package config

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

	"github.com/mitchellh/mapstructure"
	"go.uber.org/zap"

	sharedconfig "github.com/geo-platform/tenant-api/internal/shared/config"
	configruntime "github.com/geo-platform/tenant-api/internal/shared/config/runtime"
	runtimeenv "github.com/geo-platform/tenant-api/internal/shared/config/runtime/env"
	runtimefile "github.com/geo-platform/tenant-api/internal/shared/config/runtime/file"
)

type Config struct {
	Server             sharedconfig.ServerConfig   `mapstructure:"server"`
	Database           sharedconfig.DatabaseConfig `mapstructure:"database"`
	MonitoringDatabase sharedconfig.DatabaseConfig `mapstructure:"monitoring_database"`
	Redis              sharedconfig.RedisConfig    `mapstructure:"redis"`
	Cache              sharedconfig.CacheConfig    `mapstructure:"cache"`
	RabbitMQ           sharedconfig.RabbitMQConfig `mapstructure:"rabbitmq"`
	Log                sharedconfig.LogConfig      `mapstructure:"log"`
	JWT                JWTConfig                   `mapstructure:"jwt"`
	DefaultAdmin       DefaultAdminConfig          `mapstructure:"default_admin"`
	AdminUsers         AdminUsersConfig            `mapstructure:"admin_users"`
	IPRegion           IPRegionConfig              `mapstructure:"ip_region"`
}

type JWTConfig struct {
	Secret    string        `mapstructure:"secret"`
	AccessTTL time.Duration `mapstructure:"access_ttl"`
}

type DefaultAdminConfig struct {
	Username    string `mapstructure:"username"`
	Password    string `mapstructure:"password"`
	DisplayName string `mapstructure:"display_name"`
	Email       string `mapstructure:"email"`
}

type AdminUsersConfig struct {
	DefaultPlanCode string `mapstructure:"default_plan_code"`
}

type IPRegionConfig struct {
	V4XDBPath string `mapstructure:"v4_xdb_path"`
	V6XDBPath string `mapstructure:"v6_xdb_path"`
}

type Store struct {
	path string

	mu           sync.RWMutex
	cfg          *Config
	runtime      configruntime.Config
	watchedFiles map[string]fileSnapshot
	updates      chan struct{}
}

type ReloadEvent struct {
	Previous *Config
	Current  *Config
	Changes  []FieldChange
}

type FieldChange struct {
	Path string
	Hot  bool
}

func Load(path string) (*Config, error) {
	cfg, err := load(path)
	if err != nil {
		return nil, err
	}
	return cfg, nil
}

func NewStore(path string) (*Store, error) {
	cfg, err := load(path)
	if err != nil {
		return nil, err
	}
	store := &Store{
		path:         path,
		cfg:          cfg,
		watchedFiles: snapshotFiles(watchFiles(path)),
		updates:      make(chan struct{}, 1),
	}
	store.runtime = store.newRuntimeConfig()
	return store, nil
}

func (s *Store) Current() *Config {
	if s == nil {
		return nil
	}
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.cfg
}

func (s *Store) Watch(ctx context.Context, logger *zap.Logger, onReload func(ReloadEvent)) error {
	if s == nil {
		return fmt.Errorf("ops config store is nil")
	}
	if s.runtime == nil {
		s.runtime = s.newRuntimeConfig()
	}
	if err := s.runtime.Load(); err != nil {
		return err
	}
	if err := s.runtime.Watch("", func(string, configruntime.Value) {
		s.notifyReload()
	}); err != nil {
		_ = s.runtime.Close()
		return err
	}
	if logger != nil {
		logger.Info("ops config hot reload watcher started", zap.String("file", s.path))
	}
	for {
		select {
		case <-ctx.Done():
			return nil
		case <-s.updates:
			s.reload(logger, onReload)
		}
	}
}

func (s *Store) Close() {
	if s == nil {
		return
	}
	if s.runtime != nil {
		_ = s.runtime.Close()
	}
}

func (s *Store) reload(logger *zap.Logger, onReload func(ReloadEvent)) {
	next, err := load(s.path)
	if err != nil {
		if logger != nil {
			logger.Warn("ops config reload rejected", zap.Error(err))
		}
		return
	}

