"""i18n module — loads translations from app/locales/*.json.

Usage in templates: {{ 'key'|t(user.language) }}
Usage in Python:     from app.i18n import t; t("key", lang)

To add a new language:
  1. Create app/locales/<lang>.json with translation keys
  2. Done — it will be auto-detected and available in the UI
"""

import json
from pathlib import Path

_LOCALES_DIR = Path(__file__).resolve().parent / "locales"
_cache: dict[str, dict[str, str]] = {}
_loaded = False


def _load() -> None:
    global _loaded
    if _loaded:
        return
    _LOCALES_DIR.mkdir(exist_ok=True)
    for f in _LOCALES_DIR.glob("*.json"):
        lang = f.stem  # e.g. "zh", "en", "ja"
        with open(f, encoding="utf-8") as fh:
            _cache[lang] = json.load(fh)
    _loaded = True


def t(key: str, lang: str = "zh") -> str:
    """Translate *key* to *lang*. Falls back to zh, then to the raw key."""
    _load()
    # Try requested language
    val = _cache.get(lang, {}).get(key)
    if val is not None:
        return val
    # Fallback to zh
    if lang != "zh":
        val = _cache.get("zh", {}).get(key)
        if val is not None:
            return val
    # Fallback to any available language
    for translations in _cache.values():
        if key in translations:
            return translations[key]
    return key


def get_languages() -> dict[str, str]:
    """Return available languages as {code: native_name}.

    Each JSON file can optionally include a top-level ``_meta`` key
    with ``{"name": "语言名称"}`` to set the display name.
    If absent, the language code is used as-is.
    """
    _load()
    result: dict[str, str] = {}
    for lang in sorted(_cache):
        meta = _cache[lang].get("_meta", {})
        result[lang] = meta.get("name", lang)
    return result