Filters WooCommerce Orders by Payment Gateway Used

## filter-wc-orders-by-gateway.php
<?php
/**
 * Plugin Name: Filter WooCommerce Orders by Payment Method
 * Plugin URI: http://skyverge.com/
 * Description: Filters WooCommerce orders by the payment method used :)
 * Author: SkyVerge
 * Author URI: http://www.skyverge.com/
 * Version: 1.0.0
 * Text Domain: wc-filter-orders-by-payment
 *
 * Copyright: (c) 2017 SkyVerge, Inc. (info@skyverge.com)
 *
 * License: GNU General Public License v3.0
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 *
 * @package   WC-Filter-Orders-By-Payment
 * @author    SkyVerge
 * @category  Admin
 * @copyright Copyright (c) 2017, SkyVerge, Inc.
 * @license   http://www.gnu.org/licenses/gpl-3.0.html GNU General Public License v3.0
 */

defined( 'ABSPATH' ) or exit;

// fire it up!
add_action( 'plugins_loaded', 'wc_filter_orders_by_payment' );


/**
 * Main plugin class
 *
 * @since 1.0.0
 */
class WC_Filter_Orders_By_Payment {


	const VERSION = '1.0.0';

	/** @var WC_Filter_Orders_By_Payment single instance of this plugin */
	protected static $instance;

	/**
	 * Main plugin class constructor
	 *
	 * @since 1.0.0
	 */
	public function __construct() {

		if ( is_admin() ) {

			// add bulk order filter for exported / non-exported orders
			add_action( 'restrict_manage_posts', array( $this, 'filter_orders_by_payment_method') , 20 );
			add_filter( 'request',               array( $this, 'filter_orders_by_payment_method_query' ) );
		}
	}


	/** Plugin methods ***************************************/


	/**
	 * Add bulk filter for orders by payment method
	 *
	 * @since 1.0.0
	 */
	public function filter_orders_by_payment_method() {
		global $typenow;

		if ( 'shop_order' === $typenow ) {

			// get all payment methods, even inactive ones
			$gateways = WC()->payment_gateways->payment_gateways();

			?>
			<select name="_shop_order_payment_method" id="dropdown_shop_order_payment_method">
				<option value="">
					<?php esc_html_e( 'All Payment Methods', 'wc-filter-orders-by-payment' ); ?>
				</option>

				<?php foreach ( $gateways as $id => $gateway ) : ?>
				<option value="<?php echo esc_attr( $id ); ?>" <?php echo esc_attr( isset( $_GET['_shop_order_payment_method'] ) ? selected( $id, $_GET['_shop_order_payment_method'], false ) : '' ); ?>>
					<?php echo esc_html( $gateway->get_method_title() ); ?>
				</option>
				<?php endforeach; ?>
			</select>
			<?php
		}
	}


	/**
	 * Process bulk filter order payment method
	 *
	 * @since 1.0.0
	 *
	 * @param array $vars query vars without filtering
	 * @return array $vars query vars with (maybe) filtering
	 */
	public function filter_orders_by_payment_method_query( $vars ) {
		global $typenow;

		if ( 'shop_order' === $typenow && isset( $_GET['_shop_order_payment_method'] ) ) {

			$vars['meta_key']   = '_payment_method';
			$vars['meta_value'] = wc_clean( $_GET['_shop_order_payment_method'] );
		}

		return $vars;
	}


	/** Helper methods ***************************************/


	/**
	 * Main WC_Filter_Orders_By_Payment Instance, ensures only one instance is/can be loaded
	 *
	 * @since 1.0.0
	 * @see wc_filter_orders_by_payment()
	 * @return WC_Filter_Orders_By_Payment
 	*/
	public static function instance() {
		if ( is_null( self::$instance ) ) {
			self::$instance = new self();
		}
		return self::$instance;
	}


}


/**
 * Returns the One True Instance of WC_Filter_Orders_By_Payment
 *
 * @since 1.0.0
 * @return WC_Filter_Orders_By_Payment
 */
function wc_filter_orders_by_payment() {
    return WC_Filter_Orders_By_Payment::instance();
}