	s.mu.Lock()
	previous := s.cfg
	s.cfg = next
	s.watchedFiles = snapshotFiles(watchFiles(s.path))
	s.mu.Unlock()

	event := ReloadEvent{
		Previous: previous,
		Current:  next,
		Changes:  Diff(previous, next),
	}
	if onReload != nil {
		onReload(event)
	}
	if logger != nil {
		restartRequired := RestartRequired(event.Changes)
		logger.Info("ops config reloaded", zap.Bool("restart_required", restartRequired))
		if restartRequired {
			logger.Warn("ops config reload changed connection or listener settings; restart process to apply those fields")
		}
	}
}

func (s *Store) notifyReload() {
	if !s.consumeFileChange() {
		return
	}
	select {
	case s.updates <- struct{}{}:
	default:
	}
}

func (s *Store) consumeFileChange() bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	next := snapshotFiles(watchFiles(s.path))
	if len(s.watchedFiles) == 0 {
		s.watchedFiles = next
		return true
	}
	changed := !fileSnapshotsEqual(s.watchedFiles, next)
	if changed {
		s.watchedFiles = next
	}
	return changed
}

func (s *Store) newRuntimeConfig() configruntime.Config {
	return configruntime.New(configruntime.WithSource(
		runtimefile.NewSource(filepath.Dir(s.path), watchNames(s.path)...),
		runtimeenv.NewSource("OPS"),
	))
}

func Diff(previous, current *Config) []FieldChange {
	if previous == nil || current == nil {
		return nil
	}
	changes := make([]FieldChange, 0)
	add := func(path string, hot bool) {
		changes = append(changes, FieldChange{Path: path, Hot: hot})
	}

	if !reflect.DeepEqual(previous.Server, current.Server) {
		add("server", false)
	}
	if previous.Database != current.Database {
		add("database", false)
	}
	if previous.MonitoringDatabase != current.MonitoringDatabase {
		add("monitoring_database", false)
	}
	if previous.Redis != current.Redis {
		add("redis", false)
	}
	if previous.Cache != current.Cache {
		add("cache", false)
	}
	if previous.RabbitMQ != current.RabbitMQ {
		add("rabbitmq", false)
	}
	if previous.Log != current.Log {
		add("log", false)
	}
	if previous.IPRegion != current.IPRegion {
		add("ip_region", false)
	}
	if previous.JWT != current.JWT {
		add("jwt", true)
	}
	if previous.AdminUsers != current.AdminUsers {
		add("admin_users", true)
	}
	if previous.DefaultAdmin != current.DefaultAdmin {
		add("default_admin", true)
	}
	return changes
}

func RestartRequired(changes []FieldChange) bool {
	for _, change := range changes {
		if !change.Hot {
			return true
		}
	}
	return false
}

func load(path string) (*Config, error) {
	resolved := configruntime.New(configruntime.WithSource(
		runtimefile.NewSource(path),
		runtimeenv.NewSource("OPS"),
	))
	defer resolved.Close()

	if err := resolved.Load(); err != nil {
		return nil, fmt.Errorf("read config: %w", err)
	}
	settings := defaultSettings()
	if err := resolved.Scan(&settings); err != nil {
		return nil, fmt.Errorf("scan config: %w", err)
	}
	applySharedDefaults(settings)

	var cfg Config
	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
		Result:           &cfg,
		TagName:          "mapstructure",
		WeaklyTypedInput: true,
		DecodeHook: mapstructure.ComposeDecodeHookFunc(
			mapstructure.StringToTimeDurationHookFunc(),
			mapstructure.StringToSliceHookFunc(","),
		),
	})
	if err != nil {
		return nil, err
	}
	if err := decoder.Decode(settings); err != nil {
		return nil, fmt.Errorf("unmarshal config: %w", err)
	}

	if err := applyEnvOverrides(&cfg); err != nil {
		return nil, err
	}
	normalizeConfig(&cfg)
	if cfg.JWT.Secret == "" {
		return nil, fmt.Errorf("jwt.secret is required (set jwt.secret in yaml or OPS_JWT_SECRET env)")
	}
	if cfg.MonitoringDatabase.DBName == "" {
		cfg.MonitoringDatabase = cfg.Database
	}
	return &cfg, nil
}

