package server

import (
	"context"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/edgeai/gateway/internal/adapter"
	"github.com/edgeai/gateway/internal/auth"
	"github.com/edgeai/gateway/internal/config"
	"github.com/edgeai/gateway/internal/connector"
	"github.com/edgeai/gateway/internal/handler"
	"github.com/edgeai/gateway/internal/middleware"
	"github.com/edgeai/gateway/internal/observability"
	"github.com/edgeai/gateway/internal/ratelimit"
	"github.com/edgeai/gateway/internal/router"
	"github.com/edgeai/gateway/internal/scheduler"
	"github.com/edgeai/gateway/internal/session"
	"github.com/edgeai/gateway/internal/usage"
)

// Server is the main HTTP server for the AI gateway.
type Server struct {
	cfg            *config.Config
	logger         *observability.Logger
	metrics        *observability.Metrics
	HTTPSrv        *http.Server
	auth           *auth.Authenticator
	registry       *adapter.Registry
	modelMap       *router.LogicalModelMapping
	scheduler      *scheduler.Scheduler
	sessions       *session.Store
	breaker        *scheduler.CircuitBreaker
	backpressure   *scheduler.BackpressureManager
	overload       *router.OverloadResolver
	rateLimiter    *ratelimit.Limiter
	usageTracker   *usage.Tracker
	audit          *observability.AuditLogger
	timeoutMgr     *connector.TimeoutManager
	sessionCleanup func()       // 停止会话清理任务的函数
	adminSrv       *http.Server // Admin API 独立端口服务器

	healthCache     map[string]bool // adapter 健康缓存
	healthCacheTime time.Time       // 缓存时间
	healthCacheMu   sync.RWMutex    // 缓存锁

	idempotencyCache map[string]*idempotencyEntry // 幂等键缓存
	idempotencyMu    sync.Mutex                   // 幂等缓存锁
}

// New creates a new Server instance with all components wired.
func New(cfg *config.Config, logger *observability.Logger) (*Server, error) {
	// Ensure data directory exists
	dbPath := extractDBPath(cfg.Storage.SessionDB)
	if dbPath != "" {
		os.MkdirAll(filepath.Dir(dbPath), 0755)
	}

	// Initialize auth
	authPath := filepath.Join(filepath.Dir(dbPath), "auth.db")
	authenticator, err := auth.NewAuthenticator(authPath, logger)
	if err != nil {
		return nil, fmt.Errorf("init auth: %w", err)
	}

	// Initialize session store
	sessionStore, err := session.NewStore(dbPath)
	if err != nil {
		return nil, fmt.Errorf("init session store: %w", err)
	}

	// Initialize adapter registry
	registry := adapter.NewRegistry()

	// Initialize logical model mapping
	modelMap := router.NewLogicalModelMapping(cfg)

	// Initialize overload resolver
	overloadResolver := router.NewOverloadResolver(&cfg.Routing, modelMap)

	// Register adapters for each unique endpoint
	registered := make(map[string]bool)
	for _, mc := range cfg.Models {
		key := mc.Provider + "|" + mc.Endpoint
		if !registered[key] {
			switch mc.Provider {
			case "ollama":
				registry.Register(mc.Provider, adapter.NewOllamaAdapter(mc.Endpoint))
			case "vllm":
				registry.Register(mc.Provider, adapter.NewVLLMAdapter(mc.Endpoint))
			}
			registered[key] = true
		}
	}

	// Initialize scheduler
	sched := scheduler.NewScheduler(&cfg.Scheduler, logger)

	// Initialize circuit breaker
	breaker := scheduler.NewCircuitBreaker(
		cfg.CircuitBreaker.ErrorRateThreshold,
		cfg.CircuitBreaker.MinRequests,
		cfg.CircuitBreaker.WindowSeconds,
		cfg.CircuitBreaker.OpenDurationSeconds,
		cfg.CircuitBreaker.HalfOpenMaxRequests,
	)

	// Initialize backpressure manager
	bp := scheduler.NewBackpressureManager(
		cfg.Scheduler.MaxRunningTasks,
		cfg.Scheduler.MaxQueuedTasks,
		cfg.Backpressure.Level1Threshold,
		cfg.Backpressure.Level2Threshold,
		cfg.Backpressure.Level3Threshold,
	)

	// Initialize metrics
	metrics := observability.NewMetrics()

	// Initialize per-app rate limiter (令牌桶)
	refillPerSec := float64(cfg.Auth.RateLimitPerMinute) / 60.0
	rateLimiter := ratelimit.NewLimiter(float64(cfg.Auth.RateLimitBurst), refillPerSec)

