import katex from 'katex';

export interface RenderMarkdownOptions {
  preserveNewlines?: boolean;
}

/**
 * 健壮的行内 Markdown、LaTeX 公式与有序/无序列表渲染引擎
 * 支持：
 * - 块级数学公式 ($$...$$) 与行内数学公式 ($...$)
 * - 粗体 (**text** / __text__)
 * - 斜体 (*text* / _text_)
 * - 粗斜体 (***text***)
 * - 删除线 (~~text~~)
 * - 下划线 (<u>text</u>)
 * - 行内代码 (`code`)
 * - 超链接 ([text](url))
 * - 有序列表 (1. item, 2. item ...)
 * - 无序列表 (- item, * item ...)
 * - 荧光高亮 (<mark> / 预置语法)
 * - 安全内联样式标签 (<span style="...">)
 */
export function renderInlineMarkdown(content: string, options: RenderMarkdownOptions = {}): string {
  if (!content) return '';

  let text = content;

  // 1. 占位保护预处理：优先解析并提取数学公式，避免公式内部的 * 或 _ 被 Markdown 解析器误伤
  // 注意：占位符严禁使用包含 _ 或 * 等 Markdown 特殊字符，采用纯大写字母标识符
  const mathPlaceholders: string[] = [];
  const placeholderPrefix = 'XMATHTOKENX';

  // 1.1 块级独立公式 $$ ... $$
  text = text.replace(/\$\$([\s\S]*?)\$\$/g, (_, math) => {
    try {
      const rendered = katex.renderToString(math.trim(), {
        displayMode: true,
        throwOnError: false,
      });
      const idx = mathPlaceholders.length;
      mathPlaceholders.push(rendered);
      return `${placeholderPrefix}${idx}XENDX`;
    } catch {
      const idx = mathPlaceholders.length;
      mathPlaceholders.push(`<span style="color:var(--danger)">$$${math}$$</span>`);
      return `${placeholderPrefix}${idx}XENDX`;
    }
  });

  // 1.2 行内公式 $ ... $
  text = text.replace(/\$([^\$\n]+?)\$/g, (_, math) => {
    try {
      const rendered = katex.renderToString(math.trim(), {
        displayMode: false,
        throwOnError: false,
      });
      const idx = mathPlaceholders.length;
      mathPlaceholders.push(rendered);
      return `${placeholderPrefix}${idx}XENDX`;
    } catch {
      const idx = mathPlaceholders.length;
      mathPlaceholders.push(`$${math}$`);
      return `${placeholderPrefix}${idx}XENDX`;
    }
  });

  // 2. 行内代码保护 `code`
  const codePlaceholders: string[] = [];
  const codePlaceholderPrefix = 'XCODETOKENX';
  text = text.replace(/`([^`\n]+)`/g, (_, code) => {
    const rendered = `<code style="font-family:var(--font-mono);font-size:12px;background:var(--bg-subtle);color:var(--brand-500);padding:2px 5px;border-radius:4px;border:1px solid var(--border)">${escapeHtml(code)}</code>`;
    const idx = codePlaceholders.length;
    codePlaceholders.push(rendered);
    return `${codePlaceholderPrefix}${idx}XENDX`;
  });

  // 3. 粗斜体 ***text***
  text = text.replace(/\*\*\*([^\*\n]+?)\*\*\*/g, '<strong><em>$1</em></strong>');

  // 4. 粗体 **text** 或 __text__
  text = text.replace(/\*\*([^\*\n]+?)\*\*/g, '<strong>$1</strong>');
  text = text.replace(/__([^_\n]+?)__/g, '<strong>$1</strong>');

  // 5. 斜体 *text* 或 _text_
  text = text.replace(/\*([^\*\n]+?)\*/g, '<em>$1</em>');
  text = text.replace(/_([^_\n]+?)_/g, '<em>$1</em>');

  // 6. 删除线 ~~text~~
  text = text.replace(/~~([^~\n]+?)~~/g, '<del style="color:var(--text-muted)">$1</del>');

  // 7. 链接 [text](url)
  text = text.replace(/\[([^\]\n]+)\]\(([^)\s]+)\)/g, '<a href="$2" target="_blank" rel="noopener noreferrer" style="color:var(--brand-500);text-decoration:underline">$1</a>');

  // 8. 还原行内代码占位符
  codePlaceholders.forEach((codeHtml, idx) => {
    text = text.replace(`${codePlaceholderPrefix}${idx}XENDX`, () => codeHtml);
  });

  // 9. 还原数学公式占位符
  mathPlaceholders.forEach((mathHtml, idx) => {
    text = text.replace(`${placeholderPrefix}${idx}XENDX`, () => mathHtml);
  });

  // 10. 处理有序列表、无序列表与换行
  if (options.preserveNewlines !== false) {
    const rawLines = text.split('\n');
    const resultParts: string[] = [];
    let i = 0;

    while (i < rawLines.length) {
      const line = rawLines[i];
      const orderedMatch = line.match(/^(\s*)(\d+)\.\s+(.*)$/);
      const unorderedMatch = line.match(/^(\s*)[-*+]\s+(.*)$/);

      if (orderedMatch) {
        const listItems: string[] = [];
        const startNum = parseInt(orderedMatch[2], 10) || 1;
        while (i < rawLines.length) {
          const curMatch = rawLines[i].match(/^\s*\d+\.\s+(.*)$/);
          if (!curMatch) break;
          listItems.push(curMatch[1]);
          i++;
        }
        resultParts.push(
          `<ol class="doc-ol" start="${startNum}" style="margin: 6px 0; padding-left: 24px; line-height: 1.65; list-style-type: decimal;">` +
            listItems.map((li) => `<li style="margin-bottom: 4px;">${li}</li>`).join('') +
            `</ol>`
        );
      } else if (unorderedMatch) {
        const listItems: string[] = [];
        while (i < rawLines.length) {
          const curMatch = rawLines[i].match(/^\s*[-*+]\s+(.*)$/);
          if (!curMatch) break;
          listItems.push(curMatch[1]);
          i++;
        }
        resultParts.push(
          `<ul class="doc-ul" style="margin: 6px 0; padding-left: 20px; line-height: 1.65; list-style-type: disc;">` +
            listItems.map((li) => `<li style="margin-bottom: 4px;">${li}</li>`).join('') +
            `</ul>`
        );
      } else {
        resultParts.push(line);
        i++;
      }
    }

    let outHtml = '';
    for (let p = 0; p < resultParts.length; p++) {
      const cur = resultParts[p];
      if (p > 0) {
        const prev = resultParts[p - 1];
        const isPrevBlock = prev.startsWith('<ol') || prev.startsWith('<ul');
        const isCurBlock = cur.startsWith('<ol') || cur.startsWith('<ul');
        if (!isPrevBlock && !isCurBlock) {
          outHtml += '<br/>';
        }
      }
      outHtml += cur;
    }
    text = outHtml;
  }

  return text;
}

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