// calculates the payments and updates for fields to
// display the result

function calcInterestRate(P, N, M) {
	var Y = 12;
	var mid, err_mid;
	var count;

	var low  = 0.001;
	var high = 10.0;
	var count = 0;

	while(count < 30) {
		count = count + 1;
		mid = (high + low) / 2.0;
		err_mid = error(P, mid, N, Y, M);

		if(err_mid == 0.0)
			break;
		if(err_mid < 0.0) {
			low = mid;
			continue;
		}
		if(0.0 < err_mid) {
			high = mid;
			continue;
		}
	}

    var I = mid+.0001;	  
	I = parseInt(I * 10000)/100
	if (I <= 0.1) {
		alert('Interest rate is to low!  Please re-enter values ...');
    	return 0;
	}
    return I;
}

function FormatNumber(num,decimalNum,bolLeadingZero,bolParens,bolCommas){ 
        if (isNaN(parseInt(num))) return "NaN";

	var tmpNum = num;
	var iSign = num < 0 ? -1 : 1;		// Get sign of number
	
	// Adjust number so only the specified number of numbers after
	// the decimal point are shown.
	tmpNum *= Math.pow(10,decimalNum);
	tmpNum = Math.round(Math.abs(tmpNum))
	tmpNum /= Math.pow(10,decimalNum);
	tmpNum *= iSign;					// Readjust for sign
	
	
	// Create a string object to do our formatting on
	var tmpNumStr = new String(tmpNum);

	// See if we need to strip out the leading zero or not.
	if (!bolLeadingZero && num < 1 && num > -1 && num != 0)
		if (num > 0)
			tmpNumStr = tmpNumStr.substring(1,tmpNumStr.length);
		else
			tmpNumStr = "-" + tmpNumStr.substring(2,tmpNumStr.length);
		
	// See if we need to put in the commas
	if (bolCommas && (num >= 1000 || num <= -1000)) {
		var iStart = tmpNumStr.indexOf(".");
		if (iStart < 0)
			iStart = tmpNumStr.length;

		iStart -= 3;
		while (iStart >= 1) {
			tmpNumStr = tmpNumStr.substring(0,iStart) + "," + tmpNumStr.substring(iStart,tmpNumStr.length)
			iStart -= 3;
		}		
	}

	// See if we need to use parenthesis
	if (bolParens && num < 0)
		tmpNumStr = "(" + tmpNumStr.substring(1,tmpNumStr.length) + ")";

	return tmpNumStr;		// Return our formatted string!
}

function FormatPercent(num,decimalNum,bolLeadingZero,bolParens,bolCommas){
	var tmpStr = new String(FormatNumber(num*100,decimalNum,bolLeadingZero,bolParens,bolCommas));

	if (tmpStr.indexOf(")") != -1) {
		// We know we have a negative number, so place '%' inside of ')'
		tmpStr = tmpStr.substring(0,tmpStr.length - 1) + "%)";
		return tmpStr;
	}
	else
		return tmpStr + "%";			// Return formatted string!
}

function error(P, I, N, Y, M) {
  var value;
  value = P - M * (1.0 - binomial(I / Y, -N)) / (I / Y);
  return value;
}

function binomial(a, n) {
  var i;
  var sum, prow, term, cof;
  if(n < 0)
    return 1.0 / binomial(a, -n);
  sum = 1.0;
  prow = n;
  term = 1;
  cof = 1.0
  for(i = 1; i < 10; i++) {
    cof = cof * prow / i;
    prow = prow - 1.0;
    term = term * a;
    sum = sum + cof * term;
  }
  return sum;
}

function calcpayment(sInput) {
   var amt = 0;document.getElementById('amt').value;
   var ir = 0;document.getElementById('ir').value / 1200;
   var term = 0;document.getElementById('term').value * 12;
   var total=1;
   var mp = 0;
   var i=0;

	switch(sInput){
		case 'Amount':
			mp = getValue(document.getElementById('payment').value);
			ir = getValue(document.getElementById('ir').value) / 1200;
			term = getValue(document.getElementById('term').value) * 12;
			for (i=0;i<term;i++) {
			  total = total * (1 + ir);
			}
			amt = ((1-(1/total))*mp)/(ir);

			if(document.getElementById('InterestOnly').checked)
				document.getElementById('amt').value = formatCurrency((12*mp)/(getValue(document.getElementById('ir').value)/100));
			else
				document.getElementById('amt').value = formatCurrency(Math.round(amt));
		  break;
		case 'Rate' :
			mp = getValue(document.getElementById('payment').value);
			amt = getValue(document.getElementById('amt').value);
			term = getValue(document.getElementById('term').value) * 12;
			ir = calcInterestRate(amt, term, mp);
			if(document.getElementById('InterestOnly').checked)
				document.getElementById('ir').value = FormatNumber(((1200*mp)/amt),2);
			else
				document.getElementById('ir').value = FormatNumber(ir,2);
		  break;
		case 'Term' :
			if(document.getElementById('InterestOnly').checked){
				alert("Term can not be determined for Interest Only loans");
				document.getElementById('InterestOnly').checked = false;
				calcpayment('Payment');
			}
			mp = getValue(document.getElementById('payment').value);
			amt = getValue(document.getElementById('amt').value);
			ir = getValue(document.getElementById('ir').value)/100;
			var x = (Math.log(1-(amt/mp)*(ir/12)));//Math.log((1-(amt/mp)*((ir/100)/12)));
			var y = Math.log(1+(ir/12));//Math.log((1+(((ir/100)/12))));
			term = -1/12.0*(x)/y;
			document.getElementById('term').value = FormatNumber(term,2)
		  break;
		case 'Payment' :
			amt = getValue(document.getElementById('amt').value);
			ir = getValue(document.getElementById('ir').value) / 1200;
			term = getValue(document.getElementById('term').value) * 12;

