astro/packages/markdown/remark/src/remark-prism.ts

import { visit } from 'unist-util-visit';
import Prism from 'prismjs';
import { addAstro } from '@astrojs/prism';
import loadLanguages from 'prismjs/components/index.js';
const noVisit = new Set(['root', 'html', 'text']);

const languageMap = new Map([
  ['ts', 'typescript']
]);

function runHighlighter(lang: string, code: string) {
  let classLanguage = `language-${lang}`

  if (lang == null) {
    lang = 'plaintext';
  }

  const ensureLoaded = (lang: string) => {
    if(lang && !Prism.languages[lang]) {
      loadLanguages([lang]);
    }
  };

  if(languageMap.has(lang)) {
    ensureLoaded(languageMap.get(lang)!);
  } else if(lang === 'astro') {
    ensureLoaded('typescript');
    addAstro(Prism);
  } else {
    ensureLoaded('markup-templating'); // Prism expects this to exist for a number of other langs
    ensureLoaded(lang);
  }

  if(lang && !Prism.languages[lang]) {
    console.warn(`Unable to load the language: ${lang}`);
  }

  const grammar = Prism.languages[lang];
  let html = code;
  if (grammar) {
    html = Prism.highlight(code, grammar, lang);
  }

  return { classLanguage, html };
}

type MaybeString = string | null | undefined;

/**  */
function transformer(className: MaybeString) {
  return function(tree: any) {
    const visitor = (node: any) => {
      let {lang, value} = node;
      node.type = 'html';

      let { html, classLanguage } = runHighlighter(lang, value);
      let classes = [classLanguage];
      if(className) {
        classes.push(className);
      }
      node.value = `<pre class="${classes.join(' ')}"><code data-astro-raw class="${classLanguage}">${html}</code></pre>`;
      return node;
    };
    return visit(tree, 'code', visitor)
  } 
}


function plugin(className: MaybeString) {
  return transformer.bind(null, className);
}

export default plugin;