    /**
     * @class Ext.chart.Label
     *
     * Labels is a mixin whose methods are appended onto the Series class. Labels is an interface with methods implemented
     * in each of the Series (Pie, Bar, etc) for label creation and label placement.
     *
     * The methods implemented by the Series are:
     *
     * - **`onCreateLabel(storeItem, item, i, display)`** Called each time a new label is created.
     *   The arguments of the method are:
     *   - *`storeItem`* The element of the store that is related to the label sprite.
     *   - *`item`* The item related to the label sprite. An item is an object containing the position of the shape
     *     used to describe the visualization and also pointing to the actual shape (circle, rectangle, path, etc).
     *   - *`i`* The index of the element created (i.e the first created label, second created label, etc)
     *   - *`display`* The display type. May be <b>false</b> if the label is hidden
     *
     *  - **`onPlaceLabel(label, storeItem, item, i, display, animate)`** Called for updating the position of the label.
     *    The arguments of the method are:
     *    - *`label`* The sprite label.</li>
     *    - *`storeItem`* The element of the store that is related to the label sprite</li>
     *    - *`item`* The item related to the label sprite. An item is an object containing the position of the shape
     *      used to describe the visualization and also pointing to the actual shape (circle, rectangle, path, etc).
     *    - *`i`* The index of the element to be updated (i.e. whether it is the first, second, third from the labelGroup)
     *    - *`display`* The display type. May be <b>false</b> if the label is hidden.
     *    - *`animate`* A boolean value to set or unset animations for the labels.
     */
    Ext.define('Ext.chart.Label', {

        /* Begin Definitions */

        requires: ['Ext.draw.Color'],

        /* End Definitions */

        /**
         * @cfg {String} display
         * Specifies the presence and position of labels for each pie slice. Either "rotate", "middle", "insideStart",
         * "insideEnd", "outside", "over", "under", or "none" to prevent label rendering.
         * Default value: 'none'.
         */

        /**
         * @cfg {String} color
         * The color of the label text.
         * Default value: '#000' (black).
         */

        /**
         * @cfg {String} field
         * The name of the field to be displayed in the label.
         * Default value: 'name'.
         */

        /**
         * @cfg {Number} minMargin
         * Specifies the minimum distance from a label to the origin of the visualization.
         * This parameter is useful when using PieSeries width variable pie slice lengths.
         * Default value: 50.
         */

        /**
         * @cfg {String} font
         * The font used for the labels.
         * Defautl value: "11px Helvetica, sans-serif".
         */

        /**
         * @cfg {String} orientation
         * Either "horizontal" or "vertical".
         * Dafault value: "horizontal".
         */

        /**
         * @cfg {Function} renderer
         * Optional function for formatting the label into a displayable value.
         * Default value: function(v) { return v; }
         * @param v
         */

        //@private a regex to parse url type colors.
        colorStringRe: /url\s*\(\s*#([^\/)]+)\s*\)/,

        //@private the mixin constructor. Used internally by Series.
        constructor: function(config) {
            var me = this;
            me.label = Ext.applyIf(me.label || {},
            {
                display: "none",
                color: "#000",
                field: "name",
                minMargin: 50,
                font: "11px Helvetica, sans-serif",
                orientation: "horizontal",
                renderer: function(v) {
                    return v;
                }
            });

            if (me.label.display !== 'none') {
                me.labelsGroup = me.chart.surface.getGroup(me.seriesId + '-labels');
            }
        },

        //@private a method to render all labels in the labelGroup
        renderLabels: function() {
            var me = this,
                chart = me.chart,
                gradients = chart.gradients,
                gradient,
                items = me.items,
                animate = chart.animate,
                config = me.label,
                display = config.display,
                color = config.color,
                field = [].concat(config.field),
                group = me.labelsGroup,
                store = me.chart.store,
                len = store.getCount(),
                ratio = items.length / len,
                i, count, j,
                k, gradientsCount = (gradients || 0) && gradients.length,
                colorStopTotal, colorStopIndex, colorStop,
                item, label, storeItem,
                sprite, spriteColor, spriteBrightness, labelColor,
                Color = Ext.draw.Color,
                colorString;

            if (display == 'none') {
                return;
            }

            for (i = 0, count = 0; i < len; i++) {
                for (j = 0; j < ratio; j++) {
                    item = items[count];
                    label = group.getAt(count);
                    storeItem = store.getAt(i);

                    if (!item && label) {
                        label.hide(true);
                    }

                    if (item && field[j]) {
                        if (!label) {
                            label = me.onCreateLabel(storeItem, item, i, display, j, count);
                        }
                        me.onPlaceLabel(label, storeItem, item, i, display, animate, j, count);

                        //set contrast
                        if (config.contrast && item.sprite) {
                            sprite = item.sprite;
                            colorString = sprite._to && sprite._to.fill || sprite.attr.fill;
                            spriteColor = Color.fromString(colorString);
                            //color wasn't parsed property maybe because it's a gradient id
                            if (colorString && !spriteColor) {
                                colorString = colorString.match(me.colorStringRe)[1];
                                for (k = 0; k < gradientsCount; k++) {
                                    gradient = gradients[k];
                                    if (gradient.id == colorString) {
                                        //avg color stops
                                        colorStop = 0; colorStopTotal = 0;
                                        for (colorStopIndex in gradient.stops) {
                                            colorStop++;
                                            colorStopTotal += Color.fromString(gradient.stops[colorStopIndex].color).getGrayscale();
                                        }
                                        spriteBrightness = (colorStopTotal / colorStop) / 255;
                                        break;
                                    }
                                }
                            }
                            else {
                                spriteBrightness = spriteColor.getGrayscale() / 255;
                            }
                            labelColor = Color.fromString(label.attr.color || label.attr.fill).getHSL();

                            labelColor[2] = spriteBrightness > 0.5? 0.2 : 0.8;
                            label.setAttributes({
                                fill: String(Color.fromHSL.apply({}, labelColor))
                            }, true);
                        }
                    }
                    count++;
                }
            }
            me.hideLabels(count);
        },

        //@private a method to hide labels.
        hideLabels: function(index) {
            var labelsGroup = this.labelsGroup, len;
            if (labelsGroup) {
                len = labelsGroup.getCount();
                while (len-->index) {
                    labelsGroup.getAt(len).hide(true);
                }
            }
        }
    });