From 9694446b262d0a57fd5802fa6fe78ed31a355b4a Mon Sep 17 00:00:00 2001
From: nitta <nitta@fullspeed.co.jp>
Date: Thu, 11 Jul 2019 19:09:43 +0900
Subject: [PATCH 1/4] Add chart's secondary y axis.

---
 src/PhpSpreadsheet/Chart/DataSeries.php  |  38 +++-
 src/PhpSpreadsheet/Writer/Xlsx/Chart.php | 251 ++++++++++++++---------
 2 files changed, 187 insertions(+), 102 deletions(-)

diff --git a/src/PhpSpreadsheet/Chart/DataSeries.php b/src/PhpSpreadsheet/Chart/DataSeries.php
index 8056bbeea2..e90b0044ff 100644
--- a/src/PhpSpreadsheet/Chart/DataSeries.php
+++ b/src/PhpSpreadsheet/Chart/DataSeries.php
@@ -40,6 +40,9 @@ class DataSeries
     const STYLE_MARKER = 'marker';
     const STYLE_FILLED = 'filled';
 
+    const VALUE_AXIS_POSITION_LEFT  = 'l';
+    const VALUE_AXIS_POSITION_RIGHT = 'r';
+
     /**
      * Series Plot Type.
      *
@@ -103,6 +106,11 @@ class DataSeries
      */
     private $plotValues = [];
 
+    /**
+     * @var string
+     */
+    private $valueAxisPosition;
+
     /**
      * Create a new DataSeries.
      *
@@ -116,7 +124,7 @@ class DataSeries
      * @param bool $smoothLine
      * @param null|string $plotStyle
      */
-    public function __construct($plotType = null, $plotGrouping = null, array $plotOrder = [], array $plotLabel = [], array $plotCategory = [], array $plotValues = [], $plotDirection = null, $smoothLine = false, $plotStyle = null)
+    public function __construct($plotType = null, $plotGrouping = null, array $plotOrder = [], array $plotLabel = [], array $plotCategory = [], array $plotValues = [], $plotDirection = null, $smoothLine = false, $plotStyle = null, $valueAxisPosition = null)
     {
         $this->plotType = $plotType;
         $this->plotGrouping = $plotGrouping;
@@ -140,6 +148,10 @@ public function __construct($plotType = null, $plotGrouping = null, array $plotO
             $plotDirection = self::DIRECTION_COL;
         }
         $this->plotDirection = $plotDirection;
+
+        if ($valueAxisPosition === null) {
+            $this->valueAxisPosition = self::VALUE_AXIS_POSITION_LEFT;
+        }
     }
 
     /**
@@ -355,6 +367,16 @@ public function getSmoothLine()
         return $this->smoothLine;
     }
 
+    /**
+     * Get Value Axis Position.
+     *
+     * @return string
+     */
+    public function getValueAxisPosition()
+    {
+        return $this->valueAxisPosition;
+    }
+
     /**
      * Set Smooth Line.
      *
@@ -369,6 +391,20 @@ public function setSmoothLine($smoothLine)
         return $this;
     }
 
+    /**
+     * Set Value Axis Position.
+     * 
+     * @param string $valueAxisPosition
+     *
+     * @return string
+     */
+    public function setValueAxisPosition($valueAxisPosition)
+    {
+        $this->valueAxisPosition = $valueAxisPosition;
+
+        return $this;
+    }
+
     public function refresh(Worksheet $worksheet)
     {
         foreach ($this->plotValues as $plotValues) {
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
index 625fd16de2..a850b764b2 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
@@ -232,6 +232,7 @@ private function writePlotArea(XMLWriter $objWriter, \PhpOffice\PhpSpreadsheet\W
         $chartTypes = self::getChartType($plotArea);
         $catIsMultiLevelSeries = $valIsMultiLevelSeries = false;
         $plotGroupingType = '';
+        $useSecondaryYAxis = false;
         foreach ($chartTypes as $chartType) {
             $objWriter->startElement('c:' . $chartType);
 
@@ -303,13 +304,27 @@ private function writePlotArea(XMLWriter $objWriter, \PhpOffice\PhpSpreadsheet\W
             $id1 = '75091328';
             $id2 = '75089408';
 
