Custom sidebar per page

function pietergoosen_widgets_init() {
$dynamic_widget_areas = array (
				'sidebar-21'       => __( 'Page Specific Sidebar 1', 'pietergoosen' ),
				'sidebar-22'       => __( 'Page Specific Sidebar 2', 'pietergoosen' ),
				'sidebar-23'       => __( 'Page Specific Sidebar 3', 'pietergoosen' ),
				'sidebar-24'       => __( 'Page Specific Sidebar 4', 'pietergoosen' ),
				'sidebar-25'       => __( 'Page Specific Sidebar 5', 'pietergoosen' ),
				'sidebar-26'       => __( 'Page Specific Sidebar 6', 'pietergoosen' ),
				'sidebar-27'       => __( 'Page Specific Sidebar 7', 'pietergoosen' ),
				'sidebar-28'       => __( 'Page Specific Sidebar 8', 'pietergoosen' ),
				'sidebar-29'	   => __( 'Page Specific Sidebar 9', 'pietergoosen' ),
				'sidebar-30'       => __( 'Page Specific Sidebar 10', 'pietergoosen' ),
                );

foreach ( $dynamic_widget_areas as $id => $dynamic_widget_area ) {
	register_sidebar(
		array (
                'name'          => __( $dynamic_widget_area, 'pietergoosen' ),
                'id'            =>  $id,
				'description'   => __( 'Page specific sidebars above the content sidebar', 'pietergoosen' ),
				'before_widget' => '<aside id="%1$s" class="widget %2$s">',
				'after_widget'  => '</aside>',
				'before_title'  => '<h1 class="widget-title">',
				'after_title'   => '</h1>',
        ));
    }
}
add_action( 'widgets_init', 'pietergoosen_widgets_init' );

// Add dynamic sidebars that can be chosen per page
add_action('add_meta_boxes', 'pietergoosen_voeg_cspp_metabox_by');
add_action('save_post', 'pietergoosen_gradeer_post_meta_op');

function pietergoosen_voeg_cspp_metabox_by() {
	add_meta_box( 'custom_sidebar_per_page', __( 'Sidebar options', 'pietergoosen' ), 'pietergoosen_cspp_skakel', 'page', 'side', 'default');
}

function pietergoosen_cspp_skakel( $post )
{
	global $wp_registered_sidebars;

	$custom = get_post_custom($post->ID);

	if(isset($custom['custom_sidebar_per_page']))
		$val = $custom['custom_sidebar_per_page'][0];
	else
		$val = "default";

	// The actual fields for data entry
	$output = '<p><label for="pietergoosen_new_field">'.__("Choose a sidebar to display", 'pietergoosen' ).'</label></p>';
	$output .= "<select name='custom_sidebar_per_page'>";

	// Add a default option
	$output .= "<option";
	if($val == "default")
		$output .= " selected='selected'";
	$output .= " value='default'>".__('Default', 'pietergoosen')."</option>";

	// Fill the select element with all registered sidebars
	foreach($wp_registered_sidebars as $sidebar_id => $sidebar)
	{
		$output .= "<option";
		if($sidebar_id == $val)
			$output .= " selected='selected'";
		$output .= " value='".$sidebar_id."'>".$sidebar['name']."</option>";
	}

	$output .= "</select>";

	echo $output;
}

function pietergoosen_gradeer_post_meta_op($post_id){
	if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE)
		return;
	if (!current_user_can( 'edit_page', $post_id ))
		return;
	$data = $POST['link'];
		update_post_meta( $post->ID, "custom_sidebar_per_page", $data );
}