Used layout: Easy Group By.

function formatTooltipAsHours(value, ratio, id, index)
{
    return value.toFixed(2) + ' h';
}
 
function formatTooltipAsHoursWithDays(value, ratio, id, index)
{
    var hours = parseInt(value);
    var days = parseInt(hours / 24);
    value = value - days * 24;
    if (days > 0)
    {
        return days + 'd, ' + value.toFixed(2) + ' h';
    }
    return value.toFixed(2) + ' h';
}
 
var c3arg = {
    onrendered: updateFrameHeight,
    data: chartData,
    axis: {
        x: {
            type: 'category', // this is needed to load string x value
            label: {
                text: chartData.custom.xLabel,
                position: 'outer-left'
            }
        },
        y: {
            label: chartData.ytype
        }
    }
};
 
if (chartData.custom && chartData.custom.tooltip)
{
    var tooltipFunction = eval(chartData.custom.tooltip);
    c3arg.tooltip = {
        format: {
            value: tooltipFunction
        }
    };
}
 
c3.generate(c3arg);

import java.lang.reflect.Field;
import java.math.BigDecimal;
  
import org.apache.lucene.document.Document;
 
import com.atlassian.jira.component.ComponentAccessor;
import com.atlassian.jira.issue.Issue;
import com.atlassian.jira.issue.DocumentIssueImpl;
import com.atlassian.jira.issue.worklog.Worklog;
import com.atlassian.jira.issue.worklog.WorklogManager;
import com.atlassian.jira.jql.parser.JqlParseException;
import com.atlassian.jira.jql.parser.JqlQueryParser;
import com.atlassian.query.Query;
import com.atlassian.jira.util.I18nHelper;
  
import com.decadis.jira.xchart.api.ChartParam;
import com.decadis.jira.xchart.api.model.Period
import com.decadis.jira.xchart.api.util.DateUtils;
  
def i18n = ComponentAccessor.getJiraAuthenticationContext().getI18nHelper();
def wlm = ComponentAccessor.getWorklogManager();
def metaCountGroup = chartBuilder.newDataCollector();
  
JqlQueryParser jqlQueryParser = ComponentAccessor.getComponent(JqlQueryParser.class);
Query query = null;
  
try {
  query = jqlQueryParser.parseQuery(JQL);
} catch (JqlParseException e) {
  throw new IllegalArgumentException("Bad JQL: " + JQL);
}
 
def groupValueExtractorX = chartBuilder.getGrouper(GroupByX);
def groupValueExtractor = chartBuilder.getGrouper(GroupBy);
 
Field documentField;
 
try {
    documentField = DocumentIssueImpl.class.getDeclaredField("document");
    documentField.setAccessible(true);
     
    for ( Issue issue : chartBuilder.getFilterUtils().performSearch(query, user) )
    {
      Document doc = (Document) documentField.get(issue);
      for ( Worklog wl : wlm.getByIssue(issue) )
      {
        BigDecimal value = BigDecimal.valueOf(wl.getTimeSpent()).divide(BigDecimal.valueOf(3600), 4, BigDecimal.ROUND_HALF_UP);
        for ( String group : groupValueExtractor.getGroups(doc) )
        {
          for ( String groupx : groupValueExtractorX.getGroups(doc) )
          {
            String grpName = groupValueExtractorX.getResolvedValue(groupx, issue);
            metaCountGroup.addValue(value, group, grpName);
          }
        }
      }
    }
}
catch(Exception e){}
 
metaCountGroup.fillMissingValues();
 
def chartData = chartBuilder.newChartData(i18n.getText("common.concepts.time.spent"));
 
for ( String grpKey : metaCountGroup.keySet() ) {
  chartData.addGroupName(grpKey, groupValueExtractor.getResolvedValue(grpKey, null));
}
 
chartData.setXType(groupValueExtractorX.getGroupName());
chartData.setType(ChartType);
chartData.addCustomData("tooltip", "formatTooltipAsHours");
 
chartBuilder.getChartUtil().transformResult(metaCountGroup, chartData, true);
  
return chartData;