/* Credits: Bill Bowden Mortgage Services 
more calculators at: www.bowdenmortgage.com/maxmortgage.html*/

/*  THE FOLLOWING TWO FUNCTIONS CHECK THAT ALL NUMERIC VALUES ARE REAL NUMBER AND REMOVE DOUBLE DECIMALS */
function doSum(a){ 
   a.value = check(a.value);
}
function check(a) 
{
   var pest = 0;
   var b = "";
   for(i=0;i<=a.length;i++)
   {
   var u = a.charAt(i);
      if((u>="0"&&u<="9")||u==".")
      {
      	if(u=="."){
      	var pest = pest+1
      	if(pest==2){break;}}
var b = b + u;    	}}
return b;
}

/* FUNCTION CONFIRMS THAT THE VALUE ENTERED INTO A FIELD FALLS WITHIN THE PRE-DETERMINED MINIMUM 
AND MAXIMUM VALUES */
function checkNumber(quest,input, min, max, msg)
{
 var str = input.value;
 for (var i = 0; i < str.length; i++) {
        var ch = str.substring(i, i + 1)
        if ((ch < "0" || "9" < ch) && ch != '.') {
            alert(msg);
            return false;
        }
    }
  
 if(input.value!="") {
     var num = 0 + str
     if (num < min || max < num) {
      var sendn = "Question " + quest + ": ("+ msg + ")";
      var sendq = "You have entered " + input.value + ". Please enter a number between " + min + " and " + max + ".";
      fixpro(sendn,sendq);
      return false;
     }
     input.value = str;
     return true;
 }
}


/* CALLS UPON THE FUNCTIONS TO DETERMINE IF THE NUMBERS ENTERED ARE VALID AND TO 
CALCULATE THE RESULTS OF THE ENTERED DATA */
function computeField(quest,input,min,max,msage){
 doSum(input); 
 checkNumber(quest,input,min,max,msage);     
}        

/* ROUNDS OFF MONETARY NUMBERS TO TWO DECIMALS (PENNIES) */
function roundPen(n){
 if(n > 0){
   pennies = n*100;
   pennies = Math.round(pennies);
   strPennies = "" + pennies;
   len = strPennies.length;

   return strPennies.substring(0, len - 2) + "." + strPennies.substring(len -2, len);
 }
 else return 0;
}

/* CALCULATES VALUES DISPLAYED WHEN COMPUTE IS CLICKED. FIRST CHECKS THAT 
THERE ARE VALUES IN ALL OF THE FIELDS. 
THE RESULTS ARE SENT TO THE TEXT BOXES - MAXIMUM MORTGAGE AND MONTHLY PAYMENT */

function calcMax(){

if((document.maxcalc.totinc.value == null || document.maxcalc.totinc.value.length == 0)|| (document.maxcalc.totinc.value < 10000 || document.maxcalc.totinc.value > 1000000)){
fixpro('Question 1: (Annual Family Income)','Please enter a number between 10000 and 1000000.');return;}

if((document.maxcalc.protax.value == null || document.maxcalc.protax.value.length == 0)|| (document.maxcalc.protax.value < 100 || document.maxcalc.protax.value > 50000)){
fixpro('Question 2: (Annual Property Taxes)','Please enter a number between 100 and 50000.');return;}

if((document.maxcalc.proheat.value == null || document.maxcalc.proheat.value.length == 0)|| (document.maxcalc.proheat.value < 20 || document.maxcalc.proheat.value > 1500)){
fixpro('Question 3: (Monthly Heating Costs/Condo Fees)','Please enter a number between 20 and 1500.');return;}

if((document.maxcalc.debt.value == null || document.maxcalc.debt.value.length == 0)|| (document.maxcalc.debt.value < 0 || document.maxcalc.debt.value > 5000)){
fixpro('Question 4: (Monthly Debt Payments)','Please enter a number between 0 and 5000.');return;}

if((document.maxcalc.second.value == null || document.maxcalc.second.value.length == 0)|| (document.maxcalc.second.value < 0 || document.maxcalc.second.value > 5000)){
fixpro('Question 5: (Secondary Financing Payment)','Please enter a number between 0 and 5000.');return;}

if((document.maxcalc.rate.value == null || document.maxcalc.rate.value.length == 0)|| (document.maxcalc.rate.value < 2 || document.maxcalc.rate.value > 25)){
fixpro('Question 6: (Interest Rate)','Please enter a number between 2.0 and 25.0.');return;}

var RATE = document.maxcalc.rate.value/100;
var income = document.maxcalc.totinc.value;
var tax = document.maxcalc.protax.value;
var heat = document.maxcalc.proheat.value*12;
var debt = document.maxcalc.debt.value*12;
var second = document.maxcalc.second.value*12;
var compound = 2/12;
var monTime = 25 * 12;
var yrRate = RATE/2;
var rdefine    = Math.pow((1.0 + yrRate),compound)-1.0;
var purchcompound = Math.pow((1.0 + rdefine),monTime);

var maxgdsr =.32;
var maxtdsr =.42;

var GDSPAY = (maxgdsr*income) - tax - heat - second;
var TDSPAY = (maxtdsr*income) - tax - heat - second - debt;

var PAYMENT = (GDSPAY<TDSPAY) ? GDSPAY/12 : TDSPAY/12;
var MORTGAGE = (0 +((PAYMENT*(purchcompound-1.0))/rdefine))/purchcompound;

document.maxcalc.amt.value = '$'+roundPen(MORTGAGE);
document.maxcalc.pay.value = '$'+roundPen(PAYMENT);
return;
}