import { h, Fragment } from 'koishi';

/**
 * 将 GitHub Markdown 转换为 Koishi Fragment
 * 支持常见的 Markdown 语法和 GitHub 特性
 */
export function decodeMarkdown(markdown: string): Fragment
{
  if (!markdown) return [];

  const elements: (string | h)[] = [];
  let currentText = '';

  // 辅助函数：将累积的文本添加到元素数组
  const flushText = () =>
  {
    if (currentText)
    {
      elements.push(currentText);
      currentText = '';
    }
  };

  // 按行处理
  const lines = markdown.split('\n');
  let i = 0;

  while (i < lines.length)
  {
    const line = lines[i];

    // 代码块
    if (line.startsWith('```'))
    {
      flushText();
      const lang = line.slice(3).trim();
      const codeLines: string[] = [];
      i++;
      while (i < lines.length && !lines[i].startsWith('```'))
      {
        codeLines.push(lines[i]);
        i++;
      }
      const code = codeLines.join('\n');
      elements.push(h('code', code));
      elements.push('\n');
      i++;
      continue;
    }

    // 引用块
    if (line.startsWith('>'))
    {
      flushText();
      const quoteLines: string[] = [];
      while (i < lines.length && lines[i].startsWith('>'))
      {
        quoteLines.push(lines[i].slice(1).trim());
        i++;
      }
      const quoteContent = parseInlineMarkdown(quoteLines.join('\n'));
      elements.push(h('quote', quoteContent));
      continue;
    }

    // 标题（简化处理，转为加粗）
    if (line.match(/^#{1,6}\s/))
    {
      flushText();
      const text = line.replace(/^#{1,6}\s/, '');
      elements.push(h('b', parseInlineMarkdown(text)));
      elements.push('\n');
      i++;
      continue;
    }

    // 分隔线
    if (line.match(/^[-*_]{3,}$/))
    {
      flushText();
      elements.push('\n---\n');
      i++;
      continue;
    }

    // 空行
    if (line.trim() === '')
    {
      flushText();
      elements.push('\n');
      i++;
      continue;
    }

    // 普通行，处理行内元素
    currentText += line;
    i++;

    // 如果不是最后一行，添加换行
    if (i < lines.length)
    {
      currentText += '\n';
    }
  }

  // 处理剩余的文本中的行内元素
  if (currentText)
  {
    const inlineElements = parseInlineMarkdown(currentText);
    elements.push(...inlineElements);
  }

  return elements;
}

/**
 * 解析行内 Markdown 元素
 */
function parseInlineMarkdown(text: string): (string | h)[]
{
  const elements: (string | h)[] = [];
  let remaining = text;
  let pos = 0;

  while (pos < remaining.length)
  {
    // 图片：![alt](url)
    const imgMatch = remaining.slice(pos).match(/^!\[([^\]]*)\]\(([^)]+)\)/);
    if (imgMatch)
    {
      elements.push(h('img', { src: imgMatch[2], alt: imgMatch[1] }));
      pos += imgMatch[0].length;
      continue;
    }

    // 链接：[text](url)
    const linkMatch = remaining.slice(pos).match(/^\[([^\]]+)\]\(([^)]+)\)/);
    if (linkMatch)
    {
      elements.push(h('a', { href: linkMatch[2] }, linkMatch[1]));
      pos += linkMatch[0].length;
      continue;
    }

    // 行内代码：`code`
    const codeMatch = remaining.slice(pos).match(/^`([^`]+)`/);
    if (codeMatch)
    {
      elements.push(h('code', codeMatch[1]));
      pos += codeMatch[0].length;
      continue;
    }

    // 加粗：**text** 或 __text__
    const boldMatch = remaining.slice(pos).match(/^(\*\*|__)(.+?)\1/);
    if (boldMatch)
    {
      elements.push(h('b', boldMatch[2]));
      pos += boldMatch[0].length;
      continue;
    }

    // 斜体：*text* 或 _text_
    const italicMatch = remaining.slice(pos).match(/^(\*|_)(.+?)\1/);
    if (italicMatch)
    {
      elements.push(h('i', italicMatch[2]));
      pos += italicMatch[0].length;
      continue;
    }

    // 删除线：~~text~~
    const strikeMatch = remaining.slice(pos).match(/^~~(.+?)~~/);
    if (strikeMatch)
    {
      elements.push(h('s', strikeMatch[1]));
      pos += strikeMatch[0].length;
      continue;
    }

    // @mention
    const mentionMatch = remaining.slice(pos).match(/^@([a-zA-Z0-9_-]+)/);
    if (mentionMatch)
    {
      elements.push(h('at', { id: mentionMatch[1], name: mentionMatch[1] }));
      pos += mentionMatch[0].length;
      continue;
    }

    // #issue
    const issueMatch = remaining.slice(pos).match(/^#(\d+)/);
    if (issueMatch)
    {
      elements.push(h('sharp', { id: issueMatch[1], name: issueMatch[1] }));
      pos += issueMatch[0].length;
      continue;
    }

    // 普通字符
    elements.push(remaining[pos]);
    pos++;
  }

  return elements;
}