TinaCMS: prepend filename with date upon creation

config.ts

const schema = defineSchema({
  collections: [
    {
      name: "post",
      label: "Posts",
      path: "site/content/posts",
      ui: {
        filename: {
          slugify: values => {
            const postDate = values.date ? new Date(values.date) : new Date();
            return `${postDate.toISOString().split("T")[0]}-${(values.slug || "")
              .toLowerCase()
              .replace(/ /g, "-")}`.replace(/[^\w\.\/-\s]/gi, "");
          }
        }
      },
      fields: [
        {
          type: "string",
          name: "title",
          label: "Title",
          isTitle: true,
          required: true,
        },
        {
          type: "string",
          name: "slug",
          label: "Slug",
          required: true
        },
        {
          type: "datetime",
          name: "date",
          label: "Date",
          description:
            "Publish date and time (in your local time). You can change this later",
          ui: {
            timeFormat: "HH:mm"
          },
          required: true
        },
        {
          type: "string",
          list: true,
          name: "categories",
          label: "Categories",
          ui: {
            component: "tags"
          }
        },
        {
          type: "rich-text",
          name: "body",
          label: "Body",
          isBody: true,
        }
      ]
    }
  ]
});