structure.ts

import Iframe from 'sanity-plugin-iframe-pane';
import type { DefaultDocumentNodeResolver } from 'sanity/desk';

export const getDefaultDocumentNode: DefaultDocumentNodeResolver = (
  S,
  { schemaType }
) => {
  if (schemaType === 'project') {
    return S.document().views([
      S.view.form(),

      S.view
        .component(Iframe)
        .options({
          // Required: Accepts an async function
          url: `${
            process.env.NEXT_PUBLIC_VERCEL_URL || 'http://localhost:3000'
          }/api/preview`,
          // Optional: Set the default size
          defaultSize: `desktop`, // default `desktop`
          // Optional: Add a reload button, or reload on new document revisions
          reload: {
            button: true, // default `undefined`
          },
          // Optional: Pass attributes to the underlying `iframe` element:
          // See https://developer.mozilla.org/en-US/docs/Web/HTML/Element/iframe
          attributes: {},
        })
        .title('Preview'),
    ]);
  }
};