import json
from pathlib import Path


DEFAULT_LANG = "sk"
SUPPORTED_LANGS = {"sk", "cs", "en", "de", "hu", "pl", "it"}


def normalize_lang(lang: str | None) -> str:
    value = str(lang or DEFAULT_LANG).strip().lower()
    if value == "cz":
        value = "cs"
    return value if value in SUPPORTED_LANGS else DEFAULT_LANG


class Translator:
    def __init__(self, lang: str = DEFAULT_LANG, locale_dir: str | Path | None = None):
        self.locale_dir = Path(locale_dir) if locale_dir else Path(__file__).with_name("locales")
        self.lang = DEFAULT_LANG
        self.messages: dict[str, str] = {}
        self.set_lang(lang)

    def set_lang(self, lang: str | None):
        self.lang = normalize_lang(lang)
        fallback = self._load(DEFAULT_LANG)
        current = self._load(self.lang) if self.lang != DEFAULT_LANG else {}
        self.messages = {**fallback, **current}

    def _load(self, lang: str) -> dict[str, str]:
        path = self.locale_dir / f"{normalize_lang(lang)}.json"
        if not path.exists():
            return {}
        try:
            with path.open("r", encoding="utf-8") as f:
                data = json.load(f)
        except Exception as e:
            print(f"Invalid locale JSON : {e}")
            return {}
        return {str(k): str(v) for k, v in data.items()}

    def tr(self, key: str, default: str | None = None, **kwargs) -> str:
        text = self.messages.get(key, default if default is not None else key)
        if kwargs:
            try:
                return text.format(**kwargs)
            except Exception:
                return text
        return text


def available_locales(locale_dir: str | Path | None = None) -> list[str]:
    base = Path(locale_dir) if locale_dir else Path(__file__).with_name("locales")
    if not base.exists():
        return []
    return sorted(path.stem for path in base.glob("*.json"))