cleanup tags on edit

src/app/blog/write/action.ts

@@ -39,6 +39,21 @@ export async function savePostServer(
   const slug = slugify(title, { lower: true, strict: true });
 
   if (existingSlug) {
+    const post = await prisma.post.findUnique({
+      where: { slug: existingSlug },
+      include: { tags: true },
+    });
+    if (!post) {
+      throw new Error("Post not found");
+    }
+    for (const tag of post.tags) {
+      const postsWithTag = await prisma.post.count({
+        where: { tags: { some: { id: tag.id } } },
+      });
+      if (postsWithTag == 0) {
+        await prisma.tag.delete({ where: { id: tag.id } });
+      }
+    }
     await prisma.post.delete({ where: { slug: existingSlug } });
   }