+            // For secondary y axis id.
+            $secondaryId2 = '205755944';
+
             if (($chartType !== DataSeries::TYPE_PIECHART) && ($chartType !== DataSeries::TYPE_PIECHART_3D) && ($chartType !== DataSeries::TYPE_DONUTCHART)) {
                 $objWriter->startElement('c:axId');
                 $objWriter->writeAttribute('val', $id1);
                 $objWriter->endElement();
-                $objWriter->startElement('c:axId');
-                $objWriter->writeAttribute('val', $id2);
-                $objWriter->endElement();
+
+                $plotGroup = $this->getPlotGroupByChartType($plotArea, $chartType);
+                if ($plotGroup && $plotGroup->getValueAxisPosition() === DataSeries::VALUE_AXIS_POSITION_RIGHT) {
+                    $useSecondaryYAxis = true;
+                    $objWriter->startElement('c:axId');
+                    $objWriter->writeAttribute('val', $secondaryId2);
+                    $objWriter->endElement();
+
+                } else {
+                    $objWriter->startElement('c:axId');
+                    $objWriter->writeAttribute('val', $id2);
+                    $objWriter->endElement();
+                }
+
             } else {
                 $objWriter->startElement('c:firstSliceAng');
                 $objWriter->writeAttribute('val', 0);
@@ -332,12 +347,36 @@ private function writePlotArea(XMLWriter $objWriter, \PhpOffice\PhpSpreadsheet\W
                 $this->writeCategoryAxis($objWriter, $xAxisLabel, $id1, $id2, $catIsMultiLevelSeries, $yAxis);
             }
 
-            $this->writeValueAxis($objWriter, $yAxisLabel, $chartType, $id1, $id2, $valIsMultiLevelSeries, $xAxis, $majorGridlines, $minorGridlines);
+            $this->writeValueAxis($objWriter, $yAxisLabel, $chartType, $id1, $id2, $valIsMultiLevelSeries, $xAxis, $majorGridlines, $minorGridlines, DataSeries::VALUE_AXIS_POSITION_LEFT);
+        }
+
+        if ($useSecondaryYAxis) {
+            $this->writeValueAxis($objWriter, $yAxisLabel, $chartType, $id1, $secondaryId2, $valIsMultiLevelSeries, $xAxis, $majorGridlines, $minorGridlines,DataSeries::VALUE_AXIS_POSITION_RIGHT);
         }
 
         $objWriter->endElement();
     }
 
+    /**
+     * @param $plotArea
+     * @param $chartType
+     *
+     * @return DataSeries|null
+     */
+    private function getPlotGroupByChartType($plotArea, $chartType)
+    {
+
+        $groupCount = $plotArea->getPlotGroupCount();
+        for ($i = 0; $i < $groupCount; ++$i) {
+            $plotGroup = $plotArea->getPlotGroupByIndex($i);
+            $groupType = $plotGroup->getPlotType();
+            if ($groupType == $chartType) {
+                return $plotGroup;
+            }
+        }
+        return null;
+    }
+
     /**
      * Write Data Labels.
      *
@@ -521,7 +560,7 @@ private function writeCategoryAxis($objWriter, $xAxisLabel, $id1, $id2, $isMulti
      *
      * @throws WriterException
      */
-    private function writeValueAxis($objWriter, $yAxisLabel, $groupType, $id1, $id2, $isMultiLevelSeries, Axis $xAxis, GridLines $majorGridlines, GridLines $minorGridlines)
+    private function writeValueAxis($objWriter, $yAxisLabel, $groupType, $id1, $id2, $isMultiLevelSeries, Axis $xAxis, GridLines $majorGridlines, GridLines $minorGridlines, $axisPosition)
     {
         $objWriter->startElement('c:valAx');
 
@@ -556,115 +595,117 @@ private function writeValueAxis($objWriter, $yAxisLabel, $groupType, $id1, $id2,
         $objWriter->endElement();
 
         $objWriter->startElement('c:axPos');
-        $objWriter->writeAttribute('val', 'l');
+        $objWriter->writeAttribute('val', $axisPosition);
         $objWriter->endElement();
 
