// Date picker

function show_calendar(str_target, str_datetime) {
	var arr_months = ["January", "February", "March", "April", "May", "June",
		"July", "August", "September", "October", "November", "December"];
	var week_days = ["Su", "Mo", "Tu", "We", "Th", "Fr", "Sa"];
	var n_weekstart = 0; // day week starts from (normally 0 or 1)

	var dt_datetime = (str_datetime == null || str_datetime =="" ?  new Date() : str2dt(str_datetime));
	var dt_prev_month = new Date(dt_datetime);
	dt_prev_month.setMonth(dt_datetime.getMonth()-1);
	var dt_next_month = new Date(dt_datetime);
	dt_next_month.setMonth(dt_datetime.getMonth()+1);
	var dt_firstday = new Date(dt_datetime);
	dt_firstday.setDate(1);
	dt_firstday.setDate(1-(7+dt_firstday.getDay()-n_weekstart)%7);
	var dt_lastday = new Date(dt_next_month);
	dt_lastday.setDate(0);
	
	// html generation (feel free to tune it for your particular application)
	// print calendar header
	var str_buffer = new String (
		"<html>\n"+
		"<head>\n"+
		"	<title>Calendar</title>\n"+
		"	<style>\n"+
		"	body {font-family: verdana; font-size: 10px; color: #294568; padding:0; margin:0;}\n"+
		"	TD, TH, P, TD.P, TH.P, DIV {font-family: verdana; font-size: 10px; color: #294568; padding:0; margin:0;}\n"+
		"	A {color: #01295C; text-decoration: none;}\n"+
		"	A:LINK {color: #01295C; text-decoration: none;}\n"+
		"	A:VISITED {color: #001E82; text-decoration: none;}\n"+
		"	A:ACTIVE {color: #01295C; text-decoration: none;}\n"+
		"	A:HOVER {color: #001E82; text-decoration: underline; }\n"+
		"	.bar2 { border-top: white 2px solid; width: 100%; background-color: #B8CDE7;}\n"+
		"	.pad { padding: 2px; }\n"+
		"	.toprow {background: #E2EBF7;padding: 1;border-bottom: #B8CDE7 1px solid;border-right: #B8CDE7 1px solid;}\n"+
		"	.datarow {background: #FFFFFF;padding: 1;border-bottom: #B8CDE7 1px solid;border-right: #B8CDE7 1px solid;}\n"+
		"	.datarowalt {background: #F0F0F0;padding: 1;border-bottom: #B8CDE7 1px solid;border-right: #B8CDE7 1px solid;}\n"+
		"	.notcurrentmonth {font-family: verdana; font-size: 10px; color: #E7E7E7; padding:0; margin:0;}\n"+
		"	</style>\n"+
		"</head>\n"+
		"<body bgcolor=\"White\">\n"+
		"<table class=\"bar2\" cellspacing=\"0\" border=\"0\" width=\"100%\">\n"+
		"<tr><td class=\"pad\">\n"+
		"<table cellspacing=\"1\" cellpadding=\"3\" border=\"0\" width=\"100%\">\n"+
		"<tr>\n	<td><a href=\"javascript:window.opener.show_calendar('"+
		str_target+"', '"+ dt2dtstr(dt_prev_month)+"');\">"+
		"<<</a></td>\n"+
		"	<td colspan=\"5\"><b>"+
		arr_months[dt_datetime.getMonth()]+" "+dt_datetime.getFullYear()+"</b></td>\n"+
		"	<td align=\"right\"><a href=\"javascript:window.opener.show_calendar('"
		+str_target+"', '"+dt2dtstr(dt_next_month)+"');\">"+
		">></a></td>\n</tr>\n"
	);

	var dt_current_day = new Date(dt_firstday);
	// print weekdays titles
	str_buffer += "<tr>\n";
	for (var n=0; n<7; n++)
		str_buffer += "	<td class=\"toprow\">"+
		week_days[(n_weekstart+n)%7]+"</td>\n";
	// print calendar table
	str_buffer += "</tr>\n";
	while (dt_current_day.getMonth() == dt_datetime.getMonth() ||
		dt_current_day.getMonth() == dt_firstday.getMonth()) {
		// print row heder
		str_buffer += "<tr>\n";
		for (var n_current_wday=0; n_current_wday<7; n_current_wday++) {
				if (dt_current_day.getDate() == dt_datetime.getDate() &&
					dt_current_day.getMonth() == dt_datetime.getMonth())
					// print current date
					str_buffer += "	<td bgcolor=\"#FFFFCC\" height=\"25\" align=\"right\">";
				else if (dt_current_day.getDay() == 0 || dt_current_day.getDay() == 6)
					// weekend days
					str_buffer += "	<td class=\"datarowalt\" height=\"20\" align=\"right\">";
				else
					// print working days of current month
					str_buffer += "	<td class=\"datarow\" height=\"20\" align=\"right\">";

				if (dt_current_day.getMonth() == dt_datetime.getMonth())
					// print days of current month
					str_buffer += "<a href=\"javascript:window.opener."+str_target+
					".value='"+dt2dtstr(dt_current_day)+"'; window.close();\">";
				else 
					// print days of other months
					str_buffer += "<a href=\"javascript:window.opener."+str_target+
					".value='"+dt2dtstr(dt_current_day)+"'; window.close();\">"+
					"<span style=\"notcurrentmonth\">";
				str_buffer += dt_current_day.getDate()+"</span></a></td>\n";
				dt_current_day.setDate(dt_current_day.getDate()+1);
		}
		// print row footer
		str_buffer += "</tr>\n";
	}
	// print calendar footer
	str_buffer +=
		"</body>\n" +
		"</html>\n";

	var vWinCal = window.open("", "Calendar", 
		"width=225,height=175,status=no,resizable=yes,top=200,left=200");
	vWinCal.opener = self;
	var calc_doc = vWinCal.document;
	calc_doc.write (str_buffer);
	calc_doc.close();
}
// datetime parsing and formatting routimes. modify them if you wish other datetime format
function str2dt (str_datetime) {
	var re_date = /^(\d+)\/(\d+)\/(\d+)/;
	if (!re_date.exec(str_datetime))
		return alert("Invalid Datetime format: "+ str_datetime);
	return (new Date (RegExp.$3, RegExp.$1-1, RegExp.$2));
}
function dt2dtstr (dt_datetime) {
	return (new String (
			(dt_datetime.getMonth()+1)+"/"+dt_datetime.getDate()+"/"+dt_datetime.getFullYear()+" "));
}

