$(document).ready(function() {
    
    var selected_button_number = 0;
    var button_timeout = 4000;
    var button_timeout_id = null;

    var select_button_slide = function(number) {
        selected_button_number = $(number).index();
        
        $(number).siblings().removeClass("selected");
        $(number).addClass("selected");
        
        $("#button-slides")
            .filter(':not(:animated)')
            .animate({
                top: selected_button_number * -$(".button-slide").eq(0).height()
            }, "slow");
    };
    
    var previous_button_slide = function() {
        if (selected_button_number === 0) {
            select_button_slide($("#button-controls").children(":last"));
        } else {
            select_button_slide($("#button-controls").children(":nth-child(" + selected_button_number + ")"));
        }
    };
    
    var next_button_slide = function() {
        if (selected_button_number === $("#button-controls").children().length - 1) {
            select_button_slide($("#button-controls").children(":first"));
        } else {
            select_button_slide($("#button-controls").children(":nth-child(" + (selected_button_number + 2) + ")"));
        }
        clearTimeout(button_timeout_id);
        slide_timeout_id = setTimeout(next_button_slide, button_timeout);
    };
    
    button_timeout_id = setTimeout(next_button_slide, button_timeout);
});