/*! gridster.js - v0.1.0 - 2012-10-20
* http://gridster.net/
* Copyright (c) 2012 ducksboard; Licensed MIT */

;(function($, window, document, undefined){
    /**
    * Creates objects with coordinates (x1, y1, x2, y2, cx, cy, width, height)
    * to simulate DOM elements on the screen.
    * Coords is used by Gridster to create a faux grid with any DOM element can
    * collide.
    *
    * @class Coords
    * @param {HTMLElement|Object} obj The jQuery HTMLElement or a object with: left,
    * top, width and height properties.
    * @return {Object} Coords instance.
    * @constructor
    */
    function Coords(obj) {
        if (obj[0] && $.isPlainObject(obj[0])) {
            this.data = obj[0];
        }else {
            this.el = obj;
        }

        this.isCoords = true;
        this.coords = {};
        this.init();
        return this;
    }


    var fn = Coords.prototype;


    fn.init = function(){
        this.set();
        this.original_coords = this.get();
    };


    fn.set = function(update, not_update_offsets) {
        var el = this.el;

        if (el && !update) {
            this.data = el.offset();
            this.data.width = el.width();
            this.data.height = el.height();
        }

        if (el && update && !not_update_offsets) {
            var offset = el.offset();
            this.data.top = offset.top;
            this.data.left = offset.left;
        }

        var d = this.data;

        this.coords.x1 = d.left;
        this.coords.y1 = d.top;
        this.coords.x2 = d.left + d.width;
        this.coords.y2 = d.top + d.height;
        this.coords.cx = d.left + (d.width / 2);
        this.coords.cy = d.top + (d.height / 2);
        this.coords.width  = d.width;
        this.coords.height = d.height;
        this.coords.el  = el || false ;

        return this;
    };


    fn.update = function(data){
        if (!data && !this.el) {
            return this;
        }

        if (data) {
            var new_data = $.extend({}, this.data, data);
            this.data = new_data;
            return this.set(true, true);
        }

        this.set(true);
        return this;
    };


    fn.get = function(){
        return this.coords;
    };


    //jQuery adapter
    $.fn.coords = function() {
        if (this.data('coords') ) {
            return this.data('coords');
        }

        var ins = new Coords(this, arguments[0]);
        this.data('coords', ins);
        return ins;
    };

}(jQuery, window, document));

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

    var defaults = {
        colliders_context: document.body
        // ,on_overlap: function(collider_data){},
        // on_overlap_start : function(collider_data){},
        // on_overlap_stop : function(collider_data){}
    };


    /**
    * Detects collisions between a DOM element against other DOM elements or
    * Coords objects.
    *
    * @class Collision
    * @uses Coords
    * @param {HTMLElement} el The jQuery wrapped HTMLElement.
    * @param {HTMLElement|Array} colliders Can be a jQuery collection
    *  of HTMLElements or an Array of Coords instances.
    * @param {Object} [options] An Object with all options you want to
    *        overwrite:
    *   @param {Function} [options.on_overlap_start] Executes a function the first
    *    time each `collider ` is overlapped.
    *   @param {Function} [options.on_overlap_stop] Executes a function when a
    *    `collider` is no longer collided.
    *   @param {Function} [options.on_overlap] Executes a function when the
    * mouse is moved during the collision.
    * @return {Object} Collision instance.
    * @constructor
    */
    function Collision(el, colliders, options) {
        this.options = $.extend(defaults, options);
        this.$element = el;
        this.last_colliders = [];
        this.last_colliders_coords = [];
        if (typeof colliders === 'string' || colliders instanceof jQuery) {
            this.$colliders = $(colliders,
                 this.options.colliders_context).not(this.$element);
        }else{
            this.colliders = $(colliders);
        }

        this.init();
    }


    var fn = Collision.prototype;


    fn.init = function() {
        this.find_collisions();
    };


    fn.overlaps = function(a, b) {
        var x = false;
        var y = false;

        if ((b.x1 >= a.x1 && b.x1 <= a.x2) ||
            (b.x2 >= a.x1 && b.x2 <= a.x2) ||
            (a.x1 >= b.x1 && a.x2 <= b.x2)
        ) { x = true; }

        if ((b.y1 >= a.y1 && b.y1 <= a.y2) ||
            (b.y2 >= a.y1 && b.y2 <= a.y2) ||
            (a.y1 >= b.y1 && a.y2 <= b.y2)
        ) { y = true; }

        return (x && y);
    };


    fn.detect_overlapping_region = function(a, b){
        var regionX = '';
        var regionY = '';

        if (a.y1 > b.cy && a.y1 < b.y2) { regionX = 'N'; }
        if (a.y2 > b.y1 && a.y2 < b.cy) { regionX = 'S'; }
        if (a.x1 > b.cx && a.x1 < b.x2) { regionY = 'W'; }
        if (a.x2 > b.x1 && a.x2 < b.cx) { regionY = 'E'; }

        return (regionX + regionY) || 'C';
    };


    fn.calculate_overlapped_area_coords = function(a, b){
        var x1 = Math.max(a.x1, b.x1);
        var y1 = Math.max(a.y1, b.y1);
        var x2 = Math.min(a.x2, b.x2);
        var y2 = Math.min(a.y2, b.y2);

        return $({
            left: x1,
            top: y1,
             width : (x2 - x1),
            height: (y2 - y1)
          }).coords().get();
    };


    fn.calculate_overlapped_area = function(coords){
        return (coords.width * coords.height);
    };


    fn.manage_colliders_start_stop = function(new_colliders_coords, start_callback, stop_callback){
        var last = this.last_colliders_coords;

        for (var i = 0, il = last.length; i < il; i++) {
            if ($.inArray(last[i], new_colliders_coords) === -1) {
                start_callback.call(this, last[i]);
            }
        }

        for (var j = 0, jl = new_colliders_coords.length; j < jl; j++) {
            if ($.inArray(new_colliders_coords[j], last) === -1) {
                stop_callback.call(this, new_colliders_coords[j]);
            }

        }
    };


    fn.find_collisions = function(player_data_coords){
        var self = this;
        var colliders_coords = [];
        var colliders_data = [];
        var $colliders = (this.colliders || this.$colliders);
        var count = $colliders.length;
        var player_coords = self.$element.coords()
                             .update(player_data_coords || false).get();

        while(count--){
          var $collider = self.$colliders ?
                           $($colliders[count]) : $colliders[count];
          var $collider_coords_ins = ($collider.isCoords) ?
                  $collider : $collider.coords();
          var collider_coords = $collider_coords_ins.get();
          var overlaps = self.overlaps(player_coords, collider_coords);

          if (!overlaps) {
            continue;
          }

          var region = self.detect_overlapping_region(
              player_coords, collider_coords);

            //todo: make this an option
            if (region === 'C'){
                var area_coords = self.calculate_overlapped_area_coords(
                    player_coords, collider_coords);
                var area = self.calculate_overlapped_area(area_coords);
                var collider_data = {
                    area: area,
                    area_coords : area_coords,
                    region: region,
                    coords: collider_coords,
                    player_coords: player_coords,
                    el: $collider
                };

                if (self.options.on_overlap) {
                    self.options.on_overlap.call(this, collider_data);
                }
                colliders_coords.push($collider_coords_ins);
                colliders_data.push(collider_data);
            }
        }

        if (self.options.on_overlap_stop || self.options.on_overlap_start) {
            this.manage_colliders_start_stop(colliders_coords,
                self.options.on_overlap_stop, self.options.on_overlap_start);
        }

        this.last_colliders_coords = colliders_coords;

        return colliders_data;
    };


    fn.get_closest_colliders = function(player_data_coords){
        var colliders = this.find_collisions(player_data_coords);

        colliders.sort(function(a, b) {
            /* if colliders are being overlapped by the "C" (center) region,
             * we have to set a lower index in the array to which they are placed
             * above in the grid. */
            if (a.region === 'C' && b.region === 'C') {
                if (a.coords.y1 < b.coords.y1 || a.coords.x1 < b.coords.x1) {
                    return - 1;
                }else{
                    return 1;
                }
            }

            if (a.area < b.area) {
                return 1;
            }

            return 1;
        });
        return colliders;
    };


    //jQuery adapter
    $.fn.collision = function(collider, options) {
          return new Collision( this, collider, options );
    };


}(jQuery, window, document));

;(function(window, undefined) {
    /* Debounce and throttle functions taken from underscore.js */
    window.debounce = function(func, wait, immediate) {
        var timeout;
        return function() {
          var context = this, args = arguments;
          var later = function() {
            timeout = null;
            if (!immediate) func.apply(context, args);
          };
          if (immediate && !timeout) func.apply(context, args);
          clearTimeout(timeout);
          timeout = setTimeout(later, wait);
        };
    };


    window.throttle = function(func, wait) {
        var context, args, timeout, throttling, more, result;
        var whenDone = debounce(
            function(){ more = throttling = false; }, wait);
        return function() {
          context = this; args = arguments;
          var later = function() {
            timeout = null;
            if (more) func.apply(context, args);
            whenDone();
          };
          if (!timeout) timeout = setTimeout(later, wait);
          if (throttling) {
            more = true;
          } else {
            result = func.apply(context, args);
          }
          whenDone();
          throttling = true;
          return result;
        };
    };

})(window);

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

    var defaults = {
        items: '.gs_w',
        distance: 1,
        limit: true,
        offset_left: 0,
        autoscroll: true,
        ignore_dragging: ['INPUT', 'TEXTAREA', 'SELECT', 'BUTTON'],
        handle: null
        // ,drag: function(e){},
        // start : function(e, ui){},
        // stop : function(e){}
    };

    var $window = $(window);
    var isTouch = !!('ontouchstart' in window);
    var pointer_events = {
        start: isTouch ? 'touchstart' : 'mousedown.draggable',
        move: isTouch ? 'touchmove' : 'mousemove.draggable',
        end: isTouch ? 'touchend' : 'mouseup.draggable'
    };

    /**
    * Basic drag implementation for DOM elements inside a container.
    * Provide start/stop/drag callbacks.
    *
    * @class Draggable
    * @param {HTMLElement} el The HTMLelement that contains all the widgets
    *  to be dragged.
    * @param {Object} [options] An Object with all options you want to
    *        overwrite:
    *    @param {HTMLElement|String} [options.items] Define who will
    *     be the draggable items. Can be a CSS Selector String or a
    *     collection of HTMLElements.
    *    @param {Number} [options.distance] Distance in pixels after mousedown
    *     the mouse must move before dragging should start.
    *    @param {Boolean} [options.limit] Constrains dragging to the width of
    *     the container
    *    @param {offset_left} [options.offset_left] Offset added to the item
    *     that is being dragged.
    *    @param {Number} [options.drag] Executes a callback when the mouse is
    *     moved during the dragging.
    *    @param {Number} [options.start] Executes a callback when the drag
    *     starts.
    *    @param {Number} [options.stop] Executes a callback when the drag stops.
    * @return {Object} Returns `el`.
    * @constructor
    */
    function Draggable(el, options) {
      this.options = $.extend({}, defaults, options);
      this.$body = $(document.body);
      this.$container = $(el);
      this.$dragitems = $(this.options.items, this.$container);
      this.is_dragging = false;
      this.player_min_left = 0 + this.options.offset_left;
      this.init();
    }

    var fn = Draggable.prototype;

    fn.init = function() {
        this.calculate_positions();
        this.$container.css('position', 'relative');
        this.disabled = false;
        this.events();

