application.php

<?php

/**
 * This singleton object is responsible for keeping references to variables like the database object,
 * the user object, and any other variable that is required for most pages.
 *
 */
class application {
	
	/**
	 * Hold an instance of the class
	 */
	private static $instance;
	
	/**
	 * The database object.
	 *
	 * @var database
	 */
	private $db;
	
	
	/**
	 * The user object. (i.e., the user accessing the page)
	 *
	 * @var database
	 */
	private $user;
	
	/**
	 * A private constructor; prevents direct creation of object
	 */
	private function __construct() {
		// Anything that should be done every time the application starts up can go here.
		
		// We'll load the db connection
		$this->loadDatabase();
	}
	
	/**
	 * The singleton method
	 */
	public static function summon() {
		if (!isset(self::$instance)) {
			$c = __CLASS__;
			self::$instance = new $c;
		}
		return self::$instance;
	}
	
	/**
	 * Prevent users from cloning the instance
	 */
	public function __clone() {
		trigger_error('Clone is not allowed.', E_USER_ERROR);
	}
	
	/**
	 * Provide a way to get access to certain private and protected properties.
	 *
	 * @param string $key
	 * @return mixed
	 */
	public function __get($key) {
		switch ($key) {
			case 'db': return $this->db;
			case 'user': return $this->user;
			default: return null;
		}
	}
	
	/**
	 * Load the database object. This method could be called in the constructor
	 * so that the db is always present. Or, it can be called manually. This method
	 * is designed such that the db will only be loaded once. This method is chainable.
	 *
	 * @return application
	 */
	public function loadDatabase() {
		if (empty($this->db)) {
			$this->db = new database('localhost', 'user', 'pass', 'schema');
		}
		return $this;
	}
	
}

base.php

<?php

abstract class base {
	
	/**
	 * The application object.
	 *
	 * @var application
	 */
	protected $app;
	
	/**
	 * The database object.
	 *
	 * @var database
	 */
	protected $db;
	
	public function __construct() {
		// Get a reference to the application object.
		$this->app = application::summon();
		
		// Make life easier and create a shortcut to the db object (since it'll
		// probably be used a lot)
		$this->db = $this->app->db;
	}
	
}

database.php

<?php

class database {
	
	public function __construct($host, $user, $pass, $schema) {
		/*
			Initialize the database connection here, whichever way you prefer to do it
		*/
	}
	
	/**
	 * Performs a query on a database. A databaseResult object is returned.
	 *
	 * @param string $string
	 * @return databaseResult
	 */
	public function query($string) {
		/*
			Perform a query here, whichever way you prefer to do it
		*/
		
		// Let's assume that $resource is a result resource fetched from a database
		$resource = null;
		$resource = new databaseResult(databaseResult);
		return $resource;
	}
	
}

databaseResult.php

<?php

class databaseResult {
	
	private $resource;
	
	public function __construct($resource) {
		$this->resource = $resource;
	}
	
	/**
	 * Returns a row from a result resource in the form of an object.
	 *
	 * @param resource $resource
	 * @return object
	 */
	public function fetchObject($resource) {
		/*
			Fetch an object from a database result here, whichever way you prefer to do it
		*/
		
		// I'm just setting up an empty object that will pretend to have been fetched from a result resource.
		$foo = new stdClass();
		return $foo;
	}
}

user.php

<?php

class user extends base {
	
	/**
	 * An object representing the user's data loaded from the dabase.
	 *
	 * @var stdClass
	 */
	protected $data;
	
	/**
	 * Determines if this type of user is an administrator.
	 *
	 * @var boolean
	 */
	protected $_isAdmin = false;
	
	/**
	 * Determines if this type of user is an administrator.
	 *
	 * @var boolean
	 */
	protected $_isPremium = false;
	
	/**
	 * Constructs a new user object.
	 * The $userid should correspond to the primary key
	 * of the users table.
	 *
	 * @param integer $userid
	 */
	public function __construct($userid) {
		
		// Define a query string that will load the user's data.
		$q_get = sprintf('select * from users where userid = %d', intval($userid));
		
		// Load the user's data
		$result = $this->db->query($q_get);
		
		// Fetch that data in the form of an object (stdClass).
		$result = $result->fetchObject();
		
		// No need to have the password in the user object.
		unset($result->password);
		$this->data = $result;
		
	}
	
	/**
	 * Get an HTML link to the user's profile.
	 * This link is styled according to whether
	 * the user is a regular user, a premium user,
	 * or an administrator.
	 *
	 * @return string
	 */
	public function getProfileLink() {
		return sprintf('<a href="#userid=%d" class="userProfileLink">%s</a>', $this->data->userid, $this->data->name);
	}
	
	/**
	 * Is the user an administrator?
	 *
	 * @return boolean
	 */
	public function isAdmin() {
		return $this->_isAdmin;
	}
	
	/**
	 * Is the user a Premium member?
	 *
	 * @return boolean
	 */
	public function isPremium() {
		return $this->_isPremium;
	}
	
}

userAdmin.php

<?php

class userAdmin extends userPremium {
	
	protected $_isAdmin = true;
	
	public function getProfileLink() {
		return sprintf('<a href="#userid=%d" class="adminProfileLink">%s</a>', $this->data->userid, $this->data->name);
	}
	
}

userPremium.php

<?php

class userPremium extends user {
	
	protected $_isPremium = true;
	
	public function getProfileLink() {
		return sprintf('<a href="#userid=%d" class="premiumProfileLink">%s</a>', $this->data->userid, $this->data->name);
	}
	
}