package i18n

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"path/filepath"
	"sync"
)

// Translator handles translation loading and retrieval.
type Translator struct {
	mu       sync.RWMutex
	messages map[string]map[string]string // lang -> key -> message
}

// NewTranslator loads JSON locale files en.json and fa.json from the i18n directory.
// defaultLang sets the default fallback language (e.g., "en").
func NewTranslator(defaultLang string) (*Translator, error) {
	if defaultLang == "" {
		defaultLang = "en"
	}
	t := &Translator{
		messages: make(map[string]map[string]string),
	}
	// Load known locale files: en.json and fa.json located in the same package directory.
	for _, lang := range []string{"en", "fa"} {
		filePath := filepath.Join("i18n", lang+".json")
		data, err := ioutil.ReadFile(filePath)
		if err != nil {
			return nil, err
		}
		var m map[string]string
		if err := json.Unmarshal(data, &m); err != nil {
			return nil, err
		}
		t.messages[lang] = m
	}
	// Ensure default language exists.
	if _, ok := t.messages[defaultLang]; !ok {
		return nil, fmt.Errorf("default language %s not found", defaultLang)
	}
	return t, nil
}

// Get returns the translated string for a given key and language.
// Falls back to English if the key/language is missing.
func (t *Translator) Get(key, lang string) string {
	if lang == "" {
		lang = "en"
	}
	t.mu.RLock()
	defer t.mu.RUnlock()
	if msgs, ok := t.messages[lang]; ok {
		if v, ok := msgs[key]; ok {
			return v
		}
	}
	// fallback to English messages
	if msgs, ok := t.messages["en"]; ok {
		if v, ok := msgs[key]; ok {
			return v
		}
	}
	// If not found, return the key itself.
	return key
}