define(function (require) {

    return {
        init: function() {
            var last_known_scroll_position = 0;
            var ticking = false;
    
            window.addEventListener('scroll', function(e) {
                if (!ticking) {
                    window.requestAnimationFrame(function() {
                        checkScroll();
                    });
                    ticking = true;
                }
            });
            
            function checkScroll() {
                var collapsed = (window.scrollY > 0 && last_known_scroll_position <= window.scrollY)
                var sticky = window.scrollY > 0;
                document.querySelector('header').classList.toggle('collapsed', collapsed);
                document.querySelector('header').classList.toggle('sticky', sticky);
                ticking = false;
                last_known_scroll_position = window.scrollY;
            }
            checkScroll();
        }
    }
});