feat: support mobile video previews

src/languageRoutes.ts

@@ -33,3 +33,55 @@ 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;
+}