Source

// Syntax highlighting with highlight.js, loaded only when a paste is shown, one language at a time.
import type { LanguageFn } from "highlight.js";

type Loader = () => Promise<{ default: LanguageFn }>;
const LOADERS: Record<string, Loader> = {
  markdown: () => import("highlight.js/lib/languages/markdown"),
  javascript: () => import("highlight.js/lib/languages/javascript"),
  typescript: () => import("highlight.js/lib/languages/typescript"),
  python: () => import("highlight.js/lib/languages/python"),
  json: () => import("highlight.js/lib/languages/json"),
  html: () => import("highlight.js/lib/languages/xml"),
  xml: () => import("highlight.js/lib/languages/xml"),
  css: () => import("highlight.js/lib/languages/css"),
  bash: () => import("highlight.js/lib/languages/bash"),
  sql: () => import("highlight.js/lib/languages/sql"),
  yaml: () => import("highlight.js/lib/languages/yaml"),
  diff: () => import("highlight.js/lib/languages/diff"),
  go: () => import("highlight.js/lib/languages/go"),
  rust: () => import("highlight.js/lib/languages/rust"),
  java: () => import("highlight.js/lib/languages/java"),
  kotlin: () => import("highlight.js/lib/languages/kotlin"),
  swift: () => import("highlight.js/lib/languages/swift"),
  c: () => import("highlight.js/lib/languages/c"),
  cpp: () => import("highlight.js/lib/languages/cpp"),
  csharp: () => import("highlight.js/lib/languages/csharp"),
  php: () => import("highlight.js/lib/languages/php"),
  ruby: () => import("highlight.js/lib/languages/ruby"),
};

/** Larger pastes are shown without colors: highlighting them would freeze the page. */
export const HIGHLIGHT_MAX = 200 * 1024;

export const escapeHtml = (s: string) => s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");

/** The paste as highlighted HTML, or null for plain text. */
export async function highlight(code: string, language: string): Promise<string | null> {
  const load = LOADERS[language];
  if (!load || code.length > HIGHLIGHT_MAX) return null;
  const [{ default: hljs }, { default: lang }] = await Promise.all([import("highlight.js/lib/core"), load()]);
  if (!hljs.getLanguage(language)) hljs.registerLanguage(language, lang);
  return hljs.highlight(code, { language, ignoreIllegals: true }).value;
}

/** Splits highlighted HTML into lines, closing and reopening spans that cross a line break. */
export function splitLines(html: string): string[] {
  const lines: string[] = [];
  const open: string[] = [];
  let line = "";
  for (const part of html.split(/(<span[^>]*>|<\/span>|\n)/)) {
    if (part === "\n") {
      lines.push(line + "</span>".repeat(open.length));
      line = open.join("");
    } else if (part.startsWith("<span")) {
      open.push(part);
      line += part;
    } else if (part === "</span>") {
      open.pop();
      line += part;
    } else {
      line += part;
    }
  }
  lines.push(line);
  return lines;
}