Wordpress Context-Aware Page

<?php
/*
* Template Name: AJAX Page
*
* This page template responds to the request type by serving only the content for an AJAX request
* and the content wrapped in the parent layout for a normal request. This allows for loading the
* content via AJAX and the History API without the need for hash-bang URLs.
*/

$url = rtrim($_SERVER['REQUEST_URI'],"/");

$content = "";
$subtitle = "";
$subcontent = "";

//Get the sub-content
if(have_posts()){
    while(have_posts()){
      the_post();
	    $subtitle = get_the_title();
      $subcontent = get_the_content();
      $subcontent = apply_filters('the_content',$subcontent);
    }
}

if( !empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == "xmlhttprequest" ){
	header('Content-Type: application/json');
	header('Cache-Control: no-store');
	echo json_encode(array("title" => $subtitle,"content" => $subcontent));
	die();
} else {
    $ancestors = get_ancestors($post->ID,'page');
    if(!empty($ancestors)){
        $page = get_post($ancestors[0]);
        $content = $page->post_content;
        $content = apply_filters('the_content',$content);
    }

    get_header();
    echo $content;
?>

<div id='ajax-content'>
    <?php echo $subcontent;?>
</div>

<?php get_footer(); }