;(function($, window, document, undefined){

    // our plugin constructor
    var OnePageNav = function(elem, options){
        this.elem = elem;
        this.$elem = $(elem);
        this.options = options;
        this.metadata = this.$elem.data('plugin-options');
        this.$win = $(window);
        this.sections = {};
        this.didScroll = false;
        this.$doc = $(document);
        this.docHeight = this.$doc.height();
    };

    // the plugin prototype
    OnePageNav.prototype = {
        defaults: {
            navItems: 'a',
            currentClass: 'current',
            changeHash: false,
            easing: 'swing',
            filter: '',
            scrollSpeed: 750,
            scrollThreshold: 0.5,
            begin: false,
            end: false,
            scrollChange: false
        },

        init: function() {
            // Introduce defaults that can be extended either
            // globally or using an object literal.
            this.config = $.extend({}, this.defaults, this.options, this.metadata);

            this.$nav = this.$elem.find(this.config.navItems);

            //Filter any links out of the nav
            if(this.config.filter !== '') {
                this.$nav = this.$nav.filter(this.config.filter);
            }

            //Handle clicks on the nav
            this.$nav.on('click.onePageNav', $.proxy(this.handleClick, this));

            //Get the section positions
            this.getPositions();

            //Handle scroll changes
            this.bindInterval();

            //Update the positions on resize too
            this.$win.on('resize.onePageNav', $.proxy(this.getPositions, this));

            return this;
        },

        adjustNav: function(self, $parent) {
            self.$elem.find('.' + self.config.currentClass).removeClass(self.config.currentClass);
            $parent.addClass(self.config.currentClass);
        },

        bindInterval: function() {
            var self = this;
            var docHeight;

            self.$win.on('scroll.onePageNav', function() {
                self.didScroll = true;
            });

            self.t = setInterval(function() {
                docHeight = self.$doc.height();

                //If it was scrolled
                if(self.didScroll) {
                    self.didScroll = false;
                    self.scrollChange();
                }

                //If the document height changes
                if(docHeight !== self.docHeight) {
                    self.docHeight = docHeight;
                    self.getPositions();
                }
            }, 250);
        },

        getHash: function($link) {
            return $link.attr('href').split('#')[1];
        },

        getPositions: function() {
            var self = this;
            var linkHref;
            var topPos;
            var $target;

            self.$nav.each(function() {
                linkHref = self.getHash($(this));
                $target = $('#' + linkHref);

                if($target.length) {
                    topPos = $target.offset().top;
                    self.sections[linkHref] = Math.round(topPos);
                }
            });
        },

        getSection: function(windowPos) {
            var returnValue = null;
            var windowHeight = Math.round(this.$win.height() * this.config.scrollThreshold);

            for(var section in this.sections) {
                if((this.sections[section] - windowHeight) < windowPos) {
                    returnValue = section;
                }
            }

            return returnValue;
        },

        handleClick: function(e) {
            var self = this;
            var $link = $(e.currentTarget);
            var $parent = $link.parent();
            var newLoc = '#' + self.getHash($link);

            if(!$parent.hasClass(self.config.currentClass)) {
                //Start callback
                if(self.config.begin) {
                    self.config.begin();
                }

                //Change the highlighted nav item
                self.adjustNav(self, $parent);

                //Removing the auto-adjust on scroll
                self.unbindInterval();

                //Scroll to the correct position
                self.scrollTo(newLoc, function() {
                    //Do we need to change the hash?
                    if(self.config.changeHash) {
                        window.location.hash = newLoc;
                    }

                    //Add the auto-adjust on scroll back in
                    self.bindInterval();

                    //End callback
                    if(self.config.end) {
                        self.config.end();
                    }
                });
            }

            e.preventDefault();
        },

        scrollChange: function() {
            var windowTop = this.$win.scrollTop();
            var position = this.getSection(windowTop);
            var $parent;

            //If the position is set
            if(position !== null) {
                $parent = this.$elem.find('a[href$="#' + position + '"]').parent();

                //If it's not already the current section
                if(!$parent.hasClass(this.config.currentClass)) {
                    //Change the highlighted nav item
                    this.adjustNav(this, $parent);

                    //If there is a scrollChange callback
                    if(this.config.scrollChange) {
                        this.config.scrollChange($parent);
                    }
                }
            }
        },

        scrollTo: function(target, callback) {
            var offset = $(target).offset().top;

            $('html, body').animate({
                scrollTop: offset
            }, this.config.scrollSpeed, this.config.easing, callback);
        },

        unbindInterval: function() {
            clearInterval(this.t);
            this.$win.unbind('scroll.onePageNav');
        }
    };

    OnePageNav.defaults = OnePageNav.prototype.defaults;

    $.fn.onePageNav = function(options) {
        return this.each(function() {
            new OnePageNav(this, options).init();
        });
    };

})( jQuery, window , document );