CREATE TABLE IF NOT EXISTS `users` (
`uid` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(16) NOT NULL,
`password` varchar(64) NOT NULL,
`email` varchar(24) NOT NULL,
`first_name` varchar(12) NOT NULL,
`last_name` varchar(12) NOT NULL,
`accesslvl` tinyint(4) NOT NULL,
`status` tinyint(4) NOT NULL,
PRIMARY KEY (`uid`)
)

CREATE TABLE IF NOT EXISTS `vehicles` (
`uid` int(11) NOT NULL AUTO_INCREMENT,
`numplate` varchar(12) NOT NULL,
`make` varchar(12) NOT NULL,
`model` varchar(12) NOT NULL,
`engine` float NOT NULL,
`mileage` float NOT NULL,
`year` smallint(6) NOT NULL,
`color` varchar(20) NOT NULL,
`bodytype` varchar(12) NOT NULL,
`doors` tinyint(4) NOT NULL,
`fueltype` varchar(12) NOT NULL,
`geartype` varchar(12) NOT NULL,
`price` mediumint(8) NOT NULL,
`description` text NOT NULL,
PRIMARY KEY (`uid`)
)

public function login($uname, $upass, $umail)
{
  // Here's where we query our database with given information by user, which is username or email address.
	$result = $this->db->query("SELECT * FROM `users` WHERE `username` = '".$uname."' OR `email` = '".$umail."'");
	
	// Fetching associated fields in DB with the information given and storing data to the $row variable.
	$row = $result->fetch_assoc();
	
	// Checking if there are any rows found.
	if(mysqli_num_rows($result) > 0)
	{
	  // Veryfing user's password (using default function which is hashing user's input and comparing it to the password from the database field).
		if(password_verify($upass, $row['password']))
		{
		  // If password's are the same, we are creating a user's session with PHP's global variable (SESSION) with his primary key from the database, which is uid (unique identification number).
			$_SESSION['user_session'] = $row['uid'];
			
			// Rediricting 'this' object (user) to index page with the home tag.
			$this->redirect('index.php?p=home');
			return true;
		}
		
		// If user's given password is not the right now, he will not proceed and receive appropriate message.
		else
		{
			echo("ERROR: Wrong details!");
			return false;
		}
	}
}

public function register($uname, $upass, $umail, $ufname, $ulname)
{
  // First of all we gain all the data given by user's wish be reference from above. Variables in brackets are holding values insterted by user.
  
  // Hashing user's password to be stored and secured in the database.
  $upassEx = password_hash($upass, PASSWORD_DEFAULT);
  $this->db->query("INSERT INTO `users` (`username`, `password`, `email`, `first_name`, `last_name`) VALUES ('".$uname."', '".$upassEx."', '".$umail."', '".$ufname."', '".$ulname."')");
  
  // Redirecting user to the index page with home tag.
  $this->redirect('index.php?p=home');
}

<?php
	include_once 'config.php';
	
	// Check if our object (user) is logged in and if he has a parameter "logout" set to "true" in a URL bar. If so, proceed to the log out function and redirect them to the sign in page.
	if($user->IsUserLoggedIn() && $_GET['logout'] == true)
	{
		$user->logout(); // calling a function from the class_user.php to destroy user's session and unset his SUPER PHP's VARIABLE.
		$user->redirect('signin.php');
	}
?>

<?php

// First, code is trying to initialize a configuration and object (user) creation with object (navigation bar) as well.
include_once 'config.php';
include_once 'class_navbar.php';

// If user is not logged in, he will be redirected to the signin page. It is a security question, to do not let people change the webpages through the URL bars.
if(!$user->IsUserLoggedIn())
{
$user->redirect('signin.php');
}

// Fetching for the all data about user from the database.
$user_uid = $_SESSION['user_session'];
$result = $MYSQL_HANDLE->query("SELECT * FROM `users` WHERE uid = '".$user_uid."'");
$row = $result->fetch_assoc();
?>

/* Default website's navigation menu which holds Home, News, Contact and About pages. Maintain stock webpage is only shown for user with certain access level. It can be clearly read from the array below. */