        $(window).bind('resize',
            throttle($.proxy(this.calculate_positions, this), 200));
    };

    fn.events = function() {
        this.$container.on('selectstart', $.proxy(this.on_select_start, this));

        this.$container.on(pointer_events.start, this.options.items, $.proxy(
            this.drag_handler, this));

        this.$body.on(pointer_events.end, $.proxy(function(e) {
            this.is_dragging = false;
            if (this.disabled) { return; }
            this.$body.off(pointer_events.move);
            if (this.drag_start) {
                this.on_dragstop(e);
            }
        }, this));
    };

    fn.get_actual_pos = function($el) {
        var pos = $el.position();
        return pos;
    };


    fn.get_mouse_pos = function(e) {
        if (isTouch) {
            var oe = e.originalEvent;
            e = oe.touches.length ? oe.touches[0] : oe.changedTouches[0];
        }

        return {
            left: e.clientX,
            top: e.clientY
        };
    };


    fn.get_offset = function(e) {
        e.preventDefault();
        var mouse_actual_pos = this.get_mouse_pos(e);
        var diff_x = Math.round(
            mouse_actual_pos.left - this.mouse_init_pos.left);
        var diff_y = Math.round(mouse_actual_pos.top - this.mouse_init_pos.top);

        var left = Math.round(this.el_init_offset.left + diff_x - this.baseX);
        var top = Math.round(
            this.el_init_offset.top + diff_y - this.baseY + this.scrollOffset);

        if (this.options.limit) {
            if (left > this.player_max_left) {
                left = this.player_max_left;
            }else if(left < this.player_min_left) {
                left = this.player_min_left;
            }
        }

        return {
            left: left,
            top: top,
            mouse_left: mouse_actual_pos.left,
            mouse_top: mouse_actual_pos.top
        };
    };


    fn.manage_scroll = function(offset) {
        /* scroll document */
        var nextScrollTop;
        var scrollTop = $window.scrollTop();
        var min_window_y = scrollTop;
        var max_window_y = min_window_y + this.window_height;

        var mouse_down_zone = max_window_y - 50;
        var mouse_up_zone = min_window_y + 50;

        var abs_mouse_left = offset.mouse_left;
        var abs_mouse_top = min_window_y + offset.mouse_top;

        var max_player_y = (this.doc_height - this.window_height +
            this.player_height);

        if (abs_mouse_top >= mouse_down_zone) {
            nextScrollTop = scrollTop + 30;
            if (nextScrollTop < max_player_y) {
                $window.scrollTop(nextScrollTop);
                this.scrollOffset = this.scrollOffset + 30;
            }
        }

        if (abs_mouse_top <= mouse_up_zone) {
            nextScrollTop = scrollTop - 30;
            if (nextScrollTop > 0) {
                $window.scrollTop(nextScrollTop);
                this.scrollOffset = this.scrollOffset - 30;
            }
        }
    };


    fn.calculate_positions = function(e) {
        this.window_height = $window.height();
    };


    fn.drag_handler = function(e) {
        var node = e.target.nodeName;
        if (this.disabled || e.which !== 1 && !isTouch) {
            return;
        }

        if (this.ignore_drag(e)) {
            return;
        }

        var self = this;
        var first = true;
        this.$player = $(e.currentTarget);

        this.el_init_pos = this.get_actual_pos(this.$player);
        this.mouse_init_pos = this.get_mouse_pos(e);
        this.offsetY = this.mouse_init_pos.top - this.el_init_pos.top;

        this.$body.on(pointer_events.move, function(mme){
            var mouse_actual_pos = self.get_mouse_pos(mme);
            var diff_x = Math.abs(
                mouse_actual_pos.left - self.mouse_init_pos.left);
            var diff_y = Math.abs(
                mouse_actual_pos.top - self.mouse_init_pos.top);
            if (!(diff_x > self.options.distance ||
                diff_y > self.options.distance)
            ) {
                return false;
            }

            if (first) {
                first = false;
                self.on_dragstart.call(self, mme);
                return false;
            }

            if (self.is_dragging === true) {
                self.on_dragmove.call(self, mme);
            }

            return false;
        });

        return false;
    };


    fn.on_dragstart = function(e) {
        e.preventDefault();
        this.drag_start = true;
        this.is_dragging = true;
        var offset = this.$container.offset();
        this.baseX = Math.round(offset.left);
        this.baseY = Math.round(offset.top);
        this.doc_height = $(document).height();

        if (this.options.helper === 'clone') {
            this.$helper = this.$player.clone()
                .appendTo(this.$container).addClass('helper');
            this.helper = true;
        }else{
            this.helper = false;
        }
        this.scrollOffset = 0;
        this.el_init_offset = this.$player.offset();
        this.player_width = this.$player.width();
        this.player_height = this.$player.height();
        this.player_max_left = (this.$container.width() - this.player_width +
            this.options.offset_left);

        if (this.options.start) {
            this.options.start.call(this.$player, e, {
                helper: this.helper ? this.$helper : this.$player
            });
        }
        return false;
    };


    fn.on_dragmove = function(e) {
        var offset = this.get_offset(e);

        this.options.autoscroll && this.manage_scroll(offset);

        (this.helper ? this.$helper : this.$player).css({
            'position': 'absolute',
            'left' : offset.left,
            'top' : offset.top
        });

        var ui = {
            'position': {
                'left': offset.left,
                'top': offset.top
            }
        };

        if (this.options.drag) {
            this.options.drag.call(this.$player, e, ui);
        }
        return false;
    };


    fn.on_dragstop = function(e) {
        var offset = this.get_offset(e);
        this.drag_start = false;

        var ui = {
            'position': {
                'left': offset.left,
                'top': offset.top
            }
        };

        if (this.options.stop) {
            this.options.stop.call(this.$player, e, ui);
        }

        if (this.helper) {
            this.$helper.remove();
        }

        return false;
    };

    fn.on_select_start = function(e) {
        if (this.disabled) { return; }

        if (this.ignore_drag(e)) {
            return;
        }

        return false;
    };

    fn.enable = function() {
        this.disabled = false;
    };

    fn.disable = function() {
        this.disabled = true;
    };


    fn.destroy = function(){
        this.disable();
        $.removeData(this.$container, 'drag');
    };

    fn.ignore_drag = function(event) {
        if (this.options.handle) {
            return !$(event.target).is(this.options.handle);
        }

        return $.inArray(event.target.nodeName, this.options.ignore_dragging) >= 0;
    };

    //jQuery adapter
    $.fn.drag = function ( options ) {
        return this.each(function () {
            if (!$.data(this, 'drag')) {
                $.data(this, 'drag', new Draggable( this, options ));
            }
        });
    };


}(jQuery, window, document));

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

    var defaults = {
        namespace: '',
        widget_selector: 'li',
        widget_margins: [10, 10],
        widget_base_dimensions: [400, 225],
        extra_rows: 0,
        extra_cols: 0,
        min_cols: 1,
        min_rows: 15,
        max_size_x: 6,
        autogenerate_stylesheet: true,
        avoid_overlapped_widgets: true,
        serialize_params: function($w, wgd) {
            return {
                col: wgd.col,
                row: wgd.row,
                size_x: wgd.size_x,
                size_y: wgd.size_y
            };
        },
        collision: {},
        draggable: {
            distance: 4
        }
    };


    /**
    * @class Gridster
    * @uses Draggable
    * @uses Collision
    * @param {HTMLElement} el The HTMLelement that contains all the widgets.
    * @param {Object} [options] An Object with all options you want to
    *        overwrite:
    *    @param {HTMLElement|String} [options.widget_selector] Define who will
    *     be the draggable widgets. Can be a CSS Selector String or a
    *     collection of HTMLElements
    *    @param {Array} [options.widget_margins] Margin between widgets.
    *     The first index for the horizontal margin (left, right) and
    *     the second for the vertical margin (top, bottom).
    *    @param {Array} [options.widget_base_dimensions] Base widget dimensions
    *     in pixels. The first index for the width and the second for the
    *     height.
    *    @param {Number} [options.extra_cols] Add more columns in addition to
    *     those that have been calculated.
    *    @param {Number} [options.extra_rows] Add more rows in addition to
    *     those that have been calculated.
    *    @param {Number} [options.min_cols] The minimum required columns.
    *    @param {Number} [options.min_rows] The minimum required rows.
    *    @param {Number} [options.max_size_x] The maximum number of columns
    *     that a widget can span.
    *    @param {Boolean} [options.autogenerate_stylesheet] If true, all the
    *     CSS required to position all widgets in their respective columns
    *     and rows will be generated automatically and injected to the
    *     `<head>` of the document. You can set this to false, and write
    *     your own CSS targeting rows and cols via data-attributes like so:
    *     `[data-col="1"] { left: 10px; }`
    *    @param {Boolean} [options.avoid_overlapped_widgets] Avoid that widgets loaded
    *     from the DOM can be overlapped. It is helpful if the positions were
    *     bad stored in the database or if there was any conflict.
    *    @param {Function} [options.serialize_params] Return the data you want
    *     for each widget in the serialization. Two arguments are passed:
    *     `$w`: the jQuery wrapped HTMLElement, and `wgd`: the grid
    *     coords object (`col`, `row`, `size_x`, `size_y`).
    *    @param {Object} [options.collision] An Object with all options for
    *     Collision class you want to overwrite. See Collision docs for
    *     more info.
    *    @param {Object} [options.draggable] An Object with all options for
    *     Draggable class you want to overwrite. See Draggable docs for more
    *     info.
    *
    * @constructor
    */
    function Gridster(el, options) {
      this.options = $.extend(true, defaults, options);
      this.$el = $(el);
      this.$wrapper = this.$el.parent();
      this.$widgets = this.$el.children(this.options.widget_selector).addClass('gs_w');
      this.widgets = [];
      this.$changed = $([]);
      this.wrapper_width = this.$wrapper.width();
      this.min_widget_width = (this.options.widget_margins[0] * 2) +
        this.options.widget_base_dimensions[0];
      this.min_widget_height = (this.options.widget_margins[1] * 2) +
        this.options.widget_base_dimensions[1];
      this.init();
    }

    Gridster.generated_stylesheets = [];

    var fn = Gridster.prototype;

    fn.init = function() {
        this.generate_grid_and_stylesheet();
        this.get_widgets_from_DOM();
        this.set_dom_grid_height();
        this.$wrapper.addClass('ready');
        this.draggable();

