package config

import (
	"fmt"
	"log/slog"
	"path/filepath"
	"strings"
	"sync"
	"sync/atomic"
	"github.com/fsnotify/fsnotify"
	"github.com/spf13/viper"
)

// DoubaoConfig holds 火山引擎豆包 ASR credentials.
type DoubaoConfig struct {
	AppID       string   `mapstructure:"app_id"`
	AccessToken string   `mapstructure:"access_token"`
	ResourceID  string   `mapstructure:"resource_id"`
	Hotwords    []string `mapstructure:"hotwords"` // 本地热词列表
}

// SecurityConfig holds authentication settings.
type SecurityConfig struct {
	Token string `mapstructure:"token"`
}

// ServerConfig holds server settings.
type ServerConfig struct {
	Port    int  `mapstructure:"port"`
	TLSAuto bool `mapstructure:"tls_auto"`
}

// Config is the top-level configuration.
type Config struct {
	Doubao   DoubaoConfig   `mapstructure:"doubao"`
	Server   ServerConfig   `mapstructure:"server"`
	Security SecurityConfig `mapstructure:"security"`
}

// defaults returns a Config with default values.
func defaults() Config {
	return Config{
		Doubao: DoubaoConfig{
			ResourceID: "volc.seedasr.sauc.duration",
		},
		Server: ServerConfig{
			Port:    8443,
			TLSAuto: true,
		},
	}
}

// global holds the current config atomically for concurrent reads.
var global atomic.Value
var watcher *fsnotify.Watcher
var watcherMu sync.Mutex
var watchStarted bool
var watchStartErr error

// Load reads config from file (or uses defaults if file doesn't exist).
// Empty path defaults to "config.yaml".
func Load(path string) (Config, error) {
	if path == "" {
		path = "config.yaml"
	}

	v := viper.New()
	v.SetConfigFile(path)
	v.SetConfigType("yaml")

	// Set defaults
	def := defaults()
	v.SetDefault("doubao.resource_id", def.Doubao.ResourceID)
	v.SetDefault("server.port", def.Server.Port)
	v.SetDefault("server.tls_auto", def.Server.TLSAuto)

	// Allow env var overrides (e.g., VOICEPASTE_DOUBAO_APP_ID)
	v.SetEnvPrefix("voicepaste")
	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	v.AutomaticEnv()

	// Read config file (ignore error if file doesn't exist)
	if err := v.ReadInConfig(); err != nil {
		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
			return Config{}, err
		}
		slog.Warn("config file not found, using defaults", "path", path)
	}

	var cfg Config
	if err := v.Unmarshal(&cfg); err != nil {
		return Config{}, err
	}
	// Validate before storing
	if err := validate(cfg); err != nil {
		return Config{}, err
	}
	store(cfg)
	return cfg, nil
}
// validate checks required fields.
func validate(cfg Config) error {
	if cfg.Doubao.AppID == "" {
		return fmt.Errorf("doubao.app_id is required")
	}
	if cfg.Doubao.AccessToken == "" {
		return fmt.Errorf("doubao.access_token is required")
	}
	return nil
}