func applySharedDefaults(settings map[string]any) {
	cacheSettings := ensureMapSetting(settings, "cache")
	if _, ok := cacheSettings["metrics_enabled"]; !ok {
		cacheSettings["metrics_enabled"] = true
	}
}

func ensureMapSetting(settings map[string]any, key string) map[string]any {
	if settings == nil {
		return map[string]any{}
	}
	if existing, ok := settings[key].(map[string]any); ok {
		return existing
	}
	next := make(map[string]any)
	settings[key] = next
	return next
}

func normalizeConfig(cfg *Config) {
	if cfg.Server.Port == 0 {
		cfg.Server.Port = 8090
	}
	if strings.TrimSpace(cfg.Server.Mode) == "" {
		cfg.Server.Mode = "debug"
	}
	sharedconfig.NormalizeServerConfig(&cfg.Server)
	if strings.TrimSpace(cfg.Redis.Addr) == "" {
		cfg.Redis.Addr = "localhost:6379"
	}
	sharedconfig.NormalizeRedisConfig(&cfg.Redis)
	if strings.TrimSpace(cfg.Cache.Driver) == "" {
		cfg.Cache.Driver = "redis"
	}
	sharedconfig.NormalizeCacheConfig(&cfg.Cache)
	normalizeOpsRabbitMQConfig(&cfg.RabbitMQ)
	if strings.TrimSpace(cfg.Log.Level) == "" {
		cfg.Log.Level = "info"
	}
	if strings.TrimSpace(cfg.Log.Format) == "" {
		cfg.Log.Format = "json"
	}
	if cfg.JWT.AccessTTL <= 0 {
		cfg.JWT.AccessTTL = 8 * time.Hour
	}
	if strings.TrimSpace(cfg.DefaultAdmin.Username) == "" {
		cfg.DefaultAdmin.Username = "admin"
	}
	if strings.TrimSpace(cfg.DefaultAdmin.DisplayName) == "" {
		cfg.DefaultAdmin.DisplayName = "Administrator"
	}
	if strings.TrimSpace(cfg.AdminUsers.DefaultPlanCode) == "" {
		cfg.AdminUsers.DefaultPlanCode = "free"
	}
}

func defaultSettings() map[string]any {
	return map[string]any{
		"server": map[string]any{
			"port":            8090,
			"mode":            "debug",
			"trusted_proxies": sharedconfig.DefaultTrustedProxies(),
		},
		"redis": map[string]any{
			"addr": "localhost:6379",
			"db":   0,
		},
		"cache": map[string]any{
			"driver": "redis",
		},
		"rabbitmq": map[string]any{},
		"log": map[string]any{
			"level":  "info",
			"format": "json",
		},
		"jwt": map[string]any{
			"access_ttl": 8 * time.Hour,
		},
		"default_admin": map[string]any{
			"username":     "admin",
			"display_name": "Administrator",
		},
		"admin_users": map[string]any{
			"default_plan_code": "free",
		},
		"ip_region": map[string]any{
			"v4_xdb_path": "",
			"v6_xdb_path": "",
		},
	}
}

func applyEnvOverrides(cfg *Config) error {
	if v := os.Getenv("OPS_JWT_SECRET"); v != "" {
		cfg.JWT.Secret = v
	}
	if v := os.Getenv("OPS_DEFAULT_ADMIN_USERNAME"); v != "" {
		cfg.DefaultAdmin.Username = v
	}
	if v := os.Getenv("OPS_DEFAULT_ADMIN_PASSWORD"); v != "" {
		cfg.DefaultAdmin.Password = v
	}
	if v := os.Getenv("OPS_DEFAULT_ADMIN_DISPLAY_NAME"); v != "" {
		cfg.DefaultAdmin.DisplayName = v
	}
	if v := os.Getenv("OPS_DEFAULT_ADMIN_EMAIL"); v != "" {
		cfg.DefaultAdmin.Email = v
	}
	if v := os.Getenv("OPS_ADMIN_USERS_DEFAULT_PLAN_CODE"); v != "" {
		cfg.AdminUsers.DefaultPlanCode = v
	}
	if v := os.Getenv("OPS_IP_REGION_V4_XDB_PATH"); v != "" {
		cfg.IPRegion.V4XDBPath = v
	}
	if v := os.Getenv("OPS_IP_REGION_V6_XDB_PATH"); v != "" {
		cfg.IPRegion.V6XDBPath = v
	}
	if v := os.Getenv("OPS_SERVER_TRUSTED_PROXIES"); v != "" {
		cfg.Server.TrustedProxies = strings.Split(v, ",")
	}
	if v := os.Getenv("OPS_RABBITMQ_URL"); v != "" {
		cfg.RabbitMQ.URL = v
	}
	return nil
}

