import importlib.util
from pathlib import Path
import sys
import unittest


_MODULE_PATH = Path(__file__).parents[1] / "app" / "utils" / "language_policy.py"
_SPEC = importlib.util.spec_from_file_location("language_policy_under_test", _MODULE_PATH)
assert _SPEC is not None and _SPEC.loader is not None
_LANGUAGE_POLICY = importlib.util.module_from_spec(_SPEC)
sys.modules[_SPEC.name] = _LANGUAGE_POLICY
_SPEC.loader.exec_module(_LANGUAGE_POLICY)

DEFAULT_LOCALE = _LANGUAGE_POLICY.DEFAULT_LOCALE
SUPPORTED_LOCALES = _LANGUAGE_POLICY.SUPPORTED_LOCALES
locale_from_accept_language = _LANGUAGE_POLICY.locale_from_accept_language
normalize_locale = _LANGUAGE_POLICY.normalize_locale


class LanguagePolicyTests(unittest.TestCase):
    def test_supported_locales_are_thai_and_english(self):
        self.assertEqual(SUPPORTED_LOCALES, ("th", "en"))
        self.assertEqual(DEFAULT_LOCALE, "th")

    def test_normalize_locale_accepts_language_region_values(self):
        self.assertEqual(normalize_locale("en-US"), "en")
        self.assertEqual(normalize_locale("TH_th"), "th")

    def test_normalize_locale_migrates_legacy_chinese_to_default(self):
        self.assertEqual(normalize_locale("zh"), "th")
        self.assertEqual(normalize_locale("zh-CN"), "th")

    def test_normalize_locale_falls_back_for_unknown_values(self):
        self.assertEqual(normalize_locale(None), "th")
        self.assertEqual(normalize_locale("fr"), "th")
        self.assertEqual(normalize_locale(""), "th")

    def test_accept_language_uses_quality_and_skips_zero_quality(self):
        header = "zh-CN;q=1, fr-FR;q=0.9, en-US;q=0.8, th;q=0"
        self.assertEqual(locale_from_accept_language(header), "en")

    def test_accept_language_returns_default_when_no_supported_language_exists(self):
        self.assertEqual(locale_from_accept_language("ja-JP, de;q=0.8"), "th")


if __name__ == "__main__":
    unittest.main()