put defineSlugForDocument in ui folder

apps/sanity/schema/ui/define-slug-for-document.tsx

@@ -0,0 +1,41 @@
+import { defineField } from "sanity";
+import { slugify } from "../../utils/slugify";
+import { isUniqueSlug } from "../../utils/is-unique-slug";
+
+export const defineSlugForDocument = ({ prefix = '', slug }: { prefix?: string, slug?: string }) => [
+  defineField({
+    name: 'title',
+    type: 'string',
+    title: 'Title',
+    description: 'The title of the document, used for display in the Breadcrumbs.',
+    validation: Rule => Rule.required(),
+  }),
+  defineField({
+    name: 'slug',
+    type: 'slug',
+    title: 'Slug',
+    description: (
+      <>
+        Slug is a unique identifier for the document, used for SEO and links.
+        {slug && <> <strong><em>That slug can&apos;t be changed.</em></strong></>}
+        {prefix && <> The slug should start with a prefix: <strong>{prefix}</strong></>}
+      </>
+    ),
+    ...!!slug && {
+      initialValue: { current: slug },
+      readOnly: true,
+    },
+    options: {
+      source: 'title',
+      slugify: (slug: string) => `${prefix || '/'}${slugify(slug)}`,
+      isUnique: isUniqueSlug,
+    },
+    validation: (Rule) =>
+      Rule.required().custom((value) => {
+        if (prefix && value?.current && !value.current.startsWith(prefix)) {
+          return `Slug should start with ${prefix}`;
+        }
+        return true;
+      })
+  }),
+]