twiggi web-based groupware Code

<?php
// +--------------------------------------------+
// | Twiggi web-based groupware.		|
// |						|
// | For copyright and license information 	|
// | please read the COPYRIGHT file.		|
// +--------------------------------------------+

class core
{
	static $instance = false;
	private $major_version = 2;
	private $minor_version = 0;
	private $state_version = "ALPHA";
	private $root = NULL;
	private $slash = NULL;
	private $config = array();
	private $debug = true;
	private $loaded_files = array();

	private function __construct()
	{
		$this->root = realpath(".");
		$this->slash = DIRECTORY_SEPARATOR;

		$this->load_config();
	}

	public function get_instance()
	{
		if (!core::$instance)
		{
			core::$instance = new core();
		}
		
		return core::$instance;
	}

	private function load_config()
	{
		$config_file = $this->root.$this->slash."config".$this->slash."config.inc.php";
		if (!file_exists($config_file))
		{
			core_print(__FILE__,__LINE__,ERROR,$config_file." is missing");
			return;
		}

		include_once($config_file);
		$this->config = $cfg;
	}

	public function load_file($file)
	{
		if (!in_array($file, $this->loaded_files))
		{
			if (!file_exists($file))
			{
				core_print(__FILE__,__LINE__,ERROR,$file." is missing!");
				return false;
			}

			require_once($file);
			$this->loaded_files[] = $file;

			return true;
		}

		return false;
	}

	public function get_config_option($option)
	{
		if (array_key_exists($option,$this->config))
		{
			if (($this->config[$option] == NULL) && ($this->debug))
			{
				core_print(__FILE__,__LINE__,WARNING,$option." is NULL");
			}
			return $this->config[$option];
		}

		if ($this->debug)
		{
			core_print(__FILE__,__LINE__,WARNING,$option." is not a known configuration option");
		}

		return NULL;
	}

	public function get_root()
	{
		return $this->root;
	}

	public function get_slash()
	{
		return $this->slash;
	}

	public function get_version()
	{
		return $this->major_version.".".$this->minor_version." (".$this->state_version.")";
	}

	public function show_page()
	{
		print "Twiggi web-based groupware core module is up and running. Version ";
	}

	public function get_debug_mode()
	{
		return $this->debug;
	}

	public function get_module()
	{
		// For now we just return core until the module class is working...
		return "core";
	}
}

?>