	// Initialize per-app usage tracker (SQLite 持久化)
	usageDBPath := filepath.Join(filepath.Dir(dbPath), "usage.db")
	usageTracker, err := usage.NewTracker(time.Duration(cfg.Auth.UsageWindowMinutes)*time.Minute, usageDBPath, cfg.Observability.AuditRetentionDays)
	if err != nil {
		return nil, fmt.Errorf("init usage tracker: %w", err)
	}

	timeoutMgr := connector.NewTimeoutManager(&cfg.Timeouts)

	auditLogger := observability.NewAuditLogger(filepath.Dir(dbPath), logger)

	s := &Server{
		cfg:              cfg,
		logger:           logger,
		metrics:          metrics,
		auth:             authenticator,
		registry:         registry,
		modelMap:         modelMap,
		scheduler:        sched,
		sessions:         sessionStore,
		breaker:          breaker,
		backpressure:     bp,
		overload:         overloadResolver,
		rateLimiter:      rateLimiter,
		usageTracker:     usageTracker,
		audit:            auditLogger,
		timeoutMgr:       timeoutMgr,
		healthCache:      make(map[string]bool),
		idempotencyCache: make(map[string]*idempotencyEntry),
	}

	// 启动会话 TTL 自动清理任务（带日志回调）
	s.sessionCleanup = sessionStore.StartCleanupTask(cfg.Context.SessionIdleTTLMinutes, 10, func(deleted int64) {
		logger.Info("session cleanup completed",
			observability.F().
				Event("session_cleanup").
				Set("deleted_sessions", deleted))
	})

	// 启动幂等键缓存清理任务
	idempotencyCleanup := s.startIdempotencyCleanup()
	_ = idempotencyCleanup // 进程退出时自动回收

	mux := http.NewServeMux()
	s.registerRoutes(mux)

	// Apply middleware chain (order: Recovery → Logging → CORS → Auth → RateLimit → RequestID → BodyLimit → handler)
	h := middleware.RequestID(mux)
	h = middleware.BodyLimit(cfg.Server.MaxRequestBodyMB)(h)
	h = middleware.RateLimit(func(appID string) (bool, int, int) {
		info := s.rateLimiter.AllowWithInfo(appID)
		return info.Allowed, info.Limit, info.Remaining
	}, func(r *http.Request) string {
		if id := auth.GetAppIdentityFromRequest(r); id != nil {
			return id.AppID
		}
		return ""
	}, map[string]bool{"/health": true, "/ready": true, "/metrics": true})(h)
	h = s.auth.Middleware(h)
	h = middleware.CORS(cfg.Server.CORSAllowedOrigins)(h)
	h = middleware.Gzip(h)
	h = middleware.Logging(logger)(h)
	h = middleware.Recovery(logger)(h)

	s.HTTPSrv = &http.Server{
		Addr:              fmt.Sprintf("%s:%d", cfg.Server.Host, cfg.Server.Port),
		Handler:           h,
		ReadTimeout:       30 * time.Second,
		ReadHeaderTimeout: 10 * time.Second, // 防止 slowloris 攻击
		WriteTimeout:      0,                // no write timeout for SSE
		IdleTimeout:       120 * time.Second,
		MaxHeaderBytes:    1 << 20, // 1MB 限制请求头大小
	}

	// Admin API 独立端口（如果配置了 admin_port）
	if cfg.Server.AdminPort > 0 && cfg.Server.AdminPort != cfg.Server.Port {
		adminMux := http.NewServeMux()
		s.registerAdminRoutes(adminMux)

		// Admin 中间件链（与主服务器相同，但额外加 CORS）
		adminH := middleware.RequestID(adminMux)
		adminH = middleware.BodyLimit(cfg.Server.MaxRequestBodyMB)(adminH)
		adminH = middleware.RateLimit(func(appID string) (bool, int, int) {
			info := s.rateLimiter.AllowWithInfo(appID)
			return info.Allowed, info.Limit, info.Remaining
		}, func(r *http.Request) string {
			if id := auth.GetAppIdentityFromRequest(r); id != nil {
				return id.AppID
			}
			return ""
		}, nil)(adminH)
		adminH = s.auth.Middleware(adminH)
		adminH = middleware.CORS(cfg.Server.CORSAllowedOrigins)(adminH)
		adminH = middleware.Logging(logger)(adminH)
		adminH = middleware.Recovery(logger)(adminH)

		s.adminSrv = &http.Server{
			Addr:              fmt.Sprintf("%s:%d", cfg.Server.Host, cfg.Server.AdminPort),
			Handler:           adminH,
			ReadTimeout:       30 * time.Second,
			ReadHeaderTimeout: 10 * time.Second, // 防止 slowloris 攻击
			WriteTimeout:      30 * time.Second,
			IdleTimeout:       120 * time.Second,
			MaxHeaderBytes:    1 << 20, // 1MB 限制请求头大小
		}
	}

	return s, nil
}

func (s *Server) registerRoutes(mux *http.ServeMux) {
	// Health and readiness
	mux.HandleFunc("/health", s.handleHealth)
	mux.HandleFunc("/ready", s.handleReady)

