const linkTagPattern = /\{%\s*link\s+([\s\S]*?)\s*%\}/g;
const markdownLinkPattern = /^\[[^\]]*]\(([^)\s]+)(?:\s+["'][^"']*["'])?\)$/;

function escapeHtml(value) {
  return String(value)
    .replace(/&/g, '&')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;');
}

function splitLinkArgs(value) {
  const parts = [];
  let current = '';
  let bracketDepth = 0;
  let parenDepth = 0;

  for (const char of value) {
    if (char === '[') bracketDepth += 1;
    if (char === ']' && bracketDepth > 0) bracketDepth -= 1;
    if (char === '(') parenDepth += 1;
    if (char === ')' && parenDepth > 0) parenDepth -= 1;

    if (char === ',' && bracketDepth === 0 && parenDepth === 0 && parts.length < 2) {
      parts.push(current.trim());
      current = '';
    } else {
      current += char;
    }
  }

  parts.push(current.trim());
  return parts;
}

function normalizeUrl(value) {
  const trimmed = value.trim();
  const markdownLink = trimmed.match(markdownLinkPattern);
  return markdownLink ? markdownLink[1] : trimmed;
}

function getHostname(url) {
  try {
    return new URL(url).hostname.replace(/^www\./, '');
  } catch {
    return '';
  }
}

function renderLinkCard(rawValue) {
  const [title, source, rawUrl] = splitLinkArgs(rawValue);
  const url = normalizeUrl(rawUrl ?? '');

  if (!title || !url) return `{% link ${rawValue} %}`;

  const host = getHostname(url);
  const label = source?.split('@')[0]?.trim() || host || 'Link';
  const initial = label.slice(0, 1).toUpperCase();

  return `<a class="hexo-link-card" href="${escapeHtml(url)}" target="_blank" rel="external nofollow noopener noreferrer">
  <span class="hexo-link-card__icon" aria-hidden="true">${escapeHtml(initial)}</span>
  <span class="hexo-link-card__body">
    <strong>${escapeHtml(title)}</strong>
    <span>${escapeHtml(label)}${host ? ` · ${escapeHtml(host)}` : ''}</span>
  </span>
</a>`;
}

function transformText(value) {
  let matched = false;
  const transformed = value.replace(linkTagPattern, (_, rawValue) => {
    matched = true;
    return renderLinkCard(rawValue);
  });

  return matched ? transformed : value;
}

function inlineToSource(node) {
  if (node.type === 'text' || node.type === 'inlineCode') return node.value ?? '';

  if (node.type === 'link') {
    const text = Array.isArray(node.children) ? node.children.map(inlineToSource).join('') : node.url;
    return `[${text}](${node.url})`;
  }

  if (Array.isArray(node.children)) return node.children.map(inlineToSource).join('');
  return '';
}

function visit(node) {
  if (!node || typeof node !== 'object') return;

  if (node.type === 'paragraph' && Array.isArray(node.children)) {
    const source = node.children.map(inlineToSource).join('');
    const transformed = transformText(source);

    if (transformed !== source) {
      node.type = 'html';
      node.value = transformed;
      delete node.children;
      return;
    }
  }

  if (node.type === 'text' && typeof node.value === 'string') {
    const transformed = transformText(node.value);

    if (transformed !== node.value) {
      node.type = 'html';
      node.value = transformed;
    }
  }

  if (Array.isArray(node.children)) {
    for (const child of node.children) visit(child);
  }
}

export default function remarkHexoLinkCards() {
  return (tree) => {
    visit(tree);
  };
}