export interface RenderMarkdownOptions {
  preserveNewlines?: boolean;
}

type MathRenderer = (source: string, displayMode: boolean) => string;

let mathRenderer: MathRenderer | null = null;
let mathRendererLoading: Promise<void> | null = null;

export function contentHasMath(content: string): boolean {
  return /\$\$[\s\S]*?\$\$|\$[^$\n]+?\$/.test(content);
}

/** 首次遇到公式才加载 KaTeX 及其样式。没有公式的会话不请求这个包。 */
export function ensureMathRenderer(): Promise<void> {
  if (mathRenderer) return Promise.resolve();
  if (!mathRendererLoading) {
    mathRendererLoading = (async () => {
      if (typeof document !== 'undefined') {
        await import('katex/dist/katex.min.css');
      }
      const mod = await import('./katexRender');
      mathRenderer = mod.renderKatexHtml;
    })();
  }
  return mathRendererLoading;
}

function renderMathSource(math: string, displayMode: boolean): string {
  const trimmed = math.trim();
  if (mathRenderer) {
    try {
      return mathRenderer(trimmed, displayMode);
    } catch {
      // 落到转义文本，避免把未渲染的源码再送进 Markdown 规则。
    }
  }
  const escaped = escapeHtml(trimmed);
  if (displayMode) {
    return `<span class="math-pending">$$${escaped}$$</span>`;
  }
  return `<span class="math-pending">$${escaped}$</span>`;
}

/**
 * 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[] = [];
  // 每次渲染换盐，避免用户文本伪造 XMATHTOKENX0XENDX 在 escapeHtml 之后被还原成 HTML
  const tokenSalt = Math.random().toString(36).slice(2, 10).toUpperCase();
  const placeholderPrefix = `XMATHTOKENX${tokenSalt}X`;

  // 1.1 块级独立公式 $$ ... $$
  text = text.replace(/\$\$([\s\S]*?)\$\$/g, (_, math) => {
    const idx = mathPlaceholders.length;
    mathPlaceholders.push(renderMathSource(math, true));
    return `${placeholderPrefix}${idx}XENDX`;
  });

  // 1.2 行内公式 $ ... $
  text = text.replace(/\$([^\$\n]+?)\$/g, (_, math) => {
    const idx = mathPlaceholders.length;
    mathPlaceholders.push(renderMathSource(math, false));
    return `${placeholderPrefix}${idx}XENDX`;
  });

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

  // 2.5 转义剩余文本中的 HTML，防止用户/LLM 输入经 dangerouslySetInnerHTML 执行脚本
  text = escapeHtml(text);

  // 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,
    (_, label, url) =>
      `<a href="${sanitizeHref(url)}" target="_blank" rel="noopener noreferrer" style="color:var(--brand-500);text-decoration:underline">${label}</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. 处理标题 / 分隔线 / 表格 / 引用 / 有序无序列表与换行
  if (options.preserveNewlines !== false) {
    const rawLines = text.split('\n');
    const resultParts: string[] = [];
    let i = 0;

    const isBlockHtml = (s: string) =>
      /<(ol|ul|h[1-6]|table|hr|blockquote)\b/i.test(s) || s.startsWith('<ol') || s.startsWith('<ul');

    while (i < rawLines.length) {
      const line = rawLines[i];
      const headingMatch = line.match(/^(#{1,6})\s+(.*)$/);
      const hrMatch = line.match(/^\s*(?:-{3,}|\*{3,}|_{3,})\s*$/);
      const quoteMatch = line.match(/^>\s?(.*)$/);
      const tableMatch = line.match(/^\s*\|.+\|\s*$/);
      const orderedMatch = line.match(/^(\s*)(\d+)\.\s+(.*)$/);
      const unorderedMatch = line.match(/^(\s*)[-*+]\s+(.*)$/);

      if (headingMatch) {
        const level = Math.min(headingMatch[1].length, 6);
        const sizes = ['1.35em', '1.2em', '1.1em', '1.05em', '1em', '0.95em'];
        resultParts.push(
          `<h${level} class="chat-md-h" style="margin:10px 0 6px;font-size:${sizes[level - 1]};font-weight:700;line-height:1.35;color:inherit;">${headingMatch[2]}</h${level}>`
        );
        i++;
      } else if (hrMatch) {
        resultParts.push(
          `<hr class="chat-md-hr" style="border:none;border-top:1px solid var(--border);margin:10px 0;opacity:0.85;" />`
        );
        i++;
      } else if (tableMatch) {
        const tableLines: string[] = [];
        while (i < rawLines.length && /^\s*\|.+\|\s*$/.test(rawLines[i])) {
          tableLines.push(rawLines[i].trim());
          i++;
        }
        const parsedRows: string[][] = [];
        for (const tl of tableLines) {
          if (/^\|?\s*[:\-| ]+\s*\|?$/.test(tl)) continue;
          const cells = tl
            .replace(/^\|/, '')
            .replace(/\|$/, '')
            .split('|')
            .map((c) => c.trim());
          if (cells.length > 0) parsedRows.push(cells);
        }
        if (parsedRows.length > 0) {
          const head = parsedRows[0];
          const body = parsedRows.slice(1);
          const thead = `<thead><tr>${head.map((c) => `<th style="border:1px solid var(--border);padding:6px 8px;background:var(--bg-subtle);text-align:left;font-weight:600;">${c}</th>`).join('')}</tr></thead>`;
          const tbody =
            body.length > 0
              ? `<tbody>${body.map((r) => `<tr>${r.map((c) => `<td style="border:1px solid var(--border);padding:6px 8px;vertical-align:top;">${c}</td>`).join('')}</tr>`).join('')}</tbody>`
              : '';
          resultParts.push(
            `<div style="overflow-x:auto;margin:8px 0;"><table class="chat-md-table" style="border-collapse:collapse;width:100%;font-size:12.5px;line-height:1.45;">${thead}${tbody}</table></div>`
          );
        }
      } else if (quoteMatch) {
        const quotes: string[] = [];
        while (i < rawLines.length) {
          const qm = rawLines[i].match(/^>\s?(.*)$/);
          if (!qm) break;
          quotes.push(qm[1] || '');
          i++;
        }
        resultParts.push(
          `<blockquote class="chat-md-quote" style="margin:8px 0;padding:6px 10px;border-left:3px solid var(--brand-400);background:var(--bg-subtle);border-radius:0 6px 6px 0;">${quotes.join('<br/>')}</blockquote>`
        );
      } else 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];
        if (!isBlockHtml(prev) && !isBlockHtml(cur)) {
          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;');
}

/** Block executable URL schemes in markdown link hrefs. */
function sanitizeHref(url: string): string {
  const trimmed = url.trim();
  if (/^(javascript|data|vbscript):/i.test(trimmed)) {
    return '#';
  }
  return escapeHtml(trimmed);
}