refactor progress

packages/i18n/src/runtime/GetEffectiveLocale.tsx

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {hasLocaleFile} from '@fluxer/i18n/src/io/LocaleFilePath';
+import type {I18nState} from '@fluxer/i18n/src/runtime/I18nTypes';
+
+export function getEffectiveLocale<TKey extends string, TValue, TVariables>(
+	state: I18nState<TKey, TValue, TVariables>,
+	locale: string | null | undefined,
+): string {
+	if (!locale) {
+		return state.config.defaultLocale;
+	}
+
+	const normalizeLocale = state.config.normalizeLocale ?? ((locale: string) => locale);
+	const normalizedLocale = normalizeLocale(locale);
+
+	if (normalizedLocale === state.config.defaultLocale) {
+		return state.config.defaultLocale;
+	}
+
+	if (!hasLocaleFile(normalizedLocale, state.config.localesPath, state.config.defaultLocale)) {
+		state.config.onWarning?.(`Unsupported locale, falling back to ${state.config.defaultLocale}: ${locale}`);
+		return state.config.defaultLocale;
+	}
+
+	return normalizedLocale;
+}