Solution

src/createServer.js

@@ -1,8 +1,107 @@
 'use strict';
 
+const http = require('http');
+const fs = require('fs');
+
+const form = `
+  <form method="POST" action="/add-expense">
+    <input
+      type="date"
+      name="date"
+      required
+    >
+    <input
+      type="text"
+      name="title"
+      placeholder="Enter title"
+      required
+    >
+    <input
+      type="number"
+      name="amount"
+      placeholder="Enter amount"
+      required
+    >
+    <button type="submit">Send</button>
+  </form>
+`;
+
 function createServer() {
-  /* Write your code here */
-  // Return instance of http.Server class
+  return http.createServer((req, res) => {
+    if (req.method === 'GET') {
+      if (req.url === '/') {
+        res.writeHead(200, { 'Content-Type': 'text/html' });
+        res.end(form);
+      } else if (req.url === '/add-expense') {
+        res.writeHead(400, { 'Content-Type': 'text/plain' });
+        res.end('Incorrect request');
+      } else {
+        res.writeHead(404, { 'Content-Type': 'text/plain' });
+        res.end('Page not found');
+      }
+
+      return;
+    }
+
+    if (req.method === 'POST') {
+      if (req.url === '/add-expense') {
+        let body = '';
+
+        req.on('data', (chunk) => (body += chunk));
+
+        req.on('end', () => {
+          let expenseData;
+
+          if (req.headers['content-type'] === 'application/json') {
+            expenseData = JSON.parse(body);
+          } else {
+            const params = new URLSearchParams(body);
+
+            expenseData = Object.fromEntries(params);
+          }
+
+          const dateObj = new Date(expenseData.date);
+          const isValidDate = dateObj instanceof Date && !isNaN(dateObj);
+
+          const isValidTitle =
+            expenseData.title && expenseData.title.trim().length > 0;
+
+          const amount = parseFloat(expenseData.amount);
+          const isValidAmount = !isNaN(amount) && amount > 0;
+
+          if (!isValidDate || !isValidTitle || !isValidAmount) {
+            res.writeHead(400, { 'Content-Type': 'text/plain' });
+            res.end('Invalid data');
+          } else {
+            const filePath = 'db/expense.json';
+
+            if (!fs.existsSync('db')) {
+              fs.mkdirSync('db');
+            }
+
+            if (!fs.existsSync(filePath)) {
+              fs.writeFileSync(filePath, JSON.stringify({}));
+            }
+
+            // const raw = fs.readFileSync(filePath, 'utf8');
+            // const arr = JSON.parse(raw);
+            const record = {
+              date: expenseData.date,
+              title: expenseData.title,
+              amount: expenseData.amount,
+            };
+
+            // arr.push(record);
+
+            fs.writeFileSync(filePath, JSON.stringify(record, null, 2));
+
+            res.writeHead(200, { 'Content-Type': 'application/json' });
+            res.end(JSON.stringify(expenseData));
+          }
+        });
+      }
+    }
+  });
 }
 
 module.exports = {