function changedatetime(veld)
{
	var dag,mnd,jaar,uur,min;
	with (document.forms[0]) {
		dag=elements[veld+"_day"].value;
		mnd=elements[veld+"_mon"].value;
		jaar=elements[veld+"_year"].value;
		elements[veld].value=((dag!='' && mnd!='' && jaar!='')?jaar+"/"+mnd+"/"+dag:"");
		if (elements[veld+"_hr"])
			elements[veld].value+=" "+elements[veld+"_hr"].value;
		if (elements[veld+"_min"])
			elements[veld].value+=":"+elements[veld+"_min"].value;
	}
}

function changeperiod(veld,pertype)
{
	var perwkmnd,perdag,mnd,jaar,uur,min,daypicker,opt,datum;
	var weekdagen,maanden,maanddagen,max,i;
	weekdagen=Array("Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday");
	maanden=Array("January","February","March","April","May","June","July","August","September","Oktober","November","December");
	maanddagen=Array(31,28,31,30,31,30,31,31,30,31,30,31);
	with (document.forms[0]) {
		if (pertype!='') {
			document.all[veld+"_"+pertype].checked=true;
		}
		pertype=document.all[veld+"_period"].checked?"period":"date";
		perwkmnd=elements[veld+"_perwkmnd"].value;
		daypicker=elements[veld+"_perday"];
		perdag=parseInt(daypicker.value);
//alert(daypicker.value);
		daypicker.options.length=0;
		if (perwkmnd=="d") {
			document.all["daybox"].style.display="none";
		} else if (perwkmnd=="w") {
			document.all["daybox"].style.display="";
			for (i=1;i<=7;i++) {
				opt = new Option(i, i, false, i==perdag);
				daypicker.options[i-1]=opt;
			}
		} else {
			document.all["daybox"].style.display="";
			for (i=1;i<=31;i++) {
				opt = new Option(i, i, false, i==perdag);
				daypicker.options[i-1]=opt;
			}
		}
//alert(daypicker.value+perdag);
		perdag=parseInt(elements[veld+"_perday"].value);
		dag=parseInt(elements[veld+"_day"].value);
		mnd=parseInt(elements[veld+"_mon"].value);
		jaar=parseInt(elements[veld+"_year"].value);
		uur=parseInt(elements[veld+"_hr"].value);
		min=parseInt(elements[veld+"_min"].value);

		if (pertype=="period") {
			datum=new Date();
			var dezedag=datum.getDate()+1;
			mnd = datum.getMonth()+1;
			jaar=datum.getYear();
			if (perwkmnd=="d") {
				dag=dezedag-1;
			} else if (perwkmnd=="w") {
				dezedag=datum.getDay()+1;
				dag=datum.getDate()-dezedag+perdag;
				if (perdag<dezedag) dag+=7;
			} else {
				dag=perdag;
				if (perdag<datum.getDate()) dag+=maanddagen[mnd-1];
			}
			if (dag>maanddagen[mnd-1]) {dag-=maanddagen[mnd-1];mnd+=1;}
			if (mnd>12) {mnd-=12;jaar+=1;}
		}

		elements[veld].value=jaar+"/"+mnd+"/"+dag+" "+uur+":"+min;
		elements[veld+"_interval"].value=(pertype=="date")?"":perwkmnd;

		datum=new Date(jaar,mnd-1,dag,uur,min);
		document.all[veld+"_nexttime"].innerText=weekdagen[datum.getDay()]+", "+dag+" "+maanden[mnd-1]+" "+jaar+" "+uur+":"+((min==0)?"00":min);
//		document.all[veld+"_nexttime"].innerText=weekdagen[datum.getDay()]+", "+datum.getDate()+" "+maanden[datum.getMonth()-1]+datum.getMonth()+" "+datum.getYear()+" "+datum.getHours()+":"+datum.getMinutes();
	}
}