// JavaScript Document

function calcZones(form) {
 
 	var male = 0;
	var female = 1;
	var maxHR = form.maxHR.value;
	var restHR = form.restHR.value;
	var weight = 0;
	var hrDiff = 0;
		
	if (form.age.value == null ||
		 form.age.value.length == 0 ||
	 	form.restHR.value == null ||
	 	form.restHR.value.length == 0) {
 		
		alert("Please provide your age and resting heart rate in order to calculate your heart rate zones.");
		
		return;
	
	}
	
	if (form.weight.value == null ||
		form.weight.value.length == 0) {
		weight = 0;
	} else {
		weight = form.weight.value;
	}
	
	if (form.gender[0].checked) {
		gender = male;
	} else {
		gender = female;
	}
	
	
	// if maximum heart rate is unknown then calculate via the Sally Edwards calculation
	
	if (maxHR == 0) {
		if (gender == male ) {
			maxHR = 210 - parseInt(form.age.value*0.5) - parseInt(weight*0.05) - 4;
		} else {
			maxHR = 210 - parseInt(form.age.value*0.5) - parseInt(weight*0.05);
		}
	}
	
	hrDiff = maxHR - restHR;
	
	var hrAt50 = parseInt(hrDiff*0.50) + parseInt(restHR);
	var hrAt60 = parseInt(hrDiff*0.60) + parseInt(restHR);
	var hrAt70 =  parseInt(hrDiff*0.70) + parseInt(restHR);
	var hrAt80 =  parseInt(hrDiff*0.80)+ parseInt(restHR);
	var hrAt90 =  parseInt(hrDiff*0.90)+ parseInt(restHR);
	var hrAt100 =  parseInt(hrDiff)+ parseInt(restHR);
	
	// set form elements back
	
	form.maxHR.value =  maxHR;
	form.zone1.value = 	hrAt50+"-"+hrAt60;
	form.zone2.value =	hrAt60+"-"+hrAt70;
	form.zone3.value =  hrAt70+"-"+hrAt80;
	form.zone4.value =  hrAt80+"-"+hrAt90;
	form.zone5.value =  hrAt90+"-"+maxHR;
	

}


function resetCalculation(form) {

	form.age.value = null;
	form.restHR.value = null;
	form.weight.value = null;
	form.maxHR.value = null;
	form.zone1.value = null;
	form.zone2.value =	null;
	form.zone3.value =  null;
	form.zone4.value =  null;
	form.zone5.value =  null;

}