<?php
session_start();
function isLoggedIn() { return isset($_SESSION['user_id']); }
function requireLogin() {
    if (!isLoggedIn()) {
        header('Location: /login.php?redirect=' . urlencode($_SERVER['REQUEST_URI']));
        exit;
    }
}
function currentUser() { return ['id' => $_SESSION['user_id'], 'username' => $_SESSION['username']]; }