woothemes/woocommerce

<?php
/**
 * WC Queue
 *
 * @version 3.5.0
 * @package WooCommerce\Interface
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit; // Exit if accessed directly.
}

/**
 * WC Queue
 *
 * Singleton for managing the WC queue instance.
 *
 * @version 3.5.0
 */
class WC_Queue {

    /**
     * The single instance of the queue.
     *
     * @var WC_Queue_Interface|null
     */
    protected static $instance = null;

    /**
     * The default queue class to initialize
     *
     * @var string
     */
    protected static $default_cass = 'WC_Action_Queue';

    /**
     * Single instance of WC_Queue_Interface
     *
     * @return WC_Queue_Interface
     */
    final public static function instance() {

        if ( is_null( self::$instance ) ) {
            $class          = self::get_class();
            self::$instance = new $class();
            self::$instance = self::validate_instance( self::$instance );
        }
        return self::$instance;
    }

    /**
     * Get class to instantiate
     *
     * And make sure 3rd party code has the chance to attach a custom queue class.
     *
     * @return string
     */
    protected static function get_class() {
        if ( ! did_action( 'plugins_loaded' ) ) {
            wc_doing_it_wrong( __FUNCTION__, __( 'This function should not be called before plugins_loaded.', 'woocommerce' ), '3.5.0' );
        }

        return apply_filters( 'woocommerce_queue_class', self::$default_cass );
    }

    /**
     * Enforce a WC_Queue_Interface
     *
     * @param WC_Queue_Interface $instance Instance class.
     * @return WC_Queue_Interface
     */
    protected static function validate_instance( $instance ) {
        if ( false === ( $instance instanceof WC_Queue_Interface ) ) {
            $default_class = self::$default_cass;
            /* translators: %s: Default class name */
            wc_doing_it_wrong( __FUNCTION__, sprintf( __( 'The class attached to the "woocommerce_queue_class" does not implement the WC_Queue_Interface interface. The default %s class will be used instead.', 'woocommerce' ), $default_class ), '3.5.0' );
            $instance = new $default_class();
        }

        return $instance;
    }
}