$.extend($.fn, {
	multiSelect: function(o, callback) {
		// Default options
		if( !o ) var o = {};
		if( o.selectAll == undefined ) o.selectAll = true;
		if( o.selectAllText == undefined ) o.selectAllText = "Select All";
		if( o.noneSelected == undefined ) o.noneSelected = 'Select options';
		if( o.oneOrMoreSelected == undefined ) o.oneOrMoreSelected = '% selected';
		
		// Initialize each multiSelect
		$(this).each( function() {
			var select = $(this);
			var html = '<input type="text" readonly="readonly" class="multiSelect" value="" style="cursor: default;" />';
			html += '<div class="multiSelectOptions" style="position: absolute; z-index: 99999; display: none;">';
			if( o.selectAll ) html += '<label class="selectAll"><input type="checkbox" class="selectAll" />' + o.selectAllText + '</label>';
			$(select).find('OPTION').each( function() {
				if( $(this).val() != '' ) {
					html += '<label><input type="checkbox" name="' + $(select).attr('name') + '[]" value="' + $(this).val() + '"';
					if( $(this).attr('selected') ) html += ' checked="checked"';
					html += ' />' + $(this).html() + '</label>';
				}
			});
			html += '</div>';
			$(select).after(html);
			
			// Events
			$(select).next('.multiSelect').mouseover( function() {
				$(this).addClass('hover');
			}).mouseout( function() {
				$(this).removeClass('hover');
			}).click( function() {
				// Show/hide on click
				if( $(this).hasClass('active') ) {
					$(this).multiSelectOptionsHide();
				} else {
					$(this).multiSelectOptionsShow();
				}
				return false;
			}).focus( function() {
				// So it can be styled with CSS
				$(this).addClass('focus');
			}).blur( function() {
				// So it can be styled with CSS
				$(this).removeClass('focus');
			});
			
			// Determine if Select All should be checked initially
			if( o.selectAll ) {
				var sa = true;
				$(select).next('.multiSelect').next('.multiSelectOptions').find('INPUT:checkbox').not('.selectAll').each( function() {
					if( !$(this).attr('checked') ) sa = false;
				});
				if( sa ) $(select).next('.multiSelect').next('.multiSelectOptions').find('INPUT.selectAll').attr('checked', true).parent().addClass('checked');
			}
			
			// Handle Select All
			$(select).next('.multiSelect').next('.multiSelectOptions').find('INPUT.selectAll').click( function() {
				if( $(this).attr('checked') == true ) $(this).parent().parent().find('INPUT:checkbox').attr('checked', true).parent().addClass('checked'); else $(this).parent().parent().find('INPUT:checkbox').attr('checked', false).parent().removeClass('checked');
			});
			
			// Handle checkboxes
			$(select).next('.multiSelect').next('.multiSelectOptions').find('INPUT:checkbox').click( function() {
				$(this).parent().parent().multiSelectUpdateSelected(o);
				$(this).parent().parent().find('LABEL').removeClass('checked').find('INPUT:checked').parent().addClass('checked');
				$(this).parent().parent().prev('.multiSelect').focus();
				if( !$(this).attr('checked') ) $(this).parent().parent().find('INPUT:checkbox.selectAll').attr('checked', false).parent().removeClass('checked');
				if( callback ) callback($(this));
			});
			
			// Initial display
			$(select).next('.multiSelect').next('.multiSelectOptions').each( function() {
				$(this).multiSelectUpdateSelected(o);
				$(this).find('INPUT:checked').parent().addClass('checked');
			});
			
			// Handle hovers
			$(select).next('.multiSelect').next('.multiSelectOptions').find('LABEL').mouseover( function() {
				$(this).parent().find('LABEL').removeClass('hover');
				$(this).addClass('hover');
			}).mouseout( function() {
				$(this).parent().find('LABEL').removeClass('hover');
			});
			
			// Keyboard
			$(select).next('.multiSelect').keydown( function(e) {
				// Is dropdown visible?
				if( $(this).next('.multiSelectOptions').is(':visible') ) {
					// Dropdown is visible
					// Tab
					if( e.keyCode == 9 ) {
						$(this).addClass('focus').trigger('click'); // esc, left, right - hide
						$(this).focus().next(':input').focus();
						return true;
					}
					
					// ESC, Left, Right
					if( e.keyCode == 27 || e.keyCode == 37 || e.keyCode == 39 ) {
						// Hide dropdown
						$(this).addClass('focus').trigger('click');
					}
					// Down
					if( e.keyCode == 40 ) {
						if( !$(this).next('.multiSelectOptions').find('LABEL').hasClass('hover') ) {
							// Default to first item
							$(this).next('.multiSelectOptions').find('LABEL:first').addClass('hover');
						} else {
							// Move down, cycle to top if on bottom
							$(this).next('.multiSelectOptions').find('LABEL.hover').removeClass('hover').next('LABEL').addClass('hover');
							if( !$(this).next('.multiSelectOptions').find('LABEL').hasClass('hover') ) {
								$(this).next('.multiSelectOptions').find('LABEL:first').addClass('hover');
							}
						}
						
						// Adjust the viewport if necessary
						$(this).multiSelectAdjustViewport($(this) );
						
						return false;
					}
					// Up
					if( e.keyCode == 38 ) {
						if( !$(this).next('.multiSelectOptions').find('LABEL').hasClass('hover') ) {
							// Default to first item
							$(this).next('.multiSelectOptions').find('LABEL:first').addClass('hover');
						} else {
							// Move up, cycle to bottom if on top
							$(this).next('.multiSelectOptions').find('LABEL.hover').removeClass('hover').prev('LABEL').addClass('hover');
							if( !$(this).next('.multiSelectOptions').find('LABEL').hasClass('hover') ) {
								$(this).next('.multiSelectOptions').find('LABEL:last').addClass('hover');
							}
						}
						
