;(function ( $, window, document, undefined ) {
    // defaults
    var _buffer = null,
        _watch  = [],
        $window = $(window),
        plugin  = function() { }
    ;

    plugin.prototype = {
        globals: {
            pluginname: "fadethis",
            buffertime: 300,
        },
        defaults: {
            basename:       "slide-",
            speed:          500,
            easing:         "swing",
            offset:         0,
            reverse:        true,
            distance:       50,
            scrolledin:     null,
            scrolledout:    null
        },
        init: function ( elem, options ) {
            this.addelements( elem, options );

            this._setevent();
            this._checkvisibleelements();
        },
        addelements: function ( elem, options ) {
            var element         = elem === document.body    ? window    : elem,
                $element        = element === window        ? $("body") : $(element),
                base            = this,
                classbasename   = (options && options.basename) ? options.basename : this.defaults.basename
            ;
            
            if (!$element.is("[class^='" + classbasename + "']")) {

                $element.find("[class^='" + classbasename + "']").each(function() {
                    base._addelement($(this), options);
                });
            } else {
                base._addelement($element, options);
            }

            return $element;
        },
        _addelement: function ($elem, options) {
            var metadata        = $elem.data( "plugin-options" ),
                localoptions    = $.extend({}, this.defaults, options, metadata),
                item = {
                    element:    $elem,
                    options:    localoptions,
                    invp:       false
                }
            ;

            _watch.push(item);

            this._prepareelement(item);

            return $elem;
        },
        _prepareelement: function (item) {
            var cssoptionsin = {
                    opacity: 0,
                    visibility: "visible",
                    position: "relative"
                },
                direction = null
            ;

            if (item.element.hasclass(item.options.basename + "right")) {
                direction = "left";
            } else if (item.element.hasclass(item.options.basename + "left")) {
                direction = "right";
            } else if (item.element.hasclass(item.options.basename + "top")) {
                direction = "bottom";
            } else if (item.element.hasclass(item.options.basename + "bottom")) {
                direction = "top";
            } else {
                return false;
            }

            cssoptionsin[direction] = item.options.distance;

            item.element.css(cssoptionsin);
        },
        _setevent: function () {
            var base = this;

            $window.on("scroll", function(e) {
                if(!_buffer) {
                    _buffer = settimeout(function(){
                        base._checkvisibleelements( e );
                        _buffer = null;
                    }, base.globals.buffertime);
                }
            });
        },
        _checkvisibleelements: function( e ) {
            var base = this;

            $.each(_watch, function(key, item){
                if (base._isvisible(item)) {
                    if ( !item.invp ) {
                        item.invp = true;
                        base._triggerfading(item);
                        if ( item.options.scrolledin ) {
                            item.options.scrolledin.call( item.element, e );
                        }
                        item.element.trigger("fadethisscrolledin", e);
                    }
                } else if ( item.invp ) {
                    item.invp = false;
                    if ( item.options.reverse ) {
                        base._triggerfading(item, false);
                    }
                    if ( item.options.scrolledout ) {
                        item.options.scrolledout.call( item.element, e );
                    }
                    item.element.trigger("fadethisscrolledout", e);
                }
            });
        },
        _isvisible: function(item) {
            var docviewtop      = $window.scrolltop() + item.options.offset,
                docviewbottom   = docviewtop + $window.height() - 2 * item.options.offset,
                elemtop         = item.element.offset().top,
                elembottom      = elemtop + item.element.height()
            ;

            return ((elembottom >= docviewtop) &&  (elemtop <= docviewbottom) &&  (elembottom <= docviewbottom) &&  (elemtop >= docviewtop));
        },
        _triggerfading:function (item, appear) {
            appear = typeof appear !== "undefined" ? appear : true;

            var stateanimin = {
                    opacity: 1
                },
                stateanimout = {
                    opacity: 0,
                },
                direction = null
            ;

            if (item.element.hasclass(item.options.basename + "right")) {
                direction = "left";
            } else if (item.element.hasclass(item.options.basename + "left")) {
                direction = "right";
            } else if (item.element.hasclass(item.options.basename + "top")) {
                direction = "bottom";
            } else if (item.element.hasclass(item.options.basename + "bottom")) {
                direction = "top";
            } else {
                return false;
            }

            stateanimin[direction]  = 0;
            stateanimout[direction] = item.options.distance;


            if (appear) {
                item.element.stop(true).animate(stateanimin, item.options.speed, item.options.easing);
            } else {
                item.element.stop(true).animate(stateanimout, item.options.speed, item.options.easing);
            }
        }
    };

    plugin.defaults = plugin.prototype.defaults;
    plugin.globals  = plugin.prototype.globals;

    window.plugin = new plugin();

    // preventing against multiple instantiations for the same dom element
    $.fn[ plugin.globals.pluginname ] = function ( options ) {
        this.each(function() {
            if ( !$.data( window, "plugin_" + plugin.globals.pluginname ) ) {
                $.data( window, "plugin_" + plugin.globals.pluginname, "set" );
                $.data( this, "plugin_" + plugin.globals.pluginname, window.plugin.init( this, options ) );
            } else if ( !$.data( this, "plugin_" + plugin.globals.pluginname )) {
                $.data( this, "plugin_" + plugin.globals.pluginname, window.plugin.addelements( this, options ) );
            }
        });

        // chain jquery functions
        return this;
    };

})( jquery, window, document );