/*SQL*/
//createSQL.sql
CREATE TABLE `users` (
   `userID` int(11) NOT NULL auto_increment,
   `userName` varchar(30) collate utf8_unicode_ci NOT NULL default '',
   `userPass` varchar(32) collate utf8_unicode_ci NOT NULL default '',
   `userSession` varchar(32) collate utf8_unicode_ci default NULL,
   `userMail` varchar(150) collate utf8_unicode_ci NOT NULL default '';
   PRIMARY KEY (`userID`),
   UNIQUE KEY `userName` (`userName`),
   UNIQUE KEY `userMail` (`userMail`),
   UNIQUE KEY `userSession` (`userSession`),
) ENGINE=MyISAM;

INSERT INTO users SET userName = 'loginname', userPass = MD5('loginpass'), userMail = 'usermail';



/*Code*/
//login.php

<?php
    session_start();
    include_once('sessionshelpers.inc.php');

    if(isset($_POST['login'])) {
        $userID = check_user($_POST['userName'], $_POST['userPass']);
        if($userID) {
            login($userID);
        } else {
            echo '<p>You\'ve entered wrong login information.</p>';
        }
    }

    if(!logged_in()) {
        //echo <<<END
        <form method="post" action="login.php">
        <label>Username:</label> <input name="userName" type="text"><br/>
        <label>Password:</label> <input name="userPass" type="password" id="userpass"><br/>
        <input name="login" type="submit" id="login" value="Login">
        </form>
        //END;
    } else {
        echo '<p><a href="adminShit.php">Admin Portal</a></p>';
        echo '<p><a href="logout.php">Logout</a></p>';
    }
?>

//adminShit.php
<?php
    session_start();
    include_once('sessionhelpers.inc.php');

    echo '<p>You\'re ';
    if(!logged_in()) {
        echo 'not ';
    }
    echo 'logged in.<p/>';

    if(!logged_in()) {
        echo '<p><a href="login.php">Login</a></p>';
    }

    if (logged_in()) {
        echo '<p>BLA BLA BLA</p>';
        echo '<p><a href="logout.php">Logout</a></p>';
    }
?>

//logout.php
<?php
    session_start();
    include_once('sessionhelpers.inc.php');

    echo '<p>You\'re ';
    if(!logged_in()) {
        echo 'not ';
    }
    echo 'logged in.<p/>';

    logout();

    echo '<p>You\'re ';
    if(!logged_in()) {
        echo 'not ';
    }
    echo 'logged in.<p/>';

    echo '<p><a href="login.php">Login</a></p>';
?>

//sessionhelpers.inc.php
<?php
    function connect() {
        $connection = mysql_connect('host', 'username', 'password') or exit(mysql_error());
        mysql_select_db('database', $connection) or exit(mysql_error());
    }

    function checkUser($userName, $userPass) {
        if(get_magic_quotes_gpc()) {
            $userName = stripslashes($userName);
            $userPass = stripslashes($userPass);
        }
        $userName = mysql_real_escape_string($userName);
        $userName = str_replace('%', '\%', $userName);
        $userName = str_replace('_', '\_', $userName);

        $query = 'SELECT userID FROM users WHERE userName = \'' . $userName . '\' AND userPass = \'' . md5($userPass) . '\'';
        if(!$result = mysql_query($query)) {
            exit(mysql_error());
        }
        if(mysql_num_rows($result) == 1) {
            $user = mysql_fetch_assoc($result);
            return($user['userID']);
        } else {
            return(false);
        }
    }

    function login($userID) {
        $query = 'UPDATE users SET userSession = \'' . session_id() . '\' WHERE userID = ' . ((int)$userID);
        if(!mysql_query($query)) {
            exit(mysql_error());
        }
    }

    function logged_in() {
        $query = 'SELECT userID FROM users WHERE userSession = \'' . session_id() . '\'';
        if(!$result = mysql_query($query)) {
            exit(mysql_error());
        }
        return(mysql_num_rows($result) == 1);
    }

    function logout() {
        $query = 'UPDATE users SET userSession = NULL WHERE userSession = \'' . session_id() . '\'';
        if(mysql_query($query)) {
            exit(mysql_error());
        }
    }

    connect();
?>