        $(window).bind(
            'resize', throttle($.proxy(this.recalculate_faux_grid, this), 200));
    };


    /**
    * Disables dragging.
    *
    * @method disable
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.disable = function() {
        this.$wrapper.find('.player-revert').removeClass('player-revert');
        this.drag_api.disable();
        return this;
    };


    /**
    * Enables dragging.
    *
    * @method enable
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.enable = function() {
        this.drag_api.enable();
        return this;
    };


    /**
    * Add a new widget to the grid.
    *
    * @method add_widget
    * @param {String|HTMLElement} html The string representing the HTML of the widget
    *  or the HTMLElement.
    * @param {Number} [size_x] The nº of rows the widget occupies horizontally.
    * @param {Number} [size_y] The nº of columns the widget occupies vertically.
    * @param {Number} [col] The column the widget should start in.
    * @param {Number} [row] The row the widget should start in.
    * @return {HTMLElement} Returns the jQuery wrapped HTMLElement representing.
    *  the widget that was just created.
    */
    fn.add_widget = function(html, size_x, size_y, col, row) {
        var pos;
        size_x || (size_x = 1);
        size_y || (size_y = 1);

        if (!col & !row) {
            pos = this.next_position(size_x, size_y);
        }else{
            pos = {
                col: col,
                row: row
            };

            this.empty_cells(col, row, size_x, size_y);
        }

        var $w = $(html).attr({
                'data-col': pos.col,
                'data-row': pos.row,
                'data-sizex' : size_x,
                'data-sizey' : size_y
            }).addClass('gs_w').appendTo(this.$el).hide();

        this.$widgets = this.$widgets.add($w);

        this.register_widget($w);

        this.add_faux_rows(pos.size_y);
        //this.add_faux_cols(pos.size_x);

        this.set_dom_grid_height();

        return $w.fadeIn();
    };



    /**
    * Change the size of a widget.
    *
    * @method resize_widget
    * @param {HTMLElement} $widget The jQuery wrapped HTMLElement
    *  representing the widget.
    * @param {Number} size_x The number of columns that will occupy the widget.
    * @param {Number} size_y The number of rows that will occupy the widget.
    * @return {HTMLElement} Returns $widget.
    */
    fn.resize_widget = function($widget, size_x, size_y) {
        var wgd = $widget.coords().grid;
        size_x || (size_x = wgd.size_x);
        size_y || (size_y = wgd.size_y);

        if (size_x > this.cols) {
            size_x = this.cols;
        }

        var old_cells_occupied = this.get_cells_occupied(wgd);
        var old_size_x = wgd.size_x;
        var old_size_y = wgd.size_y;
        var old_col = wgd.col;
        var new_col = old_col;
        var wider = size_x > old_size_x;
        var taller = size_y > old_size_y;

        if (old_col + size_x - 1 > this.cols) {
            var diff = old_col + (size_x - 1) - this.cols;
            var c = old_col - diff;
            new_col = Math.max(1, c);
        }

        var new_grid_data = {
            col: new_col,
            row: wgd.row,
            size_x: size_x,
            size_y: size_y
        };

        var new_cells_occupied = this.get_cells_occupied(new_grid_data);

        var empty_cols = [];
        $.each(old_cells_occupied.cols, function(i, col) {
            if ($.inArray(col, new_cells_occupied.cols) === -1) {
                empty_cols.push(col);
            }
        });

        var occupied_cols = [];
        $.each(new_cells_occupied.cols, function(i, col) {
            if ($.inArray(col, old_cells_occupied.cols) === -1) {
                occupied_cols.push(col);
            }
        });

        var empty_rows = [];
        $.each(old_cells_occupied.rows, function(i, row) {
            if ($.inArray(row, new_cells_occupied.rows) === -1) {
                empty_rows.push(row);
            }
        });

        var occupied_rows = [];
        $.each(new_cells_occupied.rows, function(i, row) {
            if ($.inArray(row, old_cells_occupied.rows) === -1) {
                occupied_rows.push(row);
            }
        });

        this.remove_from_gridmap(wgd);

        if (occupied_cols.length) {
            var cols_to_empty = [
                new_col, wgd.row, size_x, Math.min(old_size_y, size_y), $widget
            ];
            this.empty_cells.apply(this, cols_to_empty);
        }

        if (occupied_rows.length) {
            var rows_to_empty = [new_col, wgd.row, size_x, size_y, $widget];
            this.empty_cells.apply(this, rows_to_empty);
        }

        wgd.col = new_col;
        wgd.size_x = size_x;
        wgd.size_y = size_y;
        this.add_to_gridmap(new_grid_data, $widget);

        //update coords instance attributes
        $widget.data('coords').update({
            width: (size_x * this.options.widget_base_dimensions[0] +
                ((size_x - 1) * this.options.widget_margins[0]) * 2),
            height: (size_y * this.options.widget_base_dimensions[1] +
                ((size_y - 1) * this.options.widget_margins[1]) * 2)
        });

        if (size_y > old_size_y) {
            this.add_faux_rows(size_y - old_size_y);
        }

        if (size_x > old_size_x) {
            this.add_faux_cols(size_x - old_size_x);
        }

        $widget.attr({
            'data-col': new_col,
            'data-sizex': size_x,
            'data-sizey': size_y
        });

        if (empty_cols.length) {
            var cols_to_remove_holes = [
                empty_cols[0], wgd.row,
                empty_cols.length,
                Math.min(old_size_y, size_y),
                $widget
            ];

            this.remove_empty_cells.apply(this, cols_to_remove_holes);
        }

        if (empty_rows.length) {
            var rows_to_remove_holes = [
                new_col, wgd.row, size_x, size_y, $widget
            ];
            this.remove_empty_cells.apply(this, rows_to_remove_holes);
        }

        return $widget;
    };

    /**
    * Move down widgets in cells represented by the arguments col, row, size_x,
    * size_y
    *
    * @method empty_cells
    * @param {Number} col The column where the group of cells begin.
    * @param {Number} row The row where the group of cells begin.
    * @param {Number} size_x The number of columns that the group of cells
    * occupy.
    * @param {Number} size_y The number of rows that the group of cells
    * occupy.
    * @param {HTMLElement} $exclude Exclude widgets from being moved.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.empty_cells = function(col, row, size_x, size_y, $exclude) {
        var $nexts = this.widgets_below({
                col: col,
                row: row - size_y,
                size_x: size_x,
                size_y: size_y
            });

        $nexts.not($exclude).each($.proxy(function(i, w) {
            var wgd = $(w).coords().grid;
            if (!(wgd.row <= (row + size_y - 1))) { return; }
            var diff =  (row + size_y) - wgd.row;
            this.move_widget_down($(w), diff);
        }, this));

        this.set_dom_grid_height();

        return this;
    };


    /**
    * Move up widgets below cells represented by the arguments col, row, size_x,
    * size_y.
    *
    * @method remove_empty_cells
    * @param {Number} col The column where the group of cells begin.
    * @param {Number} row The row where the group of cells begin.
    * @param {Number} size_x The number of columns that the group of cells
    * occupy.
    * @param {Number} size_y The number of rows that the group of cells
    * occupy.
    * @param {HTMLElement} $exclude Exclude widgets from being moved.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.remove_empty_cells = function(col, row, size_x, size_y, exclude) {
        var $nexts = this.widgets_below({
            col: col,
            row: row,
            size_x: size_x,
            size_y: size_y
        });

        $nexts.not(exclude).each($.proxy(function(i, widget) {
            this.move_widget_up( $(widget), size_y );
        }, this));

        this.set_dom_grid_height();

        return this;
    };


    /**
    * Get the most left column below to add a new widget.
    *
    * @method next_position
    * @param {Number} size_x The nº of rows the widget occupies horizontally.
    * @param {Number} size_y The nº of columns the widget occupies vertically.
    * @return {Object} Returns a grid coords object representing the future
    *  widget coords.
    */
    fn.next_position = function(size_x, size_y) {
        size_x || (size_x = 1);
        size_y || (size_y = 1);
        var ga = this.gridmap;
        var cols_l = ga.length;
        var valid_pos = [];
        var rows_l;

        for (var c = 1; c < cols_l; c++) {
            rows_l = ga[c].length;
            for (var r = 1; r <= rows_l; r++) {
                var can_move_to = this.can_move_to({
                    size_x: size_x,
                    size_y: size_y
                }, c, r);

                if (can_move_to) {
                    valid_pos.push({
                        col: c,
                        row: r,
                        size_y: size_y,
                        size_x: size_x
                    });
                }
            }
        }

        if (valid_pos.length) {
            return this.sort_by_row_and_col_asc(valid_pos)[0];
        }
        return false;
    };


    /**
    * Remove a widget from the grid.
    *
    * @method remove_widget
    * @param {HTMLElement} el The jQuery wrapped HTMLElement you want to remove.
    * @param {Boolean|Function} silent If true, widgets below the removed one
    * will not move up. If a Function is passed it will be used as callback.
    * @param {Function} callback Function executed when the widget is removed.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.remove_widget = function(el, silent, callback) {
        var $el = el instanceof jQuery ? el : $(el);
        var wgd = $el.coords().grid;

        // if silent is a function assume it's a callback
        if ($.isFunction(silent)) {
            callback = silent;
            silent = false;
        }

        this.cells_occupied_by_placeholder = {};
        this.$widgets = this.$widgets.not($el);

        var $nexts = this.widgets_below($el);

        this.remove_from_gridmap(wgd);

        $el.fadeOut($.proxy(function() {
            $el.remove();

            if (!silent) {
                $nexts.each($.proxy(function(i, widget) {
                    this.move_widget_up( $(widget), wgd.size_y );
                }, this));
            }

            this.set_dom_grid_height();

            if (callback) {
                callback.call(this, el);
            }
        }, this));
    };


    /**
    * Remove all widgets from the grid.
    *
    * @method remove_all_widgets
    * @param {Function} callback Function executed for each widget removed.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.remove_all_widgets = function(callback) {
        this.$widgets.each($.proxy(function(i, el){
              this.remove_widget(el, true, callback);
        }, this));

        return this;
    };


    /**
    * Returns a serialized array of the widgets in the grid.
    *
    * @method serialize
    * @param {HTMLElement} [$widgets] The collection of jQuery wrapped
    *  HTMLElements you want to serialize. If no argument is passed all widgets
    *  will be serialized.
    * @return {Array} Returns an Array of Objects with the data specified in
    *  the serialize_params option.
    */
    fn.serialize = function($widgets) {
        $widgets || ($widgets = this.$widgets);
        var result = [];
        $widgets.each($.proxy(function(i, widget) {
            result.push(this.options.serialize_params(
                $(widget), $(widget).coords().grid ) );
        }, this));

        return result;
    };


    /**
    * Returns a serialized array of the widgets that have changed their
    *  position.
    *
    * @method serialize_changed
    * @return {Array} Returns an Array of Objects with the data specified in
    *  the serialize_params option.
    */
    fn.serialize_changed = function() {
        return this.serialize(this.$changed);
    };


