Small class to add a replacement variable to subscription emails in the Woocommerce Follow Up Emails plugin for WordPress

FUE_Addon_Subscriptions_Extras.php

<?php
/**
 * Plugin Name: WooCommerce Follow Up Emails Extra Variable
 * Description: Add a replacement variable to subscription emails in the Woocommerce Follow Up Emails plugin for WordPress
 * Version: 1.0
 * Author: Pross
 * Author URI: http://www.pagelines.com
 * Requires at least: 4.0
 * Tested up to: 4.2
 *
 * @author Pross
 */
class FUE_Addon_Subscriptions_Extras  {

/**
  * The construct, we run our actions..
  *
  */
  function __construct() {
    add_action( 'fue_before_variable_replacements', array($this, 'register_variable_replacements'), 11, 4 );
    add_action( 'fue_email_variables_list', array($this, 'email_variables_list') );
  }

/**
  * Register the intended replacements, in this case 'subs_renew_amount'
  *
  */
  function register_variable_replacements( $var, $email_data, $email, $queue_item ) {

    $variables = array(
      'subs_renew_amount'
    );

    $variables = $this->add_variable_replacements( $variables, $email_data, $queue_item, $email );
    $var->register( $variables );
  }

/**
  * This is where the actual replacement takes place.
  * In our case we replace subs_renew_amount with the renewal price.
  *
  */
  function add_variable_replacements( $variables, $email_data, $queue_item, $email ) {

    if ( !$queue_item->order_id  ) {
      return $variables;
    }

    $order = WC_FUE_Compatibility::wc_get_order( $queue_item->order_id );

    if ( !WC_Subscriptions_Order::order_contains_subscription( $order ) ) {
      return $variables;
    }

    $variables['subs_renew_amount'] = wc_price( WC_Subscriptions_Order::get_recurring_total( $order ) );
    return $variables;
  }

/**
  * This function adds the little helper html on the right of the email edit page {subs_renew_amount}
  *
  */
  function email_variables_list( $email ) {
    global $woocommerce;

    if ( $email->type != 'subscription' ) {
      return;
    }
    ?>
    <li class="var hideable var_subscriptions"><strong>{subs_renew_amount}</strong> <img class="help_tip" title="<?php _e('Renewel Amount', 'follow_up_emails'); ?>" src="<?php echo $woocommerce->plugin_url(); ?>/assets/images/help.png" width="16" height="16" /></li>
    <?php
  }
}

/*
 * Initiate the class.
 */
new FUE_Addon_Subscriptions_Extras;