This code can be used as a base to create your own simple custom payment gateway for WooCommerce.

Add this code to your child theme’s functions.php file or via a plugin that allows custom functions to be added, such as the Dessky Snippets plugin. Please don’t add custom code directly to your parent theme’s functions.php file as this will be overwritten completely when you update the theme.

/*
Plugin Name: WooCommerce <enter name> Gateway
Plugin URI: http://woothemes.com/woocommerce
Description: Extends WooCommerce with an <enter name> gateway.
Version: 1.0
Author: WooThemes
Author URI: http://woothemes.com/
Copyright: © 2009-2011 WooThemes.
License: GNU General Public License v3.0
License URI: http://www.gnu.org/licenses/gpl-3.0.html
*/
add_action('plugins_loaded', 'woocommerce_gateway_name_init', 0);
function woocommerce_gateway_name_init() {
	if ( !class_exists( 'WC_Payment_Gateway' ) ) return;
	/**
 	 * Localisation
	 */
	load_plugin_textdomain('wc-gateway-name', false, dirname( plugin_basename( __FILE__ ) ) . '/languages');
    
	/**
 	 * Gateway class
 	 */
	class WC_Gateway_Name extends WC_Payment_Gateway {
	
		// Go wild in here
	}
	
	/**
 	* Add the Gateway to WooCommerce
 	**/
	function woocommerce_add_gateway_name_gateway($methods) {
		$methods[] = 'WC_Gateway_Name';
		return $methods;
	}
	
	add_filter('woocommerce_payment_gateways', 'woocommerce_add_gateway_name_gateway' );
}