var pmt_msg = "Inserte el plazo de amortización en años o meses";
var pmt_msg2 = "Asegurese de marcar años o meses";
var int_msg = "Inserte el tipo de interés";
var int_msg2 = "Ejemplo: 6.5% se inserta como 6.5 o 0.065";
var prin_msg = "Inserte el importe a financiar";
var prin_msg2 = "";
var m_pmt_msg = "Esta es la cuota de pago mensual";
var m_pmt_msg2 = "";
var tot_int_msg = "Este es el total de intereses a pagar";
var tot_int_msg2 = "";

function show_hlp_msg(msg_1, msg_2)
{
   document.frmLoan.msg1.value = msg_1;
   document.frmLoan.msg2.value = msg_2;
}

function clear_hlp_msg()
{
   document.frmLoan.msg1.value = '';
   document.frmLoan.msg2.value = '';
}

function valid_Num(input, min, max, field)
{
	var msg = " La casilla de " + field + " contiene datos no validos: " + input.value;
	var str = input.value;
	for (var i = 0; i < str.length; i++)
	    {
	     var ch = str.substring(i, i + 1)
	     if ((ch < "0" || ch > "9") && ch != '.' && ch!='*' && ch!='/' && ch!='+' && ch!='-')
	       {
	        alert(msg);
		input.focus();
	        return false
               }
            }
	var num = 0 + str;
	if (num < min || max < num)
	{
	   alert(field + " no es un rango valido\nRango valido entre: " + min + " - " + max)
	   input.focus()	   
           return false;
        }

	input.value = eval(input.value);
        return true;
}

function eval_field(input)
{
 if(input.length==0 || input.value == "")
   {return;}

 var field_value = input.value;
	for (var i = 0; i < field_value.length; i++)
	    {
	     var ch = field_value.substring(i, i + 1)
	     if ((ch < "0" || ch > "9") && ch != '.' && ch!='*' && ch!='/' && ch!='+' && ch!='-')
	       {
	        return;
               }
            }
  input.value = eval(input.value);
}

function computeForm(form)
{

if ((form.payments.value == null || form.payments.value.length == 0) ||
    (form.interest.value == null || form.interest.value.length == 0) ||
    (form.principal.value == null || form.principal.value.length == 0))
   {return;}

if (!valid_Num(form.principal, 100, 10000000, "Importe") ||
    !valid_Num(form.interest, .01, 99, "Interés") ||
    !valid_Num(form.payments, 1, form.pmtper[0].checked ? 480 : 40,
               form.pmtper[0].checked ? "Número de Meses" : "Número de Años"))
   {
    form.m_pymt.value = "error";
    form.tot_int.value = "error";
    return;
   }

P = eval(form.principal.value);

if(form.pmtper[0].checked)
   {T = eval(form.payments.value);}
else
   {T = eval(form.payments.value) * 12;}

I = eval(form.interest.value);

if (I >= 1)
   {
     I /= 100;
   }

I /= 12;

power = Math.pow(1 + I, T);
form.m_pymt.value = round_it((P * I * power) / (power - 1));
form.tot_int.value = round_it(eval(form.m_pymt.value * T) - eval(form.principal.value));
}

function round_it(amount)
{
  cents = amount * 100;
  cents = Math.round(cents);
  strCents = "" + cents;
  len = strCents.length;
  return strCents.substring(0, len - 2) + "." + strCents.substring(len - 2, len);
}