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File: src/jquery.gridster.js

/*
 * jquery.gridster
 * https://github.com/ducksboard/gridster.js
 *
 * Copyright (c) 2012 ducksboard
 * Licensed under the MIT, GPL licenses.
 */
;(function($, window, document, undefined) {

    var defaults = {
        widget_selector: '> li',
        widget_margins: [10, 10],
        widget_base_dimensions: [400, 225],
        extra_rows: 0,
        extra_cols: 0,
        min_cols: 1,
        min_rows: 10,
        autogenerate_stylesheet: true,
        serialize_params: function($w, wgd) {
            return {
                col: wgd.col,
                row: wgd.row
            };
        },
        collision: {},
        draggable: {}
    };


    /* Debounce and throttle functions taken from underscore.js */
    var 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);
        };
    };


    var throttle = function(func, wait) {
        var context, args, timeout, throttling, more, result;
        var whenDone = debounce(
            function(){ more = throttling = false; }, wait, true);
        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;
        };
    };


    /**
    * @class Gridster
    * @uses Coords
    * @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 {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 {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
    *     jQuery UI Draggable you want to overwrite. See
    *     http://jqueryui.com/demos/draggable/ 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.$el.find(this.options.widget_selector).addClass('gs_w');
      this.widgets = [];
      this.$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();
    }

    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));
    };


    /**
    * Add a new widget to the grid.
    *
    * @method add_widget
    * @param {String} html The string representing the HTML of the widget.
    * @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 {HTMLElement} Returns the jQuery wrapped HTMLElement representing
    *  the widget that was just created.
    */
    fn.add_widget = function(html, size_x, size_y) {
        var next_pos = this.next_position(size_x, size_y);

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

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

        this.register_widget($w);

        this.$widgets.draggable('destroy');
        this.draggable();

        this.set_dom_grid_height();

        $w.fadeIn();
    };


    /**
    * 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 = [];

        for (var c = 1; c < cols_l; c++) {
            var 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) {
            var next_position = this.sort_by_row_desc(valid_pos);
            next_position = this.sort_by_col_asc(next_position)[0];
            return next_position;
        }
        return false;
    };


    /**
    * Remove a widget from the grid.
    *
    * @method remove_widget
    * @param {HTMLElement} el The jQuery wrapped HTMLElement you want to remove.
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.remove_widget = function(el) {
        var $el = el instanceof jQuery ? el : $(el);
        var wgd = $el.coords().grid;

        this.$widgets = this.$widgets.not($el);

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

        this.remove_from_gridmap(wgd);

        $el.fadeOut($.proxy(function(){
            $el.remove();
            $nexts.each($.proxy(function(i, widget){
                this.move_widget_up( $(widget), wgd.size_y );
            }, this));
        }, 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($el) {
        var widget_grid_data = {
            'col': parseInt($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
        };

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

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

        this.add_to_gridmap(widget_grid_data, $el);
        this.widgets.push($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. It Wraps the jQuery UI Draggable Plugin.
    *
    * @method draggable
    * @return {Class} Returns the instance of the Gridster Class.
    */
    fn.draggable = function() {
        var self = this;
        var draggable_options = $.extend(true, {}, this.options.draggable, {
            // containment : this.$wrapper,
            start: function(event, ui) {
                self.$player = $(this);
                self.$helper = self.options.draggable.helper === 'clone' ?
                    $(ui.helper) : self.$player;

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

        this.$widgets.draggable(draggable_options);

      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.
    *  See http://jqueryui.com/demos/draggable/ for more info.
    */
    fn.on_start_drag = function(event, ui) {
        this.$player.addClass('player');
        this.$wrapper.addClass('dragging');
        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.drag_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.
    *  See http://jqueryui.com/demos/draggable/ for more info.
    */
    fn.on_drag = function(event, ui) {
        this.colliders_data = this.drag_api.get_closest_colliders();

        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.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.
    *  See http://jqueryui.com/demos/draggable/ for more info.
    */
    fn.on_stop_drag = function(event, ui) {
        this.colliders_data = this.drag_api.get_closest_colliders();

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

        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;

        this.$player = null;

        this.$preview_holder.remove();

        this.set_dom_grid_height();

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


    /**
    * 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) {
        this.empty_cells_player_occupies();

        var self = this;
        var cell = self.colliders_data[0].el.data;
        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 > b.row) {
               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_row_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.
    *
    * @method get_widgets_under_player
    * @return {HTMLElement} Returns a jQuery collection of HTMLElements
    */
    fn.get_widgets_under_player = function() {
        var cells = this.cells_occupied_by_player;
        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
            });
        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));
        }

    };


    /**
    * 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 upper 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;

            while (--r > 0) {
                if (this.is_occupied(tcol, r) && !this.is_player(tcol, r)) {
                    break;
                }

                if (!this.is_player(tcol, r) &&!this.is_placeholder_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 (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();

        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();

        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 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(null, 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){
            if (this.is_occupied(col, prev_row) ||
                this.is_player(col, prev_row) ||
                this.is_placeholder_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} The col target col.
    * @param {Object} The row target row.
    * @return {Boolean} Returns true if all cells are empty, else return false.
    */
    fn.can_move_to = function(widget_grid_data, col, 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;

        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(null, rows);

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

        return this.highest_occupied_cell;
    };


    /**
    * 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.$el.css('height', r * this.min_widget_height);
        // this.$widgets.draggable("option", "containment", this.$el);
        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(rows, cols) {
        var styles = '';
        var extra_cells = 10;
        var max_size_y = 6;
        var max_size_x = 6;
        var i;
        var rules;

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

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


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

        for (var x = 1; x < max_size_x; x++) {
            styles += '[data-sizex="' + (x) + '"] { width: ' +
                      (x * this.options.widget_base_dimensions[0] + (x-1)*(this.options.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--) {
                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();

                this.gridmap[col][row] = false;
                this.faux_grid.push(coords);
            }
        }
        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 rows = Math.floor(ah / this.min_widget_height) +
                   this.options.extra_rows;

        var actual_cols = this.$widgets.map(function() {
            return $(this).attr('data-col');
        });

        var actual_rows = this.$widgets.map(function() {
            return $(this).attr('data-row');
        });

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

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

        //this.support_grid_width = cols * this.min_widget_width;
        // this.support_grid_width = this.wrapper_width;

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

        //this.baseX = 0;
        if (this.options.autogenerate_stylesheet) {
            this.generate_stylesheet(rows, cols);
        }

        /* more faux rows that needed are created so that there are cells
         * where drag beyond the limits */
        return this.generate_faux_grid(rows, cols);
    };


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


}(jQuery, window, document));