// WatchAndReload starts watching config file for changes and reloads automatically.
// Empty path defaults to "config.yaml".
// Returns a function to stop watching. Can only be called once.
func WatchAndReload(path string) func() {
	watcherMu.Lock()
	defer watcherMu.Unlock()
	// Check if already started
	if watchStarted {
		if watchStartErr != nil {
			return func() {} // Previous start failed, return no-op
		}
		// Already running, return existing stop function
		return func() {
			watcherMu.Lock()
			defer watcherMu.Unlock()
			if watcher != nil {
				if err := watcher.Close(); err != nil {
					slog.Warn("failed to close config watcher", "err", err)
				}
				watcher = nil
				watchStarted = false
				slog.Info("config watcher stopped")
			}
		}
	}
	if path == "" {
		path = "config.yaml"
	}
	// Get absolute path for reliable matching
	absPath, err := filepath.Abs(path)
	if err != nil {
		slog.Error("failed to resolve config path", "err", err)
		watchStartErr = err
		// Don't set watchStarted = true, allow retry
		return func() {}
	}
	w, err := fsnotify.NewWatcher()
	if err != nil {
		slog.Error("failed to create config watcher", "err", err)
		watchStartErr = err
		// Don't set watchStarted = true, allow retry
		return func() {}
	}
	watchDir := filepath.Dir(absPath)
	if err := w.Add(watchDir); err != nil {
		slog.Error("failed to watch config directory", "err", err, "dir", watchDir)
		w.Close()
		watchStartErr = err
		// Don't set watchStarted = true, allow retry
		return func() {}
	}
	// Assign to global watcher before marking as started
	watcher = w
	watchStarted = true
	watchStartErr = nil
	// Create Viper instance for reading config
	v := viper.New()
	v.SetConfigFile(absPath) // Use absolute path for consistency
	v.SetConfigType("yaml")
	// Set defaults
	def := defaults()
	v.SetDefault("doubao.resource_id", def.Doubao.ResourceID)
	v.SetDefault("server.port", def.Server.Port)
	v.SetDefault("server.tls_auto", def.Server.TLSAuto)
	v.SetEnvPrefix("voicepaste")
	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	v.AutomaticEnv()
	// Initial read (ignore error if file doesn't exist)
	if err := v.ReadInConfig(); err != nil {
		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
			slog.Warn("config watch: initial read failed", "err", err)
		} else {
			slog.Warn("config file not found, will watch for creation", "path", path)
		}
	}
	// Start event loop in goroutine
	go func() {
		for {
			select {
			case event, ok := <-w.Events:
				if !ok {
					return
				}
				// Normalize event path for comparison
				eventPath := filepath.Clean(event.Name)
				if eventPath != absPath {
					continue
				}
				// Process Write, Create, and Rename events (common editor patterns)
				if event.Op&fsnotify.Write == fsnotify.Write || event.Op&fsnotify.Create == fsnotify.Create || event.Op&fsnotify.Rename == fsnotify.Rename {
					slog.Info("config file changed, reloading", "file", absPath, "op", event.Op)
					// Re-read the file
					if err := v.ReadInConfig(); err != nil {
						slog.Error("config reload: read failed", "err", err)
						continue
					}
					var cfg Config
					if err := v.Unmarshal(&cfg); err != nil {
						slog.Error("config reload: unmarshal failed", "err", err)
						continue
					}
					// Validate before applying
					if err := validate(cfg); err != nil {
						slog.Warn("config reload: validation failed, keeping old config", "err", err)
						continue
					}
					store(cfg)
					slog.Info("config reloaded and applied successfully")
				}
			case err, ok := <-w.Errors:
				if !ok {
					return
				}
				slog.Error("config watcher error", "err", err)
			}
		}
	}()
	// Return stop function
	return func() {
		watcherMu.Lock()
		defer watcherMu.Unlock()
		if watcher != nil {
			if err := watcher.Close(); err != nil {
				slog.Warn("failed to close config watcher", "err", err)
			}
			watcher = nil
			watchStarted = false
			slog.Info("config watcher stopped")
		}
	}
}

// Get returns the current config snapshot. Safe for concurrent use.
// Returns a deep copy to prevent external modifications.
func Get() Config {
	if v := global.Load(); v != nil {
		cfg := v.(Config)
		// Deep copy hotwords slice to prevent external modifications
		if cfg.Doubao.Hotwords != nil {
			cfg.Doubao.Hotwords = append([]string(nil), cfg.Doubao.Hotwords...)
		}
		return cfg
	}
	return defaults()
}

// store updates the global config.
// Deep copies slices to ensure immutability.
func store(cfg Config) {
	// Deep copy hotwords to prevent external modifications
	if cfg.Doubao.Hotwords != nil {
		cfg.Doubao.Hotwords = append([]string(nil), cfg.Doubao.Hotwords...)
	}
	global.Store(cfg)
}