Foundation Reveal Modal Shortcode for WordPress

/**
 * Foundation Reveal Shortcode
 * Author : Ian Armstrong (@imperativeideas)
 * Author : G.M (http://wordpress.stackexchange.com/questions/128423/passing-a-shortcode-attribute-to-a-sub-function)
 * Version 1.0
 *
 * Notes: Need to add several features including:
   + Support for manual content entry in place of a page/post slug
   + Support for hiding the close box with a shortcode parameter
   + Support for hiding/changing the background with a shortcode parameter
   + Error trapping if the same slug is entered multiple times
   + Tie this into the TinyMCE Editor as a button
   + Convert this whole thing to a class
 */

function reveal_setup($atts = array(), $content = '') {

    // Setup the static variable. Use an array to allow multiple calls per page
    static $the_modals = array();

    // if the function is called from wp_footer hook
    if ( current_filter() === 'wp_footer' ) {
        if ( is_array($the_modals) && ! empty($the_modals) ) {
            foreach( $the_modals as $amodal ) {
                echo $amodal;
            }
        }

    // if the function is called from shortcode
    } else {
        // Get the attributes (extract is bad, let's not use it)
        $atts = shortcode_atts(
            array( 'size' => 'medium', 'slug' => 'dummy' ),
            $atts,
            'reveal' // enable filtering
        );

        // prepare the_modal link
        $modal_link  = '<a href="#" data-reveal-id="' . $atts['slug'] . '">';
        $modal_link .= $content;
        $modal_link .= '</a>';

        // prepare the_modal content
        $modal_format = '<div id="%s" class="%s reveal-modal" data-reveal>';

        $the_modal = sprintf( $modal_format, $atts['slug'], $atts['size'] );

        if ( $atts['slug'] == 'dummy' ) {
            $the_modal .= 'You haven\'t called a page to be revealed in this modal! Remember to include a page slug in your shortcode call:';
            $the_modal .= '<br /><br />';
            $the_modal .= '[reveal slug="your-page-slug"]Your Link Text[/reveal]';
            $the_modal .= '<a class="close-reveal-modal">&#215;</a>';
        } else {
            wp_reset_postdata(); wp_reset_query();
            $modal_query = new WP_Query( array(
                'name'      =>  $atts['slug'],
                'post_type' =>  'any'
            ));
            while ($modal_query->have_posts()) : $modal_query->the_post();
                $modal_content = apply_filters('the_content', get_the_content());
                $modal_content = str_replace(']]>', ']]&gt;', $modal_content);
                $the_modal .= $modal_content;
                $the_modal .= '<a class="close-reveal-modal">&#215;</a>';
            endwhile;
            wp_reset_postdata(); wp_reset_query();
        }

        $the_modal .= '</div>';

        // save the modal content in the static modals array
        $the_modals[] = $the_modal; // --------> This isn't working as expected <--------

        // add the present function to wp_footer hook if it is not already added
        if ( ! has_action('wp_footer', __FUNCTION__) ) {
            add_action( 'wp_footer', __FUNCTION__ );
        }
        // return the modal link
        return $modal_link;
    }
}

add_shortcode('reveal', 'reveal_setup');