import json
from functools import lru_cache
from pathlib import Path

from flask import current_app, session
from flask_login import current_user


@lru_cache(maxsize=8)
def load_language(language: str) -> dict:
    base = Path(__file__).resolve().parent.parent / 'static' / 'i18n'
    file_path = base / f'{language}.json'
    if not file_path.exists():
        file_path = base / 'pl.json'
    return json.loads(file_path.read_text(encoding='utf-8'))


def get_locale() -> str:
    if getattr(current_user, 'is_authenticated', False):
        return current_user.language or current_app.config['DEFAULT_LANGUAGE']
    return session.get('language', current_app.config['DEFAULT_LANGUAGE'])


def translate(key: str, default: str | None = None) -> str:
    language = get_locale()
    data = load_language(language)
    if key in data:
        return data[key]
    fallback = load_language(current_app.config.get('DEFAULT_LANGUAGE', 'pl'))
    if key in fallback:
        return fallback[key]
    en = load_language('en')
    return en.get(key, default or key)


def inject_i18n():
    return {'t': translate, 'current_language': get_locale()}