(function(){
  function escapeHtml(value){
    return String(value || '').replace(/[&<>"']/g, function(ch){
      return {'&':'&amp;','<':'&lt;','>':'&gt;','"':'&quot;',"'":'&#039;'}[ch];
    });
  }
  function safeUrl(url){
    url = String(url || '').trim();
    if (!url) return '#';
    try {
      const parsed = new URL(url, window.location.origin);
      if (!['http:', 'https:', 'mailto:'].includes(parsed.protocol)) return '#';
      return parsed.href;
    } catch (_) {
      return '#';
    }
  }
  function inlineMarkdown(text){
    let out = escapeHtml(text);
    out = out.replace(/`([^`]+)`/g, '<code>$1</code>');
    out = out.replace(/\*\*([^*]+)\*\*/g, '<strong>$1</strong>');
    out = out.replace(/\*([^*]+)\*/g, '<em>$1</em>');
    out = out.replace(/\[([^\]]+)\]\(([^)]+)\)/g, function(_, label, url){
      return '<a href="'+escapeHtml(safeUrl(url))+'" target="_blank" rel="noopener">'+label+'</a>';
    });
    return out;
  }
  function renderMarkdown(markdown){
    const lines = String(markdown || '').replace(/\r\n?/g, '\n').trim().split('\n');
    if (!String(markdown || '').trim()) return '<p class="md-empty">Nothing to preview yet.</p>';
    let html = '', para = [], list = null, quote = [], code = false, codeLines = [];
    function softBreaks(value){ return inlineMarkdown(value).replace(/\n/g, '<br>'); }
    function flushPara(){ if (para.length) { html += '<p>'+softBreaks(para.join('\n'))+'</p>'; para = []; } }
    function flushList(){ if (!list) return; html += '<'+list.type+'>'; list.items.forEach(item => html += '<li>'+inlineMarkdown(item)+'</li>'); html += '</'+list.type+'>'; list = null; }
    function flushQuote(){ if (quote.length) { html += '<blockquote>'+softBreaks(quote.join('\n'))+'</blockquote>'; quote = []; } }
    lines.forEach(function(line){
      if (/^```/.test(line)) {
        if (code) {
          html += '<pre><code>'+escapeHtml(codeLines.join('\n'))+'</code></pre>';
          code = false; codeLines = [];
        } else {
          flushPara(); flushList(); flushQuote(); code = true;
        }
        return;
      }
      if (code) { codeLines.push(line); return; }
      if (!line.trim()) { flushPara(); flushList(); flushQuote(); return; }
      let m;
      if ((m = line.match(/^(#{1,3})\s+(.+)$/))) {
        flushPara(); flushList(); flushQuote();
        const level = m[1].length + 2;
        html += '<h'+level+'>'+inlineMarkdown(m[2])+'</h'+level+'>';
        return;
      }
      if ((m = line.match(/^>\s?(.*)$/))) { flushPara(); flushList(); quote.push(m[1]); return; }
      if ((m = line.match(/^[-*]\s+(.+)$/))) { flushPara(); flushQuote(); if (!list || list.type !== 'ul') list = {type:'ul',items:[]}; list.items.push(m[1]); return; }
      if ((m = line.match(/^\d+\.\s+(.+)$/))) { flushPara(); flushQuote(); if (!list || list.type !== 'ol') list = {type:'ol',items:[]}; list.items.push(m[1]); return; }
      flushList(); flushQuote(); para.push(line);
    });
    if (code) html += '<pre><code>'+escapeHtml(codeLines.join('\n'))+'</code></pre>';
    flushPara(); flushList(); flushQuote();
    return html;
  }
  function applyWrap(textarea, before, after, placeholder){
    const start = textarea.selectionStart || 0;
    const end = textarea.selectionEnd || 0;
    const value = textarea.value;
    const selected = value.slice(start, end) || placeholder || '';
    textarea.value = value.slice(0, start) + before + selected + after + value.slice(end);
    textarea.focus();
    textarea.selectionStart = start + before.length;
    textarea.selectionEnd = start + before.length + selected.length;
    textarea.dispatchEvent(new Event('input', {bubbles:true}));
  }
  function applyLine(textarea, prefix){
    const start = textarea.selectionStart || 0;
    const value = textarea.value;
    const lineStart = value.lastIndexOf('\n', Math.max(0, start - 1)) + 1;
    textarea.value = value.slice(0, lineStart) + prefix + value.slice(lineStart);
    textarea.focus();
    textarea.selectionStart = textarea.selectionEnd = start + prefix.length;
    textarea.dispatchEvent(new Event('input', {bubbles:true}));
  }
  function enhance(textarea){
    if (textarea.dataset.markdownEnhanced === '1') return;
    textarea.dataset.markdownEnhanced = '1';
    const shell = document.createElement('div');
    shell.className = 'md-editor';
    const toolbar = document.createElement('div');
    toolbar.className = 'md-toolbar';
    const tools = [
      ['B', 'Bold', () => applyWrap(textarea, '**', '**', 'bold text')],
      ['I', 'Italic', () => applyWrap(textarea, '*', '*', 'italic text')],
      ['#', 'Heading', () => applyLine(textarea, '### ')],
      ['•', 'Bullet list', () => applyLine(textarea, '- ')],
      ['1.', 'Numbered list', () => applyLine(textarea, '1. ')],
      ['“”', 'Quote', () => applyLine(textarea, '> ')],
      ['{}', 'Code', () => applyWrap(textarea, '`', '`', 'code')],
      ['↗', 'Link', () => {
        const url = window.prompt('Link URL');
        if (url) applyWrap(textarea, '[', ']('+url+')', 'link text');
      }]
    ];
    tools.forEach(function(tool){
      const btn = document.createElement('button');
      btn.type = 'button';
      btn.className = 'md-tool';
      btn.textContent = tool[0];
      btn.title = tool[1];
      btn.setAttribute('aria-label', tool[1]);
      btn.addEventListener('click', tool[2]);
      toolbar.appendChild(btn);
    });
    const panes = document.createElement('div');
    panes.className = 'md-panes';
    const write = document.createElement('div');
    write.className = 'md-write';
    const preview = document.createElement('div');
    preview.className = 'md-preview markdown-body';
    preview.setAttribute('aria-label', 'Markdown preview');

    textarea.parentNode.insertBefore(shell, textarea);
    shell.appendChild(toolbar);
    shell.appendChild(panes);
    panes.appendChild(write);
    panes.appendChild(preview);
    write.appendChild(textarea);
    textarea.classList.add('md-source');
    function update(){ preview.innerHTML = renderMarkdown(textarea.value); }
    textarea.addEventListener('input', update);
    update();
  }
  document.addEventListener('DOMContentLoaded', function(){
    document.querySelectorAll('textarea.markdown-editor').forEach(enhance);
  });
})();