if ( ! defined( 'ABSPATH' ) )
    die( "Can't load this file directly" );

class wppaGallery
{
    function __construct() {
    add_action( 'admin_init', array( $this, 'action_admin_init' ) );
    }

    function action_admin_init() {
        // only hook up these filters if we're in the admin panel, and the current user has permission
        // to edit posts and pages
        if ( current_user_can( 'edit_posts' ) && current_user_can( 'edit_pages' ) ) {
            add_filter( 'mce_buttons', array( $this, 'filter_mce_button' ) );
            add_filter( 'mce_external_plugins', array( $this, 'filter_mce_plugin' ) );
        }
    }

    function filter_mce_button( $buttons ) {
        // add a separation before our button.
        array_push( $buttons, '|', 'wppa_button' );
        return $buttons;
    }

    function filter_mce_plugin( $plugins ) {
        // this plugin file will work the magic of our button
        $plugins['wppa'] = plugin_dir_url( __FILE__ ) . 'wppa_plugin.js';
        return $plugins;
    }

}

$wppagallery = new wppaGallery();