WooCommerce add product to cart if coupon code matches existing coupon

add2cartViaCoupon.php

//Adding a hidden product to cart with applied coupon woocommerce/wordpress
//a modified version of this:http://docs.woothemes.com/document/automatically-add-product-to-cart-on-visit/

add_action( 'init', 'add_product_to_cart' );
<?php
function add_product_to_cart() {
  if ( ! is_admin() ) {
    global $woocommerce;
    $product_id = 1211;
    $found = false;
    $coupon_id = 1212;

    if(in_array($coupon_id, $woocommerce->cart->applied_coupons)){
        //check if product already in cart
        if ( sizeof( $woocommerce->cart->get_cart() ) > 0 ) {
      foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $values ) {
                $_product = $values['data'];
                if ( $_product->id == $product_id )
                    $found = true;
            }
            // if product not found, add it
            if ( ! $found )
                $woocommerce->cart->add_to_cart( $product_id );
        } else {
            // if no products in cart, add it
                $woocommerce->cart->add_to_cart( $product_id );
            }
        }
    }
}
?>