    /**
    * Creates the grid coords object representing the widget a add it to the
    * mapped array of positions.
    *
    * @method register_widget
    * @return {Array} Returns the instance of the Gridster class.
    */
    fn.register_widget = function($el) {

        var wgd = {
            'col': parseInt($el.attr('data-col'), 10),
            'row': parseInt($el.attr('data-row'), 10),
            'size_x': parseInt($el.attr('data-sizex'), 10),
            'size_y': parseInt($el.attr('data-sizey'), 10),
            'el': $el
        };

        if (this.options.avoid_overlapped_widgets &&
            !this.can_move_to(
             {size_x: wgd.size_x, size_y: wgd.size_y}, wgd.col, wgd.row)
        ) {
            wgd = this.next_position(wgd.size_x, wgd.size_y);
            wgd.el = $el;
            $el.attr({
                'data-col': wgd.col,
                'data-row': wgd.row,
                'data-sizex': wgd.size_x,
                'data-sizey': wgd.size_y
            });
        }

        // attach Coord object to player data-coord attribute
        $el.data('coords', $el.coords());

        // Extend Coord object with grid position info
        $el.data('coords').grid = wgd;

        this.add_to_gridmap(wgd, $el);

        return this;
    };


    /**
    * Update in the mapped array of positions the value of cells represented by
    * the grid coords object passed in the `grid_data` param.
    *
    * @param {Object} grid_data The grid coords object representing the cells
    *  to update in the mapped array.
    * @param {HTMLElement|Boolean} value Pass `false` or the jQuery wrapped
    *  HTMLElement, depends if you want to delete an existing position or add
    *  a new one.
    * @method update_widget_position
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.update_widget_position = function(grid_data, value) {
        this.for_each_cell_occupied(grid_data, function(col, row) {
            if (!this.gridmap[col]) { return this; }
            this.gridmap[col][row] = value;
        });
        return this;
    };


    /**
    * Remove a widget from the mapped array of positions.
    *
    * @method remove_from_gridmap
    * @param {Object} grid_data The grid coords object representing the cells
    *  to update in the mapped array.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.remove_from_gridmap = function(grid_data) {
        return this.update_widget_position(grid_data, false);
    };


    /**
    * Add a widget to the mapped array of positions.
    *
    * @method add_to_gridmap
    * @param {Object} grid_data The grid coords object representing the cells
    *  to update in the mapped array.
    * @param {HTMLElement|Boolean} value The value to set in the specified
    *  position .
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.add_to_gridmap = function(grid_data, value) {
        this.update_widget_position(grid_data, value || grid_data.el);

        if (grid_data.el) {
            var $widgets = this.widgets_below(grid_data.el);
            $widgets.each($.proxy(function(i, widget) {
                this.move_widget_up( $(widget));
            }, this));
        }
    };


    /**
    * Make widgets draggable.
    *
    * @uses Draggable
    * @method draggable
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.draggable = function() {
        var self = this;

        var draggable_options = $.extend(true, {}, this.options.draggable, {
            offset_left: this.options.widget_margins[0],
            start: function(event, ui) {
                self.$widgets.filter('.player-revert')
                    .removeClass('player-revert');

                self.$player = $(this);
                self.$helper = self.options.draggable.helper === 'clone' ?
                    $(ui.helper) : self.$player;
                self.helper = !self.$helper.is(self.$player);

                self.on_start_drag.call(self, event, ui);
                self.$el.trigger('gridster:dragstart');
            },
            stop: function(event, ui) {
                self.on_stop_drag.call(self, event, ui);
                self.$el.trigger('gridster:dragstop');
            },
            drag: throttle(function(event, ui) {
                self.on_drag.call(self, event, ui);
                self.$el.trigger('gridster:drag');
            }, 60)
          });

        this.drag_api = this.$el.drag(draggable_options).data('drag');
        return this;
    };


    /**
    * This function is executed when the player begins to be dragged.
    *
    * @method on_start_drag
    * @param {Event} The original browser event
    * @param {Object} A prepared ui object.
    */
    fn.on_start_drag = function(event, ui) {

        this.$helper.add(this.$player).add(this.$wrapper).addClass('dragging');

        this.$player.addClass('player');
        this.player_grid_data = this.$player.coords().grid;
        this.placeholder_grid_data = $.extend({}, this.player_grid_data);

        //set new grid height along the dragging period
        this.$el.css('height', this.$el.height() +
          (this.player_grid_data.size_y * this.min_widget_height));

        var colliders = this.faux_grid;
        var coords = this.$player.data('coords').coords;

        this.cells_occupied_by_player = this.get_cells_occupied(
            this.player_grid_data);
        this.cells_occupied_by_placeholder = this.get_cells_occupied(
            this.placeholder_grid_data);

        this.last_cols = [];
        this.last_rows = [];


        // see jquery.collision.js
        this.collision_api = this.$helper.collision(
            colliders, this.options.collision);

        this.$preview_holder = $('<li />', {
              'class': 'preview-holder',
              'data-row': this.$player.attr('data-row'),
              'data-col': this.$player.attr('data-col'),
              css: {
                  width: coords.width,
                  height: coords.height
              }
        }).appendTo(this.$el);

        if (this.options.draggable.start) {
          this.options.draggable.start.call(this, event, ui);
        }
    };


    /**
    * This function is executed when the player is being dragged.
    *
    * @method on_drag
    * @param {Event} The original browser event
    * @param {Object} A prepared ui object.
    */
    fn.on_drag = function(event, ui) {
        //break if dragstop has been fired
        if (this.$player === null) {
            return false;
        }

        var abs_offset = {
            left: ui.position.left + this.baseX,
            top: ui.position.top + this.baseY
        };

        this.colliders_data = this.collision_api.get_closest_colliders(
            abs_offset);

        this.on_overlapped_column_change(
            this.on_start_overlapping_column,
            this.on_stop_overlapping_column
        );

        this.on_overlapped_row_change(
            this.on_start_overlapping_row,
            this.on_stop_overlapping_row
        );

        if (this.helper && this.$player) {
            this.$player.css({
                'left': ui.position.left,
                'top': ui.position.top
            });
        }

        if (this.options.draggable.drag) {
            this.options.draggable.drag.call(this, event, ui);
        }
    };

    /**
    * This function is executed when the player stops being dragged.
    *
    * @method on_stop_drag
    * @param {Event} The original browser event
    * @param {Object} A prepared ui object.
    */
    fn.on_stop_drag = function(event, ui) {
        this.$helper.add(this.$player).add(this.$wrapper)
            .removeClass('dragging');

        ui.position.left = ui.position.left + this.baseX;
        ui.position.top = ui.position.top + this.baseY;
        this.colliders_data = this.collision_api.get_closest_colliders(ui.position);

        this.on_overlapped_column_change(
            this.on_start_overlapping_column,
            this.on_stop_overlapping_column
        );

        this.on_overlapped_row_change(
            this.on_start_overlapping_row,
            this.on_stop_overlapping_row
        );

        this.$player.addClass('player-revert').removeClass('player')
            .attr({
                'data-col': this.placeholder_grid_data.col,
                'data-row': this.placeholder_grid_data.row
            }).css({
                'left': '',
                'top': ''
            });

        this.$changed = this.$changed.add(this.$player);

        this.cells_occupied_by_player = this.get_cells_occupied(
            this.placeholder_grid_data);
        this.set_cells_player_occupies(
            this.placeholder_grid_data.col, this.placeholder_grid_data.row);

        this.$player.coords().grid.row = this.placeholder_grid_data.row;
        this.$player.coords().grid.col = this.placeholder_grid_data.col;

        if (this.options.draggable.stop) {
          this.options.draggable.stop.call(this, event, ui);
        }

        this.$preview_holder.remove();

        this.$player = null;
        this.$helper = null;
        this.placeholder_grid_data = {};
        this.player_grid_data = {};
        this.cells_occupied_by_placeholder = {};
        this.cells_occupied_by_player = {};

        this.set_dom_grid_height();
    };


    /**
    * Executes the callbacks passed as arguments when a column begins to be
    * overlapped or stops being overlapped.
    *
    * @param {Function} start_callback Function executed when a new column
    *  begins to be overlapped. The column is passed as first argument.
    * @param {Function} stop_callback Function executed when a column stops
    *  being overlapped. The column is passed as first argument.
    * @method on_overlapped_column_change
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.on_overlapped_column_change = function(start_callback, stop_callback) {
        if (!this.colliders_data.length) {
            return;
        }
        var cols = this.get_targeted_columns(
            this.colliders_data[0].el.data.col);

        var last_n_cols = this.last_cols.length;
        var n_cols = cols.length;
        var i;

        for (i = 0; i < n_cols; i++) {
            if ($.inArray(cols[i], this.last_cols) === -1) {
                (start_callback || $.noop).call(this, cols[i]);
            }
        }

        for (i = 0; i< last_n_cols; i++) {
            if ($.inArray(this.last_cols[i], cols) === -1) {
                (stop_callback || $.noop).call(this, this.last_cols[i]);
            }
        }

        this.last_cols = cols;

        return this;
    };


    /**
    * Executes the callbacks passed as arguments when a row starts to be
    * overlapped or stops being overlapped.
    *
    * @param {Function} start_callback Function executed when a new row begins
    *  to be overlapped. The row is passed as first argument.
    * @param {Function} stop_callback Function executed when a row stops being
    *  overlapped. The row is passed as first argument.
    * @method on_overlapped_row_change
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.on_overlapped_row_change = function(start_callback, end_callback) {
        if (!this.colliders_data.length) {
            return;
        }
        var rows = this.get_targeted_rows(this.colliders_data[0].el.data.row);
        var last_n_rows = this.last_rows.length;
        var n_rows = rows.length;
        var i;

        for (i = 0; i < n_rows; i++) {
            if ($.inArray(rows[i], this.last_rows) === -1) {
                (start_callback || $.noop).call(this, rows[i]);
            }
        }

        for (i = 0; i < last_n_rows; i++) {
            if ($.inArray(this.last_rows[i], rows) === -1) {
                (end_callback || $.noop).call(this, this.last_rows[i]);
            }
        }

        this.last_rows = rows;
    };


    /**
    * Sets the current position of the player
    *
    * @param {Function} start_callback Function executed when a new row begins
    *  to be overlapped. The row is passed as first argument.
    * @param {Function} stop_callback Function executed when a row stops being
    *  overlapped. The row is passed as first argument.
    * @method set_player
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.set_player = function(col, row, no_player) {
        var self = this;
        if (!no_player) {
            this.empty_cells_player_occupies();
        }
        var cell = !no_player ? self.colliders_data[0].el.data : {col: col};
        var to_col = cell.col;
        var to_row = row || cell.row;

        this.player_grid_data = {
            col: to_col,
            row: to_row,
            size_y : this.player_grid_data.size_y,
            size_x : this.player_grid_data.size_x
        };

        this.cells_occupied_by_player = this.get_cells_occupied(
            this.player_grid_data);

        var $overlapped_widgets = this.get_widgets_overlapped(
            this.player_grid_data);

        var constraints = this.widgets_constraints($overlapped_widgets);

        this.manage_movements(constraints.can_go_up, to_col, to_row);
        this.manage_movements(constraints.can_not_go_up, to_col, to_row);

