfg.Port,
			cfg.WorkspaceDir,
			cfg.InstanceID,
			cfg.EnableRedis,
		)
		if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			log.Fatalf("http server failed: %v", err)
		}
	}()

	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, os.Interrupt, syscall.SIGTERM)
	<-sigCh

	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	if err := server.Shutdown(shutdownCtx); err != nil {
		log.Printf("http shutdown failed: %v", err)
	}
	if err := manager.Close(); err != nil {
		log.Printf("lsp manager close failed: %v", err)
	}
}

func loadConfig() config {
	cwd, err := os.Getwd()
	if err != nil {
		cwd = "."
	}

	return config{
		Port:            getenv("PORT", "8080"),
		WorkspaceDir:    getenv("WORKSPACE_DIR", cwd),
		AllowOrigin:     getenv("CORS_ALLOW_ORIGIN", "*"),
		APIToken:        strings.TrimSpace(os.Getenv("LSP_API_TOKEN")),
		RequestTimeout:  getenvDuration("REQUEST_TIMEOUT", 10*time.Second),
		MaxBodyBytes:    getenvInt64("MAX_BODY_BYTES", 2<<20),
		SessionTTL:      getenvDuration("SESSION_TTL", 20*time.Minute),
		CleanupInterval: getenvDuration("SESSION_CLEANUP_INTERVAL", 2*time.Minute),
		MaxSessions:     getenvInt("MAX_SESSIONS", 256),
		InstanceID:      getenv("INSTANCE_ID", defaultInstanceID()),
		InstanceURL:     getenv("INSTANCE_URL", "http://127.0.0.1:"+getenv("PORT", "8080")),
		EnableRedis:     getenvBool("ENABLE_REDIS_STICKY", true),
		RedisAddr:       getenv("REDIS_ADDR", "10.0.0.10:6379"),
		RedisPassword:   getenv("REDIS_PASSWORD", ""),
		RedisDB:         getenvInt("REDIS_DB", 1),
		RedisKeyPrefix:  getenv("REDIS_KEY_PREFIX", "lsp-gateway"),
		InstanceTTL:     getenvDuration("INSTANCE_TTL", 30*time.Second),
		Heartbeat:       getenvDuration("INSTANCE_HEARTBEAT_INTERVAL", 10*time.Second),
		Servers: []completion.LanguageServerSpec{
			{
				Language:   "go",
				LanguageID: "go",
				Command:    getenv("GO_LSP_COMMAND", "gopls"),
				Args:       getenvArgs("GO_LSP_ARGS", ""),
			},
			{
				Language:   "javascript",
				LanguageID: "javascript",
				Command:    getenv("JAVASCRIPT_LSP_COMMAND", "typescript-language-server"),
				Args:       getenvArgs("JAVASCRIPT_LSP_ARGS", "--stdio"),
			},
			{
				Language:   "typescript",
				LanguageID: "typescript",
				Command:    getenv("TYPESCRIPT_LSP_COMMAND", "typescript-language-server"),
				Args:       getenvArgs("TYPESCRIPT_LSP_ARGS", "--stdio"),
			},
		},
	}
}

func defaultInstanceID() string {
	host, err := os.Hostname()
	if err != nil || strings.TrimSpace(host) == "" {
		host = "unknown-host"
	}
	userName := "unknown-user"
	if u, err := user.Current(); err == nil && strings.TrimSpace(u.Username) != "" {
		userName = strings.ReplaceAll(u.Username, "\\", "-")
	}
	return fmt.Sprintf("%s-%s-%d", host, userName, os.Getpid())
}

func getenv(key, fallback string) string {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	return v
}

func getenvArgs(key, fallback string) []string {
	value := getenv(key, fallback)
	if value == "" {
		return nil
	}
	return strings.Fields(value)
}

func getenvInt(key string, fallback int) int {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	parsed, err := strconv.Atoi(v)
	if err == nil {
		return parsed
	}
	return fallback
}

func getenvInt64(key string, fallback int64) int64 {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	parsed, err := strconv.ParseInt(v, 10, 64)
	if err == nil {
		return parsed
	}
	return fallback
}

func getenvDuration(key string, fallback time.Duration) time.Duration {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return fallback
	}
	parsed, err := time.ParseDuration(v)
	if err != nil {
		return fallback
	}
	return parsed
}

func getenvBool(key string, fallback bool) bool {
	v := strings.TrimSpace(strings.ToLower(os.Getenv(key)))
	if v == "" {
		return fallback
	}
	switch v {
	case "1", "true", "yes", "on":
		return true
	case "0", "false", "no", "off":
		return false
	default:
		return fallback
	}
}

func corsMiddleware(allowOrigin string) gin.HandlerFunc {
	return func(c *gin.Context) {
		c.Header("Access-Control-Allow-Origin", allowOrigin)
		c.Header("Access-Control-Allow-Methods", "GET,POST,OPTIONS")
		c.Header("Access-Control-Allow-Headers", "Content-Type,Authorization,X-API-Key")

		if c.Request.Method == http.MethodOptions {
			c.AbortWithStatus(http.StatusNoContent)
			return
		}
		c.Next()
	}
}

func apiTokenMiddleware(token string) gin.HandlerFunc {
	required := strings.TrimSpace(token)
	if required == "" {
		return func(c *gin.Context) {
			c.Next()
		}
	}

	return func(c *gin.Context) {
		provided := strings.TrimSpace(c.GetHeader("X-API-Key"))
		if provided == required {
			c.Next()
			return
		}
		c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "unauthorized"})
	}
}

func requestIDMiddleware() gin.HandlerFunc {
	return func(c *gin.Context) {
		rid := strings.TrimSpace(c.GetHeader("X-Request-Id"))
		if rid == "" {
			rid = fmt.Sprintf("req-%d", requestIDSeed.Add(1))
		}
		c.Header("X-Request-Id", rid)
		c.Set("requestId", rid)
		c.Next()
	}
}