index.php

<?php

session_start();
// print_r($_SESSION);

if(isset($_SESSION["user_id"]))
{
  $mysqli = require __DIR__ . "/database.php";
  $sql = "SELECT * FROM user WHERE id = {$_SESSION["user_id"]}";
  $result = $mysqli->query($sql);
  $user = $result->fetch_assoc();
}

?>

<!DOCTYPE html>
<html>

<head>
  <title>Home Page</title>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <link rel="stylesheet" href="styles/index.css">
</head>

<body>
  <h1>Home Page</h1>

  <?php if(isset($user)): ?>
    <p>Hello, <?= htmlspecialchars($user["username"]); ?>. You are now logged In.</p>
    <p><a href="logout.php">LogOut</a></p>

  <?php else: ?>
    <p><a href="login.php">LogIn</a> or <a href="signup.php">SignUp</a></p>
    
  <?php endif; ?>

</body>
</html>