// global field for payment plan cost with aquman.
var payment_option = 0;

// check a string that it is a floating point number
function SetFactor (frm, number, weeks) {
   payment_option = number * weeks;
   ComputeForm (frm);
}

function CheckString (str) {
   if (str == "") {
      return false;
   }
   for (var i=0; i < str.length; i++) {
      var temp = str.substring(i, i + 1);
      if ((temp < "0" || "9" < temp) && temp != '.') {
         return false;
      }
   }
   return true;
}

function ComputeForm (frm) {
   var error_msg = "Invalid number. Please enter a number";
   if (! CheckString (frm.rental_cost.value)) {
      alert (error_msg);
      return;
   }

   if (! CheckString (frm.cost_of_bottle.value)) {
      alert (error_msg);
      return;
   }

   if (! CheckString (frm.number_of_bottles.value)) {
      alert (error_msg);
      return;
   }

   if(!payment_option) payment_option = frm.default_payment_option.value;

   var saving = frm.number_of_bottles.value * 52;
   saving *= frm.cost_of_bottle.value;
   saving = saving - (-1 * frm.rental_cost.value);
   saving = saving - payment_option;
   frm.savings.value = saving;
}