How to add settings to the 'Advanced Settings' metabox within calls to action.

class.metaboxes.php

<?php

/**
*This class hooks call to action settings into the 'Advanced Settings' metabox available when editing a call to action
*/
	
if ( !class_exists('CTA_Extension_Metaboxes') ) {

	class CTA_Extension_Metaboxes
	{
		/**
		*	Initialize class
		*/
		function __construct()
		{
			self::load_hooks();
		}
		
		/**
		*	Loads WordPress Hooks and Filters
		*/
		public static function load_hooks()
		{
			/* settings for wordpress-call-to-action cpt */
			add_filter( "wp_cta_extension_data", array( __CLASS__ , "add_advanced_settings") , 10 , 1 );
			
			/* handler for empty inputs */
			add_filter( "save_post", array( __CLASS__ , "save_data_fallback") , 10 , 1 );
		}
		
		
		/**
		* Intercepts $wp_cta_data which contains all the settings and template data and injects our new advanced settings into the data array
		*
		* @param ARRAY $wp_cta_data variable containg data related to Call to Action environment
		*
		* @returns ARRAY modified version of $wp_cta_data
		*/
		public static function add_advanced_settings( $wp_cta_data )
		{

			$parent_key = 'wp-cta'; //leave this alone
			
			/* Add setting to $wp_cta_data array */
			$wp_cta_data[$parent_key]['settings']['global-placements-header'] =   array(
				'datatype' => 'setting',
				'region' => 'advanced',
				'description'  => '<h3>Global Placements</h3>',
				'id'    => 'global-placements-header',
				'type'  => 'html-block'
			);		
			
			/* Add setting to $wp_cta_data array */
			$wp_cta_data[$parent_key]['settings']['post-type-placements-header'] =   array(
				'datatype' => 'setting',
				'region' => 'advanced',
				'description'  => '&nbsp;&nbsp;<i>Placement by Post Type</i>',
				'id'    => 'post-type-placements-header',
				'type'  => 'html-block',
				'global' => true //setting global to true will make this get_post_meta() id to always be $partent_key + 'id' eg: wp-cta-post-type' where as if this was set to false the store key would contain the variation id at the end like wp-cta-post-type-1. Use this to define settings that will be applied to all call to action variations. 
			);		
			
			/* build option array of post types */
			$post_types= get_post_types( array('public'=>true) ,'names');
			
			
			$options = array();
			foreach ($post_types as $post_type ) 
			{
				if ( in_array( $post_type , array( 'revision','nav_menu_item' , 'attachment' , 'wp-call-to-action' ) ) ) {
					continue;
				}
				$options[ $post_type ] = $post_type; 
			}

			/* Add setting to $wp_cta_array using the options generate above as a dropdown. */
			$wp_cta_data[$parent_key]['settings']['post-types'] = array(
				'datatype' => 'setting',
				'region' => 'advanced',
				'label' => 'Post Types',
				'description'  => 'Place on these post types',
				'id'    => 'post-type',
				'type'  => 'multiselect',
				'options' => $options,
				'global' => true
			);

			
			/* Add setting to $wp_cta_array */
			$wp_cta_data[$parent_key]['settings']['cta_content_placement']  = array(
				'data_type' => 'setting',
				'region' => 'advanced',
				'label' => 'Placement',
				'description' => "Where would you like to insert the CTA on this page?",
				'id'  => 'content-placement',
				'type'  => 'dropdown',
				'default'  => 'off',
				'options' => array( 
									'above'=>'Above Content',
									'middle' => 'Middle of Content',
									'below' => 'Below Content',
									'widget_1' => 'Use Dynamic Sidebar Widget'
								  ),
				'context'  => 'normal',
				'class' => 'cta-per-page-option',
				'global' => true //setting global to true tells this setting to be applied to all variations and saves the setting 
			);
			
			/* send the data array back with the new settings */
			return $wp_cta_data;
		}
		
		/**
		* This hooked method will delete the wp-cta-post-type meta pair if it's empty. 
		*/
		public static function save_data_fallback( $cta_id ) {
			global $post;
			unset($_POST['post_content']);

			if ( wp_is_post_revision( $cta_id ) ) {
				return;
			}
			
			if (  !isset($_POST['post_type']) || $_POST['post_type'] != 'wp-call-to-action' ) {
				return;
			}
			
			if (!isset($_POST['wp-cta-post-type'])) {
				delete_post_meta( $cta_id , 'wp-cta-post-type' );
			}
		}
	}

	/** Load the class on fileload */
	$class['CTA_Extension_Metaboxes'] = new CTA_Extension_Metaboxes();
}