-        $objWriter->startElement('c:majorGridlines');
-        $objWriter->startElement('c:spPr');
-
-        if ($majorGridlines->getLineColorProperty('value') !== null) {
-            $objWriter->startElement('a:ln');
-            $objWriter->writeAttribute('w', $majorGridlines->getLineStyleProperty('width'));
-            $objWriter->startElement('a:solidFill');
-            $objWriter->startElement("a:{$majorGridlines->getLineColorProperty('type')}");
-            $objWriter->writeAttribute('val', $majorGridlines->getLineColorProperty('value'));
-            $objWriter->startElement('a:alpha');
-            $objWriter->writeAttribute('val', $majorGridlines->getLineColorProperty('alpha'));
-            $objWriter->endElement(); //end alpha
-            $objWriter->endElement(); //end srgbClr
-            $objWriter->endElement(); //end solidFill
+        if ($axisPosition === DataSeries::VALUE_AXIS_POSITION_LEFT) {
+            $objWriter->startElement('c:majorGridlines');
+            $objWriter->startElement('c:spPr');
 
-            $objWriter->startElement('a:prstDash');
-            $objWriter->writeAttribute('val', $majorGridlines->getLineStyleProperty('dash'));
-            $objWriter->endElement();
+            if ($majorGridlines->getLineColorProperty('value') !== null) {
+                $objWriter->startElement('a:ln');
+                $objWriter->writeAttribute('w', $majorGridlines->getLineStyleProperty('width'));
+                $objWriter->startElement('a:solidFill');
+                $objWriter->startElement("a:{$majorGridlines->getLineColorProperty('type')}");
+                $objWriter->writeAttribute('val', $majorGridlines->getLineColorProperty('value'));
+                $objWriter->startElement('a:alpha');
+                $objWriter->writeAttribute('val', $majorGridlines->getLineColorProperty('alpha'));
+                $objWriter->endElement(); //end alpha
+                $objWriter->endElement(); //end srgbClr
+                $objWriter->endElement(); //end solidFill
 
-            if ($majorGridlines->getLineStyleProperty('join') == 'miter') {
-                $objWriter->startElement('a:miter');
-                $objWriter->writeAttribute('lim', '800000');
-                $objWriter->endElement();
-            } else {
-                $objWriter->startElement('a:bevel');
+                $objWriter->startElement('a:prstDash');
+                $objWriter->writeAttribute('val', $majorGridlines->getLineStyleProperty('dash'));
                 $objWriter->endElement();
-            }
 
-            if ($majorGridlines->getLineStyleProperty(['arrow', 'head', 'type']) !== null) {
-                $objWriter->startElement('a:headEnd');
-                $objWriter->writeAttribute('type', $majorGridlines->getLineStyleProperty(['arrow', 'head', 'type']));
-                $objWriter->writeAttribute('w', $majorGridlines->getLineStyleArrowParameters('head', 'w'));
-                $objWriter->writeAttribute('len', $majorGridlines->getLineStyleArrowParameters('head', 'len'));
-                $objWriter->endElement();
+                if ($majorGridlines->getLineStyleProperty('join') == 'miter') {
+                    $objWriter->startElement('a:miter');
+                    $objWriter->writeAttribute('lim', '800000');
+                    $objWriter->endElement();
+                } else {
+                    $objWriter->startElement('a:bevel');
+                    $objWriter->endElement();
+                }
+
+                if ($majorGridlines->getLineStyleProperty(['arrow', 'head', 'type']) !== null) {
+                    $objWriter->startElement('a:headEnd');
+                    $objWriter->writeAttribute('type', $majorGridlines->getLineStyleProperty(['arrow', 'head', 'type']));
+                    $objWriter->writeAttribute('w', $majorGridlines->getLineStyleArrowParameters('head', 'w'));
+                    $objWriter->writeAttribute('len', $majorGridlines->getLineStyleArrowParameters('head', 'len'));
+                    $objWriter->endElement();
+                }
+
+                if ($majorGridlines->getLineStyleProperty(['arrow', 'end', 'type']) !== null) {
+                    $objWriter->startElement('a:tailEnd');
+                    $objWriter->writeAttribute('type', $majorGridlines->getLineStyleProperty(['arrow', 'end', 'type']));
+                    $objWriter->writeAttribute('w', $majorGridlines->getLineStyleArrowParameters('end', 'w'));
+                    $objWriter->writeAttribute('len', $majorGridlines->getLineStyleArrowParameters('end', 'len'));
+                    $objWriter->endElement();
+                }
+                $objWriter->endElement(); //end ln
             }
+            $objWriter->startElement('a:effectLst');
 
