Added support for single localization

src/modules/seo/hreflang.ts

@@ -1,11 +1,12 @@
 import type { I18nConfig, LocalizedSlugs } from '../i18n/index.js'
-
-import { buildLocalizedPath, getDefaultLocale, getLocaleCodes } from '../i18n/index.js'
+import { buildLocalizedPath, getLocaleCodes } from '../i18n/index.js'
 
 type BuildHreflangArgs = {
+  /** slug per locale for the current document, e.g. { pl: 'o-nas', en: 'about' } */
+  slugs: LocalizedSlugs
+  config: I18nConfig
   /** Absolute site origin, e.g. 'https://example.com'. Omit for relative paths. */
   baseUrl?: string
-  config: I18nConfig
   /** Home slug that collapses to the locale root. Defaults to 'home'. */
   homeSlug?: string
   /**
@@ -14,46 +15,44 @@ type BuildHreflangArgs = {
    * are omitted — an entry with no archive in that language has no URL there.
    */
   prefix?: LocalizedSlugs
-  /** slug per locale for the current document, e.g. { pl: 'o-nas', en: 'about' } */
-  slugs: LocalizedSlugs
 }
 
 /**
+ * Builds a map of locale → URL for hreflang alternate links, suitable for
  * Next.js Metadata `alternates.languages`.
  *
  * Bridges SEO and i18n: for each configured locale that the document has a
  * slug in, it produces the locale-aware path (via buildLocalizedPath),
  * optionally prefixed with an absolute origin.
  *
- * Also emits `x-default` pointing at the default locale — the version Google
- * serves when the user's language/region matches no hreflang, and the fallback
- * when the root ('/') redirect is ambiguous (Googlebot with no/foreign
- * Accept-Language).
- *
  * @example
  * buildHreflangAlternates({
  *   slugs: { pl: 'o-nas', en: 'about' },
  *   config,
  *   baseUrl: 'https://example.com',
  * })
- * // → {
- * //   pl: 'https://example.com/pl/o-nas',
- * //   en: 'https://example.com/en/about',
- * //   'x-default': 'https://example.com/pl/o-nas',
- * // }
+ * // → { pl: 'https://example.com/pl/o-nas', en: 'https://example.com/en/about' }
  */
 export function buildHreflangAlternates({
-  baseUrl,
+  slugs,
   config,
+  baseUrl,
   homeSlug = 'home',
   prefix,
-  slugs,
 }: BuildHreflangArgs): Record<string, string> {
   const origin = baseUrl?.replace(/\/$/, '') ?? ''
   const alternates: Record<string, string> = {}
 
+  // Single-locale sites have no language alternatives — hreflang describes
+  // relationships BETWEEN language versions, and there's only one. Emitting
+  // hreflang (or x-default) here would be wrong, so return empty: the page keeps
+  // its canonical, but no alternate-language links.
+  if (config.locales.length === 1) {
+    return alternates
+  }
+
   for (const locale of getLocaleCodes(config)) {
-    const path = buildLocalizedPath({ config, homeSlug, locale, prefix, slugs })
+    const path = buildLocalizedPath({ slugs, locale, config, homeSlug, prefix })
     if (path) {
       alternates[locale] = `${origin}${path}`
     }
@@ -64,7 +63,7 @@ export function buildHreflangAlternates({
   // redirect is ambiguous (Googlebot with no/foreign Accept-Language). Point it
   // at the default locale (the primary market) so search shows that version by
   // default instead of guessing. Only set when the default locale has a URL.
-  const defaultLocalePath = alternates[getDefaultLocale(config)]
+  const defaultLocalePath = alternates[config.defaultLocale]
   if (defaultLocalePath) {
     alternates['x-default'] = defaultLocalePath
   }