package i18n

import (
	"encoding/json"
	"fmt"
	"io/fs"
	"sync"
)

var (
	mu       sync.RWMutex
	messages map[string]map[string]string
	fallback string
)

func Init(fsys fs.FS, defaultLang string) error {
	mu.Lock()
	defer mu.Unlock()

	messages = make(map[string]map[string]string)
	fallback = defaultLang

	entries, err := fs.ReadDir(fsys, ".")
	if err != nil {
		return fmt.Errorf("i18n: read messages dir: %w", err)
	}

	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		data, err := fs.ReadFile(fsys, e.Name())
		if err != nil {
			return fmt.Errorf("i18n: read %s: %w", e.Name(), err)
		}
		lang := langFromFilename(e.Name())
		kv := make(map[string]string)
		if err := json.Unmarshal(data, &kv); err != nil {
			return fmt.Errorf("i18n: parse %s: %w", e.Name(), err)
		}
		messages[lang] = kv
	}

	return nil
}

func T(lang, key string) string {
	mu.RLock()
	defer mu.RUnlock()

	if msgs, ok := messages[lang]; ok {
		if v, ok := msgs[key]; ok {
			return v
		}
	}
	if msgs, ok := messages[fallback]; ok {
		if v, ok := msgs[key]; ok {
			return v
		}
	}
	return key
}

func SupportedLanguages() []string {
	mu.RLock()
	defer mu.RUnlock()
	out := make([]string, 0, len(messages))
	for k := range messages {
		out = append(out, k)
	}
	return out
}

func langFromFilename(name string) string {
	for i, c := range name {
		if c == '.' {
			return name[:i]
		}
	}
	return name
}