//	Insert commas in final answer
//	-----------------------------

function insert_commas(input) {
	var result, len;
	input += "";
	len = input.indexOf(".");
	if(len == -1) {
		len = input.length;
		result = "";
	}
	else {
		result = input.substring(len, input.length);
	}
	while(len > 3) {
		result = input.substring(len-3, len) + result;
		result = "," + result;
		len -= 3;
	}
	result = input.substring(0, len) + result;
//	result = "$" + result;

//	Need to append a zero?
	len = input.indexOf(".");
	if(len == input.length - 2) {
		result = result + "0";
	}
	return result;
}

//	Remove commas and $ from input as return as number
//	--------------------------------------------
function strip_commas(input) {
	var newnum;
	var ch;
	newnum = "";
	for(var i=0; i<input.length; i++) {
		ch = input.charAt(i);
		if(ch != ",") {
			if(ch != "$") {
				newnum += ch
			}
		}
	}
	return parseFloat(newnum);
}


function checkNum(input) {
	var oldnum;
	var newnum;
	var ch;
	oldnum = input.value;
	newnum ="";
	for(var i=0; i<oldnum.length; i++) {
		ch = oldnum.charAt(i);
		if(ch != ",") {
			newnum += ch;
		}
	}
	return parseFloat(newnum);
}

//	Check loan term (in years)
//	--------------------------

function checkNumPeriods(input) {
        input.value = checkNum(input);
        input.value = parseInt(input.value);
        if(input.value == null ||          
          input.value.length == 0 ||
          input.value == "NaN") {
                input.value = "";
        }
        else {
                if(parseFloat(input.value) <= 0) {
                        input.value = "";
                }
        }
        calcMonthly(input.form);
}

//	Check price
//	-----------

function checkTotal(input) {
        input.value = checkNum(input);
        input.value = parseFloat(input.value);
        if(input.value == null ||          
         input.value.length == 0 ||
           input.value == "NaN") {
                input.value = "";
        }
        else {
                if(parseFloat(input.value) < 0) {
                        input.value = "";
                }
        }
        calcMonthly(input.form);
        input.value = insert_commas(input.value);
}

//	Entered interest rate
//	---------------------

function checkInterest(input) {
        input.value = parseFloat(input.value);
        if(input.value == null ||          
         input.value.length == 0 ||
           input.value == "NaN") {
                input.value = "";
        }
        else {
                if(parseFloat(input.value) <= 0 || 
                   parseFloat(input.value) > 100.0) {
                        input.value = "";
                }
        }
        calcMonthly(input.form);
}

//	Entered Down Payment
//	--------------------

function checkDown(input) {
        input.value = parseFloat(input.value);
        if(input.value == null ||          
         input.value.length == 0 ||
           input.value == "NaN") {
                input.value = "0";
        }
        else {
                if(parseFloat(input.value) < 0 || 
                   parseFloat(input.value) > 100.0) {
                        input.value = "0";
                }
        }
        calcMonthly(input.form);
}

//	Calculate monthly P&I
//	---------------------

function calcMonthly(input) {
        if(input.interest.value == "" || 
           input.nper.value == "" ||
           input.price.value == "") {
                input.monthly.value = "";
        }
	else {
                i = strip_commas(input.interest.value) / 100;
                i = i / 12;
                n = strip_commas(input.nper.value) * 12;
		dp = strip_commas(input.downpayment.value);
		price = strip_commas(input.price.value);
		loan = price * (100 - dp) / 100;
                tmp = (1/i) * (1 - Math.pow(1/(1+i), n));
                tmp = loan / tmp;
                tmp = Math.round(tmp*100) / 100;
                input.monthly.value = "$" + insert_commas(tmp);

                if(input.monthly.value == null ||          
                  input.monthly.value.length == 0 ||
                    input.monthly.value == "NaN") {
                      input.monthly.value = "";	
              }
        }
}