school_compare/nextjs-app/app/(frontend)/blog/[slug]/page.tsx

import { cache } from 'react';
import type { Metadata } from 'next';
import Link from 'next/link';
import { notFound } from 'next/navigation';
import { RichText } from '@payloadcms/richtext-lexical/react';
import type { JSXConvertersFunction } from '@payloadcms/richtext-lexical/react';
import { getCachedPayload } from '@/lib/payload';
import type { Post, Media } from '@/payload-types';
import { absoluteUrl } from '@/lib/site';
import { getFlags } from '@/lib/flags';
import {
  blogPostingJsonLd,
  breadcrumbJsonLd,
  personJsonLd,
  organizationJsonLd,
} from '@/lib/jsonld';
import { CalloutBlock } from '@/components/blog/CalloutBlock';
import styles from './Post.module.css';

/*
 * ISR. Unlike the index, this route has a dynamic param and no
 * generateStaticParams, so there is nothing for the build to prerender: each
 * post is generated on first request and cached until the collection's
 * afterChange hook revalidates it. That hook is what makes an edit to an
 * already-published post appear immediately.
 */
export const revalidate = 3600;

/**
 * heroImage is `number | Media | null`: an id when the query is shallow, the
 * populated document at depth 1. Both pages query at depth 1, but narrowing
 * rather than asserting keeps it correct if that ever changes.
 */
function heroOf(post: Post): Media | null {
  return typeof post.heroImage === 'object' && post.heroImage !== null
    ? post.heroImage
    : null;
}

/**
 * Spreads the default converters and adds the one custom block.
 *
 * Without the spread, every default node type — paragraphs, headings, links —
 * loses its renderer and the post body comes out empty.
 */
const calloutConverters: JSXConvertersFunction = ({ defaultConverters }) => ({
  ...defaultConverters,
  blocks: {
    // Annotated because the generic block converter cannot infer a custom
    // block's field shape; String() guards the values regardless.
    callout: ({ node }: { node: { fields: Record<string, unknown> } }) => (
      <CalloutBlock
        tone={String(node.fields.tone ?? 'caveat')}
        body={String(node.fields.body ?? '')}
      />
    ),
  },
});

/**
 * Wrapped in React's cache() because Next calls generateMetadata and the page
 * component separately for the same request — without it, every post view runs
 * this query against Postgres twice. cache() dedupes within a single request
 * only, so it never serves one visitor's request from another's.
 */
const findPost = cache(async (slug: string) => {
  const payload = await getCachedPayload();
  const { docs } = await payload.find({
    collection: 'posts',
    where: { slug: { equals: slug }, _status: { equals: 'published' } },
    limit: 1,
    depth: 1,
  });
  return docs[0] ?? null;
});

function summarise(post: Post) {
  return {
    title: post.title,
    slug: post.slug,
    excerpt: post.excerpt,
    publishedAt: post.publishedAt,
  };
}

export async function generateMetadata(
  { params }: { params: Promise<{ slug: string }> },
): Promise<Metadata> {
  const { slug } = await params;
  const post = await findPost(slug);
  if (!post) return { title: 'Not found' };

  const hero = heroOf(post);

  return {
    title: post.title,
    description: post.excerpt,
    alternates: { canonical: absoluteUrl(`/blog/${post.slug}`) },
    openGraph: {
      type: 'article',
      title: post.title,
      description: post.excerpt,
      url: absoluteUrl(`/blog/${post.slug}`),
      publishedTime: post.publishedAt,
      // A post with a hero image shares that; one without falls through to the
      // generated share card at app/opengraph-image.tsx.
      ...(hero?.url ? { images: [{ url: hero.url }] } : {}),
    },
  };
}

export default async function PostPage(
  { params }: { params: Promise<{ slug: string }> },
) {
  const { slug } = await params;

  /*
   * Flags read at this route's own declared floor, so gating costs it nothing.
   * Checked before the post is fetched: a dark blog should not query Payload.
   */
  const flags = await getFlags(3600);
  if (flags.blog !== true) notFound();
  const namedAuthor = flags.about_page === true;

  const post = await findPost(slug);
  if (!post) notFound();

  const summary = summarise(post);
  const hero = heroOf(post);

  const jsonLd = {
    '@context': 'https://schema.org',
    /*
     * The Person entity is anchored at /about#tudor, so it is declared only
     * when that page exists. Claiming an author whose URL 404s is a worse
     * signal than attributing the post to the publisher.
     */
    '@graph': [
      blogPostingJsonLd(summary, { namedAuthor }),
      breadcrumbJsonLd(summary),
      ...(namedAuthor ? [personJsonLd()] : []),
      organizationJsonLd(),
    ],
  };

  return (
    <article className={styles.page}>
      <script
        type="application/ld+json"
        dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
      />

      <nav className={styles.crumb}>
        <Link href="/blog" className={styles.link}>Blog</Link>
      </nav>

      <h1 className={styles.heading}>{summary.title}</h1>

      <p className={styles.byline}>
        {/* Unlinked while about_page is dark; the flags are independent. */}
        By {namedAuthor
          ? <Link href="/about" className={styles.link}>Tudor</Link>
          : 'Tudor'}
        {' · '}
        <time dateTime={summary.publishedAt}>
          {new Date(summary.publishedAt).toLocaleDateString('en-GB', {
            day: 'numeric',
            month: 'long',
            year: 'numeric',
          })}
        </time>
      </p>

      {/*
        A plain <img>, not next/image: Payload already generated the sized
        derivatives on upload (Media's imageSizes), so routing it through the
        optimizer would resize an image that is already the right size.
      */}
      {hero?.url && (
        <img
          className={styles.hero}
          src={hero.url}
          alt={hero.alt ?? ''}
          width={hero.width ?? undefined}
          height={hero.height ?? undefined}
        />
      )}

      <div className={styles.prose}>
        <RichText data={post.content} converters={calloutConverters} />
      </div>
    </article>
  );
}