<!-- user.php -->
<?php
session_start();
ob_start();
$user = 'admin';
$pass = 'admin';

$action = $_GET['action'];
switch($action) {
	// Login.
	case 'login':
		$what = $_GET['what'];
		switch($what) {
			case 'process':
				$username = $_POST['username'];
				$password = $_POST['password'];

				$username = strip_tags($username);
				$password = strip_tags($password);
				$username = htmlspecialchars($username);
				$password = htmlspecialchars($password);

				if($username == $user && $password == $pass) {
					$agent = $_SERVER['HTTP_USER_AGENT'];
					$ip = $_SERVER['REMOTE_ADDR'];

					$_SESSION['login'] = 'admin';
					$_SESSION['agent'] = $agent;
					$_SESSION['ip'] = $ip;

					header('Location: index.php?action=admin');
				} else {
					echo '<p style="font-size: 12px;">Contraseña/Usuario incorrecto. Volver <a style="text-decoration: none;" href="index.php">atrás</a>';
				}
				break;

			// Login form.
			default:
				include('login_form.php');
		}
		break;

	// Logout.
	case 'logout':
		session_destroy();
		header('Location: index.php');
		break;

	// Admin page.
	case 'admin':
		if(isset($_SESSION['login'])) {
			$agent = $_SERVER['HTTP_USER_AGENT'];
			$ip = $_SERVER['REMOTE_ADDR'];

			if($agent == $_SESSION['agent'] && $ip == $_SESSION['ip']) {
				include('admin_page.php');
			} else {
				header('location: ?action=login');
			}
		} else {
			header('location: ?action=login');
		}
		break;

	default:
		include('login_form.php');
}

$page_content = ob_get_clean();
include('layout.php');
?>

<!-- admin_page.php -->
   <div class="login">
    <table border="0" width="100%" height="20px">
     <tr>
      <td align="right" valign="middle" style="padding-right: 8px;"><font style="font-size: 12px;">Conectado como: <?php echo $user; ?> | <a style="text-decoration: none;" href="index.php?action=logout">Salir</a></font>
      </td>
     </tr>
    </table>
   </div>

<!-- login_form.php -->
   <div class="login">
    <table border="0" width="100%" height="20px">
     <tr>
      <td align="right" valign="middle" style="padding-right: 8px;">
       <form action="index.php?action=login&what=process" method="POST">
        <font style="font-size: 12px;">Usuario: </font>
        <input tabindex="1" type="text" name="username" size="15" style="width: 80px;" class="loginfield" />
        <font style="font-size: 12px;">Contrase&ntilde;a:</font>
        <input tabindex="1" type="password" name="password" size="15" style="width: 80px;" class="loginfield" />
        <input type="submit" value="Entrar" name="submit" class="loginbutton" />
       </form>
      </td>
     </tr>
    </table>
   </div>

<!-- layout.php -->
   <div id="header">
    <div>
     <a href="index.php"><img src="img/banner.gif" height="110" border="0" /></a>
    </div>
   </div>
   <?php echo $page_content; ?>