			for (i=0;i<term;i++) {
			  total = total * (1 + ir);
			}
			mp = amt * ir / ( 1 - (1/total));

			if(document.getElementById('InterestOnly').checked)
				document.getElementById('payment').value = formatCurrency((amt*(getValue(document.getElementById('ir').value)/100))/12);
			else{
				document.getElementById('payment').value = formatCurrency(Math.round(mp*1000)/1000);

				amt = getValue(document.getElementById('amt').value);
				ir = getValue(document.getElementById('ir').value) / 1200;
				term = getValue(document.getElementById('term').value) * 12;

				var tir = (ir*1200);
				var tmp;
				var np;

				if(amt>=400000){
					tir = (tir-.625);
				}
				else if(amt>=300000){
					tir = (tir-.875);
				}
				else if(amt>=250000){
					tir = (tir-1);
				}
				else if(amt>=200000){
					tir = (tir-1.25);
				}
				else if(amt>=150000){
					tir = (tir-1.5);				
				}
				else if(amt<=100000){
					tir = (tir-2.5);
				}

				ntir = tir / 1200;
				total = 1;
				for (i=0;i<term;i++) {
				  total = total * (1 + ntir);
				}
				np = (amt * ntir) / ( 1 - (1/total));
				tmp = (Math.round(mp*1000)/1000) - (Math.round(np*1000)/1000)
				tir = Math.round(tir*1000)/1000
				document.getElementById('CalcResult').innerHTML = '<span style="font-size: 11pt"><center><b><span style="white-space: nowrap">If You Lower Your Rate To <i>'+tir+'%</i></span><br/><br/>New Payment: <i>'+formatCurrency(np)+'</i><br/><br/><b>Monthly Savings: '+formatCurrency(tmp)+'</b><br/><br/><b><span style="color: green">Total Savings:</span> '+formatCurrency(tmp*term)+'!</b></center></span>';
			}
		  break;
		default:
			amt = getValue(document.getElementById('amt').value);
			ir = getValue(document.getElementById('ir').value) / 1200;
			term = getValue(document.getElementById('term').value) * 12;

			for (i=0;i<term;i++) {
			  total = total * (1 + ir);
			}
			mp = amt * ir / ( 1 - (1/total));

			if(document.getElementById('InterestOnly').checked)
				document.getElementById('payment').value = formatCurrency((amt*(getValue(document.getElementById('ir').value)/100))/12);
			else
				document.getElementById('payment').value = formatCurrency(Math.round(mp*1000)/1000);
	}

  // use Math object to chop all numbers after 2 digits
  //document.getElementById('payment').value = formatCurrency(Math.round(mp*1000)/1000);
  //document.getElementById('total').value = Math.round(mp * term *1000)/1000-document.getElementById('amt').value ;
  //document.getElementById('totalinterest').value = Math.round(mp * term *1000)/1000-document.getElementById('amt').value ;
}

function formatCurrency(strValue){
	strValue = strValue.toString().replace(/\$|\,/g,'');
	dblValue = parseFloat(strValue);

	blnSign = (dblValue == (dblValue = Math.abs(dblValue)));
	dblValue = Math.floor(dblValue*100+0.50000000001);
	intCents = dblValue%100;
	strCents = intCents.toString();
	dblValue = Math.floor(dblValue/100).toString();
	if(intCents<10)
		strCents = "0" + strCents;
	for (var i = 0; i < Math.floor((dblValue.length-(1+i))/3); i++)
		dblValue = dblValue.substring(0,dblValue.length-(4*i+3))+','+
		dblValue.substring(dblValue.length-(4*i+3));
	return (((blnSign)?'':'-') + '$' + dblValue + '.' + strCents);
}

function getValue(num)
{
    var noJunk = ""
    var withDollar = ""
    var foundDecimal = 0
    var foundAlphaChar = 0
    num += "";

    if (num == "") { return(0); }
    for (i=0; i <= num.length; i++)
    {
        var thisChar = num.substring(i, i+1);
        if (thisChar == ".")
        {
          foundDecimal = 1;
          noJunk = noJunk + thisChar;
        }
        if ((thisChar < "0") || (thisChar > "9"))
        {
          if ((thisChar != "$") && (thisChar !=".") && (thisChar != ",") && (thisChar != " ") && (thisChar !="")) foundAlphaChar = 1;
        }
        else
 {
    withDollar = withDollar + thisChar
    noJunk = noJunk + thisChar
 }

 if ((thisChar == "$") || (thisChar == ".") || (thisChar == ","))
 {
   withDollar = withDollar + thisChar
 }
  }
     if (foundDecimal) { return parseFloat(noJunk); }
     else if (noJunk.length > 0) { return parseFloat(noJunk); }
     else return 0;
}

function highlight(field) {
       field.focus();
       field.select();
}

function doNewCalc(){
   var amt = 0;
   var ir = 0;
   var term = 0;
   var total=1;
   var mp = 0;
   var i=0;

