Add zIndex API to series

zIndex was not added to PlotOptions as it only makes sense
when used in a Series and not when used in Configuration
Alternate implementation to #562
Fixes #565
Fixes #331

addon/src/main/java/com/vaadin/addon/charts/model/AbstractSeries.java

@@ -30,6 +30,7 @@ public abstract class AbstractSeries extends AbstractConfigurationObject
     private String name;
     private String stack;
     private String id;
+    private Number zIndex;
 
     @JsonUnwrapped
     private AbstractPlotOptions plotOptions;
@@ -241,4 +242,14 @@ public void setyAxis(YAxis secondaryAxis) {
         setyAxis(indexOf);
     }
 
+    @Override
+    public Number getZIndex() {
+        return zIndex;
+    }
+
+    @Override
+    public void setZIndex(Number zIndex) {
+        this.zIndex = zIndex;
+    }
+
 }

addon/src/main/java/com/vaadin/addon/charts/model/Series.java

@@ -36,6 +36,22 @@ public interface Series {
      */
     void setName(String name);
 
+    /**
+     * @see #setZIndex(String)
+     * @return the visual z index of the series.
+     */
+    Number getZIndex();
+
+    /**
+     * Define the visual z index of the series. With no z index, the series
+     * defined last are on top. With a z index, the series with the highest z
+     * index is on top.
+     * 
+     * @param zIndex
+     *            to set to the series
+     */
+    void setZIndex(Number zIndex);
+
     /**
      * Sets the configuration to which this series is linked.
      * 

addon/src/test/java/com/vaadin/addon/charts/model/junittests/ChartDataSeriesJSONSerializationTest.java

@@ -4,6 +4,7 @@
 import static java.util.Collections.singletonList;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotEquals;
+
 import java.time.Instant;
 import java.time.LocalDateTime;
 import java.time.ZoneId;
@@ -18,6 +19,7 @@
 
 import com.vaadin.addon.charts.model.Configuration;
 import com.vaadin.addon.charts.model.DataProviderSeries;
+import com.vaadin.addon.charts.model.ListSeries;
 import com.vaadin.addon.charts.model.PlotOptionsLine;
 import com.vaadin.addon.charts.model.PlotOptionsSeries;
 import com.vaadin.data.provider.DataProvider;
@@ -382,6 +384,17 @@ public void serialize_ContainerWithFilteredValues_dataWasFiltered() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    public void serialize_SeriesHasZIndex_zIndexSerialized() {
+        final ListSeries dataSeries = new ListSeries(1,2,3); 
+        dataSeries.setZIndex(134);
+
+        String actual = toJSON(dataSeries);
+        String expected = "{\"zIndex\":134,\"data\":[1,2,3]}";
+        assertEquals(expected, actual);
+    }
+
+
     public static class Pair<T1, T2> {
         private T1 t1;
         private T2 t2;

examples/src/main/java/com/vaadin/addon/charts/examples/lineandscatter/BasicLineZIndex.java

@@ -0,0 +1,31 @@
+package com.vaadin.addon.charts.examples.lineandscatter;
+
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import com.vaadin.addon.charts.Chart;
+import com.vaadin.addon.charts.examples.SkipFromDemo;
+import com.vaadin.addon.charts.model.ChartType;
+import com.vaadin.addon.charts.model.Configuration;
+import com.vaadin.addon.charts.model.PlotOptionsLine;
+import com.vaadin.addon.charts.model.Series;
+import com.vaadin.ui.Component;
+
+@SkipFromDemo
+public class BasicLineZIndex extends BasicLine {
+
+    @Override
+    protected Component getChart() {
+        Chart chart = (Chart) super.getChart();
+        Configuration configuration = chart.getConfiguration();
+        PlotOptionsLine options = (PlotOptionsLine) configuration
+                .getPlotOptions(ChartType.LINE);
+        options.setLineWidth(5);
+        List<Series> seriesList = configuration.getSeries();
+        AtomicInteger seriesCount = new AtomicInteger(seriesList.size());
+        seriesList.forEach(
+                series -> series.setZIndex(seriesCount.decrementAndGet()));
+        return chart;
+    }
+
+}

integration-tests/src/test/java/com/vaadin/addon/charts/testbenchtests/BasicLineZIndexTBTest.java

@@ -0,0 +1,17 @@
+package com.vaadin.addon.charts.testbenchtests;
+
+import com.vaadin.addon.charts.examples.lineandscatter.BasicLineZIndex;
+
+public class BasicLineZIndexTBTest
+        extends AbstractSimpleScreenShotTestBenchTest {
+
+    protected String getTestViewName() {
+        return BasicLineZIndex.class.getSimpleName();
+    }
+
+    @Override
+    protected String getPackageName() {
+        return "lineandscatter";
+    }
+
+}