        /* if there is not widgets overlapping in the new player position,
         * update the new placeholder position. */
        if (!$overlapped_widgets.length) {
            var pp = this.can_go_player_up(this.player_grid_data);
            if (pp !== false) {
                to_row = pp;
            }
            this.set_placeholder(to_col, to_row);
        }

        return {
            col: to_col,
            row: to_row
        };
    };


    /**
    * See which of the widgets in the $widgets param collection can go to
    * a upper row and which not.
    *
    * @method widgets_contraints
    * @param {HTMLElements} $widgets A jQuery wrapped collection of
    * HTMLElements.
    * @return {Array} Returns a literal Object with two keys: `can_go_up` &
    * `can_not_go_up`. Each contains a set of HTMLElements.
    */
    fn.widgets_constraints = function($widgets) {
        var $widgets_can_go_up = $([]);
        var $widgets_can_not_go_up;
        var wgd_can_go_up = [];
        var wgd_can_not_go_up = [];

        $widgets.each($.proxy(function(i, w) {
            var $w = $(w);
            var wgd = $w.coords().grid;
            if (this.can_go_widget_up(wgd)) {
                $widgets_can_go_up = $widgets_can_go_up.add($w);
                wgd_can_go_up.push(wgd);
            }else{
                wgd_can_not_go_up.push(wgd);
            }
        }, this));

        $widgets_can_not_go_up = $widgets.not($widgets_can_go_up);

        return {
            can_go_up: this.sort_by_row_asc(wgd_can_go_up),
            can_not_go_up: this.sort_by_row_desc(wgd_can_not_go_up)
        };
    };


    /**
    * Sorts an Array of grid coords objects (representing the grid coords of
    * each widget) in ascending way.
    *
    * @method sort_by_row_asc
    * @param {Array} widgets Array of grid coords objects
    * @return {Array} Returns the array sorted.
    */
    fn.sort_by_row_asc = function(widgets) {
        widgets = widgets.sort(function(a, b) {
            if (!a.row) {
                a = $(a).coords().grid;
                b = $(b).coords().grid;
            }

           if (a.row > b.row) {
               return 1;
           }
           return -1;
        });

        return widgets;
    };


    /**
    * Sorts an Array of grid coords objects (representing the grid coords of
    * each widget) placing first the empty cells upper left.
    *
    * @method sort_by_row_and_col_asc
    * @param {Array} widgets Array of grid coords objects
    * @return {Array} Returns the array sorted.
    */
    fn.sort_by_row_and_col_asc = function(widgets) {
        widgets = widgets.sort(function(a, b) {
           if (a.row > b.row || a.row === b.row && a.col > b.col) {
               return 1;
           }
           return -1;
        });

        return widgets;
    };


    /**
    * Sorts an Array of grid coords objects by column (representing the grid
    * coords of each widget) in ascending way.
    *
    * @method sort_by_col_asc
    * @param {Array} widgets Array of grid coords objects
    * @return {Array} Returns the array sorted.
    */
    fn.sort_by_col_asc = function(widgets) {
        widgets = widgets.sort(function(a, b) {
           if (a.col > b.col) {
               return 1;
           }
           return -1;
        });

        return widgets;
    };


    /**
    * Sorts an Array of grid coords objects (representing the grid coords of
    * each widget) in descending way.
    *
    * @method sort_by_row_desc
    * @param {Array} widgets Array of grid coords objects
    * @return {Array} Returns the array sorted.
    */
    fn.sort_by_row_desc = function(widgets) {
        widgets = widgets.sort(function(a, b) {
            if (a.row + a.size_y < b.row + b.size_y) {
                return 1;
            }
           return -1;
        });
        return widgets;
    };


    /**
    * Sorts an Array of grid coords objects (representing the grid coords of
    * each widget) in descending way.
    *
    * @method manage_movements
    * @param {HTMLElements} $widgets A jQuery collection of HTMLElements
    *  representing the widgets you want to move.
    * @param {Number} to_col The column to which we want to move the widgets.
    * @param {Number} to_row The row to which we want to move the widgets.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.manage_movements = function($widgets, to_col, to_row) {
        $.each($widgets, $.proxy(function(i, w) {
            var wgd = w;
            var $w = wgd.el;

            var can_go_widget_up = this.can_go_widget_up(wgd);

            if (can_go_widget_up) {
                //target CAN go up
                //so move widget up
                this.move_widget_to($w, can_go_widget_up);
                this.set_placeholder(to_col, can_go_widget_up + wgd.size_y);

            } else {
                //target can't go up
                var can_go_player_up = this.can_go_player_up(
                    this.player_grid_data);

                if (!can_go_player_up) {
                    // target can't go up
                    // player cant't go up
                    // so we need to move widget down to a position that dont
                    // overlaps player
                    var y = (to_row + this.player_grid_data.size_y) - wgd.row;

                    this.move_widget_down($w, y);
                    this.set_placeholder(to_col, to_row);
                }
            }
        }, this));

        return this;
    };

    /**
    * Determines if there is a widget in the row and col given. Or if the
    * HTMLElement passed as first argument is the player.
    *
    * @method is_player
    * @param {Number|HTMLElement} col_or_el A jQuery wrapped collection of
    * HTMLElements.
    * @param {Number} [row] The column to which we want to move the widgets.
    * @return {Boolean} Returns true or false.
    */
    fn.is_player = function(col_or_el, row) {
        if (row && !this.gridmap[col_or_el]) { return false; }
        var $w = row ? this.gridmap[col_or_el][row] : col_or_el;
        return $w && ($w.is(this.$player) || $w.is(this.$helper));
    };


    /**
    * Determines if the widget that is being dragged is currently over the row
    * and col given.
    *
    * @method is_player_in
    * @param {Number} col The column to check.
    * @param {Number} row The row to check.
    * @return {Boolean} Returns true or false.
    */
    fn.is_player_in = function(col, row) {
        var c = this.cells_occupied_by_player || {};
        return $.inArray(col, c.cols) >= 0 && $.inArray(row, c.rows) >= 0;
    };


    /**
    * Determines if the placeholder is currently over the row and col given.
    *
    * @method is_placeholder_in
    * @param {Number} col The column to check.
    * @param {Number} row The row to check.
    * @return {Boolean} Returns true or false.
    */
    fn.is_placeholder_in = function(col, row) {
        var c = this.cells_occupied_by_placeholder || {};
        return this.is_placeholder_in_col(col) && $.inArray(row, c.rows) >= 0;
    };


    /**
    * Determines if the placeholder is currently over the column given.
    *
    * @method is_placeholder_in_col
    * @param {Number} col The column to check.
    * @return {Boolean} Returns true or false.
    */
    fn.is_placeholder_in_col = function(col) {
        var c = this.cells_occupied_by_placeholder || [];
        return $.inArray(col, c.cols) >= 0;
    };


    /**
    * Determines if the cell represented by col and row params is empty.
    *
    * @method is_empty
    * @param {Number} col The column to check.
    * @param {Number} row The row to check.
    * @return {Boolean} Returns true or false.
    */
    fn.is_empty = function(col, row) {
        if (typeof this.gridmap[col] !== 'undefined' &&
            typeof this.gridmap[col][row] !== 'undefined' &&
            this.gridmap[col][row] === false
        ) {
            return true;
        }
        return false;
    };


    /**
    * Determines if the cell represented by col and row params is occupied.
    *
    * @method is_occupied
    * @param {Number} col The column to check.
    * @param {Number} row The row to check.
    * @return {Boolean} Returns true or false.
    */
    fn.is_occupied = function(col, row) {
        if (!this.gridmap[col]) {
            return false;
        }

        if (this.gridmap[col][row]) {
            return true;
        }
        return false;
    };


    /**
    * Determines if there is a widget in the cell represented by col/row params.
    *
    * @method is_widget
    * @param {Number} col The column to check.
    * @param {Number} row The row to check.
    * @return {Boolean|HTMLElement} Returns false if there is no widget,
    * else returns the jQuery HTMLElement
    */
    fn.is_widget = function(col, row) {
        var cell = this.gridmap[col];
        if (!cell) {
            return false;
        }

        cell = cell[row];

        if (cell) {
            return cell;
        }

        return false;
    };


    /**
    * Determines if there is a widget in the cell represented by col/row
    * params and if this is under the widget that is being dragged.
    *
    * @method is_widget_under_player
    * @param {Number} col The column to check.
    * @param {Number} row The row to check.
    * @return {Boolean} Returns true or false.
    */
    fn.is_widget_under_player = function(col, row) {
        if (this.is_widget(col, row)) {
            return this.is_player_in(col, row);
        }
        return false;
    };


    /**
    * Get widgets overlapping with the player or with the object passed
    * representing the grid cells.
    *
    * @method get_widgets_under_player
    * @return {HTMLElement} Returns a jQuery collection of HTMLElements
    */
    fn.get_widgets_under_player = function(cells) {
        cells || (cells = this.cells_occupied_by_player || {cols: [], rows: []});
        var $widgets = $([]);

        $.each(cells.cols, $.proxy(function(i, col) {
            $.each(cells.rows, $.proxy(function(i, row) {
                if(this.is_widget(col, row)) {
                    $widgets = $widgets.add(this.gridmap[col][row]);
                }
            }, this));
        }, this));

        return $widgets;
    };


    /**
    * Put placeholder at the row and column specified.
    *
    * @method set_placeholder
    * @param {Number} col The column to which we want to move the
    *  placeholder.
    * @param {Number} row The row to which we want to move the
    *  placeholder.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.set_placeholder = function(col, row) {
        var phgd = $.extend({}, this.placeholder_grid_data);
        var $nexts = this.widgets_below({
                col: phgd.col,
                row: phgd.row,
                size_y: phgd.size_y,
                size_x: phgd.size_x
            });

        // Prevents widgets go out of the grid
        var right_col = (col + phgd.size_x - 1);
        if (right_col > this.cols) {
            col = col - (right_col - col);
        }

        var moved_down = this.placeholder_grid_data.row < row;
        var changed_column = this.placeholder_grid_data.col !== col;

        this.placeholder_grid_data.col = col;
        this.placeholder_grid_data.row = row;

        this.cells_occupied_by_placeholder = this.get_cells_occupied(
            this.placeholder_grid_data);

        this.$preview_holder.attr({
            'data-row' : row,
            'data-col' : col
        });

        if (moved_down || changed_column) {
            $nexts.each($.proxy(function(i, widget) {
                this.move_widget_up(
                 $(widget), this.placeholder_grid_data.col - col + phgd.size_y);
            }, this));
        }


        var $widgets_under_ph = this.get_widgets_under_player(this.cells_occupied_by_placeholder);
        if ($widgets_under_ph.length) {
            $widgets_under_ph.each($.proxy(function(i, widget) {
                var $w = $(widget);
                this.move_widget_down(
                 $w, row + phgd.size_y - $w.data('coords').grid.row);
            }, this));
        }

