Arkie-Library-Frontend/src/languageRoutes.ts

import type { Lang } from "./i18n";

export const localizedHomeRoutes: ReadonlyArray<{ lang: Lang; path: string }> =
  [
    { lang: "zh-CN", path: "/chinese" },
    { lang: "ja", path: "/japanese" },
    { lang: "ko", path: "/korean" },
    { lang: "vi", path: "/vietnamese" },
    { lang: "id", path: "/indonesian" },
    { lang: "ms", path: "/malay" },
  ];

function normalizePathname(pathname: string): string {
  const normalized = pathname.replace(/\/+$/, "");
  return normalized || "/";
}

export function languageForHomePathname(pathname: string): Lang | null {
  const normalized = normalizePathname(pathname);
  return (
    localizedHomeRoutes.find((route) => route.path === normalized)?.lang ?? null
  );
}

export function isHomePathname(pathname: string): boolean {
  return (
    normalizePathname(pathname) === "/" ||
    languageForHomePathname(pathname) !== null
  );
}

export function homePathForLang(lang: Lang): string {
  if (lang === "en") return "/";
  return localizedHomeRoutes.find((route) => route.lang === lang)?.path ?? "/";
}

/** Returns the URL prefix for a language (e.g. "/malay"), or "" for English. */
export function langPathPrefix(lang: Lang): string {
  if (lang === "en") return "";
  return localizedHomeRoutes.find((route) => route.lang === lang)?.path ?? "";
}

/** Detects which language a URL belongs to by inspecting the path prefix. */
export function languageFromPathname(pathname: string): Lang {
  const normalized = normalizePathname(pathname);
  for (const route of localizedHomeRoutes) {
    if (normalized === route.path || normalized.startsWith(route.path + "/")) {
      return route.lang;
    }
  }
  return "en";
}

/**
 * Prepends a language prefix to a path. Path may include `?query` or `#hash`;
 * the prefix is inserted before the pathname only.
 *
 *   localizePath("/browse", "ms") -> "/malay/browse"
 *   localizePath("/", "ms")       -> "/malay"
 *   localizePath("/browse", "en") -> "/browse"
 */
export function localizePath(path: string, lang: Lang): string {
  const prefix = langPathPrefix(lang);
  if (!prefix) return path;
  if (!path.startsWith("/")) path = "/" + path;
  if (path === "/") return prefix;
  return prefix + path;
}

/**
 * Removes any known language prefix from a pathname. Useful when comparing
 * the current route against canonical (unprefixed) paths.
 *
 *   stripLangPrefix("/malay/browse") -> "/browse"
 *   stripLangPrefix("/malay")        -> "/"
 *   stripLangPrefix("/browse")       -> "/browse"
 */
export function stripLangPrefix(pathname: string): string {
  const normalized = normalizePathname(pathname);
  for (const route of localizedHomeRoutes) {
    if (normalized === route.path) return "/";
    if (normalized.startsWith(route.path + "/")) {
      return normalized.slice(route.path.length);
    }
  }
  return normalized;
}