	// Metrics
	mux.HandleFunc(s.cfg.Observability.MetricsPath, s.metrics.Handler())

	// OpenAI-compatible API
	mux.HandleFunc("/v1/chat/completions", s.handleChatCompletions)
	mux.HandleFunc("/v1/models", s.handleModels)

	// Session management
	mux.HandleFunc("/v1/sessions", s.handleSessions)
	mux.HandleFunc("/v1/sessions/", s.handleSessionByID)

	// Task management
	mux.HandleFunc("/v1/tasks", s.handleTasks)
	mux.HandleFunc("/v1/tasks/", s.handleTaskByID)
}

// registerAdminRoutes 注册管理 API 路由到独立的 mux（运行在 admin_port）。
func (s *Server) registerAdminRoutes(mux *http.ServeMux) {
	// Admin API: API Key 管理（需要 admin 权限）
	mux.Handle("/v1/admin/keys", auth.RequireAdmin(http.HandlerFunc(s.handleAdminKeys)))
	mux.Handle("/v1/admin/keys/", auth.RequireAdmin(http.HandlerFunc(s.handleAdminKeyByID)))

	// Admin API: 用量统计（需要 admin 权限）
	mux.Handle("/v1/admin/usage", auth.RequireAdmin(http.HandlerFunc(s.handleAdminUsage)))
	mux.Handle("/v1/admin/usage/", auth.RequireAdmin(http.HandlerFunc(s.handleAdminUsageByApp)))

	// Admin API: per-app 限流管理（需要 admin 权限）
	mux.Handle("/v1/admin/ratelimit/", auth.RequireAdmin(http.HandlerFunc(s.handleAdminRateLimit)))

	// Admin API: 熔断器状态（需要 admin 权限）
	mux.Handle("/v1/admin/circuit-breaker", auth.RequireAdmin(http.HandlerFunc(s.handleAdminCircuitBreaker)))

	// Admin API: 调度器状态（需要 admin 权限）
	mux.Handle("/v1/admin/scheduler", auth.RequireAdmin(http.HandlerFunc(s.handleAdminScheduler)))

	// Admin API: 配置热重载（需要 admin 权限）
	mux.Handle("/v1/admin/config/reload", auth.RequireAdmin(http.HandlerFunc(s.handleAdminConfigReload)))

	// Admin API: 健康检查（复用主服务器逻辑）
	mux.HandleFunc("/health", s.handleHealth)
	mux.HandleFunc("/ready", s.handleReady)
}

// Authenticator returns the authenticator instance (for testing/management).
func (s *Server) Authenticator() *auth.Authenticator {
	return s.auth
}

// Start begins listening for HTTP requests.
// 如果配置了 admin_port，同时启动 Admin API 服务器。
// 启动时对所有已注册 adapter 执行健康预检，不可达的 adapter 记录警告但不阻止启动。
func (s *Server) Start() error {
	s.logger.Info("http server starting", observability.F().
		Event("server_start").
		Set("addr", s.HTTPSrv.Addr))

	// Adapter 启动健康预检
	s.checkAdaptersHealth()

	// 启动 Admin API 服务器（独立 goroutine）
	if s.adminSrv != nil {
		s.logger.Info("admin api server starting", observability.F().
			Event("admin_server_start").
			Set("addr", s.adminSrv.Addr))
		go func() {
			if err := s.adminSrv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
				s.logger.Error("admin api server error", observability.F().
					Event("admin_server_error").
					Reason(err.Error()))
			}
		}()
	}

	return s.HTTPSrv.ListenAndServe()
}

// checkAdaptersHealth 对所有已注册 adapter 执行健康预检。
// 不可达的 adapter 记录警告但不阻止启动，允许部分降级运行。
// 每个 adapter 使用独立超时，避免单个 adapter 阻塞拖累其他。
func (s *Server) checkAdaptersHealth() {
	for _, name := range s.registry.Names() {
		ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		a, _ := s.registry.Get(name)
		if err := a.HealthCheck(ctx); err != nil {
			s.logger.Warn("adapter health check failed on startup",
				observability.F().
					Event("adapter_health_check_failed").
					Set("adapter", name).
					Reason(err.Error()))
		} else {
			s.logger.Info("adapter health check passed",
				observability.F().
					Event("adapter_health_check_ok").
					Set("adapter", name))
		}
		cancel()
	}
}