$menu = array(
  'home'  		=> array('text' => 'Home',  			'url' => '?p=home',			'pageaccesslvl' => '0'),
  'news'  		=> array('text' => 'News',  			'url' => '?p=news',			'pageaccesslvl' => '0'),
  'contact'  	=> array('text' => 'Contact',  			'url' => '?p=contact',		'pageaccesslvl' => '0'),
  'about' 		=> array('text' => 'About', 			'url' => '?p=about',		'pageaccesslvl' => '0'),
  'mainstock'	=> array('text' => 'Maintain stock',	'url' => '?p=mainstock',	'pageaccesslvl' => '1'), // Required access level: 1 (administrator of level 1).
);

class class_UserNavigationMenu
{
	public static function GenerateMenu($items) 
	{	
		// User's UID is necessary in order to provide SQL results for the website and query anything to the database.
		$user_uid = $_SESSION['user_session'];
		$result = $GLOBALS['MYSQL_HANDLE']->query("SELECT `accesslvl` FROM `users` WHERE uid = '".$user_uid."'"); // Another Super global PHP's variable $GLOBALS.
		$row = $result->fetch_assoc();
		$html = "<nav class = 'navbar'>\n";
		foreach($items as $key => $item) // Iterating through items of the navigation menu.
		{
			$selected = (isset($_GET['p'])) && $_GET['p'] == $key ? 'selected' : null; // Checking selected option. This line of code is called a conditional expression. It is a shorted way of if/else procedure.
			
			if($item['pageaccesslvl'] > $row['accesslvl']) // That's why we needed to access user's database, in order to check user's access level and make sure to show them Maintain stock option or any other navigation menu item which is available for them at certain level.
			{
				continue;
			}
			
			else
			{
				// Gluing together all the navigation menu parts.
				$html .= "<a href = '{$item['url']}' class = '{$selected}' > {$item['text']}</a>\n";
			}
		}
		$html .= "</nav>\n";
		return $html;
	}
};

<head>
<meta http-equiv = "Content-Type" content = "text/html; charset = utf-8" />
<link rel = "stylesheet" href = "style.css" type = "text/css" />
<title>Welcome - <?php print($row['email']); ?></title>

<!-- Creating our navigation bar with the reference to the '$menu' variable. -->
<?php echo class_UserNavigationMenu::GenerateMenu($menu); ?>

<!-- Creation of the top blue bar with two buttons on it with the reference to my github page and to log out from the session -->
<div class = "header">

	<div class = "left">  <label><a href = "https://github.com/Jedrzej94/">github.com</a></label> </div>
	<div class = "right"> <label><a href = "logout.php?logout=true">Logged in as <?php print($row['username']); ?> (sign out)</a></label> </div>
	
</div>
</head>

<body>

<!-- Opening the body tag and starting inserting the content of the index.php -->
<div class = "content">
	
<?php 

<!-- Checking if user has a 'p' tag in his URL bar, which stands from PAGE -->
	if(isset($_GET['p']))
	{
	<!-- It is allowing us to check which item user has chosen from the navigation menu and load appropriate file -->
		switch($_GET['p'])
		{
			case "home":		include("pages\index\home.php"); break;		<!-- Great thing about INCLUDING PHP file instead of redirecting user to the file is described below. -->
			case "news":		include("pages\index\\news.php"); break;
			case "contact":		include("pages\index\contact.php"); break;
			case "about":		include("pages\index\about.php"); break;
			case "mainstock":	header("Location: pages\\vehicles\mainstock.php"); break;
			
