feat(blog): show random fallback articles in post footer navigation instead of blank spaces

lib/blog.ts

@@ -109,7 +109,7 @@ export async function getAllPostsMetadata(locale: string): Promise<Partial<PostM
 export async function getAdjacentPosts(
   slug: string,
   locale: string,
-): Promise<{ prev: PostMdx | null; next: PostMdx | null }> {
+): Promise<{ prev: PostMdx | null; next: PostMdx | null; isPrevRandom?: boolean; isNextRandom?: boolean }> {
   const posts = await getAllPosts(locale);
   const currentIndex = posts.findIndex((post) => post.slug === slug);
 
@@ -120,10 +120,31 @@ export async function getAdjacentPosts(
   // Posts are sorted by date descending (newest first)
   // So "next" post (newer) is at index - 1
   // And "previous" post (older) is at index + 1
-  const next = currentIndex > 0 ? posts[currentIndex - 1] : null;
-  const prev = currentIndex < posts.length - 1 ? posts[currentIndex + 1] : null;
+  let next = currentIndex > 0 ? posts[currentIndex - 1] : null;
+  let prev = currentIndex < posts.length - 1 ? posts[currentIndex + 1] : null;
 
-  return { prev, next };
+  let isNextRandom = false;
+  let isPrevRandom = false;
+
+  const getRandomPost = (excludeSlugs: string[]) => {
+    const available = posts.filter(p => !excludeSlugs.includes(p.slug));
+    if (available.length === 0) return null;
+    return available[Math.floor(Math.random() * available.length)];
+  };
+
+  // If there's no next post (we are at the newest post), show a random post instead
+  if (!next && posts.length > 2) {
+    next = getRandomPost([slug, prev?.slug].filter(Boolean) as string[]);
+    isNextRandom = true;
+  }
+
+  // If there's no previous post (we are at the oldest post), show a random post instead
+  if (!prev && posts.length > 2) {
+    prev = getRandomPost([slug, next?.slug].filter(Boolean) as string[]);
+    isPrevRandom = true;
+  }
+
+  return { prev, next, isPrevRandom, isNextRandom };
 }
 
 export function getReadingTime(content: string): number {