    };


    /**
    * Determines whether the player can move to a position above.
    *
    * @method can_go_player_up
    * @param {Object} widget_grid_data The actual grid coords object of the
    *  player.
    * @return {Number|Boolean} If the player can be moved to an upper row
    *  returns the row number, else returns false.
    */
    fn.can_go_player_up = function(widget_grid_data) {
        var p_bottom_row = widget_grid_data.row + widget_grid_data.size_y - 1;
        var result = true;
        var upper_rows = [];
        var min_row = 10000;
        var $widgets_under_player = this.get_widgets_under_player();

        /* generate an array with columns as index and array with upper rows
         * empty as value */
        this.for_each_column_occupied(widget_grid_data, function(tcol) {
            var grid_col = this.gridmap[tcol];
            var r = p_bottom_row + 1;
            upper_rows[tcol] = [];

            while (--r > 0) {
                if (this.is_empty(tcol, r) || this.is_player(tcol, r) ||
                    this.is_widget(tcol, r) &&
                    grid_col[r].is($widgets_under_player)
                ) {
                    upper_rows[tcol].push(r);
                    min_row = r < min_row ? r : min_row;
                }else{
                    break;
                }
            }

            if (upper_rows[tcol].length === 0) {
                result = false;
                return true; //break
            }

            upper_rows[tcol].sort();
        });

        if (!result) { return false; }

        return this.get_valid_rows(widget_grid_data, upper_rows, min_row);
    };


    /**
    * Determines whether a widget can move to a position above.
    *
    * @method can_go_widget_up
    * @param {Object} widget_grid_data The actual grid coords object of the
    *  widget we want to check.
    * @return {Number|Boolean} If the widget can be moved to an upper row
    *  returns the row number, else returns false.
    */
    fn.can_go_widget_up = function(widget_grid_data) {
        var p_bottom_row = widget_grid_data.row + widget_grid_data.size_y - 1;
        var result = true;
        var upper_rows = [];
        var min_row = 10000;

        /* generate an array with columns as index and array with topmost rows
         * empty as value */
        this.for_each_column_occupied(widget_grid_data, function(tcol) {
            var grid_col = this.gridmap[tcol];
            upper_rows[tcol] = [];

            var r = p_bottom_row + 1;
            // iterate over each row
            while (--r > 0) {
                if (this.is_widget(tcol, r) && !this.is_player_in(tcol, r)) {
                    if (!grid_col[r].is(widget_grid_data.el)) {
                        break;
                    }
                }

                if (!this.is_player(tcol, r) &&
                    !this.is_placeholder_in(tcol, r) &&
                    !this.is_player_in(tcol, r)) {
                    upper_rows[tcol].push(r);
                }

                if (r < min_row) {
                    min_row = r;
                }
            }

            if (upper_rows[tcol].length === 0) {
                result = false;
                return true; //break
            }

            upper_rows[tcol].sort();
        });

        if (!result) { return false; }

        return this.get_valid_rows(widget_grid_data, upper_rows, min_row);
    };


    /**
    * Search a valid row for the widget represented by `widget_grid_data' in
    * the `upper_rows` array. Iteration starts from row specified in `min_row`.
    *
    * @method get_valid_rows
    * @param {Object} widget_grid_data The actual grid coords object of the
    *  player.
    * @param {Array} upper_rows An array with columns as index and arrays
    *  of valid rows as values.
    * @param {Number} min_row The upper row from which the iteration will start.
    * @return {Number|Boolean} Returns the upper row valid from the `upper_rows`
    *  for the widget in question.
    */
    fn.get_valid_rows = function(widget_grid_data, upper_rows, min_row) {
        var p_top_row = widget_grid_data.row;
        var p_bottom_row = widget_grid_data.row + widget_grid_data.size_y - 1;
        var size_y = widget_grid_data.size_y;
        var r = min_row - 1;
        var valid_rows = [];

        while (++r <= p_bottom_row ) {
            var common = true;
            $.each(upper_rows, function(col, rows) {
                if ($.isArray(rows) && $.inArray(r, rows) === -1) {
                    common = false;
                }
            });

            if (common === true) {
                valid_rows.push(r);
                if (valid_rows.length === size_y) {
                    break;
                }
            }
        }

        var new_row = false;
        if (size_y === 1) {
            if (valid_rows[0] !== p_top_row) {
                new_row = valid_rows[0] || false;
            }
        }else{
            if (valid_rows[0] !== p_top_row) {
                new_row = this.get_consecutive_numbers_index(
                    valid_rows, size_y);
            }
        }

        return new_row;
    };


    fn.get_consecutive_numbers_index = function(arr, size_y) {
        var max = arr.length;
        var result = [];
        var first = true;
        var prev = -1; // or null?

        for (var i=0; i < max; i++) {
            if (first || arr[i] === prev + 1) {
                result.push(i);
                if (result.length === size_y) {
                    break;
                }
                first = false;
            }else{
                result = [];
                first = true;
            }

            prev = arr[i];
        }

        return result.length >= size_y ? arr[result[0]] : false;
    };


    /**
    * Get widgets overlapping with the player.
    *
    * @method get_widgets_overlapped
    * @return {HTMLElements} Returns a jQuery collection of HTMLElements.
    */
    fn.get_widgets_overlapped = function() {
        var $w;
        var $widgets = $([]);
        var used = [];
        var rows_from_bottom = this.cells_occupied_by_player.rows.slice(0);
        rows_from_bottom.reverse();

        $.each(this.cells_occupied_by_player.cols, $.proxy(function(i, col) {
            $.each(rows_from_bottom, $.proxy(function(i, row) {
                // if there is a widget in the player position
                if (!this.gridmap[col]) { return true; } //next iteration
                var $w = this.gridmap[col][row];
                if (this.is_occupied(col, row) && !this.is_player($w) &&
                    $.inArray($w, used) === -1
                ) {
                    $widgets = $widgets.add($w);
                    used.push($w);
                }

            }, this));
        }, this));

        return $widgets;
    };


    /**
    * This callback is executed when the player begins to collide with a column.
    *
    * @method on_start_overlapping_column
    * @param {Number} col The collided column.
    * @return {HTMLElements} Returns a jQuery collection of HTMLElements.
    */
    fn.on_start_overlapping_column = function(col) {
        this.set_player(col, false);
    };


    /**
    * A callback executed when the player begins to collide with a row.
    *
    * @method on_start_overlapping_row
    * @param {Number} col The collided row.
    * @return {HTMLElements} Returns a jQuery collection of HTMLElements.
    */
    fn.on_start_overlapping_row = function(row) {
        this.set_player(false, row);
    };


    /**
    * A callback executed when the the player ends to collide with a column.
    *
    * @method on_stop_overlapping_column
    * @param {Number} col The collided row.
    * @return {HTMLElements} Returns a jQuery collection of HTMLElements.
    */
    fn.on_stop_overlapping_column = function(col) {
        this.set_player(col, false);

        var self = this;
        this.for_each_widget_below(col, this.cells_occupied_by_player.rows[0],
            function(tcol, trow) {
                self.move_widget_up(this, self.player_grid_data.size_y);
        });
    };


    /**
    * This callback is executed when the player ends to collide with a row.
    *
    * @method on_stop_overlapping_row
    * @param {Number} row The collided row.
    * @return {HTMLElements} Returns a jQuery collection of HTMLElements.
    */
    fn.on_stop_overlapping_row = function(row) {
        this.set_player(false, row);

        var self = this;
        var cols = this.cells_occupied_by_player.cols;
        for (var c = 0, cl = cols.length; c < cl; c++) {
            this.for_each_widget_below(cols[c], row, function(tcol, trow) {
                self.move_widget_up(this, self.player_grid_data.size_y);
            });
        }
    };


    /**
    * Move a widget to a specific row. The cell or cells must be empty.
    * If the widget has widgets below, all of these widgets will be moved also
    * if they can.
    *
    * @method move_widget_to
    * @param {HTMLElement} $widget The jQuery wrapped HTMLElement of the
    * widget is going to be moved.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.move_widget_to = function($widget, row) {
        var self = this;
        var widget_grid_data = $widget.coords().grid;
        var diff = row - widget_grid_data.row;
        var $next_widgets = this.widgets_below($widget);

        var can_move_to_new_cell = this.can_move_to(
            widget_grid_data, widget_grid_data.col, row, $widget);

        if (can_move_to_new_cell === false) {
            return false;
        }

        this.remove_from_gridmap(widget_grid_data);
        widget_grid_data.row = row;
        this.add_to_gridmap(widget_grid_data);
        $widget.attr('data-row', row);
        this.$changed = this.$changed.add($widget);


        $next_widgets.each(function(i, widget) {
            var $w = $(widget);
            var wgd = $w.coords().grid;
            var can_go_up = self.can_go_widget_up(wgd);
            if (can_go_up && can_go_up !== wgd.row) {
                self.move_widget_to($w, can_go_up);
            }
        });

        return this;
    };


    /**
    * Move up the specified widget and all below it.
    *
    * @method move_widget_up
    * @param {HTMLElement} $widget The widget you want to move.
    * @param {Number} [y_units] The number of cells that the widget has to move.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.move_widget_up = function($widget, y_units) {
        var el_grid_data = $widget.coords().grid;
        var actual_row = el_grid_data.row;
        var moved = [];
        var can_go_up = true;
        y_units || (y_units = 1);

        if (!this.can_go_up($widget)) { return false; } //break;

        this.for_each_column_occupied(el_grid_data, function(col) {
            // can_go_up
            if ($.inArray($widget, moved) === -1) {
                var widget_grid_data = $widget.coords().grid;
                var next_row = actual_row - y_units;
                next_row = this.can_go_up_to_row(
                    widget_grid_data, col, next_row);

                if (!next_row) {
                    return true;
                }

                var $next_widgets = this.widgets_below($widget);

                this.remove_from_gridmap(widget_grid_data);
                widget_grid_data.row = next_row;
                this.add_to_gridmap(widget_grid_data);
                $widget.attr('data-row', widget_grid_data.row);
                this.$changed = this.$changed.add($widget);

                moved.push($widget);

                $next_widgets.each($.proxy(function(i, widget) {
                    this.move_widget_up($(widget), y_units);
                }, this));
            }
        });

    };


    /**
    * Move down the specified widget and all below it.
    *
    * @method move_widget_down
    * @param {HTMLElement} $widget The jQuery object representing the widget
    *  you want to move.
    * @param {Number} The number of cells that the widget has to move.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.move_widget_down = function($widget, y_units) {
        var el_grid_data = $widget.coords().grid;
        var actual_row = el_grid_data.row;
        var moved = [];
        var y_diff = y_units;

        if (!$widget) { return false; }

        if ($.inArray($widget, moved) === -1) {

            var widget_grid_data = $widget.coords().grid;
            var next_row = actual_row + y_units;
            var $next_widgets = this.widgets_below($widget);

            this.remove_from_gridmap(widget_grid_data);

