Codex fixes

lib/mdx.ts

@@ -17,11 +17,38 @@ export type Post = {
     content: string;
 };
 
+function readPostMetadata(data: Record<string, unknown>, slug: string): PostMetadata {
+    if (
+        typeof data.title !== 'string' ||
+        typeof data.date !== 'string' ||
+        typeof data.description !== 'string'
+    ) {
+        throw new Error(`Invalid frontmatter for post: ${slug}`);
+    }
+
+    if (!Number.isFinite(Date.parse(data.date))) {
+        throw new Error(`Invalid date for post: ${slug}`);
+    }
+
+    return {
+        title: data.title,
+        date: data.date,
+        description: data.description,
+        slug,
+        tags: Array.isArray(data.tags)
+            ? data.tags.filter((tag): tag is string => typeof tag === 'string')
+            : undefined,
+    };
+}
+
 export function getPostSlugs() {
     if (!fs.existsSync(postsDirectory)) {
         return [];
     }
-    return fs.readdirSync(postsDirectory);
+    return fs
+        .readdirSync(postsDirectory, { withFileTypes: true })
+        .filter((entry) => entry.isFile())
+        .map((entry) => entry.name);
 }
 
 export function getPostBySlug(slug: string): Post {
@@ -43,10 +70,7 @@ export function getPostBySlug(slug: string): Post {
     const { data, content } = matter(fileContents);
 
     return {
-        metadata: {
-            ...data,
-            slug: realSlug,
-        } as PostMetadata,
+        metadata: readPostMetadata(data, realSlug),
         content,
     };
 }
@@ -57,6 +81,6 @@ export function getAllPosts(): PostMetadata[] {
         .filter((slug) => slug.endsWith('.mdx'))
         .map((slug) => getPostBySlug(slug).metadata)
         // Sort posts by date in descending order
-        .sort((post1, post2) => (post1.date > post2.date ? -1 : 1));
+        .sort((post1, post2) => new Date(post2.date).getTime() - new Date(post1.date).getTime());
     return posts;
 }