const http = require('http');
const fs = require('fs');
const path = require('path');

const PORT = process.env.PORT || 3001;
const DATA_DIR = path.join(__dirname, '../data');
const DATA_FILE = path.join(DATA_DIR, 'quiz_stats.json');
const QUESTIONS_FILE = path.join(__dirname, '../questions.json');

// 保证数据目录存在
if (!fs.existsSync(DATA_DIR)) {
  fs.mkdirSync(DATA_DIR, { recursive: true });
}

// 内存中的状态缓存
let state = {
  weights: {},
  history: [],
  totalAnswered: 0
};

// 初始化状态
function initState() {
  if (fs.existsSync(DATA_FILE)) {
    try {
      const content = fs.readFileSync(DATA_FILE, 'utf-8');
      state = JSON.parse(content);
      console.log(`[Init] 已从文件载入全局数据，累计答题数: ${state.totalAnswered}`);
      return;
    } catch (e) {
      console.error('[Init] 读取已有数据文件失败，将重新初始化:', e);
    }
  }

  // 初始化默认权重
  let defaultWeights = {};
  if (fs.existsSync(QUESTIONS_FILE)) {
    try {
      const qData = JSON.parse(fs.readFileSync(QUESTIONS_FILE, 'utf-8'));
      qData.forEach(q => {
        defaultWeights[q.id] = 1;
      });
    } catch (e) {
      console.error('[Init] 读取 questions.json 失败:', e);
    }
  }

  state = {
    weights: defaultWeights,
    history: [],
    totalAnswered: 0
  };
  saveState();
}

// 异步持久化保存
function saveState() {
  const tmpFile = `${DATA_FILE}.tmp`;
  fs.writeFile(tmpFile, JSON.stringify(state, null, 2), 'utf-8', (err) => {
    if (err) {
      console.error('[Save] 保存临时数据文件失败:', err);
      return;
    }
    fs.rename(tmpFile, DATA_FILE, (renameErr) => {
      if (renameErr) {
        console.error('[Save] 原子重命名数据文件失败:', renameErr);
      }
    });
  });
}

initState();

const server = http.createServer((req, res) => {
  // 设置 CORS 标头
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type');

  if (req.method === 'OPTIONS') {
    res.writeHead(204);
    res.end();
    return;
  }

  const url = new URL(req.url, `http://${req.headers.host}`);
  const pathname = url.pathname.replace(/^\/api/, ''); // 统一兼容 /api 前缀与无前缀

  if (req.method === 'GET' && (pathname === '/stats' || pathname === '/stats/')) {
    res.writeHead(200, { 'Content-Type': 'application/json; charset=utf-8' });
    res.end(JSON.stringify(state));
    return;
  }

  if (req.method === 'POST' && (pathname === '/answer' || pathname === '/answer/')) {
    let body = '';
    req.on('data', chunk => {
      body += chunk;
    });

    req.on('end', () => {
      try {
        const payload = JSON.parse(body || '{}');
        const questionId = Number(payload.questionId);
        const isCorrect = Boolean(payload.isCorrect);

        if (!questionId) {
          res.writeHead(400, { 'Content-Type': 'application/json' });
          res.end(JSON.stringify({ error: 'Missing questionId' }));
          return;
        }

        // 更新历史记录（保留最近 100 条）
        state.history.push(isCorrect);
        if (state.history.length > 100) {
          state.history = state.history.slice(-100);
        }

        // 更新全局总数
        state.totalAnswered = (state.totalAnswered || 0) + 1;

        // 更新题目权重
        const currentWeight = state.weights[questionId] || 1;
        if (isCorrect) {
          state.weights[questionId] = Math.max(1, currentWeight - 1);
        } else {
          state.weights[questionId] = currentWeight + 3; // 答错大幅增加权重
        }

        saveState();

        res.writeHead(200, { 'Content-Type': 'application/json; charset=utf-8' });
        res.end(JSON.stringify({
          success: true,
          weights: state.weights,
          history: state.history,
          totalAnswered: state.totalAnswered
        }));
      } catch (err) {
        console.error('[Error] 处理 /api/answer 异常:', err);
        res.writeHead(500, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ error: 'Internal Server Error' }));
      }
    });
    return;
  }

  if (req.method === 'POST' && (pathname === '/reset' || pathname === '/reset/')) {
    initState();
    res.writeHead(200, { 'Content-Type': 'application/json; charset=utf-8' });
    res.end(JSON.stringify({ success: true, message: 'Stats reset' }));
    return;
  }

  res.writeHead(404, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({ error: 'Not Found' }));
});

server.listen(PORT, '0.0.0.0', () => {
  console.log(`[Server] 全局刷题服务已启动，监听端口: ${PORT}`);
});