refactor progress

packages/locale/src/resolution/AcceptLanguageNegotiation.tsx

@@ -0,0 +1,120 @@
+/*
+ * 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 type {LocaleCode} from '@fluxer/constants/src/Locales';
+import {
+	DEFAULT_LOCALE,
+	findLocaleByLanguagePrefix,
+	getLocaleByCode,
+	getPreferredLocaleForLanguageCode,
+	normalizeLocaleCode,
+} from '@fluxer/locale/src/catalog/LocaleCatalog';
+
+interface AcceptLanguagePreference {
+	locale: string;
+	quality: number;
+}
+
+export function resolveLocaleFromAcceptLanguageHeader(acceptLanguageHeader: string | null | undefined): LocaleCode {
+	if (!acceptLanguageHeader) {
+		return DEFAULT_LOCALE;
+	}
+
+	try {
+		const preferences = parseAcceptLanguagePreferences(acceptLanguageHeader);
+		const exactLocaleMatch = findExactLocaleMatch(preferences);
+		if (exactLocaleMatch) {
+			return exactLocaleMatch;
+		}
+
+		const languageFallbackMatch = findLanguageFallbackMatch(preferences);
+		if (languageFallbackMatch) {
+			return languageFallbackMatch;
+		}
+
+		return DEFAULT_LOCALE;
+	} catch {
+		return DEFAULT_LOCALE;
+	}
+}
+
+function parseAcceptLanguagePreferences(acceptLanguageHeader: string): Array<AcceptLanguagePreference> {
+	return acceptLanguageHeader
+		.split(',')
+		.map((languageToken) => parseLanguagePreference(languageToken))
+		.sort((a, b) => b.quality - a.quality);
+}
+
+function parseLanguagePreference(languageToken: string): AcceptLanguagePreference {
+	const parts = languageToken.trim().split(';');
+	const locale = parts[0].trim();
+	const quality = parseQualityValue(parts[1]);
+	return {
+		locale,
+		quality,
+	};
+}
+
+function parseQualityValue(rawQuality: string | undefined): number {
+	const qualityMatch = rawQuality?.match(/q=([\d.]+)/);
+	if (!qualityMatch) {
+		return 1.0;
+	}
+
+	const parsedQuality = Number.parseFloat(qualityMatch[1]);
+	if (!Number.isFinite(parsedQuality)) {
+		return 1.0;
+	}
+
+	return parsedQuality;
+}
+
+function findExactLocaleMatch(preferences: ReadonlyArray<AcceptLanguagePreference>): LocaleCode | null {
+	for (const {locale} of preferences) {
+		const exactMatch = getLocaleByCode(locale);
+		if (exactMatch) {
+			return exactMatch;
+		}
+	}
+
+	return null;
+}
+
+function findLanguageFallbackMatch(preferences: ReadonlyArray<AcceptLanguagePreference>): LocaleCode | null {
+	for (const {locale} of preferences) {
+		const languageCode = getLanguageCode(locale);
+		const preferredFallbackLocale = getPreferredLocaleForLanguageCode(languageCode);
+		if (preferredFallbackLocale) {
+			return preferredFallbackLocale;
+		}
+
+		const prefixMatchLocale = findLocaleByLanguagePrefix(languageCode);
+		if (prefixMatchLocale) {
+			return prefixMatchLocale;
+		}
+	}
+
+	return null;
+}
+
+function getLanguageCode(locale: string): string {
+	const normalizedLocale = normalizeLocaleCode(locale);
+	const [languageCode] = normalizedLocale.split('-');
+	return languageCode ?? '';
+}