-            if ($majorGridlines->getLineStyleProperty(['arrow', 'end', 'type']) !== null) {
-                $objWriter->startElement('a:tailEnd');
-                $objWriter->writeAttribute('type', $majorGridlines->getLineStyleProperty(['arrow', 'end', 'type']));
-                $objWriter->writeAttribute('w', $majorGridlines->getLineStyleArrowParameters('end', 'w'));
-                $objWriter->writeAttribute('len', $majorGridlines->getLineStyleArrowParameters('end', 'len'));
-                $objWriter->endElement();
+            if ($majorGridlines->getGlowSize() !== null) {
+                $objWriter->startElement('a:glow');
+                $objWriter->writeAttribute('rad', $majorGridlines->getGlowSize());
+                $objWriter->startElement("a:{$majorGridlines->getGlowColor('type')}");
+                $objWriter->writeAttribute('val', $majorGridlines->getGlowColor('value'));
+                $objWriter->startElement('a:alpha');
+                $objWriter->writeAttribute('val', $majorGridlines->getGlowColor('alpha'));
+                $objWriter->endElement(); //end alpha
+                $objWriter->endElement(); //end schemeClr
+                $objWriter->endElement(); //end glow
             }
-            $objWriter->endElement(); //end ln
-        }
-        $objWriter->startElement('a:effectLst');
 
-        if ($majorGridlines->getGlowSize() !== null) {
-            $objWriter->startElement('a:glow');
-            $objWriter->writeAttribute('rad', $majorGridlines->getGlowSize());
-            $objWriter->startElement("a:{$majorGridlines->getGlowColor('type')}");
-            $objWriter->writeAttribute('val', $majorGridlines->getGlowColor('value'));
-            $objWriter->startElement('a:alpha');
-            $objWriter->writeAttribute('val', $majorGridlines->getGlowColor('alpha'));
-            $objWriter->endElement(); //end alpha
-            $objWriter->endElement(); //end schemeClr
-            $objWriter->endElement(); //end glow
-        }
+            if ($majorGridlines->getShadowProperty('presets') !== null) {
+                $objWriter->startElement("a:{$majorGridlines->getShadowProperty('effect')}");
+                if ($majorGridlines->getShadowProperty('blur') !== null) {
+                    $objWriter->writeAttribute('blurRad', $majorGridlines->getShadowProperty('blur'));
+                }
+                if ($majorGridlines->getShadowProperty('distance') !== null) {
+                    $objWriter->writeAttribute('dist', $majorGridlines->getShadowProperty('distance'));
+                }
+                if ($majorGridlines->getShadowProperty('direction') !== null) {
+                    $objWriter->writeAttribute('dir', $majorGridlines->getShadowProperty('direction'));
+                }
+                if ($majorGridlines->getShadowProperty('algn') !== null) {
+                    $objWriter->writeAttribute('algn', $majorGridlines->getShadowProperty('algn'));
+                }
+                if ($majorGridlines->getShadowProperty(['size', 'sx']) !== null) {
+                    $objWriter->writeAttribute('sx', $majorGridlines->getShadowProperty(['size', 'sx']));
+                }
+                if ($majorGridlines->getShadowProperty(['size', 'sy']) !== null) {
+                    $objWriter->writeAttribute('sy', $majorGridlines->getShadowProperty(['size', 'sy']));
+                }
+                if ($majorGridlines->getShadowProperty(['size', 'kx']) !== null) {
+                    $objWriter->writeAttribute('kx', $majorGridlines->getShadowProperty(['size', 'kx']));
+                }
+                if ($majorGridlines->getShadowProperty('rotWithShape') !== null) {
+                    $objWriter->writeAttribute('rotWithShape', $majorGridlines->getShadowProperty('rotWithShape'));
+                }
+                $objWriter->startElement("a:{$majorGridlines->getShadowProperty(['color', 'type'])}");
+                $objWriter->writeAttribute('val', $majorGridlines->getShadowProperty(['color', 'value']));
 
