function escapeHtml(input: string): string {
  return input
    .replace(/&/g, "&")
    .replace(/</g, "&lt;")
    .replace(/>/g, "&gt;")
    .replace(/"/g, "&quot;")
    .replace(/'/g, "&#39;");
}

function formatInline(input: string): string {
  let output = input;
  output = output.replace(/`([^`]+)`/g, "<code>$1</code>");
  output = output.replace(/\*\*([^*]+)\*\*/g, "<strong>$1</strong>");
  output = output.replace(/\*([^*]+)\*/g, "<em>$1</em>");
  output = output.replace(/_([^_]+)_/g, "<em>$1</em>");
  output = output.replace(
    /\[([^\]]+)\]\(([^)]+)\)/g,
    '<a href="$2" target="_blank" rel="noopener noreferrer">$1</a>',
  );
  return output;
}

export function renderMarkdown(markdown: string): string {
  const source = markdown || "";
  const codeBlocks: string[] = [];

  let content = source.replace(
    /```(?:[\w-]+)?\n([\s\S]*?)```/g,
    (_match, code) => {
      const escaped = escapeHtml(code.trimEnd());
      const token = `@@CODEBLOCK_${codeBlocks.length}@@`;
      codeBlocks.push(`<pre><code>${escaped}</code></pre>`);
      return token;
    },
  );

  content = escapeHtml(content);

  const lines = content.split(/\r?\n/);
  const blocks: string[] = [];
  let inList = false;

  const closeList = () => {
    if (inList) {
      blocks.push("</ul>");
      inList = false;
    }
  };

  for (const rawLine of lines) {
    const line = rawLine.trim();
    if (!line) {
      closeList();
      continue;
    }

    const headingMatch = line.match(/^(#{1,6})\s+(.*)$/);
    if (headingMatch) {
      closeList();
      const level = headingMatch[1].length;
      blocks.push(
        `<h${level}>${formatInline(headingMatch[2])}</h${level}>`,
      );
      continue;
    }

    const listMatch = line.match(/^[-*+]\s+(.*)$/);
    if (listMatch) {
      if (!inList) {
        blocks.push("<ul>");
        inList = true;
      }
      blocks.push(`<li>${formatInline(listMatch[1])}</li>`);
      continue;
    }

    closeList();
    blocks.push(`<p>${formatInline(line)}</p>`);
  }

  closeList();

  let html = blocks.join("\n");
  codeBlocks.forEach((blockHtml, index) => {
    html = html.replace(`@@CODEBLOCK_${index}@@`, blockHtml);
  });

  return html;
}