<?php
session_start();
/**************************
  Processing Requirements
***************************/

// User box contents.
$_login = <<<UB
                <form method="post" onsubmit="return false">
                    Username<br /><input type="text" id="username" /><br />
                    Password<br /><input type="password" id="password" /><br />
                    <input type="button" value="Login" onclick="login()" />
                </form>
UB;
$_lguser = isset($_POST['username'])? $_POST['username'] : "";
$_logged = <<<UB
                <form method="post" onsubmit="return false">
                    <b>Welcome </b>{$_lguser}<br />
                    <input type="button" value="Logout" onclick="logout()" />
                </form>
UB;

// Helper function.
function stringFix($text){
    $pattern = array('/\t/','/\r/','/\n/','/"/');
    $replace = array('\t','\r','\n','\"');
    return preg_replace($pattern,$replace,$text);
}

/******************
  Processing Area
*******************/

// 1) Check for user session.
if(isset($_SESSION['auth_status']) && $_SESSION['auth_status'] == 1){
    $_SESSION['user_box'] = $_logged;
}

// 2) Check for login request.
if(isset($_POST['login'])){
    if($_POST['username'] == 'admin' && $_POST['password'] == 'abc123'){
        $_SESSION['auth_status'] = 1;
        $_logged = stringFix($_logged);
        echo <<<JS
        var contents = "{$_logged}";
        document.getElementById('user_box').innerHTML = contents;
        alert('Login Success!');
JS;
    }
    else{
        echo "alert('Login Failed');";
    }
}

// 3) Check for logout request.
if(isset($_POST['logout'])){
    unset($_SESSION);
    session_destroy();
    $_login = stringFix($_login);
    echo <<<JS
    var contents = "{$_login}";
    document.getElementById('user_box').innerHTML = contents;
    alert('Logout Successful.');
JS;
}
?>