<?php
class Login
{
    private $_id;
    private $_username;
    private $_password;
    private $_passmd5;

    private $_errors;
    private $_access
    private $_login
    private $_token

    public function _construct()
    {
        $this->_errors = array();       //empty array to carry error messages
        $this->_login = isset($_POST['login'])? 1 : 0; //login indicater, if login button is clicked = true else false
        $this->_acess = 0;      //access area, level of access 0 by default
        $this->_token = $_POST['token'];    //assigned form token

        $this->_id = 0; //id, default is 0
        $this->_username = ($this->_login)? $this->filter($_POST['username']) : $_SESSION['username']; // has users submitted form? filter out post username variable and assigne to username
        $this->_password = ($this->_login)? $this->filter($_POST['password']) : ''; // contains original password text, needed for validation
        $this->_passmd5 = ($this->_login)? md5($this->_password) : $_SESSION['password']; //contains password in encrypted password

        //all rely on form being submitted


    }

    public function isLoggedIn()
    {
        ($this->_login)? $this->verifyPost() : $this->verifySession(); //verify's post data and session

        return $this->_access; //checks access level
    }

    public function filter()
    {
        return preg_replace('/[a-zA-Z0-9]/','',$var); //filters bad chars
    }

    public function verifyPost()
    {
        try
        {
            if(!$this->isTokenValid())
                throw new Exeption('Invalid Form Submission');

            if(!$this->isDataValid())
                throw new Exception('Invalid Form Data');

            if(!$this->verifyDatabase());
                throw new Exception('Invalid Username or Password');

            $this->_acess = 1;
            $this->registerSession();
        }
    }
    catch (Exception $e)
    {
        $this->_erorrs[] = $e->getMessage();
    }

    public funtcion verifySession()
    {
        if($this->sessionExist() && $this->verifyDatabase();
    }

    public function verifyDatabase()
    {
        //Database Connection Info
        mysql_connect("db_location", "username", "password") or die("Could not connect to database");
        mysql_select_db("db_name") or die("Could not select databse");

        $data = mysql_query("SELECT IF FROM tablename WHERE username = '($this->_username)' AND password = '($this->_passmd5'");

        if(mysql_num_rows($data))
            {
                list($this->_id) = @array_values(mysql_fetch_assoc($data));
                return true;
            }
        else
            {
                return false;
            }
    }

    public function isDataValid()
    {
        return(preg_match('/^[a-zA-Z0-9)(5,12)$/',$this->_username) && (preg_match('/^[a-zA-Z0-9)(5,12)$/',$this->_password))? 1 : 0;
    }

    public function isTokenValid()
    {
        return (!isset($_SESSION['token']) || $this->_token != $_SESSION['token'])? 0 : 1;
    }

    public function registerSession()
    {
        $_SESSION['ID'] = $this->_id;
        $_SESSION['username'] = $this->_username;
        $_SESSION['password'] = $this->_passmd5;
    }

    public function sessionExist()
    {
        return(isset($_SESSION['username']) && isset(['password']))? 1 : 0;

    public function showErrors()
    {
        echo "<h3>Errors></h3>";

        foreach($this->_errors as $key=>$value)
            echo $value."<br>";
    }
}
?>