/*
 * Select field scroller
 *
 * Copyright (c) 2004,  Mackley F. Pexton.  All rights reserved.
 */

/**
The Select field scroller functions make and control a scrolling <select>
field.  To set up a scrolling <select> field, define the HTML as normal and
then call

	make_select_scroll(select_field_id  [, next_func, prev_func] );

The make_select_scroll() function adds an up button to the top of the list
and a down button to the bottom of the list. When the mouse hovers over the
buttons, the list is scrolled up or down.

New options are added to the list by the functions pointed to by the next_func
and prev_func arguments. If they are not assigned, standard selectScroll
functions are used to return the next or previous number in the list. The
functions are passed the <select> object as a lone argument and they should
return an Option object to insert into the list. If scrolling is at the
beginning or at the end of the list, the functions should return null to
stop the scrolling.

An alternative methodology for scrolling <select> fields is needed for Internet
Explorer 6. Its select field options do not sense mouse events. Instead
of scrolling, if the item selected from the list is the first or the last,
the list is repopulated so the last item becomes the second from the top or
the first item is placed in the second to the last place.

The keyboard's arrow keys scroll the list too.
**/

/*
 * Construct scrolling select field out of a normal select field.
 */

function make_select_scroll(id,next_func,prev_func) {

	//if (navigator.userAgent.match(/MSIE/)) return make_select_scroll.IE(id);
	// Unfortunately, only Gecko engine looks at event handlers attached to the option tags.
	if (! navigator.userAgent.match(/Firefox/)) return make_select_scroll.IE(id);

	var select_field = typeof id == 'object' ? id : document.getElementById(id);

	// Save functions used to get next and previous Options for list with the list.
	select_field.next_func = next_func ? next_func : selectScroll.next;
	select_field.prev_func = prev_func ? prev_func : selectScroll.prev;

	// Add up scroll button
	var up_opt = document.createElement("OPTION");
	up_opt.value = '';
	up_opt.text = make_select_scroll.scroll_up_button;
	up_opt.selected = false;
	up_opt.className = 'select-scroll-up';
	up_opt.addEventListener('mouseover',selectScroll.start_up,false);
	up_opt.addEventListener('mouseout',selectScroll.stop,false);
	up_opt.addEventListener('mouseup',selectScroll.stop,false);
	select_field.insertBefore(up_opt,select_field.options[0]);

	// Add down scroll button
	var dn_opt = document.createElement("OPTION");
	dn_opt.value = '';
	dn_opt.text = make_select_scroll.scroll_down_button;
	dn_opt.selected = false;
	dn_opt.className = 'select-scroll-down';
	dn_opt.addEventListener('mouseover',selectScroll.start_down,false);
	dn_opt.addEventListener('mouseout',selectScroll.stop,false);
	dn_opt.addEventListener('mouseup',selectScroll.stop,false);
	select_field.appendChild(dn_opt);

	// Add event handlers
	select_field.onchange = selectScroll.check;
	select_field.onkeypress = selectScroll.check;
}

make_select_scroll.IE = function(id,next_func,prev_func) {
	// IE does not capture events assigned to <option> tags.

	// Set up a "manual" scroll where if the first or last
	// option is selected, it is repositioned to the second
	// or second from last and the remaining options are
	// filled in with the next values.

	var select_field = typeof id == 'object' ? id : document.all[id];

	// Save functions used to get next and previous Options for list with the list.
	select_field.next_func = next_func ? next_func : selectScroll.next;
	select_field.prev_func = prev_func ? prev_func : selectScroll.prev;

	// Add up scroll button.
	// Move all options down to insert up button.
	select_field.options[select_field.options.length] = new Option();
	for (var i = select_field.options.length-1; i > 0; i--) {
		selectScroll.copy_option(select_field.options[i-1],select_field.options[i]);
	}
	select_field.options[0] = new Option(
					  make_select_scroll.scroll_up_button_IE,
					  '',false,false);

	// Add down scroll button.
	select_field.options[select_field.options.length] = new Option(
					  make_select_scroll.scroll_down_button_IE,
					  '',false,false);

