// Hlidskjalf - The server that listens to all realms
const http = require('http');

const server = http.createServer((request, response) => {
    // Like Odin processing requests from across the nine realms
    console.log(`Request from: ${request.url}`);

    // Dispatch response (like sending the ravens)
    response.writeHead(200, { 'Content-Type': 'text/html' });
    response.end('<h1>Response from Hlidskjalf</h1>');
});

// Start listening on port 3000 (establish the high seat)
server.listen(3000, () => {
    console.log('Hlidskjalf established on port 3000...');
    console.log('Now observing all realms for requests...');
});

// ❌ Browser APIs - NOT available in Node
window.alert('Hello');
document.querySelector('#app');
localStorage.setItem('key', 'value');
fetch('https://api.example.com');  // Available but different

// ✅ Node.js APIs - NOT available in browser
const fs = require('fs');
const http = require('http');
const path = require('path');
process.env.NODE_ENV;

// ✅ Available in BOTH
console.log('Hello');
setTimeout(() => {}, 1000);
const data = JSON.parse('{"key": "value"}');

// Method 1: REPL (Read-Eval-Print Loop)
// Just type 'node' in terminal
$ node
> console.log('Hello from Node!')
Hello from Node!
> 2 + 2
4
> .exit  // or Ctrl+C twice


// Method 2: Run a file
// Create app.js, then run:
$ node app.js


// Method 3: Run with nodemon (auto-restart on changes)
$ npm install -g nodemon
$ nodemon app.js

// app.js
console.log('Hello from Node.js!');

const greeting = (name) => {
    return `Welcome, ${name}!`;
};

console.log(greeting('Alice'));
console.log(greeting('Bob'));

// Run with: node app.js

// Built-in modules
const fs = require('fs');
const http = require('http');
const path = require('path');

// npm packages (install first with npm install)
const express = require('express');
const lodash = require('lodash');

// Your own modules
const myModule = require('./myModule');
const utils = require('./utils/helpers');

// Specific exports
const { readFile } = require('fs');
const { join } = require('path');

// math.js - Export functions
const add = (a, b) => a + b;
const subtract = (a, b) => a - b;
const multiply = (a, b) => a * b;

module.exports = {
    add,
    subtract,
    multiply
};

// app.js - Import and use
const math = require('./math');

console.log(math.add(5, 3));      // 8
console.log(math.multiply(4, 2)); // 8

const fs = require('fs');

// Read file (synchronous - blocks execution)
const data = fs.readFileSync('input.txt', 'utf8');
console.log(data);

// Read file (asynchronous - doesn't block)
fs.readFile('input.txt', 'utf8', (err, data) => {
    if (err) {
        console.error('Error reading file:', err);
        return;
    }
    console.log(data);
});

// Modern: Promises version
const fsPromises = require('fs').promises;
const data = await fsPromises.readFile('input.txt', 'utf8');

const fs = require('fs');

// Write file (replaces existing content)
fs.writeFile('output.txt', 'Hello, World!', (err) => {
    if (err) {
        console.error('Error writing file:', err);
        return;
    }
    console.log('File written successfully!');
});

// Append to file
fs.appendFile('log.txt', 'New log entry\n', (err) => {
    if (err) throw err;
    console.log('Log updated!');
});

// Synchronous version
fs.writeFileSync('output.txt', 'Hello, World!');

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

// Read directory contents
fs.readdir('./files', (err, files) => {
    if (err) throw err;
    console.log(files);  // Array of filenames
});

// Create directory
fs.mkdir('./new-folder', (err) => {
    if (err) throw err;
    console.log('Directory created!');
});

// Check if file/directory exists
if (fs.existsSync('./my-file.txt')) {
    console.log('File exists!');
}

const http = require('http');

// Create a server
const server = http.createServer((request, response) => {
    // This function runs for every incoming request
    response.writeHead(200, { 'Content-Type': 'text/html' });
    response.end('<h1>Hello from Node.js Server!</h1>');
});