            $next_widgets.each($.proxy(function(i, widget) {
                var $w = $(widget);
                var wd = $w.coords().grid;
                var tmp_y = this.displacement_diff(
                             wd, widget_grid_data, y_diff);

                if (tmp_y > 0) {
                    this.move_widget_down($w, tmp_y);
                }
            }, this));

            widget_grid_data.row = next_row;
            this.update_widget_position(widget_grid_data, $widget);
            $widget.attr('data-row', widget_grid_data.row);
            this.$changed = this.$changed.add($widget);

            moved.push($widget);
        }
    };


    /**
    * Check if the widget can move to the specified row, else returns the
    * upper row possible.
    *
    * @method can_go_up_to_row
    * @param {Number} widget_grid_data The current grid coords object of the
    *  widget.
    * @param {Number} col The target column.
    * @param {Number} row The target row.
    * @return {Boolean|Number} Returns the row number if the widget can move
    *  to the target position, else returns false.
    */
    fn.can_go_up_to_row = function(widget_grid_data, col, row) {
        var ga = this.gridmap;
        var result = true;
        var urc = []; // upper_rows_in_columns
        var actual_row = widget_grid_data.row;
        var r;

        /* generate an array with columns as index and array with
         * upper rows empty in the column */
        this.for_each_column_occupied(widget_grid_data, function(tcol) {
            var grid_col = ga[tcol];
            urc[tcol] = [];

            r = actual_row;
            while (r--) {
                if (this.is_empty(tcol, r) &&
                    !this.is_placeholder_in(tcol, r)
                ) {
                    urc[tcol].push(r);
                }else{
                    break;
                }
            }

            if (!urc[tcol].length) {
                result = false;
                return true;
            }

        });

        if (!result) { return false; }

        /* get common rows starting from upper position in all the columns
         * that widget occupies */
        r = row;
        for (r = 1; r < actual_row; r++) {
            var common = true;

            for (var uc = 0, ucl = urc.length; uc < ucl; uc++) {
                if (urc[uc] && $.inArray(r, urc[uc]) === -1) {
                    common = false;
                }
            }

            if (common === true) {
                result = r;
                break;
            }
        }

        return result;
    };


    fn.displacement_diff = function(widget_grid_data, parent_bgd, y_units) {
        var actual_row = widget_grid_data.row;
        var diffs = [];
        var parent_max_y = parent_bgd.row + parent_bgd.size_y;

        this.for_each_column_occupied(widget_grid_data, function(col) {
            var temp_y_units = 0;

            for (var r = parent_max_y; r < actual_row; r++) {
                if (this.is_empty(col, r)) {
                    temp_y_units = temp_y_units + 1;
                }
            }

            diffs.push(temp_y_units);
        });

        var max_diff = Math.max.apply(Math, diffs);
        y_units = (y_units - max_diff);

        return y_units > 0 ? y_units : 0;
    };


    /**
    * Get widgets below a widget.
    *
    * @method widgets_below
    * @param {HTMLElement} $el The jQuery wrapped HTMLElement.
    * @return {HTMLElements} A jQuery collection of HTMLElements.
    */
    fn.widgets_below = function($el) {
        var el_grid_data = $.isPlainObject($el) ? $el : $el.coords().grid;
        var self = this;
        var ga = this.gridmap;
        var next_row = el_grid_data.row + el_grid_data.size_y - 1;
        var $nexts = $([]);

        this.for_each_column_occupied(el_grid_data, function(col) {
            self.for_each_widget_below(col, next_row, function(tcol, trow) {
                if (!self.is_player(this) && $.inArray(this, $nexts) === -1) {
                    $nexts = $nexts.add(this);
                    return true; // break
                }
            });
        });

        return this.sort_by_row_asc($nexts);
    };


    /**
    * Update the array of mapped positions with the new player position.
    *
    * @method set_cells_player_occupies
    * @param {Number} col The new player col.
    * @param {Number} col The new player row.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.set_cells_player_occupies = function(col, row) {
        this.remove_from_gridmap(this.placeholder_grid_data);
        this.placeholder_grid_data.col = col;
        this.placeholder_grid_data.row = row;
        this.add_to_gridmap(this.placeholder_grid_data, this.$player);
        return this;
    };


    /**
    * Remove from the array of mapped positions the reference to the player.
    *
    * @method empty_cells_player_occupies
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.empty_cells_player_occupies = function() {
        this.remove_from_gridmap(this.placeholder_grid_data);
        return this;
    };


    fn.can_go_up = function($el) {
        var el_grid_data = $el.coords().grid;
        var initial_row = el_grid_data.row;
        var prev_row = initial_row - 1;
        var ga = this.gridmap;
        var upper_rows_by_column = [];

        var result = true;
        if (initial_row === 1) { return false; }

        this.for_each_column_occupied(el_grid_data, function(col) {
            var $w = this.is_widget(col, prev_row);

            if (this.is_occupied(col, prev_row) ||
                this.is_player(col, prev_row) ||
                this.is_placeholder_in(col, prev_row) ||
                this.is_player_in(col, prev_row)
            ) {
                result = false;
                return true; //break
            }
        });

        return result;
    };



    /**
    * Check if it's possible to move a widget to a specific col/row. It takes
    * into account the dimensions (`size_y` and `size_x` attrs. of the grid
    *  coords object) the widget occupies.
    *
    * @method can_move_to
    * @param {Object} widget_grid_data The grid coords object that represents
    *  the widget.
    * @param {Object} col The col to check.
    * @param {Object} row The row to check.
    * @param {Number} [max_row] The max row allowed.
    * @return {Boolean} Returns true if all cells are empty, else return false.
    */
    fn.can_move_to = function(widget_grid_data, col, row, max_row) {
        var ga = this.gridmap;
        var $w = widget_grid_data.el;
        var future_wd = {
            size_y: widget_grid_data.size_y,
            size_x: widget_grid_data.size_x,
            col: col,
            row: row
        };
        var result = true;

        //Prevents widgets go out of the grid
        var right_col = col + widget_grid_data.size_x - 1;
        if (right_col > this.cols) {
            return false;
        }

        if (max_row && max_row < row + widget_grid_data.size_y - 1) {
            return false;
        }

        this.for_each_cell_occupied(future_wd, function(tcol, trow) {
            var $tw = this.is_widget(tcol, trow);
            if ($tw && (!widget_grid_data.el || $tw.is($w))) {
                result = false;
            }
        });

        return result;
    };


    /**
    * Given the leftmost column returns all columns that are overlapping
    *  with the player.
    *
    * @method get_targeted_columns
    * @param {Number} [from_col] The leftmost column.
    * @return {Array} Returns an array with column numbers.
    */
    fn.get_targeted_columns = function(from_col) {
        var max = (from_col || this.player_grid_data.col) +
            (this.player_grid_data.size_x - 1);
        var cols = [];
        for (var col = from_col; col <= max; col++) {
            cols.push(col);
        }
        return cols;
    };


    /**
    * Given the upper row returns all rows that are overlapping with the player.
    *
    * @method get_targeted_rows
    * @param {Number} [from_row] The upper row.
    * @return {Array} Returns an array with row numbers.
    */
    fn.get_targeted_rows = function(from_row) {
        var max = (from_row || this.player_grid_data.row) +
            (this.player_grid_data.size_y - 1);
        var rows = [];
        for (var row = from_row; row <= max; row++) {
            rows.push(row);
        }
        return rows;
    };

    /**
    * Get all columns and rows that a widget occupies.
    *
    * @method get_cells_occupied
    * @param {Object} el_grid_data The grid coords object of the widget.
    * @return {Object} Returns an object like `{ cols: [], rows: []}`.
    */
    fn.get_cells_occupied = function(el_grid_data) {
        var cells = { cols: [], rows: []};
        var i;
        if (arguments[1] instanceof jQuery) {
            el_grid_data = arguments[1].coords().grid;
        }

        for (i = 0; i < el_grid_data.size_x; i++) {
            var col = el_grid_data.col + i;
            cells.cols.push(col);
        }

        for (i = 0; i < el_grid_data.size_y; i++) {
            var row = el_grid_data.row + i;
            cells.rows.push(row);
        }

        return cells;
    };


    /**
    * Iterate over the cells occupied by a widget executing a function for
    * each one.
    *
    * @method for_each_cell_occupied
    * @param {Object} el_grid_data The grid coords object that represents the
    *  widget.
    * @param {Function} callback The function to execute on each column
    *  iteration. Column and row are passed as arguments.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.for_each_cell_occupied = function(grid_data, callback) {
        this.for_each_column_occupied(grid_data, function(col) {
            this.for_each_row_occupied(grid_data, function(row) {
                callback.call(this, col, row);
            });
        });
        return this;
    };


    /**
    * Iterate over the columns occupied by a widget executing a function for
    * each one.
    *
    * @method for_each_column_occupied
    * @param {Object} el_grid_data The grid coords object that represents
    *  the widget.
    * @param {Function} callback The function to execute on each column
    *  iteration. The column number is passed as first argument.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.for_each_column_occupied = function(el_grid_data, callback) {
        for (var i = 0; i < el_grid_data.size_x; i++) {
            var col = el_grid_data.col + i;
            callback.call(this, col, el_grid_data);
        }
    };


    /**
    * Iterate over the rows occupied by a widget executing a function for
    * each one.
    *
    * @method for_each_row_occupied
    * @param {Object} el_grid_data The grid coords object that represents
    *  the widget.
    * @param {Function} callback The function to execute on each column
    *  iteration. The row number is passed as first argument.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.for_each_row_occupied = function(el_grid_data, callback) {
        for (var i = 0; i < el_grid_data.size_y; i++) {
            var row = el_grid_data.row + i;
            callback.call(this, row, el_grid_data);
        }
    };



    fn._traversing_widgets = function(type, direction, col, row, callback) {
        var ga = this.gridmap;
        if (!ga[col]) { return; }

        var cr, max;
        var action = type + '/' + direction;
        if (arguments[2] instanceof jQuery) {
            var el_grid_data = arguments[2].coords().grid;
            col = el_grid_data.col;
            row = el_grid_data.row;
            callback = arguments[3];
        }
        var matched = [];
        var trow = row;


        var methods = {
            'for_each/above': function() {
                while (trow--) {
                    if (trow > 0 && this.is_widget(col, trow) &&
                        $.inArray(ga[col][trow], matched) === -1
                    ) {
                        cr = callback.call(ga[col][trow], col, trow);
                        matched.push(ga[col][trow]);
                        if (cr) { break; }
                    }
                }
            },
            'for_each/below': function() {
                for (trow = row + 1, max = ga[col].length; trow < max; trow++) {
                    if (this.is_widget(col, trow) &&
                        $.inArray(ga[col][trow], matched) === -1
                    ) {
                        cr = callback.call(ga[col][trow], col, trow);
                        matched.push(ga[col][trow]);
                        if (cr) { break; }
                    }
                }
            }
        };

        if (methods[action]) {
            methods[action].call(this);
        }
    };


