Solution

src/createServer.js

@@ -1,8 +1,75 @@
 'use strict';
 
+const { Server } = require('http');
+const fs = require('fs');
+const path = require('path');
+
+const ALLOWED_ENDPOINTS = {
+  addExpense: {
+    route: '/add-expense',
+    methods: ['POST'],
+  },
+};
+
 function createServer() {
-  /* Write your code here */
-  // Return instance of http.Server class
+  const server = new Server();
+
+  server.on('request', (req, res) => {
+    const baseUrl = `http://${req.headers.host}`;
+    const url = new URL(req.url, baseUrl);
+
+    if (
+      url.pathname !== ALLOWED_ENDPOINTS.addExpense.route ||
+      !ALLOWED_ENDPOINTS.addExpense.methods.includes(req.method)
+    ) {
+      res.statusCode = 404;
+      res.setHeader('Content-Type', 'text/plain');
+
+      res.end('Invalid url');
+
+      return;
+    }
+
+    const bodyChunks = [];
+
+    req.on('data', (chunk) => {
+      bodyChunks.push(chunk);
+    });
+
+    req.on('end', () => {
+      const json = Buffer.concat(bodyChunks);
+      const expense = JSON.parse(json);
+
+      if (!expense?.date || !expense?.title || !expense?.amount) {
+        res.statusCode = 400;
+        res.end('Bad user input');
+
+        return;
+      }
+
+      const fileStream = fs.createWriteStream(
+        path.normalize(path.join(__dirname, '../db/expense.json')),
+      );
+
+      fileStream.on('error', (error) => {
+        res.statusCode = 500;
+        res.setHeader('Content-Type', 'text/plain');
+        /* eslint-disable-next-line no-console */
+        console.error(error);
+        res.end('Server error');
+      });
+
+      fileStream.on('finish', () => {
+        res.statusCode = 200;
+        res.setHeader('Content-Type', 'application/json');
+        res.end(JSON.stringify(expense, null, 2));
+      });
+
+      fileStream.end(json);
+    });
+  });
+
+  return server;
 }
 
 module.exports = {