-        if ($majorGridlines->getShadowProperty('presets') !== null) {
-            $objWriter->startElement("a:{$majorGridlines->getShadowProperty('effect')}");
-            if ($majorGridlines->getShadowProperty('blur') !== null) {
-                $objWriter->writeAttribute('blurRad', $majorGridlines->getShadowProperty('blur'));
-            }
-            if ($majorGridlines->getShadowProperty('distance') !== null) {
-                $objWriter->writeAttribute('dist', $majorGridlines->getShadowProperty('distance'));
-            }
-            if ($majorGridlines->getShadowProperty('direction') !== null) {
-                $objWriter->writeAttribute('dir', $majorGridlines->getShadowProperty('direction'));
-            }
-            if ($majorGridlines->getShadowProperty('algn') !== null) {
-                $objWriter->writeAttribute('algn', $majorGridlines->getShadowProperty('algn'));
-            }
-            if ($majorGridlines->getShadowProperty(['size', 'sx']) !== null) {
-                $objWriter->writeAttribute('sx', $majorGridlines->getShadowProperty(['size', 'sx']));
-            }
-            if ($majorGridlines->getShadowProperty(['size', 'sy']) !== null) {
-                $objWriter->writeAttribute('sy', $majorGridlines->getShadowProperty(['size', 'sy']));
-            }
-            if ($majorGridlines->getShadowProperty(['size', 'kx']) !== null) {
-                $objWriter->writeAttribute('kx', $majorGridlines->getShadowProperty(['size', 'kx']));
-            }
-            if ($majorGridlines->getShadowProperty('rotWithShape') !== null) {
-                $objWriter->writeAttribute('rotWithShape', $majorGridlines->getShadowProperty('rotWithShape'));
-            }
-            $objWriter->startElement("a:{$majorGridlines->getShadowProperty(['color', 'type'])}");
-            $objWriter->writeAttribute('val', $majorGridlines->getShadowProperty(['color', 'value']));
+                $objWriter->startElement('a:alpha');
+                $objWriter->writeAttribute('val', $majorGridlines->getShadowProperty(['color', 'alpha']));
+                $objWriter->endElement(); //end alpha
 
-            $objWriter->startElement('a:alpha');
-            $objWriter->writeAttribute('val', $majorGridlines->getShadowProperty(['color', 'alpha']));
-            $objWriter->endElement(); //end alpha
+                $objWriter->endElement(); //end color:type
+                $objWriter->endElement(); //end shadow
+            }
 
-            $objWriter->endElement(); //end color:type
-            $objWriter->endElement(); //end shadow
-        }
+            if ($majorGridlines->getSoftEdgesSize() !== null) {
+                $objWriter->startElement('a:softEdge');
+                $objWriter->writeAttribute('rad', $majorGridlines->getSoftEdgesSize());
+                $objWriter->endElement(); //end softEdge
+            }
 
-        if ($majorGridlines->getSoftEdgesSize() !== null) {
-            $objWriter->startElement('a:softEdge');
-            $objWriter->writeAttribute('rad', $majorGridlines->getSoftEdgesSize());
-            $objWriter->endElement(); //end softEdge
+            $objWriter->endElement(); //end effectLst
+            $objWriter->endElement(); //end spPr
+            $objWriter->endElement(); //end majorGridLines
         }
 
