/** Conservative check: does a text/plain paste look like HTML rather than prose or Markdown? */

/** Block-level tags whose balanced open+close pair marks real HTML structure. */
const BLOCK_TAGS = 'table|div|p|h1|h2|h3|h4|h5|h6|ul|ol|blockquote|section|body';

const BALANCED_BLOCK = new RegExp(
  `<(${BLOCK_TAGS})(?:\\s[^>]*)?>[\\s\\S]*?</\\1\\s*>`,
  'i'
);

export function looksLikeHtml(text: string): boolean {
  if (!text) return false;
  // Skip leading whitespace and HTML comments so a doctype/`<html>` preamble
  // behind a comment still counts.
  let head = text.replace(/^\s+/, '');
  while (head.startsWith('<!--')) {
    const end = head.indexOf('-->');
    if (end === -1) break;
    head = head.slice(end + 3).replace(/^\s+/, '');
  }
  const lower = head.toLowerCase();
  if (lower.startsWith('<!doctype html') || lower.startsWith('<html')) return true;
  // A balanced block-level element anywhere is enough; the backreference keeps
  // the open and close tag names matched.
  return BALANCED_BLOCK.test(text);
}