滚动时自动滚动到顶部元素

Question

我有三个部分home_bg，barman，galeria。我想，滚动到感觉$（window）.scrollTop（）的部分之后添加类。当此滚动<= 0.5 *高度感觉部分时，自动滚动到顶部感觉部分。

示例：http://www.dishoom.com/

  <script>
            jQuery(document).ready(function ($) {
                $(window).scroll(function () {
                       scroll = $(window).scrollTop();

                    /* scrollAnch = $("section.nomargin");*/
                    var height_check = jQuery(window).height() ;
                    $(document).mousewheel(function (event) {
                        if (event.deltaY) {
                            $(window).scroll(function () {

                                if(scroll >= $("section#home_bg").offset().top)
                                {
                                    $('section#barman').removeClass('snaps-active');
                                    $('section#galeria').removeClass('snaps-active');
                                    $('section#home_bg').addClass('snaps-active');

                                    if(scroll >= ($("section#home_bg").offset().top + (0.5*height_check)))
                                    {
                                        $('section#home_bg').removeClass('snaps-active');

                                    }
                                }
                                if (scroll >= $("section#barman").offset().top) {
                                    $('section#barman').addClass('snaps-active');
                                    $('section#galeria').removeClass('snaps-active');
                                    $('section#home_bg').removeClass('snaps-active');

                                    if(scroll >= ($("section#barman").offset().top + (0.5*height_check)))
                                    {
                                        $('section#barman').removeClass('snaps-active');

                                    }

                                }
                                if(scroll >= ($("section#galeria").offset().top)) {
                                    $('section#home_bg').removeClass('snaps-active');
                                    $('section#barman').removeClass('snaps-active');
                                    $('section#galeria').addClass('snaps-active');


                                    if (scroll >= ($("section#galeria").offset().top + (0.5 * height_check))) {
                                        $('section#galeria').removeClass('snaps-active');
                                    }


                                }


                            });

                        }


           });

                });

            });
        </script>