	//balance, amount, currentrate, newrate, oldterm, newterm, currentpayment, newpayment, savings

	amt = getValue(document.getElementById('amount').value);
	ir = getValue(document.getElementById('newrate').value) / 1200;
	term = getValue(document.getElementById('newterm').value) * 12;

	for (i=0;i<term;i++) {
	  total = total * (1 + ir);
	}
	mp = amt * ir / ( 1 - (1/total));

	document.getElementById('newpayment').innerHTML = formatCurrency(Math.round(mp*1000)/1000);

	amt = getValue(document.getElementById('amount').value);
	ir = getValue(document.getElementById('newrate').value) / 1200;
	term = getValue(document.getElementById('newterm').value) * 12;

	var tir = (ir*1200);
	var tmp;
	var np;

	if(amt>=400000){
		tir = (tir-.625);
	}
	else if(amt>=300000){
		tir = (tir-.875);
	}
	else if(amt>=250000){
		tir = (tir-1);
	}
	else if(amt>=200000){
		tir = (tir-1.25);
	}
	else if(amt>=150000){
		tir = (tir-1.5);				
	}
	else if(amt<=100000){
		tir = (tir-2.5);
	}

	ntir = tir / 1200;
	total = 1;
	for (i=0;i<term;i++) {
	  total = total * (1 + ntir);
	}
	np = (amt * ntir) / ( 1 - (1/total));
	tmp = (Math.round(mp*1000)/1000) - (Math.round(np*1000)/1000)
	tir = Math.round(tir*1000)/1000

amt = 0;
ir = 0;
term = 0;
total=1;
mp = 0;
i=0;

	//balance, amount, currentrate, newrate, oldterm, newterm, currentpayment, newpayment, savings
	amt = getValue(document.getElementById('balance').value);
	ir = getValue(document.getElementById('currentrate').value) / 1200;
	term = getValue(document.getElementById('oldterm').value) * 12;

	for (i=0;i<term;i++) {
	  total = total * (1 + ir);
	}
	mp = amt * ir / ( 1 - (1/total));

	document.getElementById('currentpayment').innerHTML = formatCurrency(Math.round(mp*1000)/1000);

	amt = getValue(document.getElementById('balance').value);
	ir = getValue(document.getElementById('currentrate').value) / 1200;
	term = getValue(document.getElementById('oldterm').value) * 12;

	var tir = (ir*1200);
	var tmp;
	var np;

	if(amt>=400000){
		tir = (tir-.625);
	}
	else if(amt>=300000){
		tir = (tir-.875);
	}
	else if(amt>=250000){
		tir = (tir-1);
	}
	else if(amt>=200000){
		tir = (tir-1.25);
	}
	else if(amt>=150000){
		tir = (tir-1.5);				
	}
	else if(amt<=100000){
		tir = (tir-2.5);
	}

	ntir = tir / 1200;
	total = 1;
	for (i=0;i<term;i++) {
	  total = total * (1 + ntir);
	}
	np = (amt * ntir) / ( 1 - (1/total));
	tmp = (Math.round(mp*1000)/1000) - (Math.round(np*1000)/1000)
	tir = Math.round(tir*1000)/1000

	tmp = getValue(document.getElementById('currentpayment').innerHTML) - getValue(document.getElementById('newpayment').innerHTML)
	document.getElementById('savings').innerHTML = '<span style="font-size: 11pt"><center><b><span style="white-space: nowrap">If You Lower Your Rate To <i>'+document.getElementById('newrate').value+'%</i></span><br/><br/><b>Monthly Savings: '+formatCurrency(tmp)+'</b><br/><br/><b><span style="color: green">Total Savings:</span> '+formatCurrency(tmp*term)+'!</b></center></span>';
	//New Payment: <i>'+formatCurrency(np)+'</i>
	//Monthly Savings: '+formatCurrency(tmp)+'</b>
	//Total Savings:</span> '+formatCurrency(tmp*term)+'!</b></center></span>';

	if (false){
		//var balance = 200000; // for example
		//var periods = 360; // 30 years
		var monthlyRate = ((rate/100.0))/12;  // 0.065= APR of 6.5% as decimal
		var monthyPayment = (monthlyRate /(1-(Math.pow((1+monthlyRate),-(term)))))*balance;

		for (var i=0; i<360; i++) {
		  var interestForMonth = balance * monthlyRate;
		  var principalForMonth = monthlyPayment - interestForMonth;
		  balance -= monthlyPayment; // probably should be -= principalForMonth see comments below
		  // output as necessary.
		}
	}
}