func normalizeOpsRabbitMQConfig(cfg *sharedconfig.RabbitMQConfig) {
	if cfg == nil {
		return
	}
	if strings.TrimSpace(cfg.GenerationExchange) == "" {
		cfg.GenerationExchange = "generation.task"
	}
	if strings.TrimSpace(cfg.GenerationRoutingKey) == "" {
		cfg.GenerationRoutingKey = "generation.task.run"
	}
	if strings.TrimSpace(cfg.DesktopTaskEventExchange) == "" {
		cfg.DesktopTaskEventExchange = "desktop.task.event"
	}
	if strings.TrimSpace(cfg.DesktopDispatchExchange) == "" {
		cfg.DesktopDispatchExchange = "desktop.task.dispatch"
	}
	if strings.TrimSpace(cfg.DesktopDispatchPublishPrefix) == "" {
		cfg.DesktopDispatchPublishPrefix = "publish"
	}
	if strings.TrimSpace(cfg.DesktopDispatchMonitorPrefix) == "" {
		cfg.DesktopDispatchMonitorPrefix = "monitor"
	}
	if strings.TrimSpace(cfg.TemplateAssistExchange) == "" {
		cfg.TemplateAssistExchange = "template.assist"
	}
	if strings.TrimSpace(cfg.TemplateAssistRoutingKey) == "" {
		cfg.TemplateAssistRoutingKey = "template.assist.run"
	}
	if strings.TrimSpace(cfg.KolAssistExchange) == "" {
		cfg.KolAssistExchange = "kol.assist"
	}
	if strings.TrimSpace(cfg.KolAssistRoutingKey) == "" {
		cfg.KolAssistRoutingKey = "kol.assist.run"
	}
	if strings.TrimSpace(cfg.ComplianceReviewExchange) == "" {
		cfg.ComplianceReviewExchange = "compliance.review"
	}
	if strings.TrimSpace(cfg.ComplianceReviewRoutingKey) == "" {
		cfg.ComplianceReviewRoutingKey = "compliance.review.run"
	}
	if cfg.PublishChannelPoolSize <= 0 {
		cfg.PublishChannelPoolSize = 16
	}
}

type fileSnapshot struct {
	size    int64
	modTime time.Time
	exists  bool
}

func snapshotFiles(files []string) map[string]fileSnapshot {
	snapshots := make(map[string]fileSnapshot, len(files))
	for _, file := range files {
		if strings.TrimSpace(file) == "" {
			continue
		}
		abs, err := filepath.Abs(file)
		if err == nil {
			file = abs
		}
		file = filepath.Clean(file)
		info, err := os.Stat(file)
		if err != nil {
			snapshots[file] = fileSnapshot{}
			continue
		}
		snapshots[file] = fileSnapshot{
			size:    info.Size(),
			modTime: info.ModTime(),
			exists:  true,
		}
	}
	return snapshots
}

func fileSnapshotsEqual(a, b map[string]fileSnapshot) bool {
	if len(a) != len(b) {
		return false
	}
	for key, left := range a {
		right, ok := b[key]
		if !ok || left != right {
			return false
		}
	}
	return true
}

func watchFiles(path string) []string {
	if strings.TrimSpace(path) == "" {
		return nil
	}
	return []string{path}
}

func watchNames(path string) []string {
	if strings.TrimSpace(path) == "" {
		return nil
	}
	return []string{filepath.Base(path)}
}