RE: need a quick help with an order total module

This message was sent from: Development
http://forums.oscommerce.com/viewtopic.php?p=163158#163158
----------------------------------------------------------------

I have got it Ian.

on flat discounts the difference in tax will ALWAYS be the same. just think about it... it doesn't matter the size of the order.  here are 2 examples:

Sub-Total:  $579.00 
Qty Discount:  -$10.00 
UPS Ground:  $7.00 
VA TAX 4.5%:  $25.61 
Total:  $601.61 

Sub-Total:  $217,993.50 
Qty Discount:  -$10.00 
UPS Ground:  $7.00 
VA TAX 4.5%:  $9,809.26 
Total:  $227,799.76 

from one extreme to the other, but the difference in tax each time is exactly the same:
(579 x.045) = 26.055
(569 x .045) = 25.605
difference in tax = .45

(217,993.5 x .045) = 9,809.7075
(217,983.5 x .045) = 9,809.2575
difference in tac = .45

thinking maybe this was just the magic of the number 10, I tried this with other values ($5, $20, and $18.56 just to throw a loop)... it works the same each time.

The difference in tax will always equal the tax rate [b]x[/b] the discount [b]/[/b] 100

so then the calculation for the re-calculation of taxes on flat rate discounts becomes:
[code]	$tod_amount = 0; 
	reset($order->info['tax_groups']); 
	  while (list($key, $value) = each($order->info['tax_groups'])) { 
		$god_amout=0; 
		$tax_rate = tep_get_tax_rate_from_desc($key); 
		$net = $tax_rate * $order->info['tax_groups'][$key]; 
		  if ($net>0) { 
			$ratio1 = ($tax_rate*$od_amount)/100;
			$god_amount = $ratio1; 
			$tod_amount += $god_amount; 
			$order->info['tax_groups'][$key] = $order->info['tax_groups'][$key] - $god_amount; 
		  } 
	  }            
	}[/code]