const express = require('express');
const path = require('path');
const fs = require('fs').promises;
const cors = require('cors');

const app = express();
const PORT = 3000;

// 路径安全验证函数 - 防止路径遍历攻击
function sanitizePath(input) {
    if (!input || typeof input !== 'string') {
        return '';
    }
    // 移除 ../ 和 ..\ 防止路径遍历
    // 移除开头的 / 和 \
    // 只保留字母、数字、连字符、下划线和点号
    return input
        .replace(/\.\./g, '')
        .replace(/^[\/\\]+/, '')
        .replace(/[\/\\]/g, '')
        .replace(/[^a-zA-Z0-9\-_.]/g, '');
}

// 验证路径是否在允许的目录内
function validatePath(fullPath, baseDir) {
    const resolvedPath = path.resolve(fullPath);
    const resolvedBaseDir = path.resolve(baseDir);
    return resolvedPath.startsWith(resolvedBaseDir);
}

// 中间件
app.use(cors());
app.use(express.json());
app.use(express.static('public'));

// API: 获取 index.md 内容
app.get('/api/index', async (req, res) => {
  try {
    const indexPath = path.join(__dirname, 'docs', 'index.md');
    const content = await fs.readFile(indexPath, 'utf-8');
    res.json({ content });
  } catch (error) {
    res.status(500).json({ error: '无法读取 index.md', details: error.message });
  }
});

// API: 解析 index.md 结构
app.get('/api/structure', async (req, res) => {
  try {
    const indexPath = path.join(__dirname, 'docs', 'index.md');
    const content = await fs.readFile(indexPath, 'utf-8');

    // 解析结构
    const structure = parseIndexMd(content);
    res.json(structure);
  } catch (error) {
    res.status(500).json({ error: '无法解析文档结构', details: error.message });
  }
});

// API: 获取指定分类的文档列表
app.get('/api/category/:category', async (req, res) => {
  try {
    const category = sanitizePath(req.params.category);

    if (!category) {
      return res.status(400).json({ error: '无效的分类名称' });
    }

    const indexPath = path.join(__dirname, 'docs', 'index.md');
    const content = await fs.readFile(indexPath, 'utf-8');

    // 解析并获取指定分类的文档
    const structure = parseIndexMd(content);
    const categoryData = structure.find(cat => cat.name === category);

    if (!categoryData) {
      return res.status(404).json({ error: '分类不存在' });
    }

    res.json(categoryData);
  } catch (error) {
    res.status(500).json({ error: '无法获取分类信息', details: error.message });
  }
});

// API: 获取指定文档的内容
app.get('/api/doc/:category/:docName', async (req, res) => {
  try {
    const category = sanitizePath(req.params.category);
    const docName = sanitizePath(req.params.docName);

    if (!category || !docName) {
      return res.status(400).json({ error: '无效的分类或文档名称' });
    }

    const docsDir = path.join(__dirname, 'docs');
    const docPath = path.join(docsDir, category, `${docName}.md`);

    // 验证路径是否在 docs 目录内
    if (!validatePath(docPath, docsDir)) {
      return res.status(403).json({ error: '拒绝访问：无效的路径' });
    }

    const content = await fs.readFile(docPath, 'utf-8');
    res.json({ content, category, docName });
  } catch (error) {
    res.status(500).json({ error: '无法读取文档', details: error.message });
  }
});

// API: 搜索文档
app.get('/api/search/:category', async (req, res) => {
  try {
    const category = sanitizePath(req.params.category);
    const currentDoc = sanitizePath(req.query.currentDoc);
    const { q } = req.query;

    if (!category) {
      return res.status(400).json({ error: '无效的分类名称' });
    }

    if (!q || q.trim().length === 0) {
      return res.json({ currentDoc: [], otherDocs: [] });
    }

    const query = q.toLowerCase();
    const docsDir = path.join(__dirname, 'docs');
    const categoryPath = path.join(docsDir, category);

    // 验证路径是否在 docs 目录内
    if (!validatePath(categoryPath, docsDir)) {
      return res.status(403).json({ error: '拒绝访问：无效的路径' });
    }

    // 读取分类下的所有文档
    const files = await fs.readdir(categoryPath);
    const mdFiles = files.filter(file => file.endsWith('.md'));

    const currentDocResults = [];
    const otherDocsResults = [];

    // 搜索每个文档
    for (const file of mdFiles) {
      const docName = file.replace('.md', '');
      const filePath = path.join(categoryPath, file);
      const content = await fs.readFile(filePath, 'utf-8');

      // 搜索匹配的行
      const lines = content.split('\n');
      const matches = [];

      lines.forEach((line, index) => {
        const lowerLine = line.toLowerCase();
        if (lowerLine.includes(query)) {
          // 获取上下文（前后各50个字符）
          const startIndex = Math.max(0, lowerLine.indexOf(query) - 50);
          const endIndex = Math.min(line.length, lowerLine.indexOf(query) + query.length + 50);
          let snippet = line.substring(startIndex, endIndex);

          // 如果不是从头开始，添加省略号
          if (startIndex > 0) snippet = '...' + snippet;
          if (endIndex < line.length) snippet = snippet + '...';

          matches.push({
            line: index + 1,
            snippet: snippet,
            fullLine: line
          });
        }
      });

      if (matches.length > 0) {
        const result = {
          docName,
          matchCount: matches.length,
          matches: matches.slice(0, 5) // 最多返回5个匹配
        };

        // 区分当前文档和其他文档
        if (docName === currentDoc) {
          currentDocResults.push(result);
        } else {
          otherDocsResults.push(result);
        }
      }
    }

    res.json({
      query: q,
      currentDoc: currentDocResults,
      otherDocs: otherDocsResults
    });

  } catch (error) {
    res.status(500).json({ error: '搜索失败', details: error.message });
  }
});

// 解析 index.md 的函数
function parseIndexMd(content) {
  const lines = content.split('\n');
  const structure = [];
  let currentCategory = null;

  for (const line of lines) {
    const trimmedLine = line.trim();

    // 匹配分类 [category]
    const categoryMatch = trimmedLine.match(/^\[(.+?)\]$/);
    if (categoryMatch) {
      currentCategory = {
        name: categoryMatch[1],
        docs: []
      };
      structure.push(currentCategory);
      continue;
    }

    // 匹配文档项 1: testa.md 或 3.1: testc1.md
    const docMatch = trimmedLine.match(/^([\d.]+):\s*(.+?)\.md$/);
    if (docMatch && currentCategory) {
      const [, number, docName] = docMatch;
      const level = (number.match(/\./g) || []).length;

      currentCategory.docs.push({
        number,
        name: docName,
        level,
        fullName: `${docName}.md`
      });
    }
  }

  return structure;
}

// 启动服务器
app.listen(PORT, () => {
  console.log(`服务器运行在 http://localhost:${PORT}`);
});