			default:			include("index.php"); break;
		}
	}

 ?>
	
</div>
</body>
</html>

<body>

	<div class = "content">
	
		<h1>Home page</h1>
		 
	</div>
	
</body>
</html>

<?php
	if(isset($_POST['btn-addveh']))
	{
		// This part of the PHP code is called only when user has pressed "Add" button with the vehicle details in.
		// It is trimming user's input from all the html tags etc. to avoid them calling code from their side.
		$numplate 	= trim($_POST['inp_numplate']);
		$make 		= trim($_POST['inp_make']);
		$model 		= trim($_POST['inp_model']);
		$engine 	= trim($_POST['inp_engine']);
		$mileage	= trim($_POST['inp_mileage']);
		$year		= trim($_POST['inp_year']);
		$color		= trim($_POST['inp_color']);
		$bodytype	= trim($_POST['inp_bodytype']);
		$doors		= trim($_POST['inp_doors']);
		$fueltype	= trim($_POST['inp_fueltype']);
		$geartype	= trim($_POST['inp_geartype']);
		$price		= trim($_POST['inp_price']);
		
		// Including vehicle's class. '../../' means we are backing up to the parent directory (master dir).
		include_once '../../class_vehicle.php';
		$vehicle = new VEHICLE($MYSQL_HANDLE); // Creating a new CLASS object and storing it into $vehicle variable.
		
		// Asking database to get number plate of the vehicle and store the results into $result variable.
		$result = $MYSQL_HANDLE->query("SELECT `numplate` FROM `vehicles` WHERE `numplate` = '".$numplate."'");
		$row = $result->fetch_assoc();
		if($row['numplate'] == $numplate) 
		{
			echo("ERROR: That vehicle has been registered before!");
		}
		
		else
		{
			// If vehicle's registration number (number plate) hasn't been found in the database, we are calling a addVehicle function with the reference parameters for the class object created before ($vehicle).
			$vehicle->addVehicle($numplate, $make, $model, $engine, $mileage, $year, $color, $bodytype, $doors, $fueltype, $geartype, $price);
		}
	}
?>

public function addVehicle($numplate, $make, $model, $engine, $mileage, $year, $color, $bodytype, $doors, $fueltype, $geartype, $price)
{
	// First we are converting user's number plate input into UPPER CASE text.
	$numplateEx = strtoupper($numplate);
	
	// And we store this object ($vehicle) into our database field with data given by user. Data was passed by reference, where the function was called.
	$this->db->query("INSERT INTO `vehicles` (`numplate`, `make`, `model`, `engine`, `mileage`, `year`, `color`, `bodytype`, `doors`, `fueltype`, `geartype`, `price`) VALUES ('".$numplateEx."', '".$make."', '".$model."', '".$engine."', '".$mileage."', '".$year."', '".$color."', '".$bodytype."', '".$doors."', '".$fueltype."', '".$geartype."', '".$price."')");
	
	// Checking if directory with the number plate exists in the 'images' folder.
	if(!is_dir("images/$numplateEx"))
	{
		mkdir("images/$numplateEx");
	}
	
	// This is where the images of the vehicle are stored and loaded by the different class functions such as print/search etc.
	$upload_dir = "images/$numplateEx/";
	
	// Checking multiple images loaded by user to be uploaded to the server.
	foreach($_FILES['inp_image']['name'] as $name => $value)
	{
		$filename = stripslashes($_FILES['inp_image']['name'][$name]);
		$extension = getExtension($filename);
		$extension = strtolower($extension);
		
		// Extension security check, if it's different than one of the below extensions we can make user stop there and force program to quit.
		if(($extension != "jpg") && ($extension != "jpeg") && ($extension != "png") && ($extension != "gif")) 
		{
		}
		
		else
		{
			$size = filesize($_FILES['inp_image']['tmp_name'][$name]);
		}
		
		// Copying file(s) to the folder.
		$image_name = $filename.'.'.$extension;
		$newname = $upload_dir.$image_name;
		$copied = copy($_FILES['inp_image']['tmp_name'][$name], $newname);
		
		// Checking if there were any problems regarding file(s) upload. We can send message or anything we wanna do if files weren't uploaded below.
		if (!$copied) 
		{
			
		}
	}
}

<body>

	<?php
	
		include_once '../../config.php';
		include_once '../../class_vehicle.php';
		$vehicle = new VEHICLE($MYSQL_HANDLE);
		$vehicle->printVehicles();
		
	?>
	
</body>
</html>