// JavaScript Document
//Javascript for calculating the interest only payments

//function for getting the payment
function getPayment(a,n,p) {
	/* Calculates the monthly payment from annual percentage
	   rate, term of loan in months and loan amount. **/
	var acc=0;
	var base = 1 + p/1200;
	for (i=1;i<=n;i++) 
		{ acc += Math.pow(base,-i); }
	return a/acc;
}

//function for getting the interest payment
function getInterest(a,n,p) {
	/* Calculates the monthly interest payment 	var acc=0;
	var base = 1 + p/1200;
	for (i=1;i<=n;i++) 
		{ acc += Math.pow(base,-i); }
	return a/acc;**/
	var interest = (a * (p/1200));
	return interest;
}
	
//function for returning the currency value
function currency(pNum) {
  //-- Returns passed number as string in $xxx,xxx.xx format.
	var tRtnValue = "";
	if (pNum != "") {
		var n = pNum.toString().replace(/\$|\,/g,'');
		if (isNaN(n)) {n = "0";}
		var tSign = (n == (n = Math.abs(n)));
		n = Math.floor(n * 100 + 0.50000000001);
		var tCents = n % 100;
		if (tCents < 10) {tCents = "0" + tCents;}
		n = Math.floor(n / 100).toString();
		for (var i = 0; i < Math.floor((n.length - (1 + i)) / 3); i++) {
			n = n.substring(0, n.length - (4 * i + 3)) + ',' + n.substring(n.length - (4 * i + 3));
		}
		tRtnValue = (((tSign)?'':'-') + '$' + n + '.' + tCents);
	}else{
		tRtnValue = 0;
	}
	return tRtnValue;
}

function replaceAll(oldStr,findStr,repStr) {
  var srchNdx = 0;  
  var newStr = ""; 
  while (oldStr.indexOf(findStr,srchNdx) != -1)  							
  {
	newStr += oldStr.substring(srchNdx,oldStr.indexOf(findStr,srchNdx));							
	newStr += repStr;
	srchNdx = (oldStr.indexOf(findStr,srchNdx) + findStr.length);           
  }
  newStr += oldStr.substring(srchNdx,oldStr.length);          
  return newStr;
}

function perform(){
	var frm = document.MORTGAGE;
	var newAmount = replaceAll(document.getElementById('amount').value,',','');
	newAmount = replaceAll(newAmount,'$','');
	var payment = getPayment(newAmount,document.getElementById('term').value,document.getElementById('apr').value)
	frm.PAYMENT.value = currency(Math.round(payment*100)/100);
	var interest = getInterest(newAmount,document.getElementById('term').value,document.getElementById('apr').value)
	frm.INTEREST.value = currency(interest);
	var savings = (payment - interest);
	frm.SAVINGS.value = currency(savings);
}