    /**
    * Iterate over each widget above the column and row specified.
    *
    * @method for_each_widget_above
    * @param {Number} col The column to start iterating.
    * @param {Number} row The row to start iterating.
    * @param {Function} callback The function to execute on each widget
    *  iteration. The value of `this` inside the function is the jQuery
    *  wrapped HTMLElement.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.for_each_widget_above = function(col, row, callback) {
        this._traversing_widgets('for_each', 'above', col, row, callback);
        return this;
    };


    /**
    * Iterate over each widget below the column and row specified.
    *
    * @method for_each_widget_below
    * @param {Number} col The column to start iterating.
    * @param {Number} row The row to start iterating.
    * @param {Function} callback The function to execute on each widget
    *  iteration. The value of `this` inside the function is the jQuery wrapped
    *  HTMLElement.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.for_each_widget_below = function(col, row, callback) {
        this._traversing_widgets('for_each', 'below', col, row, callback);
        return this;
    };


    /**
    * Returns the highest occupied cell in the grid.
    *
    * @method get_highest_occupied_cell
    * @return {Object} Returns an object with `col` and `row` numbers.
    */
    fn.get_highest_occupied_cell = function() {
        var r;
        var gm = this.gridmap;
        var rows = [];
        var row_in_col = [];
        for (var c = gm.length - 1; c >= 1; c--) {
            for (r = gm[c].length - 1; r >= 1; r--) {
                if (this.is_widget(c, r)) {
                    rows.push(r);
                    row_in_col[r] = c;
                    break;
                }
            }
        }

        var highest_row = Math.max.apply(Math, rows);

        this.highest_occupied_cell = {
            col: row_in_col[highest_row],
            row: highest_row
        };

        return this.highest_occupied_cell;
    };


    fn.get_widgets_from = function(col, row) {
        var ga = this.gridmap;
        var $widgets = $();

        if (col) {
            $widgets = $widgets.add(
                this.$widgets.filter(function() {
                    var tcol = $(this).attr('data-col');
                    return (tcol === col || tcol > col);
                })
            );
        }

        if (row) {
            $widgets = $widgets.add(
                this.$widgets.filter(function() {
                    var trow = $(this).attr('data-row');
                    return (trow === row || trow > row);
                })
            );
        }

        return $widgets;
    };


    /**
    * Set the current height of the parent grid.
    *
    * @method set_dom_grid_height
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.set_dom_grid_height = function() {
        var r = this.get_highest_occupied_cell().row;
        this.$el.css('height', r * this.min_widget_height);
        return this;
    };


    /**
    * It generates the neccessary styles to position the widgets.
    *
    * @method generate_stylesheet
    * @param {Number} rows Number of columns.
    * @param {Number} cols Number of rows.
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.generate_stylesheet = function(opts) {
        var styles = '';
        var max_size_x = this.options.max_size_x;
        var max_rows = 0;
        var max_cols = 0;
        var i;
        var rules;

        opts || (opts = {});
        opts.cols || (opts.cols = this.cols);
        opts.rows || (opts.rows = this.rows);
        opts.namespace || (opts.namespace = this.options.namespace);
        opts.widget_base_dimensions ||
            (opts.widget_base_dimensions = this.options.widget_base_dimensions);
        opts.widget_margins ||
            (opts.widget_margins = this.options.widget_margins);
        opts.min_widget_width = (opts.widget_margins[0] * 2) +
            opts.widget_base_dimensions[0];
        opts.min_widget_height = (opts.widget_margins[1] * 2) +
            opts.widget_base_dimensions[1];

        // don't duplicate stylesheets for the same configuration
        var serialized_opts = $.param(opts);
        if ($.inArray(serialized_opts, Gridster.generated_stylesheets) >= 0) {
            return false;
        }

        Gridster.generated_stylesheets.push(serialized_opts);

        /* generate CSS styles for cols */
        for (i = opts.cols; i >= 0; i--) {
            styles += (opts.namespace + ' [data-col="'+ (i + 1) + '"] { left:' +
                ((i * opts.widget_base_dimensions[0]) +
                (i * opts.widget_margins[0]) +
                ((i + 1) * opts.widget_margins[0])) + 'px;} ');
        }

        /* generate CSS styles for rows */
        for (i = opts.rows; i >= 0; i--) {
            styles += (opts.namespace + ' [data-row="' + (i + 1) + '"] { top:' +
                ((i * opts.widget_base_dimensions[1]) +
                (i * opts.widget_margins[1]) +
                ((i + 1) * opts.widget_margins[1]) ) + 'px;} ');
        }

        for (var y = 1; y <= opts.rows; y++) {
            styles += (opts.namespace + ' [data-sizey="' + y + '"] { height:' +
                (y * opts.widget_base_dimensions[1] +
                (y - 1) * (opts.widget_margins[1] * 2)) + 'px;}');
        }

        for (var x = 1; x <= max_size_x; x++) {
            styles += (opts.namespace + ' [data-sizex="' + x + '"] { width:' +
                (x * opts.widget_base_dimensions[0] +
                (x - 1) * (opts.widget_margins[0] * 2)) + 'px;}');
        }

        return this.add_style_tag(styles);
    };


    /**
    * Injects the given CSS as string to the head of the document.
    *
    * @method add_style_tag
    * @param {String} css The styles to apply.
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.add_style_tag = function(css) {
      var d = document;
      var tag = d.createElement('style');

      d.getElementsByTagName('head')[0].appendChild(tag);
      tag.setAttribute('type', 'text/css');

      if (tag.styleSheet) {
        tag.styleSheet.cssText = css;
      }else{
        tag.appendChild(document.createTextNode(css));
      }
      return this;
    };


    /**
    * Generates a faux grid to collide with it when a widget is dragged and
    * detect row or column that we want to go.
    *
    * @method generate_faux_grid
    * @param {Number} rows Number of columns.
    * @param {Number} cols Number of rows.
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.generate_faux_grid = function(rows, cols) {
        this.faux_grid = [];
        this.gridmap = [];
        var col;
        var row;
        for (col = cols; col > 0; col--) {
            this.gridmap[col] = [];
            for (row = rows; row > 0; row--) {
                this.add_faux_cell(row, col);
            }
        }
        return this;
    };


    /**
    * Add cell to the faux grid.
    *
    * @method add_faux_cell
    * @param {Number} row The row for the new faux cell.
    * @param {Number} col The col for the new faux cell.
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.add_faux_cell = function(row, col) {
        var coords = $({
                        left: this.baseX + ((col - 1) * this.min_widget_width),
                        top: this.baseY + (row -1) * this.min_widget_height,
                        width: this.min_widget_width,
                        height: this.min_widget_height,
                        col: col,
                        row: row,
                        original_col: col,
                        original_row: row
                    }).coords();

        if (!$.isArray(this.gridmap[col])) {
            this.gridmap[col] = [];
        }

        this.gridmap[col][row] = false;
        this.faux_grid.push(coords);

        return this;
    };


    /**
    * Add rows to the faux grid.
    *
    * @method add_faux_rows
    * @param {Number} rows The number of rows you want to add to the faux grid.
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.add_faux_rows = function(rows) {
        var actual_rows = this.rows;
        var max_rows = actual_rows + (rows || 1);

        for (var r = max_rows; r > actual_rows; r--) {
            for (var c = this.cols; c >= 1; c--) {
                this.add_faux_cell(r, c);
            }
        }

        this.rows = max_rows;

        if (this.options.autogenerate_stylesheet) {
            this.generate_stylesheet();
        }

        return this;
    };

     /**
    * Add cols to the faux grid.
    *
    * @method add_faux_cols
    * @param {Number} cols The number of cols you want to add to the faux grid.
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.add_faux_cols = function(cols) {
        var actual_cols = this.cols;
        var max_cols = actual_cols + (cols || 1);

        for (var c = actual_cols; c < max_cols; c++) {
            for (var r = this.rows; r >= 1; r--) {
                this.add_faux_cell(r, c);
            }
        }

        this.cols = max_cols;

        if (this.options.autogenerate_stylesheet) {
            this.generate_stylesheet();
        }

        return this;
    };


    /**
    * Recalculates the offsets for the faux grid. You need to use it when
    * the browser is resized.
    *
    * @method recalculate_faux_grid
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.recalculate_faux_grid = function() {
        var aw = this.$wrapper.width();
        this.baseX = ($(window).width() - aw) / 2;
        this.baseY = this.$wrapper.offset().top;

        $.each(this.faux_grid, $.proxy(function(i, coords) {
            this.faux_grid[i] = coords.update({
                left: this.baseX + (coords.data.col -1) * this.min_widget_width,
                top: this.baseY + (coords.data.row -1) * this.min_widget_height
            });

        }, this));

        return this;
    };


    /**
    * Get all widgets in the DOM and register them.
    *
    * @method get_widgets_from_DOM
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.get_widgets_from_DOM = function() {
        this.$widgets.each($.proxy(function(i, widget) {
            this.register_widget($(widget));
        }, this));
        return this;
    };


    /**
    * Calculate columns and rows to be set based on the configuration
    *  parameters, grid dimensions, etc ...
    *
    * @method generate_grid_and_stylesheet
    * @return {Object} Returns the instance of the Gridster class.
    */
    fn.generate_grid_and_stylesheet = function() {
        var aw = this.$wrapper.width();
        var ah = this.$wrapper.height();

        var cols = Math.floor(aw / this.min_widget_width) +
                   this.options.extra_cols;

        var actual_cols = this.$widgets.map(function() {
            return $(this).attr('data-col');
        });
        actual_cols = Array.prototype.slice.call(actual_cols, 0);
        //needed to pass tests with phantomjs
        actual_cols.length || (actual_cols = [0]);

        var min_cols = Math.max.apply(Math, actual_cols);

        // get all rows that could be occupied by the current widgets
        var max_rows = this.options.extra_rows;
        this.$widgets.each(function(i, w) {
            max_rows += (+$(w).attr('data-sizey'));
        });


        this.cols = Math.max(min_cols, cols, this.options.min_cols);
        this.rows = Math.max(max_rows, this.options.min_rows);

        this.baseX = ($(window).width() - aw) / 2;
        this.baseY = this.$wrapper.offset().top;

        if (this.options.autogenerate_stylesheet) {
            this.generate_stylesheet();
        }

        return this.generate_faux_grid(this.rows, this.cols);
    };


    //jQuery adapter
    $.fn.gridster = function(options) {
     return this.each(function() {
       if (!$(this).data('gridster')) {
         $(this).data('gridster', new Gridster( this, options ));
       }
     });
    };

    $.Gridster = fn;

}(jQuery, window, document));