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// server.js
const http = require("http");
const { URL } = require("url");

const routes = {
  "GET /": homeHandler,
  "GET /users": usersHandler,
  "POST /users": createUserHandler,
};

const server = http.createServer(async (req, res) => {
  try {
    const url = new URL(req.url, `http://${req.headers.host}`);
    const key = `${req.method} ${url.pathname}`;

    const handler = routes[key];

    if (!handler) {
      return sendJson(res, 404, { message: "Not Found" });
    }

    await handler(req, res, url);
  } catch (error) {
    console.error(error);
    sendJson(res, 500, { message: "Internal Server Error" });
  }
});

server.listen(3000, () => {
  console.log("Server running at http://localhost:3000");
});

// ===== handlers =====

function homeHandler(req, res) {
  sendJson(res, 200, { message: "Hello Node.js" });
}

function usersHandler(req, res) {
  sendJson(res, 200, [
    { id: 1, name: "Taro" },
    { id: 2, name: "Jiro" },
  ]);
}

async function createUserHandler(req, res) {
  const body = await readJsonBody(req);

  sendJson(res, 201, {
    message: "User created",
    user: body,
  });
}

// ===== utilities =====

function sendJson(res, statusCode, data) {
  res.writeHead(statusCode, {
    "Content-Type": "application/json; charset=utf-8",
  });
  res.end(JSON.stringify(data));
}

function readJsonBody(req) {
  return new Promise((resolve, reject) => {
    let body = "";

    req.on("data", chunk => {
      body += chunk;

      // 大きすぎるリクエストを防ぐ
      if (body.length > 1_000_000) {
        req.destroy();
        reject(new Error("Request body too large"));
      }
    });

    req.on("end", () => {
      try {
        resolve(body ? JSON.parse(body) : {});
      } catch {
        reject(new Error("Invalid JSON"));
      }
    });

    req.on("error", reject);
  });
}