Row objects and Cell styling

This commit introduces Row and Cell entities, that will replace the arrays passed in previously.
It also adds support for Cell styling (instead of Row styling only).

tests/Spout/Writer/RowCreationHelper.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace Box\Spout\Writer;
+
+use Box\Spout\Writer\Common\Creator\EntityFactory;
+use Box\Spout\Writer\Common\Entity\Row;
+use Box\Spout\Writer\Common\Entity\Style\Style;
+
+/**
+ * Trait RowCreationHelper
+ */
+trait RowCreationHelper
+{
+    /**
+     * @param array $cellValues
+     * @param Style|null $rowStyle
+     * @return Row
+     */
+    protected function createRowFromValues(array $cellValues, Style $rowStyle = null)
+    {
+        $row = EntityFactory::createRow([], $rowStyle);
+
+        foreach ($cellValues as $cellValue) {
+            $row->addCell(EntityFactory::createCell($cellValue));
+        }
+
+        return $row;
+    }
+
+    /**
+     * @param array $cellValues
+     * @param Style $rowStyle
+     * @return Row
+     */
+    protected function createStyledRowFromValues(array $cellValues, Style $rowStyle)
+    {
+        return $this->createRowFromValues($cellValues, $rowStyle);
+    }
+
+    /**
+     * @param array $rowValues
+     * @param Style|null $rowsStyle
+     * @return Row[]
+     */
+    protected function createRowsFromValues(array $rowValues, Style $rowsStyle = null)
+    {
+        $rows = [];
+
+        foreach ($rowValues as $cellValues) {
+            $rows[] = $this->createRowFromValues($cellValues, $rowsStyle);
+        }
+
+        return $rows;
+    }
+
+    /**
+     * @param array $rowValues
+     * @param Style $rowsStyle
+     * @return Row[]
+     */
+    protected function createStyledRowsFromValues(array $rowValues, Style $rowsStyle)
+    {
+        return $this->createRowsFromValues($rowValues, $rowsStyle);
+    }
+}