$(function () {

var nav = $("<ul>");
$("#nav").append(nav);
var h2;
$(".readme > h2, .readme > h3").each(function () {
    var item = $('<li><a href="#' + $(this).attr("id") + '">' + $(this).text() + '</a>');
    if ($(this).prop("tagName") == "H3") {
        if (!h2) {
            return;
        }
        h2.append(item);
    } else {
        h2 = $("<ul>");
        item.append(h2);
        nav.append(item);
    }
});

// Add numbering
function numberize(prefix) {
    var ch = 1;
    return function() {
        $(this).prepend('<span class="secnum">' + prefix + ch + '</span>&nbsp;');
        $("ul > li", this).each(numberize(ch + "."));
        ch++;
    }
}
$("#nav > ul > li").each(numberize(""));

// Cache selectors
var lastId,
    topMenu = $("#nav > ul"),
    // All list items
    menuItems = topMenu.find("a"),
    // Anchors corresponding to menu items
    scrollItems = menuItems.map(function() {
        var item = $($(this).attr("href"));
        if (item.length) {
            return item;
        }
    });

// Bind click handler to menu items
// so we can get a fancy scroll animation
menuItems.click(function(e){
    var href = $(this).attr("href"),
        offsetTop = href === "#" ? 0 : $(href).offset().top - topMenuHeight + 1;
    $('html, body').stop().animate({
        scrollTop: offsetTop
    }, 300);
    e.preventDefault();
});

// Recompute items position on resize
$(window).resize(function() {
    scrollItems = menuItems.map(function() {
        var item = $($(this).attr("href"));
        if (item.length) {
            return item;
        }
    });
});

// Bind to scroll
$(window).scroll(function(){
    // Get container scroll position
    var fromTop = $(this).scrollTop() + 50;

    // Get id of current scroll item
    var cur = scrollItems.map(function() {
        if ($(this).offset().top < fromTop) {
            return this;
        }
    });
    // Get the id of the current element
    cur = cur[cur.length-1];
    var id = cur && cur.length ? cur[0].id : "";

    if (lastId !== id) {
        lastId = id;
        // Set/remove active class
        menuItems
            .parent().removeClass("active")
            .end().filter("[href='#"+id+"']").parent().addClass("active");
    }
});

});