import json
from pathlib import Path
from functools import lru_cache
from typing import Any, Dict


FALLBACK_LANG = "ru"


@lru_cache(maxsize=16)
def _load_lang(lang: str) -> Dict[str, Any]:
    base_dir = Path(__file__).resolve().parents[1] / "locales"
    file_path = base_dir / f"{lang}.json"
    if not file_path.exists():
        # fallback to default
        if lang != FALLBACK_LANG:
            return _load_lang(FALLBACK_LANG)
        return {}
    try:
        return json.loads(file_path.read_text(encoding="utf-8"))
    except Exception:
        return {}


def _resolve_key(data: Dict[str, Any], dotted_key: str) -> Any:
    cur: Any = data
    for part in dotted_key.split("."):
        if not isinstance(cur, dict) or part not in cur:
            return None
        cur = cur[part]
    return cur


def get_user_lang(user) -> str:
    """Унифицированное получение языка интерфейса пользователя."""
    return (getattr(user, 'language_interface', None) if user else None) or 'ru'


def t(lang: str, key: str, **kwargs) -> str:
    """Translate key for given lang; fallback to ru and to key itself.

    Supports dotted keys and str.format(**kwargs) placeholders.
    """
    data = _load_lang(lang or FALLBACK_LANG)
    value = _resolve_key(data, key)
    if value is None and lang != FALLBACK_LANG:
        value = _resolve_key(_load_lang(FALLBACK_LANG), key)
    if value is None:
        value = key  # last resort: return the key
    try:
        if isinstance(value, str) and kwargs:
            return value.format(**kwargs)
    except Exception:
        pass
    return value if isinstance(value, str) else str(value)