// Shutdown gracefully shuts down the server.
// 等待最多 30 秒让进行中的请求完成，记录未完成任务状态。
func (s *Server) Shutdown() error {
	// 记录关机时的任务状态
	runningCount := s.scheduler.RunningCount()
	queueLength := s.scheduler.QueueLength()
	s.logger.Info("server shutting down",
		observability.F().
			Event("server_shutdown").
			Set("running_tasks", runningCount).
			Set("queued_tasks", queueLength))

	// 等待运行中任务完成（超时时间从配置读取）
	drainSeconds := s.cfg.Timeouts.ShutdownDrainSeconds
	if drainSeconds <= 0 {
		drainSeconds = 10
	}
	if runningCount > 0 {
		s.logger.Info("waiting for running tasks to complete",
			observability.F().
				Event("shutdown_drain").
				Set("running_tasks", runningCount).
				Set("drain_timeout_seconds", drainSeconds))
		for i := 0; i < drainSeconds*10 && s.scheduler.RunningCount() > 0; i++ {
			time.Sleep(100 * time.Millisecond)
		}
		remaining := s.scheduler.RunningCount()
		if remaining > 0 {
			s.logger.Warn("shutdown: tasks still running after drain timeout",
				observability.F().
					Event("shutdown_drain_timeout").
					Set("remaining_tasks", remaining))
		} else {
			s.logger.Info("all running tasks completed",
				observability.F().Event("shutdown_drain_complete"))
		}
	}

	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	s.scheduler.Stop()
	if s.sessionCleanup != nil {
		s.sessionCleanup()
	}
	if s.sessions != nil {
		s.sessions.Close()
	}
	if s.auth != nil {
		s.auth.Close()
	}
	if s.usageTracker != nil {
		s.usageTracker.Close()
	}
	if s.audit != nil {
		s.audit.Close()
	}

	if s.adminSrv != nil {
		s.adminSrv.Shutdown(ctx)
	}

	return s.HTTPSrv.Shutdown(ctx)
}

func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
	// Liveness 探针：进程存活即返回 200
	handler.WriteJSON(w, http.StatusOK, map[string]string{"status": "alive"})
}

func (s *Server) handleReady(w http.ResponseWriter, r *http.Request) {
	// Readiness 探针：检查 adapter 健康状态 + DB 连通性
	// 使用 5 秒 TTL 缓存，避免高频探针请求打满 adapter
	w.Header().Set("Content-Type", "application/json")

	ready := true
	reasons := []string{}

	// 检查所有 adapter 健康状态（带缓存）
	adapterHealth := s.getCachedAdapterHealth(r.Context())
	for name, ok := range adapterHealth {
		if !ok {
			ready = false
			reasons = append(reasons, fmt.Sprintf("adapter %s: unhealthy", name))
		}
	}

	// 检查 scheduler 是否正常
	if s.scheduler.RunningCount() >= s.cfg.Scheduler.MaxRunningTasks {
		ready = false
		reasons = append(reasons, "scheduler: at max capacity")
	}

	if ready {
		w.WriteHeader(http.StatusOK)
		w.Write([]byte(`{"status":"ready"}`))
	} else {
		w.WriteHeader(http.StatusServiceUnavailable)
		fmt.Fprintf(w, `{"status":"not_ready","reasons":["%s"]}`, strings.Join(reasons, `","`))
	}
}

// getCachedAdapterHealth 返回 adapter 健康状态，使用 5 秒 TTL 缓存。
// 缓存过期后异步刷新，首次请求或缓存过期时同步调用 adapter HealthCheck。
func (s *Server) getCachedAdapterHealth(ctx context.Context) map[string]bool {
	const healthCacheTTL = 5 * time.Second

	s.healthCacheMu.RLock()
	if time.Since(s.healthCacheTime) < healthCacheTTL && len(s.healthCache) > 0 {
		result := make(map[string]bool, len(s.healthCache))
		for k, v := range s.healthCache {
			result[k] = v
		}
		s.healthCacheMu.RUnlock()
		return result
	}
	s.healthCacheMu.RUnlock()

	// 缓存过期，同步执行健康检查
	result := make(map[string]bool)
	for _, name := range s.registry.Names() {
		a, _ := s.registry.Get(name)
		if err := a.HealthCheck(ctx); err != nil {
			result[name] = false
		} else {
			result[name] = true
		}
	}

	s.healthCacheMu.Lock()
	s.healthCache = result
	s.healthCacheTime = time.Now()
	s.healthCacheMu.Unlock()

	return result
}

func extractDBPath(connStr string) string {
	if strings.HasPrefix(connStr, "sqlite://") {
		return strings.TrimPrefix(connStr, "sqlite://")
	}
	return connStr
}