PHP Semantik, Bug fixes setup script

<?php

/** step 0 **/
if(file_exists('config.php')) {
	$step_0 = FALSE;
} else {
	$step_0 = TRUE;
}

/** step 2 **/
if(isset($_POST['hostname'], $_POST['username'], $_POST['password'], $_POST['database'])) {
	$hostname = $_POST['hostname'];
	$username = $_POST['username'];
	$password = $_POST['password'];
	$database = $_POST['database'];
	$db = new mysqli($hostname, $username, $password, $database);
	if(mysqli_connect_errno()) {
		$step_2 = FALSE;
	} else {
		$step_2 = TRUE;
		$db->close();
	}
} else {
	$step_2 = FALSE;
}

/** step 3 **/
$connection_data = "define('HOST', $hostname);\r\ndefine('USER', $username);\r\ndefine('PASS', $password);\r\ndefine('DATA', $database);";
	$handle = fopen('config.php', 'w');
	fwrite($handle, $connection_data);
	fclose($handle);
if(file_exists('config.php')) {
	$step_3 = TRUE;
} else {
	$step_3 = FALSE;
}

/** template engine **/
if(4 > $_GET['step']) {
	$step = $_GET['step'];
} else {
	$step = 0;
}

include('header.tpl');
switch($step) {
	case 0:
		if($step_0 == TRUE) {
			include('step_0a.tpl');
		} else {
			include('step_0b.tpl');
		}
		break;

	case 1:
			include('step_1a.tpl');
		break;
		
	case 2:
		if($step_2 == TRUE) {
			include('step_2a.tpl');
		} else {
			include('step_2b.tpl');
		}
		break;
	
	case 3:
		if($step_3 == TRUE) {
			include('step_3a.tpl');
		} else {
			include('step_3b.tpl');
			echo $connection_data;
		}
		break;
}
include('footer.tpl');

?>

<?php

define('HOST', 'localhost');
define('USER', 'user');
define('PASS', 'pass');
define('DATABASE', 'test');

?>