-        $objWriter->endElement(); //end effectLst
-        $objWriter->endElement(); //end spPr
-        $objWriter->endElement(); //end majorGridLines
-
         if ($minorGridlines->getObjectState()) {
             $objWriter->startElement('c:minorGridlines');
             $objWriter->startElement('c:spPr');
@@ -953,7 +994,7 @@ private function writeValueAxis($objWriter, $yAxisLabel, $groupType, $id1, $id2,
 
         if ($id1 > 0) {
             $objWriter->startElement('c:crossAx');
-            $objWriter->writeAttribute('val', $id2);
+            $objWriter->writeAttribute('val', $id1);
             $objWriter->endElement();
 
             if ($xAxis->getAxisOptionsProperty('horizontal_crosses_value') !== null) {
@@ -962,12 +1003,20 @@ private function writeValueAxis($objWriter, $yAxisLabel, $groupType, $id1, $id2,
                 $objWriter->endElement();
             } else {
                 $objWriter->startElement('c:crosses');
-                $objWriter->writeAttribute('val', $xAxis->getAxisOptionsProperty('horizontal_crosses'));
+                if ($axisPosition === DataSeries::VALUE_AXIS_POSITION_RIGHT) {
+                    $objWriter->writeAttribute('val', 'max');
+                } else {
+                    $objWriter->writeAttribute('val', $xAxis->getAxisOptionsProperty('horizontal_crosses'));
+                }
                 $objWriter->endElement();
             }
 
             $objWriter->startElement('c:crossBetween');
-            $objWriter->writeAttribute('val', 'midCat');
+            if ($axisPosition === DataSeries::VALUE_AXIS_POSITION_RIGHT) {
+                $objWriter->writeAttribute('val', 'between');
+            } else {
+                $objWriter->writeAttribute('val', 'midCat');
+            }
             $objWriter->endElement();
 
             if ($xAxis->getAxisOptionsProperty('major_unit') !== null) {

From 83bad48396b178a993973df3fd0335f98fbdce44 Mon Sep 17 00:00:00 2001
From: nitta <nitta@fullspeed.co.jp>
Date: Thu, 11 Jul 2019 19:21:28 +0900
Subject: [PATCH 2/4] Update Changelog

---
 CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f15a894f99..a4208508df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ## [Unreleased]
 
+### Added
+
+- Added chart's secondary y axis - [Issue #1072](https://github.com/PHPOffice/PhpSpreadsheet/issues/1072)
+
 ### Fixed
 
 - COUPNUM should not return zero when settlement is in the last period - [Issue #1020](https://github.com/PHPOffice/PhpSpreadsheet/issues/1020) and [PR #1021](https://github.com/PHPOffice/PhpSpreadsheet/pull/1021)

From fda9f6b3f26a30ccba9c27e43c66ed3c8299a0ee Mon Sep 17 00:00:00 2001
From: nitta <nitta@fullspeed.co.jp>
Date: Thu, 11 Jul 2019 19:21:28 +0900
Subject: [PATCH 3/4] Update Changelog

---
 CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f15a894f99..a4208508df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ## [Unreleased]
 
+### Added
+
+- Added chart's secondary y axis - [Issue #1072](https://github.com/PHPOffice/PhpSpreadsheet/issues/1072)
+
 ### Fixed
 
 - COUPNUM should not return zero when settlement is in the last period - [Issue #1020](https://github.com/PHPOffice/PhpSpreadsheet/issues/1020) and [PR #1021](https://github.com/PHPOffice/PhpSpreadsheet/pull/1021)

From c73be30e6f36d7a69e2387e8941fa18944ec23fc Mon Sep 17 00:00:00 2001
From: nitta <nitta@fullspeed.co.jp>
Date: Thu, 11 Jul 2019 19:29:28 +0900
Subject: [PATCH 4/4] Refactor a bit.

---
 src/PhpSpreadsheet/Writer/Xlsx/Chart.php | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
index a850b764b2..796ffd1ffe 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
@@ -358,14 +358,15 @@ private function writePlotArea(XMLWriter $objWriter, \PhpOffice\PhpSpreadsheet\W
     }
 
     /**
-     * @param $plotArea
-     * @param $chartType
+     * Get a DataSeries corresponds to specific chart type.
+     *
+     * @param PlotArea $plotArea
+     * @param string $chartType
      *
      * @return DataSeries|null
      */
-    private function getPlotGroupByChartType($plotArea, $chartType)
+    private function getPlotGroupByChartType(PlotArea $plotArea, $chartType)
     {
-
         $groupCount = $plotArea->getPlotGroupCount();
         for ($i = 0; $i < $groupCount; ++$i) {
             $plotGroup = $plotArea->getPlotGroupByIndex($i);