HTMLファイルをmarkdownに変換する¶

javascript: (function() {
  function clean(s) {
    return (s || '')
      .replace(/\r\n/g, '\n')
      .replace(/\u00a0/g, ' ')
      .replace(/[ \t]+\n/g, '\n')
      .replace(/\n{3,}/g, '\n\n');
  }

  function textOf(node) {
    return (node.textContent || '').replace(/\s+/g, ' ').trim();
  }

  function getCodeLanguage(codeEl) {
    if (!codeEl) return '';

    var cls = codeEl.className || '';
    var match = String(cls).match(/(?:^|\s)(?:language|lang)-([a-zA-Z0-9_+-]+)/);
    if (match) return match[1];

    var dataLang = codeEl.getAttribute('data-language') ||
      codeEl.getAttribute('data-lang') ||
      codeEl.getAttribute('data-code') ||
      codeEl.getAttribute('lang');

    return dataLang || '';
  }

  function convert(node, indent) {
    indent = indent || '';
    if (!node) return '';

    if (node.nodeType === Node.TEXT_NODE) {
      return node.nodeValue || '';
    }

    if (node.nodeType !== Node.ELEMENT_NODE) {
      return '';
    }

    var tag = node.tagName.toLowerCase();

    function childrenToText(childIndent) {
      var s = '';
      Array.prototype.forEach.call(node.childNodes, function(child) {
        s += convert(child, childIndent);
      });
      return s;
    }

    if (tag === 'script' || tag === 'style' || tag === 'noscript') {
      return '';
    }

    if (/^h[1-6]$/.test(tag)) {
      var level = parseInt(tag.charAt(1), 10);
      return '\n\n' + '#'.repeat(level) + ' ' + clean(textOf(node)) + '\n\n';
    }

    if (tag === 'p') {
      return '\n\n' + clean(childrenToText(indent).trim()) + '\n\n';
    }

    if (tag === 'br') {
      return '  \n';
    }

    if (tag === 'strong' || tag === 'b') {
      return '**' + clean(childrenToText(indent).trim()) + '**';
    }

    if (tag === 'em' || tag === 'i') {
      return '*' + clean(childrenToText(indent).trim()) + '*';
    }

    if (tag === 'code') {
      if (node.parentElement && node.parentElement.tagName.toLowerCase() === 'pre') {
        return clean(node.textContent || '');
      }
      return '`' + (node.textContent || '').replace(/`/g, '\\`') + '`';
    }

    if (tag === 'pre') {
      var codeEl = node.querySelector('[class^="language-"]') || node.querySelector('.shiki') || node.querySelector('.hljs');
      var lang = getCodeLanguage(codeEl);
      var code = codeEl ? codeEl.textContent : node.textContent;

      return '\n\n```' + lang + '\n' + clean(code).trim() + '\n```\n\n';
    }

    if (tag === 'a') {
      var href = node.getAttribute('href') || '';
      var label = clean(childrenToText(indent).trim()) || href;
      if (!href) return label;
      return '[' + label + '](' + href + ')';
    }

    if (tag === 'img') {
      var alt = node.getAttribute('alt') || '';
      var src = node.getAttribute('src') || '';
      if (!src) return '';
      return '![' + alt.replace(/\]/g, '\\]') + '](' + src + ')';
    }

    if (tag === 'blockquote') {
      var q = clean(childrenToText(indent).trim());
      if (!q) return '';
      return '\n\n' + q.split('\n').map(function(line) {
        return '> ' + line;
      }).join('\n') + '\n\n';
    }

    if (tag === 'ul') {
      var items = [];
      Array.prototype.forEach.call(node.children, function(li) {
        if (li.tagName && li.tagName.toLowerCase() === 'li') {
          items.push(convert(li, indent));
        }
      });
      return '\n' + items.join('') + '\n';
    }

    if (tag === 'ol') {
      var items = [];
      var i = 1;
      Array.prototype.forEach.call(node.children, function(li) {
        if (li.tagName && li.tagName.toLowerCase() === 'li') {
          items.push(convert(li, indent + i + '. '));
          i++;
        }
      });
      return '\n' + items.join('') + '\n';
    }

    if (tag === 'li') {
      var marker = indent || '- ';
      var content = clean(childrenToText(indent).trim());
      if (!content) return '';
      return marker + content + '\n';
    }

    if (tag === 'hr') {
      return '\n\n---\n\n';
    }

    return childrenToText(indent);
  }

  function getTarget() {
    var sel = window.getSelection();

    if (sel && sel.rangeCount > 0 && !sel.isCollapsed) {
      var container = document.createElement('div');
      for (var i = 0; i < sel.rangeCount; i++) {
        container.appendChild(sel.getRangeAt(i).cloneContents());
      }
      return container;
    }

    return document.querySelector('article') ||
      document.querySelector('main') ||
      document.body;
  }

  function makeFileName() {
    var title = document.title || 'export';
    title = title
      .replace(/[\\/:*?"<>|]/g, '')
      .replace(/\s+/g, '-')
      .replace(/-+/g, '-')
      .replace(/^-|-$/g, '');

    if (!title) title = 'export';

    return title + '.md';
  }

  function downloadMarkdown(markdown) {
    var blob = new Blob([markdown], { type: 'text/markdown;charset=utf-8' });
    var url = URL.createObjectURL(blob);
    var a = document.createElement('a');

    a.href = url;
    a.download = makeFileName();
    document.body.appendChild(a);
    a.click();

    setTimeout(function() {
      URL.revokeObjectURL(url);
      a.remove();
    }, 1000);
  }

  try {
    var root = getTarget();

    if (!root) {
      alert('変換対象が見つかりませんでした。');
      return;
    }

    var markdown = convert(root).replace(/\n{3,}/g, '\n\n').trim();

    if (!markdown) {
      alert('変換結果が空でした。');
      return;
    }

    downloadMarkdown(markdown);
  } catch (e) {
    console.error(e);
    alert('変換中にエラーが発生しました: ' + e.message);
  }
})();