	// Add event handlers
	select_field.onchange = selectScroll.IE;
}

make_select_scroll.scroll_up_button = '';	// button contents (use CSS)
make_select_scroll.scroll_down_button = '';	// button contents (use CSS)

make_select_scroll.scroll_up_button_IE = '-';	// button contents (no CSS)
make_select_scroll.scroll_down_button_IE = '+';	// button contents (no CSS)

/*
 * Select scroll control object.
 */

function selectScroll() {
	// Note: this is not really an object but rather the main program
	// called by the system timer to scroll.

	if (! selectScroll.e) return;

	if (selectScroll.dir == 'up')	selectScroll.scroll_up(selectScroll.e);
	else				selectScroll.scroll_down(selectScroll.e);

	selectScroll.timer = setTimeout('selectScroll()',50);
}

selectScroll.scroll_up = function(e) {

	var prev = (e && e.prev_func) ? e.prev_func(e) : null;

	if (prev) {

		var start = e.options.length-2;
		var stop  = 2;

		for (var i = start; i >= stop; i--) {
			selectScroll.copy_option(e.options[i-1],e.options[i]);
		}

		selectScroll.copy_option(prev,e.options[stop-1]);
	}
}

selectScroll.scroll_down = function(e) {

	var next = (e && e.next_func) ? e.next_func(e) : null;

	if (next) {

		var start = 1;
		var stop  = e.options.length-3;

		for (var i = start; i <= stop; i++) {
			selectScroll.copy_option(e.options[i+1],e.options[i]);
		}

		selectScroll.copy_option(next,e.options[stop+1]);
	}
}

selectScroll.copy_option = function(o,target_o) {
		target_o.value		= o.value;
		target_o.text		= o.text;
		target_o.selected	= o.selected;
		target_o.defaultSelected= o.defaultSelected;
}

/*
 * Functions to get next and previous values for list.
 *
 * These functions are defined here so they can be overloaded if needed.
 * They currently add one to the value at the bottom of the list or subtract
 * one from the value at the top of the list.
 */

selectScroll.next = function(e) {
	// Get next option in list, return null if at end.
	return new Option(
		((parseInt(e.options[e.options.length-2].text,10) + 1) + ''),
		((parseInt(e.options[e.options.length-2].value,10) + 1) + ''),
		false,false);
}
selectScroll.prev = function(e) {
	// Get previous option in list, return null if at beginning.
	return new Option(
		((parseInt(e.options[1].text,10) - 1) + ''),
		((parseInt(e.options[1].value,10) - 1) + ''),
		false,false);
}

/*
 * Event handlers
 */

selectScroll.start_up = function(evt) {
	selectScroll.dir = 'up';
	selectScroll.start(evt);
}
selectScroll.start_down = function(evt) {
	selectScroll.dir = 'down';
	selectScroll.start(evt);
}
selectScroll.start = function(evt) {
	evt = evt ? evt : window.event ? window.event : null;
	var target = evt.target ? evt.target : evt.srcElement ? evt.srcElement : null;

	selectScroll.e = target.parentNode;
	selectScroll.timer = setTimeout('selectScroll()',300);
}
selectScroll.stop = function(evt) {
	clearTimeout(selectScroll.timer);
	selectScroll.e = null;
}
selectScroll.check = function(evt) {
	// Check if selected item is a scroll button.
	// This can happen when user changes the value using keyboard arrow keys.

	evt = evt ? evt : window.event ? window.event : null;
	var target = evt.target ? evt.target : evt.srcElement ? evt.srcElement : null;

	// Scroll to keep off scroll buttons.
	if (target.selectedIndex == 0) {
		selectScroll.scroll_up(target);
		target.selectedIndex = 1;
	}
	if (target.selectedIndex == (target.options.length-1)) {
		selectScroll.scroll_down(target);
		target.selectedIndex = target.options.length-2;
	}
}

/*
 * IE scroller
 * Readjust the list only after it has changed.
 */

selectScroll.IE = function() {
	var target = window.event.srcElement;

	var i,last = target.options.length - 1;

	if (target.selectedIndex == 0) {
		for (i = 0; i < last-1; i++) {
			selectScroll.scroll_up(target);
		}
		target.selectedIndex = target.options.length-2;
	}
	else if (target.selectedIndex == last) {
		for (i = last; i > 1; i--) {
			selectScroll.scroll_down(target);
		}
		target.selectedIndex = 1;
	}
}