wip: i18n

questionpy/i18n.py

@@ -0,0 +1,92 @@
+from gettext import GNUTranslations, NullTranslations
+from importlib.resources.abc import Traversable
+
+from questionpy_common.environment import Environment, Package, RequestUser
+
+_DEFAULT_CATEGORY = "LC_MESSAGES"
+_DEFAULT_DOMAIN = "package"
+_NULL_TRANSLATIONS = NullTranslations()
+
+_STATE: tuple[str, NullTranslations] | None = None
+
+
+def _guess_untranslated_language(package: Package) -> str:
+    # We'll assume that the untranslated messages are in the first supported language according to the manifest.
+    if package.manifest.languages:
+        return next(iter(package.manifest.languages))
+    # If the package lists no supported languages in its manifest, we'll assume it's english.
+    # TODO: An alternative might be "C" or "unknown"?
+    return "en"
+
+
+def _build_translations(
+    mos: dict[str, Traversable], package: Package, request_user: RequestUser
+) -> tuple[str, NullTranslations]:
+    primary_lang: str | None = None
+    translations: NullTranslations | None = None
+
+    for preferred_lang in request_user.preferred_languages:
+        if preferred_lang not in mos:
+            continue
+
+        with mos[preferred_lang].open("rb") as mo_file:
+            # GNUTranslations reads the file immediately, so we can safely close it afterward.
+            lang_translations = GNUTranslations(mo_file)
+
+        if translations:
+            translations.add_fallback(lang_translations)
+        else:
+            translations = lang_translations
+            primary_lang = preferred_lang
+
+    if primary_lang and translations:
+        return primary_lang, translations
+
+    # There are no .mo files for any of the users preferred languages. We'll use NullTranslations, i.e. not translate
+    # anything, and guess at which language the untranslated messages are in.
+    return _guess_untranslated_language(package), _NULL_TRANSLATIONS
+
+
+def _get_available_mos(package: Package) -> dict[str, Traversable]:
+    result = {}
+    locale_dir = package.get_path("locale")
+    if not locale_dir.is_dir():
+        return {}
+
+    for lang_dir in locale_dir.iterdir():
+        if not lang_dir.is_dir():
+            continue
+
+        mo_file = lang_dir / _DEFAULT_CATEGORY / f"{_DEFAULT_DOMAIN}.mo"
+        if mo_file.is_file():
+            result[lang_dir.name] = mo_file
+
+    return result
+
+
+def get_state() -> tuple[str, NullTranslations]:
+    if not _STATE:
+        msg = f"i18n was not initialized. Call {__name__}.{initialize.__name__} first."
+        raise RuntimeError(msg)
+    return _STATE
+
+
+def initialize(package: Package, env: Environment) -> None:
+    # PLW0603 discourages the global statement, but the alternative would be less readable.
+    # ruff: noqa: PLW0603
+
+    global _STATE
+    if _STATE:
+        # Prevent multiple initializations, which would add multiple on_request_callbacks overwriting each other.
+        return
+
+    available_mos = _get_available_mos(package)
+
+    def prepare_i18n(request_user: RequestUser) -> None:
+        global _STATE
+        _, translations = _STATE = _build_translations(available_mos, package, request_user)
+        translations.install()
+
+    _STATE = (_guess_untranslated_language(package), _NULL_TRANSLATIONS)
+    _NULL_TRANSLATIONS.install()
+    env.register_on_request_callback(prepare_i18n)