An alternative router.php

.router.php

<?php

define('__SELF__', getcwd());

if (preg_match('/\.(?:png|jpg|jpeg|gif|js|css|html)$/', $_SERVER["REQUEST_URI"])) {
	$ext = pathinfo($_SERVER["REQUEST_URI"])['extension'];

	$extensions = [
		'js' => 'text/javascript',
		'css' => 'text/css',
		'html' => 'text/html',
		'jpg' => 'image/jpg',
		'png' => 'image/png',
		'jpeg' => 'image/jpeg',
		'gif' => 'image/gif',
	];

	if(isset($extensions[$ext])) {
		header("Content-Type: {$extensions[$ext]}");
	}

	include __SELF__ . '/../' . $_SERVER['REQUEST_URI'];
    return true;
}

if (is_dir(__SELF__ . $_SERVER['PHP_SELF'])) {
    include __SELF__ . $_SERVER['PHP_SELF'] . '/index.html';
}
else {
	$dir = rtrim(__SELF__ . '/../', "/") . $_SERVER['REQUEST_URI'];

	if(is_file($dir . 'index.html')) {
		include $dir . 'index.html';
	}
	else if(is_file($dir . 'index.php')) {
		include $dir . 'index.php';
	}
	else {
		echo "<h2>Not Found!</h2>";
	}
}