// Start listening on port 3000
server.listen(3000, () => {
    console.log('Server running at http://localhost:3000/');
});

const http = require('http');

const server = http.createServer((req, res) => {
    // Request object properties
    console.log('Method:', req.method);       // GET, POST, etc.
    console.log('URL:', req.url);             // /about, /users, etc.
    console.log('Headers:', req.headers);     // Request headers

    // Response methods
    res.writeHead(200, { 'Content-Type': 'text/html' });
    res.write('<h1>Welcome</h1>');
    res.write('<p>Path: ' + req.url + '</p>');
    res.end();
});

server.listen(3000);

const http = require('http');

const server = http.createServer((req, res) => {
    res.writeHead(200, { 'Content-Type': 'text/html' });

    if (req.url === '/') {
        res.end('<h1>Home Page</h1>');
    } else if (req.url === '/about') {
        res.end('<h1>About Page</h1>');
    } else if (req.url === '/contact') {
        res.end('<h1>Contact Page</h1>');
    } else {
        res.writeHead(404);
        res.end('<h1>404 - Page Not Found</h1>');
    }
});

server.listen(3000);

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

const server = http.createServer((req, res) => {
    let filePath = './public' + req.url;
    if (filePath === './public/') {
        filePath = './public/index.html';
    }

    fs.readFile(filePath, (err, content) => {
        if (err) {
            res.writeHead(404);
            res.end('<h1>404 - File Not Found</h1>');
        } else {
            res.writeHead(200, { 'Content-Type': 'text/html' });
            res.end(content);
        }
    });
});

server.listen(3000);

const path = require('path');

// Get file extension
const extname = path.extname(filePath);

// Set appropriate content type
let contentType = 'text/html';

switch (extname) {
    case '.js':
        contentType = 'text/javascript';
        break;
    case '.css':
        contentType = 'text/css';
        break;
    case '.json':
        contentType = 'application/json';
        break;
    case '.png':
        contentType = 'image/png';
        break;
}

res.writeHead(200, { 'Content-Type': contentType });

// app.js
const calculate = (a, b) => {
    debugger;  // Program pauses here when debugging
    const result = a + b;
    return result;
};

console.log(calculate(5, 3));

// Run with debugger:
// $ node inspect app.js

// Or in Chrome DevTools:
// $ node --inspect-brk app.js
// Then open chrome://inspect in Chrome

// Access environment variables
const port = process.env.PORT || 3000;
const dbUrl = process.env.DATABASE_URL;
const apiKey = process.env.API_KEY;

console.log(`Server will run on port ${port}`);

// Set when running (Linux/Mac):
$ PORT=8080 node app.js

// Set when running (Windows):
$ set PORT=8080 && node app.js

// 1. Install dotenv
$ npm install dotenv

// 2. Create .env file
PORT=3000
DATABASE_URL=mongodb://localhost:27017/myapp
API_KEY=your_secret_api_key_here

// 3. Load in your app
require('dotenv').config();

const port = process.env.PORT;
const dbUrl = process.env.DATABASE_URL;

// 4. Add .env to .gitignore
echo ".env" >> .gitignore

basic-informational-site/
├── index.js              # Server file
├── public/
│   ├── index.html        # Home page
│   ├── about.html        # About page
│   ├── contact-me.html   # Contact page
│   ├── 404.html          # 404 error page
│   └── styles.css        # Stylesheet
└── .gitignore

// index.js
const http = require('http');
const fs = require('fs');
const path = require('path');

const server = http.createServer((req, res) => {
    // Your code here:
    // 1. Determine which file to serve based on req.url
    // 2. Read the file with fs.readFile()
    // 3. Set appropriate headers
    // 4. Send the file content or 404
});

const PORT = process.env.PORT || 8080;
server.listen(PORT, () => {
    console.log(`Server running on port ${PORT}`);
});