import json
import os
import re

ACCEPT_LANGUAGE_HEADER_REGEX = re.compile(r"([a-zA-Z]{2,3})(-[a-zA-Z\-]+)?")


def t(*args, **kwargs):
    return TranslationHandler.translate(*args, **kwargs)


class TranslationHandler:
    translations = {}
    language = "en"
    language_available = {"en": True}
    always_reload_translations = False

    @classmethod
    def init(cls, app):
        cls.app = app
        cls.always_reload_translations = app.debug
        app.context_processor(lambda: dict(t=t))

    @classmethod
    def is_language_available(cls, language):
        if language not in cls.language_available:
            cls.language_available[language] = os.path.exists(
                cls.get_language_filepath(language)
            )
        return cls.language_available[language]

    @classmethod
    def set_language(cls, language):
        if not cls.is_language_available(language):
            cls.app.logger.info(f"Cannot find language {language}. Default to en.")
            language = "en"

        cls.language = language
        if language != "en" and (
            cls.always_reload_translations or language not in cls.translations
        ):
            cls.translations[language] = json.load(
                open(cls.get_language_filepath(language), "r")
            )

    @classmethod
    def translate(cls, string, **interpolation):
        if cls.language == "en":
            return string.format(**interpolation)

        if string not in cls.translations[cls.language]:
            cls.app.logger.warning(
                f'Unknown translation to {cls.language} for "{string}"'
            )
            return string.format(**interpolation)

        return cls.translations[cls.language][string].format(**interpolation)

    @classmethod
    def parse_language_header(cls, header):
        if not header:
            return None

        if "*" in header:
            return None

        languages = [match[0] for match in ACCEPT_LANGUAGE_HEADER_REGEX.findall(header)]
        # take the first matching one
        for language in languages:
            if cls.is_language_available(language):
                return language
        return None

    @classmethod
    def get_language_filepath(cls, language):
        return os.path.join(cls.app.root_path, f"private_static/i18n/{language}.json")