package i18n

import (
	"embed"
	"encoding/json"
	"fmt"
	"strings"
	"sync"
)

//go:embed locales/*.json
var localeFS embed.FS

var (
	mu       sync.RWMutex
	cache    = map[string]map[string]string{}
	defaultLocale = "ru"
)

// T returns a localized string for the given locale and key.
// It supports printf-style formatting via args.
// Falls back: key not found -> ru -> key itself.
func T(locale, key string, args ...any) string {
	mu.RLock()
	catalog, ok := cache[locale]
	mu.RUnlock()
	if !ok {
		catalog = loadLocale(locale)
	}
	msg, ok := catalog[key]
	if !ok && locale != defaultLocale {
		mu.RLock()
		ruCatalog, ruOK := cache[defaultLocale]
		mu.RUnlock()
		if ruOK {
			msg = ruCatalog[key]
		}
		if msg == "" {
			msg = key
		}
	}
	if msg == "" {
		msg = key
	}
	if len(args) > 0 {
		return fmt.Sprintf(msg, args...)
	}
	return msg
}

// TF is a shorthand for T with formatting.
func TF(locale, key string, args ...any) string {
	return T(locale, key, args...)
}

// SetDefault changes the default locale.
func SetDefault(locale string) {
	mu.Lock()
	defaultLocale = locale
	mu.Unlock()
}

// AvailableLocales returns locale names for which files exist.
func AvailableLocales() []string {
	entries, err := localeFS.ReadDir("locales")
	if err != nil {
		return nil
	}
	var out []string
	for _, e := range entries {
		name := e.Name()
		name = strings.TrimSuffix(name, ".json")
		out = append(out, name)
	}
	return out
}

func loadLocale(locale string) map[string]string {
	data, err := localeFS.ReadFile("locales/" + locale + ".json")
	if err != nil {
		data = []byte("{}")
	}
	var m map[string]string
	json.Unmarshal(data, &m)
	if m == nil {
		m = map[string]string{}
	}
	mu.Lock()
	cache[locale] = m
	mu.Unlock()
	return m
}