const path = require("path");
const fs = require("fs");
/**
 * 读取本地mock数据
 * @param {*} req
 */
function readMockData(req) {
  const { url, pathname, param, method } = req;
  return new Promise((resolve, reject) => {
    const filepath = path.resolve(__dirname, "./" + pathname + ".js");
    const fileExist = fs.existsSync(filepath);
    if (!fileExist) {
      const msg = `'${url}': mock data is not exist!`;
      reject({
        statusCode: 404,
        body: null,
        message: msg,
      });
    } else {
      try {
        delete require.cache[require.resolve(filepath)];
        const response = require(filepath);
        if (typeof response === "function") {
          const responseFun = response(req);
          resolve(responseFun);
          return;
        }
        resolve(response);
      } catch (err) {
        console.log("readMockError:", err);
        const msg = `'${url}': parse mock file error!`;
        reject({
          statusCode: 500,
          body: null,
          message: msg,
        });
      }
    }
  });
}
/**
 * express中间件，实现ajax mock数据功能
 * @param {*} app
 */
module.exports = function mock(app) {
  app.all("*", function (req, res, next) {
    const method = req.method.toLocaleUpperCase();
    const param = method === "GET" ? req.query : req.body;
    // 请求日志打印
    console.log(req.method, req.url, param, Date.now());
    // 只处理ajax请求
    if (
      req.headers["x-requested-with"] === "XMLHttpRequest" ||
      req.path.indexOf("/api-mock") > -1
    ) {
      readMockData({
        url: req.url,
        pathname: req.path,
        param,
        method,
      })
        .then((response) => {
          res.status(response.statusCode || 200);
          res.setHeader("Content-Type", "application/json");
          res.end(JSON.stringify(response.body));
        })
        .catch((err) => {
          res.status(err.statusCode || 404);
          res.end();
        });
    } else {
      next();
    }
  });
};