						// Adjust the viewport if necessary
						$(this).multiSelectAdjustViewport($(this) );
						
						return false;
					}
					// Enter, Space
					if( e.keyCode == 13 || e.keyCode == 32 ) {
						// Select All
						if( $(this).next('.multiSelectOptions').find('LABEL.hover INPUT:checkbox').hasClass('selectAll') ) {
							if( $(this).next('.multiSelectOptions').find('LABEL.hover INPUT:checkbox').attr('checked') ) {
								// Uncheck all
								$(this).next('.multiSelectOptions').find('INPUT:checkbox').attr('checked', false).parent().removeClass('checked');
							} else {
								// Check all
								$(this).next('.multiSelectOptions').find('INPUT:checkbox').attr('checked', true).parent().addClass('checked');
							}
							$(this).next('.multiSelectOptions').multiSelectUpdateSelected(o);
							if( callback ) callback($(this));
							return false;
						}
						// Other checkboxes
						if( $(this).next('.multiSelectOptions').find('LABEL.hover INPUT:checkbox').attr('checked') ) {
							// Uncheck
							$(this).next('.multiSelectOptions').find('LABEL.hover INPUT:checkbox').attr('checked', false);
							$(this).next('.multiSelectOptions').multiSelectUpdateSelected(o);
							$(this).next('.multiSelectOptions').find('LABEL').removeClass('checked').find('INPUT:checked').parent().addClass('checked');
							// Select all status can't be checked at this point
							$(this).next('.multiSelectOptions').find('INPUT:checkbox.selectAll').attr('checked', false).parent().removeClass('checked');
							if( callback ) callback($(this));
						} else {
							// Check
							$(this).next('.multiSelectOptions').find('LABEL.hover INPUT:checkbox').attr('checked', true);
							$(this).next('.multiSelectOptions').multiSelectUpdateSelected(o);
							$(this).next('.multiSelectOptions').find('LABEL').removeClass('checked').find('INPUT:checked').parent().addClass('checked');
							if( callback ) callback($(this));
						}
					}
					return false;
				} else {
					// Dropdown is not visible
					if( e.keyCode == 38 || e.keyCode == 40 || e.keyCode == 13 || e.keyCode == 32 ) { // down, enter, space - show
						// Show dropdown
						$(this).removeClass('focus').trigger('click');
						$(this).next('.multiSelectOptions').find('LABEL:first').addClass('hover');
						return false;
					}
					//  Tab key
					if( e.keyCode == 9 ) {
						// Shift focus to next INPUT element on page
						$(this).focus().next(':input').focus();
						return true;
					}
				}
				// Prevent enter key from submitting form
				if( e.keyCode == 13 ) return false;
			});
			
			// Eliminate the original form element
			$(select).remove();
		});
		
	},
	
	// Hide the dropdown
	multiSelectOptionsHide: function() {
		$(this).removeClass('active').next('.multiSelectOptions').hide();
	},
	
	// Show the dropdown
	multiSelectOptionsShow: function() {
		// Hide any open option boxes
		$('.multiSelect').multiSelectOptionsHide();
		$(this).next('.multiSelectOptions').find('LABEL').removeClass('hover');
		$(this).addClass('active').next('.multiSelectOptions').show();
		
		// Position it
		var offset = $(this).position();
		$(this).next('.multiSelectOptions').css({ top:  offset.top + $(this).outerHeight() + 'px' });
		$(this).next('.multiSelectOptions').css({ left: offset.left + 'px' });
		
		// Disappear on hover out
		multiSelectCurrent = $(this);
		var timer = '';
		$(this).next('.multiSelectOptions').hover( function() {
			clearTimeout(timer);
		}, function() {
			timer = setTimeout('jQuery(multiSelectCurrent).multiSelectOptionsHide(); $(multiSelectCurrent).unbind("hover");', 250);
		});
		
	},
	
	// Update the textbox with the total number of selected items
	multiSelectUpdateSelected: function(o) {
		var i = 0, s = '';
		$(this).find('INPUT:checkbox:checked').not('.selectAll').each( function() {
			i++;
		})
		if( i == 0 ) {
			$(this).prev('INPUT.multiSelect').val( o.noneSelected );
		} else {
			if( o.oneOrMoreSelected == '*' ) {
				var display = '';
				$(this).find('INPUT:checkbox:checked').each( function() {
					if( $(this).parent().text() != o.selectAllText ) display = display + $(this).parent().text() + ', ';
				});
				display = display.substr(0, display.length - 2);
				$(this).prev('INPUT.multiSelect').val( display );
			} else {
				$(this).prev('INPUT.multiSelect').val( o.oneOrMoreSelected.replace('%', i) );
			}
		}
	},
	
	// Ensures that the selected item is always in the visible portion of the dropdown (for keyboard controls)
	multiSelectAdjustViewport: function(el) {
		// Calculate positions of elements
		var i = 0;
		var selectionTop = 0, selectionHeight = 0;
		$(el).next('.multiSelectOptions').find('LABEL').each( function() {
			if( $(this).hasClass('hover') ) { selectionTop = i; selectionHeight = $(this).outerHeight(); return; }
			i += $(this).outerHeight();
		});
		var divScroll = $(el).next('.multiSelectOptions').scrollTop();
		var divHeight = $(el).next('.multiSelectOptions').height();
		// Adjust the dropdown scroll position
		$(el).next('.multiSelectOptions').scrollTop(selectionTop - ((divHeight / 2) - (selectionHeight / 2)));
	}
	
});