functions.php

<?php

/**
 * Used to store different static data.
 *
 * @var array
 */
$config = [
    'name' => 'Simple PHP Website',
];

/**
 * Displays site name. Uses $config global.
 */
function siteName()
{
    global $config;
    echo $config['name'];
}

/**
 * Displays page title. It takes the data from 
 * URL, it replaces the hyphens with spaces and 
 * it capitalizes the words.
 */
function pageTitle()
{
    $page = isset($_GET['page']) ? htmlspecialchars($_GET['page']) : 'home';

    echo ucwords(str_replace('-', ' ', $page));
}

/**
 * Displays page content. It takes the data from 
 * the static pages inside the pages/ directory.
 * When not found, display the 404 error page.
 */
function pageContent()
{
    $page = isset($_GET['page']) ? $_GET['page'] : 'home';

    $path = getcwd().'/pages/'.$page.'.php';

    if (file_exists($path)) {
        include $path;
    } else {
        include 'pages/404.php';
    }
}