Rounding error in coupon calculations

[lat9]

Add a single product to the cart (value $155.00). This product is within a category that is restricted for the coupon named "TESTME". Store uses a 6% sales tax, which adds $9.30 to the order's total. Go to checkout. On the checkout_payment page, apply the TESTME coupon. This results in a warning message "You must spend at least $0.00 to redeem this coupon.".

It turns out that the ot_coupon's get_order_total function introduces a slight rounding error when calculating the overall order total, resulting in a total of -1.7763568394003E-15 when the product value plus tax is removed. I made the following update to that function to receive the proper message: "This coupon code is not valid for any product currently in your cart. TESTME".

  function get_order_total($couponCode)
  {
    global $order;
    $orderTaxGroups = $order->info['tax_groups'];
    $orderTotalTax = $order->info['tax'];
    $orderTotal = $order->info['total'];
    $products = $_SESSION['cart']->get_products();
    for ($i=0; $i<sizeof($products); $i++) {
      if (!is_product_valid($products[$i]['id'], $couponCode)) {
        $products_tax = zen_get_tax_rate($products[$i]['tax_class_id']);
        $productsTaxAmount = (zen_calculate_tax($products[$i]['final_price'], $products_tax))   * $products[$i]['quantity'];
        $orderTotal -= $products[$i]['final_price'] * $products[$i]['quantity'];
        if ($this->include_tax == 'true') {
         $orderTotal -= $productsTaxAmount;
        }
        if (DISPLAY_PRICE_WITH_TAX == 'true')
        {
          $orderTotal -= $productsTaxAmount;
        }
        $orderTaxGroups[zen_get_tax_description($products[$i]['tax_class_id'])] -= $productsTaxAmount;
        $orderTotalTax -= (zen_calculate_tax($products[$i]['final_price'], zen_get_tax_rate($products[$i]['tax_class_id'])))   * $products[$i]['quantity'];
      }
    }
    if ($this->include_shipping != 'true')
    {
      $orderTotal -= $order->info['shipping_cost'];
      if (isset($_SESSION['shipping_tax_description']) && $_SESSION['shipping_tax_description'] != '') 
      {
         $orderTaxGroups[$_SESSION['shipping_tax_description']] -= $order->info['shipping_tax']; 
         $orderTotalTax -= $order->info['shipping_tax']; 
      }
    }
    if (DISPLAY_PRICE_WITH_TAX != 'true')
    {
      $orderTotal -= $order->info['tax'];
    }
//-bof-20140724-lat9-Fix for negative-going orderTotal value, due to teeny rounding errors during the tax calculations
    if ($orderTotal < 0) {
      $orderTotal = 0;
      
    }
//-eof-20140724-lat9
    return array('orderTotal'=>$orderTotal, 'orderTaxGroups'=>$orderTaxGroups, 'orderTax'=>$orderTotalTax, 'shipping'=>$order->info['shipping_cost'], 'shippingTax'=>$order->info['shipping_tax']);
  }

[Ajeh]

I believe that I fixed this in v1.5.3 ... to clean up the messages and such ...

Do you have specifics on the Discount Coupon setup that you used so that I can recreate it and test this?

Somewhere, I believe I posted the fix for this in v1.5.1 ... hmm ... now where did I put that ...

[Ajeh]

It might be this thread here:
http://www.zen-cart.com/showthread.p...+redeem+coupon

[lat9]

Ajeh, I installed the v1.5.3 version of ot_coupon.php in this test store and received the same "You must spend $0.00 ..." message.

[Ajeh]

Could you post the exact settings on the Discount Coupon so that I can recreate this scenario?

[lat9]

Sure, the ot_coupon settings are

Include Shipping: false
Include Tax: false
Re-calculate Tax: Standard
Tax Class: Taxable Goods

The coupon settings are

Coupon Name ::  Test Me
Coupon Amount ::  19.0000%
Start Date ::  07/08/2014
End Date ::  07/31/2014
Uses per Coupon ::  Unlimited
Uses per Customer ::  Unlimited
Valid Product List ::  --none--
Valid Categories List ::  Restrictions Apply
Date Created ::  07/08/2014
Date Modified ::  07/08/2014

I'm guessing that the 19% is the contributing factor!

[Ajeh]

Heck ... fixed that in v1.6 not v1.5.3 ...

Unfortunately, I added a few new things to Discount Coupons as well ... so trying to piece the code together to work in v1.5.3 or v1.5.0/1 is not a lot of fun ...

If I get time, I will see if I can hack it into something workable but it probably won't be pretty ...